Synopsis: Almost ten years ago today, a landmark Reinforced Concrete Building serving as General Headquarters for the Armed Forces of the Philippines was Burned for the Third Time. This paper discusses the Investigation, Design, Construction and Monitoring Procedures used in the Structural Rehabilitation. Extensive use of Computer Analyses and Design as well as Computer Aided Drafting (CAD) including computer generated 3D details of critical connections, other than speeding up the design process resulted in effective communication of Designer’s intentions in a timely manner to all concerned. The cost of rehabilitation, not to mention the preservation of the Historical Value of the Building and reduced time to occupancy led to the owner’s decision to rehabilitate rather than demolish and reconstruct this Building.
1. INTRODUCTION
The last fire at the AFP General Headquarters Building resulted in an Engineering assessment being commissioned by the client to determine the viability of further rehabilitation efforts and to determine the integrity of the various Structural Elements that were involved or exposed to the Fire. Our office was retained to undertake this study and was subsequently engaged by the owner to undertake the Detailed Engineering needed for the rehabilitation and structural upgrading of the whole Building.
This paper discusses the steps and procedures undertaken by this office from the start of the investigation, to the Detailed Analysis and Design Engineering and the inspection and monitoring during the construction.
2. ENGINEERING BACKGROUND
2.1 Investigation Phase
The Investigation Phase was done over a Three (3) month period in 1988 culminating in the submittal of a report which concluded that although major repairs would be needed, the Historically Valuable Building could be saved despite three fires and two rehabilitations, without demolishing the Historical Facade (Figure 2) which was the focal point of the whole General Headquarters Complex of Camp Emilio Aguinaldo, the Headquarters and Administrative complex of the Armed Forces of the Philippines.
2.2 Methodology
The investigation study required destructive and non-destructive tests. Numerous cores were extracted in suspect concrete after numerous Rebound Hammer Tests were performed to indicate the location of relatively weaker concrete. In addition, steel reinforcement was extracted for tensile tests in some areas to serve as bases for our subsequent Structural Analyses and Investigation.
Reinforcing bars were exposed at critical structural sections such as at Beams, Girders, Column and Slabs to determine spacing and sizes of reinforcing bars for the existing structure. Fortunately, Plans of the First and Second Rehabilitation Programs were still available and were verified to be relatively accurate except in some instances, for which field changes were required during the ongoing rehabilitation. The rehab programs undertaken prior to this study involve buildup in concrete members one on top of the other for affected areas.
2.3 Results of the Investigation
From the results of the numerous rebound hammer readings undertaken, it was already evident that there were large disparities in the strengths of the two concrete layers. Figure 3 shows the existing configuration before rehabilitation.
The lower layer for Beams and Girders is composed of what we now term as the “original” concrete used in the original construction and the “rehab” concrete on top and integrated with the R.C. Slab used in the first and second structural rehabilitation. The original concrete on the underside showed very low concrete strengths, often preventing extraction of intact cores. Evidently, the original concrete in both Wings had been affected by exposure to Fire as borne out by the rebound hammer tests, the core extraction and subsequent tests on the intact cores.
Figure 4 is a chart of the results of Unconfined Compression Tests on intact cores. Of the more than 78 cores extracted, all of the low concrete strengths (below fc’=2500 psi) were obtained on the original concrete. Zero strengths represented concrete cores which disintegrated during extraction mainly from the original concrete.
All of the later rehab concrete showed consistently high concrete strengths averaging approximately 3500 psi. These results were predicted and anticipated by the numerous rebound hammer tests before the corings were performed.
From the foregoing, we were able to make the following conclusions:
The original concrete used in the original building construction was of relatively lower strength compared to more recent Rehab Concrete. This is probably due to the following:
The original concrete had been subjected to at least two previous fires, thus damage was progressive.
Poor quality concrete was used in the original construction.
The original concrete would pose a danger to building occupants if left in its existing condition.
Newer “Rehab” concrete although being subjected to the same fire exposure during the last fire has been relatively unaffected by it.
There was no need to totally demolish or condemn the Building and only structural strengthening of the historically important Building would be required to restore it to its former function.
The strengthening and rehab measures to be implemented, would also be directed towards upgrading the structural performance of the Building and bring it up to Present Day Seismic Code Design Standards.
Other than the foregoing which were purely of technical nature, the decision to go ahead on the structural rehabilitation was also dictated by practical reasons which weighed heavily in favor of rehabilitation rather than outright total demolition and reconstruction.
The practical considerations are as follows:
The cost of structural rehabilitation is approximately thirty four percent (34%) of the cost of a totally new Building with the same floor area.
Based on the winning bid, the cost of the Civil/Structural Works for the rehab scheme amounted to only one third of the cost per square meter for the demolish/construct scheme.
Time – Time to occupancy would be greatly shortened from a minimum of eighteen (18) months for a demolish/construct scheme to about five (5) months for the rehabilitation scheme eventually adopted.
Historical Value -There was a need to preserve the historical value and architectural details of the Building.
3. ENGINEERING ANALYSES AND DETAILED DESIGN
Several findings and engineering decisions were made during the structural analyses and detailed design stages as follows:
The Preliminary Structural Analyses showed that the existing structural system even without the effects of the fire would be inadequate to sustain Seismic Lateral Forces.
The existing details, even for the rehabbed portion, will not comply with Seismic Detailing Standards for Zone 4 existing at the time as mandated by ACI 318-83 and the National Structural Code of the Philippines and therefore structural strengthening would be necessary.
In the structural analyses, the contribution of the original column core concrete was entirely neglected and the new column was idealized as a Hollow or Box Column enclosing the original concrete core. A specific custom program was developed in-house to analyze the hollow column and generate column interaction diagrams for various cases of loading.
3-D Computerized Frame Analyses were conducted. The East Wing, West Wing and Central Core were idealized as independent structures because of the provision of a Seismic Joint in the original construction. The subsequent strengthening details also preserved this Seismic Joint.
The rear portion of the Central Core was totally demolished and replaced by a new structure integrated with the existing core. This was necessary as this part was still supported on Timber Flooring during the last fire and relatively was more severely damaged.
On the basis of the analyses results, a Reinforced Concrete Seismic joint detailed to existing Code was found adequate. The most important feature of this detail is the provision of additional Vertical Reinforcing bars through the joints to provide for continuity. Confining ties were placed in addition to the confinement by additional rehab concrete on the Beams and Girders meeting at the joint. (See Figure 5)
The horizontal beam and girder bars were in turn confined within the column vertical bars. The illustration of Figure 6 shows the Rehab Scheme adopted for the Beams, Columns and Slabs.
It is important to note here that although the East Wing Columns have been earlier rehabilitated after the previous fires, it was still necessary to provide for additional vertical reinforcing bars through the joints to be confined with closely spaced ties as the existing details were found to be inadequate. Again, in the Structural Analyses of this system, the existing core concrete and reinforcing bars were neglected thus imparting a far bigger “Factor of Safety” in reality.
Negative moments for the existing Beam and Girder needed additional reinforcement for continuity and also to increase lateral load resistance. Additional reinforcing bars were also needed to increase positive moment carrying capacity.
The negative Bars were placed and confined within the new column vertical bars and new ties were integrated to confine the reinforcing bars as well as the positive moment reinforcing bars which were threaded in to the existing Beam hoops.
3.1 Computer Analyses and Design
The computer analyses and design was carried out using M-STRUDL, an enhanced microcomputer implementation of the STRUDL Software written in C Language which was popular at the time. In-house developed software for the analysis of the Hollow or Box Column was used as earlier stated as well as spreadsheet programs for generating column interaction diagrams.
4. REHABILITATION PROCEDURES
4.1 General
Great emphasis was placed on the value of effective bonding between the old and new concrete requiring the use Structural Epoxy Bonding agents. In the process, stringent surface preparation procedures were required to ensure the effectiveness of the Bonding.
We assigned a Senior Structural Engineer on full time basis to monitor and ensure that surface preparation and epoxy application are carried in accordance with the specifications and to oversee rehabilitation in general.
In addition to this, detailed structural rehabilitation procedures were included as part of the plans and specifications to set the minimum basis for rehabilitation. This included outline or step by step procedures for chipping, demolition, surface preparation, epoxy application and reinforcing bars installation. In order to forestall any misinterpretation of Plans and Specifications, the Contractor was required to submit a detailed construction methodology for acceptance and approval by the owner through the consultant. This requirement identified a lot of areas that were overlooked during the bidding stage and was very invaluable in this regard as it enabled the owner and engineer to check the Contractor’s intentions and directions for the rehab even before fieldwork started. Revisions and changes in the methodology were made in the course of construction, nevertheless, this requirement helped immensely in identifying possible problems during the implementation.
4.2 Computer Aided Drafting and Detailing
Three Dimensional (3D) drawings and reinforcing bar layouts as in Figure 6 & 7 were prepared to ensure that the intended reinforcing bars details were faithfully carried out in the field by the Contractor. Extensive use of CAD to generate 3D Plots were made. The extent of detailing required and implemented using CAD would defy manual efforts, given the time pressure. Thus, the decision to fully utilize our CAD Graphics facility which was still relatively crude at the time, to support the project and generate 95% of the drawings proved to be a wise one and was effective in ensuring a clearer understanding of the complicated reinforcing bars layouts. In addition, changes necessitated by unforeseen field conditions could be done easily by just revising the electronic files.
4.3 Detailed Rehabilitation Requirements and Procedures
Based on the findings during the investigation phase, it was decided that all original Beam and Girder concrete would have to be removed and replaced as this could fall off or spall off during an Earthquake. Because of the adequacy of the later rehab concrete for the Slabs and Top portions of Beams and Girders, it was decided to retain and integrate these with the new rehab concrete. This was a major cost saving. The existing columns’ concrete cover would have to be removed to expose the old reinforcing bars and a new rehab concrete and reinforcing bar cage were installed to envelope this core concrete. Vertical column reinforcing bars as well as Beam/Girder negative bars and positive moment bars were made continuous through the joints and confined with Hoops and Ties in accordance with ACI 318 and 315. Extensive use of shoring was specified and required as early as the bid stage in all instances to prevent any movements in the Building Frame during rehabilitation when it was very vulnerable.
Due to the fragile and weakened nature of some elements, the use of heavy Pneumatic Jackhammers was prohibited and only small hand held rotary air hammers and bush hammers were allowed to be used to demolish the original concrete. Vibrations during construction operations was carefully avoided and extensive use of shoring was required.
The existing original reinforcing bars for Beams, Girders and Columns were retained and integrated with the new rehab reinforcing bars and concrete. This in a way compensated for the setting up of creep/shrinkage stresses affecting the structural elements due to the bonding of the old and new concrete.
4.4 SURFACE PREPARATION
The original concrete cover was chipped off (Figure 9) to expose the existing reinforcing bars. Cleaning of the reinforcing bars proceeded immediately using a wet type sand blasting equipment until all the reinforcing bars were to bare white metal finish.
High pressure water spraying (Figure 8) was used immediately before epoxy application in order to remove all loose and defective concrete and for final cleaning of reinforcing bars. This utilized a 6,000 psi (41.3 Mpa) High Pressure washer. The quality of bonding surface and rough texture was assured by this final surface preparation procedure.
The tight spaces and reinforcing bars cages required epoxy application by hand brushing. It was therefore necessary to require that the epoxy would have an adequately long “overlay time” of at least six (6) hours to allow application, erection of forms and pouring of concrete. This requirement meant that the forms would have to be collapsible and allow for easy installation. Prefabricated laminated plywood forms were specified to eliminate the need to refinish the stripped surfaces.
4.5 CONCRETING
It was necessary to pour the concrete columns in two lifts with the last lift being poured monolithically with the upper Beam Column joint (Figure 10). Maximum 3/8” (9.5mm) aggregate was specified to ensure that the congested areas are effectively filled by concrete. Breather holes were punched in the slabs to prevent entrapment of air that could block the flow of concrete. Very small diameter hand held electric Driven Pencil Poker Vibrators were utilized in most instances due to the tight spaces involved. The Concrete Mix required the use of a plasticizer because of the low water cement ratio (0.42) required on top of the minimum guide specification of fc’=4000 psi (27.6 Mpa) Concrete Cylinder Compressive Strength. The low water cement ratio was required to reduce shrinkage to a minimum. Wet curing of the poured concrete elements also helped to reduce shrinkage. The more than liberal distribution of new and old reinforcing bars in a way prevented shrinkage movements that would have otherwise caused concrete to crack.
4.6 Construction Methodology
Unlike conventional construction projects, this rehabilitation project is unique in that rehab work can be started in almost all areas. However, due to priorities dictated by owner requirements and in order to further speed up the project, the contractor was required to adhere to a priority schedule which among others required completion of the roof within 40 days from award of contract. Completion of the roof would have allowed an all weather construction although extensive shoring would have been required.
Additionally, the rehab procedures dictated that no two adjacent columns would be rehabbed simultaneously so as not to unduly weaken the Building. The soundness of this requirement was amply proven during the July 16, 1990 Luzon Earthquake which registered Intensity 7.7 in the Richter Scale.
REFERENCES
ASEP (1992) National Structural Code of the Philippines Volume 1. Association of Structural Engineers of the Philippines (ASEP), Manila.
ACI (1996) ACI Manual of Concrete Practice Part 3. American Concrete Institute (ACI), Farmington Hills, Michigan.
ABOUT THE AUTHOR
Emilio M. Morales, MSCE took up his masters degree at the Carnegie Institute of Technology, Carnegie-Mellon University, Pittsburgh, PA. USA in 1980. Formerly Senior Lecturer of Graduate Division, College of Engineering, University of the Philippines, Diliman, Quezon City. Presently, he is the Technical Manager of Philippine Geoanalytics, Inc., Civil Engineering Laboratory and Principal of EM2A & Partners & Company. Committee Member, TC-11, Bureau of Product Standards Technical Committee on Steel Products.
He can be contacted at: EM2A Partners & Co., No. 17 Scout de Guia corner Scout Reyes Streets, Diliman, Quezon City. Telephone Nos. 371-18-04 & 06/ 410-29-23 to 24. Fax No. 924-98-94; E-mail: em2apart@mozcom.com.
Abstract: Testing of Fresh and hardened concrete has become routinary. This “routineness” has led to blind acceptance of the results without a real understanding of what the test results are saying and only “PASS”/“FAIL” conclusions are made on such results. However, the tests tell us what is happening or what is bound to happen if we do not heed the telltale indications that the tests are trying to convey. Oftentimes, lack of understanding of the failure or the causative mechanisms that bring about such failures are the least understood leading to wrong corrective responses or solutions. Problem identification has been said to be 80% of the solution process. Thus, there is a need to know the factors and significance of each test and the variables involved in the tests in order to arrive at solutions that directly address the problems. Most of the contents of this paper was obtained from literature more specifically from the work by Klieger et al on “ ASTM STP 160C – Significance of Tests and Properties of Concrete and Concrete-Making Materials”.and downloads from the Internet. Nevertheless, the authors hope that this paper could lead to a fuller understanding of the significance of the tests and what the test results are really telling us.
1.0 INTRODUCTION
Testing of Concrete both in the plastic and hardened states need to be carefully understood in order that adequate responses or proper corrective measures can be made to developing problems even before these develop.
Oftentimes, the test results and what they tell the end user remain as merely test results because of a lack of understanding on what these test results are really indicating to us and how they could best be used or interpreted to result in adequate and timely corrective measures to address the problem.
This paper references work by several authors from an ASTM Special Technical Publication ASTM STP 160C on the work by Klieger et al on “Significance of Tests and Properties of Concrete and Concrete-Making Materials”.and downloads from the Internet.
2.0 CONCRETE BASICS
Concrete is defined in the ASTM terminology relating to Concrete and Concrete Making Materials (C-125) as:
2.1 A composite material that consists essentially of a binding medium within which are embedded particles or fragments of aggregates.
2.2 In Hydraulic-cement concrete, “the binder is formed from a mixture of Hydraulic cement and water”.
2.3 Hydraulic cement is defined (ASTM C-219) as “a cement that sets and hardens by chemical interaction with water and that is capable of doing so under water”.
3.0 COMPONENT MATERIALS
3.1 Portland Cement
Portland Cement is the primary constituent of Portland cement Concrete.
It is defined as gray, powdery material that meets ASTM Standard C 150 and is composed primarily of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. When combined with water, Portland Cement reacts with the water to form a paste, which then becomes rigid as the reaction between the cement and water progresses. 3]
Combined with the other components such as the inert fine and coarse aggregates and water, the Portland cement reacts (Hydrates) with water, initially forming a paste which within hours hardens to form the binding medium or cementitious matrix that holds the aggregates together.
3.2 Water
Next to Portland Cement, Water is an important ingredient. Water controls the strength and workability of the mix. The water reacts with the portland Cement in a process known as hydration to form a cementitious paste that hardens with time. The hydration reaction is a complex chemical reaction which physically alters the character and properties of the original Portland cement.
The water cement ratio is a good approximate indicator of the probable strength of the hardened mix. Its control is essential to a proper mix design which will address the job requirements.
Too much water in the mix will:
Cause large shrinkages to occur if concrete is allowed to cure normally
Result in low strengths
Increased workability and flowability
There are real Reasons to use less water and these are to accomplish the following objectives:
Increased strengths
Lowered permeability
Increased resistance to the effects of weather
Better bonding with reinforcement
Less volume change from wetting and drying
Increased resistance to plastic shrinkage
If strength requirements as well as workability demands need to be met concurrently, addition of water while increasing workability can cause a retrogressive effect on the strength and increases shrinkage potential and should thus be avoided. Reduction of water in the mix would increase strength but may make the Concrete unworkable.
An alternative would be to consider the use of superplasticizers which dramatically enhances the workability and flowability of concrete while reducing the water demand and thus results in a concrete mix that will address the requirements of the project for strength and workability.
3.2.1 Water/Cement Ratio
The water/cement ratio is the weight of the total amount of water relative to the weight of the total amount of cement used per cubic meter of concrete. In simple terms, the lower the water/cement ratio or the less water used for a certain weight of paortland Cement in the mix, the better the concrete. This is true to a point. Enough water is needed to be able to place and consolidate the concrete as well as achieve complete hydration reaction.
The binding quality of the cement/water paste is due to the chemical reaction achieved when water is mixed with cement.
This reaction is called hydration. Very little water is needed for hydration. In fact, most concrete would look like a pile of rocks and be unworkable if the only water added was to hydrate the cement. Most of the water in concrete is “water of convenience” to help ease the task of placing concrete.
The more water added to concrete the thinner the paste. The thinner the paste, the less strength in the hardened concrete. The Portland Cement Association suggests using no more water than is absolutely necessary to make the concrete plastic and workable. The graph below shows the effect of the Water Cement Ratio on the the Compressive Strength of Normal Weight Type I Portland Cement concrete at varying times based on tests on American Portland Cement Concrete. 4
Fig 3.2.1 Age vs Compressive Strength for various Water Contents
3.2.2 Water in Aggregates
Water in aggregates may or may not contribute to the hydration water depending on the condition of the moisture in the aggregates.
Fig 3.2.2. Moisture content in Aggregates for different conditions.
Water in the aggregates may also increase the available water as to increase the water cement ratio.
Thus, tests to determine the Moisture content of the aggregates is necessary for mix design purposes. The condition of the aggregates during the moisture content determination is also important as it determines whether the water is available as free water that could increase the water content of the mix or not at all. By the same token, it is necessary to determine the absorption capacity of the aggregates to determine whether hydration water will be reduced by absorption of the aggregates. Essentially, the absorbed water is not available to react with the cement as hydration water. Knowing the absorbed water will allow us to compensate for mix water that is “robbed” by aggregate absorption.
Normally aggregates are tested for absorption by using “Saturated Surface Dry Condition” as it is a measure of the potential absorption when moisture content under SSD is determined by Oven drying. the moisture content determined is then used to determine the absorption loss.
3.3 Air Content
Air content measurement is important particularly for non air entrained concrete because unexpected increases in air content can have a retrogressive effect on compressive and flexural strengths. The entrapped air bubbles displaces the cement matrix thus reducing the strength to some extent.
In tropical climates, air entrainment would normally only be prescribed for marine exposures for increased resistance to water permeability but more and more, this is being replaced by fly ash to provide a denser less permeable mix. However, even in the country, air entrainment for protection of the concrete (and eventually the rebar from corrosion) is done by using Fly Ash to promote a denser packing with minimum of voids in the concrete. The microfine fly ash fills these voids while at the same time increasing mobility and allowing for strength increases although in a much more delayed setting time.
3.4 Fine & Coarse Aggregates
3.4.1 Gradation Tests
Test of fine and coarse aggregates for grain size distribution is known as a Gradation test.
Grading is the particle distribution of granular materials among various sizes. This is usually expressed in terms of cumulative percentages larger or smaller than each of a series of sizes of standard sieves.
Grading and particle size distribution affects the overall performance of concrete as follows:
Determines the relative aggregate proportions
Determines the cement and water content
Affects Workability
Durability
Porosity
Porosity
Shrinkage
The well graded the particles, the more economical is the mix. a well graded aggregate means that all the grain sizes are represented. This allows for economical, denser concrete mixes with increased strength.
Variations in grading from batch to batch can affect the uniformity of concrete.
Generally, aggregates which do not contain a large deficiency or excess of any particular size and give a smooth gradation curve, within the prescribed gradation will produce a satisfactory mix.
Providing a well graded gradation (where all prescribed particle sizes are present) will reduce the total volume of voids which otherwise will be occupied by the cement paste.
An air meter is normally used for measuring air content.
Fig 3.4.1.1 Cement Content vs % Sand Content illustrating the Significance of Sand Content to the
overall economy of the Mix expressed in terms of Cement Content demand
The Chart above shows that control of Sand content to within the prescribed guidelines will result in an economical mix. Too little sand would result in a very harsh mix and would require cement to be used as voids filler. Too much sand captures the cement paste to coat the individual grains resulting in increased cement demand.
For fine and coarse aggregates the fineness modulus (FM) is defined by ASTM C-125. The fineness modulus is obtained by adding the cumulative percentages retained (by weight) on each of the specified sieve sizes and dividing the sum by 100.
The higher the FM, the coarser is the aggregate.
Fig 3.4.1.2 Fineness Modulus Calculation for Fine Aggregates
FM is important in estimating the proportions of fine and coarse aggregate.
3.4.2 Coarse Aggregates
The strength of aggregates, and hence its influence on the concrete, is primarily dependent on its mineralogy.
Beyond this, a smaller sized aggregate may have strength advantages in that internal weak planes may be less likely to exist or would be smaller and discontinuous.
The bond between mortar and coarse aggregates will be stronger for smaller aggregates.
A rough angular surface such as in crushed aggregates will increase the bond strengths.
As the maximum size of aggregate is increased for a given slump, the water and cement content per cubic meter of concrete are decreased. The larger the coarse aggregate proportion is in the total mix, the lesser is the cement needed due to the lesser surface area compared to smaller aggregates. However, workability is affected and the mix becomes harsher with increasing aggregate size.
Flat elongated and angular shapes require more water to produce workable concrete. Hence, cement demand is increased to maintain the same WC ratio.
The larger the aggregate size, the lesser is the cement demand.
For coarse aggregates, the larger size materials tend to affect the strength of concrete particularly if the aggregates have weakened planes or discontinuities. Gap graded aggregates may sometimes be used because of deficiency in coarse aggregate sizes within a certain sieve series. This would still be acceptable provided the percentage of fine aggregates is controlled. Gap graded mixes can produce a harsher mix but adequate vibration may address the problem.
Segregation is a problem in gap grading and therefore over vibration is to be avoided and the slump limited from 0 to 3 inches.
3.4.3 Fine Aggregates
Sand is primarily a filler for the voids in concrete.
Increasing the proportion of sand in the total mix increases cement demand because of the relatively very large surface area that needs to be coated by cement paste.
Flowability and mobility of concrete is enhanced with larger sand proportions but increases cement demand.
Flat elongated and angular shaped sands such as products from crushed sand, also require more water to produce workable concrete. Hence, cement demand is increased to maintain the same WC Ratio.
Generally, the gradation for fine aggregates given by ASTM C-33 would be adequate. However, it would be preferable to limit the % passing for the two smallest sieve sizes (#50 and #100 to 15% and 3% or more respectively. This would depend on workability during placement. The higher the fines content the more workable is the concrete but also increases cement demand.
4.0 FRESH CONCRETE
4.1 SLUMP TEST
The slump test is a measure of the workability of fresh concrete. It should NOT be used for predicting strength even in an approximate way.
Fig 4.1 Diagram of the Slump Test showing how Slump is measured
4.1.1 Additional Information from the Slump Test
More information can be obtained from the Concluded Slump Tests as follows:
After removing the slump cone and measuring the slump, the concrete is tapped on the side with the tamping rod.
Two concretes with the same slump may behave differently as follows:
One may fall apart after tapping which indicates that it is a harsh mix with a minimum of fines. This may have sufficient workability ONLY for placement in pavements or Mass concrete.
Another may be very cohesive with surplus of WORKABILITY, this may be required for more difficult placement condition
4.2 The Schmidt Rebound Hammer
The rebound hammer is an impact device that indicates relative and approximate concrete strength QUALITATIVELY through the rebound of the probe which has been calibrated against concrete strengths.
It is useful in determining or locating weaker or stronger concrete qualitatively and in a relative sense or for locating areas with discontinuities and honeycombs.
It is not an accurate device even when calibrated against concrete cores extracted in the area and is not intended to replace the compression test. It should NOT be used as a basis for acceptance or non-acceptance of a particular pour.
Fig 4.2 The Schmidt Rebound Hammer with Digital Readout and Polishing Stone.
The device when used properly could give useful indications such as to where weaker vs Stronger concrete is present but only in a relative sense.
A lot of consultants think that it is an accurate and absolute determinant of Concrete compressive strength which it is not. Dependence on this as the sole reference and basis for rejection is unwarranted, unsound and NOT VALID.
4.3 Test on Concrete Core sample
Whenever the strength of hardened concrete is put to doubt, destructive testing in the form of testing concrete core samples uniaxially in accordance with ASTM C-42 is performed on the area where the questionable concrete has been laid. Coring is done using Diamond Coring bits that are thin walled. The core diameter should be no smaller than three times (3x) the size of the maximum nominal size of coarse aggregate.
Where possible, the length of the core should be at least twice the diameter (2X) of the core but other height to diameter ratios are permissible to a certain extent and corresponding correction factors are applied to the test results to compensate for the slenderness of the core sample. Reinforcing steel should not be included in the cores to be tested. If rebars do exist, the cores would have to be discarded and replaced.
When cores are taken for the purpose of strength determination, at least three cores should be taken at each location. The strength of the concrete as cored is expected to be lower than the design strength to take into account disturbance and damage effects during the sampling and testing of the cores. Values approaching 0.85 of the design concrete strength f’c or higher would be generally acceptable. 5 ]
4.4 Concrete Compression Test ASTM C-39
A concrete test as technically defined should consist of tests on at least two standard cylinders taken from the same batch or pour.
4.4.1 ACI Requirements for Compressive Strength Test
For a strength test, at least two standard test specimens shall be made from a composite sample obtained as required in Section 16. A test shall be the average of the strengths of the specimens tested at the age specified in 4.1.1.1 or 4.4.1.1 (Note 19). If a specimen shows definite evidence other than low strength, of improper sampling, molding, handling, curing, or testing, it shall be discarded and the strength of the remaining cylinder shall then be considered the test result.
To conform to the requirements of this specification, strength tests representing each class of concrete must meet the following two requirements mutually inclusive(Note 20):
The average of any three consecutive strength tests shall be equal to, or greater than, the specified strength, f’c, and No individual strength test shall be more than 500 psi [3.5 MPa] below the specified strength, f’c.
4.4.2 Failure Mechanism
Concrete failure in the compression test or in service is a result of the development of microcracking through the specimen to the point where it can no longer resist any further load.
The crack propagates through the weakest link whether it is through the aggregates or the cement matrix or both.
For ultra high strength concrete aggregate strength becomes critical and it would be better to have smaller sized aggregates so that internal weaknesses in the aggregates would not be significant as a crack initiator. Also, the use of small sized aggregates increases the aggregate interlock and increases the chances for Crack Arrest.
For normal strength concrete, failure normally propagates through the cement matrix unless internal planes of weakness in the aggregates give in more readily but the random distribution of these would arrest such crack propagation in the normally stronger aggregates.
In the compression test, because of scale effects, the planeness, perpendicularity and surface imperfections critically influence the results.
4.4.3 Factors Affecting Compressive Strength
Retempering of the mix with water in the concrete can cause a decrease in the mortar strength due to uneven dispersion of the retempering water which leads to pockets of mortar having a high water cement ratio.
If concrete is allowed to dry rapidly, the available moisture for hydration reaction will be reduced and hydration ceases.
A smaller sized aggregate may have strength advantages in that the internal weak planes may be less likely to exist.
The bond between the mortar and coarse aggregate particles will be stronger for smaller sized aggregates which have a higher curvature.
When concrete bleeds, the bleed water is often trapped beneath the coarse aggregate thus weakening the bond within the interfacial zone and allowing for weaker stress paths for cracks to initiate. Excessive bleeding will produce a high water cement ratio at the top portion leading to weakened wearing surfaces and dusting.
4.4.4 Break Patterns
Surface imperfections in the sample or the test platform can cause uneven break patterns which signal lower strength results normally.
Fig. 4.4.4 Uniaxial Test on Concrete Cylinder ASTM C-39
4.4.5 Factors Affecting the Compressive Strength Test Results:
Specimen geometry Size End conditions of loading apparatus Rigidity of Test Equipment Rate of load application Specimen moisture conditions
Fig. 4.4.5a Ideal Break Pattern is Conical and Hour Glass ShapedFig. 4.4.5b Some Break Patterns Due to Uneven
The purpose of specifying end condition requirements of planeness and perpendicularity is to achieve a uniform transfer of load to the test specimen.
Fig 4.4.5c Conventional Compression Tester on Mobile Testing LaboratoryFig 4.4.5d Spherical Platen ensures that the load is transferred evenly to the Concrete CylinderFig. 4.4.5e Surface Deformities result in uneven load Distribution causing premature Test Failure = Fictitious Low Strengths.Fig. 4.4.5f A High Capacity UTM for Testing Ultra High Strength Concrete Cylinders
Non-conforming specimens generally cause lower strength test results and the degree of strength reduction increases for higher strength concrete.
4.4.6 Specimen Size and Aspect Ratio
The ASTM Standard test specimen is a 6” Diameter x 12” high cylinder.
Compressive strength generally varies inversely with increasing cylinder size with the 6” dia cylinder as the reference size.
The ratio of specimen diameter to max aggregate should be 3:1, the accuracy of the strength test results decreases as the diameter to aggregate ratio decreases.
The L:D (aspect ratio) requirements is 2. The strength increases with decreasing L/D ratio due to end restraint. However, correction factors are allowed.
4.4.7 Requirements of Testing Machine Properties
The Test Equipment used for the Compression test :
Must be capable of smooth and continuous load application.
Must have accurate load sensing and load indication.
Must have two bearing blocks one fixed and the other spherically seated both satisfying planeness and rigidity requirements.
Distortion of testing machine or of the bearing plates due to inadequate rigidity can cause strength reductions therefore, adequate rigidity needs to be assured.
4.4.8 Rate of Loading
ASTM C-39 requires that the loading rate for hydraulically operated test frames be controlled to within 20 to 50 PSI or about 500 Lbs per second. Other than making the test procedure follow consistent rates of loading and thus remove this as a variable effect on Concrete Strength, there are other reasons for prescribing a constant rate of loading.
The apparent strength of the concrete increases with increasing loading rate and therefore the loading rate must conform to the required standard to produce consistent and accurate results.
Higher strength concrete are more affected by the loading rate.
This dependence on loading rate has been found out to be due to the Mechanism of creep and Microcracking.
Thus, it has also been found out that when subjected to a sustained load of 75% its ultimate strength, concrete will eventually fail without any further load increases.
4.5 Concrete Flexural Strength
4.5.1 Factors Affecting Flexural Strength Test Results
Specimen Size Preparation Moisture Condition Curing Where the beam has been molded or sawed to size Aggregate Size
Fig. 4.5.1 Flexural Test on Concrete
5.0 CONCRETE SHRINKAGE
Concrete shrinkage is primarily due to rapid and uneven loss of water. Therefore, improper curing of Freshly poured concrete and control of environmental factors plays a key roll in shrinkage control.
Drying Shrinkage increases with increasing water content. Therefore control of mixing water to that required only for complete hydration and desired adequate flowability is important. In case such conditions can not be met, it would be better to achieve these requirements by using water reducing plasticizers rather than by addition of more water.
Although control of total water in the mix is the primary objective to control shrinkage Cracking, other factors contribute to the overall shrinkage cracking as the following Equation would suggest.
Shrinkage cracking can be quantified or predicted based on ACI 209R-92 procedures as given in the following formula below. What is significant to note in this Formula is the contribution of other factors to the overall shrinkage magnitude which are controllable and thus points the way to the reduction of Shrinkage effects.
Prediction of Actual Shrinkage Values based on ACI 209R-92
Concrete shrinks due to moisture loss. However, the actual magnitude of ultimate shrinkage is dependent on a lot of factors as contained in ACI 209R-92.
These factors are:
Relative Humidity
Minimum Thickness
Cement Content
Slump
Air Content
Fines Content
The parameter SH is obtained from the Chart below which is dependent on the Total Water Content of the mix when laid. The chart for obtaining the above variables are given in the Appendix of this paper.
Fig. 3.2.1.2 Shrinkage Values in Millistrain vs Water Content
6.0 BLEED EFFECTS
Although not related to shrinkage, bleeding is A related surface defect that is controllable. Bleeding occurs when over-troweling happens which works up more water to the surface.
The increased water at the surface results in higher W/C which causes a low strength layer that can delaminate and cause dusting or powdering.
7.0 CONCLUSIONS
This paper has identified the various Factors affecting tests on fresh and hardened concrete and their significance in influencing test results.
A complete understanding of these Factors can definitely reduce uncertainties in determining the cause/s of “Failed test Resultsˆ and eliminate costly Guesswork and often times solutions that do not address the problem.
The Authors hope that recognition of the various factors that influence the test results could lead to a more positive and responsive solution to problems brought about by the test results.
REFERENCES
Klieger, Paul and Lamond, Joseph F. “Significance of Tests and Properties of Concrete and Concrete- Making Materials”. ASTM STP 160C.
ACI 209 R -92 METHOD OF SHRINKAGE PREDICTION.
1 Emilio M. Morales, MSCE took his Master of Science in Civil Engineering at Carnegie-Mellon University, Pittsburgh, PA. USA in 1980. He was employed as a Geotechnical Engineer at D’Appolonia Consulting Engineers. Currently, he is the Principal of EM²A Partners & Co. and concurrently serves as President for IGS Philippines, Chairman for the PICE Geotechnical Specialty Committee. He has been elevated to PhD Candidacy at the Asian Institute of Technology, Bangkok, 2 Mark K. Morales, MSc took his Master of Science in Civil Engineering at University of California – Berkeley, USA in 2004. He is the Technical Manager of Philippine Geoanalytics, Inc. and President of PGA Earth Structures Solutions
3 www.ces.clemson.edu/arts/glossary.html
4 NOTE: Slightly Lower results are obtained for philippine Cements due to lower cube compressive strengths but the chart is indicative of the relationship between Concrete Strength and W/C
5 ACI 437R-16 “Strength Evaluation of Concrete Buildings” Excerpts
Download Significance of Tests on Fresh & Hardened Concrete
Very often the Earthworks Contractor is confronted with a clear set of specifications from the Design Engineer outlining specified compaction density, moisture content and governing standards. In most instances, the contractor innocently and faithfully tries to carry out the procedure in the field without a clear understanding of what is really required and without a fundamental understanding of the Soil Mechanics principles entailed in such a “simple” task as Earthwork construction. This ignorance and oversimplification often produces disastrous results, delays in the project and financial loss to the contractor. Unfortunately, it is sometimes not only the contractor but also the Design Engineer who is ignorant of these principles, thus confounding the problem which could again further cause delays in the project. What is also dishearthening is the realization that all too often this “failure” on the part of the contractor results in countless litigation or delays because the real problem could not be identified.
The statement “problem identification is Eighty Percent of the solution” is nowhere very applicable as in this problem.
Let us consider several cases which highlight what we mean:
1.1 Runway Construction Project
A very large runway project inside a U.S. Base required a minimum of 95% of Maximum Dry Density based on ASTM D-1557 (Modified Proctor) on the subgrade which consisted of Clean Coarse Grained Materials (Granular Sand).
The contractor proceeded to do the compaction utilizing about 20 units of large Vibratory Rollers and Two (2) Water Trucks.
We were hired as the Independent Q.C. Laboratory to monitor Field Compaction. The contractor almost consistently had very large number of Field Density Test “Failures” despite numerous passes (about 10 to 12) per lane.
We were asked to look into the problem as substantial delays have been incured without significant progress. After conducting compaction trials on a 100 meter strip for half a day, we were able to achieve adequate compaction in just 3 passes!
The procedure we used in the compaction trials was immediately implemented which resulted in almost halving the vibratory compactor fleet (rented) but increased the number of water trucks to 4 at tremendous savings to the prime contractor. This also enabled the contractor to accelerate subgrade preparation by at least two (2) months.
What happened was not black magic but just the sound application of Soil Mechanics principles as we shall see later on.
1.2 Housing Project at Subic
In a housing project inside the Subic Naval Base, an American Contractor was required by the contract specifications to compact the soil to 95% of Maximum Dry Density again based on ASTM D-1557. After several rectangular slabs for the duplex housing were poured and after a heavy downpour, two of the recently poured slabs broke neatly into two at the center.
We were called in to do consulting work to solve the problem and we found out that it was a swelling soil problem.
After the study and a long protracted fight with the U.S. Navy Engineers out of Honolulu, the Navy adopted our recommendation on the basis of a “no-cost change order.”
Surprisingly, what we recommended was to bring down the compaction levels to 90% of Maximum Dry Density Based on ASTM D-698 instead of the more stringent ASTM D-1557 (Modified Proctor) (The latter having the effect of increasing the energy input or compactive effort by 4.58 times!) and to compact the soil Wet of Optimum.
Clearly this was an “Inferior” substitute that was accepted without a reduction in the contract amount.
Why was the change possible?
1.3 Lahar Project
We were again involved to do preliminary consulting work involving Lahar as a Construction Material for a significant Lahar Protection Structure.
The initial specifications called for Proctor Densities and Specified the Optimum Moisture Content required.
Since the structure would be constructed during the dry season, water was a big problem that could hamper the construction of the structure in time for the next onslaught of Lahar.
We have done preliminary work on Lahar on our own as a matter of professional interest and we knew that Lahar behaved as a clean granular soil.
Therefore, we recommended that the Lahar ought to be even compacted in a very very dry state. After a lengthy explanation and initial disbelief, everybody agreed to do so and thus eliminated an unnecessary requirement which could have even hindered the construction progress or even resulted in the specifications not being attainable in the field.
Again, a timely intervention applying sound Soil Mechanics principles saved the day for the project.
1.4 Stalled Vehicle Wheel
A hypothetical but common case which involves a car wheel stuck in a hole on loose beach sand.
As we know, accelerating only digs the wheel deeper into the ground in both cases.
Saturating the sand with sea water somehow makes the sand firm enough to hold the weight of the wheel and soon enough the vehicle is freed.
This is a commonplace solution that is done almost without the thought that Soil Mechanics principles are involved.
The solution to the foregoing case studies all have something in common, and that is a clear undestanding of the behavior and physical characteristics of the soil and application of Soil Mechanics to the solution of “simple” Earthwork Problems.
As is often the case, problems such as these have occured in the field countless times without being correctly identified and thus have resulted in significant losses to the contractor, delays in the projects and substandard quality of compacted earthfill.
Again, it must be qualified that it is not only the contractor who is to blame but also the Consulting Engineer in most instances for this state of things. Our only consolation is that the problem is not only unique to our country but also even in more advanced Western Countries.
A vigorous search of various Soil Mechanics and Foundation Engineering Books yielded only fleeting or sporadic references to these common problems we encounter in day to day Earthwork Construction where soil mechanics principles are applied.
It is the intention of this paper to unify and integrate references to these in various literature on this topic to provide a more “concentrated” understanding of Fundamental Soil Mechanics Principles as applied to Earth Compaction and Earthworks in General.
2.0 THE MECHANICS OF SOILS
In order to successfully apply Soil Mechanics to the solution of our Earth Compaction problems, it would be necessary to have a clear understanding of the fundamental principles.
However, for this paper we shall only limit ourselves to a clear understanding of Particulate Mechanics or the behavior of soils as discrete particles when acted upon by various forces such as gravity, vibration or impact, water and seepage or combinations of these forces.
We shall strive to make the problem as simple as possible even to the layman in order for him to have a fundamental grasp. We however would recommend review of various literature on the subject for those who wish to have a deeper understanding of the problem at hand.
3.0 SOIL AS A PARTICULATE MATERIAL
Under a very powerful electron Microscope, even a piece of seemingly solid mass of clay appears as an assemblage of particles with some orientation. This orientation surprisingly can be altered by reworking of the clay, addition of or removal of moisture or by altering the chemical make-up of the porewater.
Under normal conditions it would also be noted that the assemblage includes water and air. The water is either captured or adsorbed water or free water.
The process of compaction is nothing but the expulsion of air (reduction of voids in the soil). Thus, our attention is directed as to how this could be most efficiently done.
However, as we know, this assemblage that we just saw in the Electron Microscope is only but one of two major assemblages that soil can assume depending on its granulometry or Grain Size.
Soil can either be:
Coarse Grained (Sand) or Cohesionless
Fine Grained (clay) or Cohesive
The clear distinction between the two are somewhat obscured by their combinations that could be found in nature. In their unadulterated states, the differences become readily apparent or clearly distinguishable.
4.0 SOIL SHEAR STRENGTH
Particulate materials derive their strength from friction or intergranular contact and/or from bonding forces or cohesion as we know it. These bounding forces and friction prevent the particles from sliding.
The most important soil strength property that we have to deal with is the soils’ Shear Strength since most of the loading that the soil is subjected to causes the individual soil particles to slide or “shear” one against the other because of their particulate character.
Depending on the granulometry of the soil, the shear strength is either derived from electrical and chemical forces of attraction (cohesion) and repulsion as in clays or by simple grain to grain contact and friction as in Pure Granular Materials. Since shear strength depends on the integrity of the sliding resistance of the individual soil particles, it only follows that the more compact the soil becomes, the higher the shear strength and vice versa. The only way to cause this increase in strength is to lessen the interparticle distances by the expulsion of air and/or water by cementing it which is sometimes resorted as in soil cement if good materials are not readily available.
This leads us to one of the Fundamental Principle in Earth Compaction:
“Increasing Density (Strength) is achieved by decreasing the soil interparticle distance through the expulsion of air or water or both.”
As we shall see later on, reduction of interparticle distances would sometimes require addition of more water into the soil in order to dislodge more water. This statement appears to be confussing but its proof reiterates the importance of the understanding soil particulate behavior in the solution of Earthwork Problems.
5.0 MICROSTRUCTURE
5.1 Clay Microstructure
Let us now peer again at our microscope to look at a sample of cohesive or fine grained clay soil.
As we can see, the clay is composed of submicroscopic platelets surrounded by Electrical charges, a closely held layer of adsorbed water and an outer layer of loosely held water. The interparticle distances, measured in Angstroms are governed not only by the particle orientation but also by the Electrical forces of attraction as well as the thickness of the adsorbed and free water. It would take a very high input of energy in order to dislodged or remove the adsorbed layer. However, the loosely held water can be removed in the field by sample air drying or windrowing. Once the free water is removed, compaction can be attained. The particle orientation as we shall see in the succeeding table also affects some other physical performance characteristics of the soil.
5.2 Sand Particles
Obviously we do not need even a conventional microscope to be able to see the granular structure of sandy soils. In fact this can be done with the naked eye.
A very dry sand in the hand can not be squeezed into shape whereas a semi moist sand when squeezed could hold some shape until it dries out and crumbles. Surprisingly, addition of more water to saturate the sand collapses the sand as in the very dry state.
When grains of dry sand are gently deposited in a container, they fall into place in a precarious grain to grain contact. A jarring motion imparted on the container causes the grains of sand to assume a denser packing. Slight addition of water causes the sand to swell or increase in bulk while saturation with just enough water that is somehow allowed to drain causes the sand to be compacted into a dense state. This has been known to us since time immemorial as Hydrocompaction. Perhaps only the mechanism behind it is not well understood.
5.3 Microstructure of Fine Grained Soils
Fine Grained Soils, because of their sub microscopic size are influenced by Electrical and Chemical forces of attraction and repulsion This is due to the fact that the ratio of specific surface area to their volume is so large that surface electrical activity greatly influences the behavior of fine grained soils.
In nature, fine grained soils assume a flocculated or dispersed configuration as shown below depending on the manner of deposition and environmental influences that it has been subjected to.
A flocculated structure assumes a random tip to side orientation much like a “house of cards” whereas a dispersed structure have the platelets more or less aligned to each other.
The arrangement of these platelets alone have an influence on the performance and behavior characteristics of the soil.
The table above therefore suggests that we can alter the performance and behavior characteristics of the soil to suit our specific needs if only we know how.
As an example, an experiment with a clay material was made to determine the effects of compaction water on permeability. It can be noticed that although compaction density is the same left and right of optimum, the permeability values are not the same for this specific type of soil.
6.0 MOISTURE DENSITY RELATIONSHIPS
We begin with the all too familiar moisture density relationship known as the “Laboratory Proctor Test” for a clay soil.
Out total familiarity with this simple bell shaped curve and its universal acceptance as the “characteristic” compaction curve has caused most of the problems we encounter today in Earthworks compaction. Too often, it has not been realized that this is not the only shape a laboratory Proctor curve can assume and that grain size and moisture play a great part in influencing the shape of the compaction curve.
This bell shaped curve as, we shall see later on, is only applicable for fine grained soils or soils with significant plasticity as to make it perform as a clay like soil.
As we can see, at the start of the test when the soil is relatively dry, the soil assumes a flocculated structure “A” additional mechanical reworking and increasing amounts of water and subsequent expulsion of air and closing of the voids tend to produce a semi flocculated structure “B” with increasing density until a peak is attained. This peak is the maximum density that could be attained by that type of soil in the laboratory. This is expressed in terms of “Relative Compaction” which a percentage of the maximum dry density obtained in the laboratory test.
The moisture content corresponding to this maximum density is known as the Optimum Moisture Content “OMC”. Further compaction and aditional water beyond this point results in decrease in density with increasing amounts of water. The soil platelets begin to be oriented and aligned and the interparticle distances tend to widen as more and more water is captured.
We now look at the Moisture Density relationship curve for a coarse grained sand with very little or no fines.
Since the individual grains are relatively very very large compared to the clay platelets, we know that surface forces play very little influence on the behavior except at a certain moisture content range.
We see right away that the Moisture Density curve indicates two density Peaks “P1” and “P2” where density is high. The first Peak P1 occurs when the soil is very very dry (MC ‘ O) and the other Peak P2 at almost saturation conditions. We also see that between these two Peaks is a valley where density is lowest.
The reduction in density in this valley as defined by a moisture content range is known as the “Bulking Range” for this particular sand.
This reduced density is caused by surface tension forces of the water surrounding the individual grains which tend to drive the adjacent grains farther apart, causing loss of interparticle contact and collapse in the density from the previous high.
However, progressive addition of water beyond the bulking range collapses the surface tension and the additional hammer impacts increases the density again to the second Peak “P2”. The laboratory curve shows a downhill movement in density with increasing moisture content beyond saturation levels.
The real field curve shown by the dotted line suggests otherwise. The reason behind this is that in the laboratory compaction procedure, the water can not drain within the steel compaction mold and thus the soil becomes a soupy mush. However, in the field, additional water is continually drained and the Peak density is maintained.
This curve clearly shows the fallacy of specifying Proctor Compaction Procedures and an OMC for clean coarse grained soils, because definitely, the soils are insensitive to moisture content except at the very dry and very saturated conditions. Unlike clay soils which follow a typical bell shaped curve, clean coarse grained soils exhibit a typical “S” shaped curve with the Peaks P1 & P2 clearly distinguishable.
Peaks P1 & P2 may sometimes be equal but this is more of an exception than the rule and their relative maximum values could shift either way depending on the type of soil.
This soil behavior has been recognized by ASTM and standardized into two standards ASTM D-4253 “Max. Index Density of Soils using a Vibratory Table” ASTM D-4254 “Min. Index Density of Soils and Calculation of Relative Density” to arrive at a minimum and maximum density. These values are then used to compute the Relative Density DR once the Field Density is obtained.
Compaction is specified not in terms of % of MDD but rather as Relative Density DRand their relationship to each other is shown in Scalar Fashion.
Recognition of the two characteristic compaction curves (The “Bell” and the “S”) leads us to the realization that clays and sands behave very much differently when compacted and require different approaches and solutions.
We also know now that the behavior of soils can be tempered to suit our requirements as shown in the foregoing table particularly for a clayey soil.
Thus, we are led to the following conclusions:
There is not one but two General characteristic curves for soils depending on their granulometry.
The concept of Optimum Moisture Content generally does not apply to Clean Granular Soils and therefore the Proctor Standard is inappropriate or could lead to problems in the Field. Clean sands either have to be compacted very very dry or very very wet in order to achieve the maximum density.
The microstructure of the soil needs to be considered in the selection of the right compaction equipment.
For Fine Grained Soils, although density is the same for corresponding points left and right of the OMC, the performance and behavior of the soil are different due to the alteration in the microstructure arrangement.
Beyond the maximum density, additional compaction energy would be detrimental to both clays and sands as breakdown can occur causing a decrease in density. Therefore, use no more than what is necessary to attain good compaction.
For intermediate soils, it would be necessary to determine in the laboratory the characteristic behavior from zero MC to saturation levels.
In case the laboratory curve is not clearly defined or when there are doubts as to the behavior in the field, a field compaction trial would be required.
6.0 COMPACTION EQUIPMENT
Having recognized the behavioral characteristics of soils (Particulare Material) we now look at the means to achieve compaction in the Field.
However, try to remember the fundamental response of the two general types of soils to compactive effort:
Loose Clean Granular Soils because of their precarious grain to grain contact are best compacted by causing a jarring motion such as what a vibratory roller would impart.
Fine Grained Soils on the other hand respond better to a kneading type of compactive effort such as that imparted by sheepsfoot rollers and pneumatic type rollers as these tend to reorient the platelets.
We now look at the Chart below to determine the range of applicability of various compaction equipment:
We can therefore see the effective range for various compaction equipment under differing soil conditions and we recognize right away that this has something to do with the grain size (clay to rock).
At first glance, it could be said that this is a very familiar and well accepted practice.
However, it would be shocking to know that in a big project inside a U.S. Base, the Earthworks subcontractor was unable to compact the highly plastic soil despite repeated passes. Several weeks of reworks have passed before we realized that the contractor was using a Vibratory Roller on a clay soil. Over vibration of the clay soils had in fact caused the formation of Shear Cracks causing weakening of the soil! When the compactor was changed, the problems of the contractor vanished.
7.0 APPLICATIONS OF KNOWLEDGE GAINED
However, it is not only enough to know how to select the proper compactor for the job. It is also important to use this in conjunction with our knowledge of Soil Mechanics principles which we now apply:
7.1 Sands and Clean Coarse Grained Soils
Vibratory compaction works best. However, we should aid this by liberal application of water immediately ahead of the vibratory compactor. Remember, coarse grained soils compact best at the very very wet condition “P2” or at very very dry condition “P1”. Water serves as a lubricator but its total absence also prevents capillary forces from impeding the rearrangement of soil grains into a denser packing. Speed of the vibratory compactor is also important and needs to be controlled to about 2 to 4 KPH. Vibratory frequency is also essential and should nearly approach the natural frequency of the soils. Standard frequencies are in the range of 30 to 40 cps.
The static weight of the vibratory roller is also important since the dynamic force exerted on the soil is a function of the static weight. The wheels of the roller are either ballasted by water, sand or even slag in order to increase the static mass.
Because the vibratory roller causes an “advancing wave” on the top of the lift being compacted, Field Density Testing in order to be fair has to be done below this disturbed layer. It will normally be required to scrape the top 50 cms before seating the Field Density Plate in order to be able to test the actual condition of the specific lift.
Field Density testing using the Sand Cone Method (ASTM D-1556) requires extra care since the means to measure the volume is calibrated clean sand. Any jarring motion results in increased sand intake of the test hole resulting in bigger hole volume computed than the actual resulting in low compacted densities. This condition can also be caused by compaction equipment being allowed to operate very near a Field Density test in progress.
In one project, a bull headed contractor’s foreman could not be prevailed upon to stop his operations while tests were being performed nearby. He only relented when a series of “Failing” FDT results made him realize his mistake.
Back to the subject of moisture content, for clean coarse grained sands, moisture is irrelevant except for the total absence of it or its presence at saturation levels.
Thus, there is no such thing as an Optimum Moisture Content and proctor criteria is entirely inapplicable in this context.
7.2 Clays and Intermediate Soils
For Fine Grained Materials and intermediate soil types possessing significant plastic fines, sheepsfoot rollers or pneumatic tired rollers are best. The kneading action allows reorientation of the grain and allows expulsion of entrapped air.
The sheepsfoot was modelled really after the shape of a sheep’s foot perhaps based on the observations of Mr. Mc Adam. The tendency of the sheepsfoot is to walk- up by progressively compacting or densifying the lowermost layers first and walking upwards. Thus we see that topmost layers are slightly less compacted and therefore need to be bypassed when conducting a Field Density Test.
In stark contrast to clean coarsed grained soils, compaction moisture content and the Proctor criteria are fully applicable and the control of moisture during compaction is a crucial factor in the attainment of proper compaction.
Static weight is also important as it increases penetration of the sheepsfoot and increases the force pressing the platelets together.
Speed is not so critical as it is the kneading action and coverage that is important.
Vibratory motion is not necessary and is in fact harmful as it can cause build up in pore pressures in the soil and also cause shear cracking.
7.3 Lahar
Since Lahar is a byword in Central Luzon and since billions will be spent in Lahar Protection Structures, using Lahar as the primary construction material, it may be worthwhile to consider this as a separate material for this paper.
Although Lahar possess some fines, the fines are non plastic and consist of very fine ash particles.
Lahar drains easily and compacts readily as proven by river crossings which become passable as soon as the flood of Lahar subsides.
From this, we can already infer that Lahar behaves like a clean coarse grained material that it is.
Thus, Lahar is most sensitive to vibratory compaction and could compact well at very very dry or very very wet condition. Moisture control is unimportant except to see to it that either we have none of it or plenty of it during vibratory compaction.
We have done several tests on Lahar as a matter of research interest and our conclusions are as follows:
Lahar behaves as a perfectly granular material.
Lahar responds well to compaction even under ordinary vehicular loading and therefore the passage of construction traffic alone could assist compaction.
Lahar possess high initial CBR value but some degradation in the CBR strength occurs if the sample is aged at saturation conditions (this is probably due to breakdown in the ash coating the individual grains).
Significant sulfate levels were present (at least during the initial discharge) which could impair the integrity of Portland cement concrete when this is used as fine aggregate.
We have noted that several tests have been performed by some agencies which show the all too typical bell shaped curve and therefore an Optimum Moisture Content. However, it would be noted right away that compaction started at moisture contents of 3% or greater and thus the Peak “P1” remained undetected leading to erroneous conclusions and the unnecessary imposition of an Optimum Field Moisture Content.
8.0 CONCLUSIONS
The purpose of this paper would have been already truly served if the construction industry would start to recognize the differences in behavior between coarse grained and fine grained materials through the use of sound Soil Mechanics principles rather than from “feel” of guess work.
Often times, these fail in the actual field situation and the simple task of Earth Compaction becomes a costly and heartbreaking exercise.
Cracking and heaving of a Single Storey R.C. Building was initially perceived as settlement. This error led to unnecessary and costly remedial measures such as Piling for the Phase II Building which further aggravated the problem. The heaving was caused by a seemingly innocent decision during the construction stage to use Slag from a steel mill as the base course material. This Slag reacted with the highly corrosive groundwater which caused heaving of the Building and discomfort and morale problems to the Building occupants. Careful engineering study and investigation resulted in a very simple solution which saved the Building from abandonment and demolition.
INTRODUCTION
A Single Storey Precast Reinforced Concrete Research and Development Building was built in Two (2) Phases starting with the Phase I in October 1975. After the construction of Phase I, severe flooding in the area occured in October 1978. Severe cracks were observed in the Precast Post Tensioned Waffle Roof Slab and supporting Beams and Walls. Cracking and extreme waviness was also observed in the Floor Slabs, making office work very difficult. This initial cracking and distress became progressive over the years and “settlement” of the Building was suspected. Extensive structural epoxy adhesive repairs were made on the cracked portions by the original contractor. In addition full scale load tests were performed on the waffle roof slab.
Because of the suspected “settlements”, it was decided by the owner to construct Phase II on Pile Foundations. Soon after construction, cracks were also observed in this Phase II portion but in contrast to the Phase I portion, more severe cracking occurred on the walls and not on the slabs.
In the meantime, cracking continued on the Phase I structural elements despite the structural repairs. This condition was puzzling to the owners and several Engineers were consulted to look at possible remedial measures. Because of the client’s concern for the safety of its employees, abandonment and demolition of the Building were contemplated. It was at this point that our services were engaged to have a critical last look at the Building and to ascertain the cause/s of the problems. We were also asked to determine whether the progressive cracking can be arrested and the building rehabilitated with the safety of occupants being the foremost consideration.
DESCRIPTION OF THE BUILDING
The Research and Development Laboratory building was originally proposed as a two storey reinforced concrete building with precast post tensioned waffle slabs but after some distress was observed early on, the plan was abandoned. The facility was built in a low lying area in the suburban town of Pasig in Metro Manila. The area is sometimes flooded when the Marikina River overtops its Banks during a 10 year flood.
A two meter Engineered Fill was placed to elevate the Building’s Finished Ground Line from the surrounding area. A half meter layer of “heavy aggregate” base course was laid and compacted to support the slab on grade. This engineered fill and base course was laid to support the Parking, Driveway and the entire Building footprint to include the future Phase II addition. The filling and compaction for the whole area to include the proposed future Phase II addition were all done at the same time.
The center was constructed in two phases as follows:
Phase 1
This phase was constructed starting October 1975 on continuous footings supporting column loads through socket pedestals loading on to the continuous footings. Founding elevation is approximately 2.8 meters below finished floor line. The columns are 0.35m x 0.35m precast concrete columns inserted into sockets in the footing. The roof consists of approximately 1.0m x 1.0m precast waffle slabs joined together by cast in place concrete packing and post tensioning. A layer of water proofing was subsequently applied. Perimeter walls consist of 150mm CHB units and plaster finished with protruding fins also of CHB. Interior walls were also of CHB resting on the slabs. The floor is a 100mm thick reinforced concrete slab on “heavy aggregate” Base Course over the imported granular fill material.
Phase II
Phase II construction was started in August 1978 or approximately three (3) years after Phase I construction. The structural configuration is the same except that the new building was now supported on Pile foundations because of the observed distress and perceived “settlements” of the Building. This new addition was constructed by another contractor. The walls were now supported on Grade Beams with Flanges acting as continuous footings. The Grade Beams are in turn supported on Pile caps. The floor slab was still connected to the walls and columns by Dowels. Columns were embedded into the Pile caps.
OBSERVED DISTRESS
Two years after construction of the Phase I Building, Flooding occurred in October 1978. The flood waters rose to about 38 centimeters above the floor line of the Building. Although, minor cracking was observed in the Building even before October 1978, extensive cracks and more regular repairs reached its peak in 1982 and became a major problem and concern for the owner as well as the Building occupants. The corridor slabs became so wavy that normal walking was difficult and passage of pushcarts of chemicals had to be done carefully to avoid spillages. As earlier discussed, there were contrasting failure patterns and observed cracking between Phase I and Phase II construction. For clarity, these are discussed in detail separately as follows:
Phase 1 Distress
Phase I was constructed in October of 1975 on continuous footings resting on well compacted Engineered Fill. Severe cracking and extreme waviness were observed in the slabs. Maximum slab displacement is 130mm (5.21 inches) at the analytical laboratory. The 3D mesh plot of the slab deformations is shown in Fig. 1. The 2D Contour Plot is also presented in Fig. 2. Cracks have been observed in the masonry walls but were not as severe as in the Phase II Walls. A noticeable separation gap was observed between the roof and the wall with the exterior walls opening outwards. The extreme waviness of the slabs has made normal office work difficult. Desks and cabinets needed to be periodically relevelled on stilts (See Fig. 3) to prevent rolling of pens and pencils from the desk top. Fulltime carpenters had to regularly realign doors and windows to allow proper closing and opening. Light Partition Walls separated from Floor Slabs (See Fig. 4) However, the most serious effect was on the morale of the workers as they were constantly in fear that the Building is going to sink or collapse on them.
Phase 2 Distress
Soon after completion, the walls of the Phase II addition experienced more severe cracking than the corresponding walls of the Phase II portion. Waviness was detected in the slabs but somehow these were lesser in magnitude as can be seen in Figs. 1 and 2. The main indication that something was still wrong was in the extent and magnitude of cracking in the walls and constant adjustments on the doors and windows (See Fig. 3). Cracks were mainly opening upwards but in addition, some cracks tended to indicate that the walls were trying to separate from the columns (See Fig. 4). Leaks in the Precast Waffle Slab occurred, indicating movement of the roof slab. The floor slabs had perceptible bulges at the center of the panels but were not as pronounced as in the
Phase I Construction. Some Engineers consulted have even ventured as far as to say that the Piles have somehow “reduced the settlements” but no explanation could be given for the more severe cracking of the walls. These two highly contrasting distress manifestations baffled the client and the occupants of the Building. However, the general conclusion still was that the building was “settling” and that all remedies have been exhausted. Abandonment and demolition of the Building was therefore being contemplated.
INVESTIGATION
In early 1984, we were contracted by the client’s Corporate Engineering Department to undertake an investigation to unravel the seemingly conflicting failure patterns in the two buildings. Explanations were needed as to why despite substantial expenditures in Piled Foundations, the Phase II portion of the Building was still “settling” and cracking with more severe cracks in the walls than were observed in Phase I.
The investigation programme consisted of the following phases:
Soil Borings along the periphery of Phase II in order to determine underlying soil properties in the area of the piled foundation.
Test pits inside and outside of the building to retrieve soil samples and determine character of fill material in the area.
Laboratory soil classification and strength tests of soil and physical characteristics.
Laboratory chemical testing on soil leachate samples and water samples in the building.
Interviews with R&D Laboratory personnel and document review of various tests conducted for the R&D Laboratory Building relevant to the investigation.
Measurements of Ground Heave inside and outside of the building and the preparation of the subsequent Heave Contour.
Recording of observed cracks and structural features including photographs and their subsequent mapping to aid in the structural rehabilitation and repair of the building.
Analyses of possible loadings imposed on the soil by the foundation elements of the building and corresponding settlement analyses.
Understanding of construction plans furnished by the client insofar as it would assist in interpreting the responses of the various building elements to the heave forces.
The findings obtained in the foregoing investigation together with the results of various tests served as bases for the correlation and understanding of the mechanisms contributing to the observed problems in the building and outside of the building. No effort was spared to investigate possible causes of the cracks in the attempt to conclusively isolate the forces that are triggering the observed distress in the building. Immediately after our commissioning, we made exhaustive investigation and conducted interviews with Building occupants to reconstruct and piece together the chain of events. Almost all the Building occupants from the scientists to the Building Manager were of the opinion that the building was “sinking ” and that nothing further could be done to save the Building. Morale was so low that some employees interviewed thought that the investigation was another delaying tactic by the management to postpone abandonment of the Building because of the vital research studies being made at the time. All of these were proved to be untrue after a very challenging investigative work which in the end tied together all the loose ends and helped us arrive at a simple solution which saved the building. Early at the start of field work and testing, it was already clear to us that the crack patterns manifested were caused by heaving and not by settlements.
What was not clear to us at the onset were:
What was causing the heaving ?
What was the explanation for the differing crack patterns in the two phases of the building ?
Potentially expansive soils were not prevalent in the general area nor was the imported fill expansive, since it was essentially silty fine sand and therefore the agent causing the heaving had to be identified and isolated.
SOIL INVESTIGATION
The initial investigation program consisted of three boreholes around the Phase II Building to a depth of 20.0m average and several test pits outside the Building footprint. The borings were done to determine underlying soil strength parameters and also to detect the presence of potentially swelling soils. Since initially we suspected that the expansive soil was not the Engineered Fill, concentration of the soil borings was focused on natural ground about two meters below. Nevertheless, regular sampling and field classification was done starting with the base course, the Engineered Fill and the natural ground. The “Base Course” material was initially and innocently classified by the Field Engineer as “gravel base course”. It was only when we dug the test pits that we learned that this was no ordinary “gravel base” course as initially identified, since these were extremely heavy and there were large chunks that were like huge flakes in the test pit. Picks cannot even indent the material and finally, Saw cutting with a carbide blade showed that it was iron. What was also surprising to us initially was the presence of dark gray fluffy cotton like materials in the heaved portions.
SLAG USED AS BASE COURSE
Further investigation revealed to us that a well meaning and cost cutting decision was made during construction to use SLAG wastes from a steel mill as the base course material since it was free for the taking and it compacted readily. This “base course” was laid to a thickness of 0.30m to 0.50m in some places and was spread in all the proposed built-up areas including the future addition and the driveway. The gray fluffy cotton like material turned out to be SLAG that has fully expanded after corrosion (See Fig. 8 & Fig. 9). The expansion potential can be gaged from the size of the cavity and magnitude of heaving that it has caused. More numerous test pits were therefore recommended to be undertaken inside the Building footprint to verify the extent of the slag. All the additional test pits showed the uniform presence of the slag base course and the degree of expansion and corrosion that has occured underneath (See Fig. 7 & Fig. 8). Most of the test pits were excavated under the heaved areas and also some in the unaffected areas. In both cases, slag was present in varying conditions of expansion and corrosion. Levelling to determine the slab contours was also done inside the Building with the vertical Benchmark made outside the affected areas. The levelling was done using liquid level hoses because of the numerous partitions rendering optical levelling next to impossible. The results are depicted in Fig. 1 and Fig. 2.
RESULTS OF CHEMICAL TESTS ON SOILS AND WATER-R&D CENTER BUILDING
In some of our interviews, complaints were heard regarding the water from the deep well that was causing stomach problems and sometimes Diarrhea. Subsequently, we made recommendations to test the water from the deepwell and also in some of the adjacent Buildings and Factories being served by similar deep wells. The results are shown in Tabular Form in Fig. 10. The results show that most of the water from the deepwells in the area have corrosive potential as indicated by their Langelier Saturation
Index (LSI) values. Chemicals tests were performed on several soil sample Leachates and water from the Deepwell of the R&D Building. The objective of the tests is to determine corrosion potential after test pits showed the presence of slag (iron) in the general area investigated. The Langelier Saturation Index (LSI) was obtained by computation from the test parameters. The soil leachates were obtained by mixing one part of soil to one part of distilled water. The mixtures were shaken for two hours at 200 oscillations per minute and allowed to set for 24 hours.
The resulting extracts were analyzed for:
pH
Conductivity
Alkalinity
Total Hardness
Sulfates (SO4)
Chloride
Acidity
Fig. 9 tabulates the values of the various chemical tests conducted on water samples in Soil Leachates at the R&D Laboratory.
Several conclusions can be inferred therefrom as follows:
Water from R&D Laboratory and surrounding areas have corrosive tendencies. Of the thirteen (13) samples whose corrosion potential were measured using the LSI, seven (7) samples exhibited corrosive tendencies.
Chloride content for R&D well water is excessively high (about 800 to 900 ppm).
Sulfate (SO4) content of the slag is very high (975 ppm).
pH values indicate slightly basic to slightly acidic values for most of the water samples tested.
POSSIBLE MECHANICS OF CORROSION
Several possibilities could trigger the corrosion of the slag and its consequent expansion during the corrosion process. The resulting expansion has been found to increase the volume of the steel or iron by as much as 10 times its original volume, in the process generating large expansive pressures when confined.
Slag
The use of slag as a fill material proved to be detrimental as the material could corrode even in ordinary tap water given the proper environment. The slag obtained from most electric arc furnaces is slightly basic in character but contains large amounts of sulfates, manganese and other impurities from the steel making process. This is borne out by the very high sulfate content obtained in sample 5-14 of Fig. 10 from Test Pit No. 1. Because of the nature of the slag formation in the mill, vesicles were formed containing entrapped air. The large particle size (gravel to cobble size) of the slag also allowed air entrapment during the compaction process. The entrapped air promotedor accelerated corrosion because of the presence of oxygen.
Groundwater
As earlier stated, the groundwater is generally corrosive (Langelier Saturation Index Negative). In addition, chloride content is high which can trigger pitting and corrosion in the slag. The foregoing primary factors alone would already indicate the highly favorable environment to initiate and sustain corrosion. Since the total corrosion decomposition of steel or iron would be a long time dependent process, its simulation in the laboratory would for the purposes of this investigation be too long. However, samples extracted from the test pits showed varying degrees of decomposition and oxidation stages when tested in the laboratory using a NaCl solution. In order to fully understand the mechanism, the following definitions are extracted from ASTM 6-15-79a “Standard Definitions of Terms Relating to Corrosion Testing”.
Corrosion – the chemical or electrochemical reaction between a material, usually metal and its environment that produces a deterioration of the material and its properties.
Graphitic Corrosion – the deterioration of metallic constituents in gray cast iron which leaves the graphitic particles intact.
The corrosion of ferrous metals is caused by the tendency of iron (Anode) to go into solution in water as ferrous Hydroxide and displaced Hydrogen, which in turn combines with dissolved oxygen to form more water. At the same time, the dissolved ferrous hydroxide is converted by more oxygen to the insoluble ferric oxide thereby allowing more iron to go into solution.
Corrosion therefore requires liquid water (as in damp air) and oxygen (which is normally dissolved in water).
Corrosion occurs only in the presence of an ionizing medium. The most universal ionizing medium is water. No corrosion will occur in the total absence of water. The rate of corrosion is affected by the amount of dissolved oxygen present.
The dissolved oxygen could react in either of two ways:
By combining with the hydrogen film to expose the surface of the metal (which the film protects).
By combining with the dissolved ferrous hydroxide to form insoluble hydrated ferric compound and thereby allow formation of more ferrous Hydroxide.
The chloride ion solution tends to dissolve the protective coating already formed and tend to prevent new coatings being laid down thus further accelerating corrosion.
Having understood the probable corrosion mechanisms, the following can be theorized:
The corrosive groundwater as it was elevated by flooding or during the rainy season immersed the metallic slag in solution causing decomposition. Sufficient dissolved oxygen is existent in the soil and trapped in the large voids present in the slag.
The R.C. slab acted as an impermeable membrane which ensured entrapment of moisture keeping the slag in at the very least a moist environment. This ensured progressive corrosion. Because of the confinement of the surrounding soil on the slab, the slag exerted an upward pressure which offered the least resistance causing the slab to heave.
In addition to the foregoing and as can be shown in the subsequent sections, possible leakages in the pipes, more specifically in the acid and waste chemical lines could have aggravated the corrosion.
Inspection of the photographs and test pit logs (See figs. 11 & 12) clearly show that the slag layers have expanded upward and heaved the concrete pavement.
OBSERVATIONS ON THE RELATIVE MAGNITUDE OF CRACKS
With reference to the slab displacement contour map (Fig. 1 and Fig. 2), it can be shown that Phase I has heaved or displaced more than the Phase II. Although the two are supported by different foundation elements (continuous footing vs. pile foundation for Phase I and Phase II respectively), this would not really explain why there is less heaving and cracks in Phase II because if heaving of the same magnitude have occured, more damage would have resulted because of the rigid restraint offered by the piles. It is only possible then that because the slag fill have been laid out all at the same time, that substantial unconfined or unrestrained heave has already occured over time in the Phase II area before construction could take place. Unlike in Phase I, where the slab offered confinement and trapped moisture as to cause progressive heave under restraint. In addition, although it could be observed that there are relatively fewer cracks in Phase II, it can also be shown that in contrast to Phase I, the walls in Phase II are more damaged compared to the floor slab where displacements are minimal. The foregoing is explained by the fact that while substantial heaving has already transpired, the residual heave after construction, though not as large as Phase II displacements, have cracked the walls because of the relatively more rigid restraint or pullout capacity of the piles. Thus the walls were affected more than the floor.
Fig. 4 which was taken along the corridor near the interface between Phase I and Phase II showed a unique but typical crack pattern in Phase II that is not manifested in Phase I.
The crack pattern shows propagation from the floor intersecting the column line diagonally on both sides. This shows that the wall is flexing but because of the rigid restraint of the walls, has failed the wall in shear instead, because of the upward pressure on the wall footings.
Several conclusions can be made on these observations:
There is less displacement for Phase II simply because the slag has already partly expanded before Phase II was constructed.
It is not true that the pile foundation had in some way contributed to reduction of cracks. On the contrary, if the Phase II portion would have been subjected to the full heave potential of the slag as in Phase I, more damage would have occured because of the more rigid restraint.
EFFECT OF WATER AND CHEMICAL LINES
Closer inspection of the displacement contour map would show that the following areas were the most affected by the heaving in descending order.
Experimental Section
R&D Office
CENLAB Office
Technical Library
These areas have one thing in common, and this is the presence of water lines and chemical lines near the heaved areas. It is suspected that the lines have leaked or burst due to corrosion from the groundwater or galvanic corrosion with the slag (dissimilar metals in contact) or have been broken by initial heaving thus contributing to acceleration of the corrosion process. Even without the foregoing, leakage of chemicals has been detected in the PVC connections of the chemical sinks in the Experimental Section. This condition probably contributed more corrosive chemicals under the slab as to cause the extensive Heaving in the Experimental Section.
RECOMMENDATIONS MADE FOR REMEDIAL ACTION
After satisfactorily proving to the owner that the Building was actually rising due to heave and not “sinking” as originally perceived, we set out to make recommendations on remedial measures that need to be undertaken. Since the Building was not on the verge of collapse nor seriously damaged by the heaving, we submitted a three staged rehabilitation program. This was necessary as critical research work is ongoing at the time and total or major disruption could not be allowed for the time being. The following were the remedial stages as recommended:
Stage I : Release of Floor Slab from wall
The floor slabs which were originally dowelled into the perimeter walls and interior walls were recommended to be saw cut using a diamond saw. This has the effect of releasing the walls from any uplift pressures acting on the slab. This will in turn reduce the cracking on the walls and other structural elements.
Stage II : Removal of Slag Base Courses
As soon as facility work load permits, the slabs that were released by diamond saw cutting shall be removed and the slab excavated and replaced by compacted clean granular Fill. All water utilities (Drainage & Sewage) as well as chemical lines shall be inspected for damage or corrosion and if need be, replaced by PVC Pipes or Compatible Plastic Pipes in the case of the chemical lines. The columns should be inspected to determine if any pullout from the socket footings has occurred so that this could be repaired. The granular Engineered Fill Subgrade shall be tested in case any residual acidity is present and this shall then be neutralized with lime milk before the granular base course is placed and compacted.
Stage III : Monitoring and Crack Repair
We recommended installation of a permanent reference Benchmark to monitor further movements in the Building after Stage I and Stage II repairs have been implemented. In case movements have ceased, epoxy repairs of all cracks should be undertaken after thorough cleaning of all cracks.
CONCLUSION
The owner has implemented Stage I and Stage II for the Phase I structure and Stage I for the Phase II structure. In the case of the latter, the freeing of the Slabs was already sufficient to arrest further cracking of the walls. Since swelling was preinduced before Phase II Construction, the resulting heave after construction was very much less than the heaving experience in Phase I Construction.
Stage III was subsequently carried out and to this time no further distress or cracking has been reported in any of the Building Elements. The paper illustrates how a seemingly innocent decision to use “good aggregate” in the form of slag as a base course nearly caused the abandonment and demolition of a building. It also illustrates how the initial but erroneous perception of movement of the structure as being downward or “settling” has caused additional but unecessary expenditures in the form of Piled foundations for Phase II Construction. The use of Piled foundations aside from adding to the cost and giving false hopes, only aggravated the problem by increasing restraints on the walls causing more serious cracking in the latter. The investigative procedures employed led to the isolation of the slag as the agent causing the heaving of the Building and the cracking of various structural elements. The resulting simple remedial measures employed, which consisted of removal of the slag and freeing of the slab connections from to the walls, saved the Building from abandonment and demolition.
Abstract: The need for reliable, fast and inexpensive soil investigation procedures has been felt in the local construction and consulting industry. The Electric Static Cone Penetrometer (CPT/CPTU) although widely used in more developed countries has seen very limited technical and commercial applications in our country due to its near total absence in commercial testing. This paper was originally prepared as a primer for our end-user units. However, it was expanded into this paper to present the State of Practice in the gathering of soil data using the Electric Cone Penetrometer (CPT/CPTU).
The various applications and limitations of the equipment and the procedures are discussed as well as findings on the results of local correlation tests conducted in the country. Directions on future applications and enhancements are also covered to fully exploit the potential of this testing method.
1.0 INTRODUCTION
1.1 General
The Cone Penetration Test (CPT) commonly known as the Static Cone Penetration Test (as opposed to the SPT, which is a Dynamic Penetration Test) or simply the Dutch Cone Penetration test, originated in the Netherlands.
It evolved out of the need to have a relatively simple and expedient test procedure that would be more economical and cost effective when compared to the SPT and yet yield meaningful data which could be useful in site characterization and the gathering of design parameters by correlation with extensive Insitu and Laboratory Testing results.
The CPT is most useful in stratigraphic interpretation where its value is unsurpassed. Because it is a continuous test of soil resistance, it can detect minute changes in stratigraphy and consistency/density and thus give a more reliable picture of the underlying soil conditions.
Due to the wealth of data accumulated in the past throughout its evolution, soil classification is relatively well defined through correlation charts using the three basic outputs of Cone Resistance qc, Friction Sleeve Resistance fs and their ratios fs/qc known as the Friction Ratio Fr. In the case of the CPTU or Piezocone, pore pressure u is also measured leading to improvements in correlations particularly for very soft clays and borderline characterizations. Invariably, correlation with local soils are necessary, particularly for borderline correlations, but for the major generic soil types, this is fairly well established.
The Chart (after Robertson, 1991) and included as Appendix “A” is recommended for initial classification by correlations. This would normally be augmented by a limited number of Boreholes to confirm or verify the local soil characteristics specifically in Borderline correlations to come out with Detailed Stratigraphic Information on the area investigated. Gathering of design parameters for Strength (Cu, ϕ ), compressibility (M & Dr) and other parameters have also been evolved by various researchers and for routine jobs, these correlations would suffice. For more important jobs, further tests using other established methods must be necessary such as laboratory tests and correlations with other test procedures such as the Vane Shear, Pressuremeter or Dilatometer.
1.2 History
The CPT originally started in 1932 in the Netherlands when P. Barentsen used a crude device which was made of a Gas pipe, inside of which a steel rod is inserted and to which a 60 deg. Cone was attached. This assembly was pushed down by hand, the cone resistance was read by a manometer.
Improvements to this crude device were made by Begemann resulting in a Mechanical Cone Penetrometer which added an “adhesion” jacket behind the cone tip. Using this new device, the Skin Friction could be measured by means of a manometer. Readings were made every 0.20m and the Rod string (Inner Rod and Outer Rod) is advanced alternately and incrementally while recording the manometers. A method for soil classification through the Cone Resistance and Friction Resistance became possible. In 1965 Begemann was also the first to propose that the Friction Ratio Fr could be used to classify soil layers in terms of soil type. 1]
The Electric Cone Penetrometer has eclipsed the use of the Mechanical Cone Penetrometers except for very limited applications where damage to the sensitive Electric Cone Tip is possible.
The Electric Cone Penetrometer was probably first developed in Germany during the war.
It was soon recognized that this was a very important development which eliminated the uncertainties and inaccuracies associated with the Mechanical Cone Penetrometer. Among its advantages relative to the Mechanical Cone Penetrometer are:
Elimination of erroneous interpretation of test results due to Friction between inner and outer rods.
A continuous testing with a continuous rate of penetration without the need for alternative movements of different parts of the penetrometer tip and no possibility for undesirable soil movements influencing cone resistance.
The simpler and more reliable electrical measurements of cone resistance with the possibility for continuous readings and easy recording of results.
Further improvements were made such as the incorporation of an inclinometer and introduction of a pore pressure (u) measuring system resulting in the CPTU or the Piezocone.
1.3 Details of the CPT
The Cone Penetration Test (CPT) is an In-situ procedure whereby a cone of Fixed Dimensions is pushed into the ground at a constant rate of 20mm/sec + 10%. The Penetrometer Tip as used in the Modern Day Electric Cone Penetrometer consist basically of four (4) major parts. The Cone, the Sleeve, the Inclinometer and the Body.
The cone has a 60 deg. Apex with a maximum diameter of 35.7mm with a height of 30.9mm and a shoulder height of 10mm. The maximum cross sectional area of the Tip Base is 1,000 mm2 corresponding to a diameter of 35.7mm and a height of the conical part of 30.9mm.
The Friction Sleeve has an outer cylindrical surface area of 15,000 mm2 + 2% which corresponds to a sleeve length of 133.7mm and is located above the tip.
The inclinometer detects and registers the inclination of the penetrometer from the vertical which is critical to prevent damage to the sensitive parts of the penetrometer or the drill string.
The body holds the three together and contains the Electrical Strain Gages to monitor the Tip and Friction Resistances and also the inclination reading in the form of electrical signals which are transmitted via connecting cable to an analog to digital converter which records the Friction and Tip Resistance and inclination versus depth and sends them to the computer. The computer then processes these data into usable output after interpretation of the signals using the prestored Penetrometer and Inclinometer Calibration Data.
The Cone is connected to a string of Push Rod which is inserted downward at a constant rate of Penetration of 20mm/sec by a thrust machine with a push capacity of at least 5 MT to 20 MT. Depth of Penetration is automatically recorded by a Linear Transducer synchronized with the other analog signals fed into the converter.
Normally, a Friction reducer is located above the penetrometer not less than 1,000mm from it. Schematically, the set up is shown below in Fig. 1.0:
1.4 Present State of Technology
Due to its reliability and popularity, the Electric Cone had undergone numerous improvements in accuracy and performance.
In addition, and due to advances in Electronics and Computer Technology, new capabilities are being added which would make possible the gathering of other parameters needed in Geotechnical Engineering and Geoenvironmental applications.
The development of more accurate and reliable strain gages has allowed the gathering of more reliable data. Multi channel capabilities, electronics miniaturization and improvements in signal processing and conversion have allowed gathering of various data concurrently or separately such as:
Cone Resistance (qc)
Friction Resistance (fs)
Inclination ()
Pore Pressure (u)
Seismic Wave Information
Shear Modulus G
Ground Water Chemical Properties
PH
Resistivity
Conductivity
Heat Flow (T)
Density (s), Moisture Content (MC) by Nuclear Probe
The Basic Electric Cone Penetrometer as we know it today, as a result of these advances, has come to be known as a rugged, reliable and relatively cost effective In-situ testing device for Geotechnical Engineering.
1.5 Test Standardization
During its early stages of Development, various sizes and configurations from various countries were in use. In order to provide reliable data through correlations, it was recognized that standardization was highly necessary as differing Penetrometer Geometry and the test procedures could produce highly differing test results. Since to some extent, soil strength is dependent on the rate of deformation (insertion of penetrometer) it was necessary to standardize this to 20mm/sec + 10%.
Several National Standards such as the Swedish Standard for Cone Testing and the US ASTM D-3441-86 have evolved.
In a bid to unify various national standards, the ISSMFE (International Society for Soil Mechanics and Foundation Engineering) came out with a reference Test Procedure which is expected to be adopted as The world standard for Cone Penetration testing. This is expected to be revised soon.
The present Swedish Standard for Cone Testing of 1993 exclusively refers only to the Electric Cone Penetrometer by specifying that measurements shall be done by Electrical means.
The mechanical cone is used less and less today because of related inacurracies and the cumbersome test procedure involved.
2.0 OFFICE & FIELD PROCEDURES
2.1 Equipment
Essentially, the Electric Cone Penetrometer set up would include the following:
Thrust Machine 20 MT Push Capacity (normally a special purpose Built Truck)
CPT Set
Cone
Friction Reducer
Push Rod String
Cable
Field Computer & Data Logger
Field Tools for Clearing and Maintenance of CPT
Office Computer
This is shown schematically in Fig. 1.0.
2.2 Office Procedure
2.2.1 Job Diskette Preparation
In order to avoid confusion in the Field, as invariably CPT Exploration would involve numerous exploration points per project and because the system is fully automated, it is necessary to prepare the exploration plan in the office.
Normally, Job Floppy diskettes would be prepared in the office which would contain the following information:
Job Number
Project Name
Location
Client Name
Cone & Inclinometer Calibration Data
2.2.2 Calibration
In addition, regular calibration at maximum 3 month intervals are carried out in the office as mandated by ISSMFE. The calibration is done to ensure that the cone & sleeve strain gages are within tolerance using a Force Transducer that is in turn calibrated to a higher standard.
2.2.3 De Airing of the CPTU
In addition to the foregoing and in the case of the CPTU (Piezocone), the Pore Pressure Filter System needs to be thoroughly deaired in order to ensure proper response of the Pore Pressure system to minute changes in Pore Pressure during the Pore pressure Dissipation test. This is done by subjecting the Filter to immersion in glycol inside a closed chamber. Vacuum is introduced to allow the air bubbles to boil out of the Filter and the Glycol solution. The Filter is shipped to the field completely immersed in Glycol using say a plastic or rubber sheath until it is inserted into the soil.
2.3 Field Procedure
2.3.1 Field Test Operations
In the field after equipment set up, the Job Diskette is loaded and the corresponding test point location is chosen.
The test is initialized by first ensuring zero (No Load) reading on the Penetrometer for qc and fs by hanging the CPT Cone in the Drill String on air. This is recorded antomatically by the software as a correction.
Normally a hole is predrilled by Auger on the Thin Dessicated Dry Crust to prevent damage to the CPT Tip before starting penetration
The verticality of the Push Rod and Thrust machine is checked in order to ensure that the thrust is vertically aligned. The deviation should not exceed 2% and the axis of the rods should coincide with the thrust direction. Normally levelling is done by Hydraulic Jacks.
The rate of penetration shall be 20mm/sec + 10% and stops are only made for Push Rod addition or when performing Pore pressure Dissipation Tests.
Readings are taken by the instrumentation and software for qc & fs at maximum 50mm (2 inches) increments averaged to within 50mm.
Depth of penetration is also recorded and measured with an accuracy of 100mm by an automatic linear transducer (Depth Gage) with a resolution of 10mm.
Most software have real Time Screen Displays of qc, fs, Fr, Inclination θ , Pore Pressure (u) and Rate of Penetration to enable the operator to control the operation and monitor critical parameters and ensure that tests are performed properly. The results are automatically stored in the hard disk of the Field Computer and the Job Floppy Diskette after the test.
2.3.2 Maintenance and Repair
In between tests, the penetrometer is visually inspected for any damage. All the seals are also inspected and any dirt inclusions are removed or cleaned to ensure proper performance during the test. If necessary, the penetrometer can be field disassembled to replace any broken seals or O-Rings and to lubricate the O-Rings.
2.4 Office Data Reduction
The data gathered in the field contained in the Job Floppy Diskette is sent to the office and is reduced and interpreted to yield the stratigraphy of the site investigated and other data which could be used for determination of Design Parameters.
Software is also available to automatically determine soil parameters but this has to be tempered with local experience.
3.0 TEST DATA GATHERING AND PRESENTATION OF RESULTS
3.1 General
The primary purpose of the CPT is to gather soil resistance data in order to effectively characterize the soil continuously with very little gaps in the stratigraphy. Through well established correlations and augmented by local experience, the site characterization is accomplished most efficiently. In stratigraphic characterization, the electric CPT is acknowledged to be the best insitu tool because it gives a continuous resistance profile of the subsurface. Because it is relatively inexpensive to perform, numerous points could be investigated to yield a more accurate horizontal characterization of the site.
Although various parameters obtained by correlation do not replace more accurate laboratory tests, the quality of data can be upgraded by local correlation. This is done by performing a limited number of boreholes and performing laboratory classification and strength tests (shear strength and compressibility) on the samples retrieved.
Essentially, stratigraphic characterization and parameters correlation (Strength, Compressibility, Dr, Gs, etc.) are obtained by the CPT through the continuous recording of the following data:
qc – Cone Resistance
fs – Sleeve Resistance Fr – Friction Ratio = fs/qc μ – Pore Pressure (for the Piezocone)
Because the CPT is standardized (As, Ap and rate of penetration) the correlation with numerous other tests performed in the past worldwide have given a wealth of data to make such correlations reliable.
These cone data are discussed individually: 2⎦
3.2 Cone Resistance (qc)
The cone resistance is the force per unit area which is obtained by the dividing the total axial force against the tip by the cross sectional area of the Tip Base (1,000 mm2).
Thus:
Alternatively:
In the special case where u = 0 or u is negligible, qc≈qt. The cone resistance is expressed in Mpa or Kpa.
3.3 Local Side or Sleeve Friction (fs)
The local side Friction is obtained by dividing the total Friction force acting axially on the Friction Sleeve by the outer surface area of the sleeve.
In the special case where the pore pressure effects are zero or negligible, fs ≈ ft. The local sleeve friction is expressed in Mpa or Kpa.
3.4 Friction Ration (Fr)
The Friction Ratio is the ratio between the local sleeve friction (fs) and the cone resistance (qc).
The ratio is expressed as a percentage. Normally, Fr for sands is seldom over 1% and for clays is normally > 4%.
3.5 Pore Pressure u and Change in Pressure (Δ u)
With the advent of the CPTU or Piezocone, which measures pore pressure and enable the performance of Pore Pressure Dissipation Tests, more detailed tests can be performed and strength parameters for very soft soils can be obtained.
The Differential Pore Pressure ratio DPRR is the ratio between the generated pore pressure and the cone resistance at the actual level.
Recent studies have shown that even with careful procedures and corrections for pore pressure effects, the measurement of sleeve friction (fs) is often less accurate than the cone resistance.
To overcome problems associated with sleeve friction measurements, several classification charts have been proposed based on qT and pore pressures (Janbu and Senesset). The chart by Janbu & Senesset use the pore pressure parameter Bq.
Experience has shown that, although the sleeve friction measurements are not as accurate as qT and u, generally more reliable soil classifications can be made using all three pieces of data (qT , fs & u). Thus, the normal correlation charts for characterization is three dimensional. 1]
3.6 Pore Pressure Dissipation Tests 3⎦
The CPTU or Piezocone has the potential of providing estimates of the in-situ coefficient of consolidation from dissipation tests. A dissipation test can be performed at any depth by interrupting the penetration at that depth. This will be discussed in later sections.
4.0 INTERPRETATION OF CPT/CPTU DATA
4.1 General
Numerous studies and data correlation have been made in the past as the CPT/CPTU evolved from a simple penetration test to what it is today. With the advent of sophisticated electronics and test standardization, correlation with various soil parameters could be made with increasing confidence. However, as in all applications in soil mechanics, such correlations need to be tempered with local experience and local soil behavior and validated by actual Laboratory Tests until the local correlations are adequately established as to be reliable. Various soil information can be gleaned from the simple CPT Tests and when augmented with pore pressure data from the CPTU, increased accuracies and reliability can be obtained.
The following correlations and soil information may be obtained with the CPT/CPTU tests:
4.2 Stratigraphy
The CPT found its most useful and valuable application in stratigraphy and site characterization. And in this aspect, this insitu test is most superior to any existing method because it provides a continuous profile of the soil and is relatively inexpensive. Thus, more numerous test locations can be done providing a closer interval for visualization of soil conditions. For routine jobs the CPT test would suffice and for more critical jobs of large magnitude, the CPT can be augmented with a limited number of Boreholes and Laboratory Tests.
The stratigraphic characterization is obtained using the Basic CPT Data qc, fs, Fr and u.
The characterization is best done using the Three Dimensional correlation chart by Robertson (1990) and included in Appendix “A”.
Using raw CPT Data or normalized data, one can determine characteristic soil descriptions of soils using this chart. Only occassionally, when borderline cases are encountered in routine jobs, is there a need to do more detailed sampling by borings.
Robertson suggested that the charts are still global in nature and should be used as a guide to define soil behavior type based on CPT and CPTU data. Factors such as change in stress history, in situ stresses, densitivity, stiffness, macrofabric, mineralogy and void ratio will also influence classification.1]
Essentially for clays and silts, Cone Penetrometer is undrained thus measurement of Pore Pressure is important since the rate of PP Dissipation is a key to classification. Cone resistance should be corrected for pore pressure effects. In addition, measured pore pressures can also be used directly for interpretation in terms of soil design parameters.
4.3 Soil Unit Weight & Relative Density Dr
4.3.1 Soil Unit Weight (s)
Larsson and Mulabdic (1991) based on tests performed in Sweden and Norway, proposed the chart in Appendix “B” for obtaining a rough estimate of soil density for clays. This is an iterative procedure since an initial estimate of γ s is necessary to compute net cone resistance and Bq.
4.3.2 Relative Density Dr
Several relationships have been evolved for determining Relative Density (Dr) of Sands. However, ageing effects tend to increase cone resistance and no interpretation procedure could take account of ageing. Thus, to some extent, the obtained Dr should be referred to us “equivalent” Dr as recommended by Robertson. 1]
The value of Dr can be obtained from the chart in Appendix “D” or in equation form based on the values below:
4.4 Strength Characteristics
Various procedures have been evolved from which direct correlations can be obtained to yield soil strength parameters out of basic CPT data (qc, fs & u).
4.4.1 Clay & Fine Grained Soils
The undrained shear strength (Su) can be determined in several ways from empirical correlations.
The empirical correlation is of the general form
Robertson recommends the following procedures for Su determination: 1]
1) For deposits where little experience is available, estimate Su using the total cone resistance (qt) and preliminary cone factor values (Nkt) from 15 to 20. For a more conservative estimate select the upper limit.
For normally and lightly overconsolidated clays, Nkt can be as low as 10 and for stiff fissured clays as high as 30.
In very soft clays, where there may be uncertainties in the accuracy in qt estimate Su from the excess pore pressure (Δ u2) using NΔ u from 7 to 10 in the CPTU.
2) If previous experience is available in the same deposits, the value suggested above should be adjusted to reflect this experience.
3) For larger projects, where high quality field and laboratory data may be available, site specific correlations should be developed based on appropriate and reliable values of Su.
4.4.2 Coarse Grained Soils
Cone penetration in coarse grained soils is generally undrained, thus, no excess pore pressures are generated. Established correlations using large laboratory calibration chamber tests have been made with this assumption.
The procedure as recommended uses the charts in Appendix “E”.
The ϕ ′ from relatively uniform uncemented clean sand is empirically estimated from Fig. 5.56 in Appendix “E”. Figure 5.55 can be used to adjust the estimated ϕ ′ to account for variations in compressibility and Ko. A reasonably conservative value of ϕ ′ should be selected based on the range obtained.
4.4.3 Intermediate Soils (Clayey Sands to Silts)
The methods for interpretation applied for clays or sands may not be totally valid for silts as penetration in this material is partially drained. In this regard clay content of the silts is important.
It is important therefore to determine the type of drainage conditions encountered during the tests. If the design problem involves undrained loading and the CPT is undrained, then the CPT data can be interpreted in a manner similar to clay and similarly for drained loading and drained CPT in sands.
The CPTU Pore Pressure Dissipation tests could give the plot of pore pressure decay over the time the test was performed. From this data, τ 50 – the time for 50% dissipation can be obtained.
Robertson proposed a chart relating τ 50 (minutes) to Kh (cm/sec) since drainage in the CPTU is essentially horizontal.
Vertical Permeability Kv can be obtained from well established field values relating Kv to Kh after Jamiolkowski 1985 and presented in chart form below:
4.5.2 Coefficient of Consolidation (Ch)
The coefficient of consolidation Ch in the horizontal direction can be approximated from the chart as proposed by Robertson (1992) from an extension of the work by Houlsby & Teh and shown in Appendix “F” relating τ 50 as defined above and Ch (cm/sec2). The relationship between Ch and Cv – the coefficient of consolidation in the vertical direction is obtained similarly from the above table relating Kh to Kv.
5.0 DIRECT APPLICATIONS OF CPT/CPTU DATA
In the foregoing section, interpretation of CPT/CPTU Data was directed towards correlation with soil strength parameters aside from other properties such as unit weight, relative density, stratigraphy, etc. These parameters in turn can be plugged into the various formulas (Theoretical or Empirical) to yield Bearing Capacity, Settlement, etc.
However, and particularly for Driven Piles, direct applications of CPT/CPTU Data could result in direct prediction of Pile capacity. The CPT procedure is a scale model of a Pile being inserted into the ground. Thus predictions of capaity are fairly more reliable. The reason being the ability to do continuous profiling of the subsurface soil response.
Superiority of the CPT method over non-CPT methods have been confirmed in other studies. 1]
Literature is replete procedures to use data gathered from the Electric CPT/CPTU Tests directly to provide solutions such as:
Pile Capacity and Settlement
Bearing Capacity of Shallow Foundations
Settlement of Shallow Foundations
Ground Improvement Quality Control
Liquefaction Assessment
In all the foregoing, reduction factors need to be applied to CPT Values. The need for such reduction factors is due to scale effects of the test, rate of loading or insertion technique. 1]
6.0 CONCLUSION AND SUMMARY
The foregoing presents the Electric CPT/CPTU its advantages and advantages in obtaining soil parameters needed in Geotechnical Engineering and Foundation Design.
Its ease of use resulting in reduction in cost of investigation without degradation of information obtained from such tests is certainly an important consideration.
It is hoped that this paper would pave the way for increased understanding and wide acceptance of the procedure as an invaluable tool in Soil Exploration.
ABOUT THE AUTHOR
Engr. Emil M. Morales Graduated from Mapua Institute of Technology where he earned his Bachelor of Science Degree in Civil Engineering. He Finished his Master of Science Degree in the same field at Carnegie Institute of Technology, Carnegie Mellon University, Pittsburgh, PA, USA.
He worked as a Project Engineer at D’Appolonia Consulting Engineers, Monroeville, PA. Where he was involved in the preparation of Software for Data Reduction for the Menard Pressuremeter.
He attended a short course in the Use of the CPT, Pressuremeter and the Dilatometer at Texas A&M University under Dr. Briaud.
He also recently trained in CPT Operations, calibration, maintenance and Software at the facilities of A. P. Van den Berg in Heerenveen, the Netherlands.
He is currently Chairman of the ASEP Geotechnical Committee and a Life Member of the same Association. He is also a member of the ASFE – Professional Firms Practicing in The Geosciences, ASCE, ACI, CRSI & ASTM.
1] Lynne and Robertson. “Cone Penetration Testing” 1st Ed., 1997. Blackie Academic Press, London, UK
2] Swedish Geotechnical Institute. “Recommended Standard for Cone Penetration Test”. Linkoping & Swedish 1992, Swedish Geotechnical Institute.
3] Briaud, J.L. “The Cone Penetrometer Test.” 1991 FHWA Office of Technology Administration, Virginia, USA
ABSTRACT: Quality in the Construction Industry and the workplace is a necessary ingredient for success. Too often, Quality is neglected sometimes with disastrous results.
As a Professional Design Engineering and Consulting Firm, we realized very early on that we needed to formalize our Quality Control procedures into a single coherent strategy in order to assure consistency and reliability of the Checking, Peer Review and Management Review processes. These activities were necessary not only to assure quality but also to safeguard our reputation and protect the general public by ensuring safe and cost effective designs.
The opportunity came when our biggest client, who was also getting into the ISO 9000 Quality System, required that downstream contractors and service providers also qualify for ISO 9000 Accreditation. We took the challenge and became the First Filipino Engineering Consulting Firm to be accredited under the ISO 9000 System.
This paper describes our quest for ISO 9000 accreditation which we would like to share with the Profession and the Construction Industry. Admittedly, as we shall soon find out, there is not “one single” Quality System for all and that Quality Systems and procedures should be attuned and tailor made to each individual organization’s needs. However, it is hoped that conscientious adherence to the ISO 9000 Quality System Guidelines and our experiences which we share in this paper will somehow help our Industry to become one of the most efficient, safest and cost effective sector in our country.
1.0 INTRODUCTION
We got introduced to the ISO System through the backdoor. Our sister Laboratory, Philippine Geoanalytics, Inc. just completed accreditation as the First Philippine Laboratory ever to be accredited under ISO Guide 25. The quality system was therefore in place in one of our sister organizations, although in this respect ISO Guide 25 is a more stringent system than ISO 9000 in that it required checking of the technical competency of the personnel to perform Laboratory Testing Procedures.
In addition, and more importantly, we were informed by our biggest client to prepare for ISO accreditation if we are to remain as a service provider for them. This client even sponsored our attendance in their in-house ISO 9000 Briefings and Seminars in order for us to fully understand the quality system and how best to synergize with them. Our client, who was actually on the verge of obtaining ISO 9000 accreditation for most of their plants was the catalyst in speeding up our process for accreditation.
This is not however to be taken as an indication of the lack of desire from within to seek ISO accreditation. For already, we were seeing the positive effects of what ISO Guide 25 was doing for our Laboratory—Morale was up, client satisfaction was at an all time high, income had increased by leaps and bounds, lost records and books have become a thing of the past and order has finally been restored in a very chaotic environment normally found in testing laboratories.
Thus, there was a very strong and compelling reason for us to qualify for ISO 9000 Accreditation.
This paper describes our preparations, documentation process and employee orientation. It is worthwhile mentioning that we undertook this assignment using exclusively our internal resources and manpower. We did not hire a pre audit service nor engaged consultants. This had the advantage that all our employees needed to participate to ensure our success. It was gratifying for us to observe teamwork in action, as our employees were highly motivated to accomplish this task.
How this happened is also discussed in this paper.
2.0 BENEFITS OF THE ISO QUALITY SYSTEM TO THE ENGINEERING ORGANIZATION
Although some of the benefits may not be readily apparent, a Quality System formalized and religiously implemented in an Engineering Organization can confer numerous advantages to it.
Oftentimes, compliance to ISO 9000 may be driven by the desire to comply based on client pressure or requirements. Sometimes it is done in the mistaken belief that ISO 9000 Quality System by itself can increase revenues or can assure quality of products or services.
But what are the true and real benefits of ISO 9000 to an Engineering Organization? In our case, the ISO 9000 Quality System had given us numerous benefits unimaginable before which are normally the least tangible benefits and these are:
Substantial improvement in internal operations.
Elimination of lost or misplaced documents and communications.
Simplified and formalized procedures for review and quality control of designs
Reduced time of document retrieval to within 5 minutes.
Increased employee awareness of the need to preserve quality and reduce errors to a minimum.
Traceability of design and drafting errors resulting in reduced error counts.
Increased employee morale because everyone knows their role in the organization and their importance in the maintenance of the Quality System and Procedures.
The foregoing may not be readily apparent to an organization seeking accreditation for the first time and it was to us a pleasant surprise that these came free with the package.
To us as Professional Designers, the foregoing are more important than the more often Touted Benefits because of the need to increase client satisfaction and also reduce our liability exposure.
There have been cases in our experience where our preservation of certain documents had saved us from costly litigation and claims. This would not have been possible without a fool proof document Archiving/Retrieval System that the ISO 9000 guidelines suggest.
The other more common benefits are of course the following:
Increased competitive advantage due to enhanced efficiency in procedures.
Customer preference for ISO 9000 companies with established Quality Systems.
Global acceptability of the ISO 9000 accredited company.
Orderly conduct of company business governed by procedures.
If we are to be asked what is the best benefit that has resulted from our seeking ISO 9000 accreditation, it is this:
We have reduced the chances for errors remaining undetected before implementation. Although errors cannot be entirely eliminated due to human factors or computer glitches, our formalized Quality Control system gave us the assurance and feeling of confidence that somehow we will find these errors before they can do some harm or cause loss of reputation.
As a matter of fact, it is not a sin in our organization to commit an error. However, it is a cardinal sin for everyone and anyone if we let an error go undetected through our various checks and counterchecks, as outlined in our Quality System. Somehow, this has given our employees High Morale.
3.0 BASIC UNDERSTANDING OF THE ISO 9000 SYSTEM
3.1 Background
The ISO 9000 standards originated from the IOS which is located in Switzerland . IOS is the acronym in French of the International Standards Organization. The ISO standards had its roots during the Second World War where methods of assessment of quality of wartime suppliers was very critical. This evolved into the MIL Standards and their Civilian Counterparts. Countries in the EU began to accept the values of a single standard for quality management systems resulting in the publication in 1987 of the ISO 9000 Series of Standards.1
3.2 What is ISO 9000?
ISO 9000 is a set of international standards for a Basic Management System of Quality Assurance. It is intended to equalize Quality Systems between companies and countries. 1
The following are the unique characteristics of the Quality System:
Flexibility – the requirements of the system are guides only and could be changed if the practices within an organization do not exactly match the requirements.
Wholistic – the standard looks at how the whole organization assures the quality of its products and services.
Focus on Quality Process – the standard do not focus on the final results but rather on the procedures for assuring quality.
Global – the standards have worldwide application and acceptability.
Broad Application – the standards can be applied to all aspects of business or operational procedures.
3.3 The ISO 9000 Family
The ISO 9000 Standards has five parts or is really a set of Five (5) Standards as defined1] below:
ISO 9000 – “Quality Management and Quality Assurance Standards – Guidelines for Selection and Use” is written to help companies determine which of the three standards to adopt or apply for registration.
ISO 9001 – “Quality Systems – Model for Quality Assurance in Design/Development Production, Installation and Servicing” is the standard for companies engaged in all aspects of manufacturing or of the development and delivery of a service.
e.g. A consulting Engineering Firm with a fully integrated Design Engineering function.
ISO 9002 – “Quality Systems – Model for Quality Assurance in Production and Installation” – is for companies that perform functions except the design and development of products and services.
e.g. A manufacturer that builds to prints and designs of a customer. A general contractor who builds based on plans supplied by the owner’s engineers.
ISO 9003 – “Quality System – Model for Quality Assurance in Final Inspection and Test” – is intended for non manufacturing companies such as distribution or warehousing entities. ISO 9003 is applied less and less and is expected to be dropped in the future.
ISO 9004 – “Quality Management and Quality System Elements –Guidelines” – is an overview of the themes and intent of the standards.
The key word in all of the foregoing titles is “Model” because the standards represent models of quality assurance rather than compulsory standards. Companies need only to match as closely and as economically, and as practically as possible the guidelines. This means that companies need not dramatically change their methods of quality assurance to meet the ISO 9000 Standards.
3.4 What It Is and What It Isn’t
The ISO 9000 Quality System is a set of Guidelines that is flexible.
It does not dictate the procedures to be practiced nor does it require a company to change its way of doing Quality Assurance if it is logical and effective. However, it provides a set of coherent guidelines to enable companies to meet minimum standards in the Global marketplace.
The ISO 9000 Standard is a requirement for a management system, not the structure of a quality department within an organization. There is not one correct Guideline and Procedure to follow. Each must be tailor made to suit the particular company’s operations and Quality Assurance procedures.
As a minimum, the standards provide a general pattern to follow. However, deviations or omission can and do occur depending on the company’s specific way of doing business which may be unique and requiring special procedures.
Common Misconception
It is sad to note that there are still lingering misconceptions about the ISO 9000 System and the quest to get there. These misconceptions should be clarified and erased before an organization can start its travel towards ISO 9000 accreditation. Some of these misconceptions are:
It is very difficult to comply with the standards.
The standards are rigid and inflexible.
It would take a long time to successfully comply.
It is very expensive to obtain and maintain.
It must be prepared by a consultant
It must be prepared and packaged by the management because employees would look at the standards with bias.
Employee compliance must be mandated from the top.
The quality system process must be management driven all the way.
It is not necessary provided you know what you are doing.
The documentation process is a waste of time and resources.
4.0 ESTABLISHING THE QUALITY COMMITTEE
Some of the major misconceptions in ISO 9000 accreditation are:
The process should be management driven.
You need a consultant to prepare the procedures and quality system.
Employees should be handed the complete procedure for their compliance.
The foregoing are quaranteed paths to failure because more than anything else, employee direct involvement is crucial to the success of any quality system. The effort should therefore be employee driven with the full logistical and moral support of top management.
We realized this very early on and we created a Total Quality Committee drawn from rank and file, tasked to prepare the company for accreditation. The Chairman of the Total Quality Committee in our case was a Lady Middle Level Engineer at that time and the following as representatives:
Management Representative – Technical Manager and Senior Partner
Engineering Representative – Junior Engineer representing Design Group And CAD Group
Admin Representative – Senior Clerk representing Admin and Non Technical Group
Q.C. Engineer – Full time Independent member of the Committee Designated as such.
The Total Quality Committee (TQC) spearheaded the company’s program for ISO 9000 Accreditation. It independently set the goals, milestones and work objectives of the company. Top management interference was unheard of and the main function of management was to keep the activities focused and monitor progress to attain a fixed deadline we have mutually agreed upon during the formation of the TQC.
The members were free to make the necessary suggestions and draft the procedures pertinent to their areas of operation. They were given blanket authority to draw upon any company resource or personnel in order to attain the objectives set by the TQC.
Directly under the TQC but not its members were two (2) Archive and Documentation Clerks. They received guidelines and instructions on the filing and records retrieval system being evolved and undergoing dynamic revision throughout the life of the TQC. These clerks were on full time assignment and were aided by our clerks and secretaries. They were not part of the mainstream operations as their job was to compile, catalog, file and debug the system. Little did we know that this decision saved us a lot of time and was partly instrumental in clinching the accreditation for the company.
As can be seen, the TQC was employee driven and this was very crucial not only to the preparation of the Quality System and Procedures but also in the subsequent implementation and maintenance of the Quality System. The procedures, having been originated by the employees themselves were widely accepted and embraced by all. In other words, the procedures were not rammed down the throat of rank and file but were prepared, polished and nurtured by them.
This to us is the single most crucial decision leading to the success of our Quest for ISO 9000 Accreditation.
5.0 PREPARING FOR ACCREDITATION
The Total Quality Committee established the necessary documentation requirements and the procedures needed to be documented. It also set out the guidelines for the archival and retrieval system.
The Quality Manual was reviewed and continually revised to contain new procedures or revised/eliminated/ outdated/superseded procedures.
Numerous working copies were reprinted for comments by employees as soon as these have undergone revisions- each revision being issued a Revision number. Thus, everyone got involved in the process of rewriting the procedures manual. The paper generated by the preparations was humongous but it was well worth the effort and time.
We also acquired several books on the ISO System which served as reference and guide for our efforts. Our books were the poor man’s substitute to a Consultant to assist in the accreditation process.
As part of our preparations and to serve as “Dry Run” to the Pre Audit and Audit activities ahead, we conducted internal audits using the checklist published in these references.
There was a compelling need to ensure that the system is thoroughly checked and debugged as external audits are expensive. In our case the Pre Auditor came from Austria and the Auditor from India. Both have to be billeted in Five (5) Star Hotels and their airfares paid for in addition to the Audit Fees charged by their company.
Thus, we can not afford failing in both audits and no room or allowance for non- compliance reaudits, and the rallying cry for the TQC is “Hit it one Time” this battle cry had a double meaning to us because HIT is our acronym for:
H – Personal Honesty
I – Integrity
T – Technical Excellence
We aimed for single pass Pre Audit and Audit and got it, saving us a lot of anxiety and plenty of hard earned money.
Dedicated as they were, the TQC members were driven by the Chairman who almost worked full time developing and coordinating the standards preparation. To add to the incentive, the Chairman was promised and got an all expenses paid trip to Hong Kong for getting accreditation in one pass. To get accredited in one audit was to us hard earned divine providence. The Internal Audits and Dry Runs were repeated until we were very satisfied that our system met ISO 9000 Standards. The personnel were in high state of morale and eager to get it over with.
We were ready!
6.0 THE DOCUMENTATION PROCESS
The main task in the ISO 9000 Accreditation Process is to ensure adequate Documentation of Procedures and Quality Systems. This also involved creating Document Filing, Archiving and Retrieval system to ensure the traceability and retrievability of all documents that need to be stored and that meant everything except junk mail.
No project document or communication was considered unimportant as not to be logged and stored in the archives.
The archived files consisted of Project Files which in our specific case involved:
⦁ Project Communications ⦁ Project Calculations ⦁ Project Plans & Drawings (Hard Copy, CD and Bernoulli Disk Files) ⦁ Project Specifications ⦁ Project Contract File ⦁ Estimates & Quantity Take Off
All these project files were interlinked and coded to assure fast retrieval and filing.
It is worthwhile to note that as a result of systematizing our document archiving and retrieval system, we can retrieve any project document within five minutes after the request for each documents is initiated. This includes travel time from the groundfloor to the third floor of our office.
In addition, lost document or lost files have become a thing of the past.
7.0 THE ISO 9000 QUALITY SYSTEM
7.1 ISO 9000 Elements
The ISO 9000 Quality System sets out Guidelines for companies to consider in the preparation of their Quality Systems and Procedures. It identifies vital elements that may comprise the system.
Note that in this definition, there are no mandatory statements such as “required” “shall” etc. Instead the words or phrases such as “consider” “may comprise” and that the provisions are “Guidelines”.
What this suggests is that the ISO 9000 is totally flexible and does not prescribe how the system should be done. It must completely suit each individual companies product or processes.
In our case, we evaluated the Guidelines element by element, and we adopted or incorporated those elements or sub elements related to our operations.
The following are the Elements for ISO 9001:
Management Responsibility
Quality System
Contract Review
Engineering Design Control
Document and Data Control
Purchasing
Control of Customer Supplied Product
Product Identification and Traceability
Process Control
Inspection and Testing
Inspection, Measurement & Test Equipment
Inspection and Test Status
Control of Non Conforming Product
Corrective and Preventive Action
Handling, Storage, Packaging, Preservation and Delivery
Control of Quality Records
Internal Quality Audits
Training
Servicing
Statistical Techniques
In our specific instance, we deemed all the twenty (20) Elements as necessary for our system but with a lot of modifications in order to suit our way of doing business and conducting our work.
It would be necessary to acquire references and guides such as the books mentioned in our references in order to have a clear and concise General Guide in preparing the Quality Manual and Procedures.
Emphasis is placed on the word “General” because the system and procedures are unique to the individual company’s operations.
The biggest temptation, is to copy some other company’s manual. This is a big mistake and a shortcut to failure due to lack of immersion and voluntary participation of rank and file.
7.2 ISO 9000 Levels of Documentation
The ISO 9000 Guidelines is relatively flexible in terms of document structure. However, it is necessary to have several levels of documentation mutually supportive of each other in order to have a fully Integrated Quality System. In our case, we adopted the Document Structure Pyramid 2 commonly used by a lot of companies as shown below:
From the above, the documentation levels or hierarchy can be easily seen as follows:
LEVEL 1 Quality Manual – the Quality Manual answers the question: why? It is a company’s statement of philosophy and approach to quality. The Quality Manual discusses in general terms how the company complies with each element of the standard, it also includes the company’s quality objectives (such as “Zero Defects”), gives an overview of the company’s processes and contains the quality philosophy of the company.
The Quality Manual is the Bible for Quality for the company.
LEVEL 2 Procedures – The procedures document the company’s Quality Plan and defines the implementation strategy. It indicates compliance to the ISO 9000 Standards, demonstrate the processes and ensures that there are no loopholes in the system.
The procedures are process oriented and covers:
⦁ The Tasks: What? ⦁ The Responsibility: Who? ⦁ The Frequency: When? ⦁ The Department: Where?
Necessarily, the procedures should be written by the people who will use them. Not by a Consultant. Because the procedures are process oriented, we decided to Flow Chart our procedures. This had the advantage of:
⦁ Making it easily understandable by anyone reading it even without prior knowledge of flow charting. ⦁ Saving a lot of manhours and pages of paper during the preparation. ⦁ Enabling in thorough checking of the process as it was Graphical and easily checked. ⦁ Expediting the audit procedures enabling us to get accredited.
We saw the need to include 12 Flow Charts defining our operations. These are:
Proposal Preparation: New Clients Procedure Flow Chart
Awarding of Contract: New Clients Procedure Flow Chart
Awarding of Contract: Old Clients Procedure Flow Chart
Control of Client Provided Info/Data Procedure Flow Chart
Isuance of Documents and Books Procedure Flow Chart
Purchasing Procedure Flow Chart
Handling of Documents Procedure Flow Chart
Internal Audit & Reviews Procedure Flow Chart
Handling Client Request Procedure Flow Chart
LEVEL 3 Work Instructions – The work instructions answer the question How? They are the step by step instructions specific to the company’s procedures. Work instructions includes direction for doing specific tasks such as Checking and Peer Review, Document Storage and Retrieval, Handling of Complaints, etc. In our case, and for the same reasons above, we have integrated these into a procedures Flow Chart indicating the process, the documents needed or generated and the persons responsible.
The Quality Documents or Forms we generated are as follows:
Transmittal Letter
Project Summary Sheet
Request Form
Confirmation of Documents Received
Checkprint Report
Internal Project Bulletin
Internal Quality Audit
Complaints Form
Purchase Order
Quality Control Checklist
Weekly Project Monitoring
Zero-Defects Score Card Form
Statistical Record of Defects
Checklist of Client Inputs Form
LEVEL 4 Quality Records – The quality records provide evidence of the company’s compliance. They are the ongoing objective evidence of the system and evolve from the company’s procedures. The standards does not specify exactly which records to keep because the individual company has to define this depending on its process. However, most elements of ISO 9000 require Quality Records.
The records that we decided we needed to keep as a minimum are as follows:
Project Files
Hardcopy Plans
Electronic Plan Files (CD Format & 3.25 Floppy Diskettes)
In the generation of documents, it is necessary to focus on the company’s actual needs and the procedures that it implements. Some procedures may overlap and therefore can be joined into one detailed procedure. The
key thing to remember is to limit documentation to what is really essential to the Quality System defined procedures. More documents mean a larger number to manage (or neglect), fewer documents may mean larger and crammed individual documents which may decrease usefulness or reduce understanding. In addition, our Quality Manual included the following:
Quality Committee Table of Organization
Company Table of Organization
Amendments Record
Official Company Quality Policy Statement
8.0 PREPARING FOR THE PRE AUDIT AND FINAL AUDIT
In order to obtain proof of compliance that the ISO 9000 System is functional and being implemented within the company, a Third Party Independent Auditor (TPA) normally ISO certified as such would need to be engaged. The TPA would need to conduct a Pre Audit Review and as many audits as necessary until you run out of money or you obtain compliance. Because Third Party Audit is expensive, it would be necessary and imperative that the Quality system and procedures are fully debugged internally prior to Audit. Otherwise, non compliances could stretch the time and be very costly and demoralizing to both rank and file.
The Pre Audit
The pre audit is an audit conducted by the TPA in order to check: ⦁ Completeness of Quality Systems and Procedures (Elements involved) ⦁ Adequacy of Documentation to cover the company’ processes ⦁ Cursory evidence of implementation of the Quality System ⦁ Archived Documents and Document Retrieval system ⦁ Top Management commitment to the Quality System
We prepared for the pre audit as though it was our final audit. This involved at least 3 months of preparations and weekly staff orientation meetings. Each individual staff was given his own copy of the Draft Quality Manual which required voluminous printing of documents. Internal audits and peer audits were required at every step of the process. The pre audit required two (2) days to complete and to our relief, only minor non compliances were observed. Management and the TQC were briefed by the TPA on the deficiencies to prepare for the final audit. To our great relief we were told that we were ready for the final audit.
The Audit
More intense preparations were made to include training and retraining of staff in the implementation of the system. The audit, aside from being more rigid, would require individual interviews of staff chosen at random by the TPA. Everyone therefore must know the system by heart. Aside from the more detailed checks on the pre audit items, the following were done:
Interview of top management to determine level of participation or involvement in the quality process.
Meeting with the TQC to gage its inner workings and level of commitment
Individual staff interviews to determine level of understanding of the Quality System
Checking of Office Procedures
Checking that Software is validated
Test of the Document Archiving and Retrieval System
In this specific instance, several projects were randomly chosen by the TPA and related Files were requested to be presented. The retrieval time was monitored.
Also, as an example: a project was chosen and the work order and minutes of coordination meeting were requested to be exhibited.
Checkprints were asked to be displayed and compared with final plans to see whether all corrections were implemented.
The audit was conducted for three (3) straight gruelling days, and all office functions were directed towards the audit. Other activities not related to the Audit ground to a halt. That was how important the audit was to us. The TPA was crucial to us.
Besides, it would be very expensive for us not to pass the audit as the TPA had to be billeted again in a 5 Star Hotel and the Airfares (from Europe or elsewhere) had to be paid in addition to his man day rates.
9.0 COMPLIANCE AT LAST
It was a combination of very hard and dedicated work and the grace of God the Almighty that we successfully handled the audit and obtained acceptance of the company’s Quality System with a few minor comments in one pass. There was a feeling of general relief and satisfaction for a job well done.
We got our accreditation on June 14, 1996.
We had a reception to honor the members of the TQC and it also gave us the opportunity to thank our clients and announce to the world that our Quality System is at par with the World’s Best.
True to our promise, the Chairman of the TQC was given a 3 day Holiday in Hong Kong.
Morale was very high and everyone had a feeling of pride and accomplishment for a job well done!
10.0 MAINTAINING AND SUSTAINING THE SYSTEM
The effort does not stop at accreditation time. Yearly audits by the TPA are mandatory to retain Accreditation and Certification.
But to us, the incentive in maintaining the system is because we have seen that the system really works for us and has given us a very competitive advantage over peer companies.
To us, at least and to potential clients, “we are more equal among equals”. Whether this is true or not, is not the question. In our minds and our hearts we know that we are because we have a formalized system that works.
In closing, we wish to state that in this difficult times, an engineering company can survive or survive better with a formalized and working Quality System and as forces realign, the ISO 9000 accredited company is better positioned to meet a more discriminating and quality conscious client.
REFERENCES
Clement, R.B. “Quality Manager’s Complete Guide to ISO 9000”. 1993 Prentice Hall Inc., NJ.
Novack, J.L. “The ISO 9000 Documentation Toolkit”. 1987 Prentice Hall Inc. N.J. pp.20
Emilio M. Morales took up his Master’s Degree in Civil Engineering at the Carnegie Institute of Technology, Carnegie-Mellon University, Pittsburgh, PA. USA in 1981. He is formerly a Senior Lecturer of the Graduate Division, College of Engineering, University of the Philippines, Diliman, Quezon City. Presently, he is the Principal of EM2A Partners & Co., Technical Manager of Philippine Geoanalytics, Inc. and Technical Director of PGA Calibration & Metrology Laboratory. Committee Member, TC-11, Bureau of Product Standards Technical Committee on Steel Products. He is currently Chairman of ASEP Geotechnical Committee.
He can be contacted at: EM2A Partners & Co., 17-C Scout de Guia corner Scout Reyes Streets, Diliman, Quezon City. Telephone Nos. 371-18-06 / 410-29-23 to 24 Telefax No. 924-98-94; E-mail: em2apart@mozcom.com
