GOPINATH MUNIANDY

8/8/2019 GOPINATH MUNIANDY

1/97

PSZ 19:16 Wind. 11071UNlVERSlTl TEKNOLOGI MALAYSIA

1 DECLARATION OF PROJECT REPORT AND COPYRIGHT

Author's full name : GOPINATHMUNIANDYDate of birth : 16TH FEBRUARY 1981Title : FORENSIC ENGINEERING TESTING TECHNIQUES FOR STRUCTURAL ASSESMENT:

A CASE STUDY ON PRE-STRESSED REINFORCED CONCRETE BRIDGE AT KLANGVALLEYAcademic Session : 2009/2010

1 declare that this thesis i s classified as :- ONFIDENTIAL (Contains confidential information under the Official SecretAct 1972)*RESTRICTED (Containsrestricted informationas specified by theorganizationwhere researchwas done)*OPEN ACCESS I agree that my thesis to be published as online open access(fulltext)

I acknowledged that UniversitiTeknologi Malaysia reserves the right as follows:1. The thesis is the propertyof UniversitiTeknologi Malaysia.2. The Library of UniversitiTeknologi Malaysia has the right to make copies for the purposeof research only.3. The Library has the right to make copies of the thesis for academic exchange.

(NEW IC NL. /PASSPORT NO.)Date : 03 APRIL 2010

Certified by :

SIGNATURE OF SUPERVISORASSOC.PROF.IR.DR.ROSL1MOHAMAD ZIN

NAME OF SUPERVISORDate : 03 APRIL 2010

NOTES : * If the thesis is CONFIDENTAL or RESTRICTED, please attach with the letter fromthe organizationwith period and reasons for confidentialityor restriction.


2/97

''I hereby declare that I have read this project report and inmy opinion thisproject report as adequate in terms of scope and quality in fulfillment o f therequirement for the award o f the degree o f Master of Science (Construction

Management)"

SignatureName o f supervisor :Assoc. Prof. Ir Dr Rosli oha am ad ZinDate : 03 APRIL 2010


3/97

FORENSIC ENGINEERING TESTING TECHNIQUES FORSTRUCTURAL ASSESMENT: A CASE STUDY ON PRE-STRESSED

REINFORCED CONC RETE BRIDGE AT KLANG VALLEY

GOPINATH MUNIANDY

A project report subm itted in partial fulfillment of requirementfor the aw ard of the degree of

Master o f Science (Construction Management)

Faculty of Civil EngineeringUnNersiti Teknologi Malaysia

APRIL 2010


4/97


5/97

DEDICATIONS

To my dearest family members, my employer, Acre Works SdnBhd and friends.Thanksa lot for your endless support to me.


6/97

ACKNOWLEDGEMENT

I would like to express my sincere thank you and appreciation to my thesissupervisor, Assoc.Prof. II Dr Rosli Mohd Zin for giving me unconditional guidance,help and support throughout the entire period of my thesis.

Finally, I would like to express my gratefulness to my family for their supportand assistance, my friends and to all those who were directly and indirectly involved inm ak iig this thesis a success.


7/97

ABSTRACT

Integrity test on existing concrete structures is often being carried out todetermine the assessment for the structure through several aspects suchas to determinethe whether the structure is suitable for its designed use, for proposed change of usage orextension of a structure, to enswe the acceptability of structure following to anydeterioration or structural damage. The evaluation of integrity of existing concretestructures has been carried out through several testing methods and procedures such asnon destructive test (NDT) and partially destructive test using sophisticated testingtechniques. However, the criteria of selection for suitable testing method and techniquesis still are being unclear depending types of structure that need to be tested. The criteriadetermination of most suitable codes and standards specification for Malaysiaperspective is also unclear. Therefore, it is vital to study the reality in selecting mostsuitable testing method incorporatedwith most suitable codes and standardizations tocarry out integrity test on existing concrete structures in Malaysia.

This case study consisting testing on existing concrete structures using concretecore method, rebound hammer test and ultra sonic pulse velocity OJPV) on existing pre-stressed T-beam and concrete structures of anunnamed bridge in Klang Valley. Resultsobtained from testing tabulated for comparison between BS 1881& BS 6089 cubecharacteristic strength and BSEN 13791, 2007 cube characteristic strength. Selectedcivil and structural consulting engineerswas nterviewed using prepared questionnaire toidentify the selection criteria and views in selecting appropriate testing method toevaluate integrity of existing concrete structures. Finally, the factors influencingselecting the most suitable testing method and comparison of selected standard code andpractice identified.


8/97

Konkrit merupakan di antara bahan bina yang sering digunakan di dalam projekkejuruteraan awam di Malaysia. Di antara alasan penggunaanya adalah faktor ekonomidan keperluan pembaik pulihan yang rendah sepanjang tempoh keboleh khidrnatannya.Walau bagaimanapun, konkrit mengalami beberapa kerosakan dan kemerosotansepanjang hayatnya kerana kekurangan pengetahuan pada sifat dan kelakuannya.Dengan mengunakan tekn ik-t ehik untuk pemeriksaan kualiti konkrit bagi struktur yangsedia ada ama ada ujian separa musnah ataupun tak musnah, kualiti konkrit yang hendakdiuji boleh dikenalpasti. Namun, dalam persepti Negara kita, criteria untukmengenalpasti ujian konkrit bagi tujuan kajian tertentu masih tidak ada definasi denganmengambil kira kod-kod specifikasi yang tertentu. Maka, adalah pentingnya untukmembuat kajian untuk m engenalpasti criteria untuk pilihan ujian konkrit mengikut kod-kod specifikasi tertentu untuk mengenalpasti ujian yang terbaik untuk pemeriksaankualiti strukturkonkrit yang sedia ada.

Kajian ini termasuk membuan ujian konkrit yang dipilih iaitu "Schmidt reboundhammer", "Ultrasonicpulse velocity'' dan "core test". Kajian in telah dilalukan atasjambatan yang sedia ada di Pelabuhan Klang. Segala keputusan akan ditafsirkanmengunakan bentuk jadual dan graf untuk analysis. Data kajian juga telah dibezakanmengunakan kod-kod specifikasi yang dipilih untuk mendapatkan perbezaan dalampenerimaan data untuk tujuan analisis. Kajian juga dilalukan dalam bentuk temurahdengan pakar jurutera yang berpengalaman dalam bidang kajian konkrit mengunakanboring s o d selidik. Segala keputusan temuramah di pamerkan dalam bentuk jadaul dangraf. MelaIui kajian ini, mendapat tahu bahawa, ujian "concrete core" memberikan datakeputusan yang lebik relevan berbanding dengan keputusan ujian yang lain. Ujian"conaete core" juga disetujui oleh pakar-pakar jurutera yang terlibat dalam bidangkajian konkrit.


9/97


10/97

r r r rZ f i P w t Q r


11/97

2.2.2.4Determination of Pulse Velocity 212.2.2.4.1Transducer Arrangement 212.2.2.4.2Determinationof PulseVelocity by DirectTransmission 232.2.2.4.3Determinationof PulseVelocity bySemi-Direct Transmission 232.2.2.4.4Determination of Pulse Velocity by Indirector SurfaceTransmission 242.2.2.4.5Coupling the Transduceronto the Concrete 252.2.2.4.6Factor InfluencingPulse VelocityMeasurements 272.2.2.5Determination of Concrete Uniformity 312.2.2.6Detectionof Defects 322.2.2.7Examplesof Relationshipsbetween PulseVelocity and CompressiveStrength 33

2.3 Partially DestructiveTest2.3.1 Concrete Core Test2.3.2 Coresvs. Cylinders2.3.3 Coring Direction2.3.4 Top-to-Bottom Strength Variation2.3.5 Consolidation2.3.6 Effects of Curing


12/97

CHAPTER III

2.4 Codes, S tandards and Specifications 412.4.1 General Considerations 422.4.2 Different Categories of Standards 432.4.2.1 Standards 432.4.2.2Codes and Specifications 432.4.2.3Other Types of National Documents 442.4.2.4Standardisation Organisations and Som e ofthe Standards Relating to Testing of Concrete 442.4.2.4.1American Society for Testing and M aterials(ASTM) 442.4.2.4.2British Standards Institution (BSI) 46

METHODOLOGY

3.1 Introduction 483.2Docum ent Study 49

3.2.1Concrete Core Test 493.2.2Schmidt Rebound Hamm er Test 513.2.3Ultrasonic Pulse Velocity Test 52

3.3 Interview w ith Civil and S tructural Consulting EngineersUsing Q uestionnaire 53

3.3.1Contents of the Questionnaire 533.4 Comparison of Cube characteristic S trength usingBS 1881&BS 6089 and BSEN 13791:2007Euro Codes 56


13/97


14/97

LIST OF TABLES

TABLENO TITLE

Effect of temperature on pulse transmissionEffect of specimen dimensions on pulse transmissionClassification of the quality of concrete on the basis ofpulse velocity 30Rebound Hammer Test ResultsMeasurement for Rebound Hammer UPV Test locations onthe T-BeamUltrasonic Puke Velocity Test ResultsConcrete Core Compression Test ResultsEstimated In-Situ Strength throughout Interpolation fiomCorrelation CurveEstimated In-SituCube Strength for all three types of testComparison of Cube characteristic Strength using BS 1881&BS 6089 and BSEN 13791:2007E m CodesVariance between there types of test conductedVariance betweenBS 1881 and BSEN 13791

PAGE


15/97

LIST OFFIGURES

FIGURE NO TITLE

1.1 Research Methodology Flow Chart2.0 Schmidt Rebound Hammer2.1 A cutaway schematic view of the Schmidt rebound hammer2.2 Relationship between 28 day compressive strength and

rebound number for limestone aggregate concrete obtainedwith Type N-2 Hammer

2.3 Correlation curves produced by different researchers.(Greene curve used TypeN hammer; othersused Type N-2).2.4 Effect of gravel from different sources on correlation curves.

2.5 Comparison between correlation curves for crushedlimestone and siliceous

2.6(a) Direct Transmission2.6(b) Semi-direct Transmission2.6(c) Indiuect or surface transmission2.7 Pulse velocity determinations by indirect (surface) transmission2.8 Relation between ultrasonic pulse velocity and compressive

strength for concretes of different mix proportions2.9 Planes of weakness under coarse aggregate particles due to

bleeding2.10 Estimated within-member strengthvariations2.11 Longitudinal resonance frequency of concrete cores3.1 Photographs showing the process of concrete core sample testing

PAGE


16/97

Photographs showing the process of Schmidt reboundhammer testing 51Photographs showing the process of UPV testing 52Top View of T-Beam L=PBiPC-S2-EX-01 59Side View of T-Beam L=PB/PC-S2-EX-01 59Correlation Curve of UPV against Estimated In-situ Cube Strength 62Factors Influencing in Selecting Method of Testing 64Proportions of nature of test by respondents 65Responses on Partially Destructive Test Preference 65Responses on Partially Destructive Test Preference 66Responses on selection of standard codes and practice forstructural assessment 67


17/97

CHAPTER I

INTRODUCTION

1.1 Introduction

Integrity test on existing concrete structures is often being carried out todetermine the assessment for the structure through several aspects such as to determinethe whether the structure is suitable for its designed use, for proposed change of usage orextension of a structure, to ensure the acceptability of structure following to anydeterioration or structural damage such as caused by fue, blast, fatigue or overload andto ensure the serviceability or adequacy of member known or suspected to containmaterial which does not meet specifications or with design faults.

The fundamental of structural integrity and durability is to develop continuousmonitoring concepts for structural concepts for structural components and for the globalbehavior. A structure is said to have general structural integrity if localized damage doesnot lead to widespread collapse. Structural integrity has to be guaranteed by the


18/97

structural safety under ultimate and serviceability conditions and by ductility as well asredundancy of load path.

The integrity of concrete structurescan ustify by using several tests available fortesting concrete range from completely non-destructive, where there is no damage to theconcrete, through those where the concrete surface is slightly damaged, to partiallydestructive test, such as core test, and pullout and pull off test, where the surface has tobe repaired after the test. The range of properties that can be assessed using non-destructive test and partially destructive test quite large and includes such fundamentalparameters as density, elastic modules, and strength as well as surface hardness andsurface absorbtionand reinforcement location, size and distance fiom the surface. Attimes, it is also possible to check the quality of workmanship and structural integrity bythe ability of detects void, cracking and delamination.

The assessment of integrity of existing concrete structures should also taken intoconsideration of requirements of several codes, standards, specification and proceduresestablished by most countries national bodies and relevant organizations. Standards canplay important role in international co-operation when they are used in contracts. Thegrowth in international trade has resulted in a growth in the need for InternationalStandards which can be acceptable compromise between different national standards.

1.2 Problem Statement

Integrity test on existing concrete structures is being implemented widely inMalaysian concrete structures that deteriorate as the effects of structural and


19/97

environments loading take place over time. The evaluation of integrity of existingconcrete structureshas been canied out through several testing methods and proceduressuch as Non Destructive Test W T ) nd partially destructive test using sophisticatedtesting techniques. However, the criteria of selection for suitable testing method andtechniques is still are being unclear depending types of structure that need to be tested.The criteria determination of most suitable codes and standards specification forMalaysia perspective is also unclear. Therefore, it isvital to study the reality in selectingmost suitable testing method incorporated with most suitable codes and standardisationto carry out integrity test on existing concrete structures in Malaysia.

1.3 Research Objectives

The main objectives of this study are as per listed below:-

i. To identify the factors that influences in selecting the most suitable testing methodand procedures to conduct integrity test on existing concrete structures.

ii. To analyse and compare on selected codes of practice and standardization forintegrity test on existing concrete structures


20/97

1.4 Research Scope

This case study scope will be focusing on testing methods and techniques onexisting concrete structures incorporated with comparison of codes of practice andstandardisation established by BS 1881, BS 6089 and BSEN 13791. This case study isbased on several concrete core results obtained from testing carried on existing bridgeconcrete structures and pre-stressed concrete beams located in K lang Valley. The detailsof the project will not be illustrated because the project contains certain confidentialstatements.

1.5 Research Methodology

This case study will be consisting testing on existing concrete structures usingconcrete core method, rebound hammer test and Ultra sonic Pulse Velocity (WV) onexisting concrete structures of an unnamed bridge in Klang Valley. Results will betabulated for com parison between BS 1881, BS 6089 and BSEN 13791. Results will beanalyzed using calculation for cube characteristic strength and design requirement andacceptability of the results obtain from the tabulation and wrapped out with conclusionand recommendations. Recommendations will be an overview on options forstrengthening the affected structures. The methodology flow chart are shown as below asin Figure 1.1.


21/97

I DEFINE THE PROBLEM ISPECIFY THE OB JECTIVES

4LITERATURE REVIEW

I COLLECTING DATA I

DATA STUDY-Data obtained formRebound Hammer Test,Ultrasonic Pulse Velocityand Concrete Core Sam plewill be analyzed andpresented.

INTERVIEW-Interview five experiencesC&S consulting engineersusing preparedquestionnaire.

COMPARISON- BS 81 10&BS 6089 cubecharacteristic strength andBSEN 137912007 cubecharacteristic strength.

I ANALYSIS AND RESULTS ICONCLUSION AND

RECOMMENDATION

Figure 1.1: Research M ethodology Flow Chart


22/97

CHAPTER I1

LITERATURE REVIEW

2.1 Introduction

It is often to test the existing concrete structures to evaluate and determinewhether the structure is suitable for its designed use. Interest in testing of existingconcrete structures has increased considerably since 1960s, and significant advanceshave been made in techniques, equipment, and method of application. This has largelybeen a result of the growing number of concrete structures, especially those of recentorigin, that have been showing signs of deterioration. Changes in cement manufactureeincreased use of cement replacements admixtures, and a decline in standards ofworkmanship and construction supervision have all been blamed. Particular attentionhasthus been paid to development of test methods which are related to durabilityperformance and integrity.


23/97

Testing for existing concrete structures available from the range of completelynon-destructive and partially destructive. The range of properties that can be assessedusing non-destructive test and partially destructive test is quite large and includes suchfundamental parameters as density, elastic modules, and strength as well as surfacehardness and surface absorption, and reinforcement location, size and d istance from thesurface.

2.2 Non Destructive Tests (NDT)

Non-destructive testing can be applied to both old and new structures. For newstructures, the principal applications are likely to be for quality control or the resolutionof doubts about the quality of m aterials or construction. The testing of existing structuresis usually related to an assessment of structural integrity or adequacy. In either case, ifdestructive testing alone is used, for instance, by removing cores for compressiontesting, the cost o f coring and testing may only allow a relatively small number of teststo be carried out on a large structure which may be m isleading. Non-destructive testingcan be used in those situations as a preliminary to subsequent coring. (Bungey andMillard, 1996)

Typical situations where non-destructive testing may be useful are, as follows:

quality control of pre-cast units or construc tion in situremoving uncertainties about the acceptability of the m aterial supplied owing to

apparent non-compliance with specificationconfirming or negating doubt concerning the workm anship involved in batching,mixing, placing, compacting or curing of concretemonitoring of strength developm ent in relation to formwork removal, cessation of

curing, prestressing, load application or similar purpose


24/97

location and determination of the extent of cracks, voids, honeycombing and similardefects within a concrete structuredetermining the concrete uniformity, possibly preliminary to core cutting, loadtesting or other more expensive or dis~pt iveestsdetermining the position, quantity or condition of reinforcementincreasing the confidence level of a smaller number of destructive testsdetermining the extent of concrete variability in order to help in the selection ofsample locations representative of the quality to be assessedconfirming or locating suspected deterioration of concrete resulting fiom suchfactors as overloading, fatigue, external or internal chemical attack or change, fire,explosion, environmental effectsassessing the potential durability of the concretemonitoring long term changes in concrete propertiesproviding information for any proposed change of use of a structure for insurance orfor change of ownership.

2.2.1 Basic Methods for NDT of Concrete Structures

The following methods, with some typical applications, have been used for theNDT of concrete. (Taerwe and Larnbotte, 1991)

Visual inspection, which is an essential precursor to any intended non-destructivetest. An experienced civil or structural engineer may be able to establish the possiblecauses of damage to a concrete structure and hence identify which of the various NDTmethods available could be most useful for any further investigation of the problem.


25/97

Half-cell electrical potential method, used to detect the corrosion potential ofreinforcing bars in concrete.

Schmidtirebound hammer test, used to evaluate the surface hardness of concrete.Carbonation depth measurement test, used to determine whether moisture has

reached the depth of the reinforcing bars and hence corrosion may be occurring.Permeability test, used to m easure the flow of water through the concrete.Penetration resistance or Windsor probe test, used to measure the surface hardness

and hence the streng th of the surface and near su rface layers of the concrete.Cover meter testing, used to measure the distance of steel reinforcing bars beneath

the surface of the concrete and also possibly to measure the diameter of the reinforcingbars.

Radiographic testing used to detect voids in the concrete and the position of stressingducts.

Ultrasonic pulse velocity testing, mainly used to measure the sound velocity of theconcrete and hence the compressive strength of the concrete.

Sonic methods using an instrumented hammer providing both sonic echo andtransmission m ethods.

Tomography modeling, which uses the data from ultrason ic transmission tests in twoor more directions to detect voids in concrete.

2.2.1.1 Schmidt Rebound Hamm er Test

The Schmidt rebound hammer is principally a surface hardness tester. It workson the principle that the rebound of an elastic mass depends on the hardness of thesurface against which the mass impinges. There i s little apparent theoretical relationshipbetween the strength of concrete and the rebound number of the hammer. However,


26/97

within limits, empirical correlations have been established between strength propertiesand the rebound number.

2.2.1.2 Equipment for Schmidt Rebound Hamm er Test

The Schmidt rebound hammer is shown in Figure 2.0. The hammer weighs about1.8 kg and is suitable for use both in a laboratory and in the field. A schematic cutawayview of the rebound hammer is shown in Figure 2.1. Themain components include theouter body, the plunger, the hammer mass, and the main spring. Other features include alatching mechanism that locks the hammer mass to the plunger rod and a sliding rider tomeasure the rebound of the hammer mass. The rebound distance is measured on anarbitrary scale marked from 10 to 100. The rebound distance is recorded as a "reboundnumber" corresponding to the position of the rider on the scale. (Taerwe and Lambotte,1991)

Figure2.0 Schmidt rebound hammer(Source: Taerwe and Lambotte, 199 1)


27/97

2.2.1.3 General Procedure for Schmidt Rebound Hammer Test

The method of using the hammer is explained using Figure 2.1 below. With thehammer pushed hard against the concrete, the body is allowed to move away from theconcrete until the latch connects the hammer mass to the plunger, Figure 2.la. Theplunger is then held perpendicular to the concrete surface and the body pushed towardsthe concrete, Fig. 2.lb. This movement extends the spring holding the mass to the body.When he maximum extension of the spring is reached, the latch releases and the mass ispulled towards the surface by the spring, Figure 2.1~. he mass hits the shoulder of theplunger rod and rebounds because the rod is pushed hard against the concrete, Figure2.ld. During rebound the slide indicator travels with the hammer mass and stops at themaximum distance the mass reaches after rebounding. A button on the side of the bodyis pushed to lock the plunger into the retracted position and the rebound number is readfrom a scale on the body. (Bungey and Millard, 1996).

Figure 2.1 A cutaway schematic view of the Schmidt rebound hammer(Source: Bungey and Millard, 1996)


28/97

2.2.1.4Applications of Schm idt Rebound Ham mer Test

The hammer can be used in the horizontal, vertically overhead or verticallydownward positions as well as at any intermediate angle, provided the hammer isperpendicular to the su rface under test. The position of the mass relative to the vertical,however, affects the rebound number due to the action of gravity on the mass in thehamm er. Thus the rebound number of a floor would be expected to be smaller than thatof a soffit and inclined and vertical surfaces would yield intermediate results. Although ahigh rebound number represents concrete with a higher compressive strength thanconcrete with a low rebound number, the test is only useful if a correlation can bedeveloped between the rebound number and concrete made with the same coarseaggregate as that being tested. Too much reliance should not be placed on the calibrationcurve supplied with the hammer since the manufacturer develops this curve usingstandard cube specimens and the mix used could be very different from the one beingtested. (Bungey and Millard, 1996)

A typical correlation proced ure is, as follows:

( I ) Prepare a number of 1 50 mm x 300 mm cylinders (or 150 mtm cube specimens)Covering the strength range to be encountered on the job site. Use the same cement andaggregates as are to be used on the job. Cure the cylinders under standard moist-curingroom conditions, keep ing the curing period the sam e as the specified control age in thefield.

(2) After capping , place the cy linders in a comp ression-testing machine under an initialload of approx imately 15% of the ultimate load to restrain the specimen. Ensure thatcylinders are in a saturated surface-dry condition.


29/97

(3) Make 15 hammer rebound readings, 5 on each of 3 vertical lines 120' apart, againstthe side surface in the m iddle two thirds of each cylinder. Avoid testing the sam e spottwice. For cubes, take 5 reading s on each of the 4 molded faces without testing the sam espot twice.

(4) Average the readings and call this the rebound nu mber for the cylinder under test.Rep eat this procedure for all the cylinders.

(5) Test the cylinders to failure in compression an d plot the rebound numb ers against thecompressive strengths on a graph.(6) Fit a curve or a line by the m ethod of least squares.

A typical curve established for limestone aggregate concrete is shown in Figure 2.2. Thiscurve was based on tests performed during 28 days using different conc rete mixtures.

U - MCI& m sf v ~ z ow-m e~ l l . dwr

REBOUND HUHBEQ. Chsmmrr in hartront# .l pnnttkan)Figure 2.2 Relationship between 28 day com pressive strength and rebound number forlimestone aggregate concrete obtained with T ype N-2 Hammer.

(Source: Bungey and M illard, 19 96)


30/97

Figure 2.3 below shows further three calibration curves obtained by researchworkers compared to the curve supplied with the hammer identified as "Schmidt". It isimportant to note that some of the curves deviate considerably fiom the curve suppliedwith the hammer. (Bungey and Millard, 1996)

2.2.1.5 Range and Limitations of Schmidt Rebound Hammer Test

Although the rebound hammer does provide a quick, inexpensive method ofchecking the uniformity of concrete, it has some serious limitations. The results areaffected by:

1. Smoothness of the test surfaceHammer has to be used against a smooth surface, preferably a formed one. Opentextured concrete cannot therefore be tested. If the surface is rough, e.g. a trowelledsurface, it should be rubbed smooth with a carbonmdum stone.


31/97

Figure 2 3 Correlation curves produced by different researchers. (Greene curve usedType N hammer; othersusedTypeN-2).( Source: Bungey and Millard, 1996)

2. Size, shape and rigidity of the specimenIf the concrete does not form part of a large mass any movement caused by theimpact of the hammer will result in a reductionin the rebound number. In such casesthe member has to be rigidly held or backed up by a heavy mass.

3. Age of the specimenFor equal strengths, higher rebound numbers are obtainedwith a 7 day old concretethan with a 28 day old. Therefore,when old concreteis to be tested in a structureadirect correlationis necessary betweenthe rebound numbers and compressivestrengthsof cores taken fromthe structure.Rebound testingshouldnot be carried outon low strengthconcrete at early ages or when the concrete strength is less than 7MPa sincethe concrete surfacecould be damaged by the hammer.

4. Surfaceand internal moisture conditions of concreteThe rebound numbers are lower for well-cured air dried specimensthan for the samespecimens tested after being soaked in water and tested in the saturated surface driedconditions. Therefore, whenever the actual moisture condition of the field concrete or


32/97

specimen is unknown, the surface should be pre-saturated for several hours beforetesting. A correlation curve for tests performed on saturated surface dried specimensshou ld then be used to estim ate the com pressive strength.

5. Type of coarse aggregateEven thoug h the same aggregate type is used in the concrete mix, the correlationCurv es can be different if the source of the aggregate is different. An example isshown in Figure 2.4 where correlation curves for four different sources of gravel areplotted. Figure 2.5 shows the considerable difference that can occur betweencorrelations curves developed for different aggregate types ( Bungey andMillard, 1996).

Figure 2.4 Effect of gravel from different sources on correlation curves(Source: Bungey and Millard, 19 96)


33/97

Figure 2.5 Comparison between correla tion curves for crushed limestone and siliceous.(Source: Bungey and Millard, 1996)

6 .Type of cementHigh alumina cement can have a compressive strength 100%higher than the strengthestimated using a co rrelation curve based on ordinary Portland cement. Also,supersulphated cement concrete can have m g t h 50% lowm than ordinary Portlandcement.

7. Carbonation of the concrete surfaceIn older concrete the carbonation depth can be several millimeters thick and, in

extreme cases, up to 20mm hick. In such cases the rebound numbers canbe up to50%higher than those obtained on an uncarbonated concrete surface.


34/97

2.2.2 Ultra Sonic Pulse Velocity Test

Ultra sonic pulse velocity test is one of non-destructive test which can givereliable results fo r structural integrity assessment.

2.2.2.1Fundamental Principle

A pulse of longitudinal vibrations is produced by an electro-acousticaltransducer, which is held in contact with one surface of the concrete under test. Whenthe pulse generated is transmitted into the concrete fiom the transducer using a liquidcoupling material such as grease or cellulose paste, it undergoes multiple reflections atthe boundaries of the different material phases within the concrete. A complex system ofstress waves develops, which include both longitudinal and shear waves, and propagatesthrough the concrete. The first waves to reach the receiving transducer are thelongitudinal waves, wh ich are converted into an electrical signal by a second transducer.Electronic timing circuits enable the transit time T of the pulse to be m easured.

Longitudinal pulse ve locity (in kmls or mls) is given by (Bungey and Millard,1996):

V = L i TWhere

V is the longitudinal pulse velocity,L is the path length,T is the tim e taken by th e pulse to traverse that length.


35/97

2.2.2.2 Equipment for P ulse Velocity Test

The equipment consists essentially of an electrical pulse generator, a pair oftransducers, an amplifier and an electron ic timing dev ice for measuring the time interv albetween th e initiation of a pulse generated a t the transm itting transducer and its arrival atthe receiving transducer. Two forms of electronic timing apparatus and display areavailable, one of which uses a cathod e ray tube on which the received pulse is displayedin relation to a suitable time scale, the other uses an interval timer with a direct readingdigital display. The equipment should have the following characteristics. It should becapable of measuring transit time over path lengths ranging from about 100 mrn to themaxim um thickness to be inspected to an accuracy of 51%. Generally the transducersused should be in the range of 20 to 150 kHz although frequencies as low as 10 kHzmaybe used for very long concrete path lengths and as high as 1 MHz for mortars and g routsor for short path lengths. High frequency pulses have a well defined onset but, as theypass through the concrete, become attenuated more rapidly than pulses of lowerfrequency. It is therefore preferable to use high frequency transducers for short pathlengths and low frequency transducers for long path lengths. Transducers with afrequency of 50 kHz to 60 kHz are suitable for most common applications. (Fleischerand Chapm an, 1993).


36/97

2.2.2.3Applications

Measurement of the velocity of ultrasonic pulses of longitudinal vibrationspassing through concrete may be used for the following applications:

determination of the uniformity of concrete in and between membersmeasurement of changes occurring with time in the properties of concretecorrelation of pulse velocity and strength as a measure of concrete quality.determinationof the modulus of elasticity and dynamic Poisson's ratio of theconcrete.

The velocity of an ultrasonic pulse is influenced by those properties of concretewhich determine its elastic stiffness and mechanical strength. The variations obtained ina set of pulse velocity measurements made along diierent paths in a structure reflect acorresponding variation in the state of the concrete. When a region of low compaction,voids or damaged material is present in the concrete under test, a correspondingreduction in the calculated pulse velocity occurs and this enables the approximate extentof the imperfections to be determined. As concrete matures or deteriorates, the changes,which occur with time in its structure, are reflected in either an increase or a decrease,respectively, in the pulse velocity. This enables changes to be monitored by making testsat appropriate intervals of time.

Pulse velocity measurements made on concrete structures may be used forquality control purposes. In comparison with mechanical tests on control samples suchas cubes or cylinders, pulse velocity measurements have the advantage that they relatedirectly to the concrete in the structure rather than to samples, which niay not be alwaystruly representative of the concrete in situ.


37/97

Ideally, pulse velocity should be related to the results of tests on structuralcomponents and, if a correlation can be established with the strength or other requiredproperties of these components, it is desirable to make use of it. Such correlations canoften be readily established directly for pre-cast units and can also be found for in situwork. Empirical relationships may be established between the pulse velocity and boththe dynamic and static elastic modules and the strength of concrete. The latterrelationship is influenced by a num ber of factors including the type of cem ent, cementcontent, admixtures, type and size of the aggregate, curing conditions and age ofconcrete. Caution should be exercised when attempting to express the results of pulsevelocity tests in terms of strengths or elastic properties, especially at strengths exceeding60 MPa (Fleischer and Chapman, 1993).

2.2.2.4 Determ ination of Pulse Velocity

Determ ination of pulse ve locity will be throughout several considerations as perthe following.

2.2.2.4.1Transducer Arrangement

The receiving transducer detects the arrival of that component of the pulse,which arrives earliest. This is generally the leading edge of the longitudinal vibration.Although the direction in which the maximu m energy is propagated is at right angles tothe face of the transmitting transducer, it is possible to detect pulses, which have


38/97


39/97


40/97

24

2.2.2.4.4 Determ ination of Pu lse Velocity by Indirect or Su rface Transmission

Indirect transmission should be used when only one face of the concrete isaccessible, when the depth of a su rface crack is to be determined or w hen the quality ofthe surface concrete relative to the overall quality is of interest. It is the least sensitive ofthe arrangements and, for a given path length, produces at the receiving transducer asignal which has an amplitude of only about 2% or 3% of that produced by directtransmission. Furthermore, this arrangement gives pulse velocity measurements whichare usually influenced by the concrete near the surface. This region is o ften of differentcomposition from that of the concrete within the body of a unit and the test results maybe unrepresentative of that concrete. The indirect velocity is invariably lower than thedirect velocity on the same conc rete elemen t. This difference may vary from 5% to 20%depending largely on the quality of the concrete under test. Where practicable sitemeasurements should be made to determine this difference. With indirect transmissionthere is som e uncertainty regarding the exact length of the transmission path because ofthe sign ificant size of the areas of co ntact between the transducers and the conc rete. It istherefore preferable to make a series of measurements with the transducers at differentdistances apart to eliminate this uncertainty. (Fleischer and Chapman, 1993)

The transmitting transdu cer should be placed in contact with the concrete surfaceat a fixed point x and the receiving transducer should be placed at fixed increments xnalong a chosen line on the surface. The transmission times recorded should be plotted aspoints on a graph showing their relation to the distance separating the transducers. Anexample of such a plot is show n as line (b) in Figure 2.7. The slope of the best straightline drawn through the points should be measured and recorded as the mean pulsevelocity along the chosen line on the concrete surface. Where the points measured andrecorded in this way indicate a discontinuity, it is likely that a surface crack or surfacelayer of inferior quality is present and a velocity measured in such an instance isunreliable. (Fleischer and Chapm an, 1993)


41/97

2.2.2.4.5 Coupling the Transducer Onto the Concrete

To ensure that the ultrasonic pulses generated at the transmitting transducers passinto the concrete and are then detected by the receiving transducer, it is essential thatthere is adequate acoustical coupling between the concrete and the face of eachtransducer. For many concrete surfaces, the finish is sufficiently smooth to ensure goodacoustical contact by the use of a coupling medium and by pressing the transduceragainst the concrete surface. Typical couplants are petroleum jelly, grease, soft soap andkaolin/glycerol paste. It is important that only a very thin layer of coupling mediumseparates the surface of the concrete from its contacting transducer. For this reason,repeated readings of the transit time should be made until a minimum value is obtainedso as to allow the layer of the couplant to become thinly spread. Where possible, thetransducers should be in contact with the concrete surfaces, which have been cast againstformwork or a mold. Surfaces formed by other means, e.g, trowelling, may haveproperties differing from those of the main body of material. If it is necessary to work onsuch a surface, measurements should be made over a longer path length than wouldnormally be used. A minimum path length of 150 mm s recommended for directtransmission involving one mo l d e d surface and a minimum of 400 mm for indirecttransmission along one mo l d e d surface.


42/97


43/97

2.2.2.4.6 Factors Influencing Pulse Velocity Measurements

Pulse velocity can be influence by several factors which should be taken intoconsideration in achieving accurate readings.

(a) Moisture Content

The moisture content has two effects on the pulse velocity, one chemical theother physical. These effects are important in the production of correlations for theestimation of concrete strength. Between a properly cured standard cube and a structuralelement made from the same concrete, there may be a significant pulse velocitydifference. Much of the difference is accounted for by the effect of diierent curingconditions on the hydration of the cement while some of the difference is due to thepresence of ffee water in the voids. It is important that these effects are carehllyconsidered when estimating strength.

@) Temperature of the Concrete

Variations of the concrete temperature between l00C and 300C have been foundto cause no significant change without the occurrence of corresponding changes in thestrength or elastic properties. Corrections to pulse velocity measurements should bemade only for temperatures outside this range as given in Table2.0.


44/97

Table 2.0 Effect of temperature on pulse transmission(Source: Fleischer and Chapman, 1993)

(c) PathLength

The path length over which the pulse velocity is measured should be long enoughnot to be significantly influenced by the heterogeneous nature of the concrete. It isrecommended that, the minimum path length should be 100 mm for concrete wherenominal maximum size of aggregate is 20 mm or less and 150 mm for concrete wherenominal maximum size of aggregate is between 20 mm and 40 mm. The pulse velocityis not generally influenced by changes in path length, although the electronic timingapparatus may indicate a tendency for velocity to reduce slightly with increasing pathlength. This is because the higher frequency components of the pulse are attenuatedmore than the lower frequency components and the shape of the onset of the pulsebecom es more rounded with increased distance traveled. Thus, the apparent reduction ofpulse velocity arises from the difficulty of defining exactly the onset of the pulse andthis depends on the particular method used for its definition. This apparent reduction in


45/97

velocity is usually small and well within the tolerance of time measurement accuracy forthe equipment. (Leshchinsky,l992)

(d) Shape and Size of Specimen

The velocity of short pulses of vibration is independent of the size and shape ofthe specimen in which they travel, unless its least lateral dimension is less than a certainminimum value. Below this value, the pulse velocity may be reduced appreciably. Theextent of this reduction depends mainly on the ratio of the wavelength of the pulsevibrations to the least lateral dimension of the specimen but it is insignificant if the ratiois less than unity. Table 2.1 gives the relationship between the pulse velocity in theconcrete, the transducer frequency and the minimum permissible lateral dimension ofthe specimen. If the minimum lateral dimension is less than the wavelength or if theindirect transmission arrangement is used, the mode of propagation changes andtherefore the measu red velocity will be different. This is particularly important in caseswhere concrete elements of significantly different sizes are being compared.(Leshchinsky, 1992)


46/97

Table2.1 Effect of specimen dimensions on pulse transmission(Source: Leshchinsky, 1992)

(e) Effect of Reinforcing Bars

The pulse velocity measured in reinforced concre te in the vicinity of reinforcingbars is usually higher than in plain concre te of the same composition. This is because thepulse velocity in steel may be up to twice the velocity in plain concrete and, undercertain conditions, the first pulse to arrive at the receiving transducer travels partly inconcrete and partly in steel. The apparent increase in pulse velocity depends on theproximity of the measurements to the reinforcing bar, the diameter and number of barsand their orientation with respect to the propagation path. The frequency of the pulse andsurface conditions of the bar may both also affect the degree to which the steelinfluences the velocity measurements. Corrections to measured values to allow forreinforcement will reduce the accuracy of estimated pulse velocity in the concrete sothat, wherever possible, measurem ents should be made in such a way that steel does notl ie in or close to the d i e t path between the transducers.


47/97

2.2.2.5 Determination of Concrete Uniformity

Heterogeneities in the concrete within or between members cause variations inpulse velocity, which in turn are related to variations in quality. Measurements of pulsevelocity provide a means of studying the homogeneity and for this purpose a system ofmeasuring points which covers uniformly the appropriate volume of concrete in thestructure has to be chosen.

The number of individual test points depends upon the size of the structure,accuracy required and variability of the concrete. In a large unit of fairly uniformconcrete, testing on a lm grid is usually adequate but, on small units or variableconcrete, a finer grid may be necessary. It should be noted that, in cases where the pathlength is the same throughout the survey, the measured time might be used to assess theconcrete uniformity without the need to convert it to velocity. This technique isparticularly suitable for surveys where all the measurements are made by indirectmeasurements. It is possible to express homogeneity in the form of a statisticalparameter such as the standard deviation or coefficient of variation of the pulse velocitymeasurements made over a grid. However, such parameters can only be properly used tocompare variations in concrete units of broadly similar dimensions.

Variations in pulse velocity are influenced by the magnitude of the path lengthbecause this determines the effective size of the concrete sample, which is underexamination during each measurement. The importance of variations should be judgedin relation to the effect which they can be expected to have on the required performanceof the structural member being tested. This generally means that the tolerance allowedfor quality distribution within members should be related either to the stress distributionwithin them under critical working load conditions or to exposure conditions. (Reynolds,1984)


48/97

2.2.2.6Detection of D efects

The use of the ultrasonic pulse velocity technique to detect and define the extentof internal defects should be restricted to well-qualified personnel with previousexperience in the interpretation of survey results. Attention is drawn to the potential riskof drawing conclusions from single results. When an ultrasonic pulse traveling throughconcrete meets a concrete-air interface there is negligible transmission of energy acrossthis interface. Thus any air filled void lying immediately between transducers willobstruct the direct ultrasonic beam when the projected length of the void is greater thanthe width of the transducers and the wavelength of sound used. When this happens the&st pulse to arrive at the rece iving transducer will have been diffracted around theperiphery of the void and the transit time will be longer than in similar concrete with novoid. It is possible to make use of this effect for locating flaws, voids or other defectsgreater than about 100mm in diameter or depth. (Reynolds, 1984)

Relatively sm all defects have little or no effect on transmission times but equallyare probably of minor eng ineering importance. Plotting contours of equal velocity oftengives significant information regarding the quality o f a concrete unit. The method usedto detect a void is to draw a grid on the concrete with its points of intersection spaced tocorrespond to the size of void tha t would significantly affect the concrete performance.A survey of measurem ents at the grid points enables a large cavity to be investigated bymeasuring the transit times of pulses passing between the transducers when they areplaced so that the cavity lies in the direct path between them. The size of such cavitiesmay be estimated by assuming that the pulses pass along the shortest path between thetransducers and around the cavity. Such estimates are valid only when the concretearound the cavity is uniformly dense and the pulse velocity can be measured in thatconcrete.

The method is not very successN when applied to structures with cracksbecause the cracked faces are usually sufficiently in contact with each other to allow the


49/97

pulse energy to pass unimpeded across the crack. This can happen in cracked verticalbearing piles where there is also sufficient compression to hold the faces close together.If the concrete is surroundedby water such that the crack is filled with water, the crackis undetectable since ultrasonic energy can travel through a liquid.

2.2.2.7 Examples of Relationships Between Pulse Velocity and CompressiveStrength

Some figures suggested by Whitehurst for concrete with a density ofapproximately 2400kglm are given in Table 2.2. According to Jones, however, thelower limit for good quality concrete is between 4.1 and 4.7 M s . Despite thisrelationship between pulse velocity and compressive strength, ultrasonic pulse velocitymeasurements are not usually used as a means of quality control on construction sites.Unfortunately there is no satisfactory correlation between the variability of thecompression test samples, be they cubes or cylinders, and the variability of the pulsevelocity measurements. (Reynolds, 1984)

Table 2.2 Classification of the quality of concrete on the basis of pulse velocity(Source: Reynolds, 1984)

QuaIity of Concrete

excellentgood

doubtfulpoor

Very poor

Longitudinal pulse velocityW s . 1 0 3>4.5

3.5-4.53.0-3.52.0-3.0


50/97

-P ~ ( F P C S B ~ Y E S ~ ~ ~ ~ W ~ -rm'Figure 2.8 Relation between ultrasonic pulse velocity and compressive strength forconcretes of different mix proportions.(Source: Reynolds, 1984)

23 PartiallyDestructiveTest

Partially destructive test is the most efficient test to test the integrity of existingconcrete structures. The efficiency is measured since the actual material is being testedunder controlled procedures with minimum assumption. At times assumptions is beingneglected to measure the actual strength of the concrete. In this discussion, core test willbe discussed as a partially destructive test. In destructive testing, tests are camed out tothe specimen's failure, in order to understand a specimen's structural performance ormaterial behavior under different loads. These tests are generally much easier to carryout, yield more information, and are easier to interpret than nondestructive testing


51/97


52/97

Occasionally, the contractor determines the area of suspect concrete by pointingto an arbitrary location. Alternatively, the testing laboratory may core concrete in alocation accessible to its equipment. While accurate placement records are beneficial,verification by a nondestructive testing technique is prudent. Ideally, the engineer shouldbe involved in determining the location for core testing. Low cylinder strengths may bedue to errors in sampling or testing and not due to inadequate concrete. Engineers mustdecide whether the low cylinder strength indicates poor testing, a bad truckload ofconcrete, or a bad placement, then, if necessary, plan an appropriate core testingprogram. (Petersen and Poulsen, 1996)

2.3.2 Cores vs. Cylinders

Cores do not serve the same purpose as cylinders. Strength of standard cylindersrepresents the quality of concrete delivered. Cylinder compressive strength representsthe quality of concrete batching, mixing, and transportation, as well as the sampling,preparation, handling, curing, and testing of the cylinders. Strength of cores representsthe in place concrete strength. In addition to concrete batching, mixing, andtransportation, core compressive strengths represent the quality of placement,consolidation, and curing, and the techniques for obtaining and testing cores. Therefore,the relationship between core and cylinder strength varies because of the characteristicsthat each specimen represents.


53/97

2.3.3 Coring Direction

Cores obtained by drilling in the direction of concrete casting may provide ahigher strength than cores obtained by drilling perpendicular to the direction of casting.The strength difference due to drilling direction is generally attributed to bleeding infresh concrete, which creates a weak paste pocket under coarse aggregate particlesFigure 2.9 below. Because of the bleed water, the paste-to-coarse aggregate bond belowthe aggregate particles may be weaker. A load applied parallel to the weak bond opens acrack, creating a strength-decreasing flaw. However, a load applied perpendicular to theweak bond closes the crack, minimizing the effect of the bleed water layer. If thistheoryholds true, reducing bleed water minimizes the effect of coring direction. Thus, anyfactor that affects bleeding, such as the concrete mix design, mix ingredients,aircontent,and placement and consolidation techniques, also determines the strength difference ofcores drilled vertically or horizontally. Most slabs and foundations are cored parallel tothe direction of casting, resulting in no associated reduction in strength. Walls andcolumns are cored perpendicular to the direction of casting, thus a reduction in strengthmay occur. The data on the effect of coring direction is contradictory. It is quite likelythat the compressive strength of cores drilled horizontally is stronger than cores drilledvertically. Practical considerations, however, like variations in placement, consolidation,and mix variability might obscure a coring direction difference that is discernible onlyunder precise control of the mix and construction practices. The current practice in theindustry is to neglect any effect of coring direction.


54/97

2.3.4 Top-to-Bottom Strength Variation

It is generally acknowledged that concrete strength varies within a singleelement. The strength variations shown in Figure 2.10 should not be considered asabsolute numbers. Figure 2.10 is very useful, however, when planning a nondestructivesurvey to determine the likelihood of a low-strength cylinder or core locations.Laboratory test results indicate two apparent causes of the strength variation: strengthincrease at the bottom attributed to greater static pressures caused by the concrete aboveand strength decrease at the top attributed to higher water-cement ratios as a result ofbleed water.

beam CoreA CoreB

Figure 2.9 Planes of weakness under coarse aggregate particles due to bleeding.(Source: Petersen and Poulsen, 1996)


55/97

9 Locationwithinmember


56/97

and denser than cores removed between vibrators. Cores removed from the bottom arestronger and denser than those removed fiom the top. Work by several highwaydepartments' shows that a reasonable maximum decrease in a pavement core's unitweight compared to the unit weight of an ASTM cylinder is 4%.This corresponds to aloss in compressive strength of about 1200 psi. (Galan, 1976)

2.3.6 Effects of Curing

The thermal history and curing of cores is quite different than for standardcylinders. The structure's thermal environment might be better or worse than thatprovided by laboratory curing. Also, most structures aren't moist cured like a standardASTM cylinder. Field curing is unlikely to be as good as moist curing, Field concretemay be subjected to cold- or hot-weather curing conditions. High temperatures canlower concrete strength but lower temperatures could actually produce stronger concreteat later ages. The methods for obtaining and testing a core obscure the effects of curing.Curing dramatically affects the concrete surface, but has less of an effect on the interiorconcrete. The outer concrete protects the inner concrete's humidity and temperatureconditioning. When cores are tested, the restraint of the testing procedure makes mostconcrete cores fail within the middle portion of the core. Weak outer edges, affected bycuring methods, are not usually represented by the core failure mode or the resulting testvalue. The test results presented indicate that for vertical members such as walls andcolumns, curing had little effect on core strengths. For slabs, however, curing is criticalto achieving adequate core strength. Figure 2.11 below showing longitudinal resonancefrequency of concrete cores.


57/97

A9e (weeks)Figure 2.11 Longitud inal resonance frequency of conc rete cores

(Source: Morey and Kovacs, 1977)

2.4 Codes, Standards and Specifications

Codes and standardization is always has been important guidelines andmeasuring any engineering results. In evalua ting the results obtain from several testingfor structural assessm ent, more than one standard codes and specification referred.


58/97

2.4.1 General C onsiderations

One of the consequences of the Industrial Revolution era was the eventualcommunity realization that the developments taking place had to be subjected to somemeasure of control. For instance material properties had to be specified so thatmanufacturers could manufacture material with agreed minimum properties. Designengineers needed to know the minimum properties so that designs could be producedwith an appropriate factor of safety. Insurance organizations needed to be sure that therisk of failure of a structure was as low as possible to minimize insurance claims. Theend user of the technology, the general public, also needed to be sure that the technologywas safe.

In most countries national bodies were formed to provide the necessary control.For any specific topic the national body would convene a committee of representativesof all interested parties who meet to develop a draft for circulation to all interestedparties. The comm ittee formed to develop the document involves technical experts fromthe producers, the users and the general public usually represented by a regulatory body.The committee may also include representatives from technical societies and fromuniversities. The resulting 'standard' developed by th is consensus process is oftenreferred to in contracts between organiza tions to con trol the quality of work. In this casethe document is legally binding and deliberate non-compliance can result in legalpenalties being applied. Standards can play an important role in international co-operation when they are used in contracts and treaties for the supply of goods andservices between one country and another. The growth in interna tional trade has resultedin a growth in the need for International Standards, which can be an acceptablecompromise between different national standards.


59/97

2.4.2 Different Categories of Stand ard s

Standards can be categorized into many. In this section of literature review,selected codes and standardization discussed briefly.

2.4.2.1 Standards

Standards are documents that govern and guide the various activities occurringduring the production of an industrial product. Standards describe the technicalrequirements for a material, process, system or service. They also indicate asappropriate, the procedures, methods, equipment or tests to determine that therequirements have been met.

2.4.2.2 Codes an d Specifications

Standards may also be referred to as codes or specifications. One of the bestexamples of a code is the ASME Boiler and Pressure Vessel code which is a set ofdocuments that assure the safe design, construction and testing of boilers and pressurevessels.


60/97


61/97

ASTM C85-66, "Cement content of hardened Portland cement concrete", ASTM,Philadelphia, USA

ASTM C457-80, "Air void content in hardened concrete", ASTM, Philadelphia,USAASTM (2823-75, "Examining and sampling of hardened concrete in constructions"ASTM C779-76, "Abrasion resistance of horizontal concrete surfaces''ASTM C944-80, "Abrasion resistance of concrete or mortar surfaces by the rotating

cuttermethod"ASTM (2856-77, "Petrographic examination of hardened concrete"ASTM D4788-88 S tandard Test Method for detecting Delamination in Bridge Decks

using I n f k e d ThermographyASTM D6087-97 STM for Evaluating Asphalt covered Concrete Bridge Decks

using G round Penetrating RadarASTM D4580-86 (1997) Standard Practice for measuring D elamination in Concrete

Bridge Decks by SoundingASTM D2950-91 (1997) STM for Density of Bituminous Concrete in place by

Nuclear MethodsASTM C1383-98a STM for measuring P wave Speed and the Thickness of ConcretePlates using the Impact-Echo M ethod

ASTM C1150-96 STM for the Break off Number of ConcreteASTM C1040-93 STM for Density of Unhardened and Hardened Concrete in place

by Nuclear MethodsASTM C900-94 STM for Pullout Strength of Hardened ConcreteASTM C876-91 STM for Half-cell Potentials of Uncoated Reinforcing Steel in

ConcreteASTM C805-97 STM for Rebound Number of Hardened ConcreteASTM C 803-82, STM for Penetration Resistance of Hardened ConcreteASTM C801-98 STM for Determining the Mechanical Properties of Hardened

Concrete under Triax ial LoadASTM C 597-97 ST M for the Pulse Velocity through Concrete.


62/97

2.4.2.4.2 British Standards Institution PSI)

The BSI is the UK's national standards organization. Its role is to produce andpublish British Standards and information products that prom ote and share best practice.BSI serves the interests of a wide range of industry sectors as well as governments,consumers, employees and society overall, to make sure that BS British standards, ENEuropean standards and IS0 international standards are useful, relevant andauthoritative.

BS 1881 Part 102: 1983- Method for Determination of SlumpBS 1881 Part 5:1970 - Testing Concrete. Methods of testing hardened concrete for

other than strength. Determination of dynamic modu lus of elasticity by electromagneticmethod

BS 1881 Part 205:1970 - Testing Concrete. Recommendations for radiography ofconcreteBS 1881 Part 206:1986 - Testing Concrete. Recommendations for determ ination ofstrain in concrete. Advice on the use of mechanical, electrical resistance and vibratingwire gauges and e lectrical displacement gauges.

BS 1881 Part 202:1986 - Testing Concrete. Recommendations for surface hardnesstesting by rebound hammer

BS 1881: Part 114: 1983 - Methods for Determination of Density of HardenedConcrete

BS 1881: Part 116: 1983 - Method for Determination of C ompressive Strength ofConcrete Cubes

BS 1881 Part 117: 1983 - Method for Determ ination of Tensile Splitting Seen,&BS 1881: Part 118: 1983 - Method for Determ ination of Flexural StrengthBS 1881: Part 120: 1983 - Method for Determination of Compressive Strength of

Concrete Cores


63/97

BS 1881:Part 121 1983 - Method for Determination of S tatic Modulus of Elasticityin Compression

BS 1881 Part 122: 1983 - Method for Determination of Water AbsorptionBS 1881: Part 201: 1986 - Guide to the Use of Non-Destructive Methods of Test forHardened Concrete

BS 1881: Part 202: 1986 - Recommendations for Surface Hardness Testing byRebound Hammer

BS 1881: Part 203: 1986 - Measurem ent of the Velocity of Ultrasonic Pulses


64/97

CHAPTER 111

METHODOLOGY

1 Introduction

This case study will be consisting testing on existing concrete structures usingconcrete core method, rebound hammer test and ultra sonic pulse velocity (UPV) onexisting pre-stressed T-beam and concrete structures of an unnamed bridge in HangValley. Results will be tabulated for comparison between BS 1881& BS 6089 cubecharacteristic strength and BSEN 13791,20 07 cube characteristic strength. Besides that,questionnaires will be distributed to five qualified consulting engineer to get theirfeedback on the factor in selecting testing method to evaluate the integrity of existingconcrete structures. Results will be analyzed using calculation for cube characteristicstrength and design requirement and acceptability of the results obtain from thetabulation and wrapped out with conclusion and recommendations. Basically, thisdiscussion will be a case study on criteria of selecting the suitable method of testingintegrity of existing concrete structures. The methodology flow chart is shown as inFigure 1.1, chapter 111.


65/97

3.2 DocumentStudy

There were there types of testing was conducted to gather the results fordocu men t study. All the three types of testing that has been conducted briefly explainedin this section.

3.2.1 Concrete Core Test

Concrete core test were conducted on the T-Beam girder marked as L-PBPC -S2-EX-01 and on the bridge sub-structure marked as Pier B. Five (5) core sam ples weretaken from T-beam girder L-PBPC-S2-EX-01 and two (2) core samples were takenfrom Pier B crosshead. lOOmm core diameter was used in coring the core samples forthe T-beam girder since the spacing for the rebar 150mm whereas 68mm core diameterwere used to core Pier B crosshead since the rebar for crosshead is congested. Prior tocoring, cover meter were used to locate the position of the reinforcement whereverpossible as to avoid drilling through reinforcement. Hakken coring machine was used todrill the core sample perpendicular to the concrete structure using a diamond coredrilling bit. Figure 3.1 below showing the process of coring. After drilling the coresample to the required length which is 150rnm, the samples were marked clearlyindicating its location and date of drilling and take close-up photograph of the coresample near its core hole. Samples later were wrapped with spon ge and place in a boxand transport back to the laboratory. The co re samples were cut to the required lengthand examined for compaction. Selected core samples were cut and trimmed usingconcrete cutter to the required length minimum 100mm. As the final preparation beforecrushing, samples were prepared for capping using sulphur as a capping material. Thepurpose of capp ing is to provide a flat surface for both ends of core samples prior to the


66/97

crushing. Once capping completed, samples were soaked in water for 48 hours forcuring of the capping material so that the capping material does not crack under thecompressive during the cube crushing. Once he curing completed, samples were testedfor its compressive strength using. Prior to the crushing, the crushing machine tested forcalibration certificate and quality control check.

(c) (4Figure 3.1 Photographs showing the process of concrete core sample testing


67/97

3.2.2 SchmidtReboundHammer Test

Rebound Hammer test was conducted on four (4) locations on T-beam girdermarked as L-PBPC-S2-EX-01 and one (1) on bridge sub-structure marked as Pier Bcrosshead to estimate the in-situ compressive strength of concrete using themanufacturer's correlation curve. Location was marked as a box 300mm by 300mmdrawn which divided into 10 small boxes on the structure. Honeycomb and roughsurfaces was avoided. Rebound Hammer tested horizontally perpendicular to theconcrete surface as shown in Figure 3.2. Rebound Hammer test were canies out on thesmall boxes. Each boxes tested ten (10) times and data were recorded into data sheet.

(c)F i r e 3.2 Photographs showing the process of rebound hammer testing


68/97

3.2.3 Ultrasonic Pulse Velocity Test

Ultrasonic Pulse Velocity test were conducted on the five (5) core sam ples takenfrom T-beam girder marked as L-PB PC-S2-EX -01 and two (2) core samples taken frombridge sub-structure marked as Pier B, the same locations where Rebound Hammer testwere conducted. Samples were tested prior to the core crushing after the capping andcuring process has been completed. The process of ultrasonic pulse velocity is clearlyshown in Figure 3.3.

(c)Figure 3.3 Photographs showing the process of UPV testing


69/97

3 3 Interview with Civil and Structural Consulting Engineers UsingQuestionnaire

Five selected and experience civil and structural consulting engineers wereinterviewed using a prepared questionnaire. Questions on their personal views inselecting appropriate testing method to evaluate integrity of existing concrete s tructureswere raised in a very friendly approach. The sample of questionnaire used for interviewis attached in appendix A.

3.3.1 Contents of the Questionnaire

1. Question 1Questioning the personal views of the respondents on the factors that

influencing in selecting of proposing the appropriate testing method to evaluateintegrity of existing concrete structures. Respondents were given various relevantchoices of answer to give their view on app ropriate nature of testing methods.

.11. Question 2

Questioning respondent's preference in selecting either destructive ornon-destructive test to evaluate integrity of existing concrete structures.Respondents may state their view in approaching the types of basic testingmethods.


70/97

iii. Question 3Questioning respondent's preference in rating from the most agreed to the

least by giving the selected destructive tests. The respondents required to givetheir comments on rating the most preferred test method to find out theirstandings in rating the most preferred destructive testing method.

iv. Question 4Questioning respondent's preference in rating from the most agreed to the

least by giving the selected non-destructive tests. The respondents required togive their comments on rating the most preferred test method to find out theirstandings in rating the most preferred non-destructive testing method. -

v. Question 5Questioning respondents on the standards codes and practice in reinforce

concrete structural for determining the concrete strength. The respondents alsocan state their view and confident level in practicing the selected code andpractice.

vi. Question 6Questioning respondents on their preference in the method of presenting

in comparing the results obtain fiom the both destructive and partially destructivetest.

vii. Question 7This question allows respondents give their view and suggestions on the

remedial work in the event of failure in obtaining required concrete strength forexisting concrete structures.


71/97

viii. Question 8This question allows respondents to write their opinion on the common

problem w ith Malaysian engineers in facing structural integrity problems and incarrying out the remedial actions.

ix. Question 9This question allows respondents to write their suggestions when facing

structural integrity to our government bodies in improving procedures andobtaining high safety levels in structural integrity.


72/97

3.2.3 Comparison of Cube Characteristic Strength Using BS 1881& BS 6089 andBSEN 13791:2007 Euro Codes

A detailed comparison using Microsoft Excel spreadsheet programmewill be created to compare the results obtain form concrete core test. Comparisonwill be using BS 1881& BS6089 and BSEN 137912007 Euro codes. Detailcomparison will be tabulated by displaying the formula that has been used and thevariance between both code and practice to evaluate the acceptance of the selected codeand specification on the concrete core results.


73/97

CHAPTER IV

DATA ANALYSISAND RESULTS

4.1 Document Study

This case study was based on analyzing data collected from throughout adocument study on the data obtained from three different types of concrete testingmethod, outcom e of an interview with professional civil and structural consultants, andcomparison using two different engineering codes and practice. Findings on the outcomeof data were analyzed using extensive usage of computer programs. The usage ofcomputer program makes the presentation of data easier and in well presentable form forviewers. One o f computer program know n as 'spreadsh eet' is being used widely tomanipulate data especially in a form of table which involves various parameters in thecalculations.

'Spreadsheet' is a linear program using tables in a form of column and rowwhich displays the cell in the form of screen which contains relevant information,formulas, and also writings. Microsoft Excel is the most suitable 'spreadsheet' programto mange, analyze and to present data. Further more, data obtained from thecalculations can be plotted in various graphs as needed. Besides 'spreadsheet' program,


74/97

chart types from M icrosoft Excel such as pie chart and bar chart were used to representthe da ta especially for data obtained from interviews.

4.1.1 Rebound Hammer Test

As a part of structural testing to determine the estimated in-situ compressivestrength of existing concrete structures, rebound hammer test was carried out on theprecast T-beam and pier crosshead. The results obtained form the rebound hammer testconducted for this case study tabulated in Table 4.1 and the schem atic diagram of the T-beam and the locations of the rebound hammer test conducted is clearly illustrated inFigure 4.1 and Figure 4.2.

Table 4.1 Rebound hamm er results

Note: MI-M5,Rebound Hammer Test for T-Beam L-PB/PC-S2-EX-01,RH6, Rebound Hammer Test for Pier B crosshead.

RH4RH5RH6

VerticalHorizontalHorizontal

373834

353634

363938

342638

3 13638

363835

323337

423833

394336

35.836.335.9

38.038.333.0


75/97

Figure 4.1 Top View of T-Beam L=PB/PC-S2-EX-01

Figure 4.2 Side View of T-Beam L=PB/PC -S2-EX41Legend: RH-Rebound Hammer Test

C-UPV Test

Table 4.2: Measurement for Rebound H amm er UPV Test locations on the T-Beam


76/97

4.1.2 UltrasonicPulse Velocity

To derive the correlation curve of U ltrasonic Pulse V elocity against estimated in-situ cube strength from the selected core samples on the same structures, UPV testconducted on the selected core samples prior to crushing of core for compression test.Ultrasonic pulse velocity test was canied out on five core samples taken from pre-castT-beam and two samples taken form pier crosshead. Table 4.3 below showing the resultsobtained from Ultrasonic Pulse Velocity test. Ultrasonic Pulse Velocity also wereconducted on the same structures were the core sam ple were taken a t three locations onthe pre-cast T-beam and pier crosshead to determ ine the estimated in-situ cube strengththrough correlation curve obtain from the p lotting of Ultrasonic Pulse Velocity againstcore samples.

Table 4.3 Ultrasonic Pulse Velocity Test Results


77/97

4.1.3 Core Compression Test

As a part of testing method to determine the estimated in-situ cube strength andto derive the correlation curve of ultrasonic pulse velocity against estimated in-situ cubestrength, selected concrete core samples were tested under core compression testmachine and the results obtained from the core compression test is tabu lated in Table 4.4as below. Five samples were taken from pre-cast T-beam and two samples were takenfrom pier crosshead.

Tab le 4.4 Concrete Core Compression Test Results


78/97

Figure 4.3 Correlation C urve of UPV againstEstimated In-situ C ube Strength

45 -40

P 5PEi 3 O -3 25U)m9 20Ua= 15 -2li 10Y

Both data obtained from UPV and concrete core test has been used to derive acorrelation curve. Figure 4.3 showing the correlation curve derived from UPV andconcrete core test for the same samples. The estimated in-situ strength for the pre-cast T-beam and pier crosshead obtain through interpolation of data obtain for UPV andcorrelation curve . The result of estimated in-situ men-@h of existing structuresthroughout the in terpolation from correlation curve is tabulated in Table 4.5.

I----- 1

Table 4.5 Estimated In-Situ Strength through out Interpolation from Correlation Curve

3.6 3.7 3.8 3.9 4 4.1 4.2 4.3UPV (km/s)


79/97

Table 4.6 below showingdata obtainedh m he three types of test conducted onthe pre-cast T-beam and pier crosshead.

Table 4.6 Estimated In-SituCube Strength for all three types of test


80/97

4.2 Interview

As a part of data collection to evaluate the criteria in selecting the most suitabletesting method to determine the integrity of existing concrete structures, five selectedcivil and structural engineers were interviewed using a prepared questionnaire. Theoutcomeand responds well described in bar chart Figure 4.2 below.

Degreeof reafii nI epmentactual Ib I egreeofmmplex.wwigure 4.4 Factors Influencing in SelectingMethod of TestingFrom the questionnaire survey conducted, 60% of the civil and structural

engineers are prefer to have a structural integrity test which has more degree of realityin representing the actual results. The remaining 20% respondents are in opinion thatthe degree of complexity and 20% more in opinion of market availability influencesthat the selecting the method of testing to evaluate the integrity of existing structures.

I arket Availability I

When question on respondents preference on the nature of test whether partialdestructive or non-destructive raised, 80% of respondents are prefers destructive test tobe conducted in order evaluating the integrity of existing structures while 20% more arekeen in conducting non-destructive test as their choice in testing the existing structures.The proportion of preference in the nature of test to be conducted is well described inbar chart Fi-we 4.3. The preference in types of partial destructive and nondestructivetest by respondents is well described in Figure 4.4 and Figure 4.5.


81/97

Nondestructivetest

Figure 4.5 Proportions of nature of test by respondents

Out of five civil and structural engineers interviewed, all of them are stronglyagree with concrete core test as the best among other partially destructive test. Theyhave strongly suggested concrete core test is the most appropriatein determining the in-situ strength of the existing concretestructure.

I Responseon Selectionof Partially DestructiveTestI I I IConcreteCoreTest 5

0Penetrationresistance 0

I

Figure 4.6Responses on Partially Destructive Test Preference


82/97

1 Responseon Selection of Non-DestructiveTest

Figure 4.7 Responses on Partially DestructiveTest Preference

In responding to the preference to non-destructive test, three of them preferultrasonic pulse velocity and two more in the opinion that rebound hammer test is themost preferred in selecting nondestructive test to evaluate the integrity of existingconcrete structure. In their personnel view, they also have suggested more than one non-destructive test should be conducted in order to derive the correlation to obtain moreaccurate results. In their response to the selection of standard code and practice forstructural assessment to evaluate the test results, majority of them are still prefer BS1881 part 5 as preferred standard code and practice for structural assessment. Theproportion of the response for preferred standard codes and practice for structuralassessment is shown in Figure 4.6. The awareness on BSEN E m code is still pooramong the civil and strucmml consultants where there is none of them are in favor ofusing BSEN E m ode for their structural assessment. BSEN is an Ewopean suite ofcodes for structural design developed over twenty five years which by 2010 it willeffatively replaced the current British Standards as the primary basis for designingbuilding and civil engineering structures in the United Kingdom an other part of world.


83/97

(I)$30 8g.E S(n 00 -,(I) 322 %


84/97

4.3 Comparison

One of our main objectives is to analyze and compare the selected standardstructural code and practice in evalua ting integrity o f existing concrete structures. Thus,two selected standard structural code and practice were used in comparing the dataobtained. BS 1881 Part 5 and BSEN Euro codes are the two selected standard structuralcode and practice used in comparing the concrete core test results obtained form ourcase study. Five numbers of concrete core samples form pre-cast T beam and twonum bers of concrete core samples from pier crosshead were tested under compressiontest. Table 4.6 showing the comparison for estimated in-situ strength in form ofcom parison by using two selected structural code and practice.


85/97

Table 4.7Comparisonof Cube characteristic Strength using BS 18818~ S 6089 and BSEN 1 3 7 9 1 : 2 0 0 7 Euro codes

5 T-Beam GDIFNA4IC8 40Pier B

6 Crosshead PBIRICHICG 40 17.5 21.9RH SPier B

7 Crosshead PBIRICHIC7 40RH S

FailedFailedFailedFailedFailed-Failed

Failed

FailedFailedFailedFailedFailed

Failed

Failed


86/97

4.4 Results Obtained from Structural Assessment Case Study

Based on the observation from the case study, there are big variances betweenthe three types of structural test that has been conducted. The variance of results toobtain estimated in-situ strength for the existing concrete structures is between 5 . 5 ~ 1 m m ~to 22.1 ~ / r n r n ~ a sabulated in Figure 4.7. This shows the results to obtain estimated in-situ strength for existing concrete structure contents big variance from one to anothermethod of testing.

Table 4.8 Variance between there types of test conductedTypes of Structural

This variance showing that there is an inconsistent between the results obtainedfrom the three types of structural integrity test. The correlation curve derived from thecombination of ultrasonic pulse velocity and concrete core test results is just a basis tojustify other bathes of UPV results. Nevertheless, UPV results for itself can onlyrepresent the path length velocity which the durability of existing concrete can be knownthrough this. The higher the velocity, the high the durability the concrete is.


87/97

4.5 Results andFindings from Interview

Based on the questionnaire feedback, most of the civil and structural engineersare in the same opinion where they are keen in selecting or proposing the testing methodwhich can represent the actual results of existing concrete structure for structuralassessment. The testing method that can give the degree of reality in representing theactual results is given more priority in selecting the appropriate testing method. The civiland structural engineers are also aware of the latest sophisticated technology forstructural assessment of existing concrete structures such a Ferro scan and permeabilitytest which involves costly equipment.

From the interview conducted, concrete core test is the most preferred selectionby the civil and structural engineer. This is strongly proven throughout the evidencesobtained from the concrete core test results which is very realistic compare to otherresults. On the view of standard structural code and practice for structural assessment,BS 1881 part 5 is still preferred by most of the civil and structural engineers. Theexistence of BSEN Euro codes is still does not much realize by our civil and structuralengineer.


88/97

4.6 Comparison between BS 1881and BS EN 13791Euro Codes

Based on the comparison for concrete cube compression results using BS 1881and BSEN Euro codes as selected standard structural code and practice, BSEN Eurocodes have a very strict design criteria in acceptance of the estimated cube strengthresults throughout the concrete core compression test compare to BS 1881. Thisprobably the safety factors in accepting the estimated cub strength through the structuraltesting method has been increased. The strict design criteria in accepting the estimatedvalue are making the construction industry more rigid in evaluating the integrity ofexisting structures. Figure 4.8 shows the variance between BS 1881 and BSEN 13791Euro codes.

Table 4.9 Variance between BS 1881 and BSEN 13791


89/97

CHAPTER V

CONCLUSION AND SUGGESTIONS

5.1 Factor Influencing in Selecting Most Suitable Testing Method for StructuralAssessment

Throughout the case study using there selected structural testing methods forintegrity testing, the factor that influencing the selection criteria of suitable testingmethod for structural assessment can be concluded as below:-

9 Degree of reality in representing the actual results,9 Correlation that can give results equivalentto actual concrete core test results,> Destructive test which can test part of theactual sample, and> The cost for the test to be carried out and provided budget.


90/97

5.2 Com parison of Concrete Co re Results Using BS 1881&BS6089 and BSEN13791:2007 Eu ro C odes.

Based on the com parison between BS 1881& BS6089 and BSEN13791:2007 Euro codes using Microsoft Excel spreadsheet, the acceptance of theconcre te core results cab be concluded as below:-

BSEN 13791:2007 Euro Codes are more concern on the acceptance compare toBS 1881&BS6089,

> BSEN 13791:2007 Euro Codes showing the cube characteristic strength afarless