Developments fromCSIROT

C-Y'T'TT '. SSerdang Hospital in Kuala LumpurInterview with MSSA PresidentProfile on SSSS President

Radar as nondestructive testing tool for concreteNon-destructiveTests On ConcreteCubelnfoControls equipment for Mapei France lab

f"'f"' T{ E TECHNOLOGYConstructiVisionConcreteKioskTermacolRecycled aggregates for precast concrete

INCORPORATING STRUCTURAL STEEL

JUL-SEP 2002FREE COpy FOR QUALIFIED READERSMITA (P) 134/08/2002

Cone rcrc cornpressivc "trength ofviandnrd samples curing undervtnndard conditions are of urmovrimportance for quality control ofconcrete as It IS produced, Ilowever, those values can only be atveptcd as mdrcarmg the 'porcnnal"rength' of concrete and rnav <lIt"kr from the acrual 1S1 siru concretecornprcwrve vrrcngrh.

I he knowledge, a, close a,1)()'~Jblc.of the ,"-~I(Uconcretecornpressrvc vtrcngth i,. In somexuuanonv, necessary in order [0

evrrmure, for instance, t he timewhen precast concrete rucmbervcan be moved and transported, rhelime of prestressing, removal ofmould, or propping. etc,

14~UL-SEPT 2002

by Miguel C. S. Nepomuceno, Lecturer,University o[Beirn Imerior, Portugal andsergio M. R. Lopes, AssiSIlIIJl Professor,Utliversityo{Coimbra, Porwgal

concretetests on

Non-destructive

'EVENTS'CONCRETE: F"EATURE'CONCRE:TE EQUIPMENT'CONCRETE APPLICATIONS'

'NEWS'COVER STORY' STEEL F"EATURE'CONCRETE MATERIALS'STEEL APPLICATIONS'

.JUL-SEPT 200215

This fact is a direct consequence of the high numberof practical factors that can affect the rebound of theincident mass, due to the difficulty of taking into ac­count the correct influence of such factors or to re­produce similar condirions as those using on calibra­rion test.

Some professionals have pointed out that even insituations where these conditions are weUreproducedin-situ and specifically developed correlations areused, the 95 percent confidence limits on the estima­tion of compressive strength deviate 25 percent fromthe mean value [4,6]. Under ideal laboratory condi­Lions it is probable that this difference would be re­duced to 15percent [4.6J.

Figure 2 - LoadingSchmidt ReboundHammer.

Figure 1- Schmidt ReboundHammertype N.

Surface Hardness TestThis type of resri ng has being applied [0concrete sineethe 30'S and from the early attempts different meth­ods and techniques have been proposed. The methodproposed by the Swiss engineering Ernst Schmidt inthe 40'S is based on the rebound of an incident masshas been recognised as the most reliable and it is stillused nowadays (3,6).

The Schmidt hammer has been used with successto evaluate the surface hardness, with special evidencefor such apparatus type N, with an impact energy of2..207 N.m <Figure I and Figure 2). Its use is coveredbyvarious national standards such as the Recommen­dations from British Standards BS:1881:Part202 {4)

The surface hardness res is easy to operate, onlyrequires a free surface, is cheap, and causes Lessdam­age than the majority of the other non destructivetests. However its use to estimate directly the in-situcompressive strength using general established cor­relations is not recommended by many authors [6}.

Non-destructive tests (NUT) have been increas­ingly used in the last few decades for the assessmentof in-situ quality anti integrity of concrete elements,especially for estimation of in-situ concretecompressive strength. National standards are avail­able in a number of countries, notably in the UK andUSA, detailing procedures for the most firmly estab­lished testing methods. It is important to mentionthat procedures from different national standardspresent small differences.

Non-destructive tests present some significantadvantages such as speediness of operation, immedi­ate availabili ty of results. less costs and, above all, lessdamage for concrete elements under test. The NDTmethods arc specially designed for estirnarion of thein-situ concrete compressive strength and do not al­Iowa direct quanrirarivc measurement of such prop­erty. Therefore, it would be necessary to develop anduse empirical correlations. Such correlations introduceuncertainties on the results, which represent the maiodisadvantage of these tests when compared to thosemethods based on drilled cores. 10spite of that, whenbased on fum correlations, the accuracy of such esti­mations improves significantly and it could overcomesuch drawbacks [3].

Tbe NDT techniques actually available vary sig­nificantly in terms of accuracy; degree of destructioncaused to concrete elements, speed of test, immediacyof results and costs involved. Those methods havebeen traditionally used on normal strength concrete.Although, since high strength concrete is being in­creasingly used all over the world. many researchworks have been developed during rhe lase ten yearsto rest the applicability of such methods to highstrength concrete.

Tbe use of NDT methods on normal and highstrength concrete clements will be qualitatively dis­cussed on this paper, taking as reference five differ­em test methods, which imply the measurement ofother five different properties. Such properties in­dude the measurement of the surface hardness, ul­tra-sonic pulse velocity, penetration resistance, pull­out force and direct tensile strength (pull-off test).

-EVENTS-CONCRETE FEATURE-CONCRETE EQUIPMENT-CONCRETE APPLICATIONS-

-NEWS-COVER STORY-STEEL F"EATURE-CONCRETE MATERIALS-STEEL APPLICATIONS-

Figure 4 -Windsor Probe TestSystem.

Ultra-sonic Pulse VelocityTestThe ultra-sonic pulse velocity testis well studied and its use is gener­alised worldwide. This methoddocs not cause any damages onconcrete surface and it is believedto be one of the methods that canbe used to evaluarc the interiormassof concrete elements (6}.Oneof the most generalised equipmentused on concrete is the PortableUltra-sonic Non-destructive Dig­rral Indicating Tester (pUNDTnWithelectro-acoustical transducersof natural frequency of 54 kHz(Figure 3) [3). Recommendationsfor Its usc can be found, for exam­ple, on British Standards Institu­tion BS:1881:Part203 [2]

The factors which affect thetest results have been studied formanyyears and, in some cases, cor­recrion factors were developed totake into account, for example, thepresence of reinforcement bars.The ultra-sonic pulse velocity de­pends on the modulus of elasticityof the material which is related [0

The experience has sbown thatthe surface hardness test can bevery useful in situations in whichcorrelations arc not needed, forexample, to monitor large surfacesfor comparative analysis and locali­sation of crrtical zones, whereother more reliable tests can beapplied, which unfortunatelycauses more surface damage andarc more expensive.

Penetration Resistance TestPenetration resistance tests havebeen used for many years mainlysupported by the Wmdsor ProbeTest System (WPTS) and its uschas been more generalised inNorth America [6]. USA Stand­ards ASTM C803-90 [I] orBS:1881:Parr207[5) have been usedas reference. For normal strength

·EVENTS·CONCRETE FEATURE·CONCRETE EQUIPMENT·CONCRETE APPLICATIONS'

16

concrete compressive strength.Despite all [he recognised practi­cal advantages. the CPV test hassome of the problems referred torbe penetration resistance test, i.e., this rcsr doe.. not give a directreading of the concretecompressive strength, and the cor­relation .. are affected by a largenumber of factors. There existsome correction factors, but prac­rice has demonstrated that it in­troduces largeuncertainties on theresult, with consequences on theaccuracy of rhc estimation value.

It has been pointed out that,even using correlauons specificallydeveloped for a given concrete un­der good in-situ conditions, it isunlikely that the 95 percent confi­dence limits for the estimation ofthe compressive strength are bet­ter than 20 percent of the meanvalue [2,6]. Using general correla­tion curves. thi' difference couldarise to 50 percent [2,6].Using spe­cific correlation curves developedin the laborarory such 95 percentconfidence hmirs could dcviarc 10percent from the estimated meanvalue (2.6).

Correlation betweencompressive strength and pulsevelocity has shown exponentialbehaviour [2,6,12], which leads tothe loss of sensibility of the lest forhigh strength concrete, I. c., a lit­tle increase on pulse velocity cor­responds to a great increase oncompressive strength. For this rea­son the applicability LO high

Figure 3 - Ultra-sonic PulseVelocity Test Equipment.

·NEWS·COVER STORY·STEEL FEATURE·CONCRETE MATERIALS· STEEL APPLICATIONS·

strength concrete needs to be fur­ther investigated. A first attemptwas made by the authors [12] andthe obtained correlation curveshave shown a considerable varia­tion on estimation of concretecompressive strength when dealingwith concrete elements ofcompressive strength of more than70 MFa. Probably, it is a naturalconsequence of exponential corre­lation which increases consider­ably at this level of strength.

As for surface hardness test,unless a specific calibration curvecan be obtained, it is virtually im­possible to predict the absolutestrength of a mass of in-situ con­crete by pulse velocity measure­ments [2,6,u]. However, this testis useful for comparative and uni­formiry assessments.

.JUL-SEPT 2002

•

..JUL-SEPT 2DD2

Figure 6 • Removing the drilled core InIts full 65 mm length.

17

Figure 5 - Drilling a 18 mm centre hole with adrill unit.

Pull-Out TestPull-out Test is recognised. amongthe main non-destructive tests. asthat which offers more accuracy onthe estimntion of the in-situ con­crete compressive strength [),6].Recommendations for its use areprovided by British Standards BS188[:Part 207 (5l

Onc of the techniques used forthis purpose is the CAPO.:rESTSystem developed by 'Germann IJ1-

struments AlS' (Figures 5 to rr), TheLoadis applied to the capo-insert bymeans of an hydraulic jack and areaction ring of 55mm inner diam­eter. The capo-insert (2.5mm diamerer ring) is placed at a depth of 15rom.

In the last few decades, inde­pendent analytical and experimen­tal studies have been developed tounderstand how failure mechanismworks during the pull-out tests. Aconsensus has been achieved re­garding the existence of a triaxialstate of stress highly non uniformon the concrete involved the capo­insert during extraction [6,7]. Inspite of some divergence as far as

tribute to a more extensive appli­cation of this method.

test can produce on the surface andthe high cost of ammunitions andprobes are the reasons why thismethod has not been extensivelyused [9,10,11). For this reason it isunlikely that penetration resist­ance replaces the surface hardnessor the ulna-sonic pulse velocitytests for comparative analysis ofconcrete.

The traditional WPT systemhas shown to be limited to con­crete compressive strength of lessthan 40 MPa (on cylinders)[5,9,IO,lT]. However, the authorshave confirmed that the measure­ment of penetration resistance canbe extended to concretecompressive strength of at least 85MPa (on cubes of 150 mm side)using a new technique supportedby a new equipment named 'Alter­native Firing Apparatus' [9.10,11].This new technique has also shownto be adequate for normal strengthconcrete offering the advantagesof reducing the damages in com­parison to the rraditional WPTsystem [o.ro.n]. It is also impor­tant to note that the applicationcosts of this new equipment islower compared to the traditional\VPT system. This (act may con-

concrete the WPT system is usedwith silver coloured probes ofhardened steel alloy With 6.35 mmdiameter. 79.; mm length. bluntconical end with a plastic guide andthe standard power (Figure 4).

The WPTSystem causes somedamages on the concrete surfaceand. in some circumstances itsreparation can be necessary. Onthe other hand its application islimited by restrictions of minimumedge distances (to prevent split­ting) and minimum distance be­tween rwo probes (to avoid over­lapping of zones of influence).Thismay limit the use of the techniqueIn some situations. Usually thismethod is recommended for cle­ments of large surfaces like slabsor clements oflarge cross sections[3]·

The penetration resistancetests can be used in the situationsmentioned above for comparativeanalysis of similar concrete ele­ments, showing as an advantage,comparatively to the surface hard­ness and ultra-sonic pulse velocitytests. more accuracy on estimationof the concrete compressivestrength (3].

However,the damages that this

'EVENTS'CONCRETE F'EATURE'CONCRETE EQUIPMENT'CONCRETE APPLICATIONS'

'NEWS'COVER STORY'STEEL F'EATURE'CONCRETE MATERIALS' STEEL APPLICATIONS'

The Lok-tesr and Capo-testwere developed in Denmark andhave the same rest geometry andare a reference test inEurope.

Both tests have an apex angleof 61" and measure the force withwhich a 15 mm diameter discplaced at 15mm depth is extractedfrom concrete by means of an hy­draulic jack reacting over bearingring of 55 mm interior diameter.placed on concrete surface.

The pull-out rest probes can beintroduced in fresh concrete apply­ing the lok-tcst system, which re­quires the previous test planning.The capo-test system can be alter­natively used in hardened concreteat any time, through the openingand wideness of an inside hole,where an expansive ring wirh mesame diameter at the same depthas the lok-rest system is placed

The capo-test system producessome surface damages on concreteelements and, in some circum­stances, its reparation may beneeded. The lok-rest system maybe optionally applied with or wrrh­out full extraction of the insert .The second option does nor ere­ate visible surface damages. The

1B

methods. Examples of which arethe excellent correlation curves forthe compressive concrete strengthversus the pull-out force; the facrthat the number of factors thataffect the results arc considerablyreduced compared to other nondestructive tests; the possibility ofthe correlation curves to be gen­eralised to natural aggregateclasses; the cost and the procedureof this methods, which is cheapand relatively quick to operate; andfinally,(he fact that the results arcimmediately available. Its applica­bility has been mainly recom­mended in situations where a highaccuracy of results is needed [5,6,7).

Using specifically developedcorrelations (0 the studied con­crete, the 95 percent confidenceLirnirs of in-situ compressivestrength estimation in a locationcould be anticipated in the [0 per­cent deviation interval from themean value, obtained through the4 valid readings of pull-our test[5,6). Using general correlations,such as those suggested by Lok­test and Capo-test manufacturers,that interval would probably bewidened to 20 percent [5,6}.

Figure 8 - The expansion unit is inserted In the hole and the capo­Insert is fully expanded to 25 mm diameter.

.JUL-SEPT 2002

the basic failure mechanism is con­cerned, a consensus exists regard­ing the fact that the last pull-ourload is influenced by the sameproperties that influence the con­crete compressive strength [6,7].

.Manyfactors have contributedto the dissemination and to thegeneralised use of pull-out test

Figure 9 - Coupling and the 55 mm inner diametercounterpressure.

Figure 7 - Using the diamond recess router to open anInside hole at 25 mm depth.

-EVENTS-CONCRETE FEATURE-CONCRETE EQUIPMENT'CONCRETE APPLICATIONS'

-NEWS-COVER STORY-STEEL FEATURE-CONCRETE MATERIALS-STEEL APPLICATIONS'

19 .JUL-SEPT 2002

Figure 11 - Failure type Is observed for validation of resulL

minimum distances usually required for locations are lim­iting for small elements as for penetration resistance tests.

Figure 10 - Loading the instrument by turning theloading handle.

Pull-Off TestThe pull-off tests enable the dcrerminarion of direct ten­sile strength in-situ (Figures 11 and 13).The possibility ofusing this method with partial coring enables the meas­urement of such property ar different depths. For this restmethod, recommendations arc available on British Stand­ards BS 1881: Parr 207 [5]. Figures I;and 16 show a tech­nique developed by' Germann Instruments AIS' to sup­port rhrs method and called BOND- TEST System. Thissystem Includes a portable hand operated hydraulic jack,a circular steel ruskwith 75mm diameter and 30mm thick­ness and the equipment for preparation of surfaces andpartial coring of concrete.

The possibihry of esrabhshing, for a given test equip­ment and agiven concrete. a correlation between the pull­off test and the compressive strength has shown to beuseful for estimation of the In-)I(Uconcrete compressivestrength [5,6). In spite of other practical factors that canaffect rhe results, one fact that should nor be forgorren isthar pull- off test results on the surface differ (rom thoseusing partial conng and that the depth of partial coringshould be also taken into account (5.6].

A research work carried our by the authors has shownthat the applicability of pull-out rem, using the Bond­rest system, is lirmrcd to concrete clements of compressivestrength of no more then 45 MPa (on cubes of ')0 mmside) [to). It was also found OUt that rhe usc of partialcoring causes considerable surface damages and needs aconsiderable time to operate. Ilowever, partial coring ena-bles the evaluation of concrete strength at deeper layers Figure 12 - Loading the Instrument

'EVENTS'CONCRETE FEATURE'CONCRETE EQUIPMENT' CONCRETE APPLICATIONS'

'NEWS'COVER STORY' STEEL FEATURE'CONCRETE MATERIALS' STEEL APPLICATIONS'

20.JUL-SEPT 2002

[I] ASTM C80)-90 - Standard Test Method for Penetration Resistance of Hardened Concrete,Philadelphia, American Society for Testing and Materials, 1990.

[21British Standard BS 1881:Part 203: 1986- Testing Concrete: Recommendations for Measurementof Velocity of Ultrasonic Pulses in Concrete, London, British Standard Institution.

(3) British Standard BS 1881:Part 201: 1986 - Tesnng Concrete: Guide to the Use of Non-dcscructiveMethods of Test for I Iardened Concrete. London, British Standards Institution.

[41British Standard BS 1881:Part 202: 1986-Testing Concrete: Rccommendations for Surface HardnessTesting by Rebound Hammer, London, Brirish Standards Institution.

(5) British Standard BS J881:Part 207: 1992- Testing Concrete. Recommendations for the Assessmentof Concrete Strength by Ncar-to-surface Tests. London, British Standards institution.

[61BUNGEY,J. H.i MILLARD, S. G. - Testing of Concrete in Structures. 3.' ed., London, Chapman& l lall, 1996.

[7] CARINO,). Nicholas - Pullout Test, to «Handbook on Non- destructive Testing of Concrete»,Florida (EUA). CRC Press Inc., I991, p. 39 - 82.

[8]KRENCHEL. H.; PETERSEN. C.G.-ln-situ Pullout Testingwith Lok-rest, Ten Years'Experience .• International Conference on In sirul Non-destructive Testing of Concrete», Ottawa, 2-5OC<.I984·

[9) LOPES, sergio; NEPOMUCENO, Miguel - A Comparative Study of Penetration ResistanceApparatus on Concrete, in «Proceedings of rCCE/4'). Hawaii, David Hui Edition, Jut 1997,p.6J5-616.

[LO]LOPES, Sergio, NEPOMUCENO, Miguel - Evaluation of In-place Concrete Strength byNear­to-surface Tests. «rath European Ready Mixed Concrete Congress», Lisbon, APEB.June 1998,p. 338- 347·

en] LOPES, Sergio; NEPOMUCENO, Miguel- High Strength Concrete: Penetration ResistanceTests on High Strength Concrete, in "First International Conference on High StrengthConcrete.july 13-18,1997",ASCE, USA, 1999, ISBN 0-7844-0419- 4, p. 42,-433.

[12J LOPES, Sergio; NEPOMUCENO, Miguel- Non-Destructive Tests on Normal and I ligh StrengthConcrete, in "Proceedings of 26th Conference on Our World in Concrete & Structures, August27- 28, 2001, volume XX (20Ot)~, Singapore, ISBN 981-04-25'3-9. p. 53-67'

and probably, as a consequence ofthat, the obtained correlationcurves for normal strength con­crete could show agood agreementbetween pull-off force and con­crete compressive strength.

For tests performed under

Figure13- Failuretype is observed for validation ofresult.

About the authorsMiguel Costa Santos Nepomucenois a Lecturer at the University ofBeira Interior, Portugal .He has aFirst Degree inCivil Engineeringfrom the University of Beira Inte­rior. 1994;MSc. Concrete Materi­als, University of Beira Interior,1999;Ph. D Srudenr; IIe is a Mem­ber of the Portuguese Associationof Engineers since T992. J lis areaof specialisation is in ConcreteMaterials.

Sergto Manuel RodriguesLopes is an Assistant Professor,University of Coimbra, Portugal.I Ie has a first Degree in Civil En-

laboratory conditions and using 6valid readings in each location, theBritish Standards BS1881:Pan 107[51 points our that the 95 percentconfidence limits for the estima­tion of compressive strength thevalues could vary (15 percent fromthe mean value).

gineering from the University ofCoirnbra, IC)84;MSe In StructuralEngineering, Technical Universityof Lisbon, 1988; Ph.D from theUniversity of Leeds, England, U.K.,1991.He is Senior Member of thePortuguese Association of Engi­neers, 1992, was Nominated forFerry Borges Prize as one of bestpapers in International Journals,1999. His area of specialisation isin Structural Concrete. He is aMember of FIP Commission 10Management, maintenance, andstrengthening of concrete struc­tures; Mem bel' 0 f Porruguese Mir­ror groups for the norrnalizarion ofboth European Structural Con­crete Code, Eurocodc 2, and of Eu- .ropcan Concrete Standard,ENV206; and Individual memberof AC I, Portuguese StructuralConcrete Group (PortugueseCharter of fib) and PortugueseGroup of Structural Engineering<portuguese Charter of lABSE).

'EVENTS'CONCRETE FEATURE-CONCRETE EQUIPMENT-CONCRETE APPLICATIONS'

-NEWS-COVER STORY-STEEL FEATURE'CONCRETE MATERIALS'STEEL APPLICATIONS'