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I ndian St andardNON-DESTRUCTWETESTINGOFCONCRETE-METHODSOFTEST

PART 2 REBOUND HAMMER( First Reprint JUNE 1995)

tJDC 666.972 : 620*179*1

Q BI S 1992BUREAU OF INDIAN STANDARDSMqNAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002April 1992 Price Groop 3

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Cement and Concrete Sectional Committee, CED 2

FOREWORDThis Indian Standard was adopted by the Rureau of Indian Standards, after the draft finalized by theCement and Coacrete Sectional Committee bad been approved bg&+fivil Engineering DivisionCouncil.There are occasions when the various perfortiance characteristics of concrete in a structure arerequired to be assessed. In most of the cases, an estimate of strength of concrete in the structure isneeded, although parameters like overall quality, uniformity, etc, also become important in others.The various methods that can be adopted for in-si tu assessnhent of strength properties of concretedepend upon the particular aspect of strength in question. For example, if the load-carrying capacityof structural ensemble is to be assessed, carrying out a full-scale load test 8s per IS 456 : 1978 Code ofpractice for plain and reinforced concrete ( th i rd r evision ) or IS 1343: 1980 Code of practice forprestressed concrete (first revision ) is the most direct way; on the other hand when the actual com-pressive strength of a concrete in the structure is to be measured, core testing as per IS 516 : 1959&Method of test for strength of concrete is more reliable. However, both these methods are relativelycumbersome and the latter method may leave the structure damaged locally in some cases, Use is,therefore, made of suitable non-destructive tests, which not only provide an estimate of the relativestrength and overall quality of concrete in the structures, but also help in deciding whether morerigorous tests like load testing or core drilling at selected locations are required.There are various such non-destructive testing methods which can be broadly classified as those whichmeasure the overall quality of concrete, for example dynamic or vibration methods like resonancefrequency and ultrasonic pulse velocity tests; and those which involve measurement of parameters likesurface hardness, rebound, penetration, pull-out strength, etc, and are believed to be indirectly relatedto the compressive strength of concrete. In addition, radiographic, radiometric, nuclear, magneticand electrical methods are also available. Since such non-destructive tests are at best indirect methodsof monitoring the particular characteristic of concrete and the measurements are influenced bymaterials, mix and environmental factors, proper interpretation of the results calls for ce1 tain degreeof expertise. It is more so, when the data on the materials and mix proportions used in the construc-tion are not available as is often the case.In view of the limitations of the method for predicting the strength of concrete in the structure, it ispreferable that both ultrasonic pulse velocity given in Part 1 of the standard and rebound hammermethod are used in combination to alleviate the errors arising out of influence of material, mix andenvironmental parameters on the respective measurements. Relationships between pulse velocity,rebound number and compressive strength of concrete are obtained by multiple regression of themeasured values on laboratory test specimens. However, this approach has the limitation that thecorrelations are valid only for the materials and mix proportions used in the trials. The intrinsicdifference between the laboratory test specimens and in-si tu concrete, for example surface texture,moisture condition, presence of reinforcement, etc, also affect the accuracy of results. The correlationis valid only within the range of values of pulse velocity, rebound number and compressive strengthemployed and any extrapolation beyond these is open to question. The rebound hammer test is notintended as a substitute for standard compression test, but as a method for determining the uniformityof concrete in the structure and comparing one concrete with another.Because of the above limitations, the combined use of these two methods is made in another way. Inthis, if the quality of concrete is assessed to be excellent or good by pulse velocity method, only thenthe compressive strength is assessed from the rebound hammer indices, and this is taken as indicativeof strength of concrete in the entire cross-section of the concrete member. When the quality assessedis medium, the estimation of compressive strength by rebound indices is extended to the entire massonly on the basis of other colateral measurements, for example, strength of site concrete cubes, cementcontent in the concrete or core testing. When the quality of concrete is doubtful, no assessment ofconcrete strength is made from rebound indices.In most of the situations, the records ?f the original materials or mix proportions used in the strut_ /ture are not available. Therefore, cqnslderable improvisation has to be done in evolving the testingscheme and use is made of comparafive measurements made on adjoining portions of the structuresor even other structures in the vicmlty of the one in question. In doing so, an approach is taken tthe same materials and similar mix proportions and level of workmanship were employed for the t athw,

( Conti tzued on\ hi rd cover )

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I S 13311( Part 2 ) : 1992and then the compressive strength determinedas per IS 516 : 1959. The fixed load required isof the order of 7 N/mm8 when the impactenergy of the hammer is about 2.2 Nm. Theload should be increased for calibrating reboundhammers of greater impact energy and decreas-ed for calibrating rebound hammers of lesserimpact energy. The test specimens should be aslarge a mass as possible in order to minimisethe size effect on the test result of a full scalestructure. 150 mm cube specimens are preferredfor calibrating rebound hammers of lowerimpact energy ( 2.2 Nm ), whereas for reboundhammers of higher impact energy, for example30 Nm, the test cubes should not be smallerthan 300 mm.If the specimens are wet cured, they should beremoved from wet storage and kept in thelaboratory atmosphere for about 24 hoursbefore testing. To obtain a correlation betweenrebound numbers and strength of wet cured andwet tested cubes, it is necessary to establish acorrelation between the strength of wet testedcubes and the strength of dry tested cubes onwhich rebound readings are taken. A directcorrelation between rebound numbers on wetcubes and the strength of wet cubes is notrecommended. Only the vertical faces of thecube as cast should be tested. At least nine read-ings should be taken on each of the two verticalfaces accessible in the compression testingmachine when using the rebound hammers. Thepoints of impact on the specimen must not benearer an edge than 20 mm and should be notless than 20 mm from each other. The samepoints must not be impacted more than once.6 PROCEDURE6.1 For testing, smooth, clean and dry surfaceis to be selected. If loosely adhering scale ispresent, this should be rubbed of with a grind-ing wheel or stone. Rough surfaces resultingfrom incomplete compaction, loss of grout,spalled or tooled surfaces do not give reliableresults and should be avoided.6.2 The point of impact should be at least20 mm away from any edge or shape disconti-nuity.6.3 For taking a measurement, the reboundhammer should be held at right angles to thesurface of the concrete member. The test can-thus be conducted horizontally on verticalsurfaces or vertically upwards or downwards onhorizontal surfaces. If the situation demands,the rebound hammer can be held at intermediateangles also, but in each case, the reboundnumber will be different for the same concrete.

surfaces are thoroughly cleaned before takingany measurement. Around each point of observa-tion, six readings of rebound indices are taken2nd average of these readings after de!etingoutliers as per IS 8900 : 1978 becomes therebound index for the point of observation.7 INFLUENCE OF TEST CONDITIONS7.1 The rebound numbers are influenced by anumber of factors like types of cement andaggregate, surface condition and moisture con-tent, age of concrete and extent of carbonationof concrete.7.1.1 I nfl uence of Type of CementConcretes made with high alumina cement cangive strengths 100 percent higher than that withordinary Portland cement. Concretes made withsupersulphated cement can give 50 percentlower strength than that with ordinary Portlandcement.7.1.2 I nfl uence o f Type of Aggregat eDifferent types of aggregate used in concretegive different correlations between compressivestrength and rebound numbers. Normal aggre-gates such as gravels and crushed rock aggre-gates give similar correlations, but concretemade with lightweight aggregates requirespecial calibration.7.1.3 I nfl uence of Surface Condit i on and M oist ureContent of ConcreteThe rebound hammer method is suitable onlyfor close texture concrete. Open texture con-crete typical of masonry blocks, honeycombedconcrete or no-fines concrete are unsuitablefor this test. All correlaticns assume full com-pactjon, as the strength of partially compactedconcrete bears no unique relationship to therebound numbers. Trowelled and floated sur-faces are harder than moulded surfaces, andtend to overestimate the strength of concrete.A wet surface will give rise to underestimationof the strength of concrete calibrated underdry conditions. In structural concrete, this canbe about 20 percent lower than in an equivalentdry concrete.7.1.4 I nj uence of Curi ng and Age of ConcreteThe relationship between hardness and strengthvaries as a function of time. Variations ininitial rate of hardening, subsequent curingand conditions of exposure also influence theLelationship. Separate calibration curves arerequired for different curing regimes but theeffect of age can generally be ignored forconcrete between 3 days and 3 months old.

6.4 Rebound hammer test is conducted aroundall the points of observation on all accessible 7.1.5 I nfl uence of Carbonati on of Concret e Surfacefaces of the structural element. Concrete The influence of carbonation of concrete

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IS 1331.1 Part 2 ) : I992surface on the rebound number is verysignificant. Carbonated concrete gives an over-estimate of strength which in extreme cases canbe up to 50 percent. It is possible to establishcorrection factors by removing the carbonatedlayer and testing the concrete with the reboundhammer on the uncarbonated concrete.$ INTERPRETATION OF RESULTS8.1 The rebound hammer method provides aconvenient and rapid indication of the com-pressive strength of concrete by means ofestablishing a suitable correlation between therebound index and the compressive strength ofconcrete. The procedure of obtaining suchcorrelation is given in 5.2. In general, therebound number increases as the strengthincreases but it is also affected by a number ofparameters as mentioned in 7.1.

It is also pointed out that rebound indices areindicative of compressive strength of concreteto a limited depth from the surface. If the con-crete in a particular member has internal micro-cracking, flaws or heterogeneity across thecross-section, rebound hammer indices will notindicate the same.As such, the estimation of strength of concreteby rebound hammer method cannot be held tobe very accurate and probable accuracy ofprediction of concrete strength in a structureis & 25 percent. If the relationship betweenrebound index and compressive strength can bechecked by tests on core samples obtained fromthe structure or standard specimens made withthe same concrete materials and mix proportion,then the accuracy of results and confidencethereon are greatly increased.

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l!s 13311( Part 2 ) : 1992ANNEX A

Cement and Concrete Sectional Committee, CED 2ChahRun

Da H. C. VI SVB~VABAY AMembers

SEEI B. R. BHABTIKA~SHBI U. N. RATH ( Alternate )SHEI H. BFIATTACEABYADB A. K. CEATTEXJ EESEBI S. H. SUBBAXANIAX ( AlternateCHIEF E N~ NEBX ( DESIGNS )SUPEBINTENDIN~ENQINEEB

IPIpIIsrnlingIn personal capacity ( Univardy of Roorkw, Roorkee 247 667 )

B. G. Shirke & Co, PuneOrissa Cement Limited, New DelhiThe Associated Cement Companies Ltd, BombayCentral Public Works Departmeot, New Delhi

( S&S ) ( AlturMts )CEIEB ENGINEER, NAVAC+ABXDAM Sardar Sarovar Narmada Nigam Ltd, GandhioagarSIJ PERI NT~DINQ ENOIN ICEB,QCC ( Alternate )CHIEF ENQXNEEX RESEABOH-CUM-DIREOTOI~RESEARCH O&ICEB ( CONCRETE-

TECHNOLOQY ) ( Altcrnatc )DIRECYOR

I rr igation and Power Research Institute, Amritsar

JOINT DIRE CTOR ( AI tcrnatc )DIRECTOR ( CMDD ) ( N & W )DEPIXCY DIRECTOR (CMDD) (N W & S )( Alternate )SHRI K. H. GANQWALSRRI V. PATTABHI ( Altcrnatc )SHRI V. K. GIIANE KARSERI S. GOP~NAT IXSHBIR. IAMILAKABAN (Altarnate )SHBI S. Ii. GUEA TE AKUBTASHRI J . P. SANKARANARAYANAN( Alternate )DB IBSHAD MASOODDIL MD KHALID ( Alternute )J OINT DIRECTOR, STANDARDS ( B & S) ( CB-I )

J OINT DIRECTOR STANDARDS ( B & S )( CB-II ) ( Altsrnatr )SHBI N. G. JOSHISHBI P. D. KELKAB ( Alternuts )SEBI D. K. KANUNQOSHRI B. R. MEE NA ( Alfsrnate)SHBI P. KHISHNAYURTHY

SHRI S. CHAKBAVARTHY ( Altcrnate )SHRI A. K. LALSHEI T. R. BHATIA ( Alfernnfs)SHBI G. K. MAJ UMDARSHRI S. 0. RANQARI ( Alternuts 1SHBI M. K. MUK HEBJ EE

SHRI M. K . GHOSH ( Alternate )SHRI P. N. MEHTA

SHRI J . S. SAN~ANERIA ( Al&ate )MEXBER SECRETARYDII ~ECTOR ( CIVIL ) ( Alternate )SBRI NIRVAL SINQH

SHRI S. S. MI ~LANI ( Alternate )SHRI R. C. PARATE

COL R. K. SINQH ( Alterwtr)SHRI H. S. PASRICHASHRI Y. R. P~OLLSHBI S. S. SEEHBA ( Alternate )

SHRI Y. R. PHULLSHRI R. H. SHARMA ( Alternuts )DR C. RAJ KU XABDR S. C. AHLUWALIA ( Alternate )Sam G. RAMDASSERI R. C. SHABMA ( Alternate )DR M. RAXAIAHDR A. G. MADHAVA RAO ( Alternats )REPRESENTATIVESHXI A. U. RIJ H~ NGIHANISHRI C. S. SHAR~A ( Alternate )

A. P. Engineering Research Laboratories, HyderabadCentral Water Commission, New Delhi

Hyderabad I ndustries Limited, HyderabadStructural Engineering Research Ceotre ( CSIR ), GhaziabadThe India Cements Ltd, MadrasGannon Dunkerley & Company Limited, Bombay

Central Bui lding Research J ostitute ( CSI R ), RoorkeeRese;;c,oy;igos & Standards Organization ( Ministry of Railways ).

Indian Hume Pipes Co Ltd, BombayNational Test House, CalcuttaLarsen and Tourbo L imited, BombayNational Buildings Organization, New DelhiHospital Services Consultancy Corporation ( India ) Ltd, New DelhiMinistry of Transport, Department of Surface Transport ( Roadr-Wing ), New DelhiGeological Survey of India, CalcuttaCentral Board of I rrigation and Power, New DelhiDevelopment Commissioner for Cement Industry ( Ministry ofIndustry )Engineer-in-Chiefs Branch, Army HeadquartersHindustao Prefab Ltd, New DelhiCentral Road Research Institute ( CSI R ), New DelhiIndian Roads Congress, New DelhiNational Council for Cement and Bui lding Materials, New DelhiDirectorate General of Supplies and Disposals, New DelhiStructural Engineering Research Centre ( CSI R ), MadrasBui lders Association of Iodia, BombayCement Corporation of India, New Delhi

( Continued on page 5 f4

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lS 13311( Part 2 ) : 1992( Continued from fuags 4 )

MsmbsrsSARI T. N. SUBBA RANSHEI S. A. REDDI ( Alfanafr )SUPT ENQINE~~ ( D~ls~o~s )EXECUTIVEENGINEER S. M. R. DIVISION( Altarnot6SHRI S. B. SURISHRI N. CHANDEAS~K~AN ( Allrrnotr )DR H. C. VISVESVAXAYASHRI D. C. CHATTURVEDI ( Allrrnota )SHRI G. RAXANDirector ( Civil Engg )

Rcpr6srnfingGammon India Limited, Bombay

) Public Works Department, Government of TamilnaduCentral Soil and Materials Research Station, New DelhiThe Institution of Engineers ( India ), CalcuttaDirector General, BIS ( Ex-ojicio Mcmbsr )

SccrcfarySHBI N. C. BANDYOPADHYAY

J oint Director ( Civil Engg ), BIS

Concrete Subcommittee, CED 2 : 2ConzJ ancr

DB A. K. MULLJCKM6mbcrsSHEI C. R. ALIXCHANDANISHRI S. RAN~ARAJ AN (A k 6 r n a k )DE P. C. CHOWDHUBYDR C. S. VISWANATEA (&atnote )DEPUTY DIRECTOR EH )ASSISTANTDIREOTOB EH ) ( A~ fc rna fc )DIEEOTOR (C & MDD )DEPUTY DIRECTOR .=&fnata )DIRECYORJ OINT DIRECTOR A~ t s r t k I f s )SHR~ V. K. GHANEKAB

SHRI D. S. PRAKASK RAO ( & 6 fna fs )SERI B. S. GUPTA uSHRI S. K. GUHA THAKIJBTASHRI S. P. SANKKRNARAYANAN A l t 6 r n a f 6 )SHRI G. R, HARIDASSHRI N. PRABHAKAR( A~ t 6 r i i a f s )SHRI J . S. HINQORANISHRI A. P. REMEDIOS A f t smu t )SHRI LALIT KUUAR J AINJ OINT DIRECTOR STANDAEDS ( B & S )/CB-1J OINT DIRECTOR STANDARDS ( B & S )ICB-II ( A f t a r n a t r )%RI K. C. KARAMCBANDANISHRI N. K. GUPTA ( A l f6 rna fs )PROP S. KRISBNAYOORTHYSHXI K: K. NAYAR ( &fcrnntc )SERI V. M. MAD~ESHRI S. B. MALEKAIZ ( d f 6 r n a k )DE S. c. MAIJ XMANAC+IN~DIRECTOUSHBI M. KUNDD ( &6rnal6 )SHRI N. V. MERANISH~I M. K. MVKHERJ I~~SHRI N. K. SINEA I hf6fnUf6 1SHR~B.V.B.PU SERI A. D. KETK~B ( AllrrmatcSHSI Y. R. PHILSHRI S. S. SE~HBA ( ma t6 )SHEI A. S. PRASADA RANSEEI K. MINI ( Al&maf#SUPEBINTENDINO N~II~~~B ( D~IPNS )EXECUTIVEENCUN~~~B DB~I~NS )111 ( Alf6rnofr)SHBI B. T. UNWALLABRIO ( DB ) S. G. VOMBATKABP

SEIRI ?I. K. BEATTAOHAILYA &mat6 )

National Council for Cement and Building Materials, New DelhiStup Consultants Limited, BombayTorsteel Research Foundation in India, CalcuttaNational Building Organization, New DelhiCentral Water Commission, New DelhiA. P. Engiaeering Research Laboratories, HyderabadStructural Engineering Research Centre ( CSIR ), GhaziabadCentral Building Research Institute ( CSIR ), RoorkeeGanuon Dunkarley & Company Limited, BombayGammon India Limited, BombayAssociated Consulting Services, BombayIn Personal Capacity ( 36 Sneh Nagar, Wardha Road, Nagpur-15 )Research Designs and Standards Organization,( Ministry of Railways ), LucknowEngineers India Limited, New Delhi

Indian Institute of Technology, New DelhiThe Hindustan Construction Co Ltd, Bombay

National Council for Cement and Building Materials, New DelhiHindustan Prefab Limited, New DelhiPublic Works Department, BombayMinistry of Transport ( Roads Wing ), New DelhiThe Associated Cement Companies Limited, BombayCentral Road Research Institute, New DelhiStructural Engineering tiesearch Centre ( CSIR ), MadrasCentral Public Works Department, New Delhi

ID Personal Capacity ( 15/g, Rustom Baug, Victoria Road, @mby-27 ,Enginee&n.Chiefs Branch, Army Headquarters, New Delhi

5

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( Conti nued fr om second cover )situations, any significant di f ferencen the ultrasonic pulse velocity or rebound indices between themmust be due to some inherent differences in the overall quality. If the nominal grades of concrete ormix proportions are known to be different in either case, suitable allowance is made for the same ininterpretation of results.The test results on ultrasonic pulse velocity and rebound indices are analysed statistically and plottedas histograms and the lower fractiles of results are taken for assessing the quality or characteristicstrength of concrete, in line with the current limit state concepts of design.The composition of the technical committee responsible for the formulation of this standard is givenat Annex A.For the purpose of deciding whether a particular requirement of this standard is complied with, thefinal value, observed or calculated, expressing the result of a test or analysis, shall be rounded off inaccordance with IS 2 : 1960 Rules for rounding off numerical values ( revised). The number ofsignificant places retained in the rounded off value should be the same as that of the specified value inthis standard.

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Bureau of Indian StandardsBIS is a statutory institution established under the &treau of ndian Stundurds Act, 2986 to promoteharmonious development of the activities of standardization, marking and quality certification of goodsand attending to connected matters in the country.CopyrightBIS has the copyright of all its publications. No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS. This does not preclude the free use, in the course ofimplementing the standard, of necessary details, such as symbols and sizes, type or grade designations.Enquiries relating to copyright be addressed to the Director (Publications), BIS.Review of Indian StandardsAmendments are issued to standards as the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicates thatno changes are needed; if the review indicates that changes are needed, it is taken up for revision. Usersof Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of BIS Handbook and Standards Monthly Additions.This Indian Standard has been developed from Dot : No CED 2 t 3890 )

Amendments Isshed Since PublicationAmend No. Date of Issue Text Affected

BUREAU OF INDIAN STANDARDSHeadquarters:Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002 Telegrams : ManaksansthaTelephones : 3310131,331 13 75 (Common to all offices)Regional Offices : TelephoneCentral : Manak Bhavan, 9 Bahadur Shah Zafar Marg

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