Non Destructive Testing

(1)

NDT OF CONCRETE

By: Bhaskar Joshi

(2)

W

hat is

Non D

estr

uctive T

esting

???



 AcAcccorordiding ng to to ththe e AMAMERERIICACAN N StStaandndaarrds ds of of NNoonn D

Deessttruruccttiivve e TTeessttiinng g ((AASSNNTT)), , NNDDT T iis s ssaaiid d tto o bbee comprising those test methods used to examine an comprising those test methods used to examine an ob

objejectct, , mamateteririal al oor r ssysystetem m wiwiththouout t imimpapairirining g ititss future usefulness.

future usefulness.



 As per the INDIAN Standards of Non DestructiveAs per the INDIAN Standards of Non Destructive TTesestiting ng ((ISISNTNT), ), NDNDT T is is a a wwaay y of of tetesstiting ng wiwiththououtt de

dessttrrooyiyingng. . ThThis is mmeaeans ns tthahat t tthe he cocompmpononenent t cacann continue to be used and that the non destructive continue to be used and that the non destructive testing method has done no harm.

(3)

W

hy Non D

estr

uctive T

esting

??????

y

y Manner of preparation and use is poor, mainly due toManner of preparation and use is poor, mainly due to

lack of proper quality control & supervision during the lack of proper quality control & supervision during the course of construction.

course of construction.

y

y Often safety & durability of structures are given theOften safety & durability of structures are given the

go-b

go-by by permitting poor quality of y by permitting poor quality of construction.construction.

y

y At present the test used mainly as a basis of qualityAt present the test used mainly as a basis of quality

control is compression testing of cubes & it represents control is compression testing of cubes & it represents the potential strength of the concrete used.

(4)

W

hy Compress

ion testing of

cubes is

inadequate ??????????

y

y Quality Quality of concrete of concrete -- The -- The three three ´Cµ ´Cµ phenomenon.phenomenon. y

y Deliberate Deviation ?Deliberate Deviation ? y

y Not a TNot a True Representatirue Representation of on of the structure the structure due todue to

presence

presence of of Steel, Steel, VVoids, oids, Cracks.Cracks.

y

y Can only be performed during the construction Can only be performed during the construction stage.stage. y

y All All of the of the above above reasons reasons make make NDT NDT helpful helpful as as well well asas

very useful. very useful.

(5)

Objectives of Non Destructive Testing

!!!!



 TTo establish o establish homogeneity of homogeneity of concrete.concrete.



 Detection Detection of of cracks, cracks, voids voids and and other iother imperfections.mperfections.



 Monitoring changes in concrete with passage of time.Monitoring changes in concrete with passage of time.



 To establish quality of one element w.r.t. another.To establish quality of one element w.r.t. another.



 Assessment of existing Assessment of existing structure for rehabilitationstructure for rehabilitation

planning. planning.

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Types of Non Destructive Testing as per

the ISNT !!!!



 Rebound Hammer test.Rebound Hammer test.



 Ultrasonic pulse velocity test.Ultrasonic pulse velocity test.



 Electrical Resistivity test.Electrical Resistivity test.



 Half cell potential test.Half cell potential test.



 Cover meter testCover meter test



 Carbonation depth measurementCarbonation depth measurement



 Chloride determination testChloride determination test



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Rebound Hammer test !!!!!!!!!!!

(8)

About Rebound Hammer !!!!!!!!!!!!!!!



 This is basically a surface hardness test & should beThis is basically a surface hardness test & should be used only on concrete where the surface has not used only on concrete where the surface has not carbonated as the results tend to be very high & carbonated as the results tend to be very high & unrealistic on a carbonated surface.

unrealistic on a carbonated surface.



 Hence it should be used for younger concrete thanHence it should be used for younger concrete than ffoor r oollddeer r oonnee. . IIn n ccaasse e oof f oolld d ccoonnccrreette e tthhee ccaarrbboonnaatteed d llaayyeer r sshhoouulld d bbe e chchiippppeed d oofff f oorr grounded to expose the core concrete & then the grounded to expose the core concrete & then the hammer test should be conducted.

hammer test should be conducted.



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Cont««««««««««««

««..



 CONDUCT ON SMOOTH AND UNIFORM FACECONDUCT ON SMOOTH AND UNIFORM FACE



 AAVOID ROUGH SVOID ROUGH SPOTS, HONEY COMBPOTS, HONEY COMBSS



 AVOID TROAVOID TROWWELLED SURFACESELLED SURFACES



 THIN SECTIONS (< 100 THIN SECTIONS (< 100 mm) mm) SHOULD SHOULD BE BBE BAACKEDCKED UP TO A

UP TO AVOID DEFLECVOID DEFLECTIONSTIONS



 TAKE ATAKE ATLEAST 15 RTLEAST 15 REBOUND READINGS IN ANEBOUND READINGS IN ANYY ONE TEST

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Ultrasonic

(11)

About

Ultrasonic

Pulse

V

elocity

!!!!!!



 TYPES OF TESTING METHODTYPES OF TESTING METHOD



 DIRECT TRANSMISSIONDIRECT TRANSMISSION



 SEMI DIRECT TRANSMISSIONSEMI DIRECT TRANSMISSION



 SURFACE TRANSMISSURFACE TRANSMISSIONSION



 To assessing the quality & integrity of concrete byTo assessing the quality & integrity of concrete by passing ultrasound waves through the specimen / passing ultrasound waves through the specimen / RCC member under test.

RCC member under test.



 This test can also be used to determine the presenceThis test can also be used to determine the presence of

of hohoneneyycocombmbss, , vvoioidsds, , crcrackacks s etetc. c. ThThe e ininststrumrumenentt consists of

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Cont««««««««««««

««««.



 The distance between the two probes (path length)The distance between the two probes (path length) can be physically measured.

can be physically measured.



 The time of travel for the wave to pass from theThe time of travel for the wave to pass from the ttrraannssmmiitttteer r tto o tthhe e rreecceeiivveer r iis s rreeccoorrddeed d iin n tthhee ultrasonic instrument.

ultrasonic instrument.



 Hence Ultrasonic Pulse Velocity = Path length / TimeHence Ultrasonic Pulse Velocity = Path length / Time



 This veloThis velocitcity in concy in concretrete e can thcan then be relen be relateated to thed to the uniformity of concrete.

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Cont««««««««««««

«««

Q Quuaalliittyy PPuullsse e VVeelloocciitty y ( ( KKmm//sseec c ))

EExxcceelllleennt t > > 44..66

G Gooood d 44..6 6 ² ² 33..77 FFaaiir r 33..7 7 - - 33..00 P Poooor r 33..00--22..11 V Veerry y PPoooor r < < 22..11

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Electrical

(15)

About E

lectrical

R

esistivity

T

est

!!!!!!!



 TThhiis s tteesst t iis s ccaarrrriieed d oouut t tto o aasssseesss s tthhe e qquuaalliitty y // uniformity of

uniformity of concrete at various depths.concrete at various depths.



 ThThe e ininsstrtrumumenent t coconnsisissts ts of of a a ffouour r prprobobe e dedeviviccee.. Electrical current is passed through the outer probes Electrical current is passed through the outer probes &

& tthe he ppototenenttiiaal l ddrrop op is is mmeaeassurureed d bby y tthe he ininnnerer probes.

probes.



 From the current & voltage drop measurements, theFrom the current & voltage drop measurements, the resistivity of concrete can be measured.

resistivity of concrete can be measured.



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Cont«««««««««««..



 Electrical resistivity = 2(pi)aE/i (in kilo-ohm cm)Electrical resistivity = 2(pi)aE/i (in kilo-ohm cm)



 where pi = 22 / 7 = 3.14where pi = 22 / 7 = 3.14



 a = distance between pra = distance between probesobes



 E = potential difference between inner two probesE = potential difference between inner two probes in mV

in mV



 i i = = ccuurrrreennt t ppaasssseed d tthhrroouuggh h oouutteer r pprroobbees s iinn microamp

microamp



 TThhe e ppeenneettrraattiioon n oof f ccuurrrreennt t ddeeppeenndds s uuppoon n tthhee d

diissttaanncce e bbetetwweeen en tthe he pprroobbeses. . VVaarriiouous s sseetts s ooff readings are taken.

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Cont««««««««««««

«



 WWhen the RCC members to be tested are coveredhen the RCC members to be tested are covered with costly finishes like marble, granite etc. This test with costly finishes like marble, granite etc. This test can be used without having to remove such

can be used without having to remove such finishes.finishes.



 Finally, the values of the resistivity are comparedFinally, the values of the resistivity are compared against

against

C

C_o_or_rr_ro_os_si_io_on_n_R_Ra_at_te_e _R_Re_es_si_is_st_ti_iv_vi_it_ty_y

LLoow w > > 220 0 KKiillo o oohhm m ccmm LLoow w tto o mmooddeerraatte e 110 0 ² ² 220 0 KKiillo o oohhm m ccmm H

Hiiggh h 5 5 ² ² 110 0 KKiillo o oohhm m ccmm V

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Half

(19)

About Half

Cell

P

otential T

est !!!!

!!!!!!



 A Half cell is a piece of metal in a solution of itsA Half cell is a piece of metal in a solution of its o

owwn n iioonns s ( ( ccooppppeer r iin n ccooppppeer r ssuullpphhaattee)).. WWhenhen

connected to another half cell ( Silver ), a voltage is connected to another half cell ( Silver ), a voltage is set up.

set up.



 ThThiis s tteesst t ccaan n ggiivve e tthe he pprrobobaabbiililitty y oof f ccororrrososiionon a

accttiivviitty y ttaakkiinng g ppllaacce e aat t tthhe e ppooiinnt t wwhheerre e tthhee measurement of potentials

measurement of potentials are taken.are taken.



 An electrical contact is established with the exposedAn electrical contact is established with the exposed steel & the half-cell is moved across the surface of steel & the half-cell is moved across the surface of concrete for measuring the potentials.

concrete for measuring the potentials.



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Cont««««««««««««

«««««.

C

C_opper/_opper/CC_o_op_pp_pe_er_r_su_s_ul_lp_ph_hat_at_e_e _S_Si_il_lv_ve_er_r_{/ S}_{/ Si}_il_lv_ve_{er c}_{r ch}_hl_lo_or_ri_id_de_e CC_orrosion_orrosion CC_ondition_ondition >

> --22000 0 mmV V > > --11006 6 mmV V LLoow w ( ( 1100% % cchhaannccees s ))

--22000 0 tto o --33550 0 mmV V --11006 6 tto o --22556 6 mmV V IInntteerrmmeeddiiaattee

<

< --33550 0 mmV V < < --22556 6 mmV V HHiiggh h ( ( <<990 0 % % ))

<

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Cover Meter

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About Cover Meter !!!!!!!!!!!!!!!!!!!!!!



 This test is useful for the determination of concreteThis test is useful for the determination of concrete cover, location of embedded rebars & estimation of cover, location of embedded rebars & estimation of size of

size of embedded rebarsembedded rebars..



 The instrument is based on the magnetic technique &The instrument is based on the magnetic technique & is calibrated for different purposes.

is calibrated for different purposes.



 The cover thickness is important from the point ofThe cover thickness is important from the point of view of estimation of initiation of corrosion.

view of estimation of initiation of corrosion.



 The location & estimation of bar diameter becomesThe location & estimation of bar diameter becomes useful in structures where there are no structural useful in structures where there are no structural drawings available.

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Carbonation Depth Measurement !!!



 As As coconcncrerete te is is eexpxpososed ed to to aiairr, , ssomome e frfree ee wwataterer content is lost and this pore water in replaced by content is lost and this pore water in replaced by air.

air.



 AiAir r cocontntaiainining ng CaCarrbobon n didiooxixide de anand d ototheher r acacididicic g

gaassees s ccaan n rreeaacct t wwiitth h aallkkaalliinne e ccoonnssttiittuueenntts s ooff concrete

concrete, called Carbonation, called Carbonation..



 HenHencece, , prprototectectioion n prproviovided ded bby y coconcncrerete te agagaiainsnstt corrosion is lost due to carbonation as moisture and corrosion is lost due to carbonation as moisture and oxygen can act relatively easily.

oxygen can act relatively easily.



 TThhuus s wwaatteer r ² ² cceemmeennt t rraattiio o sshhoouulld d nneevveer r bbee excessive.

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Cont««««««««««««

««..



 Primary Primary factor factor controlling controlling the the rate rate of carbonation of carbonation isis the EXPOSURE CONDITIONS:

the EXPOSURE CONDITIONS:



 Concrete saturated with water is effectively freeConcrete saturated with water is effectively free from carbonation.

from carbonation.



 CCoonnccrreette e eexxppoosseed d tto o aalltteernrnaatte e ddrry y aannd d wweett atmosphere sho

atmosphere shows greatest depths of ws greatest depths of carbonation.carbonation.



 CoConncrcretete e eexpxpososed ed to to momoisist t aiair r peperrioioddicicaalllly y bbyy p

prreecciippiittaattiioon n sshhoowws s iinntteermrmeeddiiaatte e ddeepptthhs s ooff carbonation.

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Cont««««««««««««

««««



 METHOD OF ASSESSMENTMETHOD OF ASSESSMENT

DRILL INTO CONCRETE DRILL INTO CONCRETE

SPRAY PHENOLPHTHALEIN SOLUTION SPRAY PHENOLPHTHALEIN SOLUTION UNCA

UNCARBONARBONATED TED CONCONCRETCRETEE WWIILLL L SSHHOOWW BRIGTHBRIGTH

PINK STAIN PINK STAIN CA

CARBRBONONAATETED D COCONCNCRERETETE WWIILLL L NNOOT T CCHHAANNGGEE

COLOUR COLOUR

W

WITH ITH THTHE E ABABOOVE VE VIVISUSUAL AL ININDIDICACATITION ON DEDEPTPTH H OFOF

CARBONATION CAN BE EASILY MEASURED CARBONATION CAN BE EASILY MEASURED

(26)

Chloride D

eter

mination T

est !!!!!!!!!



 Apart from (or after) the carbonation of concrete,Apart from (or after) the carbonation of concrete, th

the e nanatuturral pral prototececttioion n tto o sstteeeel l is lois losst t & & ththus thus thee chlorine present in the atmosphere is free to attack chlorine present in the atmosphere is free to attack the embedded steel.

the embedded steel.



 Above a threshold value of chlorine ions along withAbove a threshold value of chlorine ions along with d

deeggrreee e oof f aallkkaalliinniitty y oof f ccoonnccrreettee, , tthhe e rraatte e ooff corrosion increases.

corrosion increases.



 Hence it becomes important to estimate the chlorineHence it becomes important to estimate the chlorine ion content to comment on the corrosion of steel.

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Cont««««««««««««

«««..



 There are two sources of chlorides:There are two sources of chlorides:



 1) either they enter the mix before casting ² cast in1) either they enter the mix before casting ² cast in chlorides. Sources can be water or inadequately chlorides. Sources can be water or inadequately washed marine aggregates.

washed marine aggregates.



 22) ) or or aafftter er tthe he ccononccrretete e haharrddeenned ed ² ² iingngrreesssseded chl

chlororiiddeses. . SSooururcces es aarre e tthe he mamarriinne e oor r iinnddususttrriiaall environment.

environment.



 ThThe e ccaasst t in in chchllororiiddees s ggenenereraalllly y aarre e chechemimiccaallllyy bound and it·s the ingressed chlorides which cause bound and it·s the ingressed chlorides which cause damage.

(28)

Cont««««««««««««

««««



 The concrete dust is to be collected by drilling andThe concrete dust is to be collected by drilling and is taken for testing. Generally the first 5 mm depth is taken for testing. Generally the first 5 mm depth is neglected.

is neglected.



 Depth increments of close to 25 mm are usuallyDepth increments of close to 25 mm are usually taken for collection of dust. Usually a minimum of taken for collection of dust. Usually a minimum of 25 gm should be taken.

25 gm should be taken.



 For accurate chloride determination, samples mustFor accurate chloride determination, samples must be prepared for chemical analysis and analysed, be prepared for chemical analysis and analysed, us

usining g eieithther er VVololhahardrd's 's memeththod od or or popotetentntioiommetetriricc titration.

(29)

Core T

est !!!!

!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!



 This is a partially destructive test that is used to co-This is a partially destructive test that is used to co-relate the various other properties of the concrete relate the various other properties of the concrete viz. UPV, electrical resistivity, rebound number etc. viz. UPV, electrical resistivity, rebound number etc.



 It is customary to take cores of 4 inch diameter forIt is customary to take cores of 4 inch diameter for compressive

compressive strength determinstrength determination.ation.



 Concrete core drilling for strength determination isConcrete core drilling for strength determination is again dependent upon various

again dependent upon various



 fafactctorors s ffor or rerelialiabibililityty. . The The coconvnverersision on of of coconcrncretetee core (typically 3 or 4 inch diameter

core (typically 3 or 4 inch diameter



 ccoorree) ) ssttrreennggtth h iinntto o ´´11550 0 mmm m ssaattuurraatteed d ccuubbeeµµ strength depends upon :

(30)

Cont««««««««««««

«««..



 1. effect of coring1. effect of coring



 2. shape factor2. shape factor



 3. size effect3. size effect



 4. direction of coring w4. direction of coring w.r.r.t. placing of .t. placing of concreteconcrete



 5. h/d ratio5. h/d ratio



 WWith so many factors contributing to the final ´150ith so many factors contributing to the final ´150 mm saturated cubeµ strength, the strength variation mm saturated cubeµ strength, the strength variation may be + / - 10% - 15%. However, it can be used may be + / - 10% - 15%. However, it can be used to confirm the results of UPV differing largely in the to confirm the results of UPV differing largely in the values & also for co-relation. Hence the UPV & core values & also for co-relation. Hence the UPV & core re

(31)

co-Limitations of

Limitations of

NDT !!!!!!!!!!!!!!!!

!!!!!!!!!



 COCORERELALATIOTION N BETBETWWEEN EEN MEMEASASURURED ED PPARARAMAMETETERER AND CONCRETE

AND CONCRETE STRENGTH IS STRENGTH IS NEVER ENEVER EXAXACTCT..



 EEFFFFEECCTTIIVVEENNEESSS S OOF F NNDDT T RREEDDUUCCEESS WWITHITH HETEROGENEITY OF THE

HETEROGENEITY OF THE MAMATERIALTERIAL



 RREESSUULLTTS S AARRE E DDEEPPEENNDDEENNT T OON N TTOOO O MMAANNYY PARAMETERS

PARAMETERS



 NORMALLY ACHIEVEABLE LEVEL OF ACCURACY ISNORMALLY ACHIEVEABLE LEVEL OF ACCURACY IS + 25%

+ 25%



 INTERPRETATION OF RESULTS REQUIRE INTUITIVEINTERPRETATION OF RESULTS REQUIRE INTUITIVE JUDGEMENT