EVALUATION OF CONCRETE HOMOGENEITY IN MASSIVE STRUCTURAL ELEMENT OF HYDROELECTRIC POWER PLANT BY MEANS OF NONDESTRUCTIVE IMPULSE RESPONSE METHOD

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1 Czech Society for Nodestructive Testig NDE for Safety / DEFEKTOSKOPIE October - November, - Seč u Chrudimi - Czech Republic EVALUATION OF CONCRETE HOMOGENEITY IN MASSIVE STRUCTURAL ELEMENT OF HYDROELECTRIC POWER PLANT BY MEANS OF NONDESTRUCTIVE IMPULSE RESPONSE METHOD Tomasz GORZELAŃCZYK, Jerzy HOŁA, Łukasz SADOWSKI, Krzysztof SCHABOWICZ Istitute of Buildig Egieerig, Wroclaw Uiversity of Techology Abstract Whe erectig cocrete structures oe may otice defects, i the form of ihomogeeities (due to improper cocrete compactio), i some areas of the structural elemets. Sice they occur o the surface such defects are easily detectable. It is, however, difficult to detect defects occurrig iside structural elemets. Nodestructive test methods ca be useful for this purpose. This paper presets tests of cocrete homogeeity iside a structural elemet costitutig a cocrete wall of the hydroelectric power plat suctio pipe, carried out usig the odestructive impulse respose method. The results of the tests showed that this method ca be successfully used to idetify cocrete zoes characterized by ihomogeeity (hoeycombig) iside massive structural elemets. Key words: cocrete, odestructive tests, impulse respose method. Itroductio Cocrete is oe of the most widely used costructio materials. All kids of structures ad structural elemets are built from cocrete. It owes its widespread use to the availability of its costituets, the relatively low costs of its productio ad the fact that it ca be used i various atmospheric coditios ad to erect structural elemets ad structures by differet methods []. I costructio practice quite ofte i some areas of cocrete structural elemets defects i the form of cocrete ihomogeeity appear. Defects of this kid particularly ofte affect massive structural elemets, which has a sigificat bearig o their durability, compressive stregth ad voids idex. There are may kids of cocrete ihomogeeity, but the most commo is the so-called hoeycombig, i.e. zoes of cocrete characterized by differet degrees of compactio, formed as a result of the improper compactio of the cocrete. As opposed to defects occurrig o the surface of structural elemets, the iteral defects are difficult to detect. They may appear oly i the course of service, whereby a repair is required to remove them. Therefore odestructive test methods are icreasigly used to evaluate the homogeeity of cocrete i buildig structures [-5]. The state-of-the-art acoustic impulserespose method is particularly suitable for this purpose. The method is described i detail i [-]. This paper presets the testig of the homogeeity of cocrete i a massive structural elemet, i.e. the cocrete wall of the suctio pipe i a hydroelectric power plat, by meas of the impulse respose method DEFEKTOSKOPIE 7 Defektoskopie rije.idd 7.., 9::5

2 . Rage of tests The impulse respose measurig apparatus was used to test a massive structural elemet costitutig the cocrete wall of a hydroelectric power plat suctio pipe. The about mm thick structural elemet was made of grade C5/ cocrete with mm maximum aggregate gradig, reiforced with smooth rebars made of A-I StS steel. Altogether tests were carried out i testig areas. I each testig area a x to x 5 grid of measurig poits was marked. The distaces betwee the poits of the grid amouted to about 5 cm. The total umber of measurig poits was about. I each of the measurig poits a elastic wave was produced i a odestructive way by meas of a special calibrated hammer with a rubber ed. The ambiet temperature, measured usig a Trotec T for quick checkig relative air humidity i the viciity of the measurig poit, was C± C while the relative humidity amouted to %±5%. At the same time the sigal was beig recorded i the graphic form, usig a geophoe, as show i fig.. The the data were trasformed to produce four maps of such characteristic parameters as average mobility, stiffess, mobility slope ad voids idex. Sice average mobility ad stiffess are the parameters used i this method exemplary tests results i the form of distributio maps of these parameters are preseted below. Fig.. Testig of massive structural elemet, i.e. cocrete wall of hydroelectric power plat suctio pipe, by meas of impulse respose apparatus. 7 DEFEKTOSKOPIE Defektoskopie rije.idd 7.., 9::5

3 . Exemplary test results ad their aalysis Below, exemplary results of the tests of the massive structural elemet costitutig the cocrete wall of the hydroelectric power plat suctio pipe are preseted for two experimetal cases. I case o. o cocrete ihomogeeity occurs. I case o. zoes of cocrete characterized by differet degrees of compactio (hoeycombig) were detected. The test results i the form of maps of average mobility ad stiffess ad histograms of the parameters, obtaied by the impulse respose method for experimetal cases ad are preseted i respectively Sectios. ad.. Case occurred i 55 of the testig areas... Experimetal case I experimetal case, mobility is costat i the whole testig area while stiffess may chage oly locally. A example here is testig area. A map ad a histogram of average mobility for this area are show i fig. while a map ad a histogram of stiffess are show i fig.. a) Colum Nr kolumy No. b),-5, 5,-,,-5, x av =7,5 m/s*n N av, m/s*n Fig.. Map of average mobility (a) ad histogram of average mobility (b) for cocrete wall of suctio pipe i testig area o.. DEFEKTOSKOPIE 7 Defektoskopie rije.idd 7.., 9::5

4 a) Colum Nr kolumy No. b),-,,-,,-,,-, x av =,9 -,,,,,,,5,,7,,9 K d Fig..Map of stiffess (a) ad histogram of stiffess (b) for cocrete wall of suctio pipe i testig area o.. As it appears from figs a ad a i most of the measurig poits average mobility is i a rage of 5- N m/s, i.e. it is withi the average, while betwee measurig poits -, -, -, -, -, -, - ad - (row o.-colum o.) stiffess rages from. to. (above the average). I the other measurig poits, stiffess is i a iterval of -., i.e. it is withi the average. As it appears from the histograms of the parameters, show i figs b ad b, the average mobility ad the average stiffess amout to respectively 7.5 m/s*n ad.9. The maps of average mobility ad stiffess ad their histograms for the suctio pipe cocrete wall i testig area idicate that o cocrete ihomogeeity occurs i this area... Experimetal case I experimetal case, differet values of the two mai parameters, i.e. average mobility ad stiffess, are obtaied. A example here is testig area o.. A map ad a histogram of average mobility are show i fig. while a map ad a histogram of stiffess are show i fig DEFEKTOSKOPIE Defektoskopie rije.idd 7.., 9::5

5 a) b) Colum Nr kolumy No.,-,,-,,-,,-,,-, 7 x av =,9 m/s*n,5,,5,,5 5, 5,5,,5 N av, m/s*n Fig.. Map of average mobility (a) ad histogram of average mobility (b) for cocrete suctio pipe wall i testig area o.. a) b) x av =, Nr kolumy 5 Colum No.,-,,-,,-,,-,,-, -,,,,,,,5,,7, K d Fig. 5. Map of stiffess (a) ad histogram of stiffess (b) for cocrete suctio pipe wall i testig area o.. As it appears from figs a ad a, betwee measurig poits -, -, -, -, -, -, - ad - (the first digit stads for the row umber ad the secod digit for the colum umber) average mobility is i a rage of - N m/s, i.e. it is above the average, while stiffess is i a rage of -.. Withi measurig poit -, average mobility rages from to N m/s (it is much below the average) while stiffess rages from to. (it is below the average). I the other measurig poits, average mobility is i a rage of - N m/s (it is below the average) while stiffess is i a rage of.-. (it is above the average). As it appears from the histograms of the parameters, show i figs b ad b, the averages of average mobility ad stiffess amout to respectively.9 m/s N ad.. The local icrease i average mobility ad the low value of stiffess idicate that the material is deformable, which may be evidece of the existece of zoes characterized by differet degrees of compactio (hoeycombig) i this area. The low values of stiffess also idicate poorer quality of the cocrete i these testig poits i compariso with the other testig poits. The preseted maps of average mobility ad stiffess ad the histograms of the parameters for the cocrete suctio pipe wall i testig area o. idicate that cocrete ihomogeeity (hoeycombig) occurs i this area. DEFEKTOSKOPIE 75 Defektoskopie rije.idd 75.., 9::5

6 . Coclusio Exemplary tests of cocrete ihomogeeity i a massive structural elemet, costitutig the wall of the suctio pipe i a hydroelectric power plat, by meas of the odestructive acoustic impulse respose method have bee preseted. The tests have demostrated that the impulse respose method ca be successfully used to evaluate the ihomogeeity of cocrete i this kid of structures with massive structural cocrete elemets. Usig this method oe ca discer zoes of cocrete differig i their degree of compactio. The odestructive tests showed that i 55 of the testig areas o cocrete ihomogeeity occurs, whereas i the other 5 areas cocrete ihomogeeities i the form of zoes characterized by differet degrees of compactio (hoeycombig) occur. Such ihomogeeities may form as a result of improper compactio of cocrete or due to the use of aggregate with gradig much exceedig the desig specificatios. Refereces. Czarecki L., Emmos P., Repair ad protectio of cocrete structures (i Polish), Polski Cemet, Kraków ().. Bugey J., Millard S., Gratham M., Testig of cocrete i structures, Taylor & Fracis, Lodo ad New York ().. Beutel R., Reihardt H., Grosse C., Glaubitt A., Krause M., Maierhofer C., Algero D., Wiggehauser H., Schickert M., Comparative performace tests ad validatio of dt methods for cocrete testig, Joural of Nodestructive Evaluatio, 7, -, pp ().. Pérez M., Gil L., Oller S., No-destructive testig evaluatio of low velocity impact damage i carbo fiber-reiforced lamiated composites, Ultrasoud, -, pp. -7 (). 5. Hoła J., Schabowicz K., State-of-the-art o-destructive methods for diagostic testig of buildig structures - aticipated developmet treds, Archives of Civil ad Mechaical Egieerig, -, pp. 5- ().. Drobiec Ł., Jasiński R., Piekarczyk A., Diagostics of reiforced cocrete structures. Vol., Methodology, field tests ad laboratory tests of cocrete ad steel (i Polish), Polskie Wydawictwo Naukowe (). 7. Davis A.: The o-destructive impulse respose test i North America: 95-, NDT&E Iteratioal,, pp. 5-9 ().. Hertlei B., Davis A.: Performace-based ad coditio-based NDT for predictig maiteace eeds of cocrete highways ad airport pavemets, Nodestructive Evaluatio of Agig Aircraft, Airports ad Aerospace Hardware, Proceedigs of SPIE 95,, Scottsdale, pp. 7- (99). 9. Ottose N., Ristimmaa M., Davis A., Theoretical iterpretatio of impulse respose tests of embedded cocrete structures, Joural of Egieerig Mechaics,, pp. -7 ().. Hoła J., Sadowski Ł., Schabowicz K., Nodestructive idetificatio of delamiatios i cocrete floor toppigs with acoustic methods, Automatio i Costructio, -7, pp (). 7 DEFEKTOSKOPIE Defektoskopie rije.idd 7.., 9::5