Ultrasonic measurements used to monitor the hydration of cement based materials are becoming an important tool in the quality assurance in production. Also, using these methods can be cost benefit for the construction companies because they can provide information about evolution of material properties in real time. In this paper ultrasonic testing is used to characterize a hydration process of cement paste. A technique is based on the system for measuring the ultrasonic pulse velocity (UPV). To obtain more information about wave propagation characteristics the technique of acoustic emission (AE) is also used. Entire waveform of the signal is recorded. AE parameters are extracted from the signal and used to characterize different processes in cement paste during hydration. An analysis is performed on cement pastes made with different water-cement ratios. Ultrasonic wave parameters are compared to the initial and final setting time using the Vicat needle test and compressive strength development.Korištenje ultrazvučnih mjerenja za praćenje hidratacije materijala na bazi cementa postaje važan alat osiguranja kvalitete u proizvodnji. Također, korištenje tih metoda može biti ekonomski isplativo za izvođačke tvrtke jer omogućavaju trenutno dobivanje informacija o razvoju svojstava materijala. U ovom radu ispitivanje ultrazvukom je primijenjeno za karakterizaciju procesa hidratacije cementne paste. Metoda mjerenja temeljena je na sustavu za mjerenje brzine ultrazvučnog impulsa (UPV). Kako bi se dobilo više informacija o svojstvima širenja valova korištena je i metoda akustične emisije (AE). Cijeli valni zapis je sniman te su iz signala izračunati parametri akustične emisije koji su korišteni za karakterizaciju različitih procesa u cementnoj pasti tijekom hidratacije. Analiza je provedena na cementnim pastama izrađenim s različitim vodo-cementnim omjerima. Parametri ultrazvučnih valova uspoređeni su s početkom i krajem vezanja dobivenim Vicatovom iglom i razvojem tlačne čvrstoće

Dunja Mikulić

Ivan Gabrijel

Nenad Bijelić

Hrčak - Portal of scientific journals of Croatia

1IntroductionUvodConcrete setting and hardening processes are the mostcritical phases during construction works, influencingproperties of a concrete structure. The transformation fromliquid to solid state is characterised with two points inhydration time: initial and final setting. The initial set isimportant because it provides an estimate when concretehas reached the point of stiffening to such an extent that itcan no longer form a monolithic element with concretepoured on top of it. The point at which final set occurs isimportant since it provides an estimate when thedevelopment of concrete strength and stiffness starts.Hardening process of concrete makes it possible for aconcrete element to carry loads. Knowing the strength of theconcrete during hardening is the tool to determine themoment of formwork removal, moment of prestressing orcalculation of the load bearing capacity.Non-destructive testing methods able to follow thesetting and hardening processes of concrete are beingdeveloped. The mostly used method is the maturity methodbased on the temperature measurements. To improveunderstanding of the hydration process and setting timesnew methods are investigated. One group of methodsconsists of ultrasonic measuring techniques. Differenttechniques have been presented by many authors. Differenttypes of ultrasonic waves are used, for example shear waves[1, 2] or longitudinal waves [3, 4, 5, 6]. Using these methodsa finer representation of the hydration process is obtained,but there are still problems left unsolved.493I. Gabrijel, D. Mikulić, N. BijelićISSN 1330-3651UDC/UDK 666.942.017:620.179.16ULTRASONIC CHARACTERIZATION OF CEMENT COMPOSITES DURING HYDRATIONIvan Gabrijel, Dunja Mikulić, Nenad BijelićUltrasonic measurements used to monitor the hydration of cement based materials are becoming an important tool in the quality assurance in production.Also,using these methods can be cost benefit for the construction companies because they can provide information about evolution of material properties in real time.In this paper ultrasonic testing is used to characterize a hydration process of cement paste.Atechnique is based on the system for measuring the ultrasonic pulsevelocity (UPV). To obtain more information about wave propagation characteristics the technique of acoustic emission (AE) is also used. Entire waveform ofthe signal is recorded.AE parameters are extracted from the signal and used to characterize different processes in cement paste during hydration.An analysis isperformed on cement pastes made with different water-cement ratios. Ultrasonic wave parameters are compared to the initial and final setting time using theVicat needle test and compressive strength development.Keywords: cement composites, hydration, ultrasonic testingPreliminary notesKorištenje ultrazvučnih mjerenja za praćenje hidratacije materijala na bazi cementa postaje važan alat osiguranja kvalitete u proizvodnji. Također, korištenje tihmetoda može biti ekonomski isplativo za izvođačke tvrtke jer omogućavaju trenutno dobivanje informacija o razvoju svojstava materijala. U ovom raduvu za mjerenje brzineultrazvučnog impulsa (UPV) ova korištena je i metoda akustične emisije (AE). Cijeli valni zapis jesniman te su iz signala izračunati parametri akustične emisije šteni za karakterizaciju različitih procesa tijekom hidratacije.Analiza je provedena na cementnim pastama izrađenim s različit metri ultrazvučnih valova uspoređeni su s početkom ikrajem vezanja dobivenim Vicatovom iglom i razvojem tlačne čvrstoće.ispitivanje ultrazvukom je primijenjeno za karakterizaciju procesa hidratacije cementne paste. Metoda mjerenja temeljena je na susta. Kako bi se dobilo više informacija o svojstvima širenja valkoji su kori u cementnoj pastiim vodo-cementnim omjerima. ParaKljučne riječi: cementni kompoziti, hidratacija, ispitivanje ultrazvukomPrethodno priopćenjeUltrazvučna karakterizacija cementnih kompozita tijekom hidratacijeUltrazvučna karakterizacija cementnih kompozita tijekom hidratacijeTechnical Gazette 17, (2010),4 493-4972Experimental works2.1Materials and mixing of methodsEksperimentalni radIn order to characterize different stages of hydration incement paste and physical changes that follow, anexperimental work is performed under laboratoryconditions to identify the setting and hardening of cementpaste using ultrasonic waves during early ages. Changes inthe ultrasonic wave parameters passing through the freshcement paste and setting time determined using the Vicattest method are analyzed. Also, the compressive strengthdevelopment of cement pastes in the first 7 days is tested.Cement used in the analysis is CEM I 42,5R. Propertiesof cement are shown in Tab. 1. A cement paste is preparedwith a water to cement (w/c) ratios 0.4, 0.5 and 0.6 byweight. The paste is mixed according to a procedure givenby the standard HRN EN 196-3. Initial and final settingtimes of the cement paste are determined using the Vicatneedle method according to the same standard. Initialsetting is the age of the cement paste when the needlepenetrating into paste stops in the range 6 ± 3 mm from thebottom of the mould. Final setting is the age at which needlepenetrates less than 0,5 mm into the cement paste. Changesin the penetration depth during the testing of setting timesare shown on Fig. 1. Time "0" on Fig. 1 is the time of mixingof cement and water.Materijali i metoda miješanja494Ultrasonic characterization of cement composites during hydrationTehni ki vjesnikč ,17, 4(2010)  493-497I. Gabrijel, D. Mikulić, N. BijelićThe compressive strength of pure cement paste is testedon the samples with dimensions 40×40×160 mm. Samplesare cured at the ambient temperature of 20 ± 1 °C andcovered with a plastic sheet to prevent evaporation. Whensamples had strengthen enough they were removed from themoulds and stored into climatic chamber where they wereair cured at the 20 ± 1 °C and relative humidity > 95 %. Thecompressive strength is tested at different time intervals (inthe first 24 hours, 24, 48, 72 and 168 hours) after mixing. Ateach time interval 3 samples were broken and the result is anaverage value of the compressive strength. Results of thecompressive strength tests are shown on Fig. 2.2.2Ultrasonic setupUltrazvučni sustavThe measuring system consists of the PortableUltrasonic Non-Destructive Digital Indicating Tester orshorter Pundit produced by C.N.S. Electronics. It generateslow frequency (54 kHz) ultrasonic pulses and measures thetime taken for them to pass from one transducer to the otherthrough the material interposed between them. Amodification of the original system was made in order to beable to record information about the time of flightcontinuously to a PC. Software was also developed forrecording data in ASCII format and controlling thefrequency of data recording. A wave signal from thereceiving transducer is also collected by an acquisition unitfor the acoustic emission (AE) measurement. Theacquisition system used is the Physical AcousticsCorporation acoustic emission 8-channel system PCI-8controlled through the AEwin software. From the recordedultrasonic waves different wave parameter, typically used inthe acoustic emission measurements, are then extracted. Aconfiguration of the ultrasonic setup is shown in Fig. 3.Transducers are set in through transmission so that speed ofthe ultrasonic wave can be calculated by knowing thedistance between the transducers and the time take for thepulse to travel between them. Distance between thetransducers i.e., length of the specimen is 7 cm. Mould usedfor testing is made of extruded polystyrene. That way thepulse is transmitted directly through the specimen and notthrough the sides of the mould.Table 1Tablica 1.Properties of the cement CEM I 42,5 RSvojstva cementa CEM I 42,5 RMineral composition, %Density,kg/m3Finenesspassing45 μm,%Blaine,m2/kg C3S C2S C3A C4AF3120 92,2 353 59,86 11,49 8,36 8,82Figure 1Slika 1.Changes in the penetration depth of standardizedneedle into the cement pastePromjene dubine penetracije standardiziraneigle u cementnu pastuFigure 2Slika 2.Compressive strength development of pure cement pastesRazvoj tlačne čvrstoće čiste cementne pasteFigure 3Slika 3.Scheme of the ultrasonic setup used during testingShema ultrazvučnog sustava korištenog tijekom ispitivanja3Analysis of ultrasonic wave characteristicsAnaliza karakteristika ultrazvučnih valovaDuring the analysis it was observed that there aredifferent wave parameters that are sensitive to the changesin the structure of cement paste. It is noticed that someparameters change rapidly during the transformation ofpaste from a liquid to hardened state and after thetransformation rate of changes drops significantly. Someother parameters show a different trend which is closer tothe trend of hardening, i.e. strength development. For thisreason ultrasonic wave parameters were divided into twocategories, the first representing the period of setting and thesecond representing hardening of the cement paste.495Technical Gazette ,17, 4(2010)  493-4973.1Setting of cement pasteVezanje cementne pasteResults obtained from the ultrasonic measurementsshowed three parameters that change significantly duringtransformation of cement paste from the liquid to solid state.Those parameters are:- Amplitude - defined as the maximum (positive ornegative) of the signal in one wave.- Duration - defined as the time from the first threshold(detection of the signal) crossing to the end of the lastthreshold crossing of the signal in one wave.- Risetime - defined as the time between the firstthreshold crossing and the peak amplitude of the signalin one wave.These parameters are shown in Fig. 4.I. Gabrijel, D. Mikulić, N. Bijelić Ultrazvučna karakterizacija cementnih kompozita tijekom hidratacijethat particles become interconnected at a higher degree ofhydration [7].From Fig. 6 it can be noticed that a parameter Durationgoes through a several maxima and minima. This could beattributed to the problematic contact between the transducerand a specimen but all mixtures seem to have similarinfluence on these variations. The first maximum at thegraphs appears at the age of the cement paste close to thefinal setting time.The Fig. 7 shows that the parameter Risetime hasrelatively low values for all cement pastes at the beginningof the ultrasonic signal appearance. Then a sudden increaseof the Risetime appears and after that values are returned tothose close to the values at the beginning. End of describedinitial changes appears at the age of the cement paste closeto the final setting time.3.2Hardening of cement pasteOčvršćivanje cementne pasteFrom the analysis of the ultrasonic signal twoparameters were found to show a different trend of changesduring the hydration of the cement paste which seemed to berelated to the changes other than the transformation fromliquid to solid state. Those parameters are:- Speed of the ultrasonic wave or ultrasonic pulsevelocity (UPV) which is calculated as the length of thespecimen divided by the time of flight andFigure 4Slika 4.AE parameters extracted from the waveformisa valaAE parametri izračunati iz zapFigure 5Slika 5.Changes in the amplitude during setting and hardeningPromijene amplitude tijekom vezanja i očvršćivanjaChanges in the Amplitude, Duration and Risetime areshown on Fig.-s 5, 6 and 7 respectively. On the figures initialand final setting times are also indicated. All ultrasonicwave parameters start to change before any change in theVicat penetration test can be observed. W/c ratio has aninfluence on all three AE parameters. Higher the w/c ratiothe changes of parameter start later. Linear correlation isfound between the start of the increase of Amplitude,Duration and Risetime and w/c ratio of the mixes.This can be explained by a larger distances between thecement particles in the mixture with a higher w/c ratio soFigure 6Slika 6.Changes of the parameter Duration during settingand hardeningPromjene parametra Duration tijekom vezanja i očvršćivanjaFigure 7Slika 7.Changes in the parameter Risetime during setting and hardeningPromjene parametra Risetime tijekom vezanja i očvršćivanja496 Tehni ki vjesnikč ,17, 4(2010)  493-497Correlation between the compressive strength and UPVis shown on Fig. 10.Although, some authors have found thatfor mortar and concrete the correlation betweencompressive strength and UPV is independent on the w/cratio [11], from the figure it can be seen that this correlationfor is dependant on w/c ration of the cement paste so ageneral model would have to take this into account. Thesedifferences can be attributed to the influence of theaggregate and interfacial transition zone in mortar andconcrete on the compressive strength and stiffness of thecement composite [12].4ConclusionZaključakBased on the obtained results it can be concluded thatdifferent ultrasonic wave parameters can be used to followthe setting and hardening of the cement paste and that notjust a speed of the ultrasonic wave can be used for thatpurpose. Different parameters which are often used in theacoustic emission technique can help us to improvepossibilities of the ultrasonic testing in this field.It is indicated that change of cement paste from liquid tosolid state could be monitored through changes in theparameters Duration and Risetime. Process of hardening isfollowed by changes in the velocity and changes in theattenuation of the ultrasonic signal through the parameterSignal strength. It was found that:- the increase of the w/c ratio reduces compressivestrength of the cement paste. This slows down wavevelocity development and the velocity has lower values.- the increase of the w/c ratio also slows down relativeSignal strength development and the values of the relativeSignal strength are lower.While changes in the wave velocity can be explainedthrough the changes of the stiffness of cement paste it is lessclear which processes govern increase of the relative Signalstrength. In order to gain more insight into the theme furtherwork will follow.AknowledgementsZahvaleThis research was performed within the scientific project "FromNano- to Macro-Structure of Concrete", 082-0822161-2990,funded by the Croatian Ministry of Education, Science and Sport.- Signal strength which is mathematically defined as theintegral of the rectified voltage signal over the Durationof the waveform.Changes in these parameters are shown on Fig.-s 8 and9. On Fig. 8 changes in the UPV are shown. Speed of theultrasound is greater in the cement paste with lower w/cratio. The first inflection point at the graphs is around thefinal setting time and appears at the speed close to 1300 m/s.This is also the point after which influence of the w/c ratioon the UPV becomes evident. On the Fig. 9 changes in therelative Signal strength are shown. Relative values of Signalstrength are used because absolute values are highlydependant on the quality of a contact between thetransducers and the specimen considering transmission ofultrasonic wave energy [8, 9]. Higher values of the relativeSignal strength are obtained for mixtures with lower w/cratio. Changes of this parameter exhibit much lagerscattering than the changes of the UPV. One reason for thiscould be related with the shrinkage of the cement pastewhich influences the amount of ultrasonic wave energytransferred into the specimen. Another reason could be thatthe UPV is primarily influenced by the stiffness of thecement paste (Elasticity modulus) while the changes in therelative Signal strength are a measure of attenuation of thesignal which is according to Vary more closely related to themicrostructure, morphology, porosity, microcracks of thematerial [10]. Therefore it is possible that the changes in therelative Signal strength are indeed governed by differentprocesses than the speed of the ultrasound. Probably bothinfluences take a part in forming its shape.Ultrasonic characterization of cement composites during hydration I. Gabrijel, D. Mikulić, N. BijelićFigure 8Slika 8.Changes of the ultrasonic wave velocityPromjene brzine ultrazvučnog valaFigure 9Slika 9.Changes in the relative Signal strength of the ultrasonic signalPromjene parametra relative Signal strength ultrazvučnog signalaFigure 10Slika 10.Correlation between compressive strength of cement pasteand UPVKorelacija tlačne čvrstoće cementne paste i UPV497Technical Gazette ,17, 4(2010)  493-4975ReferencesLiteratura[1] cementations materials by pulseecho USWR: Method, apparatus and application examples. //Cement and Concrete Research. 30, 10(2000), str. 1633-1640.[2] Voigt, T.; Shah, S. P. Properties of early age Portland cementmortar monitored with shear wave reflection method. // ACIMaterials Journal. 101, 6(2004), str.473-482.[3] Reinhardt, H. W.; Grosse, C. U. Continuous monitoring ofsetting and hardening of mortar and concrete // Constructionand building materials, 18 (2004), str. 145-154.[4] Krauss, M.; Hariri, K. Determination of initial degree ofhydration for improvement of early-age properties ofconcrete using ultrasonic wave propagation. // Cement andConcrete Composites. 28, 4(2006), str. 299–306.[5] ; ; Štirmer, N.;Application of ultrasonic methods for early age concretecharacterisation. // International Journal of MicrostructureAnd Materials Properties. 1, 3/4(2006), str. 297-309.[6] Gabrijel, I.; ; Application ofUltrasonic Measurements for Determination of Setting andHardening in Cement Paste. // Construction in the 21stCentury CITC-V / edited by Birgonul, M.T. et al. Istanbul :Florida International University, Miami, Florida, U.S.A. andMiddle East Technical University, Ankara, Turkey, 2009. str.1420-1426.[7] Van Breugel, K. Simulation of Hydration and Formation ofStructure in Hardening Cement-Based Materials. DelftUniv.Press, Delft, 1991.[8] . .; Gabrijel, I. Testing ofCompressive and Bending Strength of Concrete andMonitoring Acoustic Emission Parameters. // 7thInternational Symposium on Non-destructive Testing in CivilEngineering / Abraham, O and Derobert, X. (ur.). Nantes :Laboratoire Central des Ponts et Chaussées, 2009. str. 903-908Valič, M. I. Hydration ofMikulić, D. Sekulić, D. Bjegović, D.Mikulić, D. Milovanović, B.Mikulić, D ; Milovanović, B.[9] Philippidis, T. P.; Aggelis, D. G. An Acousto-UltrasonicApproach for the Determination of Water-to-Cement Ratio inConcrete, Cement and Concrete Research, 33 4(2003), 525-538.[10] Vary,A. The acousto-ultrasonic approach. // Duke J. C. (Ed.) /Acousto-Ultrasonics: Theory and Application. Plenum Press,NewYork, 1988., str 1-21[11] Voigt, T. The Application of an Ultrasonic Shear WaveReflection Method for Non-destructive Testing of Cement-based Materials at Early Ages: An Experimental andNumericalAnalysis, PhD thesis, University of Leipzig, 2004.[12] Mehta, P. K.; Monteiro, P. J. M. Concrete - microstructure,properties and materials, third edition, The McGraw-HillCompanies Inc., NewYork, 2006.,. .I. Gabrijel, D. Mikulić, N. Bijelić Ultrazvučna karakterizacija cementnih kompozita tijekom hidratacijeAuthors' addressesAdrese autoraIvan Gabrijel,Prof. dr. sc. dipl. ing. fizikedipl. ing. građ.Dunja Mikulić,Nenad Bijelić, dipl. ing. građ.Sveučilište u ZagrebuGrađevinski fakultetKačićSveučilište u ZagrebuGrađevinski fakultetKačićeva 26Sveučilište u ZagrebuGrađevinski fakultetKačićeva 26Zavod za materijaleeva 2610000 Zagreb, CroatiaZavod za materijale10000 Zagreb, Croatia10000 Zagreb, Croatia

Ultrazvučna karakterizacija cementnih kompozita tijekom hidratacije

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