Autogenous shrinkage of cement based composites is important property influencing number of their engineering application. Its ultimate value is predominantly determined by mineralogical composition of cement and its particle size distribution. Present paper introduces experimental study focused on the evaluation of various cements of grade CEM I 42.5 produced in Czech Republic in terms of shrinkage under autogenous conditions. Selected cement type is currently the most frequently used cement. Conducted study confirmed essential differences in ultimate values of shrinkage, which is partially determined by its specific surface area. Accompanying tests of mechanical properties indicate the influence of particle size distribution, which controls initial phases of cement hydration

Davidová, Vendula

Reiterman, Pavel

English

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

doi:10.14311/APP.2019.22.0022Acta Polytechnica CTU Proceedings 22:22–25, 2019 © Czech Technical University in Prague, 2019available online at http://ojs.cvut.cz/ojs/index.php/appAUTOGENOUS SHRINKAGE OF COMPOSITES BASED ONPORTLAND CEMENTVendula Davidová, Pavel Reiterman∗Czech Technical University in Prague, Faculty of Civil Engineering, Thakurova 7, 166 29 Prague, CzechRepublic∗ corresponding author: pavel.reiterman@fsv.cvut.czAbstract. Autogenous shrinkage of cement based composites is important property influencingnumber of their engineering application. Its ultimate value is predominantly determined by mineralogicalcomposition of cement and its particle size distribution. Present paper introduces experimental studyfocused on the evaluation of various cements of grade CEM I 42.5 produced in Czech Republic interms of shrinkage under autogenous conditions. Selected cement type is currently the most frequentlyused cement. Conducted study confirmed essential differences in ultimate values of shrinkage, which ispartially determined by its specific surface area. Accompanying tests of mechanical properties indicatethe influence of particle size distribution, which controls initial phases of cement hydration.Keywords: Volume changes, shrinkage, cement mineralogy, mechanical properties.1. IntroductionPortland cement based binder play an important rolein structural engineering worldwide. It is caused bythe efficiency of Portland cement and accessible rawmaterials for its production. Annual world productionof Portland cement is approximately 3.8Gt and dueto actual progress of economy worldwide is still rising.Traditional cement based concrete exhibits suitablevalues of compressive strength, however its low tensileperformance is the reason of the risk of crack occur-rence. There are many reasons of crack propagation;besides impacts of mechanical loadings, action of en-vironment, thermal contraction, the shrinkage ranksto the most frequent reason of cracks propagation[1, 2], Figure 1. The presence of cracks significantlylimits the service-life of concrete structures, becausecorrosion of steel reinforcement could reduce load ca-pacity of the concrete element. In addition, expansivestresses, accompanying the steel corrosion, acceleratedeterioration of the entire concrete. That is why, thereis intensive attempt to mitigate cracks origin [1, 3].Shrinkage of the concrete is complicated process,which consists of several aspects. However, it is suit-able to distinguish shrinkage in early-age and duringhardening. Especially, shrinkage at early-age wentinto general concern, because it presents period wherethe concrete is highly vulnerable to cracks propagation[4, 5]. Commonly used technological provision is thepartial replacement of Portland cement by supplemen-tary cementitious materials (SCM) such as fly ash,granulated blast furnace slag, calcined clay, or silicafume [6, 7]. However, kinetics of the hydration of thebinder is crucial aspect as well. It is well documentedon the application of silica fume, which could causeconsiderable shrinkage due to massive consumptionof Portlandite; it is well illustrated on Figure 2.Figure 1. The example of cracks propagation due toshrinkage.Besides factors of chemical shrinkage, there is num-ber of elements affecting the shrinkage during harden-ing. The dominant one is the drying, thus loss of watercontent. The main problem of drying shrinkage is thenon-linear distribution of originating stress, whichculminates on the surface. Possible crack openingconsequently accelerates moisture evaporation. Dry-ing shrinkage has dominant importance during initialcuring; poor discipline leads to massive rupture, welldocumented on Figure 1. Additionally, the shrink-age caused by carbonation could contribute, howeverits influence is minor in comparison with the dryingshrinkage [1].The measurement of concrete shrinkage is con-ducted by various experimental procedures. Auto-genous shrinkage of hardening concrete was success-fully determined using waved form, this arrangementallow contact less measurement [3]. Special silicatecomposites are often investigated by so called ‘ab-solute’ method, which is based on the volumetric22vol. 22/2019 Autogenous shrinkage of composites based on Portland cementFigure 2. Illustration of concrete shrinkage [1].measurement of sealed specimen immersed in a suit-able liquid. This procedure is very complicated in itsinstrumentation, however offers the determination ofentire chemical shrinkage. Free shrinkage in drains isthe most frequently used procedure in technical praxis[3, 5]. It is very simple and the test arrangement wellcorresponds with real conditions, because it allowsto control the curing condition. Close to that is themeasurement using traditional specimens with gluedmetal target for the fitting of the dilatometer. Allthese tests allow to obtain clear data, however theirdifferent arrangement needs precious interpretationof results obtained, because different aspects domi-nate in individual procedures. The drying shrinkagedominates during the measurement in bed, on theother hand samples with glued targets could be easilycured under specific conditions. The main aim of thispaper is comparison of Portland cements of similarclass cured under autogenous conditions to investigatetheir chemical shrinkage. Intentionally, cements withvarious finesses were selected for the study.2. Experimental programPerformed experimental program was focused on thedetermination of volume changes of Ordinary PortlandCement CEM I 42.5 produced by various producers.Chemical composition of the studied cements is intro-duced in Table 1. Selected cement type is currentlythe most frequently used cement type in Czech Repub-lic. Volume changes were measured using prismaticspecimens 20× 20× 100mm made from mortar. Usedmortar performed mix of standard sands and cementin weight ratio 3:1; water to cement ratio was set to0.45. The volume changes were monitored by usingdial test indicator in specified time intervals. Similarmethodology was used by Koťátková and ReitermanFigure 3. Used prismatic specimens.[8]. Used samples are shown in Figure 3. Concurrentlywas monitored weight of measured samples. Mechan-ical properties were determined in terms of BS EN196-1 [9] on prismatic specimens 40 × 40 × 160mmafter 3 and 28 days of curing. The aim of performedwork was to assess the autogenous volume changes,hence all samples were cured in water.3. Results and discussionVarious cements of class 42.5 R produced in CzechRepublic were studied in terms of shrinkage and ba-sic mechanical properties in time. Studied materialsexhibited different chemical composition and specificsurface. It was confirmed, as expected, that basicproperties of cement have essential influence on thestudied properties having a high engineering impor-tance. Results of the measurement of the shrinkageare shown in Figure 4; it is necessary to note, that allsamples were cured under wet condition to quantifythe influence of chemical shrinkage. However, applied23Vendula Davidová, Pavel Reiterman Acta Polytechnica CTU ProceedingsCaO SiO2 Al2O3 Fe2O3 MgO SO3 K2O Na2O LOI Blaine[%] [%] [%] [%] [%] [%] [%] [%] [%] [m2/kg]A 63.70 19.60 4.80 3.20 1.40 3.10 0.76 0.19 3.50 414B 63.80 20.60 4.80 3.40 1.40 3.20 0.74 0.20 1.40 311C 61.20 21.70 5.72 3.22 2.58 2.94 0.80 0.30 1.29 351Table 1. Properties of studied cements.Figure 4. Results of shrinkage measurement.Figure 5. Results of shrinkage measurement.24vol. 22/2019 Autogenous shrinkage of composites based on Portland cementcondition caused slow increase of the volume for allstudied materials. It is caused by the fixation of waterand air in capillary system of hardened mortar.The lowest volume changes exhibited cement withthe lowest value of specific surface area, it is well vis-ible on Figure 4, that this cement has also retardedinitial kinetics. The measurement of weight changeswell corresponds with the determination of volumechanges. On the other hand, cements with varioussurface area reached inverse trend in terms of volumechanges. It could be caused by the different parti-cle size distribution, which was not, unfortunately,studied in the paper. However, number of practicalexperiences accent unsuitability the surface area deter-mination for special problems such as volume changesand cement calorimetry. There are evident lacks onthe standard level in Czech Republic.Mechanical properties of studied cements are pre-sented in Figure 5. It can be concluded, that studiedcements exhibited similar mechanical performance,what can be expected for cements of similar class.However, detailed view on the results can offer in-teresting findings; evolution of mechanical propertiesof cement “C” is rapidly faster in early ages in com-parison with the others. It is well visible on theevolution of flexural strength. Paradoxical, cementdesignated “C” showed the highest volume changes,but lowest mechanical performance in terms of com-pressive strength.4. ConclusionPerformed experimental program was aimed at thecomparison of various cements of class 42.5 R pro-duced in Czech Republic, which all meet the require-ment of EN 197-1 [10]. Studied material exhibitedsimilar mechanical performance, however differencesin chemical composition and basic physical proper-ties caused significant differences in terms of volumechanges. The program showed, that standard require-ments, especially surface area, are not reliable crite-rion for prediction of volume changes. Present topicneeds following research with focus on the hydrationkinetics.AcknowledgementsThis study was supported by the research project FV30062“Possibilities of utilization of coal-ash from power stationsstored at stock piles”.References[1] L. Wu, N. Farzadnia, C. Shi, et al. Autogenousshrinkage of high performance concrete: A review.Construction and Building Materials 149:62–75, 2017.doi:10.1016/j.conbuildmat.2017.05.064.[2] S. A. Al-Saleh. Comparison of theoretical andexperimental shrinkage in concrete. Construction andBuilding Materials 72:326–332, 2014.doi:10.1016/j.conbuildmat.2014.06.050.[3] K. Kolar, J. Litos, Z. Bazantova, P. Reiterman.Comparison of two methods for determination of volumechanges of cement based composites. In P.Padevět,P. Bittnar (eds.), EAN 2015 – 53rd Conference onExperimental Stress Analysis, pp. 173–176. 2015.[4] A. Zemanova, R. Sovjak, J. Litos. Restrainedshrinkage test of high performance concrete ringspecimen. Advanced Materials Research 982:38–43,2014. doi:10.4028/www.scientific.net/AMR.982.38.[5] B. Kucharczyková, D. Kocáb, I. Rozsypalová, et al.Measurement and evaluation proposal of early ageshrinkage of cement composites using shrinkage-cone.IOP Conference Series: Materials Science andEngineering 379(012038), 2018.doi:10.1088/1757-899x/379/1/012038.[6] U. Haider, Z. Bittnar, L. Kopecky, et al. Determiningthe role of individual fly ash particles in influencing thevariation in the overall physical, morphological, andchemical properties of fly ash. Acta Polytechnica56:265, 2016. doi:10.14311/AP.2016.56.0265.[7] I. Nováková, L. Bodnárová, T. Stavař, R. Hela.Evaluation of disruption of concrete caused by exposureto high temperatures by initial surface absorption test.ARPN Journal of Engineering and Applied Sciences10:6299–6304, 2015.[8] J. Koťátková, P. Reiterman. Preliminary study ondesign of biological shielding concrete - Selection ofbinder. In Special Concrete and Composites 2016, vol.722 of Key Engineering Materials, pp. 173–177. TransTech Publications, 2017.doi:10.4028/www.scientific.net/KEM.722.173.[9] BS EN 196-1:2016 - Methods of testing cement.Determination of strength. Standard, British StandardsDocument, 2016. doi:10.3403/30291447U.[10] BS EN 197-1:2011 - Cement. Composition,specifications and conformity criteria for commoncements. Standard, British Standards Document, 2011.25

AUTOGENOUS SHRINKAGE OF COMPOSITES BASED ON PORTLAND CEMENT

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AUTOGENOUS SHRINKAGE OF COMPOSITES BASED ON PORTLAND CEMENT

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