Properties Research Of Early-age Shringkage And Crack Of The Cementitious Materials

Many building materials, cementitious materials are used widely in civilengineering, the amount of the cementitious materials is largest, which leads to theconsumption of resource and energy. Problems of concrete early-age shrinkage andcrack of concrete are hot issues, which are more concerned at home and abroad, themechanism of early-age shrinkage can be better explained by the self-desiccationphenomenon of the concrete. The internal relative humidity of concrete reduces leadto early-age shrinkage of the concrete. Therefore, it has an important significance forthe shrinkage deformation to study internal relative humidity of concrete. With thedevelopment of modern concrete technology, concrete structure cracking is veryprominent at early ages, and the main reason of early-age cracking of concrete iscaused by the restricted shrinkage.The influence of different supplementary cementitious materials (SCM) and thewater to binder ratio of cement pastes on the cementitious materials shrinkage underthe different curing conditions was studied in this paper. The results showed that:water to binder ratio was a major factor in the shrinkage of cement paste, withdecreasing the water to binder ratio, the shrinkage increases. Different types anddosages of mineral admixtures affected the shrinkage differently, and the effect ofdifferent SCMs on autogenous shrinkage (AS) was the most obvious with the filmcuring condition.The internal relative humidity (IRH) of the cementitious materials was measuredby TES1360A digital Humidity/Temperature Meter with precision capacitive sensorsunder different curing conditions. It was clarified that there was a clear correlationbetween the shrinkage and the internal relative humidity of the cementitious materialsunder different curing conditions, and the linear relationship between the shrinkageand the internal relative humidity of cement pastes with SCM was established byusing the regression theory.By experimental studying of the autogenous shrinkage test and the axial tensilestrength of different cement pastes, using JC4-10reading microscope to record thesteel restricted cracking of the composite cement paste, the variation of theautogenous shrinkage of the composite cement pastes was studied. Equations wereestablished to describe the relationship among AS, tensile strength and crack area of the cement paste with SCM.The steel strain of the different cement pastes was tested by using DH3815Nstatic strain gauge, and the trend of the shrinkage stress of the cement pastes wasanalyzed. The influence of different SCMs and water to binder on the steel restrictedcracking of the cementitious materials was researched, in order to calculate thestresses within the cementitious materials under the steel reinforced conditions.Formula of the internal stress of the cement pastes was derivated, and the theoreticalsolution of the internal stress of the cement paste under the steel restriction conditionswas expressed.