Assessment of cracking in concrete due to hydration heat and autogenous shrinkage

This paper presents the results of an experimental study conducted to simulate the generation of thermal stresses due to hydration heat considering various restraint conditions by using thermal stress measuring device (TSD). It was found that influence of early-age properties of concrete on generation of thermal stresses such as elastic modulus; thermal dilation coefficient; and transitional thermal creep can be incorporated using TSD due to the simultaneous development of temperature and the corresponding stress in restrained specimen from the very beginning. Moreover, additional tests were conducted to study the effect of temperature rise due to early hydration on measurement of early-age autogenous shrinkage (AS). Early-age Autogenous shrinkage of specimens obtained with (semi-adiabatic condition) and without any temperature change (isothermal condition) was quite different. Therefore, it is suggested to control the isothermal conditions while measuring AS. Underestimation of early-age AS would cause serious errors while predicting the time of shrinkage induced cracking especially in HPC. Basic creep model was evaluated with respect to AS. It was found that for low w/c concrete, as well as at an early age of normal strength concrete, a significant difference exist between apparent (including AS) and real basic creep (excluding AS). It is recommended to modify the current basic creep model with respect to AS in order to prevent from possible errors and some other computational problems.