Effect of aggregate on shrinkage crack-resistance of steam cured concrete

A simple test method to characterize the shrinkage crack-resistance (SCR) of steam cured concrete is advanced. It includes the estimation of time of appearance of first crack on specimens and SCR coefficient as well as parameters of concrete stress state to this period. The SCR of steam cured conventional concrete and micro-concrete of two compositions with compressive strength of approximately 20 MPa was studied. It was observed that the conventional concrete had the highest SCR. The appearance of cracks on specimens from this type concrete was detected after 49 days of drying exposure. The micro-concrete, prepared from sand with a fineness modulus of 0.36, had the lowest SCR: the first crack on specimens appeared after 34 days of their drying. The tensile stress, free shrinkage, tensile strain capacity and SCR coefficient of concretes at the beginning of crack-generation were calculated.