Mortar film thickness on the autogenous shrinkage of concrete: Test and simulation

Coarse aggregate (CA) accounts for the largest volume in concrete, which has significant impact on the performance of this building material such as workability, strength and shrinkage. Based on the determination of specific surface area for CA through simple sieving curve, mortar film thickness (MFT) of fresh concrete is numerically calculated. Relationship between MFT and CA content is acquired as three-stage model with critical volume fractions of 17% and 67%. Autogenous shrinkage of concrete with various CA volume fractions were experimentally eval-uated through integrated shrinkage test devices. Zero-time of autogenous shrinkage is determined based on the expansion-shrinkage behavior of concrete mixtures at very early age. The ultimate autogenous shrinkage of concrete decreases monotonously with increasing amount of CA or decrease in MFT. By comparing to existing theoretical and empirical models, new prediction model of autogenous shrinkage based on MFT is proposed with high correlation coefficient for concrete containing various CA content.