Quantification of coarse aggregate constraint on mortar shrinkage in concrete under drying condition

Quantifying the constraint effect of coarse aggregates on mortar shrinkage is essential for predicting the bulk shrinkage of concrete. This study investigated the formation and evolution of tensile strain/stress shells around coarse aggregate in concrete under dry conditions by using digital image correlation and lattice fracture modelling. The average constraint shell thickness and constraint index were proposed to quantify the range and degree of coarse aggregate constraint on mortar shrinkage. The results indicated that constraint range increased as size of coarse aggregates increased, with the growth rate of 0.079. The constraint degree of coarse aggregate is positively correlated with aggregate size and mortar drying shrinkage. Notably, the formation of drying-induced micro-cracks also consumes more drying shrinkage forces, resulting in lower bulk drying shrinkage in concrete. At last, a mathematical model was developed to predict the bulk drying shrinkage of concrete based on constraint index and then validated against experimental results.