Understanding restraint effect of coarse aggregate on the drying shrinkage of self-compacting concrete

• An aggregate skeleton dispersion model of SCC was proposed and the restraint mechanism of aggregate was analyzed.
• The relation between mortar coating thickness and the drying shrinkage of was established.
• The restraint mechanism of aggregate was clarified based on the aggregate skeleton dispersion model and theoretical analysis.
• Coarser aggregate provides better restraint on the volume deformation of mortar.

Coarse aggregate serves as a restraint on the shrinkage of cement mortar, while the previous investigations mainly focused on normal vibrated concrete. In this study, effects of coarse aggregate volume and gradation on the drying shrinkage of self-compacting concretes (SCCs) were studied, and the mortar coating thickness (HMCT) was defined and calculated based on an aggregate skeleton dispersion model. The results indicate that the shrinkage of SCCs was mainly influenced by the HMCT and the restraint of coarse aggregate. With the decrease of coarse aggregate volume, the shrinkage of SCCs increased remarkably, which is due to the increment of HMCT. In another aspect, when coarse aggregate volume kept constant, the shrinkage of SCCs decreased with the increase of HMCT, which can be attributed to the better restraint effect of coarser aggregate. Further, the maximum tensile stress induced by the aggregate restraint was calculated based on the elasticity theory. A larger size of aggregate induced a higher aggregate restraint coefficient and theoretical elastic stresses on the mortar.