Cracking of limestone calcined clay blended concrete and mortar under restrained shrinkage

This work is investigating restrained shrinkage induced early age cracking of limestone calcined clay (LC) blended concrete and mortar. A series of ring tests was conducted on LC blended concretes with 44% replacement of General Purpose (GP) cement and reference GP cement-only concretes. In addition, autogenous shrinkage and total shrinkage of concretes, mortars, and pastes were monitored to investigate the effect of the addition of LC on the different shrinkages and subsequent restrained shrinkage induced cracking. Results showed that LC blended concrete cracked earlier than the control mixes due to a high stress rate which is a function of the shrinkage of the restrained concrete ring. However, the autogenous shrinkage of concrete, rather than the total shrinkage, significantly influenced the early age cracking of LC blends. The ratio (total/autogenous) of shrinkage rates was proportional to the time to cracking for all mixes. The dependency of cracking on early-age autogenous shrinkage was further corroborated by the ring test results using LC blended mortar mixes considering various replacement levels ranging from 14% to 59%. Less early-age autogenous shrinkage in the LC blend with 59% replacement contributed to delayed cracking compared to other mortar mixes.