On the origin of eigenstresses in lightweight aggregate concrete

Abstract

This paper concerns the origin of eigenstresses in lightweight aggregate concrete (LWAC) caused by autogenous deformation and drying shrinkage. Autogenous deformation of LWAC, drying shrinkage of lightweight aggregates (LWAs) and drying shrinkage microcracking of special composites containing LWAs were investigated. From this study a number of differences between LWAC and normal weight concrete (NWC) emerged. In sealed conditions, the internal curing provided by saturated LWAs causes expansion of the cement paste at early-age. Since no de-bonding of LWAs occurs, the expansion of the cement paste results in tensional stresses in the aggregates. When drying of the LWAC occurs, expansion changes into shrinkage. Like the aggregates in NWC under both sealed and drying conditions, the LWAs are compressed. The restraining effect of LWAs is lower than that of normal weight aggregates due to lower elastic modulus and shrinkage of LWAs upon drying. These aggregate properties lead to lower eigenstresses and greater bulk shrinkage in drying LWAC when compared to NWC. On the other hand, additional stresses due to non-uniform shrinkage might be larger in LWAC, because of steeper moisture gradients in combination with reduced aggregate-restraint.