Effect of lightweight aggregate pre-wetting on microstructure and permeability of mixed aggregate concrete

Abstract

The influence of lightweight aggregate (LWA) pre-wetting on the chemical bound water and pore structure of the paste around aggregate as well as concrete permeability were investigated. The results show that, in early age the dry LWA has significant effect on the formation of dense paste around it and improving the concrete impermeability. However the prewetted LWA has strong water-releasing effect in later age, which increases the hydration degree of the paste around it, and makes the adjacent paste develop a structure with low porosity and finer aperture, furthermore the concrete impermeability can be improved. It is suggested that, as for concrete with low durability requirement, the LWA without pre-wetting treatment can be used as long as meet the workability requirement of fresh concrete, the good impermeability of concrete can be gained as well. As for concrete with high durability requirement, the prewetted LWA should be used, and the pre-wetting time should be extended as long as possible, in order to optimize the concrete structure in long term, and improve the concrete durability.