Effect of Pre-wetting Lightweight Aggregates on the Mechanical Performances and Microstructure of Cement Pastes

The water absorption and desorption processes of different types of lightweight aggregates were studied. Subsequently, the influences of pre-wetting lightweight aggregates on compressive strength, microhardness, phase composition, hydration parameters and micromorphology of the cement pastes were investigated. The results showed that the water absorption and desorption capacities of the lightweight aggregates increased with the decrease of the densification degree. With the addition of pre-wetting lightweight aggregates, the compressive strength of the cement pastes would increase. Moreover, the enhancement effect was more obviously with the desorption capacity of pre-wetting lightweight aggregates increasing. Especially, sample S1 with pre-wetting red-mud ceramisites had the highest compressive strength, of which increased to 49.4 MPa after 28 d curing age. The reason is that mainly because the addition of pre-wetting lightweight aggregates can promote the generation of C-S-H gels in the interfacial zone, and the hydration degree of the interfacial zone increases with the water desorption of pre-wetting lightweight aggregates increasing. It is contributed to optimize the microstructure to enhance microhardness of the interfacial zone, resulting in the compressive strength of the cement-based materials improving. Therefore, the pre-wetting lightweight aggregates with high porosity and strength are the potential internal curing agents for high-strength lightweight concretes.