The mechanism of curing regimes on the macroscopic properties and microstructure of ultra-high performance concrete with lightweight aggregates

The internal curing effect of lightweight aggregates (LWA) enables ultra-high performance concrete (UHPC) to achieve lightweight and high-strength, but the performance and microstructure evolution mechanism of lightweight ultra-high performance concrete (L-UHPC) under different external curing regimes is still unclear. In this paper, L-UHPC was prepared using LWA from industrial waste, and the effect of water absorption of LWA on the properties of L-UHPC was investigated. Based on this, the evolution of performance and microstructure of L-UHPC under different curing regimes was investigated using nitrogen adsorption method, X-ray diffractometer, scanning electron microscope and nanoindentation techniques. The study shows that the best internal curing effect is achieved when the LWA is pre-wetted with water for 24 h. External thermal curing significantly improves the performance of L-UHPC, with dry heat curing having the best effect. The coupling effect of internal and external curing improves the density of the interface transition zone and reduces porosity, resulting in L-UHPC compressive strength >155 MPa and density <2100 kg/m3.