The effect of curing regimes on the hydration products of lightweight ultra-high performance concrete: From experiments to MD simulations

Abstract

The hydration products and microstructure of ultra-high performance concrete are influenced by the curing regime. In this study, the influence of curing regimes on the hydration products of lightweight UHPC was explored using experiments and molecular dynamics (MD) simulations. Experimental results show that the high temperature stimulates the pozzolanic activity of silica fume and fly ash promoting the hydration reaction of cement. AFt is decomposed to AFm under high temperature conditions, and the high temperature and high pressure promote C-A-S-H gel to transform into denser Tobermorite crystals. On this basis, the realistic molecular models of C-A-S-H gel corresponding to the hydration product of lightweight UHPC under different curing environments were established. The simulation results indicate that the mechanical properties of C-A-S-H were improved significantly after steam and autoclave curing compared with standard curing. The molecular models of lightweight UHPC exhibit an increased level of ductility and indentation modulus in comparison to ordinary Portland cement, which can be attributed to the inclusion of Al phase and a higher degree of silicate chain polymerization.