20 / 2022-03-09 21:12:13

The effect of curing regimes on the hydration products of lightweight ultra-high performance concrete: Experiments and MD simulations

Curing regimes,Hydration products,Lightweight UHPC,Molecular dynamics simulations

The curing regimes have significant effect on the hydration products and microstructure of ultra-high performance concrete (UHPC). The aim of this paper is to investigate the effect of different curing regimes, including standard curing, steam curing and autoclave curing, on the hydration products of lightweight UHPC through experimental techniques (e.g., XRD, TG-DSC, NMR, and SEM-EDS) and molecular dynamics (MD) simulations. The results obtained from experiments show that, with the increase of curing temperature, the overall hydration degree of cement gel in lightweight UHPC was improved, as the high temperature stimulates the pozzolanic activity of silica fume and fly ash promoting the hydration reaction of cement. Besides, the AFt was decomposed to AFm and the C-S-H gel was transformed into denser Tobermorite crystals under autoclave curing regimes. Further, based on the experimental results of Ca/Si ratio, Al/Si ratio, Qⁿ species and MCL (mean chain length), realistic C-(A)-S-H molecular models of lightweight UHPC under different curing regimes were constructed and MD simulations were performed to study the effect of curing regimes on the structure, dynamic and mechanical properties of C-(A)-S-H at nanoscale. The results indicate that Ca, Al, and Si atoms in the C-(A)-S-H model of lightweight UHPC form strong interactions and stable structure. However, the dynamic properties of C-(A)-S-H under standard curing is lower than that under steam and autoclave curing. The mechanical properties of C-(A)-S-H system was improved significant after steam and autoclave curing comparing with standard curing which agrees well with experimental results. This paper could provide new insights into the evolution of hydrates and microstructure of UHPC due to curing regimes in terms of experiments and simulation studies.