Evolutionary characteristics of microstructural hydration and chloride diffusion in UHPC

Abstract

This paper presents the evolutionary characteristics of microstructural hydration and chloride migration in ultra-high performance concrete (UHPC). The physicochemical interactions of constituents are simulated in conjunction with a random walk algorithm. When the hydration of cementitious pastes proceeds, accompanied by the evolution of hardening, the quantity of silicates becomes larger alongside irregularly dispersed byproducts (calcium silica hydrate, C-S-H, and calcium hydroxide, CH). Owing to the formation of pozzolanic C-S-H consuming CH, the silicate reactions of UHPC are less than the reactions of the ordinary concrete. The implications of tricalcium silicate (C3S) are notable for the early-age strength gain of UHPC in comparison with its dicalcium silicate (C2S) counterpart. The matured pozzolanic reactions and invariable packing density of UHPC are responsible for preserving the proportion of silica fume in the mixtures. Relative to UHPC, the ordinary concrete releases more heat caused by exothermic reactions that are a function of saturated pores and silica fume with the contribution of C3S. Regarding corrosion durability, the chloride contents of a bridge deck cast with the ordinary concrete exceed the content of a deck with UHPC. As part of technology transfer, the notion of performance-based design applies and practice guidelines are suggested.