This research 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. The computed responses of the UHPC mixtures at a compressive strength varying from f’c = 149 MPa to 164 MPa are comparatively evaluated for a curing period of 28 days against those of ordinary concrete involving f’c = 30 MPa to 45 MPa. When the hydration of cementitious pastes proceeds, 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.