Role of ionic diffusion in heat flow and chemical shrinkage of tricalcium aluminate hydration subjected to thermo-chemo-electrical coupled fields

Abstract

The role of ion diffusion in the heat flow and chemical shrinkage of tricalcium aluminate (C3A) hydration was investigated using the proposed multi-ionic reactive transport model for C3A hydration. Ion diffusion, dissolution, and precipitation reactions were coupled in the governing equation of the chemical field during C3A hydration in the presence of gypsum. Ion diffusion and chemical reactions were also governed by the electric and temperature fields in the model. Theoretical computations were performed relating ion diffusion to heat flow and chemical shrinkage during all stages of C3A hydration. Excellent agreement was achieved by comparing the simulation results and the experimental data under various conditions. The effects of the gypsum content, specific surface area (SSA), and curing temperature on the ion diffusion, electrical potential, heat flow, and chemical shrinkage were numerically studied. The results indicated that (1) higher gypsum contents, SSAs, and curing temperatures increased the ion concentration gradient and improved the supersaturation concentration of sulfate near the C3A surface; (2) higher gypsum contents led to faster decreases in the Ca2+ and SO42− concentrations before the depletion of gypsum; and (3) the gypsum content affected the phase assemblage through spatial and temporal evolution of the ionic species. The proposed model may guide the design of the C3A-gypsum system and can be extended to optimize the fluidity and setting properties of the cement paste.