Hydration kinetics of cement–iron tailing powder composite cementitious materials and pore structure of hardened paste

Abstract

Cement–iron tailing powder composite cementitious materials (CT-C-CMs) is the research object of this study. Accordingly, hydration heat tests were implemented to analyze the hydration heat release law. To investigate the hydration kinetic course, the Krstulovic–Dabic model was applied. Moreover, the pore structures in hardened paste were investigated. With the aim of understanding the hydration characteristics of CT-C-CMs, the findings of this study are as follows. The hydration reaction of CT-C-CMs undergoes five phases: rapid reaction, induction, acceleration, deceleration, and stability, but the second hydration exothermal peak occurs later. The increase in hydration temperature accelerates the hydration reaction. The addition of iron tailing powder (IT-P) reduces the reaction rate and gross heat release of hydration of cementitious materials (CMs), and the degree of reduction increases with the IT-P dosage. The Krstulovic–Dabic model can well simulate the hydration kinetics of CT-C-CMs. The hydration reaction of CT-C-CMs is a complex process with a multistage reaction mechanism. It undergoes three stages: nucleation and crystal growth (NG), interactions at the phase boundary (I), and diffusion (D). Temperature increase can accelerate the transformation of the control mechanism of hydration reaction. When the temperature rises to 65 °C, the hydration reaction virtually shifts directly from stage NG to D. The hydration temperature and IT-P content have different effects on the reaction order (n) and reaction rate constant (K’i (i = 1, 2, and 3)). Under the same curing conditions, the porosity of CT-C-CMs is larger than that of pure cement hardened paste. Moreover, porosity increases with the IT-P dosage. The addition of IT-P enables the pore structure of the hardened paste of CT-C-CMs to improve. Under certain curing conditions, IT-P can refine the pores such that the proportion of pores that are less than 50 nm in size increases. When the curing age is 90 d, the most probable pore size of CT-C-CMs is less than that of pure cement.