Kinetic Study on Accelerated Mineral Carbonation Curing of Cement-Based Materials

Fixing CO₂ permanently in building materials and reducing the energy consumption in steam curing, the mineral carbonation (MC) curing of cementitious materials is attracting increasing interest as a novel curing technology and promising CO₂ utilization route. Since previous analyses on carbonation kinetics of cement matrix are limited to the condition of natural carbonation of hardened paste applying the carbonation depth, it is essential to determine the rate-controlling step along with the accelerated carbonation of cement in MC curing.

In this study, the gas-solid reaction models were applied to the MC curing process. The traditional P.O.42.5 OPC was employed to prepare 2cm×2cm×2cm cubes for carbonation experiments under different curing conditions (pressure, temperature and water-to-binder ratio). According to the fitting results of different gas-solid reaction kinetic models, the MC curing of cement showed a progressive product-layer-diffusion limited kinetics despite different influencing factors. For the initial stage of reaction, the linear fitting slightly deviated from the given theoretical value (1/2), which should be attributed to the results of temperature rise from chemical reaction and the corresponding outward diffusion of residual pore water. The apparent rate constant of the product-layer diffusion controlling stage remained stable under different pressure (0.5–2.5 MPa) and show positive correlation to the curing temperature. Thus for MC curing of cementitious materials, the methods for further enhancement of CO₂ uptake in the limited curing time could be designed according to this diffusion-controlled nature.