Computer simulations of the hydration-carbonation processes in reactive magnesia cement systems

Reactive magnesia cement systems can gain significant strength through their hydration-carbonation processes, providing novel and green construction products. The influencing factors of the hydration-carbonation processes of reactive magnesia cement has been experimentally identified to be the MgO content, water content, porosity and curing conditions, including CO₂ concentration, relative humidity and temperature. It has been found that nesquehonite is formed at a temperature range of 10°C to 50°C under accelerated carbonations of reactive magnesia cement systems. In this paper, a discrete microscopic model is proposed to simulate the microstructure formation of reactive magnesia cement systems under the effect of accelerated carbonation. To be more specific, the initial microstructure of fresh cement before reaction is simulated as a result of digitized particle packing using the technique of Cellular Automata. Then the Lattice Boltzmann Method was applied to simulate the dissolution and precipitation behaviour of MgO under the influence of accelerated carbonation in a diffusion-controlled system to form the final porous microstructure. The percolation threshold of the microstructure was analysed to predict the transportation duration of CO₂ into cement paste. This model provides microstructure with adjustable micro-properties of cement paste, which includes different cement particle size distribution, MgO content, porosity, degree of hydration and degree of carbonation.