Computer Simulation of the Hydration-Carbonation Process of Reactive Magnesia Cement

M. Wang*, A. Al-Tabbaa

(1) Department of Engineering, University of Cambridge, UK

(2) Department of Engineering, University of Cambridge, UK

Abstract

Reactive magnesia cement can gain significant strength through its hydration-carbonation processes, providing a novel and green construction material. It has been intensively studied at the University of Cambridge for its application as cementitious material.  The influence factor of the hydration-carbonation process of reactive magnesia cement has been experimentally identified to be MgO content, water content, porosity, different curing conditions including CO₂ concentration, relative humidity and temperature etc. It has been found that nesquehonite is formed at temperature range of 10°C to 50°C under accelerated carbonation for reactive magnesia cement. On the other hand, the involvement of CO₂ in the microstructure development of reactive magnesia cement brings the research interest of the interaction between CO₂ and the percolation of porous cement paste regarding simulation aspect of cementitious material. In this paper, a discrete microscopic model is proposed to simulate the microstructure formation of reactive magnesia cement under the effect of accelerated carbonation.  To be more specific, initial microstructure of fresh cement before reaction is simulated as result of digitized particle packing using the technique of Cellular Automata. Then Lattice Boltzmann Method is 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 is analysed to predict the transportation duration of CO₂ into cement paste. Additionally, Shang-Cheng (SC) model is used to simulate the distribution of the entrained air bubble in cement paste before the reaction. 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, and the related transport properties. This model can be used to provide microstructural basis for macro-scale and meso-scale models to predict the strength, shrinkage and thermal properties of the material both in bulk cement paste and interfacial transition zone (ITZ).

Keywords: accelerated carbonation; reactive magnesia cement; microscopic modelling