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The interfacial transition zone (ITZ) percolation is an effective parameter reflecting the connectivity of ITZs in cementitious materials, and its emergence may accelerate the penetration of inimical ions. In the existing literature on ITZ percolation, aggregates are generally simplified as the identical-shaped particles and the thickness of the ITZ phase around them is set to be uniform, which differs greatly from the realities and may cause the large deviation. To determine the ITZ percolation with the response of different phases in a more realistic way, a more satisfying three-dimensional (3D) polyphase model of concrete is developed, in which the convex ovoids and polyhedrons are separately adopted to represent the sands and gravels. The realistic nonuniform ITZ is also assigned for these aggregates based on their specific sizes and the W/C for the cement matrix. By coupling these models with the continuum percolation theory in statistical physics, the influence of individual phases on the global percolation threshold ϕ agg,c of ITZs is further studied by the simulation. The results reveal that the models here provide a smaller percolation threshold ϕ agg,c than the previous prediction models containing the simplistic uniform ITZs. There is reason to believe that these results in the work would be closer to the actual threshold in the realistic circumstance.

Magnesium phosphate cement (MPC), which belongs to chemically bonded phosphate ceramics, is commonly applied as a repair material and waste stabilization/solidifications. However, studies on the influence of CO2 on the phase assemblages in MPC are limited. A thermodynamic simulation approach is employed to explore the influence of CO2 on the equilibrium phase assemblage of MPC. The mechanisms of natural and enforced carbonation of MPC have been investigated in this work. The results disclose that Mg carbonates are less likely to precipitate in magnesium ammonium phosphate cement (MAPC) cured under CO2, while MgCO3·3H2O is the only carbonation product of magnesium potassium phosphate cement (MKPC). The carbonation resistance of MAPC is better than that of MKPC. The increase of activity of magnesia employed in MPC obviously enhances the formation of brucite and slightly promotes the carbonation of MPC. [ABSTRACT FROM AUTHOR]