Cement hydration is the underlying mechanism for the strength development in cement-based materials. The structural and electron-ic properties of calcium silicates should be elucidated to reveal their difference in hydration reactivity. Here, we comprehensively compared β-C2S and M3-C3S and investigated their structural properties and Bader charge in the unit cell, during surface reconstruction and after single wa-ter adsorption via density functional theory. We identified different types of atoms in β-C2S and M3-C3S by considering the bonding character-istics and Bader charge. We then divided the atoms into the following groups: for β-C2S, Ca and O atoms divided into two and four groups, re-spectively; for M3-C3S, Ca, O, and Si atoms divided into four, four, and three groups, respectively. Results revealed that the valence electron distribution on the surface was more uniform than that on the unit cell, indicating that some atoms became more reactive after surface relaxa-tion. During water adsorption, the electrons of β-C2S and M3-C3S were transferred from the surface to the adsorbed water molecules through position redistribution and bond formation/breaking. On this basis, we explained why β-C2S and M3-C3S had activity differences. A type of O atom with special bond characteristics (no O–Si bonds) and high reactivity existed in the unit cell of M3-C3S. Bader charge analysis showed that the reactivity of Ca and O atoms was generally higher in M3-C3S than in β-C2S. Ca/O atoms had average valence electron numbers of 6.437/7.550 in β-C2S and 6.481/7.537 in M3-C3S. Moreover, the number of electrons gained by water molecules in M3-C3S at the surface was higher than that in β-C2S. The average variations in the valence electrons of H2O on β-C2S and M3-C3S were 0.041 and 0.226, respectively. This study further explains the differences in the hydration reactivity of calcium silicates and would be also useful for the design of highly re-active and environmentally friendly cements.

Chongchong Qi;Xinhang Xu;Qiusong Chen

School of Resources and Safety Engineering,Central South University,Changsha 410083,China;School of Molecular Science,University of Western Australia,Perth 6009,Australia

矿物冶金与材料学报

[1]Chongchong Qi;Xinhang Xu;Qiusong Chen-.Hydration reactivity difference between dicalcium silicate and tricalcium silic-ate revealed from structural and Bader charge analysis)[J].矿物冶金与材料学报,2022(02):335-344

silic

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