Molecular dynamics simulation of the structure of calcium silicate hydrates .1. Ca4+xSi6O14+2x(OH)(4-2x)(H2O)(2) (0<=x<=1)

Molecular dynamics has been used to simulate the structure of calcium silicate hydrates (CSH) having Ca/Si ratios of 0.66 and 0.83. In the absence of labile calcium, silicon nuclear magnetic resonance (NMR) shows that the tetrahedral chains move closer together than predicted by the tobermorite model initially adopted, This proximity may lead to bridging between the chains, In the presence of labile calcium, there is a partial rupture of the chains, as seen with NMR, The instability of the bridging tetrahedra in the initial structure causes this rupture, The dissociation of a water molecule releases the oxygen necessary for the reaction. The rupture of the chains creates two new types of tetrahedra in the structure (Q1(2H) and Q1(1H)). (C) 1996 Academic Press, Inc.