Reactive molecular dynamics simulation of the mechanical behavior of sodium aluminosilicate geopolymer and calcium silicate hydrate composites

This paper for the first time used reactive molecular dynamics (MD) simulation to study the mechanical behavior of geopolymer binder (GB) and calcium silicate hydrate (CSH) composites. Specifically, GB-CSH composites with different Ca/Si ratios for the CSH phase were constructed and their mechanical behavior in terms of ultimate tensile strength, fracture toughness and strain energy release rates were investigated. It was observed that the Ca/Si ratio of CSH greatly affects the mechanical response of the composite. Increasing the Ca/Si ratio from 1.2 to 1.65 created more disorder in the silica layers in CSH and decreased the mechanical properties of the composite. However, the completely glassy CSH at a Ca/Si ratio of 2.0 showed slight improvement of mechanical properties due to high three-dimensional (3D) tetrahedral network. A detailed analysis of bond evolution and bond angle distribution showed their direct correlation with the observed mechanical response. The failure of the GB-CSH composites were always governed by the breaking of Si-O bonds within the CSH, near the GB-CSH interface. Low Ca/Si ratio structures showed more SieO bond breakage, while in high Ca/Si ratio structures, deformation mobilization was accompanied by significant change in bond angles within GB.