ASSESSING SHEAR STRENGTH OF SILICA-NASH GEOPOLYMER COMPOSITE USING MOLECULAR DYNAMIC SIMULATION

Alkali aluminosilicate hydrate (NASH) geopolymer has been utilized as an environmentally friendly binder to replace conventional cement-based binders for ground improvement. Because shear strength is one of the critical mechanical properties in assessing the performance of geopolymer-improved soils, this study investigated the shear strength of silica-NASH geopolymer (S-G-S) composite using molecular dynamic simulation to simulate the shear behavior of geopolymer-improved soils in the molecular scale. The NASH geopolymer was first successfully constructed, which showed comparable modulus of elasticity to the observed experimental results, followed by adding silica layers to develop an S-G-S composite using geometry optimization and isobaric-isothermal ensemble simulation. The obtained interfacial shear strength of the developed S-G-S composite increased as shear velocity increased. In addition, the higher interfacial shear strength of the S-G-S composite than the shear strength of geopolymer-improved soils in literature implies the shear failure of geopolymer-improved soils is unlikely to occur at the soil-geopolymer interface. The framework shown in this study can be used as a reference model to provide molecular-scale insight into the shear behavior of geopolymer-improved soils under the variation of many influencing factors (soil mineralogy, temperature, and alkali activator content).