LAUSR

Abstract Geopolymers are alkaline cements composed of aluminosilicate units. The molecular structure of some geopolymers is sodium-aluminosilicate hydrate (N-A-S-H). Impurities containing calcium and magnesium are of significant importance in various types of geopolymer materials, as these impurities affect the mechanical properties of the geopolymer. In this study, the effects of different percentages of impurities on the modulus of elasticity of two types of geopolymer structures (N-A-S-H and slag) were investigated using molecular dynamics simulations. A recently introduced and modified N-A-S-H structure was used in the simulations. The molecular structure of blast furnace slag was also used to confirm and validate the molecular simulation results. The main reason for comparing the results of molecular dynamics simulations of the N-A-S-H structure with those of slag was the availability of laboratory results for slag-based geopolymers in the technical literature. The proposed molecular structure of slag based on its constituents is (N,C)-A-S-H. This structure is the most similar to N-A-S-H. The simulation parameters were selected based on data available in the literature. For the amorphous form of N-A-S-H, several simulations were performed to determine the mean modulus of elasticity. Then, additional simulations were carried out to investigate the effect of impurities on the modulus of elasticity of geopolymer materials. The results were in good agreement with the available laboratory results. The results showed that with an increasing percentage of calcium in the N-A-S-H structure, the modulus of elasticity increased. On the other hand, with an increasing percentage of magnesium impurities in the slag and N-A-S-H structures, the modulus of elasticity decreased. The overall results showed that the molecular dynamics simulation method is a good tool to complement laboratory studies for investigating the mechanical properties of geopolymers.