Combining experiments and molecular dynamics simulations to investigate the effects of water on the structure and mechanical properties of a coal gangue-based geopolymer

•The geopolymers were investigated by a combination of experiments and molecular dynamics simulations.•The molecular model of Na2Si2O5 is used as the basis to construct the structural model of different H2O/Al coal gangue-based geopolymers.•The effect of H2O/Al on the microstructure of geopolymers was investigated by XRD, RDF, elastic modulus, etc. methods.•The rationality of the proposed geopolymer model was verified, and it was demonstrated that the Universal force field is also applicable to the simulation and calculation of this geopolymer model.•It is beneficial to the reasonable application of coal gangue in geopolymer field. The effects of water on the structure and mechanical properties of a coal gangue-based geopolymer were investigated experimentally and compared with the results of molecular dynamics simulations. The chemical composition and crystalline phases of the raw materials were analyzed via X-ray fluorescence and X-ray diffraction (XRD) after 28 days of curing, and the mechanical properties were tested. Molecular structure models for H2O/Al ratios of 2.5, 3, and 3.5 were established using molecular dynamics simulation software, and structural optimization and molecular dynamics simulations were performed under the universal force field. Based on the obtained results, the energy and temperature change curves, simulated XRD spectrum, radial distribution function, hydrogen bonding, mean squared displacement, and mechanical properties of the amorphous geopolymer were analyzed. The rationality of the molecular model was verified through comparison with the results of the molecular dynamics simulations and experiments, and as the H2O/Al ratio increased within a given range, the energy and temperature stability time of the system are decreased, the area of the dispersion peak is decreased, the amorphous phase is increased, the diffusion degree of Si and Al in the system is decreased, the length of Si-O bond, Al-O bond, H-O bond and O-O bond is shortened, and the structure is more stable. The mechanical properties obtained from the experiment were also improved.