Geopolymers, synthesized through alkaline activation of aluminosilicates, have emerged as a sustainable alternative for traditional ordinary portland cement. In spite of the satisfactory mechanical performance and sustainability-related benefits, the large scale acceptance of geopolymers in the construction industry is still limited due to poor understanding of the composition-property relationships. Molecular simulation is a powerful tool to develop such relationships, provided the adopted molecular structure represents the experimental data effectively. Towards this end, this paper presents a new molecular structure of sodium aluminosilicate hydrate geopolymer gels, inspired from the traditional calcium silicate hydrates gel. In contrast to the existing model-where water is uniformly distributed in the structure-we present a layered-but-disordered structure. This new structure incorporates water in the interlayer space of aluminosilicate network. The structural features of the new proposed molecular structure are evaluated in terms of both short-and medium-range order features such as pair distribution functions, bond angle distributions, and structure factor. The structural features of the newly proposed molecular structure with interlayer water shows better correlation with the experimental observations as compared to the existing traditional structure signifying an increased plausibility of the proposed structure. The proposed structure can be adopted as a starting point towards realistic multiscale simulation-based design and development of geopolymers.

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This paper evaluates fracture toughness of sodium aluminosilicate hydrate (N-AS -H) gel formed through alkaline activation of fly ash via molecular dynamics simulations. The short-and medium-range order of constructed N-AS -H structures shows good correlation with the experimental observations signifying the viability of the N-AS -H structures. The simulated fracture toughness values of N-AS -H (0.4-0.45 0.5) appears to be of the same order as the available experimental values for fly ash-based geopolymer mortars and concretes. These results suggest the efficacy of the molecular dynamics simulation towards obtaining realistic fracture toughness of N-AS -H which is otherwise very challenging to obtain experimentally and no direct experimental fracture toughness values are yet available. To further assess the fracture behavior of N-AS -H, number of chemical bonds formed/broken during elongation and their relative sensitivity to crack growth are evaluated. Overall, the fracture toughness of N-AS -H presented in this paper paves the way for multiscale simulation-based design of tougher geopolymers.

This paper implements molecular dynamics (MD) simulation using reactive force field (ReaxFF) to evaluate the atomistic origin of the interfacial behavior in the overmolded hybrid unidirectional continuous carbon fiber low-melt PAEK (CFR-LMPAEK)-short carbon fiber reinforced PEEK (SFR-PEEK) polymer composites. From the MD simulation, it was observed that the interfacial properties improve with increasing maximum processing temperature and injection pressure although such an improving trajectory gets saturated beyond specific limits. The interfacial strength and fracture response of the hybrid polymer system at the interface are also evaluated. The mechanical responses obtained from MD simulation are used as adhesive properties in the macroscale finite element analysis (FEA)-based single lap joint (SLJ) model where the interfacial behavior between the adherends (CFR-LMPAEK and SFR-PEEK) is implemented using cohesive zone model (CZM). The simulated FE results show a good correlation with the SLJ experimental data. Thus, by linking the interfacial properties at the molecular scale to the performance of the interfacial bond at the macroscale, the comprehensive approach presented here opens up various efficient avenues toward atomistically engineered performance tuning in hybrid overmolded fiber-reinforced polymer composites to meet desired large-scale performance needs.