Upshaw et al. (in preparation)

The results of a reactive molecular dynamics study on the effect of the potassium-to-calcium (K:Ca) molar ratio on the formation of potassium aluminosilicate hydrate (K-A-S-H) structures are presented in this paper. The gel structures were produced through the reaction of aluminum and silicon monomers with potassium- and calcium-based activator compounds using the LAMMPS package, and post-processing was completed using the LAMMPS and OVITO packages. The produced structures were validated by comparing key bond lengths and angles, aluminum and silicon central atom coordinations, x-ray diffraction (XRD) spectra, densities, and molecular water content to results previously published in the literature. The results of the study showed that a K:Ca ratio of 2.0 produced not only the K-A-S-H structure, but also calcium silicate and aluminosilicate hydrate products. However, ratios of 4.0 and greater did not show the same evidence of these structures. In fact, the inclusion of calcium at a K:Ca ratio of 4.0 only seemed to introduce disorder into the system to the detriment of the formation of the geopolymer structure. In general, this study showed that reactive molecular dynamics simulations provide researchers a cost-effective method to study multiple parameters involved in geopolymer synthesis.

Upshaw et al. (in preparation)

The results of an experimental study of the effect of differing ratios of natural aggregate replacement with recycled concrete aggregates on the properties of both ordinary Portland cement concrete and a metakaolin-based geopolymer concrete are presented in this paper. Utilizing both coarse and fine recycled concrete aggregates in fresh concrete mixes can positively impact the sustainability of the concrete industry by alleviating strain on landfills and reducing carbon emissions. However, doing so has detrimental impacts on several concrete properties such as density, compressive strength, static elastic modulus, and durability. This study aims to address those issues by incorporating a metakaolin-based geopolymer binder with silica fume and calcium compound additives. Results of the study showed that the detrimental impacts on important concrete properties can be dampened by the inclusion of this geopolymer binder. Additionally, it was shown that minimum concrete requirements set forth by ACI 318-14 can be achieved utilizing the developed geopolymer binder with up to 70% by weight of the total concrete aggregates replaced with recycled concrete aggregates. This study also demonstrates the efficacy of using calcium compounds to improve the mechanical properties of geopolymer concretes cured in ambient conditions. Overall, conclusions can be drawn from this study that recycled concrete aggregates can be utilized at high replacement ratios for general structural concrete applications.