Recent issues pertaining to climate change have led to significant interest in sustainable material technologies that possess lower environmental footprints. One such technology is alkali-activated materials (AAMs), which has been proposed as a potential technology to replace ordinary Portland cement (OPC), since OPC is responsible for ~8% of anthropogenic CO<sub>2</sub> emissions. It has been shown that AAMs, which gain their strength from interactions between an alkali source and a precursor material, can reduce CO<sub>2</sub> emissions from the concrete industry by up to 80-90%. Here, we reveal a fundamental charge balancing mechanism at the atomic level in AAMs, which leads to new stable strength-bearing phases. This mechanism is responsible for various atomic re-arrangements and triggers chain reactions that take place during the incorporation of alkalis in these complex phases. Using first-principles calculations, the stabilities of these phases are evaluated. The calculated bulk modulus values, diffusion barriers, formation energies and bond strengths show that the charge-balanced alkali-containing phases have the same levels of stability as compared to OPC phases. The atomistic properties and new model structures associated with this fundamental charge balancing mechanism will pave the way to a deeper understanding of the impact of alkali activation on the resulting gel phase and enhance the uptake of environmentally friendly construction materials.

Nanoscale charge balancing mechanism in alkali substituted C-S-H gels from first-principles calculations

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.