"Uncovering and Optimizing the Chemical Mechanisms in Alkali-activated Materials and Related Engineering Systems"
With the world facing a climate crisis due to increasing CO2 emissions, there is pressing need to develop and implement sustainable construction/engineering materials across the globe. Alkali-activated materials (AAMs) are one such sustainable alternative to conventional ordinary Portland cement (OPC) concrete; however, questions remain regarding the long-term performance of AAMs which is hampering implementation of this sustainable solution in the construction industry. Furthermore, for OPC-based concrete, the use of extensive clinker substitution to reduce CO2 emissions has led to changes to the underlying chemistry of the main binder gel, where it is uncertain how these novel supplementary cementitious materials augment the long-term properties (e.g., gel stability and pore structure) of the cement paste. Here, I will outline how fundamental materials research is addressing the long-term performance unknowns of AAMs and certain OPC-based systems, where we are linking key experimental techniques with atomistic and larger length scale simulations. To assess gel/binder stability in Ca-rich AAMs, we have used density functional theory (DFT) and synchrotron-based X-ray pair distribution function (PDF) analysis to investigate the influence of alkali substitution on the structure and thermodynamics of calcium-alumino-silicate-hydrate (C-A-S-H) gel. Furthermore, the pore structure of concrete strongly impacts long-term durability, where the pore network and permeability of the gel phase(s) are known to control the rate of degradation. I will outline our recent progress in the development and implementation of a mesoscale modeling methodology to simulate the formation of the binder gels and pore network in AAMs, along with key experimental data (e.g., small-angle neutron scattering and quasi-elastic neutron scattering) capable of tracking the evolution of the pore network and associated water dynamics immediately after mixing.