"Currently, the annual global cement production is estimated to be 3.3 billion tons1. Even though the CO2 emissions associated with the final product, concrete, are low, the massive scale of production, means that the cement industry accounts for 5-8 % of the global annual anthropogenic CO2 emissions3. One of the most effective ways to improve sustainability is the blending of Portland cement with supplementary cementitious materials (SCMs)2,3. However many local sources are fully exploited and a decline in production of blastfurnace slags and fly ash is expected due to future developments in steel and electricity production4. Therefore locally available alternatives to these traditional SCMs need to be found to achieve higher cement replacement levels and a more sustainable cement industry.Unravelling the impact of this expanding and diversified group of SCMs on the hydration reactions and performance of cement constitutes a major scientific challenge. The diversity of SCMs calls for novel generic approaches that will enable direct prediction and control of performance; compared to the current practice of case-by-case empirical testing.This project proposes a novel interdisciplinary approach, building on the geological background of the fellow combined with the materials science perspective of the host. Novel concepts of surface chemistry, recently developed in geochemistry, will be applied to the behaviour of SCMs in cement. The focus will be on investigating the effect of SCM and solution chemistry on the rate of the nanoscale surface processes of dissolution and precipitation. The impact of SCMs on the product assemblage and microstructure will be modelled and compared to experiment, exploiting recent breakthroughs in thermodynamic and microstructure modelling of cement systems. Finally, the results obtained will be transferred to practice through practical methodologies for testing SCM reactivity in a basic laboratory environment."