Cement Interfaces: Current Understanding, Challenges, and Opportunities.

Cement and concrete are rapidly growing in demand and pose many unresolved chemistry questions at particle interfaces, during hydration reactions, regarding the role of electrolytes and organic additives. Solutions through developing greener, more sustainable formulations are needed to reduce the high carbon footprint that amounts to 11% of global CO2 emissions. Cement is a multiphase material composed of calcium silicates, aluminates, and other mineral phases, produced from natural and low-cost industrial sources, which undergoes complex hydration reactions. This perspective highlights current research challenges and opportunities for new chemistry insight, including intriguing colloid and interface science problems that involve mineral surfaces, electrolytes, polymers, and hydration reactions. Specifically, we discuss (1) characteristics of cement phases, supplementary cementitious materials, and other constituents, (2) hydration reactions and the characterization by imaging and NMR spectroscopy, (3) the structure of hydrated cement phases including calcium-silicate-hydrates at different scales, (4) quantitative simulation techniques from the atomic scale to microscale kinetic models, and (5) the function of organic additives. Focusing on new directions, we explain the benefits of integrating knowledge from inorganic chemistry, acid-base chemistry, polymer chemistry, reaction mechanisms, and theory to describe mesoscale cement properties and bulk properties upon manufacturing.