CAREER: Nanoscale Interfacial Phenomena and Reaction Kinetics of Calcium Silicate Minerals in Cements

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

This Faculty Early Career Development (CAREER) award is to advance the understanding of portland cement reactions and mechanisms at the micro- and nanoscales. Portland cement is a critical material for civil infrastructure, with around 4 billion tons of cement produced annually worldwide, and the majority of cement is used as the binder in concrete, which is used to build structures, bridges, buildings, dams, roadways, ports, airfields, and other critical civil infrastructure. Despite the widespread application, the fundamental reactions and kinetics of how cement reacts with water to serve as the binder in concrete are poorly understood. This research studies two minerals in cements, tricalcium silicate and dicalcium silicate, which comprise around 75% of the cement composition. This study quantifies the fundamental kinetics and mechanisms that govern how tricalcium silicate and dicalcium silicate react with water at the nanoscale, which will provide new insights into the reactivity of cements. By understanding the fundamental hydration reactions in cements, the longer-term goal of the research is to develop high performance concrete that is more durable and sustainable, thereby ensuring improved resiliency and safety of American civil infrastructure. The experimental data from this award will be used to refine a kinetic Monte Carlo model of surface dissolution, resulting in a more robust model to gain insights into cement reactivity. An education component of the research will expand outreach to K-12 students through programs at Virginia Tech and at the Science Museum of Western Virginia to learn about cement and concrete, how cement reacts with water to make concrete, and the important role that concrete has in civil infrastructure. The primary challenge to understanding cement reactions with water is that there are a significant number of competing dissolution and precipitation reactions owing to a dynamic solution chemistry. The aim of this project is to simplify the problem by first understanding the reactions of specific minerals found in cements before scaling the complexity to systems with different solution compositions. Specifically, this study evaluates the real-time nanoscale dissolution rates of calcium silicate surfaces through in situ 3D surface topography measurements by spectral modulation interferometry. Coupled with additional characterization by X-ray reflectivity, X-ray photoelectron spectroscopy, and electron microscopy, these data will quantify the spatiotemporal variability of rate constants and define the mechanism through which a calcium silicate surface interacts with an aqueous solution. Subsequently, these data will be integrated into a kinetic Monte Carlo model of surface dissolution to yield a more accurate prediction of dissolution kinetics. The key contribution of this work is to advance new characterization techniques to accelerate the quantification and understanding of cement hydration, including the derivation of fundamental kinetic rates and mechanisms that can be integrated into computational materials science models of hydration. This contribution is significant because the data will revolutionize the understanding of how kinetic phenomena are involved in cement hydration, which will unlock new techniques or materials to rapidly advance towards improved sustainability in concrete materials. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.