Jennings – Some Observations Relating Kinetics, Chemistry, and Product Structure of Hydrating Cement Paste

Hamlin Jennings

Northwestern University


One goal of cement chemistry is to identify the chemical mechanisms that control the transformation of cement powder plus water into a solid mass of products, which, depending on reaction conditions, exhibits a spectrum of properties, both chemical and physical.  Information about kinetics provides one piece of the puzzle, which must be nested into information about chemistry, structure of product at many scales, and distribution of products throughout the microstructure. The most common way of measuring kinetics is to measure heat generated as a function of time. This has led to dividing the reaction into several stages, the most researched being the induction period, a period of slow reaction that can be adjusted by admixtures over a broad range, technically important to concrete technology. A first principles understanding of the mechanisms behind accelerators and retarders remains one of the major challenges of cement chemistry. Some of what we know is gained from rate of hydration, but a picture that includes equilibrium chemistry and structure at many levels is far from complete. Furthermore, relationships between kinetics (controlled by admixtures) and properties remain rich with possibilities.



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