Predicting Chemical Shrinkage in Hydrating Cements

Abstract

This paper presents a prediction of chemical shrinkage volume created during the hydration of two cements over time using a thermodynamic model. Chemical shrinkage in hydrating cements is a result of internal volume change over time within sealed conditions due to exothermic reactions during hydration and the resulting precipitation of solid hydrates. Each precipitated phase will contribute to chemical shrinkage due to their individual reactions and stoichiometric properties. As these factors (including early age, drying and autogenous nature) contribute to the overall shrinkage of concrete which may cause long-term performance problems, they are important properties to understand. The current paper presents a thermodynamic model that quantifies the chemical shrinkage volume created during the first 1000 days of hydration using the cemdata18 database and a series of discrete solid phases (DSPs) to represent C-S-H, which has not been quantified in the literature to date. DSPs account for the amorphous and poorly crystalline nature of C-S-H in cement, and its incongruent dissolution behavior of C-S-H as calcium is released in solution more so than silicon. A description of chemical shrinkage in hydrating cements is provided, along with a review of past methods used to quantify its development over time. The paper also shows the linear relationship between chemical shrinkage and the overall degree of hydration.