Study of Shrinkage Restraint Effects at Early-Age in Alkali-Activated Slag Mortars

Abstract

Alkali-activated materials are being increasingly studied nowadays as hydraulic binders. In order to be enrolled in different civil engineering applications, several properties must be characterized. This study focuses on their cracking risk by shrinkage restraints. The current paper summarizes the experimental and numerical results of a project assessing the development of early age properties of an alkali-activated slag mortar. First, an experimental campaign was held in order to quantify hydration heat release and hydration kinetics, to determine the time evolution of the Young modulus and the tensile strength and to measure free shrinkage strains, all in autogenous conditions. Second, two modelling approaches for mechanical properties and shrinkage development were compared. The results showed that the classical approach to characterize the hydration kinetics based on semi-adiabatic calorimetry results isn’t suitable for the studied binder because of slow hydration and low heat release. Numerical work was finally conducted in order to predict stress development of a massive structure of alkali-activated slag mortar subjected to internal (self) and external strains’ restraints (at mesoscopic and macroscopic scales).