Early Age Properties Development of Concrete with Different Slag Contents

Abstract

This paper describes how slag cement concrete is characterized with many advantages, which leads to its intensive use in the construction industry in Belgium. However, it may exhibit a high sensitivity to cracking at early age in case of restrained shrinkage. The understanding of this behavior involves an in-depth analysis of the early age deformations. First, an experimental investigation of the mechanical properties (compression strength, elastic modulus) and the microstructure evolution (hydration kinetic and hydrates development) was performed on three concretes containing different slag proportions (0%, 42% and 71% of the mass of binder), but with identical total binder content, in order to understand the effect of slag on these parameters. Second, the autogenous deformations were measured from casting time on concrete cylinders under isothermal conditions. The apparent activation energy and the time of initial set were also evaluated in order to analyze these deformations. The apparent activation energy is used to convert the actual age into equivalent age to express the concrete properties independently of the temperature variations. The time of initial set from which the strains are expressed is determined by ultrasonic detection and by the Kelly-Bryant method.