Determination of the setting time of environmentally friendly cement-based binders: mortar vs concrete

The recent awareness of the cement industry with current environmental imperatives has motivated much research on the possibilities of substitution of clinker, responsible for substantial emissions of CO2 by mineral additives, by-products of various industries. In this study, the concretes investigated are designed as to ensure a limited early age cracking risk despite a massive substitution of up to 75% of clinker. In this framework, many studies have highlighted the interest that present mix designs combining the benefits of various additions, particularly ground-granulated blast-furnace slag and limestone micro-filler. The aim of this study is to evaluate the impact of environmentally friendly cement-based binders on the setting time of concretes and corresponding mortars by means of a standard method (ASTM C403), early age compressive strength, very early age elastic modulus by means of classical extensometer and with a TSTM device and by means of ultrasonic measurements. The main advantage of this last method is that it allows a continuous non-destructive measurement of the P-waves and S-waves transmission velocity. Critical influence of both the binder’s composition and the aggregate content has been observed on the setting process. Whereas correlations between mechanical properties and final setting time can be determined, the latter cannot be linked to the chemical behavior of both mortar and concrete.