An exploratory study of FA-based hybrid binder with alkaline sulfates as activator

Abstract

Hybrid binders emerge as an intermediate solution to further decrease the clinker factor in cementitious systems without unfavorable slow development of microstructure. There is an amount of fly ash that is not yet used in the production of cementitious materials due to its limited reactivity. Therefore, by the election of an appropriate activator and small contents of Portland cement, it may be possible to provide an acceptable behaviour in terms of early-age strength and at the same time to achieve a valorization of these supplementary cementitious materials. This paper presents results of an exploratory study for the activation of a low calcium fly ash in hybrid systems. In literature previous studies have proved the synergy effect between GGBFS and FA in AAMs. For these reasons, low amounts of GGBFS with a lower carbon footprint than PC were also incorporated into some mixes. The interaction Portland cement/activator seems to control the early age behaviour. Life Cycle Assessment calculations for mortars are also presented. By comparing the different mixes in a cradle-to-gate oriented analysis, an estimation of the eco-efficiency of each of the systems was obtained. The results demonstrated that the addition of sodium sulfate was the most effective approach for hybrid binders containing FA and GGBFS, increasing not only the heat release but also the compressive strength.