Enhancing sustainability of amorphous-wollastonitic hydraulic binders through incorporation of supplementary cementitious materials

Abstract

In cement industry the use of supplementary cementitious materials (SCMs) play an important role in the reduction of CO2 emissions by allowing a decrease in clinker content. The present work investigates the incorporation of four different SCM into an amorphous wollastonitic hydraulic (AWH) clinker, which requires alkaline activation with a sodium silicate solution. This alkaline activation process could potentially allow the use of some SCMs as precursors within the SCM+AWH mixture. Hence, besides physical, pozzolanic, or latent hydraulic capabilities, the SCM incorporation would also enhance the system reactivity at early and later ages due to their alkaline activation. In this study, pastes and mortars were made by individually replacing 25 %wt of the AWH clinker with fly ash (FA), limestone filler (L), calcined clay (CC), and ground granulated blast furnace slag (GGBFS). The influence of the SCM incorporation on the hydration kinetic, phase development, and compressive strength was assessed and compared to 100 % AWH samples. The first seven days of the reaction were followed using isothermal calorimetry, and compressive strength tests were performed after 2, 7, and 28 days of hydration, the hydrated samples were characterized using thermogravimetry and X-ray diffraction analysis. The main results indicate that in mortars, both FA and the CC acted as fillers, displaying similar results as the L mixture mortar. However, the high compressive strength of the FA blend pastes, and the high heat release of the CC blend reveal a potential for alkaline activation. With the incorporation of the GGBFS, a synergy between the AWH binder and this SCM was observed, this addition led to an increase in the reaction kinetics, heat released, and compressive strength results at all ages. The positive results were attributed to the GGBSF activation with the alkaline solution, causing a rise in temperature and enhancing the dissolution of the AWH binder. Moreover, on mortars at 28 days of hydration, the compressive strength ratio AWH/(AHW+SCM), was superior to 0.75 on all samples, suggesting a positive interaction between the clinker and the SCM. Overall, the findings presented in this work contribute to at least a 25 % reduction in CO2 content associated with AWH clinkers, resulting in material-related CO2 emissions at 255 kg/ton clinker

Keywords

• Alkaline activation
• Amorphous-wollastonitic binder
• Cement
• Supplementary cementitious materials