Effect of Limestone Powder on Microstructure of Ternary Cementitious System

The pressure to reach sustainability favours the development of ternary composite cement. The synergistic effect on mechanical behaviour at 28 days between limestone powder (LP) and pozzolanic additives, i.e. fly ash (FA) and blast furnace slag (BFS), has been documented. In order to better understand the synergistic effect, this article investigated the effect of LP on the microstructure of PC-FA and PC-BFScementitious system. The mineralogy and pore structure were determined after 28 days of curing at 20°C and 95% relative humidity. The mineralogy in pastes was identified by means of X-Ray diffraction (XRD) and thermogravimetry (TG). The pore structure was evaluated by Mercury intrusion porosimetry (MIP). The results showed that neither monosulfoaluminate nor ettringite was found in any of the XRD patterns. Instead, carboaluminate was observed. Hemicarboaluminate produced in FA-PC or BFS-PC system transformed into monocarboaluminate with the addition of LP. The porosity was enlarged compared with LP-free paste system. It seems that both the physical and chemical effect of LP contribute to the synergistic effect on mechanical behaviour of cementitious system hydrated up to 28 days.