Waste Eggshell Valorization as Limestone Alternative for Portland Cement

This study investigates and optimizes the heat treatment of eggshells to achieve performance comparable to that of limestone. Characterization of the eggshell powder revealed that it contained about 6% organic impurities by mass from the egg membrane. The effect of the organic content is not significant at 15% cement replacement. However, the influence of organic content imparted highly hydrophobic properties, which compromised paste flow, clinker hydration, and mortar strength at 35% cement replacement. Rheological measurement concluded that paste mixture with untreated eggshell powder displayed a higher static yield stress but lower dynamic yield stress. Moreover, mortars with untreated eggshell exhibited higher shrinkage values compared to mortars with limestone powder. Heat treatment effectively denatured the organic content within the eggshell powder, addressing these weaknesses. Beyond a heat treatment temperature of 300˚C, mortars with eggshell powder demonstrated strength comparable to that of mortars made with limestone. At 500˚C, all organic influences in the eggshell powder that hindered flowability were eliminated, resulting in a hydrophilic nature akin to that of limestone. Hence, waste eggshells can be effectively valorized to produce blended cement at 35% clinker replacement.