Valorization of Waste Eggshell as a Limestone Alternative for High-Volume Incorporation into Portland Cement

The incorporation of waste eggshell powder into portland cement presents an innovative strategy for decarbonizing the cement industry. Eggshell powder exhibits properties similar to limestone; however, its effectiveness in portland cement is often hindered by organic impurities and heterogeneous surface characteristics. This study investigates the heat treatment of waste eggshell powder to enhance its performance to a level comparable to limestone powder. Characterization revealed that eggshell powder contains approximately 6% organic impurities by mass from the egg membrane. These organic components impart superhydrophobic properties, inhibiting the interaction between mixing water and the blended cement, which can compromise paste flow, cement hydration, and mortar strength. Rheological measurements showed that pastes incorporating unincinerated eggshell powder exhibited higher static yield stress, which indicate more difficulties in pumping, spreading, and compacting. At the same time, the paste has a lower dynamic yield stress due to delayed hydration. Heat treatment effectively denatured the organic content, mitigating these limitations. Beyond 300°C, mortars with eggshell powder demonstrated compressive strength comparable to those containing limestone powder. At 500°C, all organic impurities were eliminated, rendering the eggshell powder hydrophilic, similar to limestone powder. Scaling heat treatment to an industrial level would incur minimal costs and carbon emissions compared to portland cement production. Thus, waste eggshells can be effectively valorized for blended cement, achieving a 35% portland cement replacement.