Study on the Mechanical Development of Alkali Coral Cementitious Materials Excited by Weak Alkali and the Formation, Development and Evolution of Gel Structure

In this study, alkali-activated materials (AAMs) were developed using finely ground coral powder (CP) and granulated blast furnace slag (GBFS) as the primary raw materials, weak alkali as the activator, and sea sand as the fine aggregate. The influence of raw material composition on the macro-mechanical properties was analyzed. Further, combined with micro-analysis techniques, the characteristics of micro-crystal formation and transformation, governed by raw material properties, and the formation and development mechanism of the enhanced micro-gel structure were elucidated. The results indicate that the activation effect of Ca(OH)2 is significantly superior to that of Na2CO3. The excessively high calcium content and insufficient silicon and aluminum content in CP hinder gel formation and mechanical properties development. GBFS addition optimized the calcium-silicon-aluminum ratio and significantly improved CP reactivity. Also, compressive strength is enhanced considerably, accompanied by continuous optimization of the micro-gel structure as the GBFS content increases. At a GBFS-to-CP optimal ratio of 1:1, compressive strength of 21.8 MPa could be achieved at 28 days of age. However, the strengthening effect significantly reduced for the GBFS content > 50%. GBFS promotes the continuous formation of a zeolite-like phase gel structure, leading to a substantial improvement in compressive strength.