Effect of aluminosilicate precursors and curing regime on physico-mechanical durability and microstructural characteristics of coral geopolymers (Cor-Geo): Cleaner production for coral islands

This study investigated the mechanical, durability, microstructure, carbon footprint and cost characteristics of new-generation metakaolin-based geopolymer composites. Instead of GBFS, 25 % metakaolin was used, and 25 % and 50 % coral fine aggregate (CFA) was used instead of coral filler (FC). The produced coral geopolymers were cured at 30 degrees C (24 h) and 80 degrees C (8 h). The apparent porosities of coral geopolymers cured in the ambient cured range from 7.3 to 9.2 %, and those heat cured vary between 3.8 and 6.2 %. The immersion water absorption of the ambient cured coral geopolymers exceeded 5 %, while the water absorption of the heat-cured specimens was much lower than 5 %. The dry unit weights of coral geopolymer are between 2100-2200 kg/m3. In ambient cured coral geopolymers, compression strength up to 40 MPa was obtained after 24 h, while compression strength of almost 100 MPa was obtained after 8 h of heat curing. The ambient cured capillary water absorption of the mix with 50 % CFA was 3.5 kg/m2, while the capillary water absorption of the specimen without CFA and heat cured was less than 0.5 kg/m2. Exposed to 750 degrees C, the compression strength of all coral geopolymers was more than 10 MPa. The compression strength of the samples exposed to MgSO4 decreased by 10-60 %. The CO2 emissions of coral geopolymers range between 328 and 340 kgCO2/kg, and their costs between 411 and 442 USD/m3. As a result, it has been determined that geopolymer composites can be used for both prefabricated and construction sites in coral islands with coral aggregates.