The effect of carbon curing and thermal curing on the strength of geopolymer mortars and efflorescence assessment

Abstract

The intensification of global warming has been linked to increased carbon dioxide (CO₂) emissions, with the construction industry among the main contributors. Portland cement production plays a significant role in these emissions, encouraging the development of alternative materials with a lower environmental footprint. Among these alternatives are geopolymers, produced through the alkaline activation of aluminosilicate-rich residues such as fly ash and metakaolin, with the possibility of incorporating additives like biochar. This study evaluated the effect of thermal and carbon curing on the mechanical strength and efflorescence of geopolymer mortars with and without biochar, using two mix designs (REF-5 and BCA-6). Specimens were subjected to three curing conditions: ambient, thermal, and carbon. Results showed that ambient curing led to the best mechanical performance (21.1 MPa for REF-5 and 19.3 MPa for BCA-6), while thermal and carbon curing resulted in lower values. The inclusion of biochar improved early-age strength (14 days) and significantly reduced surface salt accumulation, indicating lower susceptibility to efflorescence. It is concluded that the use of geopolymers with biochar under ambient curing presents a viable and sustainable alternative to Portland cement, although thermal and carbon curing did not show mechanical advantages.