Performance and Sustainability of Alkali-Activated Mortar Incorporating Corncob Biochar and Recycled Powder

Recycled powder (RP) and biochar have shown significant application potential in the field of green building materials due to their cementitious activity and carbon sequestration properties. In this study, alkali-activated mortar (AAM) was prepared by replacing part of the slag powder with RP and adding corncob biochar (CB). The effects of RP and CB contents on the mechanical properties, drying shrinkage, microstructure, and environmental benefits of the AAM were systematically studied. The results showed that the drying shrinkage of the AAM decreased with increasing RP and CB contents, while the mechanical properties first increased and then decreased with increasing content. At 10% RP and 3% CB, the AAM exhibited optimal mechanical properties, with a 28-day flexural strength of 8.8 and a compressive strength of 62.5 MPa. Microstructural analysis revealed that CB had a significantly porous structure, effectively reducing the drying shrinkage of AAM. The drying shrinkage of specimen A-20-4 at 56 days was 11.7% lower than that of specimen A-20-0. Furthermore, RP and CB did not produce any new substances within the alkali-activated system. CB and RP had significant environmental benefits, with the CO₂ emissions of A-20-4 being 59.2% lower than those of ordinary cement mortar. This study contributes to the research and application of CB and RP in AAM, offering positive implications for the sustainable development of the building materials industry and environmental protection.