New insights into the effects of silicate modulus, alkali content and modification on multi-properties of recycled brick powder-based geopolymer

Abstract

Utilizing recycled brick powder (RBP) as a green precursor to prepare alkali-activated RBP-based geopolymer (AABG) not only broadens the existing system of alkali-activated materials but also achieves the high-value and low-carbon utilization of clay brick waste. This paper aims to systematically investigate the influence of silicate modulus and alkali content of the alkali-activator on the multi-properties AABG, while proposing multi-path modification methods to optimize AABG performance. Substituting an appropriate amount of metakaolin with RBP contributes to optimizing the performance of metakaolin-based geopolymers. However, the micro-macro properties of AABG are significantly inferior to those of metakaolin-based geopolymer. Under the same silicate modulus, the micro-macro properties of AABG first improve and then deteriorate with the increase in alkali content. With the alkali content of 8%, the AABG owns the best microstructure and macro properties. When the alkali content remains constant, an appropriate increase in the silicate modulus of alkali-activator contributes to the performance enhancement of AABG mortar. The average pore diameter of AABG-1.2M-8%, AABG-1.4M-8%, and AABG-1.4M-4% paste is 69.4 nm, 61.8 nm and 111.9 nm. Overall, the AABG with 1.6M silicate modulus and 8% alkali content shows good performance. For the multi-path modification methods of AABG, decreasing the w/b ratio of AABG can enhance its compressive strength and permeability resistance. Besides, increasing the curing temperature of AABG can optimize its micro-pore structure and macro-properties, achieving optimal performance at a curing temperature of 80°C. Finally, mixing Ca(OH)2 into AABG promotes the formation of more C-A-S-H, thereby further enhancing the AABG performance. Optimizing the silicate modulus, alkaline content and modification methods, it is feasible to produce AABG with superior micro-macro properties.