Upcycling of recycled brick powder as a substitute for precursor and sand in completely recycled geopolymer: From micro to macro perspective

Upcycling of recycled brick powder (RBP) as an eco-friendly precursor for sustainable geopolymer is an effective pathway for the high-value recycling of clay brick waste. This study investigates the feasibility of preparing completely recycled geopolymer by substituting RBP for both FA-GGBS precursors and river sand (RS), aiming to optimize the RBP substitution method and percentages to achieve a sustainable geopolymer with high performance, as well as to reduce the demand for precursors and RS. RBP exhibits certain alkali-activation reactivity and favorable micro-aggregate filling effects, demonstrating the potential to simultaneously replace both the precursor and aggregate. Substituting a high proportion of RBP for precursors is detrimental to the geopolymerization reaction, resulting in a deterioration in the micro-macro properties of geopolymer. However, replacing an appropriate amount of RS with RBP can refine the microstructure and enhance the mechanical strength and permeability resistance of geopolymer. At an appropriate substitution rate of RBP, the positive effects of replacing RS with RBP on the geopolymer performance can offset the adverse effects of replacing precursors with RBP. By optimizing the RBP substitution percentages for precursors and RS, completely recycled geopolymer meeting various performance requirements can be prepared. When the RBP substitution rate for precursor-RS is 0 %-0 %, 30 %-0 %, 0 %-30 %, 30 %-30 %, and 50 %-50 %, the 28-day compressive strengths of the blending geopolymer are 69.0, 63.3, 78.1, 67.4, and 55.0 MPa, respectively.