Utilization of recycled fired clay brick as a supplement in an acidic environment to create geopolymer materials based on volcanic ash

This work aimed to assess how recycled fired clay brick affects the physical, microstructural and compressive strengths of volcanic ash based geopolymer materials made in an acidic environment. The volcanic ash was substituted with 0, 10, 20, 30 and 40 wt.% of recycled fired clay brick powder. A phosphoric acid solution with a molarity of 10 M is utilised as hardener. When the amount of recycled fired clay brick is increased from 0 to 40 wt.%, the compressive strengths of the geopolymer materials rise from 23.19 to 62.22 MPa, water absorption and porosity decrease from 7.73 to 5.96% and from 13.66 to 11.61%, respectively. The compact and dense microstructures can be observed on the micrographies of the acid-based geopolymer materials. It can be concluded that incorporation of recycled bricks into volcanic ash improves cohesion between the two aluminosilicate sources in the presence of phosphoric acid, resulting in higher compressive strength of acid-based geopolymers.