Influence of adding silica sand powder on the macroscopic properties and microscopic pore structures of waste-fired clay brick-based geopolymers

The task of this research is to examine the behavior of silica sand powder on the macroscopic properties and the microscopic pore structures of non-calcined and calcined waste-fired brick-based geopolymers. In the R³ reactivity test, calcined waste-fired bricks release 460 J/g, while non-calcined waste-fired bricks release 457 J/g. The findings highlight that the compressive strength of waste-fired clay brick-based geopolymers increases from (44.96 ± 1.17) to (54.45 ± 1.73) MPa after the addition of 30 g of silica sand powder. When 40 g of silica sand is added, it decreases from (54.45 ± 1.73) to (50.71 ± 1.69) MPa. The compressive strength rises from (53.16 ± 1.69) to (64.89 ± 1.96) MPa when 10 g of silica sand powder is added to the calcined waste-fired clay brick. It decreases from (64.89 ± 1.96) to (49.04 ± 1.32) MPa if 40 g of silica sand is added. The mercury intrusion porosimetry results demonstrate that the geopolymers contain mesopores and macropores. The range of pore size diameters of the calcined waste-fired clay brick-based reference geopolymer (5–60 nm) is smaller than that of the waste-fired clay brick-based geopolymer (5–94 nm). It was found that the addition of 30 and 10 g of silica sand powder to geopolymers made from non-calcined and calcined waste-fired clay bricks, respectively, tended to increase siloxane chains, convert macropores into inaccessible finer pores.