Performance evaluation of fly ash–copper slag-based geopolymer bricks

This study investigates the production and evaluation of geopolymer bricks made from a blend of fly ash, copper slag, soda ash activator, and sand as fillers. Locally abundant industrial and mining waste materials were selected as the primary components. The bricks were synthesized using two binders: 60% fly ash with 40% copper slag, or 70% fly ash with 30% copper slag. Both were milled with the activator at a 0.2 soda ash-to-precursor ratio. Fine sand was added to the mixes at 1:2 and 1:3 binders-to-sand ratios. The bricks’ physical, mechanical, and durability properties were examined through compressive strength, modulus of rupture, density, water absorption, drying shrinkage, and efflorescence test, and their performance was compared to established industry standards. The experimental findings indicate that bricks made with 60% fly ash, 40% copper slag, and a 1:2 binder-to-sand ratio exhibited optimal compressive strength (9.64 MPa) and water absorption (7.5%) at 28 days of curing age. Conversely, there was only a marginal increase of up to 4.7% in the strength of the formulation with 70% fly ash and 30% copper slag, attaining a compressive strength of 4.9 MPa between the curing ages. Furthermore, the results indicated a positive correlation between the density and compressive strength of the geopolymer bricks at similar curing ages. The bricks’ density showed minimal variation with curing age and the highest modulus of rupture value observed was 2.5 MPa. The optimal bricks also exhibited relatively low linear shrinkage, good resistance to efflorescence, and met the relevant industry standards.