Formulation of geopolymer binder based on volcanic-scoria and clay brick wastes using rice husk ash-NaOH activator: Fresh and hardened properties

The present study investigated the influence of the replacement of waste clay bricks (WB) by volcanic scoria (Zg) on the fresh and hardened properties of geopolymer binders for potential construction applications at ambient temperature. Geopolymer paste samples were prepared using Zg as raw material blended with WB ranging from 0 to 50 wt% of total raw materials. Alternative alkaline activator used for the geopolymer synthesis was prepared by mixing rice husk ash (RHA) and 6 mol/L of NaOH solution. The geopolymers were cured at room temperature for 28 days, then subjected to mechanical property tests; microstructural and macrostructural characterization studies. Results showed that both flowability and setting time of geopolymer mixtures decreased with increases in WB content. The reduction in workability could be attributed to increase in the relatively rough surface of WB particles, which resulted in inter-particle friction. Flexural strength increased from 4 to 12 MPa while the compressive strength 24–52 MPa with the increase in WB up to 50%. The WB powders enriched Al content in mixtures, establishing the Si-O-Al bonds, confirmed by 27Al MAS NMR spectroscopy exhibiting the more Al(IV) sites integrating the N-A-S-H network. Incorporating the WB powders contributed to the development of densified matrix.