Strength enhancement of pumice-based geopolymer paste by incorporating recycled concrete and calcined oyster shell powders

Abstract

In this research, the effect of recycled materials powder on the properties of pumice-based geopolymer paste was studied. Two waste materials viz., ground recycled concrete (RC) and calcined oyster shell (CS) were used to replace pumice powder (PM) at 0–50% by weight. Sodium hydroxide (NaOH) with a concentration of 10 M and sodium silicate (Na2SiO3) solutions at the ratio of 1.00 were used as alkali-activators. A liquid to binder ratio of 0.60 was used for all mixes. Compressive strength and microstructure analysis of geopolymer paste by SEM/EDS, XRD, FTIR, and MIP were tested. The results showed that the compressive strength increased with increasing RC and CS contents. Maximum 28-day compressive strengths of 27.1 and 26.6 MPa were achieved by incorporating 50%RC and 50%CS, respectively. The morphology analysis indicated that the crystalline phases of calcium silicate hydrate (C-S-H) were formed and coexisted with the geopolymer gel, which increased the density and homogeneity, and decreased the pore size of geopolymer pastes. Based on the results, it can be concluded that both RC and CS can be used to enhance the properties of pumice-based geopolymers.

Keywords

• Geopolymer paste
• Pumice
• Recycled concrete
• Calcined oyster shell
• Compressive strength
• Microstructure