Mechanical and Microstructural Properties of Geopolymer Incorporated with Copper Slag Activated by Phosphoric Acid

Abstract

Abstract In this study, fly ash (FA), a kind of aluminosilicate precursor, is activated by phosphoric aid (H3PO4) to produce a silico-aluminophosphate geopolymer. This study aims to assess the viability of substituting M-sand with varying proportions, ranging from 0 % to 100 %, of copper slag in geopolymer mortar. The alkaline-activated geopolymer mortar was produced by using sodium hydroxide (NaOH) and sodium silicate. The phosphoric acid-activated geopolymer (PGP) samples were produced by changing parameters such as the liquid/solids (L/S) ratio, curing temperature, and molarity of H3PO4. The L/S ratios examined were 0.8, 0.9, and 1.0, whereas the molarities of H3PO4 employed were 8 M, 10 M, and 12 M. An assessment was conducted on the compressive strength, scanning electron microscope (SEM) examination, Fourier-transform infrared spectroscopy, X-ray diffraction, and energy dispersive X-ray analysis of PGP. The findings indicated a positive correlation between the compressive strength and the molarity, whereas a negative correlation was observed between the compressive strength and the L/S ratio. The highest compressive strength obtained was 41.1 MPa, which occurred when the optimum concentration of H3PO4 was 10 M. The formation of the P-O-Si-O-Al-O polymeric structure contributed to the strength of the phosphoric acid-based FA geopolymer. The SEM images demonstrated that the geopolymer samples containing 100 % copper slag and a L/S ratio of 0.9 exhibited a compact and uniform microstructure, resulting in enhanced strength characteristics.