Effect of Sea Sand and Recycled Aggregate Replacement on Fly Ash/Slag-Based Geopolymer Concrete

Abstract

The purpose of this study is to investigate the impact of recycled aggregate and sea sand replacement on fly ash slag-based geopolymer concrete (GPC). An orthogonal array design is employed to obtain the optimum mix proportions, and geopolymer mixes are prepared using slag percentages of 10%, 20%, and 30% slag in fly ash/slag-based GPC. Sodium hydroxide (NaOH) solution is prepared at three concentrations (8, 12, and 16 mol/L). The mechanical properties of the geopolymer mixes are determined based on the tensile strength, compressive strength, flexural strength, and elastic modulus. GPC is prepared using water-binder ratios of 0.3, 0.4, and 0.5 at 0%, 25%, 50%, 75%, and 100% of recycled aggregate (RA) replacement. The results showed that the variation in the RA replacement ratio had little effect on the strength and elastic modulus of sea sand geopolymer concrete (SS-GPC), but it had a significant effect on river sand geopolymer concrete (RS-GPC). The RA replacement ratio also showed a noticeable change in the damage surface of the specimens. In addition, sea sand (SS) hinders the hydration reaction of the geopolymer in the early stage and reduces the early strength of the GPC; however, in the later stages, the effect becomes insignificant. Compared with OPCC, the energy consumption and CO 2 emission of GPC are respectively reduced by 34.3% and 36.3% when using natural aggregate (NAs), and by 34.9% and 38.3% when using recycled aggregate.

Keywords: Geopolymer concrete, Recycled aggregate, Sea sand, Mechanical properties, microstructure, Fly ash