Engineering properties of geopolymer concrete composites incorporated recycled plastic aggregates modified with nano-silica

The novel approach of reusing recycled plastic in construction instead of landfilling has gained recognition. However, the inclusion of recycled plastic aggregates (RPA) tends to have a negative impact on various concrete properties. Previous studies have explored surface treatment techniques to mitigate these effects. Nevertheless, there is limited research on enhancing the properties of RPA geopolymer concrete (GPC) through the addition of nano-silica (NS) particles in to the GPC mixtures. This study aims to experimentally investigate the properties of GPC incorporating RPAs modified with NS particles. The experimental program consists of seventeen mixtures divided into three stages. In the first stage, the effect of NS addition on the performance of GPC mixtures was evaluated. Moreover, the effect of different percentages of RPAs was investigated in the second phase. In the third stage, the optimum percentage of NS particles found in the first stage was utilized to improve the performance of GPC mixtures which aggravated in the second stage. The total binder content for all mixtures was 450 kg/m3 which contained 90% of ground granulated blast furnace slag (GGBFS) and 10% silica fume. In the first stage the GGBFS was replaced by 1%, 2%, 3%, and 4% NS particles, while, in the second stage, the natural fine aggregate was replaced by RPAs at six volume fractions (5%, 10%, 20%, 30%, 40%, and 50%). The fresh behaviour of all GPC mixtures was investigated to assess the flowability, setting and cohesiveness of the mixtures. The mechanical behaviour was evaluated for compressive strength, splitting tensile strength, modulus of elasticity, flexural strength, and stress-strain behaviour. Moreover, the microstructure characteristics were investigated to illustrate the modifications that occurred in the microstructure scale. The results indicated that the addition of an optimum percentage of NS particles can significantly restore most properties of RPA-GPC which were degraded due to the addition of RPAs. This technique can help the construction industry to safely use the RPAs in the GPC mixtures without concern about their negative impact on concrete performance.