Valorization of geopolymer technology for the production of sulfate resisting normal and lightweight sustainable concrete

The impact of sulfate attack on both regular and lightweight geopolymer concrete, as well as its properties, has been investigated, including the examination of its microstructural behavior over immersion time. The binders used were an equal mix of slag and fly ash, activated with 10 M sodium hydroxide. The control concrete mix design was 1:1.5:2.8 (binder: fine aggregate: coarse aggregate), with aluminum slag partially replacing 10% of the slag to produce lightweight geopolymer concrete. The curing process was conducted in seawater for up to 6 months to assess the stability of the concrete mixes. The characterization of the hardened mixes was performed using XRD, FTIR, and SEM techniques, along with compressive strength and bulk density measurements. The results revealed that the strength of the geopolymer concrete mixes increased for the first month of immersion, followed by a gradual decline over the next 6 months, but still remained equal to or greater than the control (28 days). XRD, FTIR, and SEM analysis confirmed that the three-dimensional geopolymer chains filled most of the matrix pores. However, for the lightweight matrix, voids were more widely distributed within the matrix, which contributed to the decreased density when aluminum slag was used as an additive.