Sustainable activator: the usability of anodizing cleaning solution for the synthesis of alkali-activated soil-fly ash

This research is to investigate the usability of a recycled NaOH solution remaining after the anodizing procedure to modify subgrade soil, where its uniaxial compressive strength value must be at least 1033 kPa to meet the minimum resilient modulus. Different percentages of fly ash, i.e., 10% to 50%, were used to evaluate the influence of fly ash/solid and activator/fly ash ratios on the performance of the activator at room temperature. The results of uniaxial compressive strength and indirect tensile strength illustrate that the anodizing cleaning solution works well to develop alkaline activation processes. Its best performance was observed for the fly ash/solid and activator/ash ratios equal to 20% and 1.146, respectively. Indeed, a higher activator content/fly ash associated with a lower Si/Al and fly ash/solid ratios lead to maximum mechanical improvement for a low Na concentrated activator. Microstructural analyses showed binding gel formation along with clay minerals transformations.