Influence of acetic acid waste solution as mixing water on early hydration, compressive strength, and microstructural properties of concrete

Utilizing the waste solution generated from acetic acid treatment of recycled coarse aggregate (RCA) as the mixing water in the concrete presents a sustainable approach that eliminates secondary waste, effectively transforming this treatment into a zero-waste process. This research aim was to investigate the influence of waste solutions on early-stage cement hydration and later-age compressive strength of concrete. In-situ Raman spectroscopy was employed to continuously monitor the transformation of cement clinker phases into hydration products for the first 1–8 h of hydration. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) were performed to investigate the microscopic mechanisms through which the waste solutions affect the hydration process and microstructural development of concrete. The results showed that the use of waste solution promoted the early formation of calcium silicate hydrate (C-S-H), ettringite, and calcium hydroxide (C-H). Although the compressive strengths at 7 and 28 days were similar to those of the tap water mix, the strength increase of up to 19.3 % was observed at 90 days. This improvement was supported by phase composition and microstructural analyses, which revealed additional C-S-H formation and calcite precipitation. The results provide the valuable insight into the potential applications of the waste solution in sustainable concrete production.