Sustainable utilization of concrete wash water: A critical overview of fresh and hardened properties

The global construction industry seeks sustainable solutions for its primary waste stream, concrete wash water (CWW). This alkaline, solids-laden effluent from ready-mix operations requires careful management. While numerous studies exist, a clear gap remains in the literature: a holistic understanding is hindered by fragmented and inconsistent findings stemming from the lack of a unified framework to interpret the performance of different CWW types and experimental designs. This review addresses this gap by adopting a narrative, critical approach supported by a structured literature search (1994-2025). It establishes a performance-oriented classification distinguishing raw slurry, settled supernatant, reclaimed effluent, dried sludge, and beneficiated water. Analysis reveals untreated CWW typically reduces workability (5-30% slump loss) and accelerates setting time due to its high pH and suspended solids. A central contribution is resolving the dichotomy in compressive strength: mixes targeting a constant slump often show strength gains (3-20%) from a lower effective w/c ratio, whereas fixed-w/c designs exhibit strength reductions (5-15%) from dilution effects. Durability outcomes are complex; some studies report reduced water absorption and porosity, while others note increased chloride permeability unless supplementary cementitious materials (SCMs) are used. Innovative treatments, particularly CO₂ mineralization and synergistic combinations with pozzolans like zeolite, demonstrate significant promise to stabilize CWW chemistry and enhance performance. By contextualizing results within this unified framework, this review clarifies existing contradictions and outlines future research priorities in long-term durability, rheology, economic feasibility, and large-scale implementation for the sustainable integration of CWW in construction.