Reuse of waste water from ready‐mixed concrete plants

Purpose The purpose of this study is the examination of the properties of waste water obtained from a ready‐mixed concrete plant and its utilization potential as mixing water for concrete production. Design/methodology/approach Samples of waste water from several points of a water recycling process from a ready‐mixed concrete plant were examined for their chemical properties (Cl ‐ , SO 4 2‐ , alkalies, total solids, pH) and compared with the specifications applied for concrete mixing water. Also samples of dry sludge powder from the water‐recycling process tank were taken and tested for their chemical composition, particle size distribution, mineralogical composition and thermogravimetrical results. The water samples were examined for their behavior in concrete specimens with and without admixtures and also for their effect in water demand and setting times in cement pastes. Findings All tests showed that waste water is suitable for concrete mixing water and that it can be used without any treatment or dilution, thus contributing to water saving. Practical implications Waste water from ready‐mixed concrete plants is classified as waste hazardous for disposal due to its high pH value (over 11.5). Very few ready‐mixed concrete plants that recycle waste water follow a complicated process through multiple overflows and a stage of neutralization, with HClaq addition. Originality/value It is obvious that the results of this investigation contribute to the protection of the environment from hazardous waste water disposal and the ready‐mixed concrete industry from fresh water costs and any additional cost for buying and conserving an unnecessarily complicated water‐recycling system.