The use of CO₂-treated wash water as mixing water in concrete

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University of New Brunswick


Concrete is the most widely used construction material and the process of concrete production is responsible for the consumption of large amounts of water. Cleaning of concrete mixer trucks also consumes a massive quantity of water and it generates concrete wash water which has significant environmental and financial concerns. Reuse of wash water to produce fresh concrete is identified as a potential solution, but untreated wash water affects fresh concrete properties. The main objectives of this study are to treat wash water with carbon dioxide (CO₂) in order to eliminate the problems encountered with untreated wash water and to investigate the possibility of replacing potable water with CO₂-treated wash water for the production of concrete. This study was conducted in three phases; chemistry of wash water, mortar testing, and concrete testing. Several chemical and physical properties, such as pH, bound water contents, cation and anion concentrations in wash water, surface and bulk resistivity of concrete, and compressive strength of concrete and mortar, were analysed during this study. Freeze-thaw resistance of concrete produced with CO₂-treated wash water was also examined. CO₂-treated wash water demonstrated impressive performance. Particularly, 75 and 100% CO₂-treatment successfully prevented further hydration of the cementitious component of wash water. Moreover, almost all concrete and mortar mixtures produced with CO₂-treated wash water displayed comparable or better results than the control mixtures. Results have shown that the solids in CO₂-treated wash water have cementitious properties and have contributed to strength development. Based on the results obtained from this study, it was concluded that CO₂-treated wash water can be used as mixing water in concrete.