| Summary: | A study was conducted into the quality of recycled water at a ready-mix concrete plant to determine its suitability as mixing water for concrete. Concrete mixes made at a water/cementitious ratio (w/cm) of 0,5, with or without 50% ground granulated blast-furnace slag, and mortars of 0,47 w/cm were prepared using municipal and recycled water. Recycled water was used to replace municipal water at various proportions of 0, 30, 50 and 100%, then used as mix water. Tests were done on fresh and hardened concretes and mortars. The chemical impurities present in the recycled water satisfied the limits given in SANS 51008 /EN 1008 and ASTM C 94 for mix water. The use of recycled water as mix water led to a slight reduction in slump of concrete or flow of mortar. Hydration heat output and air permeability were not affected, and mortar compressive strengths increased with a rise in the proportional amount of recycled water used in the mix. In mortars, the use of 100% recycled water gave a substantial increase in strengths of up to 8%. Within the limitations of this study, it was found that recycled water from ready-mix concrete plants can be suitable for use as mix water in concrete-making.
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