This paper investigates the effect of using wastewater on the properties of high strength concrete. Wastewater samples were collected from three car washing station in Muscat area. The collected wastewater samples were mixed together and chemical analysis was carried out. Four water samples, including a controlled potable (tap) water were analysed for pH, total dissolved solids (TDS), chloride, hardness, alkalinity, and sulfates. Chemical analysis results showed that although the chemical

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... itions of wastewater were much higher than those parameters found in tap water, the water composition was within the ASTM standard limits for all substance indicating that the wastewater produced can be used satisfactorily in concrete mixtures. High strength concrete mixtures were prepared using different proportions of wastewater and water-to-cement ratio of 0.35. The percentage of wastewater replaced ranged between 25-100% of tap water used in concrete. For each concrete mixture, Six 150mmx150mmx150mm cubes, three 300mmx150mm dia. cylinders and three 100mmx100mmx500mm prisms were cast. Slump, compressive, tensile and flexural strengths were determined at 28-day of curing. Cube compressive strength was also determined at 7-day of curing. Also, initial surface absorption test was conducted at 28-day of curing in order to assess the durability of concrete. Results indicated that the strength of concrete of the mixtures prepared using wastewater was comparable with the strength of the control mixture. Also, the water absorption of concrete is not affected when wastewater was used.