Nowadays the global trend in construction industry is to reduce the cost, saving energy and preserving the environment. Using other industries' waste material as a construction material is one of several methods followed to meet these trends. Management of solid waste is considered as one of the most significant environmental issues not only in a country like Oman, but globally as well. Around 1.7 million tons of solid waste is yearly generated in Oman. More than 120 million tons of constriction demolition waste is yearly generated over the world. Besides, 10-30 % of solid wastes produced from construction field (concrete wastes and aggregate) in Oman is just dumped in the landfill area without any further use. In this paper, the influence of replacing the demolition waste with coarse aggregate on the mechanical properties of concrete was studied in terms of compressive, flexural, and tensile strengths, and workability. The concrete properties were evaluated by replacing of 20, 30 and 40% of coarse aggregates with demolition waste in the mix proportion of C-35 concrete and the experiment's results were compared with each other as well as with the conventional one, based on two different periods of 7 and 28 days. The results were satisfactory so it could be concluded that replacing of up to 40% of coarse aggregates with construction and demolition waste is still safe and not causing dramatic reduction in the concrete strength.