International Science and Technology Journal

Aggregate is considered a vital component of the concrete industry. It is occupied about 70 to 80% of the total volume of concrete, in addition to decrease cost of making aggregate compared to the cement industry[1,2]. The aim of this paper is to increase the ratio of sand to total aggregate by replacing part of the coarse aggregate and adding it to the sand while maintaining the same total amount of aggregate in all concrete mixtures in order to reduce the cost and environmental pollution resulting from the manufacture of coarse aggregate. soft aggregate is mostly natural sand, it is advisable to exploit the largest amount of it provided that it does not affect the properties of concrete. In this study, the ratios of soft aggregate to total aggregate were determined as follows 0.38-0.45-0.48. Experimental results show that an increase in the proportion of soft aggregate from 0. 38 to 0. 45 by 10% can lead to improvement of concrete strength. This improvement can be reduced at the level of increase to 15%. Increased soft aggregate leads to a decrease in the concrete workability. Key words: High strength concrete, Workability, sand aggregate ratio, water cement ratio, surface area.