<p> Concrete posses more compressive strength compared to mortar of the same cement: aggregate ratio. Here in this study two different coarse aggregates of basalt black stones of 20mm maximum size, were utilised. namely crushed washed basalt stone and unwashed basalt stones. The mix ratio and water/cement ratio adopted for the study was 1:2:4 and 0.6 respectively. Twelve concrete cubes (150mm x 150mm x 150mm) were cast for each coarse aggregate type of which four were crushed at each maturity age namely; 7, 14, 21, and 28 days. The 28 day strengths of the concretes made with crushed washed basalt stone unwashed basalt stones were. 24.0 N/mm2, and 19.9 N/mm2 respectively. Consequently, it was concluded that the strength of concrete depends greatly on the internal structure, surface nature and shape of aggregates.</p>