A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1992

This experimental investigation deals with the influence of aggregate content on the compressive and flexural strengths of a high strength concrete having a 28-day compressive strength of 85 MPa on cylindrical specimen. In addition, the effect on workability and modulus of elasticity of concrete in compression was also determined. The primary objective was to establish the optimum aggregate-cement ratio(A/C) and the sand-aggregate ratio(S/A) of a high strength concrete mix proportion. These ratios were determined based on the compressive strength achievement within a minimum slump value of 150mm. Limestone and basalt aggregates were used for strengths and workabilities comparison. Test results indicated that the optimum A/C ratio for limestone and basalt concretes was 3.25 and 3.0 respectively. Better strengths and workabilities were achieved when using limestone aggregate. It appeared that concrete slump was independent of the aggregate type when the A/C ratio fell below 2.5. The flexural and compressive strengths were found to increase with increasing A/C ratio. So was the modulus of elasticity of concrete in compression. However, the flexural strength increased at a relatively slower rate than its compressive strength. It was found that for a given W/C and S/A ratio, the compressive strength decreased as the cement content was increased but with improved workability. Too low a water-cementitious material ratio might also result in a reduction in strength. Using the optimum A/C ratio of 3.25 for limestone concrete, the cotTesponding optimum S/A ratio was found to be 0.4, in which case the slump, compressive and flexural strengths were found to be maximum.