The effect of aggregate concentration upon the strength and modulus of elasticity of concrete

Synopsis The paper presents details of art investigation into the effect of aggregate concentration upon the strength and modulus of elasticity of concrete in both uniaxial tension and uniaxial compression. The test results relate to cement paste and to mixes containing 20 to 80% by volume of a graded aggregate. Emphasis was placed on accurate determination of the specific gravity and absorption of the constituent aggregate size fractions in an attempt to maintain a constant free water Icement ratio in the various mixes. The specimens were continuously rotated during the setting period in order to minimize settlement of the aggregate particles. The results suggest that the strength of cement paste in tension and in compression is reduced by the addition of 20% by volume of graded aggregate, falling to a minimum value at a volume fraction of 30 to 35% and then increasing with further addition of aggregate. In contrast, the modulus in tension and in compression increases with the addition of aggregate and the measured values are compared with theoretical predictions based upon the laws of mixtures.