Effects of aggregates and microfillers on the flexural properties of concrete

A flexural strength theory for concrete based on the elastic-plastic theory was derived. In the tests performed the failure criterion of the plain concrete beam was found to be the tensional rupture strain ε_u which had the value of 0·000 16 irrespective of the different concrete compositions. The elastic-plastic flexural strength f_tp was shown to be almost a linear function of the modulus of elasticity of concrete. The problem of enhancing the flexural strength of concrete was transformed into the problem of increasing the modulus of elasticity of concrete. Concrete was modelled as a three-phase material consisting of aggregate, binder matrix and transition zone phases. The transition zone between the binder matrix and the aggregate particulates was reasoned to be around the aggregate particles which had a diameter exceeding 75 μm. The modulus of elasticity of concrete was modelled by an improved law of mixtures in which an adhesion factor was introduced. The adhesion factor takes into account the bond interaction between aggregate particulates and the binder matrix. The results of the theory derived were compared with the test results from concretes in which three different aggregates and two microfiller types, mainly, were used.