A statistical model for mechanical properties based on the microstructure of concrete

The aim of the present study was to develop a statistical model for the static strength of concrete, which would be based on the Optical micro-structural analysis of concrete. The composition of concrete was analysed optically and modelled as a composite material using the statistical theory of combined parallel and serial systems of basic elements. Concrete is modelled as a composite material consisting of aggregate particles, cement paste and voids. The voids include pores larger than 15 my m in diameter and microcracks over 15 my m in length. The length of microcracks is modelled as a fictive crack corresponding to the modified Griffith's theory. The pores are also modelled as fictive cracks in accordance with the method of Bache. The location of the cracks is modelled statistically against the Poisson distribution. The random distribution of the crack direction has been taken into account in the model. The compressive and bending tensile strengths of six test specimens were calculated with the model of combined parallel and serial systems, using the results of optical microstructural analysis of the samples. The calculated values were compared with the test results. The deviation of the calculated values from the test resuIts varied from 2.5 % to 17 % (mean 6 %) in the case of compressive strength and from 0 % to 26 % (mean 10 %) in the case of bending tensile strength. The greatest source of error was the approximative optical analysis of the microcracks, which is to undergo further development.