The influence of microstructure geometry on the scale effect in mechanical behaviour of heterogeneous materials

There are a significant number of factors which have impact on the scale effect in the mechanical behaviour of composite materials. In this paper, the influence of the microstructure on this phenomenon is examined. In particular, how the results of the uniaxial compression test are affected by the microstructure geometry is verified. For the purposes of this study, two different materials are chosen, i.e. pure gypsum and mortar. Firstly, the microstructures of the two considered materials are compared with the use of different microstructure measures, i.e. attenuation profiles, porosity and pore size distributions, calculated based on the images obtained from the X-ray microCT. Then, a series of uniaxial compression tests is performed for a large number of cylindrical specimens made of the two materials under study. Four different sample diameters are assumed in order to investigate the size effect in the considered composites. For both materials, the results of uniaxial compressive strength and the Young modulus are presented. The relationship between the microstructure of the material and the scale effect in mechanical properties is proved. The scale effect is more demonstrable in the case of the material which exhibits a more heterogeneous microstructure.