Quasi-brittle materials like cement-based composites, rocks, and bricks are subjected to a number of environmental loadings throughout the life cycle of buildings. For instance, fluctuation of the ambient temperature (climatic cycles or fire) causing a variety of physical and chemical transitions resulting in structural changes and affecting the mechanical properties. In this work a special mixture containing glass spheres and Portland cement was evaluated by a combination of four-point bending and time-lapse X-ray computed tomography to verify the feasibility of this novel combined method.
The effect of temperature on the behavior of investigated material in terms of sphericity of the present glass spheres and the way of crack propagation under load together with its influence to mechanical fracture parameters was studied. The described methodology was used especially to be able to monitor these changes throughout the loading process, as the characterization of the fracture surface using conventional optical methods is possible only after the complete fracture of the specimen and total damage of used material results in loosening of the matrix and filler to such an extent, that the results of these methods may be very distorted. It has been proven that the developed method can be used to characterize the internal structural changes in building materials and thus contribute to the understanding of the fracture processes during mechanical loading. Up to 600°C the glass spheres stay spherical and the crack is propagating through the interfacial transition zone, while at higher temperatures the glass loses its shape and the newly formed pores cause also cracks within the inclusions. The relationship between compressive strength and the maximum loading temperature was confirmed.