CHARACTERISATION OF THERMAL-LOADED CEMENT-BASED COMPOSITES BY COMBINED TIME-LAPSE TOMOGRAPHY AND THE FOUR-POINT BENDING TEST

Abstract

Quasi-brittle materialslike cement-based composites, rocks,and bricksare subjected to a number ofenvironmental loadings throughout the life cycleof buildings. For instance, fluctuation ofthe ambient temperature (climaticcyclesor fire) causing a variety of physical and chemical transitionsresultinginstructural changesand affectingthe 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 tomographyto verify the feasibility of thisnovel combined method.The effectof temperature on the behavior of investigatedmaterial in terms of sphericity of the present glass spheresand the way of crack propagation under load together with its influenceto mechanical fracture parameterswas studied.The described methodology was used especially to be able to monitor these changes throughout the loading process, asthe characterization of the fracture surface using conventional optical methods is possible only after the complete fractureof the specimenandtotal 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 hasbeen 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 temperaturewas confirmed

Keywords

• fine-grained cement-based composites
• quasi-brittle material
• x-ray computed tomography
• instrumented four-point bending test
• crack path