Characterization of brick and brick–mortar interface under uniaxial tension

Abstract

Softening is a gradual decrease of mechanical resistance under a continuous increase of deformation imposed on a material specimen or structure. It is a salient feature of quasi-brittle materials like clay brick, mortar, ceramics, rock or concrete, which fail due to a process of progressive internal crack growth. Such mechanical behavior is commonly attributed to the heterogeneity of the material, due to the presence of different phases and material defects, like flaws and voids. The initial stresses and cracks as well as variations of internal stiffness and strength cause progressive crack growth when the material is subjected to progressive deformation. Initially, the micro cracks are stable which means that they grow only when the load is increased. Around peak load an acceleration of crack formation takes place and the formation of macro cracks starts. The macro cracks are unstable, which means that the load has to decrease to avoid an uncontrolled growth. In a deformation controlled test the macro crack growth results in softening and localization of cracking in a small zone, while the rest of the specimen unloads. For tensile failure this phenomenon has been well identified for concrete but very few results exists for masonry. In the present paper, the results of an extensive set of tests, carried out at University of Minho, including brick specimens and masonry specimens under uniaxial tension will be presented. Both tensile strength and fracture energy are quantified, for different bricks and different types of brick-mortar interface.