Determining aggregate size & shape effect on concrete microcracking under compression by means of a degree of reversibility method [Conference Object]

Abstract

It is an established fact that Interfacial Transition Zone (ITZ) between aggregate and mortar matrix, is the weakest area in the concrete composites. Crack initiation and propagation along the ITZ depends on the stress concentration in the ITZ and also to the matrix quality surrounding it. Under uniaxial compression tensile strains are produced in the transversal directions creating cracks along the axial direction. Thus, evaluation of the degree of reversibility (degree of reversible strain) with the level of loading determines the extent of microcracking (permanent damage) within the material at a certain loading level. The recorded strains provide an indirect method for understanding and quantifying the general relationship between stress level and crack development. In this study the effect of the aggregate size and shape and also the mortar matrix quality on the degree of reversibility were evaluated by subjecting the specimens to three different compressive stress levels (40, 60 and 80% of ?<inf>c</inf>). Experiments were designed and carried out on mortars with two different w/c ratios containing single spherical, cylindrical and prismatic steel aggregates of different sizes. The degree of mechanical interlocking and internal stress concentration around the aggregate, related to the aggregate surface characteristics, has a significant influence on microcracking behaviour of concrete. Furthermore, aggregate surface characteristics become more pronounced with increased matrix quality.