Microstructure and its relationship to fracture in portland cement mortar and concrete

This research explores the relationship between the geometry of crack propagation and mechanical properties of mortar and concrete. The crack deflection and branching are measured using several microscopy techniques along with image analysis of crack profiles intruded by a low melting-point alloy. The toughness measured by mechanical testing, the fracture surface geometry, phases and elastic properties identified by image analysis and microscopy, along with the crack branching relationships are used to predict the increase in the toughness of these materials with respect to the flat-crack toughness using a micromechanical model. The effect of the model parameters, microscopy techniques, material elastic properties, void modeling and branching ratio were investigated. The parametric analysis and modeling conditions determine a nearly uniform flat-crack toughness for the cement matrix of the mortar samples and a higher flat-wrack toughness for the cement matrix of the concrete samples. The trend toward a single toughness value may be an indication that there is a single material parameter to describe the fracture energy of these materials.