Two-parameter Fracture Model Research Articles

Image analysis techniques for characterization of pore structure of cement-based materials

This paper explores several image analysis techniques that provide insight into the nature of pore structure as observed in backscattered electron images of polished sections. Image analysis techniques used in this study include sizing, two-point correlation, and fractal analyses. The spatial parameters computed by these techniques have potential for relating microstructure to material properties. Specimens include plain cement paste, pastes with silica fume, and mortars. Tests include determination of total porosity, mercury intrusion porosimetry (MIP), compression and flexural testing. The two-parameter fracture model is used to characterize fracture properties. Pore size distribution from MIP is compared to pore size distribution derived from BSE images.

The Interfacial Transition Zone and its Influence on the Fracture Behavior of Concrete

AbstractConcrete specimens of constant water-to-cement ratio and varying amounts of gravel aggregate were tested under 3-point bend. The fracture toughness of the composite and surface roughness of the paste are determined. Fracture parameters obtained from the Two ParameterFracture Model (TPFM) such as the critical stress intensity factor (KIc) and critical effective crack extension (Δao) are found to be related to the average surface roughness of the paste. The Interfacial Transition Zone (ITZ) and the bulk paste are distinguished by different values of roughness. The surface roughness of the area adjacent to the aggregate particle is evaluated as a function of the distance from the aggregate surface. In particular, the surface roughness of the paste near the aggregate is greater than that of the paste far from the aggregate, and it decreases with distance from the aggregate. The higher roughness of the paste near the aggregate indicates that aggregate particles, and more specifically the ITZ associated with them, act to toughen the paste in concrete.

Experimental methods for determining fracture process zone and fracture parameters

For quasi-brittle materials like concrete, rock and ceramic it is not possible to determine fracture toughness using laboratory-sized specimens and linear elastic fracture mechanics. This inapplicability of the conventional fracture mechanics is due to fracture process zone, R- curve type of behavior and precritical stable crack growth. In this keynote paper, a two-parameter fracture model developed at Northwestern University is described. The model is based on observations of fracture processes using laser holography as well as acoustic emission measurements.