An improved understanding of the influence of w/c ratio and interfacial transition zone on fracture mechanisms in concrete

The interfacial transition zone (ITZ) is significantly influenced by the water/cementitious materials (w/cm) ratio and governs the overall strength and fracture properties of concrete. Even though an ample number of studies on this topic are available in the literature, there is a lack of unified conclusions pertaining to the influence of w/cm ratios on various fracture characteristics and the underlying mechanisms. In this study, an attempt was made to investigate fracture characteristics (such as the size of the fracture process zone (FPZ), fracture energy, traction-free cracks (TFCs), toughening mechanisms) for varying ITZ properties and water/cement (w/c) ratios. Plain concrete beams of size 700 × 150 × 80 mm (l × d × b) with varying w/c ratios were tested under centre-point loading by controlling the crack mouth opening displacement. The acoustic emission (AE) technique was used to assess the internal damage parameters. A novel method was developed for identifying the TFC tip and the FPZ size using AE event location data at different stages of loading. The role of the ITZ on the fracture mechanisms of different types of concrete was also assessed. Evaluation of the fracture energy revealed that its relation with the w/c ratio is affected by the type of concrete.