Influence of mix composition and strength on the fracture properties of self-compacting concrete

• Role of composition parameters of SCC mixes on their fracture behaviour examined.
• Specific fracture energy increases as coarse aggregate volume fraction increases.
• Increase in paste to solids ratio results in large decrease in fracture energy.
• Increase in water to binder ratio reduces specific fracture energy.
• Critical crack opening is dominated by the coarse aggregate volume.

Self-compacting concrete (SCC) has undergone extensive investigations that have led to confidence in its fresh and hardened properties, yet its composition variations raise concerns as to its fracture behaviour. This paper presents the results of an experimental study on fracture behaviour of SCC mixes differing by the coarse aggregate volume, paste to solids ratio (p/s) and water to binder (or cementitious material (w/cm  )) ratio. First the size-dependent fracture energy (GfGf) has been determined using the RILEM work-of-fracture test on three point bend specimens of a single size, half of which contained a shallow starter notch (notch to depth ratio = 0.1), while the other half contained a deep notch (notch to depth ratio = 0.6). Then the specific size-independent fracture energy (GFGF) was calculated using the simplified boundary effect formalism in which the variation in the fracture energy along the unbroken specimen ligament is approximated by a bilinear diagram. Finally, the bilinear approximation of the tension softening diagram corresponding to GFGF has been obtained using the non-linear hinge model. It is found that GFGF and the critical crack opening (wc  ) are dominated by the coarse aggregate volume in the mix and the mix grade. The larger the coarse aggregate volume (or the smaller the paste to solids ratio) the larger are both the mix toughness (GF)(GF) and the critical crack opening (wc  ). However, the higher the mix grade the larger is the mix toughness (GF)(GF) but the lower is the critical crack opening (wc).