Studying the Effect of Silica Fume on the Fracture Toughness and Fracture Energy of Self-Compacting Lightweight Concrete

Self-compacting lightweight concrete (SCLC) is one type of concrete that its usage has widely increased. The use of some additives in the production of SCLC can both reduce its costs and improve its properties. The effects of different cement replacement materials have been studied by several researchers. Jalal et al. (2012) claimed that the use of silica fume could improve the electrical resistance and mechanical properties of self-compacting concrete, and reduce its water absorption. Moreover, the use of silica fume in normal concrete improves the bond between aggregate and paste surfaces, and it has positive effects on fracture toughness, compressive strength and tensile strength (Lam et al., 1998). To simulate the fracture behavior of concrete in numerical models of concrete, depending on the model, some parameters such as fracture energy, fracture toughness and critical effective crack-tip opening displacement ( or δc), which generally are known as fracture parameters, must be determined. In this regard, Peterson (1980) showed that the fracture parameters are significantly affected by water to cement ratio (w/c) and the quality of aggregate. In other words, by reducing w/c or using stronger aggregate, the fracture energy of concrete increases. In this study, the effect of w/c and silica fume on the fracture toughness and fracture energy of SCLC has been investigated. Therefore, by making six mix designs and 126 concrete specimens, fracture parameters, mechanical properties and the workability of fresh concrete were carefully studied. Initially, four mix designs with the w/c of 0.37, 0.42, 0.47 and 0.52 were made. Afterwards, by replacing 0, 5% and 10% of the weight of cement with silica fume, the effects of changing this parameter on the fracture parameters of SCLC were studied.