Investigating fracture characteristics and ductility of lightweight concrete containing crumb rubber by means of WFM and SEM methods

Abstract

The use of lightweight and recycled materials such as crumb rubber due to unknown behavior in concrete can change the cracking behavior and fracture parameters. On the other hand, nowadays, using waste materials as a substitute for natural aggregates in concrete is an effective solution to environmental problems. This study investigated the effect of crumb rubber on the main fracture characteristics and ductility of lightweight concrete (LWC). For this purpose, a part of aggregates replaced with crumb rubber in volume of 4 different percentages (5, 10, 15 and 20%). The main experiment in this research was three-point bending tests that were performed on notched beams. Fracture parameters were determined using two different methods, Work of Fracture Method (WFM) and Size Effect Method (SEM). The results show that by increasing the replacement percentage of crumb rubber instead of fine aggregates from 0 to 20%, the total fracture energy (GF) and characteristic length (Lch) in WFM increase by 63% and 99%, respectively. Also, By increasing the crumb rubber replacement up to 20% in LWC, the initial fracture energy (Gf), length of fracture process zone (Cf) and fracture toughness (KIC) in SEM has increased 1.92, 3.4 and 1.14 times, respectively, compared to lightweight concrete without rubber, while the brittleness number (β) decreased in SEM. Furthermore, the results showed that the fracture surface, the size of the plasticity zone of the crack tip decreases with the reduction of the crumb rubber content. Finally, the ratio of fracture energy obtained from WFM. GF, to initial fracture energy obtained from SEM, Gf, for lightweight concrete containing crumb rubber was approximately 2.8. On the other hand, this study can put a step forward in the fracture mechanics field for sustainable LWC mixtures.