Pulverization is a general strategy used prior to any practical application of recycled waste tire rubber (WTR). Mechanical grinding, in use currently, is an inefficient technique due to low-quality rubber powder production and certain indispensable additional pretreatments. The aim of this study is to propose a novel pulverization technique of WTR by ultrahigh pressure water jet. Efficient pulverization of WTR was accomplished by water jet without any pretreatment. Powder characteristics, including particle size distribution (PSD), surface area, thermal behavior and chemical structure changes, were investigated. The curing, mechanical and morphological properties of natural rubber (NR) vulcanizates filled with ground tire rubber (GTR) from water jet pulverization (WJPULV) were evaluated. The results indicate that GTR granules from WJPULV possess a quite fine PSD and large surface area, show similar thermal degradation behaviors to the original WTR and have been partially devulcanized. The improvement of tensile and tear strength of the composites reveals that GTR from WJPULV can be added up to 40 phr without adverse effect. The morphological analysis corroborates the homogeneity of GTR in the NR matrix. All findings confirm that water jet can be an excellent choice for pulverization of WTR.

Fracture toughness is used to characterize rock resistance to fracturing and it is important in theoretical research and engineering applications. Mode-I fracture toughness can be predicted on the basis of an empirical relationship between fracture toughness (K_IC) and tensile strength (σ_t). In underground engineering, rocks are often subjected to different temperatures. Therefore, this paper explores the effect of temperature on the relationship between mode-I fracture toughness and tensile strength. The results show that the change trends in the K_IC and σ_t values of rocks at temperatures from 20 °C to 600 °C are broadly consistent with each other. For rocks heat-treated to the same temperature, the K_IC of the rock increases with an increase in σ_t. This positive correlation between K_IC and σ_t is different in rocks heat-treated to different temperatures. Critical crack propagation radius (r_IC) is an important factor in the relationship between K_IC and σ_t and is related to the type of rock and the conditions under which it is tested. For the same rock, r_IC is quite different after it has been exposed to different temperatures. The positive correlation between K_IC and σ_t results from a similarity in the fracture morphology and properties of failure when rock is destroyed in fracture and tensile tests.