Waste rubber powder (RP) was subjected to chemical modification by using different concentrations of oxidizing agents such as nitric acid and 30% hydrogen peroxide solution. This treatment leads to introducing some functional groups onto the surface of RP. The chemically modified RP was incorporated in natural rubber mixes either alone or in combination with carbon black (HAF). The physicomechanical properties of NR vulcanizates obtained were studied and compared to NR vulcanizates filled with untreated RP. It was found that the chemically modified RP improves tensile strength and aging resistance of NR vulcanizates compared with untreated RP.

Waste rubber powder (RP) was processed in a Brabenderpremixer under various conditions in the presence of reclaiming agents toconvert the RP into plastic mass (reclaimed rubber), then the obtained reclaimwas blended with both NR and SBR in different ratios. It was found that thebehavior of the reclaim in both NR and SBR is the same. The rheometriccharacteristics show that by increasing the reclaim ratio, the curing time wasdecreased and consequently the cure rate index was increased. Also themaximum torque of the same rubber compounds was decreased. The physico-mechanical data of the reclaim/NR and reclaim/SBR blends showthat the tensile strength as well as elongation at break were decreased withincreasing the reclaim ratio in the blend. On the other hand the equilibrium swellingwas increased. However one can replace about 10–30% of NR or SBR by thereclaim without sacrificing the essential characteristics of the rubber vulcanizates.

No abstract

The fracture resistance of asphalt mixture is an important property directly related to pavement distresses, such as cracking. This paper reports the investigation of a newly-developed semicircular bending (SCB) test as a candidate test for the fracture resistance characterization of asphalt mixtures. Thirteen Superpave mixtures, designed with four different binder types (AC-30, PAC-40, PG70-22M, and PG76-22M) and four different compaction levels (Ndesign = 75, 97, 109, and 125), were considered in this study. The SCB tests were conducted at 25°C using a three-point bending fixture in a MTS testing system. The fracture resistance was analyzed based on an elasto-plastic fracture mechanics concept of critical strain energy release rate, also called the critical value of J-integral (Jc). Preliminary results indicate that the JC values were fairly sensitive to changes in binder type and nominal maximum aggregate size (NMAS) used in Superpave mixtures. This study suggests that the SCB test could be a valuable correlative tool in the evaluation of fracture resistance of asphalt mixtures.

The fatigue fracture behavior of three asphalt mixtures is studied using semicircular specimen geometry. These mixtures consist of a control, a crumb rubber (CR) modified asphalt mixture, and a chemically modified crumb rubber (CMCR)-asphalt mixture. The mixtures are designed to meet the Superpave PG grade as close as possible, and the two rubber mixtures contain the same weight percent of crumb rubber. The number of fatigue cycles and the hysteresis loops are recorded at various intervals of crack lengths. Three specimens are tested from each material under tension-tension load control conditions at a frequency of 0.5 Hz. The maximum and minimum fatigue loads are kept constant for the three asphalt mixtures. It has been found that the chemical modification of the crumb rubber effects a pronounced improvement in the fatigue lifetime, the energy release rate, and the crack speed over the Downloaded from entire range of energy release rate of the asphalt mixture in comparison with the control and the crumb rubber mixtures. Scanning electron microscopy of the fatigue fracture surfaces (ahead of the initial crack tip) of the three mixtures is performed to identify the fracture features of each mixture. Ridges with increased intensity and frequency are associated with the second stage of the fatigue process of the CMCR mixture. These ridges are formed due to microstretching of the binder, and appear to be responsible for the superior fatigue fracture resistance of the CMCR-asphalt mixtures in comparison with the control and the CR mixtures.