A study on the significance of the crumb rubber classification on the ductility test for rubberized asphalt binder

Several types of modifiers have been used as additives into asphalt cement in order to enhance the performance of the Hot Mix Asphalt for road pavements such as PVA, SBS and crumb rubber. The aim of the present work is to study the effect of the crumb rubber classification according to the size of scrap tires, i.e., car and truck tires, on the behavior of the modified asphalt ductility test and Marshall mechanical properties of the asphalt concrete specimens. Samples of asphalt cement had been modified by using two types of crumb rubber: car crumb rubber (CCR) and truck crumb rubber (TCR). Mixing temperature (150-180 degrees C), contact time (20-60 min), CCR (10-20 wt%) and TCR (0-4 wt%) were tested to establish the mathematical correlations of the ductility response using a central composite design rotatable and uniform. Minitab-17 was performed for the regression and the graphical analysis of the obtained results. The optimum values of the operating variables that give (24 cm) of ductility response were (180 degrees C) of mixing temperature, (21 min) of contact time, (18 wt%) of CCR and (3.5 wt%) of TCR. The results showed an obvious enhancement of Marshall stability and flow according to these optimum values, 13 kN and 4 mm, respectively, in comparison with the unmodified binder in spite of minimizing the ductility value.