EXPERIMENTAL EVALUATION OF HOT MIX ASPHALT MODIFIED WITH DIFFERENT ADDITIVES

Abstract

Premature failures, including the development of early cracks, potholes are the major causes of the high annual road maintenance cost of Bangladesh. Modification of traditional bitumen by different types of polymers could be an effective solution to reduce this huge maintenance cost of pavement. To incorporate this modification in the conventional flexible pavement of our country, this study investigated the effect of Pyrolysis Carbon Black (PCB) and Polypropylene (PP) on both bitumen and bituminous mix. Pyrolysis Carbon Black (PCB), an elastomer and one of the by-products of the scrap tire pyrolysis process, had been recognized as one of the most efficient modifiers in several studies. Being a waste product, modification of asphalt with PCB could contribute to waste management problems as well. 2%, 3%, 5%, 10% and 15% PCB of total bitumen content was used for modification. Another modifier used for modification was polypropylene (PP). For polypropylene, the percentages used were 1 %, 2%, and 3%. Based on the results of two individual polymers, two combinations consisting of both PP and PCB were prepared as well. To ensure a homogeneous blending, all the modified bitumen was prepared through the wet process by using a mechanical blending device. Penetration, softening point, ductility, specific gravity tests were performed on unmodified and modified bitumen for evaluating the physical properties. The penetration and ductility values showed a decreasing trend with increased polymer content for all types of modified bitumen. But an increasing trend had been observed in the case of a softening point. The mechanical properties of the bituminous mix ii were investigated through Marshall, Indirect Tensile Strength (ITS) test. To investigate the resistance to moisture damage, the retained Marshall stability test was performed on some specific bituminous mix. The stability of the bituminous mix with 3% PCB was approximately 51% greater than that of the unmodified mix. In the case of PP modified bitumen, a 22 % increase was found in stability value for the incorporation of 3 % PP in neat bitumen. The stability of the two combinations of PCB and PP increased by 29% from that of the unmodified bituminous mix. Significant improvement was observed in retained Marshall stability and ITS value for polymer modification. The retained stability increased from 74% to 90% for a combination of 3% PCB and 2%PP. The highest ITS and retained Marshall stability was observed for combined modified bitumen consisting of 3% PCB and 2%PP. From this study, it was confirmed that modification of bituminous mixes with PCB and PP could decrease the premature failure problem of Hot Mix Asphalt (HMA) pavement to some extent by increasing resistance to moisture damage, high-temperature susceptibility, load-bearing capacity. The findings of this study would motivate the road agencies of the country to use the modified bitumen instead of conventional bitumen to enhance the performance of the flexible pavement.