Study on the prospects of using polymers in butuminous binder and mixes

Abstract

In this investigation an attempt is made to study the possibility of blending some selected polymers with bitumen using low cost manual cooking device and thereby exploiting the potential of polymer modified binder in pavement construction in Bangladesh. Other objectives of the research were to study the properties of modified binder and mixes through laboratory experimentations. The qualitative improvement of polymer modified binder and mixes are studied by comparing their characteristic properties with that of unmodified bitumen and bituminous mixes. In this study low density polyethylene (LOPE), poly propylene (PP), ethylene vinyl acetate (EVA) and polyvinyl chloride (PVC) are tested to check their mixing compatibility with bitumen. In order to perform the necessary blending operation, a manually operated simple milling device is fabricated. For laboratory investigation of polymer modified binder and mixes, LOPE is selected as a modifier of bitumen and a total of four modified binders and mixes are prepared with 2.5%, 5%, 7.5% and 10% LOPE contents. The rheological properties of unmodified binder and LOPE modified binder are evaluated by comparing parameters like specific gravity, penetration, ductility, softening point, loss on heating and viscosity. The stripping and coating test is also performed to examine the effect of water and temperature on the coated aggregates. In addition, a non-conventional "film thickness" test is carried out to compare the binder film thickness on aggregate coated with unmodified and modified bitumen. The performance of modified bituminous mixes is evaluated by determining stability, flow, density and void in the mixes. The study results reveal that properties like penetration, ductility and specific gravity of the LOPE modified binder decrease while the softening point and viscosity increase with the increase in concentration of the LOPE in the bitumen. Experimental results indicate that the LOPE polymer reduces the binder's temperature susceptibility and improves consistency by significant amounts. The film thickness experiment conducted with solid steel spheres shows that the binder coating thickness increases significantly with the increase of the LOPE content in the bitumen. With 10% LOPE content, the increase of film thickness was about 150% as compared to that of the unmodified binder. The coating and stripping tests sho,w that the coating of the LOPE modified bitumen on aggregate is stronger than that of unmodified bitumen on aggregate. From this test it is also observed that better adhesive property of the modified binder makes the bituminous mixes more impermeable to water and delays the stripping process. The Marshall stability results shows that LOPE increases the stability values of the compacted mixes significantly with increasing LOPE content in the bitumen. It is indicated further that the addition of 10% polymer in the binder increases the resulting mixture stability by about 34%. The flow values as obtained in the Marshall tests show slightly increasing pattern with the LOPE content, whereas unlike stability, the density of the compacted mixes slightly decreases with the increase of LOPE content in the bitumen. The effect of LOPE on air void (Va), void in mineral aggregate (VMA) and void filled with asphalt (VFA) is found insignificant. The study also reveals that the blending of pure forms of polymer with bitumen can be done by using manual cooking device, but there is a need for fabricating a thermostatically and mechanically controlled blending system to blend waste polymers and to facilitate large-scale production of polymer modified binder.