Abstract:
Modified asphalt concrete is one of the important construction materials for flexible pavements. The addition of polymers and natural hydrocarbon modifiers to enhance the properties of asphalt concrete over a wide temperature range in paving applications has been the common practice. Currently these modified asphalt mixtures are relatively expensive. However, recycled polymers and rubber added to asphalt have also shown similar results in improving the performance of road pavements.
In this study, an attempt has been made to use low density polyethylene (LDPE) obtained from plastic waste and crumb rubber obtained from worn out vehicle tyres. The aim was to optimise the proportions of LDPE in the bitumen binder using the ‘wet process’ and crumb rubber aggregates in the hot mix asphalt (HMA) using the ‘dry process’. The Marshall method of bituminous mix design was carried out for varying percentages of LDPE namely 2%, 4%, 6%, 8% and 10% by weight of bitumen binder and 1%, 2%, 3%, 4% and 5% crumb rubber by volume of the mineral aggregates. The characteristics of bitumen modified with LDPE were evaluated. The modified asphalt mix was also evaluated to determine the different mix characteristics.
The results from laboratory studies in terms of the rheological properties of the LDPE modified bitumen binder showed an increase in viscosity, softening point and stiffness of the binder. The optimum Marshall stability values for HMA mixtures containing 2% crumb rubber tyre and 4% LDPE were found to be 30% higher than the conventional asphalt concrete mix. The wheel tracking test done at 50ºC was 9.81mm rut depth showing a good rutting resistance of the optimized mixture compared to the conventional asphalt mixes. The Modified Lottman test gave a Tensile Strength Ratio value of 0.979 which indicates a low degree of moisture susceptibility of the modified asphalt mix. The above results showed improved properties of the asphalt mixture. The economic assessment done using the present worth of costs indicated a reduction in maintenance cost due to the extended service life of the modified asphalt pavement.
