The scarcity of resources especially in the energy sector (eg. oil sector) and the shortage of new supplies of natural materials have affected the road building industry. There is a need for a reduction in temperature in the production of hot mix asphalt (HMA) to conserve energy and the need to conserve scarce resources such as virgin aggregates to produce HMA.
With the dwindling supply of new resources and spiraling cost of materials, the use of Reclaimed Asphalt Pavement (RAP),a recycled material obtained from deteriorated roads is a suitable way to conserve non-renewable resources that is aggregates and bitumen used for asphalt mixes. Most road authorities allow the incorporation of not more than 30% of RAP in hot mix asphalt to avoid any detrimental effects on the mix properties.
The increase in asphalt materials prices encouraged the road construction industry to strive for the use of higher percentages of RAP to reduce the cost of road projects. A higher addition of RAP should enhance the value of the recycled pavements and have the potential for reducing the quantity of waste materials. However, the use of RAP in HMA still requires mixing and compaction temperatures similar to the conventional HMA.
Recent advances in technology has allowed the temperature for mixing and compaction of asphaltic concrete mixes to be lowered compared to the mixing and compaction temperatures for conventional hot mix asphalt. Warm Mix Asphalt (WMA) allows a reduction in the mixing and compaction temperatures by using additives such as sasobit, which is a paraffin wax derived from coal gasification process. The chemical composition of sasobit can be described as fine crystalline materials in long -chain hydrocarbons, composed from 40 to 115 carbon atoms. The melting point of sasobit is about 100 degree celcius and it is completely dissolved in bitumen at temperature above 115 degree Celsius. Mixing temperature for WMA is reduces to a range of about 115 to 135 degree Celsius, which is substantially lower than the mixing temperature of 150 to 160 degree Celsius used for conventional hot mix asphalt.
Therefore, there are enormous benefits of incorporating high percentages of RAP in WMA mixes, namely the reduction of energy to produce HMA and conservation of non-renewable resources (aggregates and bitumen) used for asphalt mixes.
This research investigated and compared the performance of WMA containing 30%, 40% and 50% of RAP by weight of the mix with the conventional asphaltic concrete. The performance of the mixes was compared by measuring the stiffness value, moisture susceptibility and rutting depth.
It was found that the warm mix asphalt using sasobit-additive and containing high percentage of RAP could produce mix with similar performance to the conventional HMA mix and complied to all Public Work Department of Malaysia's specification requirement. This shows that WMA added with up to 50% RAP has the potential to save production costs in terms of lower energy requirements and also savings in terms of raw materials used (due to high amount of recycled material added in the mix), without compromising the performance of the mix as it adheres to all requirements and specifications.
This study/invention received a Gold award in the Invention Innovation and Design Exposition 2014 UiTM Shah Alam.