Impact of Additives on the Foamability of a Road Paving Bitumen

Because of the needs for the increased efficiency and environmental concerns that now emerge environmentally friendly techniques are more sought for and more commonly utilized in the road paving industry. Typical asphalt mixes are produced in temperatures exceeding 150˚C depending on the type of asphalt binder used, but new techniques are being developed, permitting decreased production and paving temperatures. One of the most effective techniques that are being studied are the Warm Mix Asphalt and Half Warm Mix Asphalt methods utilizing water based bitumen foaming that allow production of asphalt mixes at temperatures as low as 100˚C. Due to the extremely low processing temperatures, it is often difficult to obtain satisfactory results regarding the physical and mechanical properties of the resulting mixes, specifically the resistance to moisture the damage and resistance to the permanent deformation being in concern. As these issues were found to be originating in the inadequate coating of aggregates, a surface active agent in amounts of 0, 2% - 0, 6% and synthetic wax in amounts of 1, 0% - 2, 5% were added to 50/70 paving bitumen to improve its foamability and coating potential. Foaming characteristics were established in terms of bitumen foam expansion ratio ER and its half-life HL as a function of foaming water content ranging from 1, 5% to 4, 0%. It was found that the addition of surface active agent in the amount of 0, 6% resulted in the most favourable foaming performance at 2, 5% foaming water content, resulting in a doubling in expansion ratio and more than a 2, 5 times increase in half-life compared to the base bitumen. It is believed that the improved foaming characteristics of the bitumen would significantly benefit the performance of a subsequent warm or half-warm asphalt mix.