Asphalt flow improvers - a new technology for reducing mixing temperature of asphalt concrete mixes with high resistance against permanent deformation.

Asphalt flow improvers in the form of Fischer-Tropsch wax and Romontan wax have emerged successfully from an extensive program of laboratory testing and road trials to assess their suitability as modifiers for rolled asphalts and gussasphalt. They produce flow improvement effects in hot asphalt mixes that enable mixing temperatures to be reduced by 20 - 40.C. Below the temperatures used in laying and compaction, these materials produce a stepwise increase in asphalt viscosity and stiffness. This results in a significant improvement in the stability (resistance to deformation) of the asphalt under operational conditions of high ambient temperatures and heavy traffic. The data gathered so far show that low temperature properties are not adversely affected. The higher density that is achieved on compaction greatly improves the life span of asphalts in service. Although these benefits can be realised by using flow improvers alone as bitumen additives, they are especially suitable as co-modifiers for polymer modified Bitumen PMB 45 and PMB 25 grades since they significantly improve handling and compactibility. Based on current experience, the recommended level of additivation with asphalt flow improvers is 3 % wt. of the binder quantity. Till the end of 2002 about 3 million m. of asphalt pavements would be laid successfully in Germany. For the covering abstract see ITRD E135448.