Eight trial lengths of dense bitumen macadam (DBM) roadbase, seven with modifiers intended to improve performance, were laid at TRL. The modifications included polymer additives, harder grade bitumens and a metallic modifier. Tests carried out on the binders alone were used to predict their performance in a DBM roadbase for the majority of the modifications investigated. Measurements of the elastic modulus of each material were used in an analysis of structural properties, which confirmed that the polymer modified bitumens did not confer any significant improvement. The principal reasons for this are the low binder content of roadbase macadams and the fairly narrow temperature range experienced by the roadbase (compared with a wearing course of hot rolled asphalt). The material with the harder binder and that with a metallic modifier offered about a 20 per cent reduction in thickness over the control material for an equivalent design life. However, the performance of the metallic modifier in other trials has been variable. (A)
Abstract