Review of the development and uses of hard grade asphalts in France

Abstract

Hard grade paving asphalts, i.e., having a penetration at 25 ​°C lower than 25 ​mm/10, have experienced, in France, a significant development over the last forty years, linked to the development of high modulus asphalt concrete for rehabilitation then for new construction of road pavements. In the first part, this paper provides a review of the evolution of asphalts in France over the past sixty years towards the use of harder penetration grades and a limitation of the evolution of the asphalt in the mixing plant to avoid early cracking of the pavement. Current recommendations in relation to climatic conditions are mentioned. Rheological characteristics of different hard asphalts produced in France are presented including data on the effect of ageing tests rolling thin film oven test (RTFOT) and pressure ageing vessel (PAV). Hardening of hard asphalt after RTFOT+PAV is comparable to that of softer asphalts. The performance related to low temperature cracking is less which limits the use of plain hard asphalt in pavements subjected to severe winter conditions and requires polymer modification. The specifications for hard grade paving asphalts based on traditional empirical tests included in the European standard developed in the mid 2000s and the choices made in France are presented. A comparison of the specifications for hard grade paving asphalts in the European standards and of those proposed for China shows that the European specifications are more stringent as regards consistency and evolution after ageing tests.