Evaluation of tools for measuring the workability of bituminous asphalts

Abstract

Since the beginning of 2000's, the development of WMA, Warm Mix Asphalt, allowed the Road companies to meet expectations regarding sustainable development by lowering the fabrication and laying temperatures (reduction of 30 to 50°C). However, this development also highlighted, on the jobsite, an unidentified problem with HMA, Hot Mix Asphalt: a lesser workability during mechanized and especially manual laying, for several WMA processes. This experimentation, part of research thesis results, aims to study the development of a relevant and discriminating test for the evaluation in laboratory of the workability of bituminous asphalt. Two ways were explored; the one uses a classic equipment of road laboratories, the GSC, Gyratory Shear Compactor test, by varying the parameters (vertical strength, rotation speed); the other one is based on the use of the workability device called "Nynas", from now European standardized, with varied parameters. The work was conducted on the same classic asphalt formula with different bitumen grades, and variable temperatures of manufacturing. This parametric study allowed, first of all, to confirm the reduction in workability of asphalts with the reduction in the temperature of manufacturing. It showed the limits of the GSC, a very good test for compactibility but not for workability of asphalt. It also highlighted the interest of the Nynas workability device after a good choice of test parameters for a real relevance of the test result.