How to Evaluate with Relevance the Compactability of Warm Mixes Using the Gyratory Compactor (GC)

The development of Warm Mix Asphalt (WMA) requires the control of the performances at laying temperatures to ensure those at service life temperatures. A simple lowering of mixing temperature can reduce the workability and the compactability of asphalt mixture. So, several techniques such as additivation and foaming are proposed to avoid or reduce this laying issue. The shear gyratory compactor (GC) conventionally evaluates the compactability but different approaches can be used to analyse data. This paper aims to assess the relevance of these methods by an experimental program conducted on two WMA (with EVOTHERM® technology WM30 additive developed by Ingevity and foam process) compared with a conventional hot mix asphalt (HMA), at three compaction temperatures. The classic exploitation of GC’s data (i.e. considering the void content at a given number of gyrations) is not relevant to evaluate the effect of the decrease in temperature on the compactability. The calculation of compactability indices (CEI), used to obtain a level of compaction (90%, 92%, and 95%), is interesting but takes more time. The calculation of performance ratios is the simplest and most relevant approach. The use of liquid additive seems the most promising towards the compactability.