ABSTRACT
Warm Mix Asphalt (WMA) has grown in production over the past years due to its various advantages, such as reduced greenhouse gas emissions, lower energy consumption and reduced compaction temperature among others. In Brazil, it was not until few years ago that warm mixes set off. With typical temperature reductions of around 30°C below the Hot Mix Asphalt (HMA) production, the use of surfactant additives has proved effective also in enhancing bitumen coating and lubrication of the asphalt binder in the mixture—arguably, yielding and improvement in WMA workability at lower temperatures. This research evaluated the workability of warm mixes accounting the Construction Densification Index (CDI), obtained in the compaction curve of a Superpave Gyratory Compactor (SGC) and also by means of air voids control achieved in Marshall specimens. Torque measurements during the mixing process improved the discussion along with mineral particle distribution obtained from digital image processing. The experiment tested a standard dense HMA and equivalent WMA varying both mixes on their production and compaction temperatures at −15°C, −30°C and −45°C of the reference HMA (143°C), totalling seven analysed mixtures. The results showed no workability variation on the mixes production but an improvement on the compactability; the latter being highly sensitive to surfactant presence and to temperature decrease. In general, the mixtures at reduced temperatures only reach the proper compaction using WMA surfactant additive. The tests carried out allow the conclusions that the addition of WMA surfactant additive enables a decrease in the compaction temperature of about, at least, 30°C without significant loss in workability and improving particle homogeneity in the mixes.
