Short-term performance of plant-mixed warm stone mastic asphalt

Warm-mix asphalt (WMA) is gaining attention in the pavement industry because of its environmental benefits. WMA would be especially useful if it could be applied to heat-sensitive mixes, such as stone mastic asphalt (SMA). However, before these SMA mixes are used with warm mix additives, the performance of the mixes must be examined. A study was conducted to verify the early-age performance of a warm SMA with an Evotherm 3G additive. An Evotherm SMA and a conventional SMA were evaluated and compared with in situ lightweight deflectometer testing and comprehensive laboratory tests, including complex modulus, wheel track, indirect tensile strength, and semicircular bending fracture. Gyratory-compacted specimens made with fresh plant mixtures were tested in the lab at various curing periods; lightweight deflectometer tests were conducted in the field directly on an Illinois expressway overlay immediately after compaction up to 24 h. The results showed that at the same curing period, the early-age performance of the Evotherm SMA was generally comparable to that of the conventional SMA. The curing process increased the dynamic modulus of both Evotherm SMA and conventional SMA but did not significantly affect other laboratory test results. The onsite modulus of the Evotherm SMA was found to be less than that of the conventional SMA at the same temperature. However, because of the lower compaction temperature, the pavement constructed with the Evotherm SMA could be opened to traffic earlier than could the pavement constructed with the conventional SMA while providing the same modulus.