Impact of Incentives on In-Place Air Voids

Specifying agencies face an on-going challenge with how to get the best quality hot-mix asphalt (HMA) overlays possible within the limits of available funding. Specifications for HMA have evolved from recipe type to end product statistically based specifications for acceptance, with a future trend towards performance related specifications. The Arizona Department of Transportation (ADOT) has been using some form of an end-product specification for HMA for about 20 years. The initial version of this specification was not a true incentive specification; positive pay lots could only be used to offset penalties and could not result in incentive pay. In 1990, this specification was changed to include a true incentive when the percent within limits was 100. Corresponding to this change, a drop in average in-place air voids from around 8.5% to 7.5% was seen. This reduction in in-place voids is expected to translate to improved pavement performance especially with respect to fatigue life. Although it is not easily possible to quantify the dollar value of this improved performance, ADOT believes that it more than offsets any additional costs incurred by the use of an incentive for compaction.