|Abstract:||This report presents the comparative life cycle assessment (LCA) between warm stone mastic asphalt (SMA) and conventional
SMA. Specifically, the study evaluated and compared the life cycle environmental and economic performances of two mixtures: a warm
SMA binder course mixture with a chemical additive and a control hot SMA binder course mixture. Both of these mixtures were utilized
as part of a complete overlay project on the Veterans Memorial Expressway (I-355) near Chicago as part of the Illinois Tollway system.
The results of this study indicate that the warm SMA provides significant environmental benefits compared to the control hot SMA.
When the mixing temperature was decreased from 325 to 280 oF (168 to 138 oC), the overall environmental impact of the material,
production, transportation, and placement was reduced by 6.4% due to the use of warm mix additive. More environmental benefits can
be expected if the mixing temperature is further lowered. It was also concluded that using warm mix additive slightly increases the initial
construction cost of SMA pavement. However, the warm SMA overlay allows for traffic to be opened earlier, so the user cost caused by
traffic delay is reduced, and the total economic cost of the warm SMA is lower than that of the control SMA. In addition, the warm SMA
allows for the use of a higher percentage of RAP because of less binder aging. With a 10% increase in RAP usage, the initial
construction cost of the warm SMA becomes 3.5% lower than that of the control SMA. The overall performances of the control SMA and
the warm SMA were compared by calculating a weighted environmental and economic score and the total cost (environmental, agency,
and user costs). Both the weighted score and total cost data show that the warm SMA provides better overall performance compared to
the control SMA. Therefore, besides being more environmentally friendly, the warm SMA is also economically competitive compared to
the control SMA.
This study didn’t include the cost benefits of the warm SMA due to an extended paving season and longer hauling distance because
these benefits are difficult to quantify. In addition, the warm SMA may reduce the risk of poor compaction during construction, which
ensures long-term pavement performance, and therefore saves costs related to maintenance and rehabilitation.