Cost
Of concern is the initial cost for asphalt plants to purchase warm-mix equipment and/or additives. This cost can vary, but is relatively small compared to normal operation costs and the purchase can quickly pay for itself.
The WMAC process generates a net savings of $1.29 / short ton compared to HMAC. This net savings was estimated by multiplying the fuel savings (0.41 gallons of diesel / short ton)ii of WMAC compared to HMAC by the average 2013 cost of diesel ($3.90 / gallon)iii and adding the cost chemical additives cost (0.30 / short ton).
Use of the plant foaming process requires a capital expenditure to modify an existing plant. In 2015, the Asphalt Pavement Association of Oregon (APAO) reports that it’s about $30,000 to get a system up and operational, which is down substantially from 5 to 6 years ago when it was in the neighborhood of $50,000. APAO also reports that most producers seem to prefer the plant foaming process as it represents a one-time expenditure and the plant can produce hot or warm mix asphalt pavement “at a flip of a switch”.
Operational Effects
Besides reducing energy costs, lower heating temperatures are beneficial to the health of construction workers, neighbors, and passersby since fewer oils are volatized and emitted into the nearby air. The lower temperatures make for a more comfortable work environment; particularly in areas with hot summer temperatures or areas with little airflow, like tunnels. WMAC cools more slowly, compared to HMAC, due to a smaller difference between the temperature of WMAC and the ambient air temperature. This extends the paving season since pavement can be laid in cooler temperatures. In addition, warm-mix asphalt can be hauled over longer distances, and freshly paved roads can return to operation sooner than if they were paved with HMAC.
Selecting the appropriate mix design is critical to the use of asphalt concrete materials. Staff involved in the purchasing materials or bidding projects that include these materials, should select the mix design properties needed for the environmental conditions, traffic loading and available materials. Quality control testing to ensure longevity of the project is important.
Local Availability
In order for municipal governments to specify and purchase WMAC for construction projects, local asphalt production plants within a certain geographic radius need to have WMAC production capacity. While the initial capital investment for the warm mix equipment is relatively small, the investment risk from the plant’s perspective may be large. In order to make such an investment the plant will need to be confident in the scale and timing of local demand for a warm mix product. It becomes a bit of a “chicken or the egg” problem. In order to build understanding and acceptance of warm mix products by public works department and local contracts they need production capacity in order to complete test projects to increase demand for warm mix products. On the flip side, asphalt producers don’t want to make the investment until the demand exists to support the investment.
These challenges are evidently being overcome as the tons of WMAC being consumed in the U.S. has steadily increased between 2009 and 2012.
The City of Eugene, Oregon (see the case study) has had success in implementing WMAC in its projects due to local circumstances. The City of Eugene is the largest local consumer of asphalt products in their area. Once they made the decision to begin specifying WMAC on its projects, all three local asphalt plants invested in the warm mix equipment.
