Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
develops to the point that it can be used in place of hot-mix asphalt on all roadways
nationwide, the estimated GHG reductions would be 2.9 mmt CO2 annually (NCHRP 25-
25 Task 45, draft work in progress). Benefits from warm-mix asphalt will take longer to
realize since the warm mix asphalt industry is in its infancy in the U.S. with only a few
demonstration projects per year.
Costs
It is difficult to quantify costs of fly ash usage, but in general concrete made by replacing
some Portland cement with fly ash will cost less than concrete made with all Portland
cement due to the higher cost of Portland cement versus fly ash. However, as the
percentage of Portland cement substituted with fly ash rises the need for some chemical
additives offsets these cost savings.
The cost of warm-mix asphalt is somewhat uncertain due to its current small-scale usage.
However, a recent research project (Anderson et al., 2008) has produced some estimates
based on fuel savings as well as the increased costs due to the capital costs of additional
equipment and material costs of chemical additives. Considering the range of costs given
for each of these, the costs and cost savings are estimated at best cancel each other out to
keep the cost of warm-mix asphalt the same as hot-mix asphalt. At worst, overall costs
could increase by around $3-4 per ton of asphalt plus around $100,000 of capital costs per
asphalt production company.
Cobenefits
Alternative material production techniques have some cobenefits, in addition to
reductions in air pollution and fuel consumption associated with less energy-intensive
technologies. For example, recycling fly ash and aggregate for use in concrete creates a
use for these materials previously viewed as waste and keeps them out of landfills.
Warm-mix asphalt can reduce plant emissions by 30–40 percent for SO2, 50 percent for
VOC, 60-70 percent for NOx, and 20–25 percent for particulates. It also provides some
benefits for paving (such as the ability to pave in cooler temperatures) and also reduces
worker exposure to aerosols and hydrocarbons (FHWA, 2008).
Feasibility
Fly ash has been used in concrete since the early 1950s and does not require additional
research on its performance. However, the use of fly ash in concrete requires careful
attention to differing characteristics of the concrete and evaluation to ensure that the fly
ash concrete meets the engineering requirements of individual projects. The availability
of fly ash or other cementitious materials for concrete blending also may be limited in
some areas, since these are by-products of other industrial activities.
Additional research and development is needed on warm-mix asphalt to evaluate field
performance and adapt it to U.S. materials and production practices. However, a recent
international scan tour to evaluate European practice concluded that with additional
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