All of the content of the old PavementCouncil.org web site is preserved in the new site. Some of the imported content is not in a format that supports tags, so we are going through the older posts to make sure they are readily found through the tag cloud. The old web site included links to two studies that are of interest because of what they say about the long term, life cycle benefits of maintaining pavements.
The first study was presented at the First International Conference on Pavement Preservation held in 2010 in Newport Beach. The conference focused on high traffic, thoroughfare roadway pavements rather than the parking lots and low-traffic roads where asphalt- and refined tar-based emulsion sealants are used. One of the papers presented at this conference, Energy Usage and Greenhouse Gas Emissions of Pavement Preservation Processes for Asphalt Concrete Pavements by J. Chehovits & L. Galehouse, also concerned roadway pavements with a focus on energy use and GHG emissions of new and major repaving projects versus energy use and GHG emissions of pavement maintenance operations. The goal of pavement maintenance programs is the same for roadways and parking lots. The Chehovits & Galehouse paper describes the rationale for pavement maintenance thusly:
Use of pavement preservation treatments extends the remaining service life of asphalt concrete pavements. These treatments typically include spray applied surface seals, thin overlays, crack treatments, chip seals, slurry seal/micro surfacing, surface recycling and others. Each preservation treatment reduces damaging effects of aging and deterioration of the pavement surface layer and helps protect the integrity of the underlying pavement structure. If proactive preservation treatments are not used, pavements deteriorate more rapidly and require major rehabilitation with structural overlays or reconstruction much earlier.
While the preservation treatments are not precisely the same, they are similar enough to sealant emulsions that the energy use profiles and GHG emissions are likely in the same ball park. Chehovits & Galehouse found significant energy and GHG emissions savings are achieved when using pavement preservation techniques. Their findings concerning energy savings were summarized as follows:
New construction, major rehabilitation, thin HMA overlay, and HIR have the highest energy use and range from 5,000 to 10,000 BTU/yd2– yr (6.3-12.6 MJ/m2-yr). Chip seals, slurry seals, micro-surfacing, and crack filling utilize lower amounts of energy per year of extended pavement life and range from 1,000 to 2,500 BTU/yd2– yr (1.3-3.3 MJ/m2-yr). Crack seals and fog seals use the least amount of energy per year of extended pavement life at less than 1,000 BTU/yd2-yr (1.3MJ/m2-yr).
The overall conclusion of the study was:
To minimize energy use and GHG emissions over the life of a pavement, all preservation treatments should be utilized as appropriate to the maximum extent possible for the existing pavement conditions.
The second study was authored by D. Schechtman as part of the New York-New Jersey Harbor Study conducted by the New York Academy of Sciences. Schechtman conducted a limited life cycle analysis (LCA) and reported the results in a paper titled Life Cycle Analysis: An Economic Input Output and process based LCA comparison between unsealed concrete and sealed asphalt parking lots’ upstream environmental impacts. Conducting a full life cycle analysis is a complicated undertaking, involving analysis of the many different activities from natural resource extraction to the final disposition of a product at the end of its useful life. Schechtman described his work as follows:
…we have conducted a comparison of the upstream environmental impacts of refined coal-tar sealed, asphalt sealed, and unsealed concrete parking lots. This analysis is limited to estimating the “upstream” environmental impacts – only those associated with the manufacturing, and installation of parking lots.
One conclusion of the LCA was as follows:
In assessing which lot has the lowest overall environmental impact in the upstream phase (manufacturing and installation), the result will depend on which indicator you value the most. If toxic emissions (non-GWP compounds) were of the greatest concern then the asphalt lot, specifically the asphalt lot sealed with refined coal-tar based sealant, would be the best option for the upstream phase. [emphasis added]
The difference between coal tar- and asphalt-based sealants were much smaller than the difference between those two and a concrete paved surface. A second conclusion was that, if concerned about downstream (that is, post-application) “Global Warming Potential” (GWP) impacts, the higher initial and maintenance costs of concrete might be “the clear choice.”