1996

Häkkinen, Tarja; Mäkelä, Kari

The object of the study has been to assess the environmental impact of concrete and asphalt road pavements. The assessment is based on the estimation of service life of road pavements and the environmental burdens caused by their production, use and disposal. Also taken into account is the influence of the pavement on fuel consumption by traffic, noise, lighting requirements and dust formation. The functional unit studied is 1 km of pavement of the Tampere motor way assuming passage of 20 000 vehicles per day. The time scale is 50 years. On the basis of the results the environmental burdens of concrete pavements significantly depend on the cement content of concrete. Consequently, the environmental profile of concrete pavement also significantly depends on the depth of the concrete layer. The environmental burdens from paving and maintenance are rather low compared with those caused by production processes of high-strength concrete. On the contrary, the significance of lighting during 50 years is high. The dust emissions of the concrete pavement studied are mainly induced by abrasion and salting of the pavement. The significance of pavement materials, paving, maintenance and lighting is low compared with the environmental burdens caused by traffic during 50 years. With respect to the effect of material properties of pavement on fuel consumption, it was assumed that the influence on fuel consumption related to the surface texture is the same for both pavements, the difference in E-modulus does not influence the fuel consumption for the heavy vehicles and that the measured differences in rolling resistance have no influence on fuel consumption. However, any difference in fuel consumption of traffic due to pavement materials would significantly affect the result. For example, a roughly 0.1 - 0.5% decrease in fuel consumption of traffic due properties of concrete pavement would bring "savings" in emissions of the same order of magnitude than those from all the other parts of the life cycle of concrete roads. On the basis of the results the environmental burdens of asphalt significantly depend on the bitumen content of asphalt. In addition, the manufacture of asphalt including drying of aggregate materials significantly accounts for the environmental burdens of asphalt pavement. The result also significantly depends on the maintenance operations presumed. The result was assessed using different valuation methods. The differences between asphalt and concrete scenarios are rather low according to the Swiss, Dutch and Norwegian ecoscarcity methods. According to the Swedish ecoscarcity method the scenario based on concrete is environmentally more negative than scenarios based on asphalt. In contrast, according to the eco-category methods and EPS system, the scenarios based on asphalt are more disadvantageous than those based on concrete. The determining environmental burdens of asphalt pavement are carbon dioxide, sulphur dioxide and nitrogen oxide emissions, dust and energy consumption. The same is true with respect to concrete pavement. The negative impact for concrete is partly due to the high valuation factors for mercury and cadmium according to the Swedish political targets.