The construction, operation, and maintenance of road pavements are responsible for significant greenhouse gases emission in the United States. At the construction stage, the U.S pavement network takes up to 460 million tons of crushed aggregate (Santero, Loijos, & Ochsendorf, 2013). More emission happens during the extraction of raw materials used in the construction of the pavements. Additionally, road transport in the country is responsible for 87% of the total carbon dioxide emitted from the transport sector (Santero et al., 2013).
There are various ways through which greenhouse gases emissions as a result of concrete pavements can be reduced. One is by reducing embodied emissions. These are the emissions released during the manufacturing and construction of paving materials. Ways through which these emissions can be reduced include increasing production efficiency, substituting less emission-intensive materials, and utilizing fewer natural resources (Santero et al., 2013). Another way of reducing greenhouse emissions in the pavements is by increasing albedo. Since albedo quantifies the amount of incoming solar radiation that the pavement surface reflects, increasing it decreases the climate impact from direct radiative forcing and urban heat island effect. Greenhouse gas emissions by pavements can also be reduced through increased carbonation. This is a chemical process where carbon dioxide is sequestered in the concrete naturally. Usually, only minimal carbonation is done for in-situ concrete pavements. Emissions due to concrete pavements can also be reduced by reducing vehicle fuel consumption. The consumption of a car partly depends on the design, maintenance, and materials used in the construction of pavements. However, not all vehicle consumption is affected by pavement-related issues (Santero et al., 2013).
The above reduction measures can be implemented through various strategies. Embodies emissions can be reduced by increasing fly ash cement replacement. Fly ash has expedited carbonation and hence using more of its content will increase the carbonation coefficient, thereby reducing emissions (Santero et al., 2013). Increasing albedo can be achieved through the use of white aggregates. As discussed earlier, albedo enhances the pavement surface’s reflectivity, thus increasing it increases radiative forcing and decreases urban island effect. Using white aggregates is a strategy that will further enhance the reflectivity of the pavement’s surface (Santero et al., 2013). Increased carbonation can be achieved through EOL waste concrete management. This entails crushing and stockpiling concrete for at least a year whereby it will sequester about 28% of the initial carbon dioxide released from the carbonation. The issue of vehicle fuel consumption can be solved by adding an extra rehabilitation each ten years, which will consequently translate to a smoother ride. The consumption of a car is highly determined by the roughness of the road. Research indicates that reducing the roughness of 4 meters per kilometer can reduce fuel consumption by 2.8% in trucks and 4.2% in cars (Santero et al., 2013). Embodied Emissions can be reduced through the use of advanced design models that will prevent over-design. Avoiding over-design also entails the optimization of materials used in the construction of the pavements. Advanced models used in the design process to help in avoiding overdesign can be termed as the best technology for concrete paving. An example is the Mechanistic-Empirical Pavement Design Guide (MEPDG) models used in the creation of alternative designs using similar service life and traffic inputs.
The success of the above strategies can be evaluated not only through emission reduction, but also through cost-effectiveness. This is because even though the end requirement is for reduced pollution, it is imperative that it is achieved at minimal costs. Evaluation for cost-effectiveness is done using life cycle costs analysis (LCCA) principles (Santero et al., 2013). The method makes it easy to evaluate the economic impacts of the pavements and is widely used by the Department of Transport to make decisions between distinct design alternatives.
- Santero, N., Loijos, A., & Ochsendorf, J. (2013). Greenhouse gas emissions reduction opportunities for concrete pavements. Journal of Industrial Ecology, 17(6), 859-868. doi: 10.1111/jiec.12053