Mix Design and Benefit Evaluation of High Solar Reflectance Concrete for Pavements

The use of cool paving materials, or cool pavements, has been identified as one strategy that can help mitigate the urban “heat island” effect. One method of creating a cool pavement is to increase the solar reflectance, or albedo, of its surface. This increase can be achieved by many existing paving technologies. This study explores alternative ways of creating high-albedo concrete for use in pavement applications. The key approach is to make concrete whiter by replacing cement with whiter constituents. Fly ash and slag are used as the main constituents because they are environmentally friendly, readily available, and already familiar to the concrete industry. Compared with a conventional concrete mix, concrete mixes containing fly ash have lower albedo, whereas concrete mixes containing slag have higher albedo. Of all mixes tested, the mix with 70% slag as cement replacement achieves the highest albedo of 0.582, which is 71% higher than the conventional mix. It also has better compressive strength as tested at 7 and 28 days and modulus of rupture as tested at 7 days. The production of high solar reflectance concrete consumes 43.5% less energy and results in less emission of pollutants and greenhouse gases (by 20% to 60%). Furthermore, the analysis of some urban cities shows that the implementation of this high solar reflectance concrete could increase the city albedo by 0.02 to 0.07. This amount of albedo modification has the potential to benefit economics and the environment in many ways, ranging from decreasing energy demand to improving air quality.