Practicality and Sustainability of Using HVFA for Concrete Sidewalks

Fly ash, a by-product of coal burning electric power plants, has been used as a partial replacement for Portland cement in concrete for over 70 years. Currently, the typical replacement range is limited to 15 to 25 percent. Although the use of fly ash in concrete has increased over the last 20 years only about 20% of fly ash generated is used in concrete. Recent interest in increasing the sustainability of concrete has resulted in the study and use of high volume fly ash (HVFA) concrete, which can contain up to 50% or more fly ash replacement. In this study, a locally produced Type C fly ash was used to examine the practicality and sustainability of using HVFA concrete for sidewalks at a university campus. Eight mortar mixtures, containing 0, 20, 60 and 90% fly ash replacement were tested for their strength development characteristics. The target mortar strength was 27.6MPa (4000 psi) at 28 days based on guidance provided by a local concrete contractor. Hydrated lime was added to mixtures containing 60% and 90% fly ash, to determine the ability of lime to enhance the chemical activation. Following the outcomes of compressive strength testing an overall life cycle assessment (LCA) was conducted using SimaPro7 software to determine the environmental impacts of concrete made with these increasing amounts of fly ash. The compressive strength test results showed that mortar mixtures containing 60% fly ash and lime can be designed to fulfill the requirement of strength suitable for concrete sidewalk construction. The LCA indicated that replacing cement with 60% fly ash has significant impacts on reducing embodied carbon dioxide emissions and raw material consumption in the concrete manufacturing process.