Energy and Greenhouse Gas Emissions Trade-Offs of Recycled Concrete Aggregate Use in Nonstructural Concrete: A North American Case Study

Abstract

The retirement of aging concrete infrastructure is resulting in significant material flows of concrete debris in the economy. A proposed outlet for this debris is new concrete: the debris can be crushed into small particles and used in place of virgin aggregate. This form of recycling lessens use of aggregate resources, but its consequences are less clear in terms of energy use and greenhouse gas emissions. To examine these impacts, we develop life-cycle inventory models of the manufacturing of recycled concrete aggregate from debris. Results from these models are then used in life-cycle models of nonstructural concretes containing varying proportions of recycled concrete aggregate. For scenarios in which virgin and recycled aggregates are locally available, only 20% recycled aggregate substitution is beneficial. This corresponds to a modest reduction in energy use and greenhouse gas emissions: up to 15 MJ/m3 and 1.20 kg CO2-eq./m3 of concrete, respectively. Only when virgin aggregate must be transported large distances are higher levels of substitution beneficial, in terms of the metrics studied.