Paper - The need for more sustainable structural materials is of increasing interest around the world driven by issues such as climate change and consumption of non-renewable resources. The concrete industry produces around 7% of global CO2 emissions. Recycled concrete aggregate (RCA) and Portland limestone cement (PLC) are two commercially available products that can help reduce the construction industry’s impact on the environment. RCA is regularly used in low risk applications such as road-base, parking/driveway pavements, and drainage fill but has not been accepted for use in higher risk structural applications such as deep beams and floor slabs. The goal of this research is to assess whether concrete containing RCA and PLC has a significant beneficial impact on the environment. The material and structural performance of five (5) mixes containing PLC and various levels of RCA were investigated. Two gradations of Aggneo Pro, Lafarge’s controlled quality RCA product, were used: a coarse RCA with 20-7 mm gradation and a granular RCA with 20-0 mm gradation. Up to 30% replacement of aggregate with RCA was tested for the coarse RCA and up to 20% replacement for the granular RCA. The first phase of the investigation involved a full materials testing program and found that the fresh and hardened properties were comparable to conventional concrete for all 5 of the RCA replacement levels. The second phase of testing evaluated the structural performance of the mixes. The mixes were evaluated by testing reinforced concrete slab specimens in three and four point bending to evaluate the shear and flexure capacity provided by each of the mixes. The initial results of the structural tests showed that 4 out of 5 of the RCA mixes performed at the same level as the benchmark mix. Since the experimental results showed that the RCA mixes have the potential to replace conventional aggregate, a life cycle analysis (LCA) was used to evaluate the environmental impact of structures made with PLC and RCA concrete against similar structures made with conventional concrete. Three different locations, with different populations and proximity to metropolitan areas, were used in the LCA to evaluate the benefits of using RCA in each case. Quantitative results for the environmental impact of each scenario are given based on life-time green house emissions and carbon footprints. Conclusions on the best use of PLC and RCA concrete are also given.
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