Comparative LCA of concrete with natural and recycled coarse aggregate in the New York City area

Abstract

The purpose of the present study is to compare the environmental impacts of using coarse natural aggregate (NA) and coarse recycled concrete aggregate (RCA) to produce concrete in the New York City area, by means of a unique LCA framework that incorporates comprehensive regional data. A comparative environmental impact assessment study was performed on the critical processes of the life cycles of NA and RCA concretes. For this purpose, concrete ready-mix plants, construction and demolition waste (CDW) recycling plants, NA quarries, and other producers and distributers of concrete raw materials, in addition to CDW landfills in the New York City area, were located. NA and RCA concrete mix proportions that result in the same compressive strength of concrete were used. Also, the environmental impact that would be caused if CDW was landfilled rather than processed into RCA was measured. In the New York City area, replacing NA with RCA as a concrete aggregate does not affect the environmental impact of concrete production significantly. However, if CDW is recycled only for the purpose of producing concrete aggregate, the avoided landfilling of the CDW will be a result of producing RCA concrete. When avoided landfilling is accounted for, the magnitude of some of the environmental impact indicators for RCA concrete is significantly lower than those of NA concrete (16 and 17% for acidification and smog formation, respectively). In addition, it was found that the impact from transporting RCA to ready-mix plants is on average 37% less than that caused by transporting NA to the plants. Sensitivity analyses and normalization of the results revealed that the environmental impact of changing the type of concrete aggregate from NA to RCA is negligible compared to the total environmental burden of New York City. If RCA concrete is used for all types of construction projects in the NYC area, achieving a significant reduction in the environmental impacts is unlikely. Future work is needed to study specific projects in the region that are categorized based on demand for transportation and cement (the largest environmental stressors of concrete production) to determine for which type of project the use of RCA concrete has the highest environmental benefits.