We undertake Life Cycle Assessment (LCA) of the cumulative energy demand (CED) and global warming potential (GWP) for a portfolio of 10 multi-family residences in the U.S. We argue that prior LCA ...studies of buildings use an inconsistent boundary for processes to be included in the supply chain: The operational phase includes all energy use in a building, but supply chains for the production of appliances, equipment and consumables associated with activities done in the building are neglected. We correct this by starting the analysis with an explicit definition of a functional unit, providing climate controlled space, and including processes associated with this functional unit. Using a hybrid LCA approach, the CED for low, mid and high-rise multi-family residences is found to increase from 30, 34, to 39 GJ/m2, respectively. This increase is due to the need for energy-intensive structural materials such as concrete and steel in taller buildings. With our approach, the share of materials and construction of total life cycle energy doubles to 26%, compared with a 13% share that would be obtained with inconsistent system boundaries used in prior studies. We thus argue that explicit definition of functional unit leads to an increase in the contribution of supply chains to building energy life cycles.
Concrete is one of the most abundantly produced and commonly used construction materials in the world. The production of cement—the main binder in concrete—is energy-intensive, using roughly ten ...times the national average ratio for energy to gross output of goods and services. Given the high demand for concrete globally and the amount of energy used to produce cement, it is worthwhile to find lower embodied-energy materials to partially replace cement to improve the environmental impacts of concrete without decreasing the concrete performance. One such potential cement replacement is the panel glass found in discarded cathode-ray tubes (CRTs). It is against this backdrop that this study aimed to investigate the technical feasibility and the environmental impacts of using a novel blend of recycled glass and CRT panel glass as pozzolanic material for replacing a portion of ordinary portland cement (OPC) in concrete. Additionally, this study simultaneously looked at the concrete functional performance and environmental impact, and the study was performed at an industrial scale using existing production infrastructure, production volumes, standardized testing, and a life-cycle assessment (LCA) to support the functional testing and environmental impact quantification. Results show that the novel blend of glass met the required performance standards, and when it was blended with cement, the mixture produced concrete with similar or improved functional performance and significantly reduced environmental impacts across all examined impact categories. Future work is needed to examine the additional benefits of diverting CRTs from their current end-of-life pathways and de-risking CRT storage.
Life cycle assessment (LCA) has been used for decades to study the environmental impacts of the built environment. This study extends work in this area by completing an LCA of the cumulative energy ...demand (CED) and global warming potential (GWP) of low, mid and high-rise multi-family dwellings. Using a hybrid LCA, this study finds that the CED and GWP for low, mid and high-rise multi-family residences increases from 37, 39, to 42 GJ/m 2, and 3.6, 3.8, and 4 tCO2eq/m2 on average, respectively. As with previous studies, the operation phase dominates total life cycle energy, but with smaller share of 77% to 87%. A follow-up study examines how uncertainty in the energy intensity of materials might affect a building LCA. The exploration led to development of a knowledge-based bounding approach to mitigate uncertainty. Knowledge-based bounding maps knowledge of a product, such as country of origin or recycled content, to numerical uncertainty bounds. Gathering additional information about the product in question can shrink these bounds and, through an iterative process, reduce uncertainty until the goals of an LCA are met. Developing knowledge-based bounds for steel, this study finds that if steel type, recycled content and country of origin are all unknown, the life cycle carbon dioxide equivalent emissions of steel can vary from .7 to 5.9 kg tCO2eq per kg of steel. In contrast, with knowledge that the steel is un-alloyed, and, has a 64-100% recycled content, uncertainty bounds are reduced to .8-1.4 kg tCO 2eq/kg steel. These two bounds are applied in life cycle assessment of concrete and steel framed buildings. The 0.7 to 5.9 kg tCO2eq emissions per kg of steel bound leads to ranges for the life cycle emissions too wide to distinguish the preferability of steel and concrete framed buildings. However, the lower bounds, 0.8-1.4 tCO2eq/kg of steel, shows unambiguously that steel-framed buildings have lower CO2 emissions.
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