Detailed Results
Energy Consumption:
Energy consumption refers to the embodied energy of the materials within the building. Embodied energy includes all energy, direct and indirect, used to transform or transport raw materials into products and buildings, including inherent energy contained in raw or feedstock materials that are also used as common energy sources. (For example, natural gas used as a raw material in the production of various plastic (polymer) resins.) In addition, the model captures the indirect energy use associated with processing, transporting, converting and delivering fuel and energy. Athena EIE reports embodied energy in Mega-Joules (MJ).”
The model reports that production and construction of the concrete superstructure would require 109 millon MJ (30.3 million kilowatt hours) of energy. Approximately 4% of that total is consumed in the construction phase and approximately 1% of the total is consumed in the demolition and disposal phase. The remaining 95% is consumed in the manufacturing of the building materials. Transportation of materials during all phases accounts for approximately 7% of the total. Approximately 80% of this energy is estimated to come from fossil fuels.
For the steel superstructure, the model reports that production and construction would require 31.8 million MJ (8.8 million kilowatt hours) of energy. Approximately 5% of that total is consumed in the construction phase and approximately 0.6% is consumed in demolition and disposal. The remaining 94% is consumed in manufacture of the construction materials. Transportation of materials during all phases accounts for approximately 6% of the total. Approximately 54% of this energy would come from fossil fuels. The dominant non-fossil fuel contributor is feedstock fuels (fuel materials used as ingredients in production processes), which contribute 38%. In this case, the majority of feedstock fuels consist of coal used to produce coke, which is burned to fuel blast and basic oxygen furnaces and to add carbon to steel. It is likely that the majority of the carbon in this coal is released to the atmosphere as a product of combustion; however, an exact percentage was not included in information reviewed for this project.
Energy use is of concern because of the environmental damage caused by extraction of fuels from the environment, increased scarcity of energy supplies, and emissions and waste produced in energy production (e.g. emissions and ash from burning of fossil fuels, or waste from nuclear power plants). To help guage the significance of the above figures, consider that total annual global energy consumption is on the order of 235 quadrillion MJ. Thus, the annual energy consumption of 6 billion people is only about 2 million times the total for the concrete superstructure. While the energy consumed in producing the superstructure is small in comparison to the global total, it is significant as an amount of energy consumed through the decision and activities of one individual or organization. A steel superstructure would result in the consumption of approximately one third as much energy as a concrete superstructure and, based on this impact category alone, would be the preferred choice.
Natural Resource Use:
Natural Resource Use is calculated by the Athena EIE model based on the mass of different resources required to produce various materials. These amounts are reported as a composite index to make equivalent the contribution of various resources whose extraction has varying levels of environmental impact. Athena SMI developed subjective scores of the relative environmental effects of different resource extraction activities. The scores were combined into a set of resource-specific index numbers, which are applied as weights to the amounts of raw resources used, producing "ecologically weighted kilograms" that account for ecological carrying capacity effects of extracting resources. All resources have a weight of 1 except for limestone (1.5), iron ore (2.25), coal (2.25), and woodfiber (2.5). This composite index represents a subjective weighting. This weighting does not include any social or economic effects of resource use that builders may want to consider when choosing materials. However, the concrete superstructure consumes approximately six times the mass resources that the steel superstructure does when measured in either weighted or unweighted units. Results reported in the Summary Results section are based on weighted units while the results below are in unweighted units. Reported results do not include consumption associated with transportation.
According to the model, production of a concrete superstructure would require the consumption of 62,632 tons of materials including constituents of concrete and steel reinforcements, process chemicals, fuels, and other substances for use in the manufacturing phase. Some of this mass, including substances such as flyash for concrete and scrap steel, is the product of recycling operations. However, the majority of the materials are extracted from environmental stocks. Additionally, 5.8 million gallons of water would be used in various manufacturing processes. This figure is reported separately because the water is not consumed (i.e. it still exists after use). However, this figure is significant because the water undergoes heating, pH adjustment, the addition of pollutants at concentrations below those regulated by discharge permits, or other changes that can affect the ecosystems into which the water is introduced upon discharge.
Production of a steel superstructure is estimated to require the consumption of 9,665 tons of the same types of materials reported for the concrete superstructure. The proportion of recyclable materials used for the steel superstructure is potentially higher due to the higher quality of secondary steel products. However, approximately 11 million gallons of water would be used to manufacture the steel superstructure, which is roughly double the usage for producing the concrete superstructure.
Impacts from resource use are similar to those of energy consumption and include the environmental effects of extraction, increased resource scarcity, and by-products of use in industrial processes. Reducing the mass of material consumed helps to reduce the effects of industrial processes on the landscape and the environment in general. Production of a steel superstructure uses roughly one sixth the amount of resources used to produce a concrete superstructure and, based on this impact category alone, would be the preferred choice. Discussion of water use is presented in the Water Emissions portion of this section.
Toxics Use
Based on a review of typical production processes for mining raw materials and producing concrete and steel, processes for the production of steel appear to involve more toxic substances than processes for the production of concrete. Concrete manufacture consists primarily of the mixing and physical conditioning of inorganic mineral powders and aggregates. The major toxic substances associated with concrete manufacture include airborne particulates, such as silica dust. The major chemical toxins used are basic plant maintenance supplies (solvents, paints, lubricants and oils, etc.) and paint wastes for concrete products which are painted prior to shipment.
Steel manufacture involves heat treatment of iron ore and coal, which produces various solid and gaseous by-products containing hydrocarbons and heavy metals. Metal rolling, shaping, and finishing processes use large amounts of toxic materials including acid pickling baths, solvents for cleaning, and heavy metals for plating operations. For the steel superstructure model, Athena EIE uses basic carbon steel which likely undergoes basic pickling and forming processes. The model also uses galvanized steel decking, which undergoes plating via dipping in a molten zinc bath.
Using toxic materials in industrial processes requires the production and transportation of those materials, which have their own environmental and health and safety implications. Many toxic materials are extensively recycled within industrial processes, minimizing the amount of material needed. However, these materials eventually become spent and are either released into the environment or transported to a disposal facility and disposed of, becoming an environmental liability in either case. Additionally, workers handling these materials are at higher risk for exposure and injury than if they were not working with hazardous materials. Precise figures for concrete and steel are not available; however, based on the above qualitative analysis, concrete production likely uses less toxic chemicals than steel production on a mass basis. However, due to the high content of iron and steel used as rebar and in the flooring for the concrete superstructure, as well as the higher mass of material needed for a concrete structure, it is likely that production of a concrete superstructure for the East Campus Project building would involve more toxic substances than a steel superstructure.
Transportation of Materials
Transportation of Materials is intended to capture the environmental effects of transporting materials from production facilities to the building site. Impacts in this category are proportional to the distance of production facilities from the building site and to the mass of material needed to be transported. Web-based query searches of the US Environmental Protection Agency Resource Conservation and Recovery Information System (RCRIS) database indicate that facilities located within New England produce both steel and concrete. Therefore, material required to build a superstructure out of either steel or concrete is available locally. Thus, no significant difference between the material transportation requirements of the two alternatives is apparent. This analysis should be revisited once candidate material suppliers are identified to determine if transportation of materials becomes a significant factor between the two material choices. (Note that any disparity in transportation requirements based on the mass of the materials to be transported for production is accounted for in impact categories evaluated using the Athena EIE).
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