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| STEEL vs. CONCRETE |
| GREENING EAST CAMPUS |
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| Solid Waste Production Solid Waste Production is reported by Athena EIE by mass (kg). No distinction is made between hazardous and non hazardous wastes. According to the Athena EIE results, manufacturing a concrete superstructure would produce 2,169 tons of solid waste. Over 99% of this is produced during the manufacturing phase. Approximately 63% of the waste is concrete waste and blast furnace slag and dust, the remainder being unspecified. If the building materials are not recycled during the demolition and disposal phase, then the mass of the superstructure itself (47,155 tons) should be added to this total. The potential for recyclability is discussed in the Recyclability of Materials portion of this section. Manufacturing of the steel superstructure would produce a total of 600 tons of solid waste, of which 25% is produced during the construction phase, the remainder being produced during the manufacturing phase. This waste consists of roughly the same components at the same proportions as the wastestream for the concrete superstructure. Again, these results do not include the mass of the superstructure itself (7,754 tons). The accumulation of non-hazardous solid waste leads to the unproductive use of land for landfills, increases in emissions from incinerators. Hazardous waste contributes to a host of environmental problems from ecosystem damage to contamination of water supplies and fish stocks to human sickness and death from direct exposure. Available data does not indicate the proportion of the waste produced by each superstructure that is hazardous or non-hazardous. A steel superstructure produces approximately one-fourth the amount of solid waste produced by a concrete superstructure and, based on this impact category alone, would be the preferred choice. However, the proportion of each wastestream that is hazardous may change the significance of these results. The presence of toxic substances in production processes is discussed in the Toxics Use portion of this section. Recyclability of Materials Structural steel is often recycled and can be used to produce high-quality secondary products. High-strength concrete cannot be recycled to produce product of a similar quality. Recycled concrete is used primarily as fill and base material. It can also be used as aggregate for new concrete; however, it then needs to be combined with cement. Additionally, according to the Athena EIE model, a concrete superstructure, at 47,155 tons, would require approximately 6 times the mass of material of a steel superstructure of 7,754 tons. Transportation of this extra mass would create additional environmental impacts. Based on this impact category alone, a steel superstructure is the preferred choice. Air Pollution Emissions Athena EIE reports emissions to air as a composite index. The value reported is based on the amount of air needed to dilute the total amount of substances emitted to acceptable concentrations (below regulatory criteria for ambient air quality). The model uses the single substance that would require the most dilution to determine the dilution value on the assumption that the same air can contain less hazardous concentrations of other contaminants as well and still be safe. This does not account for any potential chronic synergistic effects that may arise from the combined actions of various pollutants. The valuation of different substances in this index is based on the physical properties of the substances measured and not on subjective valuation. However, it accounts only for toxicity and not for other potential impacts from air pollution such as acid rain. The Athena EIE results report that production of a concrete superstructure would result in the emission of 11,841 tons of pollutants into the air. Carbon dioxide from the manufacturing phase accounts for 98 percent of this. Other pollutants tracked include organics (VOCs, methane and others), inorganics (NOx, SOx, and metals), and acid gases. The results indicated that 1,761 tons of pollutants would be emitted into the air as a result of the steel superstructure’s production. Like concrete, 98 percent of the total is carbon dioxide from the manufacturing phase. Air pollution causes a great number of environmental and human health problems, including global warming; increased rates of asthma and other ailments among humans; acid rain, leading to the acidification of water bodies and the deterioration of built infrastructure, and aerial deposition of toxics such as heavy metals on soils downwind of emitting facilities. The production and construction of the steel superstructure emits approximately one-seventh the amount of air pollutants that the production and construction of a concrete superstructure would emit and, based on this impact category alone, is the preferred choice. Water Pollution Emissions Water Pollution Emissions are reported by Athena EIE as a composite index based on the amount of water needed to dilute the total amount of substances emitted to acceptable concentrations (below regulatory criteria for drinking water quality). The model uses the single substance that would require the most dilution to determine the dilution value on the assumption that the same air can contain less hazardous concentrations of other contaminants as well and still be safe. This does not account for any potential chronic synergistic effects that may arise from the combined actions of various pollutants. The valuation of different substances in this index is based on the physical properties of the substances measured and not on subjective valuation. However, it accounts only for toxicity and not for other potential impacts from water pollution such as ecosystem damage. The Athena EIE results indicate that production and construction of a concrete superstructure would result in the release of 58 tons of pollutants into water bodies, more than 99 percent of which result from the manufacturing phase. The results for production and construction of a steel superstructure indicate a release of 5 tons of pollutants into waterbodies, greater than 99 percent of which result from the manufacturing phase. However, the composite index value reported for the steel superstructure is almost three times that for the concrete superstructure, indicating that the pollutants released during steel production are much more harmful to waterbodies than those released during concrete production. Of the tracked pollutants, the steel superstructure results in more phenol and oil and grease released than does the concrete superstructure in absolute terms. This explains much of the difference because phenol is weighted heavily in the Athena Water Pollution Composite index. Water pollution affects (drinking)water supplies, fish stocks, and ecosystems through toxicity and changes to pH, nutrient content and other chemical properties of lakes, rivers, and streams. Based on the Athena EIE data on the relative impacts of various common pollutants, a steel superstructure would have nearly three times greater of an impact than a concrete superstructure. Therefore, based on this impact category alone, concrete is the preferred choice. Global Warming Potential Global Warming Potential (GWP) represents the amount of greenhouse gases emitted during production, construction, and disposal of superstructure materials. Athena EIE reports GWP as a composite index in units of CO2 equivalents. Concentrations of substances other than CO2 are multiplied by a factor that represents their heat trapping capacity relative to that of CO2. This index does not include any subjective evaluation as the weighting of different substances is based on their physical properties. The model reported that the concrete superstructure would result in the emission of greenhouse gases whose effects are estimated to be equivalent to 11,959 tons of CO2. 98 percent of these emissions are reported to be from the manufacturing phase. For the steel superstructure, the model estimates emissions of 1,781 tons of CO2 equivalent. Again, 99 percent of these emissions are reported to be from the manufacturing phase. Global warming is potentially the world’s most serious environmental problem. Based on climate modeling and documented ambient temperature changes, scientists have predicted that global warming could lead to an increase in severe weather, shifting of agricultural zones and rainfall patterns, rising sea levels and other deleterious effects. The steel superstructure would contribute to global warming only one-seventh as much as a concrete superstructure would and, based on this impact category alone, represents the preferred choice. Production Worker Health and Safety: Fatal Occupational Accidents Rates of fatal occupational accidents are calculated using statistics from the US Bureau of Labor Statistics and are only representative of domestically produced materials. Results for a concrete superstructure are based on figures from the crushed and broken stone and sand and gravel mining and the concrete, gypsum, and plaster products manufacturing industries (SIC codes 142, 144, and 327, respectively). Results for a steel superstructure are based on figures from the metal mining, coal mining (these figures were multiplied by 0.03 to account for the proportion of coal production used in coke manufacture), blast furnace and steel mills, and fabricated structural metal industries (SIC codes 10, 12, 3312, and 3441, respectively). Average figures of annual fatal occupational injuries for the years 1996 to 2001 were averaged and divided by the sum of total employment figures for each sector from the year 2000 to obtain rates of fatal occupational injuries per 100 workers. The average rate of fatal occupational injuries for workers contributing to the production of concrete is 0.0135 injuries per 100 workers. The average rate of fatal occupational injuries for workers contributing to the production of structural steel is 0.0138 injuries per 100 workers. Worker health and safety is often highly related to workers rights and labor equality. In the U.S. occupational health and safety standards are high and great effort is made to ensure the safety of workers. Variation in health and safety performance measures in the U.S. is more often an indicator of the inherent danger of production processes for any number of reasons. Fatal occupational injuries during production can also be seen as a human cost of consuming a particular product. In this case, the above data indicate that there is no significant difference in the rate of fatal occupational injuries per 100 workers for production of either concrete or structural steel for domestically produced materials. Production Worker Health and Safety: Non-Fatal Injuries and Illnesses Non-fatal injury and illness rates were obtained from the US Bureau of Labor Statistics. Results for a concrete superstructure are based on figures from the crushed and broken stone and sand and gravel mining and the concrete, gypsum, and plaster products manufacturing industries (SIC codes 142, 144, and 327, respectively). Results for a steel superstructure are based on figures from the metal mining, coal mining (these figures were multiplied by 0.03 to account for the proportion of coal production used in coke manufacture), blast furnace and steel mills, and fabricated structural metal industries (SIC codes 10, 12, 3312, and 3441, respectively).17 Production of concrete involves 9.23 injuries or illnesses per 100 workers. Production of steel involves 10.45 injuries or illnesses per 100 workers. Worker health and safety is often highly related to workers rights and labor equality. In the U.S. occupational health and safety standards are high and great effort is made to ensure the safety of workers. Variation in health and safety performance measures in the U.S. is more often an indicator of the inherent danger of production processes for any number of reasons. Injury and illness during production can also be seen as a human cost of consuming a particular product. In this case, the above data indicate that steel production involves a rate of injury and illness 12% higher than that of concrete production for domestically produced materials. Based on this impact criteria alone, concrete would be the preferred choice. NOTE: The modeled environmental impacts occur primarily in the manufacturing phase, their magnitude is proportional to the amount of material used. Therefore, if more accurate figures for the amount of material required for each superstructure system is obtained, the Athena EIE results for environmental impact can simply be multiplied by the ratio of the figures reported above and the new figures for total material used to obtain a more accurate result of environntal impacts. The Steel vs. Concrete case study analysis contains errors that make it unsuitable for reference other than as a template for similar analysis using more accurate data. Errors related to results from the Athena EIE tool do not in any way indicate a defect in the tool itself and are likely due to operator error. At the time the research was conducted the author of the Steel vs. Concrete case study was not experienced in structural engineering, or in operation of the Athena EIE tool. No attempt was made to solicit assistance from the Athena sustainable Materials Institute to correct these errors. Athena Sustainable Materials Institute, reports that the Athena EIE is capable of performing the analysis in the Steel vs. Concrete case study correctly and that, "typical steel superstructures will embody more energy and result in more air and water emissions, but produce fewer greenhouse gases, use less material resources and generate fewer solid wastes than a comparable concrete superstructure. So there are trade-offs when specifying either material. References Athena SMI. Undated. Athena Environmental Impact Estimator Electronic Help Documentation. Introduction: Interpreting Athena Results. Jones, K. 1999. The Density of Concrete, from the Hypertextbook.com website. Edited by Glenn Elert. Available from http://hypertextbook.com/facts/1999/KatrinaJones.shtml. Internet Accessed 2 December 2002. The Associated General Contractors of America. Undated. Concrete Recycling Facts. Available from http://www.agc.org/Environmental_Info/concrete_facts.asp. Internet accessed 2 December 2002. United Nations Environment Program. 1996. Life Cycle Assessment: What It Is and How To Do It. US Bureau of Labor Statistics website at http://www.bls.gov/iif/oshwc/cfoi/cftb0155.pdf and http://www.bls.gov/iif/oshwc/osh/os/ostb1001.pdf. Both addresses were accessed on 17 November 2002. US Energy Information Administration. Undated. Coal Industry Annual 2000 Available from http://www.eia.doe.gov/cneaf/coal/cia/cia_sum.html. Internet accessed 2 December 2002. US Environmental Protection Agency Office of Compliance Sector Notebook Project. 1995. Profile of the Non-Metal Non-Fuel Mining Industry. September. US Environmental Protection Agency Office of Compliance Sector Notebook Project. 1995. Profile of the Stone, Clay, Glass, and Concrete Products Industry. September. US Environmental Protection Agency Office of Compliance Sector Notebook Project. 1995. Profile of the Metal Mining Industry. September. US Environmental Protection Agency Office of Compliance Sector Notebook Project. 1995. Profile of the Iron and Steel Industry. September. US Environmental Protection Agency. 2002. Resource Conservation and Recovery Act Information Database. Available at http://www.epa.gov/enviro/html/rcris/rcris_query_java.html. Internet accessed 24 Novermber 2002. |
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