CHAPTER 3 Life cycle of SS frame and RC frame
3.9 Parameters for comparison of differences between structural steel and RC
3.9.2 Parameters for comparison environmental sustainability differences
The Canadian Wood Council (1997) studied the Green House Gas (GHG), polluted air, solid waste, and ecological resource usage produced by steel, wood and RC buildings from a life cycle view. It reported that all of the four categories were produced in greater quantities by concrete buildings than steel buildings.
Eaton and Amato (1998) studied two office buildings with full air- conditioning, and reported that there was no significant difference between the environmental performance (in terms of embodied energy, embodied CO2 and operating energy/CO2) of steel framed office buildings in comparison with concrete framed office buildings. They concluded that energy consumption and CO2 emission could be used as relevant environmental parameters for life cycle assessments.
Jửnsson et al. (1997) used the method of LCA to compare the environmental impact of the structure of concrete versus steel frames in buildings throughout their life cycle. In their study, 50 years was assumed to be a building's service life. Eight parameters that weighted heavily were the use of fossil fuels, CO2, electricity, NOx, SOx, alloy materials and waste. By using three quantitative assessment methods -- the Environmental Priority Strategies in product design (EPS), the Environmental Theme Method (ETM) and the Ecological Scarcity Method (ESM) -- they concluded that the span between the highest and lowest values were not significant enough to draw any conclusions about what frame
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has the lowest environmental impact in spite of steel frames registering a slightly higher environmental impact than the other frames.
Lin (2003) investigated the CO2 emission and solid waste produced by steel and RC buildings in Taiwan. He found that CO2 emission and solid waste produced by RC structures was about 1.5 times that of a steel structure, from material production to the demolition stage. Furthermore, the solid waste produced by a RC structure is about 4 times that of a steel structure in demolition stage.
Peyroteo et al. (2007) compared the environmental impact of reinforced concrete versus steel structures. In their study, five parameters were selected in order to make the assessment. According to the values regarding the parameters caused by the manufacturing and transport of necessary materials, the energy consumption, water consumption, CO2 emission and NOx emission of steel structures were presented as being greater than reinforced concrete structures. Although the SO2 emission of reinforced concrete does more damage to the environment, the difference is only 0.8kg. Therefore, it was concluded that RC structures are friendlier to the environment. However, the fact that the steel is a resource that may reach a recyclable rate of 100% was not considered in their study. The environmental impact caused by demolition was not taken into account either.
Contrary to Peyroteo‘s results, Guggemos and Horvath (2005) from the US and Su et al. (2008) from China published their opposing results which found that energy consumption and other polluted air emissions produced by RC buildings are greater than those produced by steel buildings. Furthermore, Guggemos and Horvath (2005) pointed out that steel buildings have greater quantities of Volatile Organic Compound (VOC) and heavy metal (Cr, Ni, Mn) emissions.
Achulitz et at. (2000) studied the environmental impact from another perspective, using recyclability and disposition. They found that steel is 100%
recyclable and constitutes approximately 50% of the raw material for the production of crude steel worldwide. The recycling of steel is very much
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simplified by its magnetic properties. This guarantees the fast sorting of building debris. Steel and iron products that are disposed of in landfill sites decompose to oxidized products without harming the environment.
The parameters used by these studies and comparative result are shown in Table 3.4.
Table 3.4 Research on environmental impacts by concrete and steel building
Authors/year
--country Parameters Concrete/Steel
Canadian Wood Council (1997) --Canada
Green House Gas 1.24 times
Polluted air 1.17 times
Solid waste 1.44 times
Ecological resources usage 1.7 times
Eaton and Amato (1998)
embodied energy, embodied CO2 and operating energy/CO2
no significant difference
Lin (2003) --Taiwan
CO2 emission 1.5 times
Waste 4 times
Guggemos and Horvath (2005) --US
Energy use, CO2, CO, NO2, particulate
matter, SO2, and hydrocarbon emissions Concrete > Steel Volatile organic compound (VOC) and
heavy metal (Cr, Ni, Mn) emissions Concrete < Steel
Peyroteo et al.
(2007) --Portugal
Energy consumption, Water consumption,
CO2 emission, NOx emission Concrete < Steel
SO2 emission Concrete > Steel
Su et al. (2008) --China
Life-cycle energy consumption Steel:
75.1%*Concrete Environmental emissions Concrete > Steel
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The best way to deal with material waste is not to create it in the first place (Gavilan & Bernold, 1994). Tam and Le (2008) recommended the following measures to reduce waste in the design and construction stages: a) use long-
Authors/year
--country Parameters Concrete/Steel
Liew (2007) --Singapore
Minimum waste
Steel is not wasteful material, and all waste can be recycled
Health and aesthetic
Steel construction is a safety process
Recycling
All steel can be recycled, and on 45% of current steel use is from a recycled source
Reuse
Steel components can be
dismantled and reused
Zhou (2005) --China
Solid waste Steel < RC
Water consumption during construction
Steel < RC because of the dry construction Burgan and
Sansom (2006) Waste minimization Steel is better
than RC
Tam and Le (2008) Waste
Steel frames may produce less waste because of long-life and prefabrication
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life construction materials, such as steel; b) use environmentally-friendly construction methods, such as prefabrication; c) use recyclable materials; d) reuse materials; e) use secondary materials; and f) Avoid complex and labor- intensive operations.
With reference to the indicators addressed in section 2.4.5, as well as the parameters above, the following parameters have been identified to indicate the differences between the environmental sustainability of RC frames and steel frames.
Material consumption. This category includes the material recycling rate, the material reuse rate, the potential for being recycled (material recyclability), the potential for being reused (material reusability), and the material waste rate.
CO2 emission.
Water consumption during construction.
Noise produced during construction