The quantitative data collected during the case study is included in Appendices 1 to 3. This disaggregated data has been processed using the BCSA Carbon Footprint Tool v3 to establish the aggregated carbon emission of the steelwork under study. The footprint tool is based on PAS 2050 (2008) and Defra (2010) guidelines, the latter being consistent with the Greenhouse Gas Protocol (WBCSD and WRI, 2004).
BCSA is a UK national organisation whose primary objective is to promote the use of structural steelwork in the construction industry. Its members include the steelwork contractors involved in the design, fabrication and erection of steelwork; suppliers of material and; professionals involved in the specification, certification and erection techniques. The Carbon Footprint tool is one of the professional services that the body provides to its members, which includes all UK steel contractors. The tool has been developed by the Steel Construction Institute (SCI), a leading and independent UK provider of technical expertise to the steel construction industry.
The tool has been designed to calculate the carbon footprint produced by a steelwork contractor through its manufacturing and business operations. The manufacturing aspect covers emissions resulting from the manufacture, transportation and erection of the steelwork whereas the business aspect covers all other day-to-day activities of the company including administration and design. These two emissions are then combined to come up with the overall company footprint.
Alternatively, the tool can just be utilised to calculate the carbon footprint of steel manufacture and erection of a particular project. The BCSA Carbon Footprint Tool was utilised for this second purpose and, as no specific company data was collected as part of this research, the simplified approach was followed.
Whilst the case study was limited to the fabrication, transportation to site and erection phases of the steelwork, the footprint tool considers all the other upstream phases. The
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boundary condition for the footprint tool is therefore cradle to end-of-erection on site. Furthermore, the benefits of recycling at the end of life have been factored into footprint tool using the Worldsteel (2011b) system expansion method.
Owing to the dominance of carbon dioxide in GHG emissions and the lack of available data in
many of the other anthropogenic gases, the tool relies on the available CO2 data. The tool
considers all the three scopes of GHG emissions as defined by the Greenhouse Gas Protocol: Scope 1 (emissions from sources owned or controlled by the Subcontractor); Scope 2 (indirect GHG emissions from the generation of purchased electricity consumed by the Subcontractor) and; Scope 3 (other indirect emissions that result from the activities of the Subcontractor, although not under its control). The following sections describe how each phase of the steelwork, which happened to be all hot-rolled, was considered in the carbon footprint tool.
7.3.1
Production
The case study only recorded the quantities of the fabricated steelwork. Therefore for the incoming steel intermediate products for the factory, a 7% increase has been applied to the finished product to cater for wastage (6.8%) and temporary steelwork (0.2%) as described in Sections 8.4 and 10.3 respectively. The emission factors shown in Table 7.2 were then applied to these quantities to obtain the production carbon impact. As mentioned above, a sensitivity analysis has been carried out for the recyclability of steel using the Worldsteel (2011b) system expansion method and the impact is already included in these emission factors.
Table 7.2: Emission factors for steel production including end-of life recycling (SCI, 2011)
Steel Element Emission Factor (kgCO2e/kg) Comment
Plate 0.97
Tubes 0.92 Assumed to include square and rectangular hollow sections Sections 0.79
Angles and Channels 0.79
7.3.2
Transportation to manufacturer
The same steel quantities as in Section 7.3.1 above were considered in this section. The type of vehicle, weight laden and distance travelled from the supplier to the factory was not studied in this research and so default information was used for the tool:
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• Distance travelled - 250km
• Type of vehicle - articulated truck
• Weight laden – 50%
• Return trip – empty
The total transport emissions factors shown in the Table 7.3 below are made up of direct (from combustion during delivery) and indirect (from production of the fuel) portions, as derived from Defra (2010).
Table 7.3: Articulated diesel freight transport emission factors (SCI, 2011)
Weight laden kgCO2e per vehicle km
Direct Indirect Total
0% 0.709 0.136 0.845
50% 0.942 0.181 1.123
60% 0.988 0.190 1.178
7.3.3
Manufacture
The quantities of incoming steel intermediate products described in Section 7.3.1 above were used to work out the carbon emission for this phase. Wastage is worked out as the difference in quantities between the fabricated and incoming products.
The energy required by the contractor to manufacture this steelwork was not studied in this research and consequently, an estimated value of 2.55 kWh/kg of fabricated steel was used as discussed in Section 8.4.
7.3.4
Transport to site
From the data in Appendix 3, it was estimated that trucks loads were generally between 50% to 100% weight laden, considering that the articulated diesel freight used for the transportation of all the steelwork to site had a net capacity of 33 tonnes. From the study carried out in Chapter 10, approximately 1505 Mt of steelwork from Romania was delivered to site in 73 truckloads. This works out to an average truck load of about 19.5Mt, roughly 60% weight laden. The return trips were considered to be totally empty, meaning 0% weight laden. The applicable emission factors are also shown in Table 7.3 above. The actual quantities of finished components recorded during the study were used in this calculation.
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7.3.5
Erection
Due to all the variables that are linked to each particular site, the accuracy of average emission data that is available in the industry and can be applied to the erection phase is very low. The following information, derived from Appendix 1, has been entered into the BCSA footprint tool for the erection of the 4747 tonnes of Assembly Hall steelwork:
• Cranes – three mobile cranes that spent 54, 35 and 18 weeks on site each, giving a
total of 107 weeks;
• MEWP – eight Mobile Elevated Working Platforms (MEWP) that spent 54, 48, 27, 18,
18, 14, 4 and 4 weeks on site each, giving a total of 187 weeks;
• Forklifts – five forklifts that spent 18, 18, 18, 9 and 9 weeks on site each, giving a total of 72 weeks.
7.4
Summary
This section looked at the different approaches and tools that are used to assess carbon footprint in the industry, which include LCA, LCI and carbon footprint tools. The aggregated embodied carbon coefficients for the four most common structural materials (brick/block, concrete, steel and timber) were established from the ICE. A closer look at the BCSA Carbon Footprint tool was then taken, including the manner that the disaggregated data from the case study will be entered into this footprint tool.
It has been established above that direct comparison of results from carbon footprint tools is difficult due to the adoption of different approaches and boundary cases, even when the background data is coming from the same source. The following chapter will now cover the embodied carbon of steel in more detail.
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