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Concrete In Australia : March 2013
Concrete in Australia Vol 39 No 1 47 understanding of the most appropriate methods to be used in accordance with ISO 14040, as noted by Peters (2010), the industry still recognise calculations based on methods and means not in accordance with these standards: • Greenhouse gases considered: Due to a number of reasons (mainly associated with legislation and emission trading agreements) a number of industries (including cement) generally report on carbon dioxide emission only. e most widely used version of the popular Bath University Inventory of Carbon and Energy (Version 1.6) is based on carbon dioxide emissions only data. • Boundary Conditions: Not all studies identify a strict product system boundary. Moreover, not all studies identify the same product boundary systems. Some studies tend to include operatives/labourers transport to the place of the work while other studies (including studies based on PAS 2050: 2008) exclude these impacts. e treatment of waste and byproduct burdens is also another boundary issue where different solutions exist. Even the definition of the functional unit (eg is it a brick or 1 m2 of brickwork with a U Value of 0.3 W/m2K?) can have an overall impact on what should and should not be included. • Input-output vs Assembled: LCA based carbon footprints are usually built using a wealth of Life Cycle Inventory (LCI) primary information on factory production, efficiency and materials use. is wealth of data helps considerably in capturing the impact of production efficiency factors (such as raw material use efficiency, waste generation, efficiency of machines used, etc) in the final footprint results. Some of the publicly available precast concrete carbon footprints are not based on proper LCIs and are instead built on an assembled footprint based on assumed concrete mixes, raw material use level, waste generation levels, energy consumption levels, transport distances, etc LCA-based carbon footprints are apparently more accurate. • What standards to use: It is important to note that there are differences between various standards and methodologies, even if these were based on the same GWP principle. PAS 2050 includes a co-product/byproduct impact allocation rule which is slightly different to the one generally accepted in ISO 14044 and other standards. e BRE Environmental Profile accounts for end-of-life re-carbonation of concrete but the new prEN15804 may include this in a separate information module known as "Module D". e treatment of byproducts under prEN15804 will differ considerably from other standards. e treatment of some concrete ingredient materials (such as steel) is expected to be different and more strict under EN15804 or ISO14067 compared to the older EN14044. 2.3 Secondary information sourcing, data quality and criteria for comparisons ISO 14044 (Section 18.104.22.168) sets a number of requirements for the quality of data to be used in LCA studies including time/geographical/technology coverage of data, precision, completeness, consistency, quality of data sources and levels of uncertainty with assumptions made. European standard PD CEN/TR 15941 also sets similar requirements. However, unavailability of detailed information might sometimes lead researchers to work with data quality limitations, and this could have a defining role in the determination of the overall results and recommendations of a carbon footprinting study. e impact of factors mentioned at 2.1, 2.2 and 2.3 should not be underestimated: Table 1 shows results from studies carried out at different years looking at a range of precast products. e table shows that the overall proportions (for a generic product) are close. However, the overall carbon footprint values are completely different. is is mainly due to the difference in means used to build these carbon footprints: • It is understood that the Addtek (currently known as Consolis) Environmental Product Declaration for precast hollowcore flooring was based on a Life Cycle Inventory in accordance with ISO 14040 s requirements at the time (ISO 14040 was modified later in 2006) using primary data from the company s factories in Sweden, along with sourced secondary data for emissions associated with the upstream of the supply chain. e value used for cement s carbon footprint appears to be based on carbon dioxide emissions only and the reinforcement steel used is not all from recycled origins. e contribution of the latter caused this relatively higher impact. • e "Generic Precast" carbon dioxide emission value Table 1. Contribution of different factors to precast concrete products cradle-to-gate greenhouse gas emissions as demonstrated at a number of studies and references. EPD for Swedish Hollowcore (Alexander et al, 2003) Generic Precast (Hammond & Jones, 2011) German pipe Study (Specht & Lorenz, 2010) Cement production 68% 74% 84.82% Transport to factory 1% 2.5% unknown (included with other impacts) Precast factory 10.7% 16% 7.82% Other impacts 20.3% (includes reinforcement) 7.5% 7.36% Cradle-to-Gate emission value (Kg CO2e per tonne) 207.2 180 136