2nd generation concrete construction: carbon footprint accounting

Abstract

Purpose-Construction contractors and facility managers are being challenged to minimize the carbon footprint. Life cycle carbon-equivalent (CO2-e) accounting, whereby the potential emissions of greenhouse gases due to energy expenditure during construction and subsequent occupation of built infrastructure, generally ceases at the end of the service life. However, following demolition, recycling of demolition waste that becomes incorporated into 2nd generation construction is seldom considered within the management of the carbon footprint. This paper aims to focus on built concrete infrastructure, particularly the ability of recycled concrete to chemically react with airborne CO2, thereby significantly influencing CO2-e estimates. Design/methodology/approach-CO2-e estimates were made in accordance with the methodology outlined in the Australian National Greenhouse Accounts (NGA) Factors and were based on the energy expended for each life cycle activity from audited records. Offsets to the CO2-e estimates were based on the documented ability of concrete to chemically react with airborne carbon dioxide ("carbonation") and predictions of CO2 uptake by concrete and recycled concrete was made using existing predictive diffusion models. The author's study focused on a built concrete bridge which was demolished and recycled at the end of the service life, and the recycled concrete was utilized towards 2nd generation construction. The sensitivity of CO2-e and carbonation estimates were tested on several different types of source demolition waste as well as subsequent construction applications using recycled concrete (RCA). Whole-of-life CO2-e estimates, including carbonation of RCA over the 1st and 2nd generations, were estimated and contrasted with conventional carbon footprints that end at the conclusion of the 1st generation. Findings-Following demolition, CO2 capture by RCA is significant due to the more permeable nature of the crushed RCA compared with the original built infrastructure. RCA also has considerably greater exposed surface area, relative to volume, than a built concrete structure, and therefore more highly exposed surface to react with CO2: it therefore carbonates more comprehensively. CO2-e estimates can be offset by as much as 55-65 per cent when including the contribution of carbonation of RCA built within 2nd generation infrastructure. Further offsets are achievable using blended fly ash or slag cement binders; however, this study has focused on concrete composed of 100 per cent OPC binders and the effects of RCA. Originality/value-Construction project estimates of life cycle CO2-e emissions should include 2 nd generation applications that follow the demolition of the 1st generation infrastructure. Life cycle estimates generally end at the time of demolition. However, by incorporating the recycled concrete demolition waste into the construction of 2nd generation infrastructure, the estimated CO2-e is significantly offset during the 2nd generation life cycle by chemical uptake of CO2 (carbonation). Th...

Carbon sequestration and storage in the built environment

“…Similarly, 18-21% of initial emissions could be sequestered by a reinforced concrete structure which accounted for recycling at the end-of-life (Andersson et al, 2013). Using recycled concrete, when accounting for second generation carbonation, can offset 55-65% of total emissions for a structure (Collins, 2013). Utilising waste CO 2 to form stable carbonatebased construction materials is another way in which carbon is stored by cementitious materials.…”

CO2 emissions from facility services

“…There is no shortage of specific literature on the carbon footprint of companies (Svensson and Wagner, 2011) or products (Demisse Gemechu, 2013; Fatarella et al , 2015). Also, in the area of buildings and building materials, there are publications on carbon footprints (Hitchin, 2013; Dixit et al , 2016; Victoria et al , 2017) and CO 2 reduction (Collins, 2013; Schwartz, 2016). On the other hand, there is very little information on the carbon footprint of services.…”

The Case for Sustainable Concrete Waste Management in Qatar

“…The research suggests that more atmospheric CO2 would be absorbed by concrete produced with RCA-incrushed form-over its life cycle, in comparison to NA concrete (Corinaldesi et al, 2010). This is because the surface area of exposure in RCA and the total carbonation process taking place during the concrete life cycle is extended (Collins, 2010(Collins, , 2013Lagerblad, 2005). This incremental environmental benefit using RAC has also been studied by Collins (2013).…”