A comparative cradle-to-gate life cycle assessment of three concrete mix designs

Michael W Tait,Wai M Cheung

doi:10.1007/s11367-016-1045-5

Abstract

The concrete industry faces challenges to create concrete mix designs that reduce negative environmental impacts but also maintain high performance. This has led to ‘greener’ cementitious materials being developed which can decrease the use of traditional Portland cement (PC). This study intended to carry out a ‘cradle-to-gate’ life cycle assessment (LCA) on concrete mix designs containing different cementitious blends. The aim of this study was to obtain the overall environmental impact, with a particular focus on carbon dioxide (CO2) emissions of three concrete mix designs: CEM I (100 % PC content), CEM II/B-V (65 % PC content, 35 % Fly Ash (FA) content) and CEM III/B (30 % PC content, 70 % ground granulated blast furnace slag (GGBS) content). Evaluations of the three concrete mixes were performed using ‘SimaPro 8’ LCA software. A comparative cradle-to-gate LCA of these mixes has not currently been explored and could present a new insight into improving the environmental impact of concrete with the use of secondary materials. Recommendations from this work would help the industry make key decisions about concrete mix designs. Results show that Mix 2 (CEM II/B-V) and Mix 3 (CEM III/B) could potentially be taken forwards to improve their environmental impacts of concrete production. With respect to optimum mix design, it is strongly recommended that GGBS is selected as the addition of choice for reducing CO2 emissions. FA does still considerably improve sustainability when compared to PC, but this work proved that inclusion of GGBS environmentally optimises the mix design even further. Advantages of using GGBS include lower CO2 emissions, a substantial reduction of environmental impacts and an increased scope for sustainability due to the higher PC replacement levels that are permitted for GGBS. Due to mix designs enabling a higher contribution of GGBS additions, it would also indicate an increased positive effect regarding waste scenarios. The main contribution of this work demonstrated that concrete can be produced without loss of performance whilst significantly reducing the negative environmental impacts incurred in its production. The results obtained from this work would help to define the available options for optimising concrete mix design. The only material variations in each mix were the different cementitious blends. So, by determining the best option, a platform to make recommendations can be established based upon cementitious materials.

Highlights

IntroductionConcrete is the most widely used construction material on the planet (Henry and Kato 2014; Flower and Sanjayan 2007), and concrete production is believed to be responsible for up to 8 % of all CO2 emissions worldwide (Pade and Guimaraes 2007; Huntzinger and Eatmon 2009), 2.5 % of all UK CO2 emissions and the third largest source of CO2 emissions in the USA (Habert and Roussel 2009; Huntzinger and Eatmon 2009)
fly ash (FA) does still considerably improve sustainability when compared to Portland cement (PC), but this work proved that inclusion of ground granulated blast-furnace slag (GGBS) environmentally optimises the mix design even further
Advantages of using GGBS include lower CO2 emissions, a substantial reduction of environmental impacts and an increased scope for sustainability due to the higher PC replacement levels that are permitted for GGBS

Summary

Introduction

Concrete is the most widely used construction material on the planet (Henry and Kato 2014; Flower and Sanjayan 2007), and concrete production is believed to be responsible for up to 8 % of all CO2 emissions worldwide (Pade and Guimaraes 2007; Huntzinger and Eatmon 2009), 2.5 % of all UK CO2 emissions and the third largest source of CO2 emissions in the USA (Habert and Roussel 2009; Huntzinger and Eatmon 2009). Cement manufactures commit about 5 % of global and 2 % of UK CO2 emissions (Pade and Guimaraes 2007). Any modifications to concrete mixes are substantial when attempting to reduce negative environmental impacts and increase its sustainability. Sustainability consists of three main pillars: environmental, economic and social. Environmental performance has extended into all phases of a product’s life cycle and always comes at a cost (Cheung et al 2015; Cheung and Pachisia 2015). These costs can be reduced through careful consideration at the early stages, for instance, material selection and mix design in concrete production

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