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Life-Cycle Assessment of Concrete: Decision-Support Tool and Case Study Application

  • Author(s): Gursel, Aysegul Petek
  • Advisor(s): Horvath, Arpad
  • et al.
Abstract

Globally, construction and operation of the built environment is recognized as a significant source of greenhouse gas emissions (GHG). About 40% of anthropogenic GHG and 40% of raw materials use are assigned to buildings. Concrete, the most widely used man-made material, is used in buildings because of its flexibility and adaptability, its low maintenance requirements during the service life of the structures, and the economic and widespread accessibility of its constituents. The substantial production and consumption of global concrete manufacturing accounts for more than five percent of the human-related carbon dioxide emissions annually, mostly attributable to the production of cement clinker. However, environmental impacts are not limited to only GHG emissions. The analysis and quantification of the overall environmental impacts of concrete manufacturing and its application in building projects requires a holistic approach that is known as life-cycle assessment (LCA).

In this dissertation, a new process-based LCA tool (GreenConcrete LCA) was developed for the purpose of evaluating the environmental impacts of concrete from extraction of its raw materials to the end-of-life stage. The GreenConcrete LCA has MS Excel and web versions, both of which have the capability of calculating and comparing the LCA of different concrete mixtures designed for specific project purposes. In the tool, not only the direct but also the supply-chain impacts of manufacturing processes of concrete and its materials are evaluated. The integration of regional variations and technological alternatives within the tool offers a wide range of applicability and flexibility for users in the U.S. and worldwide. The new tool will ultimately allow policy makers, researchers, architects, civil engineers, and government agencies to assess the environmental sustainability of concrete in various building construction projects.

With the help of the tool, sensitivity analysis was conducted. GWP reduced significantly with the replacement of ordinary portland cement with supplementary cementitious materials (SCMs) such as fly ash and slag in concrete. Additionally, it was shown that environmentally and structurally advantageous concrete mixtures could be made with high-volumes of fly ash and limestone. A wide range of early and long term strengths were attainable depending on the selected mixture proportion. GHG emissions and criteria air pollutants were also successfully reduced and were in all cases similar to or lower than for ordinary portland cement concrete.

The concrete and steel frame versions of a dormitory building in Istanbul were also analyzed. Results from the case study showed that the operation phase dominated in GWP and energy consumption, which is consistent with literature results.

Finally, Turkish cement and concrete sector case study scenario analysis show that reductions in CO2-eq emissions can be achieved through, strategic choice of locations for cement and concrete plants for local and international distribution of products by less carbon-intensive modes of transportation, i.e., rail and water; switching to lower-carbon fuels in cement kilns, and expanding the use of biofuels and electric vehicles in delivery of cement and concrete products; Improvements in energy efficiency by installation of existing best available technologies for new plants and replacing older technologies for existing plants, switching to less carbon-intensive energy sources for electricity generation, integration of waste heat recovery systems in cement plants for off-grid electricity generation and using more energy efficient equipment in cement and concrete plants, use of alternative raw materials as sustainable waste management and GHG emission reduction options. Although these strategies can have great potential to abate CO2-eq emissions in cement and concrete industry both in Turkey and globally, technical, regulatory, and economic challenges are still considered obstacles against implementation of new approaches.

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