Evaluating the use of limestone calcined clay cement and recycled concrete aggregates for reducing the carbon footprint of concrete structures

Abstract

The accelerated pace of urbanization and globalisation has led to wide scale environmental impacts. Urbanization is highly dependent on new infrastructure which relies particularly on concrete as the most used building material. The cement and concrete industries have therefore become major contributors to global CO2 emissions. Hence, there is a growing need to implement sustainable alternatives to conventional concrete which have reduced equivalent carbon dioxide (eCO2) footprints, reduce the utilisation of non-renewable resources, and which still ensure the long-term performance of modern concrete structures. This paper evaluates the viability of using two alternative materials, limestone calcined clay cement (LC3) concrete and concrete produced using recycled concrete aggregates (i.e., recycled aggregate concrete or RAC) in the design of new concrete structures. Through a comprehensive literature analysis, representative values of concrete compressive strengths and eCO2 emissions released during material manufacturing and transportation were selected. Based on these selected values, a desktop study was completed, which investigated three hypothetical reinforced concrete building designs incorporating (i) concrete with natural aggregates (i.e., the control structure), (ii) LC3 concrete and (iii) RAC. In terms of sustainability, this study found that utilizing LC3 or RAC in a new building could reduce total building eCO2 emissions by up 14%. However, the extent of this reduction was found to be dependent on the quality of the material constituents and the transportation distances associated with each material constituent. Compared to LC3 concrete, the total eCO2 associated with design scenarios utilizing RAC was highly-dependent on distance between where recycled concrete aggregates were crushed and the concrete batching plant. These results provide promising evidence to evaluate the adequacy and reliability of these new sustainable materials for wide-scale applications in the construction industry.