Decarbonization of Engineered Cementitious Composites (ECC)

Abstract

Mitigating CO2 emissions has emerged as one of the most critical global challenges. The concrete industry comprises approximately 8% of global CO2 emissions due primarily to the large carbon footprint from ordinary Portland cement production. Concrete's brittle nature necessitates early infrastructure reconstruction and rehabilitation, leading to high operational embodied carbon emissions throughout its service life. Engineered cementitious composites (ECC) have demonstrated a capacity to enhance structural fatigue resistance and reduce CO2 emissions during the use phase through their high tensile performance and crack width control capability. However, ECC's high cement content and use of synthetic fiber incur substantial economic and environmental costs. Therefore, there is an urgent need to address ECC’s high embodied carbon footprint during the production phase if it is to be used as a sustainable alternative to traditional concrete. The goals of this doctoral research encompass the development of strategies to decarbonize ECC while maintaining its unique ductile performance and showcasing its economic and environmental competitiveness compared to regular concrete. Three major approaches are proposed in this research, including carbon sequestration through carbonation curing, the use of industrial waste materials (IWMs), and the employment of localized materials. The impacts of carbonation curing on ECC are investigated, such as changes to mechanical and micromechanical properties. With the incorporation of IWMs, a low-carbon sustainable WPE-ECC is designed by substituting virgin polyethylene fiber with waste polyethylene fiber (WPE) from waste marine fishing nets. The low carbon ECC’s mechanical properties, including compressive, tensile, flexural strength, and ductility, are examined. Considering the increasing cost and limited availability of commonly used IWMs such as fly ash and manufactured silica sand, a case study of the Kingdom of Saudi Arabia examines replacing these materials with locally available alternatives, namely volcanic ash and desert sand, to mitigate the embodied carbon and cost associated with long-distance material transportation. A localized self-stressing ECC is developed and optimized to mitigate challenges posed by alternative materials and ensure a sufficient working time window and mechanical performance of the ECC. The reductions of embodied carbon footprint and cost for each of these three approaches are quantified and compared to conventional concrete materials. Results indicate that carbonation curing significantly improves fatigue life and reduces the midspan deflection of ECC. CO2-cured ECC exhibits approximately 20% CO2 uptake per cement mass. Carbonation curing increases ECC’s flexural strength and promotes effective crack width control, resulting in reduced post-fatigue crack width. The positive impact of carbonation curing on the fatigue behavior of ECC can simultaneously lower the embodied and operational carbon of ECC structural members during service. In the case of the IWMs method, the findings suggest that carbonation-cured WPE-reinforced ECC has only 50% of the CO2 footprint and 67% of the cost of conventional concrete. Meanwhile, this low-carbon ECC maintains at least 4 MPa tensile strength and 6% tensile ductility, demonstrating the feasibility of developing environmentally-friendly construction materials without compromising high performance for civil infrastructure applications. Similarly, the localized self-stressing ECC exhibits comparable mechanical performance to other ECC grades, showing the feasibility of replacing FA and silica sand with locally available materials, resulting in a low-carbon ECC with promising implications for practical construction applications. This research provides three distinct approaches for ECC decarbonization that can be integrated with one another, offering a potential pathway into the construction industry that urgently needs to be decarbonized.