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Lookup NU author(s): Dr Xiang XieORCiD,
Dr Haoyu HuangORCiD
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Concrete is a versatile material widely used in the construction industry for centuries. With the growing investment in this sector, about 30 billion tons of concrete are produced each year, responsible for at least 8% of the world’s carbon emissions. Meanwhile, the surging amount of waste generated by the construction industry, known as Construction and Demolition (C&D) waste, becomes a significant threat to the environment. To accelerate the sustainable agenda, Recycled Aggregates (RAs), processed by C&D waste recycling plants, are reused in concrete production to reduce the depletion of Natural Aggregate (NA) sources, thus contributing to the circular economy in construction. Several studies have been conducted to assess the life cycle impact of adopting RA on reducing carbon emissions for concrete production, taking into account factors, such as the Recycled Aggregate Concrete (RAC) mixture design, carbon dioxide uptake, and transportation of RAs. However, in addition to the Life Cycle Assessment (LCA) at a macro or national level for concrete production, it is also important to assess the impact of using RAC on individual buildings at a micro or local level. On the one hand, compared with NAs, RAs are more porous and less dense due to the mortar adhering to their surface, and the compromised mechanical performance shortens the service life of structures with RAC. Furthermore, the chloride resistance of RAC is relatively low, not sufficient to protect reinforcing steel from corrosion. As a result, the additional embodied carbon from extra repair and maintenance or due to reduced building lifespan needs to be considered. On the other hand, most of the recycled concrete is applied to building envelope components. The thermal resistivity and capacity of RAC increase with an increase in the replacement ratio of recycled aggregate, particularly coarse aggregate. It is the two sides of the same coin. Although energy-saving in hot climates, in cooler climates such as the UK, buildings with high thermal capacity require more energy for heating and increase carbon footprint due to the combined heating loading required from the envelope and the internal spaces. This paper provides a life cycle assessment framework for evaluating the whole life carbon footprint variation when using RAC in buildings. Besides the reduced embodied carbon from recycled raw materials, the stochastic service life model is established to estimate the time to corrosion-induced cracking and additional embodied carbon from repair actions or equivalently from the shortened lifespan is calculated. Moreover, the Cambridge Housing Model (CHM) is utilised in this framework to model the energy demand and corresponding operational carbon, subject to the modified thermal resistance of the envelope because of the use of RAC in English residential buildings. Beyond the immediate and most noticeable reduction of embodied carbon from concrete production, the LCA framework for evaluating the whole life carbon footprint of individual residential buildings gives a fair and long-term judgement on the costs and benefits of using RAC in buildings. In future work, the change of climate for England due to global warming and the decarbonisation of the UK electricity supply will be incorporated into the framework to give more accurate suggestions on RAC usage in buildings.
Author(s): Xie X, Huang HY
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: 11th International Conference on Industrial Ecology
Year of Conference: 2023
Acceptance date: 07/04/2023