Assessment of waste-integrated concrete products: a cradle-to-cradle perspective

Abstract

Abstract Purpose Bricks and roof tiles are commonly employed in construction, posing environmental challenges due to their substantial use of natural resources. Efforts to mitigate these concerns include the integration of recycled materials. However, within the framework of life cycle assessment (LCA), it is imperative to ascertain that the incorporation of recycled materials enhances the sustainability of the product across its entire life cycle. This research presents a thorough cradle-to-cradle LCA of concrete bricks and roof tiles integrated with waste materials utilized in Australia housing construction compared to conventional Portland cement-based concrete products. The research also examines how the selection of allocation methods for raw materials impacts the results of the LCA during the manufacture stage of the concrete products. Methods This study conducts a cradle-to-cradle LCA of waste-integrated concrete bricks and roof tiles, using pond ash and unwashed recycled glass sand due to their widespread availability and proven performance. It examines three allocation methods (no allocation, mass, and economic allocation) for the initial raw waste materials for a cradle-to-gate boundary application (the allocation method is excluded from the secondary use of the recycled materials). LCA modelling is performed using SimaPro 9.3.0.3 software, with data support from Ecoinvent v.3.8 (2021) and AusLCI v.1.42 (2023) databases with system models based on the cut-off approach. Results and discussion The study highlights that integrating waste materials into bricks and roof tiles reduces environmental impacts across most categories compared to conventional products. The combination of pond ash and recycled glass sand can reduce GWP by 9.86% and 8.21% for roof tiles for bricks within the cradle-to-gate scenario. Mass and economic allocation contribute to slightly higher impacts, approximately 0.789–1.188% and 0.061–0.138%, respectively. Waste-integrated concrete products generally exhibit lower environmental impacts across midpoint categories compared to conventional products in the cradle-to-cradle boundary. GWP waste-integrated bricks and roof tiles are lower than those of conventional products by 8.00–8.72% and 5.51–6.35%, respectively. Moreover, among the three post-demolition scenarios, when credits for waste material substitution are not considered, recycling demolished material into recycled aggregates utilizing the standard recycling method emerges as the most environmentally advantageous approach, outperforming landfilling and recycled demolished aggregate using the advanced recycling method. However, when credits are assigned for the utilization of recycled materials, Scenario 3 demonstrates lower environmental impacts than Scenario 2, except for ODP in WCB and WCR. The production of ultrafine powders as SCMs in Scenario 3 reduces GP cement demand, further lowering the impacts and emphasizing the importance of adopting a lifecycle perspective in LCA to fully capture the benefits of recycling. Conclusions and recommendations Incorporating pond ash and unwashed recycled glass sand holds promise for mitigating environmental impacts. Recycling demolished concrete as recycled aggregate for concrete using standard recycling methods was found to be the best scenario at end-of-life compared with sending to landfill and using advanced recycling methods. A deliberate selection of raw materials, coupled with exploring the advantages of integrating innovative cementitious materials and substituting aggregates, is crucial for advancing an environmentally conscious recycling process. Additional research and development are vital to identify the most effective combinations for utilizing waste materials in concrete products, thereby improving sustainability without compromising performance.

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