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Carbon Sequestration by Recycling Cement, Aggregates, and Concrete

As the world’s largest producer of construction waste, China’s recycling and related policies are of the biggest concern to the world. However, the effective disposal and reuse of this waste has become an important issue since currently China still has a very low recycling ratio compared to developed countries, and most of the waste concrete was only simply broken and used as low-grade recycled aggregates for subgrade cushion, cement stabilized crushed stone, and filler wall. In this paper, a concrete cycle model focusing on how to effectively recycle and utilize waste concrete is put forward to prepare high quality recycled concrete, especially through a series of technical means, such as effective separation, carbon sequestration, and reactivation. Producing high quality recycled concrete can not only replace traditional concrete but also effectively reduce the consumption and waste of raw materials. What’s more, the calculation results show a potential of significantly carbon sink; for every ton of recycled cement produced, the CO2 emission could be reduced by 0.35–0.77 tons compared to ordinary Portland cement, corresponding to a reduction of 47%–94%; and for every ton of recycled concrete produced, the CO2 emission could be reduced by 0.186 tons compared to normal concrete. A yearly CO2 sequestration of 1.4–3.08 gigatonnes could happen if the ordinary Portland cement could be replaced by the recycled cement around the world. Taking the currently accumulated construction and demolition (C&D) wastes globally, the production of recycled cement, recycled aggregates, and recycled concrete could induce a significant carbon sink in the world.

Future studies could further explore the mechanisms by which carbon sequestration affects the performance of recycled aggregates, as well as how to apply this to practical construction projects in order to promote the sustainable development of building materials. Currently, there is a dearth of facilities for the complete recycling of carbonated waste concrete, which has resulted in a paucity of empirical data and may potentially lead to discrepancies between the calculated outcomes and the actual scenario. The integration of effective separation, carbon sequestration, and activation technologies can lead to the production of high-quality recycled concrete, thereby reducing the environmental footprint of the construction sector and promoting a sustainable future.

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