The urgency for the application of sustainable use of construction waste for greener environment and recycled aggregates (RA) can be associated with CO₂ reduction, waste landfilling, shortage of raw materials and expenditures. Production of 1 tonne of natural aggregates (river sand and crushed stone) emits 23–33 kg CO₂, while the production of 1 t of recycled concrete aggregates from RA generates 12 kg CO₂.

The coarse and fine aggregates are the largest component of concrete. The consumption of natural aggregates has increased with the production and utilization of concrete. Fig. 1 shows the origin of natural aggregates and their amounts for different countries. Crushed rock, river sand and gravel are the most used aggregates. However, their amounts are declining and their drawing leads to serious problems.

Fig. 1. Aggregates Production in millions tonnes in different countries.

Recycling concrete provides sustainability several different ways. The simple act of recycling the concrete reduces the amount of material that must be landfilled. Moreover, using recycled concrete aggregates reduces the need for natural aggregates. This in turn reduces the environmental impact of the aggregate extraction process. By removing both the waste disposal and new material production needs, transportation requirements for the project are significantly reduced. Following are two examples where RA were used in construction of buildings.

         1. Bundesgartenschau decorative concrete elements, Germany

In 1999, large concrete elements were used to beautify the landscape for the Federal Gardening Exhibition (Bundesgartenschau) in Magdeburg, Germany (Fig. 2). Some of these decorative elements were manufactured using coarse RA from crushed clay bricks, crushed concrete or their mixture.

Fig. 2. Jahrtausendturm in Magdeburg, Germany.

        2. Office building, Mannheim-Neuostheim, Germany

The RA were used office building, Mannheim-Neuostheim (Fig. 3) and the concrete mixes was Type 2 RA, which contained relatively high quantities of components coming from crushed masonry elements.

Fig. 3. Office building in Mannheim-Neuostheim

In addition to the resource management aspect, recycled concrete aggregates absorb large amount of carbon dioxide from the surrounding environment. The natural process of carbonation occurs in all concrete from the surface inward. There is probably no better way of raising awareness of successful application of RA in construction industry than by demonstrating their success in the shape of full-scale trials ^1–3.

References

1. Nedeljković, M., Visser, J., Šavija, B., Valcke, S. & Schlangen, E. Use of fine recycled concrete aggregates in concrete: A critical review. Journal of Building Engineering 38, 102196 (2021).
2. Silva, R. V., de Brito, J. & Dhir, R. K. Use of recycled aggregates arising from construction and demolition waste in new construction applications. Journal of Cleaner Production236, 117629 (2019).
3. Zhang, L. W., Sojobi, A. O., Kodur, V. K. R. & Liew, K. M. Effective utilization and recycling of mixed recycled aggregates for a greener environment. Journal of Cleaner Production236, 117600 (2019).