- Written by Eduardo Souza
- January 10, 2022
Much has been said about circularity in the construction industry. Inspired by nature, the circular economy works in a continuous process of production, resorption and recycling, self-managing and naturally regulating itself, where waste can turn into supplies for the production of new products. It is a very interesting concept, but it faces some practical difficulties in everyday life, whether in the demolition / disassembly process, or in the correct disposal of materials and waste; but mostly due to the lack of technologies available to recycle or give new use to construction materials. About 40% of all waste generated on Planet Earth comes from civil construction, and a good part of it could be recycled. Concrete is an especially important material because of its large carbon footprint in production, its ubiquity and massive use, and also because of the difficulty of recycling or reusing it.
Until recently, we have been able to crush demolished concrete structures which produce aggregate material consisting of smaller parts of concrete. This, in turn, often ends up being used for restricted processes such as down cycling (in materials with a more limited range of uses than the original material). Through this simple crushing process, the fragments end up used as base materials for structures such as roads, or other similar uses. Due to the low quality of the secondary aggregates, their exchange rate for the primary material is limited to around 30% – a very unsatisfactory level to ensure the desired quality of concrete, due to the excessive amounts of cement and chemical additives it contains.
Through the patented reCO2ver process, Sika has developed a highly efficient process to separate and reuse demolished concrete components and increase the quality of recycled aggregates. The process consists of the synergy of a chemical-mechanical treatment of concrete demolition waste.
The technology involves the surface carbonation of the cementitious matrix (when carbon dioxide is dissolved in water or an aqueous solution), which is softened and removed with friction. Through this process, newly exposed surfaces are obtained, which are capable of carbonating even more until obtaining cement-free aggregates.
Concrete / mortar demolition waste can be separated into “secondary aggregates” for recycling at a quality level that is similar to that of traditional raw materials; such as a powder that is usable as a secondary raw material in various applications. That is, old concrete is broken down into individual parts – gravel, sand and limestone – in a simple process that also sequesters around 50 kg of CO2 per ton of crushed concrete demolition waste. Comparative tests have shown that structures built with the new recycled content concrete perform similarly to an entirely new structure. With this, the technology provides a reduction of around 40% in the use of water and up to 25% in cement, in addition to using concrete waste to sequester CO2 in the atmosphere, both by reducing the need for cement and by partially replacing the clinker for the fine powder generated in the process.
Thomas Hasler, CEO of Sika, points out that “In the five largest EU countries alone, roughly 300 million tons of old concrete are generated every year. With complete recycling of these materials, up to 15 million tons of CO2 emissions can be captured. We are convinced that our new process has the potential to benefit both our customers and the environment.”
By saving natural resources and achieving a viable technology for recycling concrete, the company is able to turn this material around, from a polluter to an important agent of change for the world.
Link: https://www.archdaily.com/972748/concrete-recycling-is-already-a-reality
