What is most optimal when it comes to concrete in a circular perspective? That question has long been up for debate in the construction industry. The focal point of the discussion is whether there are real climate benefits to be gained by promoting the recycling of crushed concrete as an aggregate in new concrete in relation to other material utilization. It could be, for example, that crushed concrete is used as an unbound base layer under roads, as is suggested by, among others, the EU’s waste hierarchy.
A question of climate potential
Stefania Butera works at the Danish Technological Institute, where she is a senior specialist in, among other things, life cycle assessments (LCA). And even though an LCA can help to answer which application has the greatest climate potential for the concrete, the answer is not clear-cut and therefore the Norwegian Technological Institute has gone a step further to find a solution.
– What we can see is that different LCAs have reached different conclusions in relation to the climate potential of concrete. That is why we have chosen to dig a little deeper and have prepared a critical analysis of both calculation assumptions, framework conditions and decisive parameters, explains Stefania Butera. She herself has been the author of a recently published report on concrete in a circular perspective.
35 percent of construction waste is concrete
Both in Denmark and at EU level, concrete constitutes the largest fraction of construction waste. According to figures from the Danish Environmental Protection Agency from 2020, concrete as a pure fraction makes up just under 35 percent of the total amount of construction waste, when soil, asphalt, paving material and ballast are subtracted.
– As it is today, the possible treatment methods for concrete waste are either direct recycling, where entire concrete elements/products are taken out and reused again, recycling, where the concrete is crushed and used as aggregate in new concrete, or material recovery, where waste materials are used, for example, in crushed form as unbound bearing layers under roads and in squares, explains Stefania Butera.
Aggregate better than recovery
Stefania Butera has prepared a (non-exhaustive) mapping of the most relevant studies in the area, in order to illuminate and put into perspective the existing knowledge about climate potentials from recycling, reuse and recovery of concrete in an LCA perspective. It concludes,
that based on the analysis carried out, recycling of concrete waste as aggregate in new concrete should be considered in priority over recovery in a number of cases.
– If one or more of the following conditions apply, then one must think of concrete waste as an aggregate in new concrete rather than recovery. This applies if the concrete waste is of high quality, for example concrete for aggressive or extra aggressive environmental impact, and at the same time it is correctly sorted and thus not mixed with other concrete waste for lower environmental impact, and where a use in the production of high-quality concrete has been identified , or which require aggregates of a higher quality than gravel pit materials. Another factor that is decisive is if there are local recycling options. It can, for example, be used at the same place as the demolition or close by and perhaps by using a mobile crushing plant. The last aspect is if you can reuse the concrete waste in concrete recipes/products without increasing the cement content, explains Stefania Butera.
Requires further analysis
The conclusion also means that a closer, case-specific analysis is needed to shed light on the concrete conditions for each individual project, as these can be decisive for whether the use of aggregates made from recycled concrete ultimately leads to a climate saving – or instead, it constitutes an, albeit typically limited, climate-related burden.
