How recycling concrete could accelerate sustainable construction
As the population continues to grow, the development of physical environments continues. We use newly cast concrete as an efficient, strong and relatively low-cost building material, but it emits unsustainable amounts of CO₂ as a result. It is reckoned that four billion tons of cement annually equate to 8% of the global emissions.
Concrete production is a costly affair to nature, with its destructive CO₂CO2 emissions. Apart from this, demolition amounts to the careless disposal of that investment. The process of demolition when an asset reaches its end of life mostly results in piles of rubble, with a significant scale of waste.
Cembureau, the European cement organisation, calculates that 450-500 million tons of construction waste are generated in Europe alone annually. In the United States of America (USA), experts reckon concrete could be up to 85% of construction waste. It is simply cheaper, quicker and easier to knock things down and start over.
An era of reuse
We have seen in recent years that it is possible to reuse and adapt projects and old structures to avoid demolition. We are also seeing a move to reuse of building materials locally. Obviously, sometimes there are some constraints and limitations at play here, as not all structures and materials can (or should) safely be conserved.
The increasing deployment of circular economy principles, where current building components are designed for future reuses, is good to see – but this is still nascent, and it remains the case that only certain existing structures are likely to be adaptable to new uses.
Demolition still looms
It is important to shift the focus to deconstruct and not demolish. Although steel and timber are recycled, concrete recycling still lags.. To deconstruct a building, is considerably more costly and time-consuming than demolition. Viewed with a clear sense of urgency from the net-zero goal that every organisation must now face, the incentives to adopt a new approach become quite persuasive.
Benefits of recycling and reuse:
Immediate CO₂ savings: Every cubic metre of reused concrete can theoretically prevent a new cubic metre from being cast, saving over 250kg of carbon dioxide.
Greater stability: Reused concrete has the advantage of greater volume stability than brand new concrete, having endured creep and shrinkage when fitted within its original structure.
Proven strengths: The inability to test concrete (before it is cast) means structures are built with onerous strength reduction factors that allow for material variability.
Readiness for off-site construction: Governments and the industry are already advocating more off-site construction which, for concrete, means precast.
How can this be done?
Reused concrete components aren’t top of architects’ or engineers’ minds, nor are clients or building owners demanding them. We need a mindset and paradigm shift for this to be sustainable in the long run and benefit the environment.
Designers must be able to specify used components if the practice is to become normalised, accepted and widespread.
The possibilities for reused concrete are considerable. The goal is to reduce the production of new virgin material as widely and quickly as possible, not to make like-for-like.
Projects proving how this can be done help to establish that this is a resource whose value we’re simply ignoring.
A rewarding idea
Building owners view the shell of their existing old structure as valuable, financially and reputationally. Our cities are rich with concrete, often in a condition as good – if not better – than the day it was cast.
With just a small change in mindset among practitioners across the sector, from investors and developers to architects and engineers can finally start to apply the “make once, use many” ethos to concrete.