Sunday, March 29, 2015

Reused concrete - 6 points towards a rolling circular economy

The circular economy is recent years' sustainability buzzword. For concrete, it is an essential and ongoing search for better used of the raw materials (first generation) as well as the second generation materials.
[Image of the demolition of a large movie theater, Photo by Trondur Dalsgaard via]

Recycling seen from the heavy industry
Recycling and resource economy is not my speciality. So, leading up to my previous post about recycling concrete, I interviewed leading voices of the Danish concrete industry. Known to be as heavy an industry to move anywhere as their product when hardened, the opinion here is that business as usual is good. And reuse as excellent road-fill cannot be topped as the best - and only way to reuse the sky-high 95% of the concrete waste from infrastructure and buildings. It is nice to extend the life of the material yet it is unlikely to enter an extra cycle of use from here.

[Mixed concrete and asphalt waste. Image via

Since this is my private blog, however, there is room to have doubts about this single and and, let's admit it, single-minded opinion.

I have lately attended a number of recycling conferences. I have collected six points towards a better circular economy for concrete.

1. Know the source and the quality of your second generation material. This is the great challenge for all materials in construction. It is a matter of strength for construction materials, and to locate beautiful old windows treated with lead-based paint, railway sleepers with all sorts of nasty heavy metals, concrete with PCB, etc.

2. No extra cement to compensate. New concrete made from a mix of first and second generation concrete materials (gravel, sand, and larger aggregate) has been made and without using the extra cement to compensate for unknown qualities. - it is not a commercial practice.

3. New structures need not be constructed to last 100 years. The Danish industry produces high-quality concrete. Producing concrete of a slightly lower quality may be the consequence of using secondary materials - and this may be just fine.

4. Empirical tests
Concrete strength is always tested for any batch of mixed construction concrete - for reused concrete as well.
[Image of compression test of concrete cylinder via]
[Numerous cylinders are cast and tested for all construction projects. Image via]

5. National regulations need to change approach from 'construction waste' to  'construction resource' The national regulations for waste materials were developed as such, that is - looking at second generation materials as waste and not resources. This means that rules are too strict to work with in practice.

6. Show me the money
New national strategy for resource efficiency point at a more material conscious practice that should be simple 'and only cost a bit more' as a speaker from the secretary of the environment said during a presentation. This is obviously a major challenge - who should pick this extra expense? And why not make economic incentives to reuse more? If you can run a business, there is a market.

In the 1970s demolition companies would actually bid how much they would pay to enter their projects because buildings contained value that these 'material brokers' would disassemble and cash in on. - today it is the opposite. It is expensive for clients to demolish buildings. - When we see the change back, it will be a sign that the circular resource agenda is actually on its way, rolling.