Feb 13, 2023

Construction-trash talk (or: the problem with circular construction materials)

Last week I had mentioned that we are running out of rocks and crushed stone to use in construction.

I dug deeper on how recycling and circularity of construction & demolition waste (CD&W) might or might not help fix the raw material shortage we are running into.

To understand this, I had to understand what waste is generated on construction sites, what the CD&W is made of, and where it goes.

(I focused this post on the US market; European and Australian markets will have different specifics but will be directionally same ballpark)

Construction & demolition waste increased by +340% compared to 1990. While – interestingly – municipal solid waste “only” icreased by +40%. We create disproportionately more construction trash than household trash.

The big 6 components that make up construction waste are:

• Concrete
• Asphalt pavement
• Wood
• Gypsum (from drywalls)
• Bricks and clay
• Metals (steel, copper, aluminum and others)

All other materials fall into the “any others” bucket. An example of “others” would be asphalt roof shingles.

Concrete makes up 70% of all construction waste. 22% are asphalt pavements and wood. Bricks, clay, gypsum, metals, and any others together make up 8%.

When it comes to “where does it all go”, brief time for definition:

• Re-cycled means something is re-used in (broadly) the same way as before. For example, asphalt pavement re-used to build new asphalt pavement.
• Down-cycled means something is not just dumped but used in an energetically lower yield than its prior use. For example, burning wooden doors as fuel.
• Un-cycled means something is just dumped in a landfill. Here it’s not even used as fuel or as an aggregate to fill a hole for a new site.

To the numbers:

20% are re-cycled. The majority here is asphalt pavement. Some concrete is recycled. Some minor recycling of wood and metals.

56% are down-cycled. Vast majority is concrete (mostly re-used as aggregate). Some down-cycling of pavement, wood, gypsum, bricks and clay.

24% are un-cycled and just dumped. Again, a good share of this is concrete, but surprisingly much is wood. The majority of bricks, clay, gypsum and any others goes here. Reasons are diverse, but two of the bigger reasons are that separation is too costly or that adverse materials are contained.

What all these numbers tell me is that creating a stream of homogeneous supply of recycled construction materials is really difficult – and really key. The two biggest levers to improve our recycling rate are (1) concrete and (2) wood.

• For concrete, someone has to fix the separation to be economically scalable.
• For wood framing, I have seen approaches to remove nails – that is generally useful, but holes remain and since wood ages, the structural integrity decreases. That’s why it gets down-cycled.
• For wooden door frames, hardwood floors, and similars: they have visual properties that lead to in-homogeneous supply at scale (every door looks a little different)

Who’s fixing construction waste at scale using technology? I.p. looking for robotics and software-led approaches

Sources:

EPA | General Kinematics | University of Michigan