Making cement puts out a lot of CO2. Making concrete needs a lot of sand. Both are big problems.
Yes, concrete is wonderful stuff. It can last millennia if you build it like the Romans did. Much of our modern world is made of concrete. Vince Beiser has written a new book about it, The world in a Grain: The story of sand and how it transformed civilization, and has an excerpt published in the Globe and Mail.
As we have noted many times (and is the subject of the book), concrete is only about ten percent cement; the rest is sand, gravel (the aggregate) and water. Mining, dredging and stealing that sand has become a huge problem. Beiser concludes in the Globe:
Concrete is essentially just sand and gravel glued together with cement. It is also by far the most widely used building material on Earth. We consume twice as much of it every year as steel, aluminum, plastic and wood combined…. It’s an almost magically cheap, easy way to quickly create roads, bridges, dams and housing for huge numbers of people. An estimated 70 per cent of the world’s population now lives in structures made at least partly out of concrete.
We’ve started to think twice about how much oil we can burn, how many forests we can cut down, how many fish we can harvest from the sea. It’s time to start thinking about how much concrete we can afford.
So what can we do? We have dozens of posts on TreeHugger about this, but Ottawa architect Toon Dressen laid it out in a series of tweets that distill some of the best thinking on the subject; they are a model of concision.
1. Preserve what we've got
1) preserve, renovate and adapt the concrete buildings we already have; saves on landfill, and means less/no new concrete; that’s an easy one, but means appreciation of the built environment as part of our #economic and #cultural fabric.— Architects DCA (@ArchitectsDCA) August 26, 2018
The great brutalist buildings by Paul Rudoph and others are being lost at a rapid rate, often before the concrete in them has totally set (it can take decades). Other concrete structures are taken down instead of being adapted to new uses. More in TreeHugger: In praise of Brutalist Architecture.
2. Maintain it properly
2) use concrete in new buildings in the most durable way possible; keeping buildings dry, free from decay, and adaptable so that they last; invest in durability, quality (see point 1: apprecation of #architecture is critical)— Architects DCA (@ArchitectsDCA) August 26, 2018
Seminal projects like Robin Hood Gardens were lost because they were not maintained or adapted. As Carl Elefante says, the greenest building is the one already standing. But as the University of Toronto has shown with the Robarts Library, Brutalist concrete buildings can be maintained and adapted and loved. As I wrote about it:
It's not about cute or ugly, it is about making use of what we have instead of just throwing everything away because somebody is tired of it. In that light, the Robarts Library looks more beautiful every day.
3. Use less of it
3) use concrete sparingly: integrate wood in mass timber CLT to sequester carbon and build sustainable buildings that meet society’s needs— Architects DCA (@ArchitectsDCA) August 26, 2018
This is TreeHugger territory; wood, particularly with new technologies like Cross Laminated Timber and Dowel Laminated Timber, can replace concrete in a lot of uses. Even if the buildings are sitting on concrete foundations, they will be smaller because the buildings are lighter. I have written:
Everyone recognizes that there is a critical role for concrete, and it is not like we can do without the stuff; we are not likely to start building bridges and highways out of wood, although that has been done. But where we can replace concrete, we should be doing so. And buildings are a logical place to start, using established or new wood construction technologies.
4. Stop sprawl
4) carefully think/plan concrete structures like bridges, roads, etc to put them on a road diet, and focus on transit, rather than more roads to further #sprawl— Architects DCA (@ArchitectsDCA) August 26, 2018
Help put Miss Concrete and Miss Blacktop out of a job. In the book, Beiser points out that asphalt paving is really like concrete, but with bitumen instead of cement. It is also mostly sand.
Concrete, as we have seen, is also the handmaiden of the automobile. One promotes dependence on the other. The more roads you build, the more traffic you generate, which means more carbon emissions from tailpipes.
5. Recycle it
5) integrate sustainable concrete using waste byproducts, recycled material.— Architects DCA (@ArchitectsDCA) August 26, 2018
This seems obvious, but in fact is not so easy. Worldwide, 17 percent of landfill is concrete-based waste because about the only use for it is roadbeds. According to Wikipedia, "Crushed recycled concrete can sometimes be used as the dry aggregate for brand new concrete if it is free of contaminants, though the use of recycled concrete limits strength and is not allowed in many jurisdictions." So really, it is back to points 1 and 2: preserve what we've got.
Really, I could have just retweeted instead of expanding on this, since it says it all. The most important message from the book and from the tweets is that concrete is a terrific building material, but we have to use it properly, use as little of it as we can, and be smart about it.