By Alice Friedemann www.energyskeptic.com author of “When Trucks Stop Running: Energy and the Future of Transportation”, 2015, Springer and “Crunch! Whole Grain Artisan Chips and Crackers”. Podcasts: KunstlerCast 253, KunstlerCast278, Peak Prosperity
Concrete is an essential part of our infrastructure. And it’s all falling apart, as Robert Courland’s 2011 book Concrete Planet makes clear.
Courland writes that some of our infrastructure may last even less than a century. For example, in the ocean, concrete shows signs of decay within 50 years according to Marie Jackson at Lawrence Berkeley National Laboratory.
In a world that’s shrinking from declining energy resources, topsoil, aquifers, and minerals, it’s time to construct buildings that last and maintain the ones we have.
The problem is the iron and steel rebar reinforcement inside. Cracks in cement can be fixed, but when air, moisture, and chemicals seep into reinforced concrete, the rebar rusts, expanding in diameter up to seven-fold, which destroys the surrounding concrete.
This will eventually destroy nuclear reactors, spent nuclear fuel pools, and nearby waste containers (in 2009 the only contender for a nuclear waste disposal site after 40 years and $10 Billion of studies is Yucca Mountain, but it was put off limits by Energy Secretary Steven Chu in order to get Henry Reid elected).
Some concrete will last longer than others. The shortest lifespans are the most exposed infrastructure subjected to freeze/thaw cycles, vibration, heavy trucks, and salt to melt snow such as roads, bridges, airport runways, canals, parking garages and lots, sidewalks, etc.
Well-maintained buildings and other structures where cement is cracking on the outside, but sealed or patched quickly, will last longer than those that aren’t. Inside concrete will last even longer.
All rocks weather, and natural disasters can crack and expose the steel rebar to corrosion, shortening its lifespan, so in the end, concrete structures are temporary: coal and natural gas power plants, buildings, homes, and skyscrapers; dams, levees, water mains, barges, sewage and water treatment plants and pipes, schools, subways, corn and grain silos, shipping wharves and piers, tunnels, shopping malls, swimming pools, and so on will waste away.
Replacing these structures as energy declines will be far more difficult than maintaining them properly, so hopefully this will be a top priority when our throwaway society is no longer possible.
Fixing instead of rebuilding will also reduce CO2, since cement is a generates quite a bit since it takes a lot of energy to produce cement, around 450 grams of coal per 900 grams of cement produced, or from 4 to 7% of global carbon dioxide emissions per year.
Courland says that engineers and architects have known about concrete’s short lifespan for a long time, yet either refuse to admit it or don’t think it matters. The main theme of this book is that it does matter, as Courland explains in these three excerpts:
1) The lifespan of concrete is not only shorter than masonry, it “is probably less than that of wood…We have built a disposable world using a short-lived material, the manufacture of which generates millions of tons of greenhouse gases.”
2) “Even more troubling is that all this steel-reinforced concrete that we use for building our roads, buildings, bridges, sewer pipes, and sidewalks is ultimately expendable, so we will have to keep rebuilding them every couple of generations, adding more pollution and expense for our descendants to bear. Most of the concrete structures built at the beginning of the 20th century have begun falling apart, and most will be, or already have been, demolished”.
3) The world we have built over the last century is decaying at an alarming rate. Our infrastructure is especially terrible:
- 1 in 4 bridges are either structurally deficient or structurally obsolete
- The service life of most reinforced concrete highway bridges is 50 years, and their average age is 42 years….
- Besides our crumbling highway system, the reinforced concrete used for our water conduits, sewer pipes, water-treatment plants, and pumping stations is also disintegrating. The chemicals and bacteria in sewage make it almost as corrosive as seawater, reducing the life span of the reinforced concrete used in these systems to 50 years of less.”
Perhaps the American Society of Civil Engineers (ASCE) would agree. Below is their 2009 report card for America’s infrastructure (all of these use at least some, if not a lot, of concrete).
- C+ Solid Waste
- C Bridges
- C- Public Parks and Recreation, Rail
- D+ Energy
- D Aviation, Dams, Hazardous Waste, Schools, Transit
- D- Drinking Water, Inland Waterways, Levees, Roads, Wastewater
Their 2013 report card states we need over $3 trillion to fix this. But ASCE says nothing about the short life of concrete anywhere on their website, let alone demand that future projects be built to last. The ASCE 2013 report card didn’t mention that we need to build millennia-long lasting concrete buildings, roads, bridges, dams, schools, drinking water pipes and facilities, and levees in the future.
Alan Weisman’s in his book, “The World Without Us”, writes of places abandoned by people, such as Chernobyl. It doesn’t take long for vegetation to crack and take over buildings, roads, and other concrete structures. For example, consider what knotweed can do:
Knotweed can pierce tarmac and crack concrete foundations, causing serious damage to infrastructure, and grow up to a meter per month. In winter the underground rhizome survives and can grow as much as 14 meters long and 3 meters deep. The rhizome can even survive burial by volcanic lava and send up rock-piercing shoots when the surface cools. “A plant like that will laugh at concrete foundations,” says Mike Clough of Japanese Knotweed Solutions in Manchester, UK (Pain).
There is a program to make better concrete at the National Institute of Standards & Technology Engineering Laboratory. One programs is researching how to prevent concrete from cracking in a program called REACT: Reducing Early-Age Cracking Today. In 2007, the National Infrastructure Improvement Act, to establish a National Commission on the Infrastructure of the United States, passed in the Senate but failed in the House.
Update 2013: Engineers are working on making better concrete. The fixes below will extend lifespan one time:
- Using bacteria that emit limestone to self-heal concrete by mixing tiny capsules of these bacteria within concrete that multiply when a crack breaks the capsule open. The bacteria also use up oxygen that would have corroded the steel bars. Whether this can be done or not is not clear since concrete is a very hostile place for bacteria due to high alkalinity, and as the concrete cures, it’s likely to crush many of the microcapsules.
- Filling the concrete with polymer microcapsules that break open and turn into a water-resistant solid when exposed to sunlight, filling in the crack.
- Add spores of bacteria that can last for 50 years and food for them so that when concrete cracks, they form a glue to fix it. This is a one-time-only fix though.
- Coat rebar to protect it from rust. This special rebar takes 20 years longer to rust.
It is hard to make concrete last
Concrete tends to be made from local gravel, stone, and sand since these are very heavy and so expensive to move any distance. So the best recipe will likely vary a bit from place to place.Steel also varies in what alloys were used, how strong and corrodable it is, and asphaltic concrete will vary depending on the crude oil source of the bitumen. It’s often mentioned that Roman concrete lasted because of the use of volcanic ash, perhaps the Romans just lucked out with good local materials. And Rome didn’t have to deal with the freeze-thaw cycle, rust from steel rebar, heavy trucks, and other modern insults. Dealing with all these local materials makes it hard to come up with a one-formula fits all solution to long-lasting concrete.
According to David Fridley at Lawrence Berkeley National Laboratory: Even though Roman concrete was superior to what he have now, we use concrete for far more applications now than the romans did, many of which require rebar. “Concrete has very high compressive strength, so it is the best material for foundations, arches, domes, etc. for which weight is the major concern. However, concrete has very poor tensile strength, so applications that require resistance to bending (such as a beam) requires the addition of rebar, as the tensile strength of steel is quite high (but compressive strength low). The Romans didn’t use their concrete for such applications. Rebar inevitably corrodes, leading to expansion (tensile stressing), cracks, spalling, and ultimately, failure. According to an article in Nature Geoscience last fall (http://www.nature.com/ngeo/journal/v9/n12/full/ngeo2840.html), carbonation of cement is substantial, with the impact of increasing the acidity of the concrete, and thus susceptibility of the rebar to corrosion. There’s not a rebarred concrete structure today that could last a millennium.
Peak Energy and Concrete
This reminds me of the verses from the Talking Heads Nothing But Flowers out of my head:
There was a factory
Now there are mountains and rivers
There was a shopping mall
Now it’s all covered with flowers
The highways and cars
Were sacrificed for agriculture
Once there were parking lots
Now it’s a peaceful oasis
This was a Pizza Hut
Now it’s all covered with daisies
And as things fell apart
Nobody paid much attention
Why waste our remaining energy to make concrete? At this point it seems crazy to build projects with short-term concrete we KNOW will only last for decades. Once we stop repairing our concrete (and cement) structures, they will quickly fall apart.
Why try to rebuild our infrastructure and create vastly more greenhouse gases?
Our descendants won’t be driving much. They’ll probably wish we had converted most of the roads to farmland, which will take centuries even after the cement is gone for the soil to recover — why not start now? Stop maintaining roads in the national forests, rural areas, and wherever else it makes sense –let them return to gravel, jackhammer and remove the rubble while we still have the energy to do so.
De-paving and de-damming would also restore streams, fisheries, wetlands, and ecosystems for future generations.
Future generations eventually won’t have the energy to maintain, repair, or rebuild very many concrete structures in a wood energy based civilization. Courland says it takes one cord (4 x 4 x 8 feet) of wood to make 1 cubic yard of lime.
Those of you downstream from large dams might be interested to know that Courland says they are still “undergoing the curing process, thus forestalling corrosion. It will be interesting for our descendants to discover whether the tremendous weight of these dams will continue to put off the rebar’s corrosion expansion”.
Failing dams are a double tragedy, since electricity from hydro-power will be especially valuable as one of the few (reliable) energy sources in the future.
Peter Taylor, in “Long-life Concrete: how long will my concrete last?” closes hes 2-13 paper with The need for long-lasting pavement systems is growing as budgets decrease,traffic increases,and sustainability becomes more important.Increasing complexity of concrete mixtures and the demands being placed on them means that “business as usual” is no longer acceptable”
James Howard Kunstler writes that surburbia will be seen as one of the greatest wastes of energy and resources in the future. It goes way beyond that. Our infrastructure is one-third and one-half concrete. It’s all a waste.
A wasteland. There will be absurd amounts of concrete rubble — what the hell are people in the future going to do with 300 billion tons of concrete? Build sheep fences?
Pain, Stephanie. 3 July 2014. How to kill knotweed: Let slip the bugs of war. NewScientist.