I live in the Sierra Nevada Mts. of central California. I have been using the Quadlock ICF product for a number of years which is a panelized system rather than a prefabricated 'block'. It provides insulation on both surfaces and the concrete core can vary from 4" to 24" in width depending upon the application.
The most durable structures in this area were constructed of stone masonry and date back to the gold rush era. That is pretty recent compared to buildings around the world but I think masonry has proven itself as regards durability and longevity. Keeping a roof on the structure is the key and that will always require regular maintenance it seems.
My current thoughts have migrated to the living roof concept for long term low maintenance functionality. But there are issues with that as well. I guess if you are expecting a free lunch you may end up hungry!!
Great article Chris, the best metaphor and reality of our insubstantial age, my eyes are contemplating the long pathways of rebar of our new light rail system as I walk home through Dublin. They only closed the last of the old tram lines in the 1960's.
I watched a documentary recently on space-archaeology where a specialist was still able to identify the buried walls of a turf-built, Viking age building, maybe in the Shetland Islands, from a satellite 300 miles above the earth.
Yagasjai's question about residential construction triggered my memory about several articles I have seen in the past few months concerning traditional, poured concrete foundations in Connecticut residences.
Apparently, a concrete company which poured thousands of foundations over the years was using a type of rock in the aggregate which leaches a chemical that prematurely causes the concrete to weaken and ultimately collapse. Insurance companies have taken the position that this is not a condition covered by homeowner's policies. At least one court case has held that a homeowner's discovery of the condition came after the statute of limitations had run. No recovery could be made against the contractor who built the house. If I remember correctly, the concrete company is out of business so there is no recovery from them.
The result is a number of home owners with collapsing foundations, some to the point of the property being condemned, with no alternative but to replace the foundation in its entirely. Unfortunately the present cost for doing so can be more that the value of the property.
Going forward the infrastructure issues will not be just with public structures. I fear much of the residential housing built in the last "boom" times will not hold up over the long hall.
Friends and family thought we were crazy when we bought our now one hundred eighteen year old house. My stone foundation has not crumbled. The four by six, post and beam, frame has not sagged. The trees harvested to build the structure are now housing the fifth generation of inhabitants. We did make substantial improvements to plumbing, heating, insulation and electric, resulting in a house that will stand the test of time but has all the modern bells and whistles.
Many railroad bridges in my area (Eastern New York), even on heavily used lines have remained unpainted for years. They are slowly rusting away even as heavy rail traffic (perhaps 5-10 thousand rail cars a day on a double track line near me) passes over. This is also true of several active rail bridges over the Hudson River. Well constructed steel bridges will not last if not painted.
Over the weekend, I was able to take a close look at the rail bridge over the mouth of the West River in Brattleboro, VT from a kayak. It had been so long since the unpainted, but still used (by Amtrak and freight) bridge had been even cleaned that several 4-5 foot tall trees were growing out of the debris that had accumulated on the girders below the rail bed at the sides of the bridge. The two well constructed old stone and mortar piers that supported the bridge had once held a double track, but there has been only one at least since I lived in Brattleboro from 2001-2006.
It’s good to hear what you have to say on that matter. Please watch out #or quakes and slides where you live. One never knows WHERE an overdue quake will strike, and the Kern Valley Graben is one of the active though unusual faults in the system.
During my working life, I was a practicing geotechnical engineer. I've seen lots of deteriorating concrete structures. Roadway deicers (salt) and/or deleterious aggregate - cement interactions were usually the cause. I've also been involved in destroying many structures that were still functioning well. They were functionally obsolete and no longer served the present need. In many of them, the rebar looked just as pristine as when it was originally placed. The key is to protect the rebar from environmental degradation.
It is hard to estimate future needs and build accordingly. Budgetary constraints dominate the decision making process. If another firm convinces the client that they can produce a satisfactory product for less money, the client will place additional pressure to cut costs … or jump ship. Do you think management was happy with an engineer who stood his ground? There were lots of downstream consequences to consider.
That said, I really enjoyed the links that DRS78750, Michael_Rudmin, and Bankers Slave provided. I spent a few hours yesterday looking at their websites. Innovators who have these niches really open the possibilities for alternates to the standard accepted templates.
Here's a 5 minute video showing a temporary test structure constructed of sand with bed sheets as reinforcement. They loaded it with Jersey barriers. According to standard accepted calculations, the factor of safety (when fully loaded) was 0.088. In other words, it carried over 11 times the weight that it was predicted to carry before failure should have occurred. I certainly wouldn't use bed sheets as reinforcement in a "real" project, but it highlights the inadequacy of our current state of knowledge.
Hundreds of thousands of orphaned and abandoned oil wells left over from the first rape and pillage of Pa are venting methane into the environment. Where is the plugging plan? Not one more permit for one new hole until all the others ard plugged. That should keep them busy for oh say a century or so.
The Victoria Bridge from Montreal was built in the 1860s if I remember correctly, for a railway off Montreal Island to the South Shore - as an iron tube on stone supports. It was later modified to add also automobile and truck traffic, and it has that scary (especially on a motorbike) steel grid roadbed. But it is still in use after all these years. It is seldom is closed or down to 1 lane for repairs, like the relatively recent Mercier and Champlain bridges on which we are spending tens of millions of dollars every year trying to keep useable. It seems that stone is a lot more durable than re-enforced concrete, especially with salt spread on roadways for winter de-icing, causing salt-water run-off and seepage.
We seem to have learned enough from bad experiences in Quebec, to stop using horizontal re-enforced concrete beams for overpasses after some collapses of these structures after less than 40 years. Recent construction uses steel for horizontal beams, and should be durable in the case of I-beams or channel shapes, which are open, inspectable, can have all surfaces re-painted and made of thick steel. I have doubts about some overpasses I have seen built recently with box beams which are 4-sided, closed, and made of thinner steel, that can provide similar initial strength with less weight. I think that this design can eventually trap moisture and salt water inside and corrode from within, without it being visible or repairable. The thinner steel will also take a lot less time to rust through under these conditions. By the time we learn the lesson from this, we could be in a very different world for energy, materials and financing constraints.
The corrosion and eventual failure of steel reinforced concrete is just one example of Entropy - a law of physics that states everything returns to its natural state, or fromorder to disorder. We use energy to alter the condition of something, but it will always eventually return back to the way it was. The moment you finish cutting the grass in your yard, it begins to grow again (that's entropy). As soon as you finish painting the house, it starts to age (entropy). My wife often complains that as soon as she finishes cleaning the house, it starts to become dirty again (I've learned not to respond unsympathetically, "Of course it does - it's a law of the universe"). As it relates to this article, the trick is how to postpone the entropy (or maximize the lifespan) of our infrastructure by utilizing the most efficient use of energy and resources.
I have been the general contractor on three houses and another large structure I built for myself utilizing ICFs (Insulated Concrete Forms), with the first being a home built in 1999. Although ICF construction is great for energy efficiency, it does not solve any of the problems noted with rebar. In ICF construction, a foam block is used as the form and typically consists of approximately 2-1/2" of foam on both the inside and outside. The inside of the form is about 6" wide (or larger) and contains webbing onto which steel rebar is attached and then the concrete is poured. If there is a problem with steel rebar degradation, then ICFs will provide no improvement over precast or poured-in-place concrete onto which insulation is subsequently attached. Unfortunately, I just finished utilizing ICF construction for my current house that was just completed a year ago (Chris - couldn't you have written this article a few years earlier?!). I used steel stud framing, suspended concrete slabs and all PVC trim to minimize any organic material that would degrade over time, and thereby hopefully last hundreds of years (or so I thought).
As the previous owner of a large property management company, one of our primary functions was the constant maintenance and repair of buildings and grounds. I witnessed the poor quality of current wood-framed home construction that is prevalent everywhere, and wondered how long these structures would last. Considering that older buildings utilized more massive structural members, how many 300-year old buildings are still standing in the area where you live? How about 200-year old or even 100-year old buildings? I live near Williamsburg, Virginia, and almost none of the colonial buildings you see there are original. They have all been rebuilt. How are we going to rebuild the millions of homes constructed just during the past few decades when fossil fuels and resources become scarce?
Just over a hundred years ago, labor was relatively cheap and materials were expensive. Since that time (thanks to abundant and cheap fossil fuels), it has reversed - labor is now expensive and materials are relatively cheap. In the not-so-distant future, I believe labor will be expensive and materials will be expensive. Then what will we do with all of the massive amount of degrading homes and infrastructure we have built?
Chris's article initiates the critical discussion and importance of building things to last, particularly while we still have the resources available.
Perhaps reinforced concrete used in homes is less of a problem than that which is exposed to the elements? I just built a new home for a client on a site where 2 old cabins had been situated. The cabins were gone but the slabs remained. The structural engineer had us leave the slabs and cap over them. They were about 50 years old and looked solid. We doweled into them in a few spots, but mostly covered them with compacted fill and poured the new slab about 2 feet higher off grade.
Since residential slabs are almost 100% shielded from elements by the structure on top and the vapor barrier underneath, I have to wonder if they won't perform better than the bridges that allow moisture and air to contact the rebar?
After my previous submission, I performed a little research about the advisability of using rebar in concrete. I am not an engineer, but information searches do report that rebar used in marine and bridge construction is placed under greater stresses than normal building construction. In building construction, it is critical that rebar not protrude through the concrete, or even be within a few inches of an exterior wall. Concrete is somewhat porous, and that moisture can continue the oxidation of the steel near the surface and cause it to expand. The new void allows space for more moisture, resulting in more oxidation and expansion. The area near the surface subsequently fails, and is called spalling. If you look at the picture Chris posted at the beginning of this article, you can see that the rebar lies within a few inches of the surface - which was a mistake by the installation contractor. Had the rebar been placed a little deeper into the concrete (with no exposed ends), it likely would not have failed.
You can read more about the subject at: https://www.quora.com/Why-do-highway-builders-allow-rebar-to-rust-before-pouring-concrete-Isnt-that-eventually-going-to-destroy-the-concrete
I am a builder and have blogged about this issue with concrete before and have almost NEVER seen any mention of the issue of rebar concrete. I have seen the Pantheon as well: 2000 years and unsupported and unreinforced. The first concrete highway built in the 19th century is somewhere in new England and was unreinforced and supposedly still in use Concrete spalls from the oxidation of rebar and other causes. That is well known. Now we are finally starting to see "Greenbar" being specified which is green epoxy painted steel rebar. It may work real well but has not stood the test of time and bending it too much can cause it to crack breaking the bond. Other metals have been tested like aluminum bronze rebar which could last forever in concrete but it is a bit pricey. The other issue is how much energy is used to make concrete from limestone. Because it takes so much energy it SHOULD last 2000 years and using rebar which wont corrode within it is an obvious mandatory step. Failure in corrosive environments really speeds up the corrosion. Salt is used on roads and just kills concrete bridges. The Interstate bridge in MN that failed lasted what 30 or 40 years? And what did they replace it with? you guessed it. Corrosion resistant rebar should be code everywhere for all concrete. Another issue is why not use steel bridges instead of concrete? They last a long time and the new coatings and alloys give them exceedingly long life. And why not build rail bridges instead of car bridges? How much longer will we have petroleum based private automobile transportation after oil becomes scarce or expensive? Steel bridges are fantastically cheaper than concrete, last a long time and are completely recyclable and repairable as well with cheap labor and simple tools. There are rail bridges in India over 100 yrs old. Did you think about concrete dams and concrete port structures? A failure of a main concrete dam say on the Columbia could cause cascading failures of the dams downstream. The dams fortunately are extremely thick but had they used corrosion proof rebar, they would almost certainly last 2000 years. I am grateful someone with a large audience finally has addressed this problem.
Here is a link to an article that gives an overview of the manufacturing process for basalt rebar. Originally produced in Russia, now by a company in Houston, TX. http://www.monolithic.org/link-to/basalt-fiber-rebar
"It is still somewhat more expensive than steel, so it is first being used where steel has disadvantages. It can quickly replace stainless steel and epoxy-coated steel on a cost basis when regulatory hurdles are cleared."
Here is a link to a reseller that will give you some idea what small quantities cost.