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How Vile is Concrete?

 
pollinator
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How vile do you consider concrete to be?

I ask this question because over on a WOFATI Build, the topic came up, and I guess I never have considered concrete that vile in terms of green-building, but I have a cement mixer, and my own gravel pit, and so I make concrete for myself.

At my farm, I have used it to make concrete pads for sheep pens, concrete pads for buildings, ramps, three different countertops, flooring for chickens in a wooden building, grout for hand split slate in an entryway, chimneys, etc
My mantra has always been: Do as much as you can for yourself. The reason is often economics, but also quality.

Now I do not have a limestone quarry so I have to buy the Portland cement, which is about $13. I typically use 5 bags per cubic yard, so it costs me $65 a cubic yard, with a Redi-Mix Truck costing me $120 per cubic yard…about half the cost.

As for being “green”, I know that even buying bags of Portland cement is iffy because it is energy intensive, but at the same time, while I have my own forest, log, saw those logs into lumber on my sawmill, ultimately that lumber must be held together by nails, and smelting steel is energy intensive too.

So just how vile is concrete? I often wonder if it really is that bad, or if it is so often used, that people just make it more vile than it really is, just because they want an excuse to build out of non-tradional mterials.
 
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It probably depends on how much use the concrete structure gets, and for how long.

On the "not vile" end of the spectrum we have concrete that has been in service for a couple thousand years.  


And on the other end of the spectrum we have massive structures that received a few weeks of use and then were promptly abandoned.
 
pollinator
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Hi Travis,

Being that concrete last a very long time, from my perspective, it's a good use of resources and energy, if you build things to last. In housing, it can reduce expended energy cooling in the summer, and if set into the ground a bit, that can reduce heating in the winter. Only concrete is long lasting set deep in the ground, so it's a no brainer, when it comes to energy efficiency in building. People tend to look at resources and energy in the short term, so lets expand on that thinking: After all, humankind is but a blip in geological history, so wisdom dictates geological history carries knowledge worth weighing. When the earth makes rock, its energy intensive, yet since the rock lasts through the ages, its an efficient use of that energy. Being no shortage of rocks, gives good testimony to this fact. Dirt takes longer to make then stone, like Igneous rock for example, as dirt is the proven byproduct of that eroding stone. So be it dirt or clay, these products are more time and energy extensive in its making, geologically speaking, not to mention less aboundant then stone: with organic matter as a byproduct of that dirts efforts. So to chose between building materials like dirt, or concrete, I think concrete is a good use of resources: as rock has less energy and time expended in its creation. Put the dirt to work growing food and other renewable resources, plus harvesting carbon to further increase fertility; then let that which isn't productive in such ways be built with. Concrete can also be 100% recycled, and used for other purposes in building lasting homes.  Concrete is a renewable resource, that will last through the ages, like the stone it was made from. Personally, I think making stuff out of concrete is good. I would just add, spend the extra money or effort, to make what you build last through the ages, and it's energy well spent.
 
pollinator
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How it is used is crucial. If you "reinforce" it by pouring it around rebar, which, in the presence of moisture, which readily moves through concrete, swells as it rusts, destroying it from the inside in a matter of decades, it doesn't matter how long it would have lasted for. In that application, I think it's pretty vile.

If everything but the portland is sourced on-site, it becomes considerably less vile. Much less, if there's no rebar time-bomb embedded within it.

I think that the best use of portland is probably as 5-10% of a rammed earth or compressed earth block mix, which makes it go further and last longer. And no rebar time-bomb.

I think the other issue, though, is that of suitability for the task. Is concrete necessary in the application, or could it be done without?

-CK
 
master steward
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Concrete is traditionally mixed at around 7% to 15% cement. By that measure, concrete uses the same or up to 50% more energy to make as rammed earth at 5% to 10% cement.. In the real world, I'd call that a wash. It's not like there is an order of magnitude difference between concrete and cement-fortified rammed earth, they are approximately the same thing. There is about 15GJ of energy embedded in the steel  of a (half ton) rammed earth press. That's enough energy to make 11 tons of cement, or about 100 tons of concrete. If the rammed earth is only giving us a 50% savings on energy consumption, then we'd need to make 200 tons of rammed earth blocks to break even on embedded energy costs. For some applications, a monolithic pour is preferred over blockwork.

Cement is often a by-product of other processes, such as generating electricity or smelting metals. If the materials were not used in concrete, they would be dumped into landfills. Making cement accounts for about 1.5% of energy use, while driving and HVAC account for 54% of energy use.  If I were interested in making the world a better place by using less energy, my efforts would get 36X more traction by focusing on reducing expenditures on transportation and  HVAC.

The manufacture of cement releases carbon-di-oxide into the atmosphere. The curing of cement removes about half of the CO2 that was released in it's manufacture. So while it's not 1:1, it's close enough to balanced for me.
 
pollinator
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Chris Kott wrote:How it is used is crucial. If you "reinforce" it by pouring it around rebar, which, in the presence of moisture, which readily moves through concrete, swells as it rusts, destroying it from the inside in a matter of decades, it doesn't matter how long it would have lasted for. In that application, I think it's pretty vile.

If everything but the portland is sourced on-site, it becomes considerably less vile. Much less, if there's no rebar time-bomb embedded within it.

I think that the best use of portland is probably as 5-10% of a rammed earth or compressed earth block mix, which makes it go further and last longer. And no rebar time-bomb.

I think the other issue, though, is that of suitability for the task. Is concrete necessary in the application, or could it be done without?

-CK




So... how do you use concrete without steel/rebar, for reinforcement and for tying other materials into the concrete, in structural applications?

I am thinking specifically about A: earthquakes, a concern for any structure in my area, and B: shop and barn structures that will see heavy equipment in and around them...

I have seen coated rebar... it looked rather ineffective to me, any thoughts?
 
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I never thought about the vileness of concrete until I came across permies.  I have used about 5 cubic yards of hand mixed concrete in making perimeter and interior footings for our house build.  People think we are crazy for building a pier and beam foundation, but had I gone that route I would have ended up using at least 30 yards of concrete to make stem walls and a slab.  There is 18" drop from front to rear of the building site, so there would have been a lot of fill work done as well.  So, as vile as concrete may be, pier and beam uses a fraction of the concrete that a "normal" slab would have used.  And, when you consider that the oak trees I had to cut down are going to live on in the timber frame of our home, I feel pretty good about that too.

Unless we opt to go back to living in caves, we have to alter the environment we live in to some extent.  Come to think of it, even living in caves alters that environment significantly.  My goal is to build a home to code while having the least negative impact on the environment where I'm building.  This involves not only the construction process, but the impact of living in the home for years to come.  Its a real challenge.  To some, we are out of our minds because we aren't paying someone to put in a big honking slab and throw up a stick built house with vinyl siding and fake brick trim on the foundation.  To others, we aren't going natural enough.  And I'm ok with that because we are building the house that we want and trying to be as environmentally responsible as we can.

Now, I will have to confess that when I build my garage/shop, I will do a concrete slab floor.  I'm sorry, but this old man needs to be able to scoot around on a creeper or a seat when he's working on vehicles.  I've crawled around on enough grass and gravel working on cars that I'm going to treat myself to that luxury before I die!
 
Travis Johnson
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Dillon Nichols wrote:So... how do you use concrete without steel/rebar, for reinforcement and for tying other materials into the concrete, in structural applications?

I am thinking specifically about A: earthquakes, a concern for any structure in my area, and B: shop and barn structures that will see heavy equipment in and around them...

I have seen coated rebar... it looked rather ineffective to me, any thoughts?




It depends on the application. I use very little rebar in my projects, but for good reason, most of my projects are for concrete slabs.

It gets down to the reality that concrete is incredibly robust in compression, but poor in tensile strength. With steel, the opposite holds true. You have to think of it like a floor joist, where the load is pressing down, so the top of the floor stringer is in COMPRESSION, and the bottom of the floor stringer is in tension. If a floor stringer was made out of concrete (like a concrete bridge girder) the top is very strong, but the bottom third needs steel to keep the concrete from pulling apart and cracking.

In a concrete slab, you have gravel or soil holding up the bottom of the slab, so there is very little tensile forces in the bottom third of the slab, it is all in compression, which is concretes greatest strength. In short, rebar is not required.

I just had a friend last week who is trying to build a house without a mortgage, but does not know much about building. He is pouring a concrete footer, and spent a whole day putting in rebar, and yet went with a three bag mix of concrete which is VERY weak. He actually should have saved his money and put in no rebar, and bought more bags of Portland cement per cubic yard. That is because we live in Maine, and most of Maine is within 10 feet of bedrock. He had to jackhammer the ledge so he could get a level footer. So he did not need rebar. His footer is 100% in full compression because it is sitting on ledge rock, and there is no "bending" to induce tensile strength forces in his footer. He should have put in more Portland cement though so his concrete does not fall apart under its compression load.
 
Travis Johnson
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I think for a lot of homesteaders and builders Earthcrete has its place, and I feel so strongly about that, that when I did my classes on sheep farming, I mentioned Earthcrete.

Earthcrete is using the existing soil, then mixing it with Portland cement, and then mixing in water and letting it harden. It can be mixed in a cement mixer too, but the greatest advantage of Earthcrete is in vast slabs. That is because it is so easy and cheap to make. A cement mixer is not even required!

All you do is take a rototiller and till up the soil to a consistent depth, say 4 or 6 inches. Then calculate how many bags of Portland cement you need to make an earthcrete slab that size and depth. I use 5 bags of Portland cement per cubic yard (27 cubic feet) of earthcrete. Spread the cement powder out as even as you can, and then rototill again until the earth/cement is consistently mixed. Now using a hose or buckets of water, add in the appropriate amount of water, and mix again with to rotortiller. After that, the earthcrete is troweled and finished just like you do any other concrete project.

And by the way, if you do not have a rototiller, they can be rented for a project like this.
 
steward
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Side note on earthcrete...  I think it would be wise to wear a respirator while spreading and mixing the cement into the dirt.
 
gardener
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Right now, they are repaving a five mile section of highway near me. It is six lanes wide and being done with concrete (since it's a grade with snow removal operations). The slab they are pouring is two feet thick. I think that's somewhere in the neighborhood of 150,000 cubic yards of concrete. On this one highway. In this little stretch of barely populated California. Now imagine how much concrete is being used in infrastructure projects around the world... and how many yards it's sucking up. Now think about how many cubic yards a person uses in a foundation for a house.

My point here is, if you are concerned about the environmental impact of cement production — that's a valid concern — but has almost nothing to do with using concrete on an individual level. Military and infrastructure projects are going to use up several orders of magnitude more than individuals ever can.

If you're worried about it being personally toxic, as far as I know concrete is one of the safest materials you can build with. You need to be careful when mixing and drilling into it (wear a mask), but otherwise it's a stable, 100% recyclable material (smash up concrete, mix it with cement, and you get more concrete). When it eventually crumbles, it wears away to chemically stable rocks.

Also, as an aside on this note:

How it is used is crucial. If you "reinforce" it by pouring it around rebar, which, in the presence of moisture, which readily moves through concrete, swells as it rusts, destroying it from the inside in a matter of decades, it doesn't matter how long it would have lasted for. In that application, I think it's pretty vile.



This is not quite right. Rust is triggered by water, but the active ingredient is oxygen. When rebar is encased in concrete, oxygen can no longer reach the steel to corrode it. Any concrete that only lasts decades was built extremely poorly. A properly designed concrete beam will happily last for centuries. That's not to say there isn't a lot of shoddy concrete jobs around the world. But then again, there's a lot of shoddy jobs of all kinds around the world. I will tell you this: concrete of any form or function without reinforcement, will fail with 100% certainty. Even fence post anchors have reinforcement (with the pressure of the dirt acting as reinforcement).
 
pollinator
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It would appear that the "vileness" argument hinges upon the simple question, is the energy use needed to create portland cement justified by the usefulness, longevity and stability of end product?  In many (or even most) cases I would say, "Yes, it's completely justified".

That energy use is reasonable, in my humble opinion, if the concrete is incorporated in a long-term solution that otherwise would require ongoing maintenance and replacement.  Something like a foundation for a building—yes, there are alternatives, but none that are as strong, stable, inexpensive and lasting as good old concrete.  

When is concrete vile?  A couple of thoughts come to mind.  It's vile when its used to make dams that destroy rivers.  Long after the dam has silted-up and destroyed native fish runs, it stills sits there in the river.
Around the nation, hundreds of these worthless relics still exist.

Concrete is vile when its used to make impermeable surfaces (like we have all over Los Angeles, my home country) where water is forced to quickly rush away to the sea rather than infiltrate into the ground.  As you travel around the Southern California area, hundreds of miles of creeks and rivers are nothing more than oversized concrete gutters, intended to minimize erosion while maximizing the fast movement of water off the streets and out to the ocean.  And then we have the temerity to steal water from hundreds of miles away (the Colorado river, Owen Valley, etc.) and make no connection between the billions of gallons we quickly whisk away, and the billions more that we import.

I like how many European cities do not use asphalt to pave their city streets, but use interlocking concrete paver blocks.  Yes, the manufacture of these paving stones requires the use of portland cement, but because they don't have to be replaced EVER, in the long run, they use less energy to pave the street than having to slurry-coat the street every 3rd year, and grinding the old asphalt out every 25 years and laying a new top coat.  And, as mentioned above, interlocking concrete pavers allow water to infiltrate through the street into the subsoil below.  That alone is a worthy trade-off for me, particular in dry climates like the one I live in.

As for toxicity, there is none with concrete.  Pressure treated lumber (for example) would be an alternative to concrete, but its a toxic and corrosive nightmare.

All in all, from my perspective there is a place for concrete as an appropriate technology in permaculture.
 
Travis Johnson
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This whole topic has ben very encouraging. I always felt like a Permie-Heathen because I kind of liked concrete. It has a lot of useful, long-term properties that works well. So to hear others see it as being a worthwhile material to work with, has really been nice to hear.

But if you do not have a gravel, or feel gravel mining is against your morals, or want lightweight concrete...do not despair. My Grandfather needed concrete flooring on an old timber framed barn for his 50,000 broiler chickens, so he used sawdust as the medium instead of gravel in the mix. The floors held up for 27 years of scrapping by tractor every 6 weeks. It was waterproof, smooth, and light weight!

But there is a caution here, concrete is not as heavy as people think. Yes, it is 3000 pounds per cubic yard, but I did the calculations on my concrete countertops and a square foot of 2-inch-thick concrete countertop is only 18 pounds. A wooden kitchen cabinet is MORE than able to hold that little bit of weight up. I mention this because I have heard people say, "I hope you beefed up your cabinets before pouring that concrete", but it really is not that heavy.

 
pollinator
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I expect to spend about $5000 on slab and block work for a house in the Philippines. Probably another $2000 on a block biogas unit and very large block swamp cooler with a block solar chimney. Also a block swimming pool.

I stayed in a house that would be less than $1000 to replace and it's perfectly serviceable. If we spend $10,000 overall, it will be a far above average house.

 The house will never be heated or cooled beyond the use of natural means, so over its lifetime, that offsets the small amount of concrete. The floor doesn't need reinforcement and doesn't need to be very thick. No frost. The walls will be reinforced and I will probably spring for the coated stuff that isn't as prone to rusting. The exterior will be given a water-tight stucco.

I expect tropical vines to be the main thing that controls concrete temperature . By not letting the sun hit the concrete, it will be easier to keep cool.

Many of the properties I've looked at have their own stone and the labor to break it from the ground is quite inexpensive. So if I go with stone facing, it will be real. Lots of unemployed people so that the most ethical route.

I see some houses here that are being built to last centuries and some will probably fall down in 10 or 20 years. I will supervise every bit of work myself and not skimp on powder. I'll make sure that water isn't flowing over it constantly.

When excavating close to limestone bedrock, picks and sledge hammers are used to break up surface rocks. It is usually mixed in place so it's very easy to incorporate available aggregates. I've been looking into getting a jaw crusher so that any rock smaller than a basketball can be reduced to make different grades of aggregate. Useful for trail building and it's something that can be rented out when not needed.

Typical old style housing is coconut planks and everything else bamboo. They usually last 20 years or less. No way to control temperature or bugs.
 
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