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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.
 
pollinator
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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.
 
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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
 
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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?
 
pollinator
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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.
 
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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.
 
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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).
 
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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.

 
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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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Travis Johnson wrote: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.



We're building a little goose house for two geese. It'll be just a bit more than 16 square feet. Could we mix the cement and soil without a rototiller? How would we go about it? (My only experience with cement/concrete is making little paver stones for presents and filling in post holes, and one time mixing concrete in a wheelbarrow while building houses in Mexico...but that was half my life ago when I was a teenager!)
 
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John Wolfram wrote: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.  

]


This is not concrete as we know it today. Roman concrete is quite different from Portland cement-concrete.

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.



This is not quite right. If designed accordingly, a reinforced concrete structure will stay where it is for, well, almost forever. It will be very very expensive though (we can build any roman structure with ease today but they will be very expensive) and there is no need to build something like that unless you are building a nuclear power plant. For example we design suspension bridges considering a life span of 100 years, houses for 25-50 years (this time value is used in statistics to decide how to consider factors in the design - it does NOT mean that the building will die in 50 years).  So the rust issue turns into "how we can postpone this problem for statistically, say, 50 years". Many experiments were done and people have come up with two quick and dirty ways.
One of them is for every reinforced-concrete member. Concrete that covers rebars is called cover concrete. İf the thickness of cover concrete is greater than a certain value than water or oxygen cannot penetrate, so rebars do not rust. Every national code recommends different values, but - quick and dirty- foundations it is minimum 7,5 cm (3 inch), for members subjected to rain etc it is 2,5-5 cm (1-2 inch) etc.
For members under tension (pure tension or bending), you will need to make crack analysis and try to keep crack width under certain values. If the cracks are small enough, water molecules cannot get through.
So, yeah, if properly designed it is not a time-bomb.

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?


Travis Johnson wrote:
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.


Actually you have to use rebar (or mesh) in concrete structures. There are limited exceptions to this rule (dams and some slabs). The reason is, roughly, concrete shrinks by time. It gets smaller. So you put reinforcements to keep the volume, so it does not crack. This reinforcement is called minimum reinforcement, which is 0.5-1% of the total area of cross section of the member. 1% is what is used if you are going to build something without calculations.
Slabs also crack, they are not immune to volume change. But we limit their sizes, 4 feet to 4 feet, so we actually predefine cracks. So if you are going to pour a slab that is 16*16 feet, you pour 4 4*4 slabs. But even that is the case, in practice, we usually increase the dimensions a bit (6*6 or 8*8) and put minimum reinforcement. It is a mess to pour small blocks and slabs with no reinforcements crack anyway, due to settlement. Min reinforcement helps that.

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


In some cases you cannot put 4 inch thick cover concrete, due to some factors such as sulfur attack (which "eats" concrete). I don't see any practical reasons to use it in our cases unless soil is very acidic. Actually you want rebars to have rough surface, a bit of rust is not bad, it's good. It binds better with concrete.

Travis Johnson wrote:
It gets down to the reality that concrete is incredibly robust in compression, but poor in tensile strength. With steel, the opposite holds true.


I feel the need to clarify this. Steel has almost same tensile strength with its compressive strength. Steel members are usually very "thin" compared to their length so they are slender. Slender members buckle under compression and that gives the impression that steel is week in compression.

Travis Johnson wrote:
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.



Defining the ratios (sand, gravel and cement) is actually quite a simple calculation if you know sizes. Rule of thump, 7 to 1 (7 volumes of sand to 1 volume of cement) is used for simple applications (things that are not under load -  such as max 2 feet high retaining walls). Mostly 5 to 1 is used (such as slabs sitting on surface). Never forget to water it every day after you pour concrete. You can dismantle framework a day after pouring and it will have enough strength in 7th day.

Hope it helps!
 
Chris Kott
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But it is still susceptible to infiltration via mechanical damage.

I am not saying not to use concrete. I am saying I want to avoid it, and that for most purposes, I could use rammed earth or cement-stabilised compressed earth block.

Something that lasts only 50 years without maintenance, and only 100 years with constant maintenance, doesn't qualify as permanent in my books. The remains of Roman projects are many times that old.

Do we need to build on that timeline? No, we don't, and as changeable as our tastes are, planned obsolescence infected the building trade a long time ago. But I reject that kind of thinking as short-sighted, and one of the causes of all the waste we produce.

-CK
 
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One of the reasons why the modern types of concrete are used, is that it take vastly less material to build things. It can take 3-5 times as much physical material to build using normal masonry and unreinforced concrete.

There is a YouTube called Practical Engineering where the guys talks about civil engineering topics in 10 minute chunks. He has a short (5 playlist) about Concrete where he talks about the practical engineering related to concrete and its use. Since it was so short, I just included the individual videos. Here is the full playlist.

What is Concrete?


Why Concrete needs Reinforcement?


Does Rebar Rust?


Was Roman Concrete better?


What is Prestressed Concrete?
 
pollinator
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Chris

I'm not sure I see your whole reasoning here.

Don't your concrete alternatives also use cement? And cement is the questionable product, right? So we have concrete under a different name, not much if any benefit.

Concrete alternatives are not any stronger than concrete and they don't last any longer, right? So no structural or functional advantage there...

Concrete done incorrectly doesn't turn out well, but that is true of any process and concrete has a huge body of knowledge and installed base that all can reference, That means concrete work has a significantly better chance of turning out right, simply because practical info is widely available, calculations have become standard and there is a high probability that expertise  is close and immediately and cheaply available when needed; not so much for alternative formulations. Doing it right the first time is terribly important because when a building process doesn't perform to spec, there is a good chance it won't be used or used fully or for it's planned life cycle; and that it may well have to be redone - so double all costs and impact, at least.

Multiply the track record over thousands of installations, apply statistics and concrete may turn out to be way "better" when all actual costs are factored in.

I'm not really expert here, but that's the way it looks to me, so far.

Regards,
Rufus
 
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Personally I consider concrete a good thing if it is well used.  If used properly it is my belief it extends the lives of things like homes or reduces the labor or other energy costs.  Things I expect to change, low use etc should not be made out of concrete but long life things or high use things most certainly concrete should be at least considered.  I will disagree with the homes having a life expectancy of 30 to 50 years statement.  Homes last something on the order of a century or centuries if well built.  While it is high embodied energy if it promotes a longer product life with less effort that energy is likely recovered over time.

Take something like a sidewalk.  You will quickly say a flagstone or cobble stone walk will work just as well and have a lower embodied energy  And I will agree.  But it is harder to shovel snow over and a higher risk of injury doing it.  Why?  because the more places that stick up the more places to hook a shovel and possibly injury. It is also has a higher tripping risk for the same reasons.  Any of those accidents cost time and energy.  And it is higher maintenance and that costs time and energy too.  So I will argue that if it is high use, stays a long time that the embodied energy cost will mostly balance out and even if it doesn't the convience will pay for it.  Low use sidewalks on the other hand should be simpler materials.

As for the comments about rebar etc please remember we have many better options today.  We can look at history and see those failures but they take time.  For example structures in our canal system are failing because of rebar corroding but they have been in place nearly 100 years.  Going forward though we have better options like fibercrete, fiberglass rebar, basalt rebar as well as hardeners, waterproofing agents and plastiziers here now  and up coming we have the change to geopolymer concrete(aka roman concrete) with its longer life and lower embodied energy.

I have watched with interest the things on rubble filled foundations etc and other answers.  But most likely for now I will choose concrete because I have 50 years experience with it and have seen the ways it fails and succeeds over that time.  Plain and simply put I am more likely to be able to do a good job with it and in building a home I don't want to have to waste the resources to rebuild the home 30 or 50 years out.

So I am going to say concrete used properly is only a tiny bit vile and pays for itself other ways and ends up being a good thing used properly.


 
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Howdy everyone.

Just some thoughts, to riff off all of the amazing answers above (mentioning everything from cover concrete, to the use of alternate reinforcement). I think that Part of the problem we face lies in definitions and perceptions. So too, many more ecologically harmful aspects of contemporary reinforced concrete (not mass concrete) lie in contemporary construction industry practices, with the need for timetables, efficiency, and compliance with certain code and engineering mandates. Which are largely based on how concrete is being used (as tensile stress bearing structural elements, for example). All of this influences how we often see concrete and Portland cement. But perhaps it need not be this way.

I think that looking at concrete's past with a broader view of what it really is, and expanding conversation and information/idea exchange with engineers, natural builders, architects, code enforcers, will all help create a broader conversation in which concretes, be then clay based (seeing Cob as a type of concrete, for example) or lime based, or portland cement based, are seen more broadly as different approaches and tools more suited in some cases, or others.

In fact, modern concrete evolved out of the use of rammed earth, through Tabby. Which is from the Arabic Tabiyya, through Spanish and Portuguese Tapia or Tabia. Military or Royal Tapia is lime stabilized, a technique from the North African Maghreb. It's lime stabilized rammed earth. It is, in fact, a form of concrete. Just as ancient Roman concrete was based on a lime, mixed with various kinds of earth (not only volcanic Pozzolana. The Romans used many kinds of sands and earths in their concrete composition) and rammed in wood forms, with layers of stone aggregate (Caementum, whence we get the word cement from). But concrete itself is pre-Roman however. The Carthaginians and other North African civilizations used forms of lime based concrete in Punic cities, as well as rammed earth, centuries before the Romans started using the technique. It's likely the Romans learned about lime mortar, much less than concrete, from their interactions with Phoenician/Punic cultures and the Greeks. The persistence of the technique mainly in North Africa and Iberia, long after it died out in the other Roman areas, is a clue to this.

Spanish uses of Tapia/Tabia in colonial Mexico Florida, Texas etc. as well as the familiarity of some African slaves who used it indigenously in their own cultural contexts, led to the adoption of rammed Tabby, in the American South and East Coast. It was a sea shell based lime concrete. "Tabby" eventually evolved into "Gravel wall" construction. Interest in concrete "gravel wall" construction increased as interest in Pise/rammed earth in France was exported to America and England, and interest in natural, and then artificial, hydraulic cements increased. A few years ago someone on this forum (I cannot recall who) very kindly directed by attention to the early history of French Beton. Well, French Beton (concrete) evolved out of the tradition of pise - rammed earth. All of these influences, between North Africa, Southern Latin Europe, Latin America, England, and North America, all internationally came together in the 19th century as literature and travel enabled the exchange of ideas on these matters. French, English, and American concrete technique and material eventually evolved, each country influencing each other. There are really interesting the webs of influence, from France to England to America to France and England, back and forth, as invention and technique increasingly refined what we know as modern concrete evolved.

All that Concrete is is simply a binder with aggregates. If Portland cement is the binder then clay or silty earth is an aggregate just like sand, or ground pumice, or ground recycled glass. Or sawdust. These are all concrete, full stop. In modern building codes and textbooks concrete is defined as Portland cement with aggregates, be they sand, gravel, crushed stone, or other aggregates.  But in reality concrete is any binder - be it clay, lime, gypsum, or Portland cement (or natural cements) with aggregate - be it sand and gravel, or boulders (so-called plum concrete)

In this sense, Cement stabilized rammed earth IS concrete anyway. Even non-stabalized rammed earth is essentially concrete. So too with Earthcrete, it's just concrete with dirt as the aggregate. Hempcrete IS concrete. It's concrete with shredded hemp as the aggregate (and either lime, or Portland cement, as the binder). How we look at the thing influences how we vile we see it. Concrete is a really broad modality that can encompass many types of materials.  Technically asphalt is even a kind of concrete. The binder is tar, but we don't want that....
 
Simon Malik
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Again, I question why concrete should be seen as vile, but I also question why it shouldn't be used with other more natural materials. To complement their properties.

Chris Kott wrote:
"Something that lasts only 50 years without maintenance, and only 100 years with constant maintenance, doesn't qualify as permanent in my books. The remains of Roman projects are many times that old. "



I think the thing is though normal, plain gray, Portland cement based concrete actually doesn't have to only last 50 - 100 years. Done well the stuff can last longer than the Roman projects. Brown sugar as a set retarder to gain greater strength, wood ash  and crushed brick aggregate as Pozzolans, thsi stuff can be dirt cheap (no pun intended) and strength concrete. Rufus points to the body of knowledge. Most really bad concrete was done in an era with much, much, less awareness of the issues that can affect concrete. Every decade the amount of knowledge on how to produce durable concrete goes up.

We collectively know far more now than we did in 2009, or 1999. But the concrete of the 90s and late 80s was far more sophisticated than the concrete of the 40s and 50s. And even back then, people knew things that - were it not for short changing price concerns, laziness, or limited information availability, could have massively extended concrete's life back then. The US Government was doing experiments with blending old fashioned natural Rosendale cement with Portland cement to make far more durable highway concrete, for example. Market pressures drove natural cements out of business. Only now, with niche restoration and natural building markets, is the stuff coming back - but horrendously expensive. A broader market, better distribution, and more acceptance of natural cement as a durability enhancing additive to Portland cement concrete - or an alternative for people who want to do concrete with lower embodied energy ( outside of transportation....) could help increase knowledge of it. In Europe there seems to be a far more active, and well moneyed, market for natural hydraulic limes and cements. Much of it, I think, is because of heritage architecture needs. If only this could increasingly translate over to the USA, and in ways more affordable to DIY less affluent builders ...

There are a lot of commonly available, well known in niche markets, concrete additives - some quite natural - that easily produce concrete far more durable than anything the Romans were capable of. In fact, we could produce Roman style concrete, using their ingredients, that outdo what they were capable of. Using their own stuff, because we have better structural and material knowledge.

I think normal concrete, which when done well can last a thousand years, can complement other alternative techniques like cob, rammed earth, unfired adobe, or low fired burnt mud bricks - if the costs of experimenting and and architects, engineers, building code divisions inspectors were informed, aware, and interested and in more conversation with natural builders. And if natural building communities continue to not only share ideas and perspectives - like everyone is doing here - but were capable of more aggressive advocacy and - of course - had more money to play with Natural or alternative building enthusiasts, and Permaculture enthusiasts, all need more aggressive lobbyists and public outreach.

But I feel as if people should be more friendly to, and willing to consider the potential benefits of, ordinary gray concrete. The stuff isn't so bad. It just wants someone to use it in better ways.

C. Letellier wrote: "Personally I consider concrete a good thing if it is well used.  If used properly it is my belief it extends the lives of things like homes or reduces the labor or other energy costs.  Things I expect to change, low use etc should not be made out of concrete but long life things or high use things most certainly concrete should be at least considered.  I will disagree with the homes having a life expectancy of 30 to 50 years statement."



I agree. The thing with homes is that modern American homes are actually build with life expectancies of 20 - 30 years (and only in rare cases 50). Most so-called 'custom' tract homes have life expectancies of 30 years tops. Quality on stick framed US houses has steadily declined from the late 70s/early 80s on. It's planned obsolescence, and contemporary builders alone aren't be be blamed - this is somewhat market driven as well.

There are custom home builders, increasingly, who are doing higher quality work. They are in a minority. Kids born in the average built to minimal code requirements McMansion will see their family home start falling apart at the seams when they are in their 30s to early 40s, and their parents in their 50s to 60s.

I think if someone is building something to last a long time, with minimal maintenance, normal concrete done properly - just like properly done bearing masonry - can last centuries.

Rufus Laggren wrote:
"Concrete alternatives are not any stronger than concrete and they don't last any longer, right? So no structural or functional advantage there...
Concrete done incorrectly doesn't turn out well, but that is true of any process and concrete has a huge body of knowledge and installed base that all can reference, That means concrete work has a significantly better chance of turning out right



I agree, but I believe the concrete alternatives actually are forms of concrete anyway, there are semantics, perceptions, definitions - I think that just because modern reinforced concrete has this huge body of knowledge doesn't mean that we shouldn't explore other alternatives. For example, rammed earth or lime based concretes are vapour breathable, a solidly concrete house needs careful attention to ventilation because it;s essentially airtight, especially with energy efficient windows and doors. Many modalities of commercial green architecture see airtight structures as a good thing. But there are trade-offs. Lime based concrete, or lime reinforced rammed earth, is more vapour permeable. This can lead to fewer problems with condensation and damp. Of course done properly, with detail paid to ventilation, you could pour a monolithic concrete box and dome and minimize condensation problems. That comes in the design.

There are contexts in which Portland cement is more expensive than other alternatives. Not in Europe and North America, but there are huge areas in which Portland cement is extremely dear. Better understanding of lime concretes, ir clay and earth alternatives, existing vernacular uses of rammed earth, etc., can open up natural, healthy, beautiful homes to people who wouldn't be able to afford properly done and detailed reinforced concrete homes.

Portland cement based reinforced concrete can, and should anyway, play a role in alternatives. Seismicity is a huge issue in many parts of the world. Someone interested in more natural building could use earth based types of masonry and, for example, do monolithic concrete bond beams, plinth ground beams, reinforcing columns, foundations to overcome seismic issues.

Heck, in North America, where cement is cheaper and yards of readymix are more affordable, concrete is still astonishingly expensive. So too is the engineering needed to spec out slabs, walls, etc. Especially for a DIY builder. Market pressures (including house and real estate valuations, the mortgage and lending market, a huge commercial market able to pay top penny for skilled contractors) all push up the costs of concrete. So too, permitting. In my wife's country everything is done in concrete. Stick building would be both extremely expensive and extremely undesirable. The idea of building with wood is seen as insane. So the market responds, wood - in a Mediterranean country with large forests - would be a niche luxury accent material. Panelling, and just raw scaffolding and formwork material. Concrete is expected for structural work, and is priced in a way that home builders, even families building incrementally, can easily afford it. In other countries concrete is more expensive. Markets dictate a lot. Every place has different needs.

I think all of this stuff can complement each other. Concrete and Concrete alternatives. Hempcrete, or sawdustcrete, for example, has insualtive properties as well as mild compressive strength. Earthcrete may be a good way of diverting waste earth fill, and get something useful out of it.

There's more than one way to peel a pear. If someone wants to actually peel pears, anyway. There's also more than one way to peel an orange. Oranges and pears, though dissimilar fruit, can be really tasty together in a fruit salad.

I think masonry (especially structural bearing masonry), ordinary concrete, and earth based monolithic masonries (cob, rammed earth - which are all types of natural concrete anyway), lime based masonries and concretes, and other alternatives can all work together - in the mind of an imaginative knowledgable architect or builder - to make healthy, more natural, and very long lasting homes. And I don't see why they shouldn't work together..
 
Travis Johnson
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I personally feel that the Roman Workings are rather over-rated. I say that because while many are in existence, most are not working for the purpose they were engineered for. Just because parts of them can be seen 2000 years later, it does not mean we should consider them superior. While we have only been on this farm since the mid 1600's, there are things I can show you that my ancestors did, like rock walls, stone foundations, and earthworks for farming, other than one foundation, I know of none that serve a purpose any more.

It is all about maintenance.

You can have some really old houses made of wood, several in my town are from the 1700's, but it is not because they built those homes in a superior way (quite the opposite actually), but because they have continuously been maintained.

It is like that with concrete and steel. It is well known that a steel bridge lasts twice as long as a concrete one, however, the cost of maintaining steel is so much more expensive (due to painting it above a waterway), that they build them out of concrete instead. Because of that, concrete bridges are cheaper.

Myself, I recently built a bridge for my farm out of wood. It even sits on a wood foundation. I did build it out of rot resistant wood granted, but it costs me $16.50 to build, and took 8 hours of construction time. A plastic culvert would last a lot longer, but I can build 11 bridges for the price of that (1) plastic culvert, and it looks better too.
 
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We are wrestling with this issue at the moment. We need a flood friendly downstairs, as in needs to be able to be occasionally completely submerged, and a concrete slab with brick walls and tiled surfaces is the obvious choice as it can be easily pressure cleaned. We hope to extend our tiny flood prone art deco house that is perched high on stilts and embrace the flood rather than hide from it and use the space under our house for living. We want indoor outdoor connection and are trying to design something that we can open large doors up, take some minimal furnishings upstairs (including kitchen appliances) and let the flood flow through.
But I am stuck in the concrete issue.
Personally, I opt for longevity of material and building soundly for a long time, because most materials are costing the earth somewhere, and obviously earth building in a flood zone is out of the question! I had always wanted an earthen floor... but it just wouldn't suit flood. So from that point of view it seems ok to concrete.
But concrete just FEELS so dead, you can't feel the hum of life from the earth. It is also cold and hard on the legs and i suffer a lot of pain if I walk on concrete. The other consideration is the highly reactive soil in our area, down on the flood plain the top soil is sandier but underneath the clay still expands and contracts a lot with moisture. The hill where my village is, is called the fairymount and its part of the reason I feel this is a beautiful place. the earth is alive and it dances. up on the ridge any concrete is a no no, slabs crack and I've seen a house starting to be pulled down the hill from the weight of concrete and the movement. Here the movement is slight but it becomes amplified up the massive posts and so we have lovely terracotta tile someone places in the kitchen that just should not have been used over a timber floor and is all cracked. Everything needs some flexibility. Traditionally houses here were built in timber on posts to allow movement.
So my other thoughts... float a recycled timber floor across timber joists. but low to the ground. This is the traditional way of living with flood, but if the timber sits in water too long it starts to rot. actually the long timber posts that hold up my house have started to rot at the base from sitting in standing water last flood. The plan is to chop of a bit and raise them onto steel stirrups to extend their life another fifty years.  The timber floor would stay damp a while after flood too. And I worry about the bacteria and mosquitos having shallow water potentially sitting  under the house after the flood subsides.
The third option is a bit experimental so i am unsure if it would pass council approval, but it would involve deep layers of gravel screed and tamped down layers of gravel covered in high quality stone pavers. we've been musing over whether we could heat the pavers, or even float them on pedestals with the heating running beneath? pedestal paving technique is used on rooftop patios where the weight of sand would be a problem and uses recycled plastic plinths which the tiles clip into and the weight holds it all together without mortar.  while I know that would certainly allow water to drain better, would it also allow it to seep up faster? the flood waters rise gently here as we are a good distance across the flood plain and don't have to worry about rushing water.
Any ideas  or thoughts?
Do you think concrete feels dead or stops some sort of spiritual connection to the earth? Why would concrete feel dead compared to stone or clay brick which still feel warm and alive?
 
Victoire Peverill
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I found this great video of a build with a 'slabless assembly' There is a lot of technical info.
insulated slabless slab
Technical animation explaining how it works.
slabless slab animation
 
Travis Johnson
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I think most of it is perception.

You step into a hotel and the lobby I teeming with marble and wool carpeting, but as soon as you enter the back stairwell, it is boring ole concrete. It might not even be painted, just boring, monolithic concrete. And that is just one example. Look at any architecture and the important parts are built of something different like wood or stone, but the more utilitarian parts are just concrete. In my own home I covered my concrete slab floor with carpeting even though it reduced the effectiveness of my radiant floor heat some, just because concrete is rather boring.

As for connectivity, it is perception as well I think. Concrete is all earth...limestone, rock and sand. It is hardly different from stone as marble and granite come from the earth too. But again, it is boring ole concrete so there is no connection to it.

In my house...I don't know...I poured my own concrete countertops so there is some connection to them on a personal level, but not a whole lot to be honest with you. But I think there is some because some things have been done to it. It is not just worked to make functional...to put into a specific shape, but treated so that it has color. It is a "finished" product so to speak, so it changes my perception of it.

In your case, you could put down concrete and have the concrete polished. Its not super great looking, but at least it is not boring old concrete and the inspection team cannot deny you making it look better. Or you could paint it, or put some other finish on it. Do a search for polished concrete, penny floors, or what have you, and you will see that a lot has been done to improve the finished look of concrete.
 
Victoire Peverill
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I don't mind the look of polished concrete at all! Even without the epoxy finishes and gloss. The aggregates sparkle. I guess what I mean is a spiritual feeling, and it probably wouldn't make sense if you don't believe in that or feel it! But logically you're right, its all been dug outta the earth somewhere and it has rock in it, but it feels like it stops the earth below breathing or something... I don't know. And its too hard on the legs. But perhaps there is something in that idea of personal connection. Maybe it can feel loved. A terrazzo style concrete floor would be perfect architecturally for my 80yr old art deco house. But I'm not sold yet.
Cost wise I wonder how the gravel floor would compare to a poured slab?
 
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Travis,

I love this question!  It goes right to the heart of the complexity of energy use problems/debates.  

On the one hand, Portland cement is one of the most energy intensive products currently made by mankind.  Most people don’t realize just how much energy goes into making a batch of cement.

On the other hand, Portland cement is literally the foundation for our homes and livelihoods.  It is incredibly useful, flexible in application, sturdy and durable.

Though I have to say this with caution and qualifications, I think that despite the intense amount of energy and therefore pollution associated with cement, it is a sort of necessary evil for our culture.

Great question!

Eric
 
Travis Johnson
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I think the answer to how vile concrete is Eric, may be in how I use homemade lumber (called rough sawn lumber here).

I have my own sawmill, so I use a lot of rough lumber, but here is the thing. In using rough lumber, I will saw the logs right down to the bark. By this I mean, I get a LOT of lumber out of the log. I do this because a lot of times I need lumber, but it may not require strength. Like yesterday, I was framing out a new bathroom but it did not need a lot of strength, just something to hold up some ceilings, some wallboard, and the like. By visualizing each use, I can select rather crappy lumber, and use it. Like bark on a 2x4...it is no big deal if that edge is inside a closet. So that is what I do. I use crappy lumber.

Now understandably, no one would buy a bark-laden 2x4 from a lumberyard, but if I can get (6) 2x4's more out of a log even if they are bark-laden...to me it is okay. I can use those rather crappy 2x4's somewhere.

But that same thing could be done with concrete.

As I said in my original post, I use a 5 bag mix...but I do not have too. If a use is not going to have that much load, I could cut back on the strength and only use a 4 bag mix...or a 3 bag mix. (Bag means, number of 94 pound bags of Portland cement to the cubic yard.)

Or a Permie person could use bigger sized rock to reduce the amount of cement needed.

The point is, matching either the cement to gravel ratio, or matching the aggregate size to the anticipated load; could really go a long way to stretching how much Portland cement is used. And that is okay. It will reduce costs too.



 
Dale Hodgins
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I'm seriously considering a ferro-cement roof. Strong, durable and not likely to blow away in a typhoon. There are good quality grouts that can stand up to torrential rainfall.

 The most commonly used alternative is sheet metal of dubious quality.
.....
My biggest issue with concrete, is the huge amounts of fake stone that would technically last hundreds of years, but in reality, the average fake stone facing has a shorter lifespan than vinyl siding. I checked it out. A lot of it gets used in commercial settings where they rip it off after just a few years, in order to have a different look. But even in household situations, it's not real rock and it gets treated as a disposable facade.
 
Travis Johnson
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You certainly bring up a good point regarding fake rock.

I am not a huge fan of anything fake, and vinyl siding being one of them. I log too much to ever nail up what amounts to a barrel of crude oil on the side of my house. I use natural cedar shingles, but admit fire danger in Maine is not an issue.

A good, real rock for me is slate, just because where I live has a lot of slate. This goes along with my mantra of "doing as much for myself as I can". But slate is cheap if a person has to buy it too.
 
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From my perspective, I thing we need to look at all building and material on a scale.  Certainly, we strive for best practices, but, realistically, the real issue becomes those best practices available to us.  On a scale of Wonderful to Horrible, I normally consider any option within 1/3 of the scale on the Wonderful side to be worth considering.  For me, it isn't a matter of being the best (though that would be nice); it is matter of being better.

 
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