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Toxicity of Concrete: discuss...

Jonathan Hontz


Joined: Feb 12, 2012
Posts: 36
Location: Denver, CO
I've had two separate people bring up the idea that concrete is toxic. Both times it was in relation to urbanite near where food was going to be grown, and both times it seemed pretty ridiculous.

Concrete dust is dangerous when inhaled in large quantities, just as most any dust is, but the substance itself is fairly inert. I recognize that there are additives that can be put into concrete during manufacture or pouring, and that most of them are sealers or dyes to protect or enhance the appearance of concrete. Concrete also requires huge amounts of electricity to produce if using an electric kiln, and no matter what is used to fire the kiln, the process releases gigantic amounts of carbon dioxide. Calling the concrete "toxic" in this regard is just a mis-identification, as it's the process that is toxic and not the substance itself.

About the only substance used in concrete production as a replacement for some of the Portland cement that goes into it, fly ash, usually contains heavy metals, although this material isn't used everywhere, and I question how much of it is freed up when the concrete disintegrates.

Any thoughts or experiences with urbanite or concrete in this regard? I'm not terribly worried about it, but should I be avoiding the stuff wherever I'm growing edibles?


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Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 3820
Location: Victoria British Columbia-Canada
    
  53
The soil on Vancouver Island is acidic. Concrete is alkaline. So I intend to use concrete scrap wherever needed to correct ph. Sometimes I'm paid to remove very old stuff. This can be crushed to produce a low grade gravel. If this gravel is screened, the larger stuff has more rock while the fines contain more of the lime. Older concrete around here is made from glacial till, so crushing will expose other needed nutrients.

The only materials I will avoid are batches from gas stations and other polluted sites.

Stone and brick are often coated in lime mortar. I have cleaned both for re-sale by mixing them with maple leaves. The acids in the leaves work on the lime. A year later I have clean brick and stone and improved soil. It's a huge labour saver.

The old footings on my truck are soft enough that every hammer strike reduces them. This stuff will break down decades earlier than will top quality bank vault grade materials.



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Morgan Morrigan


Joined: Oct 16, 2011
Posts: 1400
Location: Verde Valley, AZ.
i thought the only thing you had to worry about was PH change when it is fresh, and getting rained on the first few times.

There is a new "green" concrete that uses less than 10% of the energy to make. Uses mining slag instead of ash and clinkers.

http://www.tgdaily.com/sustainability-features/61612-green-cement-modeled-on-roman-buildings?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+tgdaily_all_sections+%28TG+Daily+-+All+News%29


Get involved -Take away the standing of corporations MovetoAmmend.org
Julie Helms


Joined: Dec 06, 2011
Posts: 110
Location: SC Pennsylvania, Zone 6b
My husband just finished building me a large cinder block raised bed. I'm sure hoping there is nothing wrong with growing food near concrete...


http://woolyacres.wordpress.com/
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 3820
Location: Victoria British Columbia-Canada
    
  53
Often concrete blocks are referred to a cinder blocks even if they contain no cinders. Pensylvania, being an area with plentiful smelters may very well produce blocks with a cinder component. Call the manufacturer.
Julie Helms


Joined: Dec 06, 2011
Posts: 110
Location: SC Pennsylvania, Zone 6b
We purchased them at Lowe's and Home Depot and both called them concrete blocks. I've just always referred to them as cinder blocks. I didn't know there was a difference.
Jonathan Hontz


Joined: Feb 12, 2012
Posts: 36
Location: Denver, CO
The only materials I will avoid are batches from gas stations and other polluted sites.


This is a very real concern of mine. Concrete seems to sop up oil and hang onto it, and if it's been driven on, it will probably have picked up all kinds of tire grime which I don't want anywhere near my food.

Morgan Morrigan wrote: There is a new "green" concrete that uses less than 10% of the energy to make. Uses mining slag instead of ash and clinkers.


Not picking on you for this, but merely commenting on the scare quotes: that ignores the energy used in the mining activity that produced the slag, of course.

We purchased them at Lowe's and Home Depot and both called them concrete blocks. I've just always referred to them as cinder blocks. I didn't know there was a difference.


Technically, there's the difference that Dale mentioned, but "cinder block" is a vernacular term in PA where I grew up. I've also used and heard Hollywood block quite a bit, but they all refer to the same material, cinders or no.

There are quite a few additives that can be added to concrete to increase its resistance to the corrosion of rebar, and many other properties such as workability, curing time, and pump-ability can be changed with them. I suspect those are mostly used in batches destined for major concrete construction; bridges, buildings, and roads for example. The use of additives probably increases as the oversight by inspection and permitting increase. Simple sidewalk and step pours, where I think a whole bunch of urbanite originates, is probably not mixed with these agents because it's not necessary and adds cost.

I'm very curious if anyone has tested soil that's been in contact with concrete, or otherwise noticed any "allelopathic" effects from the stuff. I've never noticed it, but having heard it a couple of times, I wonder if it's true or just urban myth.

Stone and brick are often coated in lime mortar. I have cleaned both for re-sale by mixing them with maple leaves. The acids in the leaves work on the lime. A year later I have clean brick and stone and improved soil. It's a huge labour saver.


This is ingenious. I just cleaned some the old-fashioned way, with a hammer and cold chisel, and I was concerned about the mortar as well. Much less curious about this, as I know it's mostly lime, and lime is a great amendment in acidic soils. So that's where the mortar ended up: in the soil.
Amedean Messan
pollinator

Joined: Nov 11, 2010
Posts: 802
Location: Burlington, NC - Woodland, Clay - Zone 7
    
  26
"Ok everyone, we can calm down now because it was a false alarm", lol!

It is good practice that we question our methods but I hope to put a little fears away. The answer to be concerned about toxicity is "yes" and "no". Yes and only rarely, if you have coal ash aka "fly ash" with excessive levels of toxins, but in fairness it is similiar in composition to volcanic ash which is a main component in volcanic soils. As we all know volcanic soils are prized for high mineral content producing healthy crops but little discussed about trace elements of toxic metals which are a constant reality in nature. We all live with a degree of ambiguity in our exposure to toxins and our bodies naturally function, ask Dr Charlotte Gerson if you get the chance. Unless you happen to have a rare exemption or just got bad luck in product choice, the answer is generally "no", concrete is considered safe. Personally, I would not eat off of concrete dishes my entire life to proactively produce any possible risk of exposure but that is just me.

Just like soil quality, variations fluctuate in material elemental exposure depending where they are from originally. This is the nature of the beast on this planet so try not to contemplate too much before a phobia ensues and your quality of life is greatly depreciated. If you have good reason or are seriously curious, send a sample to a lab and get test results. I believe some states do this free through the agricultural departments.


Those who hammer their swords into plows will plow for those who don't!
Jonathan Hontz


Joined: Feb 12, 2012
Posts: 36
Location: Denver, CO
I should probably clarify that I am not at all worried about concrete. I use quite a bit of urbanite, since I just happened to have some available. I am curious as to whether or not there is any merit to the arguments made by others that it is toxic. I'm getting the impression that the arguments are hogwash, or at least not true enough to pay any further attention. I know that it's become a popular material in the urban areas because it is plentiful and cheap, and I certainly don't want to be perpetuating a silly rumor for such a handy resource.
kent smith


Joined: Sep 05, 2010
Posts: 211
Location: Pennsylvania
cinder blocks were made from volcanic cinders, not cinders for coal burning. Fly ash a by product from burning coal is a common additive to most concrete. It has some cement like properties as in is does set up like cement and it is a cheap filler.
kent


Kent
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 3820
Location: Victoria British Columbia-Canada
    
  53
kent smith wrote:cinder blocks were made from volcanic cinders, not cinders for coal burning. Fly ash a by product from burning coal is a common additive to most concrete. It has some cement like properties as in is does set up like cement and it is a cheap filler.
kent


In the 1930s there were several makers of cinder blocks in the eastern U.S. who used fly ash,from coal burning, also called clinker to produce blocks. Agregate was sometimes slag or other industrial waste. They were cheap but lacked uniformity that is obtained from todays concrete blocks. I have drilled through these blocks. They are softer and they have a burnt smell. Dust from these blocks burns like hell if it gets in the eyes. Sulphuric acid, I presume.

Volcanic ash is also used to produce blocks. Roman concrete used volcanic ash. The most famous and well preserved example of a Roman concrete structure is the Pantheon, a giant domed structure.
Ken Peavey
steward

Joined: Dec 21, 2009
Posts: 2168
Location: FL
    
  54
Concrete lasts a long time. The older concrete may contain impurities such as the fly ash mentioned above, but older concrete is hard to come by. The use of concrete in residential structures did not become commonplace until well after WWII due to cost and transportation demands as concrete is heavy and needs to be continuously mixed during transit. By the time concrete became regularly used in residential structures, production methods had become streamlined, with standardized ingredients-this is the concrete used since the 60s. The stuff you will encounter most of the time is harmless. There will always be the issue of lime leaching into the soil, but this takes decades. Avoid concrete from driveways as oil and leaded gasoline offer contaminants.

Concrete and mortars used in industrial settings are another story altogether. The processes requiring its use demand special ingredients-alumina and crystallized silica is common in thermal applications (boilers/furnaces), with some exotic materials used in extreme situations. I've worked with titanium mortars and brick made with hexavalent chromium. It's not likely you would encounter this stuff, EPA rules dictate containerized disposal. It's rare to encounter this kinda thing in a residential area, but every now and then someone had an exotic hobby. A general rule of thumb: if it looks weird, it probably is, move on to something else.


Seed the Mind, Harvest Ideas.
http://farmwhisperer.com
Jonathan Hontz


Joined: Feb 12, 2012
Posts: 36
Location: Denver, CO
Ken Peavey wrote:Concrete and mortars used in industrial settings are another story altogether.


This is what I suspected, but I have no experience with it. The more radical the thing done with the material, the more additives probably need to be mixed in to get it to do the job. Bearing the weight of people on foot isn't terribly demanding unless those people are walking 100 feet over a body of water, for example.

What is titanium-based mortar used for?
Ken Peavey
steward

Joined: Dec 21, 2009
Posts: 2168
Location: FL
    
  54
titanium dioxide based mortar-pulp mill, as a mortar and grout for tile to seal tanks which contain caustic liquids.
chrome bricks for coal gasification power plants-they take some massive abuse and heat
ruby brick-power plants
carbon brick-black like a hole in the world-lines tanks for phosphoric acid production used with furfuric resin mortar
alumina brick-kilns, furnaces, dryers
shale brick-lower acid concentrations such as drainage ditches internal to the plant

This stuff does not last long in some applications. The abuse received demands repair or replacement regularly. The old stuff going to special landfills or hazmat dump sites.
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 3820
Location: Victoria British Columbia-Canada
    
  53
Ken, do you wear an asbestos type mask whenever you're inside a Kiln, boiler,stack etc. ?
Ken Peavey
steward

Joined: Dec 21, 2009
Posts: 2168
Location: FL
    
  54
different gear depending on the situation. Tyvex suit with N95 particulate respirator works for most jobs. Head to toe, one piece goretex or rubber suits with full face respirator for sulfuric acid, same thing plus an air line for caustic. I won't do work in drug plants-triple layer sealed suit with self contained breathing. It gets HOT in those things. We do some low grade Hazmat cleanup now and then. Oil spills need rainsuits and rubber gloves. Lots of rubber, always a hardhat, sometimes a harness, lifeline, lots of climbing. There are some unconventional protective methods-we slather ourselves in diaper rash ointment when doing demo on lime kilns-keeps us from getting burned, and our skins gets so soft and smooth. Imagine a bunch of roughnecks smelling like perfumed diapers! Then there is duct tape-seals the gaps between gloves/boots and suits-hve to cut your way out when you need to #1.

The demolition is the messy part-lots of dust that need not be inhaled. Putting the stuff back in ain't so bad, the material is in good shape.
Jonathan Hontz


Joined: Feb 12, 2012
Posts: 36
Location: Denver, CO
Amazing stuff. I certainly wouldn't use any of this in my garden, but it helps to know it exists in any case.

Ken, have you ever been on Dirty Jobs?
kent smith


Joined: Sep 05, 2010
Posts: 211
Location: Pennsylvania
Ken, I appreciate your experiences having worked in less than health industries most of my life.
Jonathon, as a past front range resident, I would think that using concrete is less of a toxicity issue than other things in the front range. Each time I would drive down I-70 from my past home on squaw pass into denver to work I would see the heavy brown cloud as drove down into it. The funny thing was that I never noticed it when I lived down there, but when I moved to the mountains I could feel it in my respirtory system when I went to work. I had to wonder how much crap I was exposed to in the metro area besides the air, (water, emf, metals). I worked for a company that was next to I-70 near the mouse trap and we did air monitoring in the plant since we were a food producer and we did see toxicity from what I beleive was being next to the highway. I remember seeing report of that whole globeville area testing higher in things like asbestos, lead, heavy metals and other things from both the freeway and industry in the area. I have to wonder if the toxicity of anything in re used concrete is as bad as what most folks have in their environments that they are unaware of on a daily exposure.
kent
Jonathan Hontz


Joined: Feb 12, 2012
Posts: 36
Location: Denver, CO
kent smith wrote:Jonathon, as a past front range resident, I would think that using concrete is less of a toxicity issue than other things in the front range. Each time I would drive down I-70 from my past home on squaw pass into denver to work I would see the heavy brown cloud as drove down into it.

Ah, the brown cloud. That's a whole different thread right there. We're up on the west side of the valley, so most of it settles down lower than the house, but we can still see it when there's a temperature inversion. The other issue out here is Rocky Flats, the infamous nuclear weapons facility that's about 15 miles NW of here. Some things can't be helped. I can't get people to drive less, but I can certainly control what I build my planters with. We must pick our battles.
Suzy Bean
steward

Joined: Apr 05, 2011
Posts: 940
Location: Stevensville, MT
    
    8
Paul and Anna Birkas discuss natural swimming pools, the DVD and the subject (part 2) in this podcast.

They talk about the toxicity of concrete.


www.thehappypermaculturalist.wordpress.com
Jonathan Hontz


Joined: Feb 12, 2012
Posts: 36
Location: Denver, CO
The good: thank you for linking to the podcast, as I didn't notice that they talked about it. That makes three people who've raised the issue of toxicity in concrete to me.

The bad: after listening to the discussion, the jury is still out. I think the most important thing to remember is that concrete is porous, which can be difficult to remember when you're dealing with such a hard, robust material. Because it is porous, it will hold onto many things that come into contact with it, including toxins. In those cases, yes, concrete is toxic. However, there are probably far more instances of concrete being used for applications that don't expose it to harmful substances, and there's little if any danger from using it if you're in a pinch.

I'd also like to point out that in the podcast, cement and concrete are used interchangeably, but they're not the same thing: cement is the binding agent that holds aggregate together to make concrete. Also, the burns that Ms. Birkas described getting from handling cement are a result of the lime found in it. The lime changes chemically when water is added to the cement, which is what cures it. The curing process also thereby eliminates the burning, which is why you won't get a chemical burn from concrete if you touch your skin to it. If I remember my mason's chemistry correctly, that is.
David Wechsler


Joined: Jan 15, 2012
Posts: 9
Location: St. Louis, MO
I would like to add to the conversation that if you're planning on growing on or in concrete containers, it may be a good idea to try some DIY phytoremediation - that is, grow certain plants that tend to sop up heavy metals and other toxins. Check out wikipedia's List of Hyperaccumulators for suitable plants. One such plant is sunflower - so depending upon the toxins present within concrete, it may be worth growing some in your concrete container first, and then be sure to destroy (not compost) the plant. Look for a local household hazardous waste program for specifics.

If you want to accelerate the process, consider electrifying the soil mass using a DC power supply such as a battery or solar cell.


David Wechsler
- Founder, ElectricFertilizer.com
- Interested in engineering, permaculture, energy medicine, and technology-enhanced ecological systems
Cory Arsenault


Joined: Mar 03, 2011
Posts: 55
Location: Ottawa, Canada
    
  10
Will Hooker who give that online NC State Intro to Permaculture course mentioned that he puts a chunk of concrete in his rain barrels as the lime in them will absorb heavy metals.

In terms of the natural pond, one thing I'd keep in mind is that concrete will absorb oxygen. Supposedly the discovered that was why the oxygen levels in the Biosphere 2 project kept dropping unexpectedly.
Nicola Marchi


Joined: Sep 20, 2011
Posts: 73
    
    3
Okay, I just spoke to an old professor of mine who works with precast concrete manufacturers and has had several masters students make theses on the toxicity of concrete, long term effects of different admixtures and components, and another one which isn't coming to me right now.

What he told me was that heavy metals in concrete, become inert. The only tiny debate in the industry was whether or not effects like acid rain could leach the heavy metals from it.

One of his masters students has just finished a thesis where she interviewed several people running studies on leaching at different PHs and the study concluded that as long as the heavy metals are in the concrete they are inert and can't be leached from it.

I imagine there are several caveats to the inertness of the metal, they have to be in a concrete matrix to be inert. Therefore, when you saw or smash concrete, that dust you release, might very well have heavy metal particles suspended mid air unless they are somehow still attached to the concrete. It should be noted that the quantity of heavy metals is still very small, but they will most likely be there.

What does this mean? Concrete is very stable and breaks down extremely slowly, care need only be taken when breaking concrete so that the particle size is as large as possible (i.e. smashing it with a sledgehammer will create less minuscule particles than going at it with a concrete saw.)
M Marx


Joined: Feb 14, 2012
Posts: 57
Location: Los Angeles
some of the furnaces used in making concrete burn things like tires, medical waste, and toxic waste -- things the epa won't let normal incinerators burn b/c they are too toxic. So, while it may not be toxic in the concrete, it seems making concrete is probably not a good long term plan in it's current form.
so add it to the list of modern standard techniques that are pretty bad environmentally overall.
http://www.rachel.org/files/rachel/Rachels_Environment_Health_News_1147.pdf
http://www.slate.com/articles/health_and_science/green_room/2011/11/cement_plant_pollution_leads_to_a_fight_in_chanute_kansas.single.html
http://earthjustice.org/news/press/2010/air-pollution-deal-reached-between-feds-13-states-and-leading-cement-manufacturer
Nicola Marchi


Joined: Sep 20, 2011
Posts: 73
    
    3
All too true, in fact the same professor says they're currently testing a viable polymer that mixes like and could replace concrete. Unfortunately I wasn't able to get much more out of him other than the fact that it's for the "green" markets.
Andrew Hebard


Joined: Mar 03, 2011
Posts: 5
I was thinking of putting in some permanent two-foot-high raised beds near my house and was planning to use brick over a concrete footer. Reading through this thread, it seems that the jury is still out on concrete. Just curious if anyone has any suggestions for an alternative way of building a permanent (and attractive) raised bed.
L. Jones


Joined: Apr 29, 2012
Posts: 80
Location: NW Mass Zone 4 (5 for optomists)
M Marx wrote:some of the furnaces used in making concrete burn things like tires, medical waste, and toxic waste -- things the epa won't let normal incinerators burn b/c they are too toxic. So, while it may not be toxic in the concrete, it seems making concrete is probably not a good long term plan in it's current form.


Why can they burn those horrifying things? Because the cement kiln is burning hot enough to actually destroy them. Toxic waste - detoxified. Medical waste - rendered harmless. Tires certainly burning cleaner and offsetting other fuel than when you stack them in a pile and they catch on fire in the open, where they are almost impossible to put out. They (of those three feedstocks) are most likely to have a few things that might survive the fire, but there might actually be a scrubber on the stack, which there certainly isn't over at the tire fire.

Puddnhead McCoy wrote:I was thinking of putting in some permanent two-foot-high raised beds near my house and was planning to use brick over a concrete footer. Reading through this thread, it seems that the jury is still out on concrete. Just curious if anyone has any suggestions for an alternative way of building a permanent (and attractive) raised bed.


So long as you don't try to fill it with blueberries, it will be just fine. If you want to do blueberries, line it (with horrible petrochemical plastic or rubber films!) - otherwise the lime in the concrete and mortar is an issue for acid loving plants. If you wait until this jury is unanimous, you won't ever get much done. Brick beds have been used for hundreds of years without a problem.


Muddling towards a more permanent agriculture. Not after a guru or a religion, just a functional garden.
William James
volunteer

Joined: Sep 22, 2010
Posts: 662
Location: Northern Italy
    
  14
Would anyone have problems with using rock that eventually becomes cement?

My friend works in a cement rock quarry and can get me "rocks". They're actually pieces of the mountain that they blow up. We know the rocks eventually end up in sacks of concrete.

The rocks look very grey and cement-ish. Just wondering if the minerals in that rock over time might damage my site.

Thanks,
William
Nicola Marchi


Joined: Sep 20, 2011
Posts: 73
    
    3
Short answer is: "you'll be fine"

Long answer is: "as long as you don't attempt to force acid loving plants in a place where immediate runoff from these rocks come, you shouldn't have any problems. You should ask, just to be sure, how they're gathered but you shouldn't really have any trouble with them otherwise."
Tokunbo Popoola


Joined: Mar 19, 2013
Posts: 159
Location: Sacramento, CA
    
    1
what about the slag in the concrete from blacksmithing . or making steel beams can you grind it up and reuse it later or grow in it or anything? at some point recycling needs to be in the mind set with concrete even if it's 100 years away
Nicola Marchi


Joined: Sep 20, 2011
Posts: 73
    
    3
I completely agree that we should be thinking about how to recycle concrete. Unfortunately I don't have an answer on how suitable crushed concrete is to grow in.

My personal opinion, which is not based on a study or experimentation, is that you want to keep the concrete in as large of chunks as possible. The more surface area, the more the pieces of concrete can erode, which releases its aggregates into the soil. Now, Iron supposedly increases in bioavailablity as the soil becomes more acidic (http://www.ext.colostate.edu/mg/gardennotes/222.html) so you could make a case that it's going to be a more alkaline soil because of the concrete, on the other hand, with ph stratification and the building of soil, I think it very likely that you will form acidic spots in a crushed concrete bed if you're building soil.

Now if instead of annuals, or low perennial shrubs, trees were planted there, and all you were looking to eat from the trees was fruit, I think it's better since I remember reading in one of my books that fruit trees generally store pollutants in the wood, trying to keep the fruit as non-toxic as possible.
chris ether


Joined: Jun 25, 2014
Posts: 1
Hello everyone. I have been studying Architecture the past 3 years and have recently come across this problem myself. I am sorry to say I think concrete is a disgusting man made construction material that has taken over the earth. There is far far too much of it in the world and if people keep carrying on the way they do then it will not take long for them to replace all the natural beauties of the world with unnatural concrete. Defend the stuff as much as you like, it is still always going to be unnatural. it can never replace the earths oxygen system (billions of trees it cut down to create space), nor the earthy soil that is hidden away underneath it. What if i told you that for the entire existence of the concrete ( a very long time) it lets of fumes which damage the environment but the human eye cannot see this. And as for the billions of concrete foundations in the soil, this definitely does contaminate the soil with unnatural processes, which then contaminates the worms etc, which then contaminates the chickens and birds and so on..

What everybody needs to do to overcome the situation and all the lies we have been fed to us over the past 200 years. is learn about the earths natural beauty. Hemp. it has over 50,000 positive uses and is the best thing the world. it has been used since the beginning of mankind, and even tho i have no hard evidence, due to all the lies and hiding of the truth, I strongly believe it was used to pour liquid stone and create the pyramids. I have to go now. but please, the whole world, need to address the problem we are all involved in and come together as one so we can tackle it together and go natural
 
 
subject: Toxicity of Concrete: discuss...
 
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