I am always looking for new gardening beds, ways to construct raise beds, and since my grandmother has recently stated that she needs raised beds, I became interested in building raised beds out of cinder block. I saw some beautiful examples of raised cinder block beds on Pinterest and other sites.

cinder block raised garden bed

Here is another example of  a raised cinder block bed that I think it beautiful.

Raised beds at San Diego National Convention Garden Tour 2004

The problem with these beds is that I don’t know if the building material is safe for growing food. It’s obvious that people do grow garden foods in raised cinder block beds, but what is in the cinder blocks? The ornamental garden shown above has treated timbers as its base, and I wouldn’t want to grow in that. I do have some branches from fallen trees, so I was thinking maybe I could use those to build cinder block beds, but then I saw a post about how cinder blocks may be contaminated with “cinder ash,” a by-product of the coal industry. That’s not what I want to grow food in.

I am offering a warning of the possibility of poisons in this product and stressing that I would never grow my food in it. The product Fly Ash is used as a Portland Cement replacement for up to 30% of the cement used to manufacture these products. For those of you unaware, Fly Ash is a by product of burning coal. The EPA is and has for the last year been doing a study to decide whether or not to label Fly Ash as a Hazardous Waste due to the high levels of mercury, arsenic, and lead; leaving some “Industry Folk” to refer to concrete as the “New Asbestos” or the “New Lead Paint”. Though there is no definite date set for a decision the ball has started rolling.

That was a Facebook post, and since I generally don’t believe anything I read on Facebook, I thought I would check into the ways in which concrete or “cinder blocks” are made. Are they really made with cinders from burning coal?

Someone’s blog post, with unnamed sources, says that cinder blocks are made with coal ash:

Hazardous waste.  Yes, there are small amounts of heavy metals in concrete products.  Typically the main composition of Class C fly ash contains 3.5 to 40% calcium oxide, 0.5 to 40% aluminum oxide, and 2.5 to 25% Magnesium oxide.  However smaller percentages of strontium, chromium, nickel, lead, arsenic, cadmium, and other heavy metals are also present which cause it to be classified as hazardous waste by the EPA.

The spherical particle size of coal fly ash varies from 5-120 microns which is similar to that of silty sand to silty clay.  The good news is that this material is bonded, insoluble, and immobile in concrete.  However if the concrete or blocks are pulverized in destruction or become soluble with acids, the surface area exposed is greatly increased and the heavy metals may become mobile.  Example: You would not want to use pulverized concrete to “lime” a garden where it could be acted upon by microbes and organic acids.

Since soil decomposes plant materials that become acidic, any decomposition process could, ostensibly leach if exposed to acids.

I did a quick Wikipedia search on cinder blocks and fount that their source for defining cinder blocks came from the dictionary, not necessarily proof that cement blocks are cinder blocks:

Those that use cinders (fly ash or bottom ash) are called cinder blocks in Canada, the US and New Zealand, breeze blocks (breeze is a synonym of ash)[1] in the UK and New Zealand, and hollow blocksin the Philippines.

Apparently it’s all in the name. Are the blocks used in the raised beds made of concrete or cinder? Now, I don’t know which is which. How to tell?  Menards lists the blocks that I had thought of as cinder blocks as concrete blocks. Maybe cinder blocks were made of ash residue, but cement blocks are made of cement aggregate?

Menards’ website says that the blocks I have always called “cinder blocks” are actually concrete blocks, not made of cinders:

  • Standard gray color
  • Made of strong and durable concrete
  • Made in the USA
  • Exceeds ASTM C-90 certified for strength and absorption

Mendards also says they are made by Midwest Manufacturing. I looked up Midwest Manufacturing, but I didn’t see any mention on their website of the way they manufactured cement blocks, nor their chemical composition. Then, I looked up another website, for a report from the coal mining industry that was published in 2014:

“The regulatory uncertainty that has impeded the beneficial use of coal ash for half a decade has finally come to an end,” affirms ACAA Executive Director Thomas Adams. “EPA’s decision to regulate coal ash as a ‘nonhazardous’ material puts science ahead of politics and clears the way for beneficial use of ash to begin growing again— thereby keeping ash out of landfills and disposal ponds in the first place.”

Such use has trended negatively against historical patterns since the agency initiated CCR management and disposal rulemaking in June 2009. The proposed rule offered two CCR classification options under Resource Conservation and Recovery Act: Subtitle D, tasking states with significant coal ash handling, storage and disposal oversight; and, Subtitle C, inviting “hazardous waste” labeling of landfill-bound ash and federal scrutiny of material management and disposal. The latter option sparked concern among cement and concrete interests over the stigma fly ash would carry as a material with essentially the same chemical properties as one EPA labeled hazardous. ACAA and allied groups endorsed aspects of the Subtitle D option, the course EPA ultimately chose.

According to ACAA’s most recent “Production and Use Survey,” released two days before the EPA final CCR rule, coal ash utilization hovered below 2008 levels for the fifth consecutive year in 2013. If the past five years had simply remained equal with 2008’s utilization, the association estimates, 26.4 million tons less coal ash would have been disposed.

“As an organization devoted to using coal ash in environmentally responsible and technically sound ways, we look forward to finally being able to focus all of our attention back on growing these uses,” Adams affirms. Coal ash has never qualified as a “hazardous waste” based on its toxicity, he adds, as its trace levels of metals are comparable to those materials it replaces in common recycling applications.

None of this tells me anything other than the fact that the EPA didn’t register fly ash as a carcinogen, which means nothing to me, as I don’t believe the EPA defines anything as a carcinogen. The EPA seems to live in a constant state of denial at odds with the rest of the world; however, when there is a market for an industrial waste product, the EPA seems quick to determine that waste product non-hazardous. In the lead-up to the 2014 decision from the American Coal Ash Association, the complaint was that there was a lot of ash left over from producing coal that the Coal Ash industry didn’t know what to do with and then wanted to “recycle” by means of selling it to concrete manufacturers. When the EPA found that the American Coal Ash Association wanted to sell the coal ash, it determined that coal ash was safe to “recycle” by selling it to concrete manufacturers. Notice that there is no information about how coal ash was determined safe for humans. The history of the 2014 decision was outlined in this article published in 2009, which outlines the coal waste product and then the EPA’s recognition that it was safe (with unpublished methods) after a market was created for the coal ash waste product:

According to ACAA’s “Production and Use Survey,” 51.4 million tons of coal combustion products (CCP) were beneficially used in 2013 —down from 51.9 million tons in 2012 and well below the 2008 peak of 60.6 million tons. In the closely watched category of fly ash consumed in concrete mixes, utilization increased only slightly to 12.3 million tons, up by 577,705 tons over 2012, but still below 12.6 million tons in 2008.

The decline occurred as the U.S. Environmental Protection Agency proposed coal ash management regulations that could have designated the material as “hazardous waste” when disposed. A final rule issued in late December averts that label and acknowledges the large volume of recycling embodied in ASTM C618-grade fly ash marketing and related concrete specifications.

Prior to the final rule, ACAA observed growing numbers of ash producers, specifiers and customers restricting coal ash use in light of the regulatory uncertainty and publicity surrounding EPA rulemaking activities. “Regulatory certainty is imperative if we are to increase volumes of coal ash that are beneficially used rather than disposed,” Executive Director Thomas Adams noted upon release of the 2013 Production and Use Survey results. “People don’t just wake up one day and decide to recycle more. It takes planning and investment that are difficult to justify in an environment of regulatory uncertainty and misleading publicity about the safety of coal ash.”

The decline in 2009-13 recycling volumes stands in stark contrast to the previous decade’s trend, he adds: “In 2000, when the recycling volume was 32.1 million tons, the EPA issued its Final Regulatory Determination that regulation of ash as a ‘hazardous waste’ was not warranted. Over the next eight years, EPA also began actively promoting the beneficial use of coal ash and the recycling volume soared to 60.6 million tons.

Strangely enough, and aren’t all things with the EPA strange, the EPA began “actively promoting the beneficial use of coal ash” after the market for its purchase was created. The big question for me is: is there cinder ash or coal mining residue in the blocks I want to buy at Menards to build a raised garden bed?

I am reminded of a section of a book I just bought and read about the science of soil acidity, in The Garden Explored (2013) by Mia Amato , and the woman writes in chapter 3 that her family had a Douglas fir at Christmas that they planted, and it languished near the garage until her father repaired the garage with a mix of lime and cement, upon which followed rains and a leaching of chemical components into the soil that made the tree shoot up in height over that summer. This was an encouraging story until I realized that concrete leached something into the soil, and then if that concrete is contaminated with coal ash residue, it doesn’t seem safe to eat.

My sister just suffered through the removal of all the large trees in her yard in her Midland house when Dow chemical announced that the soil in her neighborhood was contaminated with dioxin and that trees in her yard were also contaminated. Dow wouldn’t have cleaned it up but for regulatory forcing, and Dow removed all the plants, soil, and trees that were contaminated from contaminated soil. Isn’t that what had happened to the woman in the story about the family Christmas tree next to the garage?

I looked up the following table on Wikipedia under the search term “concrete” to find the following handy table:

Property Portland
(ASTM C618 Class F)
Fly Ash
(ASTM C618 Class C)
Fly Ash
SiO2 content (%) 21.9 52 35 35 85–97
Al2O3 content (%) 6.9 23 18 12
Fe2O3 content (%) 3 11 6 1
CaO content (%) 63 5 21 40 < 1
MgO content (%) 2.5
SO3 content (%) 1.7
Specific surfaceb
370 420 420 400 15,000–
Specific gravity 3.15 2.38 2.65 2.94 2.22
General use
in concrete
aValues shown are approximate: those of a specific material may vary.
bSpecific surface measurements for silica fume by nitrogen adsorption (BET) method,
others by air permeability method (Blaine).

Fly ash is the coal ash waste product. So, it’s not as simple as a nomenclature to determine if the blocks are cinder or cement, because cement often includes cinder ash.

Wikipedia lists the following description for concrete or cement:

A major component of concrete is cement, which similarly exerts environmental and social effects.[54]:142The cement industry is one of the three primary producers of carbon dioxide, a major greenhouse gas (the other two being the energy production and transportation industries). As of 2001, the production of Portland cement contributed 7% to global anthropogenic CO2 emissions, largely due to the sintering of limestone and clay at 1,500 °C (2,730 °F).[78]

Concrete is used to create hard surfaces that contribute to surface runoff, which can cause heavy soil erosion, water pollution, and flooding, but conversely can be used to divert, dam, and control flooding.

Concrete is a contributor to the urban heat island effect, though less so than asphalt.[79]

Workers who cut, grind or polish concrete are at risk of inhaling airborne silica, which can lead tosilicosis.[80]

Concrete or cinder blocks both could have fly ash or coal manufacturing residue in them. Does this mean that it’s good for growing garden beds for food consumption? It appears that even the people who support the addition of fly ash or coal cinder into cement blocks or cinder blocks outright assert that the material isn’t for consumption:

“In North America, the burning of coal for power generates about a half a cubic foot per person per year,” explains Bruce King, P.E., director, Ecological Building Network, San Rafael, Calif., and author of the book, “Making Better Concrete: Guidelines to Using Fly Ash for Higher Quality, Eco-Friendly Structures.”

“That’s a bucket of ash in the name of every man, woman and child in America, every year,” he says. “Whether we like it or not, we have to do something with it.”

“Even the guys who sell fly ash would tell you not to put this stuff on your pancakes,” quips King. “Like most of the substances in the natural world, fly ash is not for consumption or respiration. Does that mean we—or rather, the EPA—should formally declare it a hazardous substance, thus ending any chance of beneficial reuse or recycling?”

If this stuff isn’t for consumption, why recycle it? Well, it seems that most people don’t lick buildings, and under this premise, fly ash additive or coal waste could be added to cement to make it stronger if only, if only the EPA would allow it to be “recycled.” Note that a large part of the recycling drive is that the coal industry has created a toxic product that pollutes the environment, so it needs some way to add this waste product to something, and concrete seems to be the mix:

CalStar’s patented process actually takes this even further as fly ash fully replaces cement in their products, which are also not fired in an energy-intensive kiln. As a result, the company reports an 85% reduction in energy and CO2 emissions for their products. It’s easy to see why so many companies have put so much emphasis on fly ash as a “green” path forward.

Fly ash is also known to increase the concrete’s durability, so “longer service life means that much less material and energy will be used to repair, rebuild or replace constructions,” adds Kren.

Furthermore, fly ash enhances concrete performance—including increased strength, improved sulfate resistance, decreased permeability, a reduction in the water/cement ratio required, and enhancement of pumpability and workability of the concrete, according to Shepherd.

Of course, the other reality that needs to be dealt with is the sheer volume of fly ash which is produced by coal combustion every year

There is the very real possibility that encasing something hazardous in stone may be considered a way to dispose of something so toxic that it pollutes anything it touches. Greenbuilder.com says that the coal waste/fly ash becomes chemically different when heated in the cement mix; however, I can’t find out who has validated this “finding” that coal waste becomes inert when heated in a cement slurry:

In fact, when concrete is produced, “much of the fly ash reacts with the Portland cement products of combustion to become, get this—calcium silicate hydrate—the same mineral that gives concrete its strength,” explains Michael Chusid, RA, FCSI, CCS, principal of the Tarzana, Calif.-based architectural technology consulting firm, Chusid Associates. “Any trace amount of heavy metal gets entrapped in the hydrated cement crystals and will have a very difficult time becoming liberated.”

Filling in more details on this unique chemical reaction, David Shepherd, AIA, LEED AP, sustainable development director, Portland Cement Association, Skokie, Ill., explains, “unlike some encapsulation techniques which coat a contaminant with material to ‘glue’ it into place, fly ash chemically reacts with cement during the hydration process and becomes an integral part of the new crystalline structure.”

Consequently, many independent building professionals, and even some environmental groups, are on board with the EPA’s current position that the encapsulated use of fly ash is a very good alternative to sending the ash to the landfills where it faces a greater risk of environmental catastrophe such as the collapse of a Tennessee Valley Authority’s fly ash containment structure in 2008, which sent 5.4 million cubit yards of toxic sludge across 300 acres in Kingston, Tenn.

It appears, for the time being, that there is no nomenclature solution to my problem of using either cinder or cement blocks in creating a raised bed for my grandmother to garden in, as it appears that coal waste products in the form of fly ash are added to both cinder blocks and concrete.

If fly ash/coal waste is already being added to cement, we may well be in the same position with any of our buildings in the U.S., safe unless we lick them or eat out of them. We also may cause a leaching of dangerous chemical contaminants if we put soil or organic matter that is naturally acidic into cement blocks and that acid change makes the chemicals of the fly ash/coal waste additive leach out into our food, a form of licking that I don’t want to try.

Think  I am crazy to think about licking buildings, or even mentioning whether they are edible, there are, in fact, salty buildings that people lick, like the Salt Palace in Saline, Texas.

Saline, Texas

Or, there is a salt hotel in South America, in Bolivia’s Salar de Uyuni,

Palacio de Sal Uyuni

I, personally, would not lick the salt walls in the Palacio de Sal Uyuni, as this salt from Bolivia contains a large amount of lithium, which is used in manufacturing batteries here in the United States.

Bolivia holds about 43% of the world’s lithium reserves;[13] most of those are located in the Salar de Uyuni.

Lithium is concentrated in the brine under the salt crust at a relatively high concentration of about 0.3%. It is also present in the top layers of the porous halite body lying under the brine; however the liquid brine is easier to extract, by boring into the crust and pumping out the brine.[14]

Actually, we covered this in a class I taught on South American Geography, and while the buildings made from salt brick in the Bolivian salt flats are stunning to look at, I wouldn’t consider them safe to lick. I also wouldn’t consider the concrete blocks made in the U.S. here safe to lick or eat plants out of, either. I will have to settle for shots like this, and perhaps plan a succulent garden that I won’t eat and neither will Grandma Kay.

Cement Block Raised Beds

Safe To Grow Ornamentals Not Food

Of course, if you would prefer not to support the coal mining/burning industry, it appears cement beds are out, as well. I am off to find the next garden wonder, and hope I don’t find any toxic political mess in that newest solution. I will keep you posted.