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Mozayique Mosaic

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Maverick Wright
Maverick Wright

Where To Buy Fly Ash Concrete !!TOP!!

REPORT ABSTRACT: Uncertainty in the supply of Class F fly ash due to impending environmental restrictions has made it imperative to find and test alternate sources of supplementary cementitious materials (SCMs) that can provide similar strength and durability benefits to concrete as Class F fly ash. This project summarizes the key findings of research that was conducted to characterize and evaluate the performance of eight natural pozzolans, commercially available in Texas, to assess their potential as Class F fly ash replacements in concrete. Of the eight pozzolans tested, six were found to be viable alternatives for Class F fly ash. Methods to further enhance the performance of these SCMs were explored and guidelines are provided on the optimum SCM replacement levels for different applications. Finally, recommendations are presented on how to improve current testing practices for SCMs.

where to buy fly ash concrete


When it comes to pouring hundreds of yards of concrete, consistency is a big deal. Consistency in fresh properties and long-term performance, load after load. Consistency in availability. Consistency in chemical make up. Consistency in supply-chain availability. Research data [08] in pumice-blended cement mix designs quantifies a performance consistency that fly ash rarely can.

When you think of green building materials, coal is probably the last thing that comes to mind. Coal is, in most practical applications, neither green nor is it a building material. On the contrary, coal is responsible for a large chunk of the greenhouse gas emissions and air pollution that is produced worldwide. But in an ironic twist, coal is also responsible for the emergence of fly ash concrete, a new building material that could help curb carbon emissions in the construction industry.

To deal with both of those problems, the construction industry had the clever idea to start formulating concrete out of fly ash, substituting fly ash for Portland cement (the primary ingredient in most concrete). Surprisingly, fly ash has several characteristics that make it a perfect ingredient for concrete: It has great strength and durability (although we're still waiting to see how it performs long-term), and of course, it's cheap. And because it's a recycled material, it helps to prevent concrete companies from unnecessarily mining for other materials to make concrete.

Everybody wins, right? In many ways, fly ash concrete does look like a winner, but there are still some lingering concerns about the safety of surrounding ourselves with too much fly ash. Coal is a material that's full of harmful substances, and there are still some questions about whether heavy metals would be able to leach from concrete made with coal ash. Concerns have also been raised over whether using fly ash would expose builders to lawsuits and exempt them from insurance coverage. Continue reading to learn more about how fly ash concrete is made, and to figure out if it is indeed safe.

In America, more than 50 percent of our electricity comes from coal-fired power plants, where coal is ground into a fine powder, placed in a boiler, and burned at very high temperatures. The heat from the boiler produces steam, which is used to spin a turbine and produce electricity. Burning coal is a very dirty process, but modern coal plants have pollution-control equipment that prevents all of the particulate matter from leaving smokestacks. When that equipment is cleaned, we're left with coal ash [source: Dewan].

Because coal power is so widely used, fly ash is one of the most abundant industrial byproducts on Earth. So instead of putting it in storage ponds that are just waiting to spill, it makes sense for companies to put it to good use as a construction material. Not only does using fly ash in concrete prevent those heavy metals from being released back into the environment, it also keeps cement makers from mining new raw materials.

One potential solution to the storage and disposal problem that could help prevent spills like the one in Tennessee is to use fly ash as a building material. When used in concrete, fly ash is generally believed to be fairly safe. Although it often does contain known carcinogens, the harmful effects are thought to be neutralized when fly ash is added to concrete mixes.

OK, let's put our lab coats on for a minute and get down to the chemistry of how fly ash works and what makes it special. We keep saying that fly ash is a good substitute for Portland cement, but what exactly is Portland cement? Funny you should ask. It's only the most common type of cement in use around the world, and the main ingredient in most types of concrete. Lime and silica make up the bulk of Portland cement, and it also includes aluminum and iron. Most types of Portland cement contain a mix of limestone, chalk, shells, and a variety of clay, shale and sand. Producing Portland cement is a very energy- and resource-intensive process, which is why it makes sense to look for a good substitute [source: Portland Cement Association].

Geopolymer concrete is the technical name for fly ash or any other type of concrete made from synthetic aluminosilicate materials (materials made with aluminum, silicon and oxygen). When fly ash is added to a cement mixture, it isn't just filler, it actually reacts with the other compounds that are in Portland cement and becomes part of the matrix. It's rich in alumina and silicate, which causes it to react with alkaline solutions to produce a binding aluminosilicate gel. The resulting product is an excellent substitute for the traditional ordinary Portland cement [source: van Riessen].

Today, concrete mixes in which up to 25 percent of the cement is replaced with fly ash are common, and some concrete makers are replacing as much as 50 percent. But higher concentrations of fly ash require increased testing, because the results can vary.

From a builder's standpoint, the most important thing about fly ash concrete is its performance, and it doesn't disappoint. Adding fly ash to the mix has the ability to improve concrete, because changing the composition of concrete can add strength and durability. The resulting material is less porous than typical Portland cement, and it's more resistant to corrosion and premature deterioration [source: Ideker]. In addition to being more durable than ordinary Portland cement, fly ash concrete is more acid- and fire-resistant, and it demonstrated higher compressive and tensile (stretching) strength.

In many ways, fly ash concrete is the ultimate paradox. Fly ash comes from one of the biggest sources of air pollution and carbon dioxide emissions on Earth, and yet it's considered to be a green material. What's the deal? The main reason that fly ash is considered to be eco-friendly when used in construction is because it's a recycled material. If power companies are going to burn coal and produce fly ash anyway, it makes sense to put it to good use, especially if it can save money and energy in the construction sector.

Making cement from scratch is a very energy-intensive process. Conservative estimates say that concrete production contributes between 5 and 8 percent of greenhouse gas emissions worldwide, but it could be even higher. We currently produce more than 2.6 billion tons of Portland cement per year, and that number figures to increase as populations climb, unless some greener option emerges to supersede it.

That's where fly ash concrete comes in. Fly ash concrete has the ability to simultaneously curb global carbon emissions while developing better and more durable infrastructure that wouldn't need to be rebuilt as often. In fact, one study even noted that fly ash bricks also have the ability to store carbon dioxide from the environment, adding another green benefit [source: Liu].

The U.S. Green Building Council seems to agree about fly ash's green cred; the preeminent arbiter of all matters relating to green building issues, Leadership in Energy and Environmental Design (LEED), credits substituting fly ash concrete for at least 40 percent of ordinary Portland cement [source: Portland Cement Association]. A life-cycle assessment, which is an analysis of every stage of production from cradle to grave, shows that replacing ordinary Portland cement with fly ash concrete can decrease carbon emissions by as much as 90 percent. That's largely because fly ash is a recycled material, and replacing new Portland cement with fly ash prevents unnecessary carbon dioxide emissions, and because it's more durable it doesn't need to be torn up and replaced as often [source: Salton].

Of course, fly ash isn't without controversy. Because fly ash is a byproduct of coal, which itself is full of heavy metals and toxins that can be dangerous, concern has been raised that buildings made from fly ash concrete could be harmful to people.

The biggest challenge to fly ash came in 2008, following the massive fly ash spill at the Kingston Fossil Plant in Tennessee (see sidebar). Then, a few weeks later, there was another smaller fly ash spill in Alabama that kept fly ash in the news. Those spills and the resulting cleanup and news coverage put fly ash on the Environmental Protection Agency's (EPA) radar and prompted environmental activists to call for tougher regulations. Since then, the EPA has been weighing whether or not to classify fly ash as hazardous waste, and although the agency has stated that such a classification wouldn't affect fly ash that's used to make concrete, observers from the construction industry have been skeptical [source: Purdy].

But is it really safe to live in a building that's made of coal? The safety of fly ash in concrete has been hotly debated. While geopolymer concrete has been proven to leach dangerous elements like arsenic, chromium and selenium, at least one study has shown that adding calcium can help reduce the leachability of heavy metals [source: Sanusi]. However, many questions still remain about what will happen to the heavy metals and other substances in fly ash once the concrete breaks down and is disposed of [source: Post]. 041b061a72


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