Talk:Fly ash

message: This article seems to be based on  which appears to be a work of the US government and hence in the public domain.
There are two uses of fly ash in portland cement concretes.  One is as a substitute for cement, and its related reactant, lime (calcium hydroxide). Up to 25% of cement can be replaced by fly ash, which results in early strength and improved workability.  This decreases the dollar cost of the concrete, but at an often overlooked cost.  The fly ash consumes the lime to form the cementitious calcium silicates.  This depletes the lime with the result that the pH will begin to decline from 12.3 to some value approaching 8.2, decreasing the field of stability of the cementitious phases.  This can and does weaken the strength of the mortar.  Thus the statement that fly ash increases the durability of concrete may not be correct.
The second use of fly ash is as the fine aggregate in portland cement concrete.  In this role, fly ash replaces some of the fine sand.
The increase in durability when using fly ash in concrete is mainly related to the sphere shape of the fly ash, resulting in higher compaction and the reduced water cement ratio. The consumption of free the hydration product (lime)also results into increased durability and avoids bleaching of the lime out of the concrete.
I would like to point out what may be a minor error in this article. The article states that "...Class F fly ash. This fly ash is not pozzolanic in nature, and contains less than 10% CaO. Possessing pozzolanic properties, the glassy silica and alumina of Class F fly ash requires ..." This substance cannot be both "not pozzolanic" in nature and "possessing of pozzolanic properties" from one sentence to the next. Seems like a logical flaw or at least a compositional flaw in that the author may have been trying to focus in on the silica and alumina portion of the fly ash. It does not flow correctly and I recommend rewording this portion of the article.  —Preceding unsigned comment added by 152.120.255.250 (talk) 17:35, 18 November 2009 (UTC)
replies: text: Disagree. There is a separate article for bottom ash. There is also an overview article at Coal combustion products. Moreau1 (talk) 23:09, 27 March 2021 (UTC)
thread_title: Fly ash

message: This article is overly US-centric, you cannot accurately speak of the composition of fly ash without making reference to a particular source of the coal. As this is based on US government sources, it is undoubtebly US coal, but this point must be clear. This is true of several other points within the article which are made in ignorance of the fact that they only refer to the US.
:Not the original section creator here- Another issue I see arising in this article is vague terminology about regulation, and where regulation has taken place. I've placed a Where? tag in the disposal section, for example, where I could not find reference to where a 1% emission regulation/law was enacted. Knowing there is a lot of talk on this page about regulation and government action, it important to provide sources so that the jurisdiction is clear. Kwkintegrator (talk) 22:09, 12 January 2021 (UTC)
thread_title:  US-centrism 

message: I've shifted and significantly trimmed this section - it didn't belong at the start of the article, and was very non-encyclopedic in tone/style - it basically read like a summary of someone's speech (which it apparently was, according to the note tacked onto the bottom of it). Anyway, it's now at the end of the article along with the environmental issues section, with links to the silicosis article added instead of vague nonspecific discussions of lung damage due to crystalline silica. The section on advising control measures for communities close to fly ash processing facilities also didn't belong in an article like this.Johnprovis (talk) 12:47, 6 January 2008 (UTC)
thread_title:  Exposure concerns section 

message: The really interesting — but controversed — link about radioactivity in fly ash is dead. Asr (talk) 10:33, 29 January 2008 (UTC)
thread_title:  Dead link 

message: Would E.Sn0=31337= like to give some suggestions on what they would like to see cleaned up? Adding a tag and then not commenting doesn't seem particuarly constructive. Njfuller (talk) 21:16, 8 February 2008 (UTC)
thread_title: Cleanup

message: I'm a bit afraid of the statement made regarding fly ash being nontoxic - considering that its pozzolanic behavior allows it to immediately produce a pH of >12 (in some cases) and that plenty of nasty oxoanions are immediately solubilized (chromate being one), I just don't see how it can be considered nontoxic.  Whoever constructed the page MUST be careful to ensure that words like "nontoxic" aren't used too freely.  —Preceding unsigned comment added by 146.141.15.34 (talk) 13:22, 12 May 2008 (UTC)
thread_title:  Afraid 

message: I would like a way to include a fair and balanced description on how Emgold Mining Corporation is creating recycled and manufactured stone products from fly ash.  It looks like what I have included seems like an advertisement, but I am having a challenge regarding how to cut down or edit the section without omitting key data.  I'd really like some suggestions, thanks kindly.  —Preceding unsigned comment added by Emgold (talk • contribs) 15:52, 16 July 2008 (UTC)
replies: text: Your user name is the same as the company's, so you must be here to promote it's products.  Please see the Wikipedia:Autobiography and Wikipedia:Spam policies. --ChrisRuvolo (t) 22:04, 16 July 2008 (UTC)
thread_title:  Ceramext  

message: The strong emphasis on beneficial uses of coal fly ash, along with the minimization of environmental issues, leads me to question the objectivity of this article.  I would like to see it flagged for industry bias.  
Some of the resources for serious discussion of the problem of coal fly ash disposal include:  
http://www.ilovemountains.org/tvaspill  
http://www.earthjustice.org/library/reports/epa-coal-combustion-waste-risk-assessment.pdf 
And EPA's documents are here:
http://www.epa.gov/osw/nonhaz/industrial/special/fossil/index.htm
And here:
http://www.epa.gov/osw/nonhaz/industrial/special/fossil/fsltech.htm
Wkovarik (talk) 13:38, 12 January 2009 (UTC)
replies: text: So fix it. "Fly ash" has an accepted definition as "ash caught from flue gas" rather than "ash extracted from grate clinker" and that's not specific to coal burning for power generation - as previously mentioned, incinerators will generate this too (if they have any sort of flue gas filtration). This article is indeed worded in a way that's closely tied to coal power, but that ought to be fixable by editing. Andy Dingley (talk) 13:51, 12 January 2009 (UTC)
thread_title:  Industry bias 

message: Henry Liu intends to license his technology in 2008 but that is long gone. What happened?  
Agreed- this is at least a year or two old... Oct 2009... needs to be updated.
—Preceding unsigned comment added by 82.132.139.33 (talk) 20:08, 2 August 2009 (UTC)
thread_title:  Bricks Section Out Of Date  

message: This sentence needs to be fixed:  "In the past, fly ash was generally released into the atmosphere, but pollution control equipment mandated in recent decades now require that it be captured prior to release."  It should not say that capture is required by the equipment.  Is the pollution control equipment mandated by legislation enacted in recent decades, or by regulations promulgated in recent decades?  Federal or state or both?
Steve Wise (talk) 11:53, 12 August 2009 (UTC)
thread_title:  Pollution control equipment mandate 

message: The current text (below) regarding fly ash geopolymers is misleading and inaccurate.
:"It should be noted that when the total carbon footprint of the alkali required to form geopolymer cement is considered, including the calcining of limestone as an intermediate to the formation of alkali, the net reduction in total CO2 emissions may be negligible. Moreover, handling of alkali can be problematic and setting of geopolymer cements is very rapid (minutes versus hours) as compared to Portland cements, making widespread use of geopolymer cements impracticle (sic) at the ready mix level."
Using calcium hydroxide from calcined limestone as the alkali-activator would be rather pointless unless you were making a hybrid with portland cement. In that case, the high carbon footprint is due to the portland cement content. The alkali-activators normally used for geopolymers are sodium hydroxide and sodium silicate.  Since the sodium hydroxide typically comes from the electrolysis of salt water, its carbon foot print largely depends upon that of the electricity used.
The setting of geopolymer cements is not "very rapid (minutes versus hours)."  This is incorrect.  To the degree geopolymer setting time is problematic is it in the other direction.  Depending upon the source materials and PH, some geopolymers will not set at all without the addition of heat, typically something under 100C for one to two days.  Geopolymer cement and concrete mix designs with setting times of several hours and high early curing times of approximately one day are normal.  See the Australian company Zeobond http://www.zeobond.com for an example of a redi-mix truck-deliverable geopolymer concrete.
If whoever posted the paragraph quoted above is using either lime or high calcium fly ash and experiencing setting times in minutes versus hours, the product they are ending up with is not a geopolymer.  Using 10 to 14 molar sodium or potassium hydroxide and adding a bit of something like boric or citric acid makes a workable geopolymer cement with the 20+% CaO fly ash available in my locale (interior Alaska).
209.112.135.214 (talk) 20:16, 18 January 2011 (UTC)
thread_title:  Geopolymers 

message: An update to this section is the new studies indicate the utilization of higher percentages of Fly Ash is possible. As an example, in a study performed in by Askarian et. al., 2018 Fly Ash was was utilized up to 50% with promising results in fresh, hardened and durability test. 
There is NO support for the assertion  "Fly Ash often replaces up to 30% by mass of Portland cement" (added emphasis) as added by user 207.32.18.129 on 9 October 2012. Unless there are objections or a valid citation, then at best all that can be said is "Untreated fly ash may replace up to 25%, although the typical maximum range is 15-20%" (per Schneider, M.; Romer M., Tschudin M. Bolio C. (2011). "Sustainable cement production - present and future". Cement and Concrete Research 41: 642–650). 
Of course, anyone operating with concrete contractors knows that even in the US (in the "good old days" before the EPA concerns), 10% was largely the norm but this is largely anecdotal and I would not state such an anecdotal fact. The Schneider "statistic" is best seen as a "typical maximum" range, rather than common practise.
For example, the total cementitious market is typically defined as OPC + Blast Furnace Slag + Fly Ash, where Fly Ash is typically stated at 10% of OPC.  — Preceding unsigned comment added by 213.66.81.80 (talk) 10:57, 27 May 2013 (UTC)
thread_title:  A lot of subjective bias. 

message: The article is missing information on Class N fly ash as described in ASTM C618. Also the chemical description of Class F and C fails to mention the usage of SiO2 + Al2O3 + Fe2O3 usage for determining class of fly ash (ASTM C618-12A Table 1)
205.236.14.89 (talk) 14:24, 13 November 2014 (UTC)
replies: text: It isn't missing, it's omitted because Class N is defined in C618 as "Raw or calcined natural pozzolans", so is not a type of fly ash. I agree that the classification section needs improvement, though - and needs to include the EN definitions of classes as well as the ASTM ones. This is done much better in the Cement article, I'll try to have some input here (and bring across information) as time permits... Johnprovis (talk) 10:25, 12 February 2016 (UTC)
thread_title:  Missing Class N, Poor Description of ASTM C618 Standards 

message: Hello fellow Wikipedians,
I have just added archive links to  on Fly ash. Please take a moment to review my edit. If necessary, add  after the link to keep me from modifying it. Alternatively, you can add  to keep me off the page altogether. I made the following changes:
*Added archive https://web.archive.org/20100823025712/http://www.nviro.com:80/soil.html to http://www.nviro.com/soil.html
When you have finished reviewing my changes, please set the checked parameter below to true to let others know.
Cheers.—cyberbot IITalk to my owner:Online 01:37, 12 February 2016 (UTC)
thread_title:  External links modified 

message: Hello fellow Wikipedians,
I have just modified one external link on Fly ash. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
*Added archive http://www.webcitation.org/5QDfIot5I?url=http://www.fhwa.dot.gov/infrastructure/materialsgrp/flyash.htm to http://www.fhwa.dot.gov/infrastructure/materialsgrp/flyash.htm
*Added  tag to http://www.denverpost.com/breakingnews/ci_25977591/dukeville-concerns-over-coal-ash-5-things-know
When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.
Cheers.—InternetArchiveBot (Report bug) 06:36, 2 January 2017 (UTC)
thread_title:  External links modified 

message: This article and :Pulverised fly ash (PFA) cover the same ground. It would seem prudent to merge the PFA content here.  Velella  Velella Talk   23:02, 5 June 2017 (UTC)
replies: text: Klbrain (talk) 21:56, 20 October 2018 (UTC)
thread_title: Merge from Pulverised fly ash

message: The article, particularly its introduction, implies that fly ash is solely from the combustion of coal, when in reality fly ash is a catch-all term for ash entrained in the flue gas from a combustion process. Given the increased importance of biomass firing over the last decade (especially outside the US, particularly in Europe) and the significant differences in fly ash composition, I feel that the article is outdated, and that it may need substantial changes (particularly in the Introduction, Chemical Composition and Classification, and Compliance sections) and a shift away from its US-centric nature.
Leerobbo92 (talk) 17:40, 15 September 2018 (UTC)
thread_title:  Introduction and Scope 

message: It does not make sense to state the magnification of a photomicrograph in reproductions, as in the figure caption.
The magnification depends on the display size and zoom factor. 
Please remove. 2001:A61:2BC5:201:CC90:E655:C2DE:47DF (talk) 17:08, 12 December 2023 (UTC)
thread_title:  Magnification