Talk:Fly ash

From Wikipedia, the free encyclopedia

Contents 1 Fly ash 2 US-centrism 3 Exposure concerns section 4 Dead link 5 Cleanup 6 Afraid

[edit] Fly ash

This article seems to be based on [1] 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. Int his 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.

[edit] US-centrism

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.

[edit] Exposure concerns section

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)

[edit] Dead link

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

[edit] Cleanup

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)

[edit] Afraid

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)