Failed Artificial Reef with old car tires

[dberry]

I'm not so sure coal fly-ash is a good material to include in an artificial reef, even if mixed into concrete. Fly-ash tends to have high concentrations of arsenic, lead, and other heavy metals that can leach out into water. That's why folks in the Carolinas are so concerned about fly-ash piles collapsing into the flooded rivers in recent days.

 

[Wookie]

I'm not so sure coal fly-ash is a good material to include in an artificial reef, even if mixed into concrete. Fly-ash tends to have high concentrations of arsenic, lead, and other heavy metals that can leach out into water. That's why folks in the Carolinas are so concerned about fly-ash piles collapsing into the flooded rivers in recent days.

Well, it's interesting you say that. I happen to know quite a bit about it, as I used to fix radioactive flyash in concrete. As you probably know, the setting of concrete is a chemical reaction, not a physical reaction. That's why we install moorings in the bard bottom substrate with Portland Type 2. It reacts chemically to harden, and pouring it underwater does not stop the reaction.

It also chemically binds the metals found in the flyash. So the lead, arsenic, uranium, plutonium, cesium, and chromium found in flyash (and radioactive flyash) is bound chemically to the limestone, and no longer posing a health threat, as it is no longer leachable. That isn't a word, but the test for heavy metals is Toxic Characteristic Leaching Procedure (TCLP). Once flyash is chemically bound to cement, it no longer can leach.

Of course, if you have flyash stored in huge piles along the flooded rivers, well, then, all bets are off.

 

[Schwob]

Well, it's interesting you say that. I happen to know quite a bit about it, as I used to fix radioactive flyash in concrete. As you probably know, the setting of concrete is a chemical reaction, not a physical reaction. That's why we install moorings in the bard bottom substrate with Portland Type 2. It reacts chemically to harden, and pouring it underwater does not stop the reaction.

It also chemically binds the metals found in the flyash. So the lead, arsenic, uranium, plutonium, cesium, and chromium found in flyash (and radioactive flyash) is bound chemically to the limestone, and no longer posing a health threat, as it is no longer leachable. That isn't a word, but the test for heavy metals is Toxic Characteristic Leaching Procedure (TCLP). Once flyash is chemically bound to cement, it no longer can leach.

Of course, if you have flyash stored in huge piles along the flooded rivers, well, then, all bets are off.

^^^... interesting...^^^
Wanted to like your earlier post, but the flyash thing made me hesitate... Am going to unhesitate now while still being very reserved about it, but nevertheless thinking "interesting"...

 

[Wookie]

^^^... interesting...^^^
Wanted to like your earlier post, but the flyash thing made me hesitate... Am going to unhesitate now while still being very reserved about it, but nevertheless thinking "interesting"...

Fair enough. Google "HP&L flyash reef va fogg site galveston texas" and see if there are any leachate reports.

Can't find any reports. Hang on....

@sea_ledford is the environmental weenie for Texas Parks and Wildlife. Chris, what is the leachate from the flyash block look like?

 

[dberry]

Well, it's interesting you say that. I happen to know quite a bit about it, as I used to fix radioactive flyash in concrete. As you probably know, the setting of concrete is a chemical reaction, not a physical reaction. That's why we install moorings in the bard bottom substrate with Portland Type 2. It reacts chemically to harden, and pouring it underwater does not stop the reaction.

It also chemically binds the metals found in the flyash. So the lead, arsenic, uranium, plutonium, cesium, and chromium found in flyash (and radioactive flyash) is bound chemically to the limestone, and no longer posing a health threat, as it is no longer leachable. That isn't a word, but the test for heavy metals is Toxic Characteristic Leaching Procedure (TCLP). Once flyash is chemically bound to cement, it no longer can leach.

Of course, if you have flyash stored in huge piles along the flooded rivers, well, then, all bets are off.

I'll bow to your superior knowledge of flyash leachate, but I'll reserve a bit of caution when it comes to Arsenic and Lead (as opposed to the rare earth elements - U, Pu, Ce, and such). Arsenic and Lead tend to be easily reduced to low valent states that won't chemically bind to the Portland as strongly as those other elements you mentioned. Physical entrapment in the bulk of the cement would limit leaching, but I wouldn't be surprised if any surface exposed to water (including cracks) would eventually leach As and Pb. That said, the real proof of the pudding is in the tasting... i.e actual measurements of leach rates.

 

[Wookie]

I'll bow to your superior knowledge of flyash leachate, but I'll reserve a bit of caution when it comes to Arsenic and Lead (as opposed to the rare earth elements - U, Pu, Ce, and such). Arsenic and Lead tend to be easily reduced to low valent states that won't chemically bind to the Portland as strongly as those other elements you mentioned. Physical entrapment in the bulk of the cement would limit leaching, but I wouldn't be surprised if any surface exposed to water (including cracks) would eventually leach As and Pb. That said, the real proof of the pudding is in the tasting... i.e actual measurements of leach rates.

This study https://www.hindawi.com/journals/amse/2016/7101243/ did not look at Arsenic, but the other 7 metals showed impressive bonding rates.

 

[dberry]

This study https://www.hindawi.com/journals/amse/2016/7101243/ did not look at Arsenic, but the other 7 metals showed impressive bonding rates.

Yes, that article makes the case that most fly-ash metals are tightly bound in Portland cement (although Cu and Cr are still fairly leachable).

And while I'm generally against leaching of any amount of toxic metals into the ocean, the low leach rates and high dilution factors probably mean it's not significant. That is, there is a natural (background) amount of metals in sea water that will always be present, and a slow trickle from the cement blocks isn't going to change things much. (And for the tests in that paper, the cement blocks were ground down to bits no bigger than a pea. Leaching from a big block would be considerably slower.)

 

[Wookie]

Yes, that article makes the case that most fly-ash metals are tightly bound in Portland cement (although Cu and Cr are still fairly leachable).

And while I'm generally against leaching of any amount of toxic metals into the ocean, the low leach rates and high dilution factors probably mean it's not significant. That is, there is a natural (background) amount of metals in sea water that will always be present, and a slow trickle from the cement blocks isn't going to change things much. (And for the tests in that paper, the cement blocks were ground down to bits no bigger than a pea. Leaching from a big block would be considerably slower.)

Spoke to Dale Shively, head of the Texas Parks and Wildlife Artificial Reef Program. His email to me indicated that flyash does not make a significant contributor to leaching heavy metals into the surrounding waters, and the flyash blocks were put in their list of approved materials for making artificial reef structures. However - The program stopped because they could no longer obtain flyash for the blocks. I have no idea what coal burners fdo with their flyash, but it seems to be a commodity, and not a waste.

 

[dberry]

Fly-ash as commodity? Someone needs to tell that to Duke Energy!

 

[MaxBottomtime]