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Old 11/12/2017, 11:42 PM   #1
Twinfallz
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Coral Skeleton Dividing Wall

So I've made the wall, below, using coral skeletons, coral gravel, rocksalt & white cement.
It has set, but needs to cure in fresh water to let the rocksalt & lime from the cement leach out.
I'm using a TDS & a pH meter & comparing the readings against a control of dead coral also in tap water.
The plan is to soak the wall in seawater after the TDS reading has ceased rising, but I'm wondering if I should also soak the wall in a vinegar solution first?

Any opinions would be welcomed.




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Old 11/13/2017, 05:27 AM   #2
salty joe
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I used a Portland cement/sand mix and the first time I soaked it, the pH spiked. I added enough muriatic acid to take pH to 7 and let it soak for a week or so. It hasn't been a problem since.

BTW, I let my structure dry, bone dry, before the acid bath. I think that makes a difference.


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Old 11/13/2017, 02:04 PM   #3
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Quote:
Originally Posted by salty joe View Post
I used a Portland cement/sand mix and the first time I soaked it, the pH spiked. I added enough muriatic acid to take pH to 7 and let it soak for a week or so. It hasn't been a problem since.

BTW, I let my structure dry, bone dry, before the acid bath. I think that makes a difference.
That makes sense. Use the acidic water to absorb the some minerals from the concrete, reducing pH.

I've first got to let the rocksalt fully dissolve. First reading on my TDS meter after soaking overnight was >10,000ppm. Next overnight reading was 1,270ppm. Once it settles down to around 200ppm I'll test the pH & take it from there.


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Old 11/13/2017, 06:38 PM   #4
der_wille_zur_macht
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Curing in acid reduces the strength of the concrete. If you've got a structure where strength is already questionable (thin concrete, big weird aggregate, rock salt creating voids) it might be best to aim for the most strength possible, which would be curing damp, letting it air dry, then submersing in water until the pH stops rising (which will be a few weeks to several months depending on the thickness, water change frequency, etc.)


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Old 11/13/2017, 07:37 PM   #5
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Quote:
Originally Posted by der_wille_zur_macht View Post
Curing in acid reduces the strength of the concrete. If you've got a structure where strength is already questionable (thin concrete, big weird aggregate, rock salt creating voids) it might be best to aim for the most strength possible, which would be curing damp, letting it air dry, then submersing in water until the pH stops rising (which will be a few weeks to several months depending on the thickness, water change frequency, etc.)
Good points. And putting cement in some acids makes it turn yellow also. Although I would have only used a weak vinegar solution.

After letting it air dry I'll put it in salt water and check on pH.


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Old 11/13/2017, 07:37 PM   #6
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Yes, damp cure makes a big difference. I kept mine damp for a couple weeks before drying it.


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Old 11/13/2017, 07:40 PM   #7
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It shouldn't be in saltwater until it's totally stable and inert (and ready to use). Any soaking or testing of pH prior to that should be in freshwater - both for final strength and speed of cure (it'll take a lot longer in saltwater).


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Old 11/13/2017, 08:15 PM   #8
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Smile

Quote:
Originally Posted by der_wille_zur_macht View Post
It shouldn't be in saltwater until it's totally stable and inert (and ready to use). Any soaking or testing of pH prior to that should be in freshwater - both for final strength and speed of cure (it'll take a lot longer in saltwater).
Yes I let it air dry first & I have had it in a tub of fresh water ever since.
The TDS has fallen dramatically very quickly as I expected.

My tap water has a pH of 9.5 as does my RODI water. So that wont have too far to fall LOL.


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Old 11/13/2017, 08:18 PM   #9
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Quote:
Originally Posted by salty joe View Post
Yes, damp cure makes a big difference. I kept mine damp for a couple weeks before drying it.
My wall doesn't need a lot of strength, but I don't want it to crumble either.
It's way past that point. I'm very happy with it's strength & crumble factor


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