Concrete raise pH?

I think for our application we have to get our terms straight.

I am going to let the cement HARDEN for one or two days (possibly longer). This is just to allow it to get enough strength so that it won't crumble or break.

As for fully CURING, I am not concerned about this, as long as it is sufficiently strong in my tank.

What I do think is important is LEECHING most if not all of the lime out of the cement. This is done by soaking it in water continuously, and changing the water once it becomes saturated with lime - usually a film appears on top of the water. (NOTE: this is not the same as CURING because to cure it has to be dry, whereas to LEECH it needs to be wet.)

So I think we're talking about two different things - to CURE the cement to the point where it is strong enough to use, and to LEECH out any lime so that it is aquarium-safe.

Disclaimer: Uhhh, I pretty sure that what I am saying is right...:confused: but I could be wrong.....


.....maybe....;)
 
Welll, hardening, curing and lack of leaching are all about the same thing. The leaching occurs when any soluable solids become waterborne and leach out of the concrete. This will happen less and less as time goes on. Again, the tests Carpguy plans to do should prove interesting.
 
Originally posted by wetmanNY
Just chatting while you wait? Indeed. Forty-four posts in the first day?

Isn't this your bus? Let me help you on it.

(Why is Sting glowing? Must be orcs about.
Click to expand...

Just got that...very subtle, WetmanNY.
 
Originally posted by ejmeier
I think for our application we have to get our terms straight…
I am going to let the cement HARDEN for one or two days (possibly longer).…

As for fully CURING, I am not concerned about this…

What I do think is important is LEECHING most if not all of the lime out of the cement…

(NOTE: this is not the same as CURING because to cure it has to be dry, whereas to LEECH it needs to be wet.)

So I think we're talking about two different things - to CURE the cement to the point where it is strong enough to use, and to LEECH out any lime so that it is aquarium-safe.
Click to expand...

This is exactly the area where I'm dissatisfied with my googling.

We obviously have to let the concrete harden enough to be able to move it and manipulate it, but curing as a process is going to start on its own schedule. Two or more days in and its taking place with or without you.

My googling (no actual experience here) has revealed that curing is a process -- hydration -- that chemically changes the concrete. Concrete doesn't just dry, there's a chemical reaction that takes place and this reaction requires water. To cure properly it doesn't need to be dry. It shouldn't be dry. An overly dry cure will result in cracking and possibly flaking or crumbling. We don't really need to worry about strength, but we do need at least a decent cure to avoid cracking.

After this chemical change is the lime free to dissolve out into the water column or is it locked into some bond? What sort of pH havoc should we expect from cured concrete? (Those of you who are chemically inclined should feel free to jump in here :D )

From what I have been able to sort out, the lime (calcium oxide) reacts with water to form calcium hydroxide, which is still basic but much less soluble and reactive. I think this may be a dangerous addition to a CO2 enriched planted tank, since calcium hydroxide will react with CO2 to form calcium carbonate :( . Maybe not as much of a problem in a regular tank.

I'll try to have something setup by next Wednesday or Thursday and will start a thread on it in DIY. So far I was thinking of something like this:
Using two different concretes (a grout and a more normal Portland-type) I'll make 4 regularly sized bricks (2 of each). 2 go into separate water containers (maybe 5g tanks) to cure submersed with water changes, and two are cured wet with towels, submersed once or twice a week to get readings. I'll measure pH, GH, KH, temperature vs. a control, and size (expansion). After a few weeks of this I'll coat all 4 with epoxy and test 2 in plain water, 2 in CO2 enriched test tanks.

Any thoughts, comments, suggestions?

This has been on my mind all summer and I feel like its time to get it sorted out…
 
That's WAY more than I would ever be willing to do.:D

I would agree that the lime that is leeching out of the cement could be harmful for tanks with a high CO2 content.

Here is about all I know on the subject in regard to MARINE applications:

Most people will let it "cure" (or whatever you want to call it) fully submerged for six weeks. This is the time that most people have found to be sufficient. By sufficient, I mean that if you put the cement in water, it will not raise the pH (which is presumably from the lime content that leeches out - water saturated with calcium hydroxide has a pH of around 12). So once all of the lime is done leeching out (no more pH increases observed) then the rock is "safe" to put into the tank - (but cured, I have no idea...)

You can also speed the process by using an acid instead of water. I have heard of people using muriatic acid in there cure baths to speed the process - it shaves off maybe a week or two.

Hope this helps.....

PS - If you want a good way to cure a small rock with a lot of water changes - put it in the tank of a toilet (the top part). Every time you flush it gets close to a 100% water change, and its so easy...:)
 
If you watch us poor New Yorkers operate for a while, its all about maximizing the available space.

I like plants and I like loaches. Small tanks fit in small apartments, space is always at a premium.

So what if I built a caveworks that could double as a series of terraced planters, got rid of those pesky rocks taking up good floor space…

Unplugged the TV, got all the time I need.
 
Carpguy, you could achieve that with a slurry of natural aquarium gravel and safe epoxy. Just add enough mixed epoxy to make the gravel slightly wet, then either apply the mixture over pvc tubes or pour it into molds. You can clean whatever tools you use with acetone.
 
I've been looking into a few different methods including epoxy with sand, synthetic resin with sand, etc. They mostly seem like they'd be better for molds than for modeling. Trial and error. I've got a few mold ideas as well.

The concrete bit has been floating around my head a little while now, so its mostly curiousity at this point. From what I've been able to sort out so far, its probably not a good idea for my kind of tank.

This is for aesthetics and a custom fit. I'm not trying to save time or money. I'm trying to spend time and money -- carpguy at play. I'm looking to set up a ridiculously nice pair of 30s. Apartment living: think big, work small.

If I can come up with something I'm happy with I'll post it. I think its about time I move past the drawing board.

If it weren't for these d@M& forums I'd probably have just put a little tank on an end table and have been happy with it. You folks keep putting ideas in my head :D .
 
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