Silence - cast in the blasting sand, but stop by a feed store and get some Calcium carbonate - you want the stuff used for "feed mixing", also called scratch sand or grit; they feed it to chickens - much better then the blasting sand, IMO, for using in the cement. And it is cheep, lol - $4 for a 50# bag.
I do use a small portion of OS to add texture, a handful per batch. The whole phosphate thing is anecdotal at best - if you worry about it, you can always find a bit laying around the bags at the feed store. Scrape some up and take it home. Test it for phosphates. Natural looking rock comes more from casting technique then from what you use to make it. Strictly speaking, I think the mix that makes the most realistic texture is probably just cement and sand, using a
little salt on the outside, here and there to give a little visual diversity, but this mix won't make particularly good rock for filtration as it will tend to have a tight matrix.
Altpersona that sounds like a cool thingy to have. Could probably be converted rather easily, but think about this before you do so. Calcium precipitate will coat the interior and require a lot of elbow grease and CLR (or equivalent) to clean out. While I'll be the first to cheer on attempts at producing a curing chamber, that is a very expensive piece of equipment to use this way...
As far as pressure goes, well one can use no pressure, just steam, or ???
What I've posted is pretty much what I have on pressure steaming. Something around 150psi or more is used for high pressure curing. I know the little pressure cooker I saw at Wally-World for $20 says it goes to 10psi.
Feel free to PM me to talk about idea's, or better yet, post them here so others can contribute if they wish to.
Now run with it
MMM and
Rusty, in the cement industry, they measure ingredients by volume. As Rusty guessed, concrete is fairly forgiving.
This is an interesting link about mixing concrete, but ignore the video:
http://matse1.mse.uiuc.edu/concrete/bm.html
And this picture shows about how dry the mix should be - though for our purposes, I recommend it just a hair drier than the picture shows it:
In a perfect world, the industry would use weight, as well as the metric system, but the problem with that is that aggregates all have differing weights. For example, if one uses silica sand and pea gravel, the weights on those items will be pretty high. Now say you wanted to use limestone sand and perlite. You would have a
lot of perlite to make the same mass as the equivalent volume of pea gravel. So the industry, and hence the folks working in the industry, would have to know the conversions for weights on different aggregates. And then you get to the cement itself. "Cement" doesn't have a specific weight, per se. The stuff that makes up the clinker can vary from plant to plant, recipe to recipe - cement from Plant Z might weigh slightly more then the same volume of cement from Plant Y - so would you need less? Even humidity can add weight to a bag of cement. So to keep it simple, and because cement and concrete are fairly forgiving, they use volume to measure.
As far as your rocks go, if it is hard, use it. At least until you have made new rock that is better. Even the densest rock you can make, (the cow pats), will still provide some biological filtration. You can regulate it to the sump later on. Honestly, in terms of "good concrete", denser rock has a better ability to withstand the various chemical attacks that concrete in saltwater can face. Denser cement is made with a bit more water then we use, and they choose different aggregates and use a different ratio of cement to aggregate as well.
Now,
MMM. Did you ever call Quikrete about the colorant, and how it will perform in a marine environment (safety-wise)? That stench you mentioned from the colored rock is the main thing that has me worried about your situation. If you haven't, I would seriously consider doing so. Based on the info about the product, I can't imagine it being
bad for the system, though
not great might be an answer - but that smell. Rust and blood both have a certain stench, and if I remember correctly, the colorant had a lot of iron oxide in it - the smell could be something as innocuous as the iron oxide sort of mixing with the calcium hydroxide and getting pulled out during the kure or it could be something else completely unrelated...
HTH
