Otto Knepp

Thanks for all the info, everyone. I recently got interested in Roman cement/concrete again, and remembered I had made this thread while browsing permies. I've got to admit I don't browse permies particularly often, and when I do, I rarely post.

I have another question, and was wondering what would be a good mix to use to make lime based concrete blocks? I'm thinking of something like a steel reinforced concrete block wall, but with something even stronger than portland.

Nicole Alderman wrote:He doesn't think that koi would do well in that kind of set-up. Duck poop produces too much ammonia, and the dissolved solids would get too high. The ducks stirring up sediment could irritate the fishes' gills. A quote from him, "I mean, you could do it, but you're going to need massive filters that completely negate any hope of financial gain."

How big of a pond are you looking at having? How many ducks are you planning to have? How many hours/day would the ducks have access to the pond? How many water changes do you want to do? Willows and other emergent pond side plants, like cattails and wapatos, take up a lot of nitrogen. Another quote from him, "If you had at least 50,000 gallons with only, like, 3 ducks, and lots of plants, maybe you could pull it off. I'm just guessing on numbers, though--you'd have to test the water frequently for nitrates and ammonia. Duck poop is not like fish poop.

Carp is the most common fish used in rice-duck-azolla/duckweed-fish farming methods. The fish don't seem to mind the ducks too much.

Well, I'm not actually building anything at all, just trying to get information. I'm designing my dream home. So far my plan is to do a reverse brick veneer: i.e. conventional framing outside, brick inside. Theoretically however, this would be used as an exterior finish/stucco. I've heard a lot of mixed info about the strength and durability of plain lime putty mortar. I also live in a very hot area, where I would probably have to hose down the lime much too often for it to set properly.

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Hope this helps.

Thanks for the info Vern. I looked up tabby and have been reading up on it for a few hours. It doesn't seem to be hydraulic though, its just regular slaked lime made into concrete with shells as the aggregate. Maybe you read my post as talking about hydrated (slaked) lime, but I'm asking about hydraulic lime: lime based mixtures that require water to set, much like modern portland cement. The Romans used hydraulic lime cements to make massive concrete structures that are still standing thousands of years later, and they didn't even use reinforcement like we do today.

The reason I'm asking is because despite acting like portland cement in many ways, they still maintain the 'breathability' of plain lime mortar/cement/plaster while being much stronger.

I've been reading up on roman cement and how superior is was and still is to modern portland cement. They used well aged lime putty, and added what is called pozzolan. It initially was a volcanic ash from near the city of Pozzuoli. They later discovered powdered marble and brick would also work. Modern pozzolans include coal fly ash, silica fume, and rice hull ash. Adding a pozzolan to lime makes it set with water, instead of absorbing CO2 from the air.

The thing is, I don't even know where to get these things, and personally would rather not use coal ash. I thought about firing kitty litter, but most of the things I've read about using brick as a pozzolan mention that its due to the transformation of kaolin into metakaolin during firing, and kitty litter is bentonite, not kaolin.

If concrete is out, you might want to go with some kind of paving stone or brick.

Cement making is a pretty simple process. The raw materials are mainly limestone and clay/sand, with a touch  of alumina and iron oxide thrown in as a flux. This is heated very hot, and it kind of fuses together into chunks called clinker. The clinker is powdered to make cement. The only real issue as far as contamination is if the kiln is coal fired, then there may be small amounts of heavy metals from the coal. I doubt much gets in, as I was talking with the quality control supervisor at a cement plant that uses Colorado bituminous in their kiln a few months ago (a job interview actually. Didn't get it) and there isn't even enough fly ash incorporated into the cement to contribute to a pozzolanic effect. It just has a small effect on the silica ratios. I honestly wouldn't be very worried about heavy metal contamination.

If you wanted to be hardcore, you could make your own cement. Joseph Aspidin made his first batch of Portland cement by heating limestone and clay on his stove.

Edited for spelling