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#16
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Concrete?
RichToyBox wrote:
Concrete, whether truck mixed or gunnite/shotcrete is made of Portland Cement, sand, water, coarse aggregate (gravel or crushed stone) and admixtures. The sand, water and coarse aggregates should not pose any problems. Most of the admixtures are used in such small quantities and are bound in the concrete, so I don't see a problem with them, either. I will cover some admixes that you might want to use later. When Portland Cement hydrates (reacts with water) it produces the calcium silicate hydrate gel which is the stuff that makes the concrete stong and water tight. It also produces as by-products heat which can lead to expansion and then on cooling contraction that will cause cracking, and it produces calcium hydroxide. The calcium hydroxide is in the form of pore water, which comes to the surface, the pH of which is about 13. In air, the calcium hydroxide solution reacts with carbon dioxide to form calcium carbonate which is essentially just limestone, neutral pH. The calcium carbonate blocks the pores making the concrete both stronger at the surface and more watertight. It takes time exposed to air to get the carbonation layer formed. With the high water table in NO, I don,t think it would be possible to keep an empty concrete pond to allow the drying, since they make ships of concrete. The longer concrete cures the strionger and more watertight the concrete becomes. Curing requires a reasonable temperature, which you have, and a constant supply of moisture. So as soon as the pond has been poured, keep the concrete moist for a few days and then fill it with water. Water is the best and worst thing for concrete. During mixing and placement the less water the concrete has, the stronger and more water tight the concrete. Some of the mix water will leave the concrete through what is referred to as bleeding, where the solids settle and the water flows to the surface, leaving pores that are an avenue for water and chemicals to get back into the concrete and cause problems. The concrete will set up before all this mix water can leave, so some of it is just spreading the solid ingredients out and not providing any strength in the end. After placement, the concrete should not be allowed to dry, since the hydration reaction requires water and this reaction, suipposedly goes on forever. So the longer the concrete can be protected from drying the better. The concrete ponds that I have seen that do not have some form of waterproofing membrane painted on are usually allowed to sit for a year before any fish can go in, doing acid additions, water changes, and pH monitoring to see when the pH stabilizes at a safe level. The leaching of the calcium hydroxide will continue for a long time, but will decrease in rate, so the pond water will finally stabilize. As far as admixtures, there are 3 or 4 that you might want or need. Air entraining admixture is a must in northern climates to provide freeze thaw protection to concrete, but it also provides some improvement in the watertightness of concrete. Set retarder slows the initial harding of the concrete to provide a little extra time place and finish the concrete, and the warmer the concrete the faster it sets, so this one I think would be a must. Set retarders will usually allow for less water in the mixture. Water reducers, especially super water reducers, will allow the flow of the concrete to be much higher with the use of less water or for the same flow, reduce the water significantly. Now you can also get plastic fibers mixed with the concrete that will help to reduce any cracking by providing some small scale reinforcement of the surfaces, don't use it to replace the real steel reinforcement. Sorry for the length of the dissertation, but I felt a complete answer required this. Hope it helps. You sound quite knowledgeable about concrete. Perhaps you could enlighten me about my pool to pond conversion. I have a plastered Shotcrete pool built in 1987. Looks very good with a few spalling pits in the plaster. I plan to overpour concrete in the 8'1/2" deep end to raise the entire bottom to about 4' deep. I plan to put packed dirt over the plaster and pour 4" of concrete. Do I need to knock off the plaster around the sides so the edges of the new concrete floor mate with the Shotcrete? For fish, do I need to coat the new concrete and old plaster with Epoxy or will normal pool paint be alright? Chip |
#17
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Concrete? Sorry
Sorry,for the double send, it told me the 1st one didn't go thru. Chip |
#18
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Concrete?
"Chip" wrote:
RichToyBox wrote: Concrete, whether truck mixed or gunnite/shotcrete is made of Portland Cement, sand, water, coarse aggregate (gravel or crushed stone) and admixtures. The sand, water and coarse aggregates should not pose any problems. Most of the admixtures are used in such small quantities and are bound in the concrete, so I don't see a problem with them, either. You seem quite knowledgeable about concrete, so if you'll allow me I have a couple of questions. I have a plastered Shotcrete diving pool built in '87. Planning to convert it to a swimming pond with fish. Plan to raise the 8.5' deep end to 4' with dirt overpoured with concrete. 1) Do I need to take off the plaster around the sides, so the new concrete floor edges mate with the old Shotcrete? 2) Will I need to tie in the floor re-bar to the old wall's re-bar or even use re-bar in the new floor at all. 3) For fish, do I need to coat the old plaster and new concrete floor with Epoxy or will normal pool paint do? Chip Hi Chip, Just my 2 cents worth, but instead of doing more concrete work, why not fill with sand or dirt to the contour you want. Then use regular pond liner. That way, if you ever want to convert back to a pool you can. San Diego Joe 4,000 - 5,000 Gallons. Koi, Goldfish, and RES named Colombo. |
#19
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Concrete?
In article ,
San Diego Joe wrote: "Chip" wrote: RichToyBox wrote: Concrete, whether truck mixed or gunnite/shotcrete is made of Portland Cement, sand, water, coarse aggregate (gravel or crushed stone) and admixtures. The sand, water and coarse aggregates should not pose any problems. Most of the admixtures are used in such small quantities and are bound in the concrete, so I don't see a problem with them, either. You seem quite knowledgeable about concrete, so if you'll allow me I have a couple of questions. I have a plastered Shotcrete diving pool built in '87. Planning to convert it to a swimming pond with fish. Plan to raise the 8.5' deep end to 4' with dirt overpoured with concrete. 1) Do I need to take off the plaster around the sides, so the new concrete floor edges mate with the old Shotcrete? 2) Will I need to tie in the floor re-bar to the old wall's re-bar or even use re-bar in the new floor at all. 3) For fish, do I need to coat the old plaster and new concrete floor with Epoxy or will normal pool paint do? Chip Hi Chip, Just my 2 cents worth, but instead of doing more concrete work, why not fill with sand or dirt to the contour you want. Then use regular pond liner. That way, if you ever want to convert back to a pool you can. I agree, the liner is such a better way to go. -- To reply by email, remove the word "space" |
#20
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Concrete?
San Diego Joe wrote:
"Chip" wrote: RichToyBox wrote: Concrete, whether truck mixed or gunnite/shotcrete is made of Portland Cement, sand, water, coarse aggregate (gravel or crushed stone) and admixtures. The sand, water and coarse aggregates should not pose any problems. Most of the admixtures are used in such small quantities and are bound in the concrete, so I don't see a problem with them, either. You seem quite knowledgeable about concrete, so if you'll allow me I have a couple of questions. I have a plastered Shotcrete diving pool built in '87. Planning to convert it to a swimming pond with fish. Plan to raise the 8.5' deep end to 4' with dirt overpoured with concrete. 1) Do I need to take off the plaster around the sides, so the new concrete floor edges mate with the old Shotcrete? 2) Will I need to tie in the floor re-bar to the old wall's re-bar or even use re-bar in the new floor at all. 3) For fish, do I need to coat the old plaster and new concrete floor with Epoxy or will normal pool paint do? Chip Hi Chip, Just my 2 cents worth, but instead of doing more concrete work, why not fill with sand or dirt to the contour you want. Then use regular pond liner. That way, if you ever want to convert back to a pool you can. San Diego Joe 4,000 - 5,000 Gallons. Koi, Goldfish, and RES named Colombo. Thought of that, and even thought of using the multiple sand bags approach. Still might. Don't know the $ vs effort trade-off. Might be a fair bit cheaper, but a lot more sweat. Oh, well, I can use the exercise. One problem is that in addition to the main floor drain and skimmer, I have 14, count'em 14, other drains/returns that were the old pool's cleaning system. I would like to have these available in the new pond. Punching through and sealing the liner that many times scares me a little. What are the list's experiences with sealing plumbing through the liner? Chip |
#21
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Concrete?
http://www.geocities.com/richtoybox/pondintro.html
Zone 7A/B Virginia "Chip" wrote in message ... RichToyBox wrote: Concrete, whether truck mixed or gunnite/shotcrete is made of Portland Cement, sand, water, coarse aggregate (gravel or crushed stone) and admixtures. The sand, water and coarse aggregates should not pose any problems. Most of the admixtures are used in such small quantities and are bound in the concrete, so I don't see a problem with them, either. You seem quite knowledgeable about concrete, so if you'll allow me I have a couple of questions. I have a plastered Shotcrete diving pool built in '87. Planning to convert it to a swimming pond with fish. Plan to raise the 8.5' deep end to 4' with dirt overpoured with concrete. 1) Do I need to take off the plaster around the sides, so the new concrete floor edges mate with the old Shotcrete? 2) Will I need to tie in the floor re-bar to the old wall's re-bar or even use re-bar in the new floor at all. 3) For fish, do I need to coat the old plaster and new concrete floor with Epoxy or will normal pool paint do? Chip I would use a good clean sand or gravel for the fill. Dirt settles, even if compacted fairly well. If you use sand, fill the sanded bottom with water to a height above the sand to break the water tension that allows us to make sand castles, and the sand should become very well compacted. I would remove the plaster from the sides and slightly roughen the concrete, then use an acrylic bonding agent to get the concrete to bond as well as possible. The sloped bottom will need more concrete removed where the new floor ties into the old floor, since the minimum thickness of concrete should be 2 of the concrete rock thicknesses and 3 is better. The reinforcement is needed to prevent what would be called temperature cracks from being large. All concrete shrinks. With low water to cement ratios and continuous moist curing, the shrinkage is reduced. This reduction in shrinkage may be sufficient to prevent any cracking, and the use of rebar will distribute the shrinkage tension throughout the concrete to further reduce chances of cracks. The rebar does need to be tied into the walls and floor, though not tied to the existing steel. Drill holes into the existing concrete to obtain bond. I would drill the holes at different angles giving a chinese handcuff type friction, rather than making them parallel to each other. The reinforcement of the floor could be done with wire mesh reinforcement. Slab thickness should be 6 to 8 inches thick. A proper bottom drain with 4" pipe should be installed prior to concrete, so pipe friction will be minimized from bottom drain to pump. As for a coating, the ones that I am seeing used on other pond construction are rubberized urethane type mixtures, similar to the spray on truck bed liners. I wouldn't think an epoxy would be needed, except as a crack repair material. The regular pool paint should be designed to work with concrete and would be adequate. -- RichToyBox |
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