Probably longer than we will be alive
My understanding is as concrete ages the ph does go towards acidic. Learned that while reading up on the condo collapse in Florida
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To lower the PH of the cured concrete you need a driver, the most common cause of this is carbonation.
Water and/or water vapor from below grade combine with carbon dioxide in the entrained air to form carbonic acid. Over time, carbonic acid infiltrates the concrete and, through a process called carbonation, combines with the calcium hydroxide to create calcium carbonate. It is the calcium carbonate that lowers the pH of the concrete, eliminating the protective layer around the steel.
Carbonation itself is not the cause of corrosion, it just lowers the PH as you mentioned, and it creates a corrosive environment at the surface of the reinforcing steel.
In situations where concrete has deteriorated, carbonation is one of the usual culprits.
In the case of the Condo in Florida there were likely multiple factors.
The buildings close proximity to the ocean and the swimming pool above the parking garage likely introduced both chlorides and carbonation into the concrete matrix. As pointed out above once the PH drops deterioration of reinforcing steel begins.
As steel corrodes, iron oxide, or rust is formed. This rust occupies a much greater space than the steel from which it was created. When embedded in concrete, corroding steel produces significant internal pressures. These pressures eventually result in the formation of subsurface cracks and spauling. Recall the pictures from the pool equipment room where large portions of the concrete had spalled off completely exposing the reinforcing steel in multiple locations.
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I apologize, I didnât intend to turn this thread into a science project.
I am going to just say this again, just follow the directions.
I think a practice pour is a good idea as @JDE suggested.
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I think you posted good info, interesting read.
I argee with 72ponyâŚjust follow the directions.
John did you end up sweeting your MR1 during the pour? Asking for a friend.
No, I punked outâŚI told myself just do it by the directionsâŚ
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Hello.
I had two questions about your suggestions. I donât know much about concrete.
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How much soap per 60# bag, and type of soap?
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I was told to keep the slab for my garage wet for 5 days so it would cure hard. Yet I n the directions, they tell you to dry off the excess water with a towel. You mentioned keeping it wet also. Standing water or just a damp towel?
I appreciate any advice.
id recommend getting two or three extra bags and do a test pour in some kind of container you will learn alot. I didnât use any soap but used a regular spoon not heaping of sugar per bag to slow set time a bit. If its under 60 degrees where you are you can use less. Once you get all the concrete into the machine hopefully within an hour or hour and a half and get the stiffeners and table in then you soakup the excess water. Wait until you cant really thumb press the concrete and then you trowel it. Once its troweled at like hour 5/6 then you keep it wet. you can read about it on line.
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Just follow the directions. Langmuir states if you keep it wet, itâll get powdery, and lots of people have stated they had to scrub and clean the powder off the top. I followed the directions, and had a nice glossy top finish that was hard and smooth, no scrubbing required.
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its only if its wet during the trowel process. once its set up after troweling wet doesnt matter. you just need to pull the excess water out of the float.
I used Sakcrete 6000psi mix and initially wet it to the manufacturers recommendations - which is quite a dry mix. I think itâs essential that you rent a small mixer, it helps get a better mix and it takes a shorter time. If the mix is stuff, itâs key to get it into the tub as fast as possible or you will have difficulty putting in the stiffeners and baseplate. We tried the sugar trick, not sure it really made any difference.
I had 3 helpers (mostly because my friends are curious and free lol) which really made the experience fun - one guy was full time mixing, one pounding and vibrating and the other two placing/finishing. I think you can do this fine without a vibrator, just hammering, but it sure helps. I had zero surface water, the surface finish was perfect.
The plate was a bear because mine is oversized and has outriggers (will create a thread on that one) but we got it in, using rocking and light vibration/hammering. Easily the most worrisome part of the pour.
Once the concrete was left to settle for a few minutes, we did a bunch of detaling, especially around the drains and posts. Once that was good, say about 30 mins, final trowel, and then I flooded the tub up to the top of the drains with clean water, pouring the water on top of the plate as not to damage the finish. The does a few things - one checks the concrete for high spots since itâs essentially the same as a epoxy flood coat, and it âpond curesâ the concrete. That water covering all the concrete sat for 7 days, with the occassional topping up, and then drained and dried. I cleaned and ground down a few spots that were a bit high (just use a small grinder with a grinding disk, works great). That is where I am now, on day 3 of drying. I am keeping the heaters on to get a good secondary cure and preparing for the epoxy. Oh, BTW, zero powdering.
Almost all manufacturers of concrete recommend waiting 28 days before epoxing the slab since the concrete does not reach a 99% cure until then and is still letting off moisture, but Langmuir is going for 5 days. I have not heard any reports of delamination or separation of the epoxy so I guess that works, but I decided to stretch it to 14 days. I am trying to keep distracted with other projects.
Have fun!
Cheers,
Mike
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I followed the directions exactly and had the same consistency they showed in the video, however, it was only about 10% humidity and it dried out way fast in the pan and I got almost no cream to the top to be able to smooth out. Got an extra gallon of epoxy to fill it all in.
how long did it take you to get it all mixed?
Three of us and a mixer, only about a half hour.
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huh weird you got no cream
Got a little, but not enough to make it smooth.
I had none, the mix was stiff within minutes. Thankfully I was able to get the baseplate set. But it was unworkable to cleanup the surface. I had to use two gallons of epoxy to finish it. The good news is it should be fine.
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Im curious to know what concrete is being used on the machines being preassembled which will be shipped? And how is LS moving the finished machines?
Im a far cry from a concrete expert, so if im concerned about cracking if I ever move the machine, am I better off with reinforced âcrack resistantâ mix or prograde higher strength early strengtg mixes?