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View Full Version : Salt(water) on Concrete (rocks)


lakee911
10/06/2006, 04:29 AM
This is for those of you making your own rocks....I recently had a sidewalk poured, and the guy told me not to throw any salt on it for up to two years as it would eat up the concrete before it's cured. Two years!?

So, those doing the DIY rocks, are they dissolving in your tanks?

Jason

frh674
10/06/2006, 06:32 AM
....the guy that told you this... I believe doesn't know what he's talking about. if you throw the salt on the concrete while it's drying(still very wet) it could pit some but thats it.

69vette
10/06/2006, 06:55 AM
The cure time for concrete is 30 days, not 2 years.

jasalmanza
10/06/2006, 07:41 AM
On the contrary, I use rock salt in my mix to make to rocks more porus....

zenfro
10/06/2006, 10:50 AM
I've been wondering about salt in DIY rocks as well. From the articles below, it sounds like both opinions are correct (except for the 2 year cure time). Sounds like salt is bad for concrete in freeze/thaw conditions, but if they go through that in the tank, that would be the least of your worries.

Ask The Builder (de-icing w/ rock salt) (http://www.askthebuilder.com/008_Deicing_Salts_And_Concrete.shtml): says that concrete is weak under tension. rock salt melts the ice, the water penetrates the concrete, salt actually increases the amount of water penetrating, and if it freezes, it expands and can damage the concrete.

Concrete Deterioration Study (http://www.ctre.iastate.edu/pubs/semisesq/session1/cody/): (emphasis added)

"Samples were experimentally deteriorated using wet/dry, freeze/thaw, and continuous soak conditions in solutions of magnesium chloride, calcium chloride, sodium chloride, magnesium acetate, magnesium nitrate, and distilled water in order to determine relative deterioration activities. Magnesium chloride was most destructive. Calcium chloride was next, and sodium chloride was relatively benign. Magnesium acetate produced severe crumbling and moderate fracturing, and magnesium nitrate caused moderately severe deterioration by crumbling and discoloration."

So it sounds like using rock salt for tank rocks is fine, just make sure the salt you get from Home Depot/Lowe's etc. is sodium chloride.

lakee911
10/06/2006, 11:39 AM
Hmm ... Concrete does take typically 28 days to develop its full rated strength, but it doesn't fully quit curing for an extended period of time. I guess it depends on how long its been and what it is. I guess its been ok in the tanks. Thanks!

bklynmet
10/06/2006, 06:14 PM
Properly proprtioned concrete mix should attain it's mix capacity in 28 days. It's symantics.

Concrete will continue well after that - especially in the presence of moisture. There are tiny cacpillaries in concrete that retain moisture and continue the concrete hydration.

What your contractor told you has to do with salt (sodium cloride) penetrating and causing some weakening as zenfro researched. The freeze thaw aspect is independant of the chemical nature because it is a mechanical action of the ice expanding and popping the concrete (that is weak in tension).

Now the issue with your sidewalk, a properly finished concrete surface would provide greater protection that one that that wasn't. Providing a roughened surface (for traction so people don't slip when it gets wet) actually makes the councrete a little more porous. If your ever in a manufacturing plant, look at the concrete floors and you'll notice they're smooth compared to a sidewalk. This is to keep some of the harsher chemicals from readily penetrating into the concrete.

In my opinion, save yourself from having a lawsuit from someone slipping on ice on your sidewalk by throwing salt on it to melt the ice.

Bryan
10/08/2006, 03:47 AM
The concrete in the Hoover Dam is still curing, engineers state it may take 120 years to fully cure.

http://en.wikipedia.org/wiki/Hoover_Dam

lakee911
10/08/2006, 10:16 AM
Hmm ... good point, bkly.

I had seen something about that on TV, Bryan. Neat, huh?

Thanks