salt on concrete

[John Dirks Jr]

I've been reading about how concrete can be damaged by putting salt on it in the winter. There is discussion about the quality of the installation as having a role in salt affecting concrete.

I've seen newer driveways that have damage where the contractor claimed it was caused by salt. I've been putting salt on the 40 year old concrete at my for years and I have no visible damage.

What do you know about the subject and how do you explain damage in one instance and not in another?

[Inspectorjoe]

From what I understand, concrete is most vulnerable to freeze related damage in it first year and overuse of de-icing materials can make it even more susceptible. You can see examples of that where you have damage at the driveway apron at the street, but little or none on the rest of the walk.

That said, properly mixed and installed concrete still shouldn't spall. Spalling usually originates with problems with the mix or improper installation.

[kurt]

That said, properly mixed and installed concrete still shouldn't spall.

That's most of the problem. Hardly any concrete is properly mixed and none of it is placed and finished satisfactorily nowadays.

[Tom Raymond]

Concrete continues to cure for a long time (the Hoover dam is still curing) so your driveway is going to be a whole lot harder than one poured more recently. Concrete is a lot more complex than most people think and there are dozens of variables that affect the charecteristics of the finished product, from air entrainment to aggregate size to even the speed and number of turns in the drum. Then you need to consider variables at placement such as weather conditions, site prep, whether the mix was hot or not, the time between placement and finishing, and the finish technique. I'd wager there are millions of yards placed every year that should have been rejected, for some reason contractors would rather tear out a few failed jobs than wait an hour or two for a fresh load when they should.

Tom

[esch]

Guessing,

Chemically colder with salt, more expansion pressure, higher spalling risk?

Matt

[John Kogel]

That said, properly mixed and installed concrete still shouldn't spall.

That's most of the problem. Hardly any concrete is properly mixed and none of it is placed and finished satisfactorily nowadays.

I've got pictures of a newer condo building balcony that was ruined by a tenant sprinkling salt on it.

They might have had 3 days of heavy frost in 3 years, but that's how they done it on the prairie, by gum.

[johncollins]

I've got pictures of a newer condo building balcony that was ruined by a tenant sprinkling salt on it.

They might have had 3 days of heavy frost in 3 years, but that's how they done it on the prairie, by gum.

Is that in BC, Canada? I read that there lots of poorly built condos up there...

[Charlie R]

It is not recommended to use de-icing chemicals on concrete that has cured less than one year. I remember getting that from a structural engineer who specialized in concrete. The heat generated by the chemical can cause spalling of the top of the cold concrete. Personal experience as I used to be associated with large scale snow removal operations and I used to fight with people all the time on this, but the evidence would show each spring.

[hausdok]

Concrete continues to cure for a long time (the Hoover dam is still curing) so your driveway is going to be a whole lot harder than one poured more recently. Concrete is a lot more complex than most people think and there are dozens of variables that affect the charecteristics of the finished product, from air entrainment to aggregate size to even the speed and number of turns in the drum. Then you need to consider variables at placement such as weather conditions, site prep, whether the mix was hot or not, the time between placement and finishing, and the finish technique. I'd wager there are millions of yards placed every year that should have been rejected, for some reason contractors would rather tear out a few failed jobs than wait an hour or two for a fresh load when they should.

Tom

I agree with Tom,

I think it's not so much that salt damages concrete; it's that the concrete might not have been mixed and properly cured. For instance, I remember mixing mortar for my father one really cold winter when he was running block for the foundation for an addition to a cowbarn and he had me adding calcium chloride to the mix in very specific amounts. He said it was to make the mortar "set up faster by preventing it from cooling too quickly." I had no idea what he was talking about; so I just did what I was told. 25 years later I was going through the Q Course at Ft. Bragg when they taught us the same thing.

Here's a little gem from the part about considerations when placing concrete in cold weather from FM 5-428 - The US Army Concrete and Masonry Field Manual; you can find it under "Library" and "File Downloads" on the menu bar above.

Using accelerators. Do not substitute accelerators for proper curing and frost protection. Also, do not try to lower the freezing point of concrete with accelerators (antifreeze compounds or similar products), because the large quantities required seriously affect compressive strength and other concrete properties. However, you may use smaller amounts of additional cement or such accelerators as calcium chloride to speed up concrete hardening in cold weather, as long as you limit it to no more than 2 percent of calcium chloride by weight of cement. But be careful in using accelerators containing chlorides where an in-service potential of corrosion exists, such as in prestressed concrete or where aluminum inserts are planned. When sulfate-resisting concrete is required, use an extra sack of cement per cubic yard rather than calcium chloride.

My guess is that the concrete in question wasn't properly mixed or cured in the first place.

ONE TEAM - ONE FIGHT!!!

Mike

[Chad Fabry]

The coarse aggregate plays a huge part in spalling resistance. Some aggregates are hygroscopic and thus "pop" from ensuing freeze thaw cycles. Once the surface is violated, the issue is exacerbated by the resulting pockets and standing water.

Using steel finishing tools or even over finishing with magnesium tools is a death sentence as well.

[Marc]

Using steel finishing tools or even over finishing with magnesium tools is a death sentence as well.

How so? Most of my floats are magnesium.

Marc

[Chad Fabry]

Using steel finishing tools or even over finishing with magnesium tools is a death sentence as well.

How so? Most of my floats are magnesium.

Marc

over finishing with magnesium- it separates the fines and brings up too much fat and water.

[kurt]

If you're bringing up too much water, that's often due to there being too much water.

Well placed concrete is damn near "dry".

When I use my mag float and work it hard, I bring the wondrous creamy to the top, and the sand and aggregate work to the bottom. The result is almost like a tempered layer on top.

If salt was the primary culprit, my sidewalks would be gone. I dump about 200 lbs. a year on my south walk, and have done so for about 15 years. The walk is in fine condition. That's because I put it in right about 17 years ago.

Not saying salt is OK, but the idea that it kills concrete is a result of lots of factors, salt only being one of them.

And, of course you don't put it on when the concrete is curing; that'll kill it.

[Chad Fabry]

Well placed concrete is damn near "dry".

Just yesterday I placed concrete in a crawl with about 24" of clearance to the joist bottoms. I had a mid range plasticizer in the mix which yielded an effective 10 slump for a mix with very little water.

It wasn't self leveling, but it was super easy to move around; it was the best 4 bucks a yard I've ever spent.

[Les]

http://www.concrete.org/members/freedownloads.asp

This is the best site I know for concrete related issues. I have worked with their members for several legal cases and learned an enormous amount about concrete.

In Michigan we have problems with folks using lawn fertilizer for de-icer because salt kills grass.

About 85years ago I was at a St Louis ASHI chapter education session that dealt with concrete and the challenges of using it in the Mid-East. Really cool class and of course I can't remember who taught it!

[Erby]

About 85years ago I was at a St Louis ASHI chapter education session that dealt with concrete and the challenges of using it in the Mid-East. Really cool class and of course I can't remember who taught it!

Damn Les, you and ASHI are both older than I thought. Congrats on the long life! [:-monkeyd[:-monkeyd [:-monkeyd

[kurt]

Well placed concrete is damn near "dry".

Just yesterday I placed concrete in a crawl with about 24" of clearance to the joist bottoms. I had a mid range plasticizer in the mix which yielded an effective 10 slump for a mix with very little water.

It wasn't self leveling, but it was super easy to move around; it was the best 4 bucks a yard I've ever spent.

What's the brand name of the plasticizer? I'm not knowledgeable about that class of additives.

[Chad Fabry]

Well placed concrete is damn near "dry".

Just yesterday I placed concrete in a crawl with about 24" of clearance to the joist bottoms. I had a mid range plasticizer in the mix which yielded an effective 10 slump for a mix with very little water.

It wasn't self leveling, but it was super easy to move around; it was the best 4 bucks a yard I've ever spent.

What's the brand name of the plasticizer? I'm not knowledgeable about that class of additives.

Glenium

I'll be using it again- it takes a lot of the oomph out of the equation.

Set time was unaffected as far I can tell.

[Les]

.........as I have said many times - stuff between your ears and stuff under your finger nails! Gotta be balanced.

[Charlie R]

Many de-icers contain calcium magnesium acetate (CMA), which is proven to cause deterioration of concrete. If you go to http://www.ossian.com/ you can follow their link to all sorts of studies that show the effects of various ice-melters on concrete.