How come some concrete is pitted from winter salt and some isn't?

[vtsnowedin]

The same plant can put out dozens of different mixes with cement factors from four bags to a cubic yard to ten bags to a yard and with add-mixtures like fly ash and ground mill slag along with air en-training agents and water reducers. The stuff the state puts in their bridge decks has all the bells and whistles and often tests 6000psi or better but cost $900 per cubic yard complete in place. The contractor pouring a private driveway for a price ordered something less and then may have done all the other bad things Mossroad mentioned and a few more. Not all concrete crews have the same knowledge and skill.

[2LaneCruzer]

Reminds me of a story my Dad told to me many years ago. During WWII, he ran an aggregate plant that produced limestone and Gypsum, and most of their production went to a cement kiln in another part of the state. He said they got a phone call from the kiln manager, telling them to not ship any more material, as their QC tests were all failing, and they had to find out what the problem was, and do it fast. To make a long story short, some of the employees in the lab had cut and eaten a big watermellon, and the juice had made its way into the test cells, causing the concrete to fail. It was known in the industry as "The Great Watermellon Wars". A few years ago, I had the pleasure of discussing this with the manager of a local cement kiln...he laughed, and said that sugar will cause cement not to set up. If they ever have problems with a batch that has to be dumped, they put sugar in so that it won't set up in their equipment.

[Stimw]

What time of year were they poured? They might have put antifreeze in it. ???? (I think it is calcium chloide)

[sixdogs]

What time of year were they poured? They might have put antifreeze in it. ???? (I think it is calcium chloide)

Don't know but I have seen lots of flaking and pocked marked driveways and can't recall seeing any at any gas stations.

[/pine]

The finisher may also have a little influence.

Good point...

and several factors apply...

finishing...if enough "mud" was not "floated" to the surface a lot of fine aggregate gets exposed when troweling brooming etc.. this leaves the finish vulnerable...

FWIW....portland cement is ground so fine that it will pass through a sieve that will hold water (surface tension)...
Some of the first swimming pools were made with CMU's then skimmied over on the inside with nothing but portland, some very fine sand and enough to make a brush-able slurry...
Personally...I use portland and bonding agent (no sand) to make slurry for sealing things like water reservoirs, foundation walls etc...

[Rock knocker]

Air entrained helps, and if the finisher worked it too hard/much or too much water to make it easy for the finisher

[don45640]

Yes! Many reasons........most have been mentioned. But age is also a factor.(1) Concrete needs a year of good curing time before it will resist salt at all.
(2) Might be freeze-thaw damage along with or without salt.Concrete in moist shady areas will fare worst.
(3) Different sealers will resist moisture at a totally different level.
(4) Concrete which has been poured non-commercially will usually not be strength tested,but gas station may have had Geo-Tech or some other testing company present.At least they may have taken their own test cylinders.
(5) Yes,a homeowner is more likely to get flyash or a weaker mix.
(6) The test mentioned above also includes an air entrainment test which ensures levels don't exceed specs for outdoor concrete,which is usually 4-8% total air which includes naturally occurring and entrained by admixture.
(7)The gas station may have used super plasticizer,which increase strength and density tremendously by pouring dryer crete.
(8)Then LASTLY the finisher CAN ruin a finish by floating or troweling in surface water. don-ohio concrete contractor and finisher from 1970-1996 (:^)

[adirondackmtnman]

Yes! Many reasons........most have been mentioned. But age is also a factor.(1) Concrete needs a year of good curing time before it will resist salt at all.
(2) Might be freeze-thaw damage along with or without salt.Concrete in moist shady areas will fare worst.
(3) Different sealers will resist moisture at a totally different level.
(4) Concrete which has been poured non-commercially will usually not be strength tested,but gas station may have had Geo-Tech or some other testing company present.At least they may have taken their own test cylinders.
(5) Yes,a homeowner is more likely to get flyash or a weaker mix.
(6) The test mentioned above also includes an air entrainment test which ensures levels don't exceed specs for outdoor concrete,which is usually 4-8% total air which includes naturally occurring and entrained by admixture.
(7)The gas station may have used super plasticizer,which increase strength and density tremendously by pouring dryer crete.
(8)Then LASTLY the finisher CAN ruin a finish by floating or troweling in surface water. don-ohio concrete contractor and finisher from 1970-1996 (:^)

Flyash doesn't necessarily mean a weaker mix, it can make for a more workable mix, and it does boost the overall strength of the concrete after full cure due to the secondary cementitious effect. Most problems we see spalling/chipping, exposed aggregate related are all too often caused by the concrete finisher 'blessing' the surface of the concrete with water to make it easier to finish. this dilutes the water/cement ratio of the surface of the concrete to a weakened point, and once the protective finish surface is gone, it opens the concrete up to attack from a plethora of environmental factors....ie, moisture combined with freeze/thaw cycles, salt, mechanical destruction from plows/tractor buckets, acid rain, etc, etc...Point being, there are almost limitless explanations as to why the concrete could be doing what it's doing, from the cement powder/aggregate used to produce the concrete, the plant operator's use of water in the mix, the truck driver's use of water, condition of the fins in his mixer drum, number of revolutions he put on the mixer before discharge, environmental conditions for the placement of the concrete, ie too hot/cold, windy, rainy, etc. The contractor's level of hurriedness, methods of placement/finishing/curing, and the customer's treatment of the concrete post placement are all very important factors in the long term durability of the product...

[crazyal]

Interesting. When I poured the slab for my garage the price difference between 3000 psi and 4000 psi was only a couple of bucks a yard so I went with 4000 with fiberglass. I really didn't know too many questions to ask. In the near future I would like to pour a driveway between the garage and house. I'm always looking for tips.

[sixdogs]

Interesting. When I poured the slab for my garage the price difference between 3000 psi and 4000 psi was only a couple of bucks a yard so I went with 4000 with fiberglass. I really didn't know too many questions to ask. In the near future I would like to pour a driveway between the garage and house. I'm always looking for tips.

Well, some pits from winter salt and some doesn't and from what I'm learning, the PSI strength of the concrete seems to be the deciding factor.