Date: October 27, 2014
Effects of Salt on Concrete
Salt does not damage concrete, but the effects of salt can. That sounds weird, so we’ll explain. Salt does not chemically react with hardened concrete. Salt does however lower the freezing point of water, attract moisture, and increase pressure of frozen water. Salt can also increase the freeze-thaw cycles if the temperature fluctuates between 15°F and 25°F. Concrete scaling can occur in the absence of salts too if there were problems at installation.
The better quality the concrete and placement, the less likely that salt’s effects will have an adverse effect.
Here are some ideas that might help:
- The easiest thing is to use a good sealer. It’s very inexpensive. We have received lots of calls this past spring and in most cases, there was no sealer used. Sealer keeps the water out of the micropores. Our Concrete Store can make specific recommendations.
- Order concrete at 4,000 psi or greater.
- Use of a water reducer in the mix will minimize water in the mix (stronger concrete), yet maintain flowability (keep it easy and cheap to place). Excessive water will lower the strength of the concrete and if that water becomes trapped it could also have additional weakening effects on the surface. The moment pressure of trapped ice exceeds the tensile strength of the concrete… POP. Adding just 1 gallon of water per cubic yard can:
- Increase slump 1 inch
- Decrease compressive strength 150 to 200 psi
- Waste about 1/4 bag of cement
- Increase shrinkage by 10%
- Have an ACI Field Technician test for air, slump and strength of the concrete. This is something you can hire out, or you can certify one of your own employees and just outsource breaking the cylinder for strength testing.
- Stress no salt on the concrete in the first two years and never allow dicers that contain ammonium sulfate or ammonium nitrate. After all that, why keep the salt off? Concrete hydrates pretty much forever and gets stronger with time. The more time it gets to come up to strength the less likely ice pressure will exceed the tensile strength of the concrete. We recommend sand as it is cheap and environmentally friendly.
Here are a couple of links to more resources: