FREEZE THAW PROTECTION FOR EXPOSED SLAB, JOINTS AND GROUT 1

[Lesali]

I'm working on a project with an exposed mat foundation - 30" thick. It will be subject to freeze thaw cycles. I plan on using 3000 psi w/ 7% AE. I have a few questions on what more I can do to ensure durability.
[ol 1]
[li]Would a concrete sealer be of help for the slab?[/li]
[li]And, I will need some construction joints. Has anyone used PVC water stops (or some other product) to prevent water getting into the joints and causing cracking?[/li]
[li]And how about the grout under base plates. I've seen cases where the exposure has decimated the grout. Is there a solution here? One supplier suggested it is impossible to add Air Entrainment to grout.[/li]
[/ol]

 

[jayrod12]

1. My bet would be no, more often because it is usually poorly installed so never ends up working as designed.
2. Yes have used them. In flatwork they might not be so bad but in vertical applications they were not tied off enough and moved a lot during the pours. We've been told a bead of sika swell in the middle of the joint and then a cant strip of caulking after the forms are removed generally work as well and are easier to do.
3. Talk to sika about this. Their tech department is very knowledgeable and would likely have come across this situation before.

 

[fel3]

For Q1, what about one of the Xypex admixtures or surface treatments? I have only used Xypex as a surface treatment for concrete protection in sewage wet wells, but I noticed that they advertise improved freeze-thaw durability.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[Ron]

I would increase to 4000 psi and use 6 to 7 percent air. You can add a sealer, but it is temporary. Xypex won't help to any great degree. There is nothing better for durable concrete than to have a proper mix design and control the delivery, placement and curing.

 

[concretemasonry]

Here, the better and larger concrete suppliers will not even deliver concrete for sidewalks or driveways unless it is 4000 psi and 5% to 7% air. The dispatchers do an initial screening by asking if it is exterior flat work or just a interior basement floor slab. The drivers have the authority to not unload if they see the job is exterior flat work and the dispatchers just reroute the load to another job and the regular contractors know the policy.

The suppliers would rather lose a single small job than get tangled up in a legal battle with owners and contractors. The result is that the higher strengths are common and material cost difference is minimal compared to the cost to deliver concrete a few miles. - For those suppliers that are in both concrete and aggregates, they say that concrete is the most expensive way to sell aggregate considering the plant investment and the extremely high truck costs (purchase, maintenance wages, fuel and scheduling).

Of course, if an engineer specifies a 3000 psi strength for a project they will deliver it and always can monitor the delivery logs (batching weights, batch time, transport time, waiting time and unloading time)in case there is a problem with the concrete. - It is a lot different than when I was working for the local DOT as a concrete inspector when we just grabbed aggregate samples and made cylinders for state projects. That was good summer work for an engineering student considering the long hours and banking overtime to get checks in the fall when I was back in school. It made the 2:00 AM or 4:00 AM starts for large jobs worthwhile.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Lesali]

Thanks to all for the feedback.