Slab on Grade
Slab on Grade
(OP)
I was at an ACI Dinner/Meeting last night and the discussion was related to slabs on grade. The speaker, Paul Okamoto, noted that sawcutting should occur within an hour of the slab surface starting to drop in temperature after the initial rise. Is anyone familiar with this? With a laser temperature measuring device it should be pretty easy to determine when to start.
Dik
Dik






RE: Slab on Grade
RE: Slab on Grade
RE: Slab on Grade
He mentioned a free FEM program that he uses for slab design and I sent him eMail earlier today to get the name of it.
My wife's quite sick and I didn't have the time to stay and chat with him. I thought he was very well informed, an excellent speaker and very practical with a lot of 'hands-on' experience.
..., and the meal was OK.
Dik
RE: Slab on Grade
RE: Slab on Grade
RE: Slab on Grade
One point for someone on site is that sawcuts if done to early will chip the concrete edge even though being capable of supporting man and machine.
I believe its a bit of an art to determine when to sawcut because theres so many variables to consider on site.
Concrete will always crack in the wrong places anyway for whatever reason.
However just because its cracked doesn't mean it necessarily failed.
RE: Slab on Grade
RE: Slab on Grade
RE: Slab on Grade
12 to 24 hours is way too long; sawcutting should be done within 6 or 8 hours after finishing. If not, then you may as well let it continue to crack and sawcut/rout the cracks afterwards. Soffcut saws are great and allow you to sawcut within a couple of hours of finishing.
It is a bit of a myth that waiting for the next day and sawcutting deeper will improve the cracking. Not the case. IMHO, the three items for SOG construction are the strength, the slump and sawcutting at the correct time. It is also a myth that using low strength concrete is best because of the minimal cement content. Better to have high strength. I usually spec a max 3" slump... contractors hate it, but it's good for the slab; superplasticisers work really well.
Dik
RE: Slab on Grade
RE: Slab on Grade
That's a shame, as the Soff-Cut saws are readily available in most countries. Not cheap, but nothing is that is any good. I have had contractors specifically request permission to use Soff-Cut to expedite their next operation, which should be curing, but unfortunately is not always the case.
I agree with dik about his 3 items, but would add curing and joint design, especially for industrial floors.
RE: Slab on Grade
Also of utmost importance is not to restrain the concrete pavement in any way, but again its great in theory but sometimes just not possible in practice to do. No matter how soon the concrete is cut or the strength or slump if its restrained in some way it will crack.
RE: Slab on Grade