Control Joint in Curb

[PAeng22]

I have a 32ft x 42ft pile cap foundation with a 6" x 6" wide curb all around. The pile cap will be poured first with dowels projecting. The curb will be poured next. It has one #4 bar in the long direction. My question is this: Should I cut control joints in the curb at say 10' intervals or will the curb not crack since it is dowelled into the cap and reinforced. I'm using f'c=4000 conc with w/c ratio=.45 and 6% air entrainment. If I need control joints how long after the pour can/should they be cut?

 

[bolmanlp]

i do a lot of kerbs for Slabs on grade (I am English and we spell it differently) and have never cut a control joint...you need good qa/qc on the mix, well placed forms, good curing, and an experienced concrete placement company - I normally work in remote locations in Mexico with batch plants and I have to contend with very hot temperatures as well and have never had a crack in a kerb. Good luck

 

[Ron]

dmsbeam....Yes, I would put control joints in the curb. They should be spaced 8-10 feet apart and should be placed as soon after the concrete placement as possible, preferably as you are finishing the curb.

Dowelling will not stop cracks from occurring and the longitudinal rebar will not stop them either, it will just hold them tightly together.

I have to contend with very hot temperatures as well and have never had a crack in a kerb.

This defies all practicality of concrete technology. I would suggest that you look at some of those curbs that have been placed...you'll find the cracks.

 

[hokie66]

Agree with Ron. The curb will crack because it is restrained, and when the concrete shrinks, cracking is inevitable. If you don't mind the cracks, no problem. Sawcut joints are one way of attempting to make the cracks occur where you prefer.

 

[dik]

Agree with the other two dudes... and they should be cut 6 to 8 hours after finishing the curb (kerb). Since the curb is dowelled into the pile cap, the sawcut can cut the longitudinal bar... depth of cut should be approx 3".

Dik

 

[hokie66]

Why not 6"?

 

[dik]

Sure... 6" is better... just a little more work...

Dik

 

[hokie66]

To me, sawcutting a joint part way through an element when the unsawed part is visible makes little sense. Sort of like sawing a slab close to a column, and leaving the rest to crack. The sawing really is only to make cracks straight, to make them look better, and they don't look better when partially done...just my opinion.

 

[dik]

Sure...

Dik