Question for all you Civils out there
- Thread starter MechGuy
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MechGuy
Well-known member
Well I bought the house about 4 years ago new, and the gap has slowly formed since then... I'm a bit ashamed to admit that I've probably been staring at this gap for a solid 2-3 years at least and saying to myself "you know, I should probably fix this!"
But I don't see any cracks in the garage slab or around the foundation so I'm hoping no major damage has been done so far.
A friend of mine who I work with who is a civil recommended getting some cheap fiber board that is used for sidewalk expansion joints instead of the grout. My only concern with that is cutting and fitting this fiberboard in around the rebar that is connected between the garage slab and the driveway. What do you all think about that route?
I know I know.. pictures forthcoming after work!
D
Dexman PE
There's rebar between the garage and the driveway slab, and the driveway is still moving?
FLBuff PE
Multi-disciplinary engineer
I would hope that the driveway slab is NOT connected to the garage slab with rebar. That is a major no-no in the geotech world. If you do that, you are asking for cracks that will form from differential movement of the garage and driveway slab. So, you shouldn't have to caut and form around the rebar. Each slab might have rebar in them, but hopefully they are not connected.
MechGuy
Well-known member
There is definitely rebar going from the garage slab to the driveway. I might just have to leave work early to take some pictures... I don't know if I can wait 
FLBuff PE
Multi-disciplinary engineer
Standard language in our reports states that exterior slabs should be separated from foundations and interior slabs. :dunno:There is definitely rebar going from the garage slab to the driveway. I might just have to leave work early to take some pictures... I don't know if I can wait
D
Dexman PE
yeah, different expansion rates due to varying temperature swings. This would definately lead to some significant cracking.Standard language in our reports states that exterior slabs should be separated from foundations and interior slabs. :dunno:There is definitely rebar going from the garage slab to the driveway. I might just have to leave work early to take some pictures... I don't know if I can wait
Unless the rebar is "sleeved" and only used to prevent vertical settling. The sleeve would allow the two slabs to expand/contract properly, but would prevent any vertical movement...
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MechGuy
Well-known member
OK, my wife was good enough to take some pictures and send them to me! What a gal
After looking at the pictures I realize my mistake... there is some concrete in front of the garage slab that has rebar connecting to the driveway. The garage door actually comes down directly after the garage slab.
So what do you all think? Does this shed some light on anything?
After looking at the pictures I realize my mistake... there is some concrete in front of the garage slab that has rebar connecting to the driveway. The garage door actually comes down directly after the garage slab.
So what do you all think? Does this shed some light on anything?
FLBuff PE
Multi-disciplinary engineer
It's a little hard to tell from the pictures, but is the crack a uniform width along the diveway? Is it just a horizontal crack, or is there some vertical movement as well?
Edit: Also, in the third picture, there is a crack on the slab near the slip joint between the sections; this could indicate movement at the outside of the slab section with the crack.
Edit: Also, in the third picture, there is a crack on the slab near the slip joint between the sections; this could indicate movement at the outside of the slab section with the crack.
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Chucktown PE
Well-known member
Those appear to be dowelled in to allow for lateral movement and restrict vertical movement. I would go with the non shrink grout option. I would use a bonding agent and paint it on the garage slab to get the non shrink grout to stick.
MechGuy
Well-known member
I believe it's just a horizontal gap... if there is any vertical movement I think it is very small.
D
Dexman PE
MechGuy
Well-known member
OK, at the risk of sounding really dumb here -- that's the black stuff on top, right?
Chucktown PE
Well-known member
Yes
Road Guy
Well-known member
if you were to ask a geotech that was being paid for their opinion they would tell you to tear out the whole thing, undercut 3 feet, replace with #57 stone, and repour the driveway...
of course there usually not the ones spending the money so thats the cadillac approach (sorry geo-techs, but thats how i see it whenever we call them)
of course there usually not the ones spending the money so thats the cadillac approach (sorry geo-techs, but thats how i see it whenever we call them)
D
Dexman PE
D
Dexman PE
Additionally, they would recommend post-tensioning the driveway, installing foundation beams, and adding #11 bar on 4" centers...if you were to ask a geotech that was being paid for their opinion they would tell you to tear out the whole thing, undercut 3 feet, replace with #57 stone, and repour the driveway...
of course there usually not the ones spending the money so thats the cadillac approach (sorry geo-techs, but thats how i see it whenever we call them)
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FLBuff PE
Multi-disciplinary engineer
Hey! I'm trying to help.if you were to ask a geotech that was being paid for their opinion they would tell you to tear out the whole thing, undercut 3 feet, replace with #57 stone, and repour the driveway...
of course there usually not the ones spending the money so thats the cadillac approach (sorry geo-techs, but thats how i see it whenever we call them)
:brick: And the hits just keep on coming.Additionally, they would recommend post-tensioning the driveway, installing foundation beams, and adding #11 bar on 4" centers...if you were to ask a geotech that was being paid for their opinion they would tell you to tear out the whole thing, undercut 3 feet, replace with #57 stone, and repour the driveway...
of course there usually not the ones spending the money so thats the cadillac approach (sorry geo-techs, but thats how i see it whenever we call them)
I agree that if it is just horizontal, fill as others have recommended. I'll take my geotech and enviro self back to writing reports. :sniff:
MechGuy
Well-known member
I was just going to fill it with dirt, but I figured I should at least so something that looks like I've given more than a half assed attempt at fixing the problem.
If I don't I risk my wife saying the inevitable quote: "Aren't you an engineer??"
If I don't I risk my wife saying the inevitable quote: "Aren't you an engineer??"
cement
gray haired dude
it has been cold, so it could be shrinkage...
ok, more seriously, the rebar dowels might be bridging a void under the driveway or even the garage floor. can you see down there? if it looks like there are extensive voids, the mud jack guy might be needed.
a proper mud jack aka pressure grouting, would have a guage on the pump to see the resistance of the placement area. i.e. 0-5 psi would indicate a void, 5 to 80 would indicate poorly compacted soil, then over 80 or 100 psi the slab would start to lift. I'm picking these numbers from distant memory, but you get the idea.
the non - shrink grout is a good idea if there is little or no void under the slabs, you should work it in with a trowel to make sue it fills the space at the bottom. then top it with a sealer as described above.
ok, more seriously, the rebar dowels might be bridging a void under the driveway or even the garage floor. can you see down there? if it looks like there are extensive voids, the mud jack guy might be needed.
a proper mud jack aka pressure grouting, would have a guage on the pump to see the resistance of the placement area. i.e. 0-5 psi would indicate a void, 5 to 80 would indicate poorly compacted soil, then over 80 or 100 psi the slab would start to lift. I'm picking these numbers from distant memory, but you get the idea.
the non - shrink grout is a good idea if there is little or no void under the slabs, you should work it in with a trowel to make sue it fills the space at the bottom. then top it with a sealer as described above.
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