Adding to existing drive

[jk96]

I'm getting ready to form up and pour another section of concrete with the goal of eventually bringing the concrete up to the front of the house. Current slab is 5" thick. I'm wondering what the best method is to add to the existing slab. Should the existing slab be drilled and rebar epoxied in order to tie the two together or should the two slabs be allowed to float independently with an expansion joint?

 

[hawkeye08]

I don't know the answer to your concrete, but that looks like a Ferris IS2100Z perhaps?

 

[RedNeckRacin]

What type of soils do you have and what type of subbase do you have? Free floating slabs are easier but may shift more than desirable. Obviously if you can tie them together with rebar it will be better.

 

[jk96]

I don't know the answer to your concrete, but that looks like a Ferris IS2100Z perhaps?

Exmark LazerZ. Didnt have any Ferris dealers nearby a few years back so I didn't look at the Ferris mowers.

 

[jk96]

What type of soils do you have and what type of subbase do you have? Free floating slabs are easier but may shift more than desirable. Obviously if you can tie them together with rebar it will be better.

Soil drains well. Not sure of the mix. There is a decent amount of clay in spots. Sub base is 3-4" of rock that is well packed since construction 3 years ago. I've got the bits to drill the concrete and tie in. Just need to pick up some epoxy.

 

[Redlands Okie]

For sure drill holes and drive in rebar, epoxy helps. We usally use the same size of drill bit as the rebar diameter is. You need rebar pins on both sides of any cracks, existing saw cuts or expansion joints. Then the rest of the edge can be spaced out. 12 inch to 24 inch apart for the pins, more pins is better. Put rebar in the new concrete if at all possible. Not getting into a long discussion on if rebar is needed, or if fiber mesh or wire is good enough. Nothing replaces rebar. Try to plan ahead where saw cuts will be after you pour. Put rebar on both sides of the saw cuts about 6 inches away and then fill in between as needed. Once again 12 to 24 inch or in between, more rebar is better. #3 rebar ( 3/8 inch ) is prolly ok, #4 is better and less likely to be bent in shipping and handling. Perhaps a extra rebar at the edge where you drive up on to the new drive section. Any existing saw cuts or cracks will have a tendency to continue into the new concrete at the same place. So keep that in mind when planing your saw cuts. 40 ft of concrete in general between expansion joints as a rule of thumb10 ft squares after saw cutting is usually about as far as you want to go. . Pack the base before you pour !

 

[jk96]

For sure drill holes and drive in rebar, epoxy helps. We usally use the same size of drill bit as the rebar diameter is. You need rebar pins on both sides of any cracks, existing saw cuts or expansion joints. Then the rest of the edge can be spaced out. 12 inch to 24 inch apart for the pins, more pins is better. Put rebar in the new concrete if at all possible. Not getting into a long discussion on if rebar is needed, or if fiber mesh or wire is good enough. Nothing replaces rebar. Try to plan ahead where saw cuts will be after you pour. Put rebar on both sides of the saw cuts about 6 inches away and then fill in between as needed. Once again 12 to 24 inch or in between, more rebar is better. #3 rebar ( 3/8 inch ) is prolly ok, #4 is better and less likely to be bent in shipping and handling. Perhaps a extra rebar at the edge where you drive up on to the new drive section. Any existing saw cuts or cracks will have a tendency to continue into the new concrete at the same place. So keep that in mind when planing your saw cuts. 40 ft of concrete in general between expansion joints as a rule of thumb10 ft squares after saw cutting is usually about as far as you want to go. . Pack the base before you pour !

Thanks for taking the time to write up such a detailed post. I'm planning #4 bar with an 18" grid with extra bar on around the edges. Will probably just continue the existing saw cuts forward into the new slab. I was planning on using a 5/8 drill bit in order to get enough epoxy in the hole and around the bar. Sounds like you don't recommend this?

 

[Cord]

Generally, the best method is to have the apron (the slab next to the structure) bear on the foundation wall with the outside edge supported on frost footings. In your case you could get by by pinning it to the existing slab. Generally the problem is settlement of the backfilled material at the foundation wall. As this material settles the slab becomes unsupported and you end up with cracks. Now the settled apron slab is pointed towards the foundation and the cracks allow the water to enter the soil causing freeze-thaw expansion issues.

 

[Redlands Okie]

Thanks for taking the time to write up such a detailed post. I'm planning #4 bar with an 18" grid with extra bar on around the edges. Will probably just continue the existing saw cuts forward into the new slab. I was planning on using a 5/8 drill bit in order to get enough epoxy in the hole and around the bar. Sounds like you don't recommend this?

The tighter the fit the better, we often do no even use epoxy on pins for items such as driveways. Just hammer in the rebar pins.

 

[jk96]

Generally, the best method is to have the apron (the slab next to the structure) bear on the foundation wall with the outside edge supported on frost footings. In your case you could get by by pinning it to the existing slab. Generally the problem is settlement of the backfilled material at the foundation wall. As this material settles the slab becomes unsupported and you end up with cracks. Now the settled apron slab is pointed towards the foundation and the cracks allow the water to enter the soil causing freeze-thaw expansion issues.

The slab next to the house foundation and stem walls was poured about 3 years ago during initial construction. I'm simply tying into the existing slab to extend the driveway out so nothing new being poured next to the foundation.