I am planning to install trench drain in front of my garage. The driveway to the garage is asphalt (less than 2" thick), and the space between the trench drain and asphalt will be filled with concrete. I am wondering whether the concrete will nicely meet the edge of the asphalt if I just pour concrete up to the asphalt without any form. Or, to have a better joint between concrete and asphalt, would it be better if I build a form for a concrete, pour concrete inside the form and fill the rest with asphalt patch? Underneath the asphalt driveway is soil.

2 Answers 2


If, when pouring the concrete right up against the asphalt, you end up with parts of the concrete that taper or feather out to less than say about 1.5 -> 2.0 inches thick you will have trouble keeping the concrete in one piece. The thin parts are likely to fracture and break off.

I suspect that if you rented a concrete type saw and cut off the asphalt in a nice square edge that you could then pour the concrete right up to it without a form. You will want to make sure the concrete is at least 3.5 -> 4.0 inches thick to make sure it stands up to be driven upon and changes of weather through winter seasons (if you live in a place where it freezes in winter).

  • You'll want to add stone under the concrete as well. Many times we'll do a control joint that's straight and let the concrete slush into the asphalt. Then the next time that the asphalt is replaced the contractor should sawcut the control joint and butt the asphalt right up to the concrete.
    – Dano0430
    Mar 17, 2021 at 21:21

If you saw cut the asphalt, you've got a nice edge for a premade expansion joint. You'll get a crack there anyway, so might as well start with a joint.

enter image description here https://www.wrmeadows.com/concrete-expansion-joints/

  • Generally speaking, you don't need an expansion joint next to asphalt. Asphalt is considered a flexible pavement and expansion joints are needed predominantly for long stretches of concrete that expand. (Think long roads, driveways or stretches of curb) or old/new joints. It might give you a nice break away joint though. In the OP's question the concrete can slush under the asphalt. If any future concrete work was done on the trench drain it would pull up the asphalt driveway.
    – Dano0430
    Mar 17, 2021 at 21:19

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