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.
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).
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.