Re: motor operated gates
backer rod is a round foam filler. Kind of like a string with a large diameter, made of foam.
I've run some tank monitors with cable installed in concrete the way you are talking about. We cut about a 1" deep slot, usually using two blades side by side on the concrete saw. We don't make 90 degree turns (eventually cuts the cable), instead we make 45 degree turns. We like to sandwich the cable between the backer rod. So after we make the cut, we push down a run of backer rod, then we install the cable and then push in another run of backer rod. Fill it with a one part urethane self leveling concrete caulk.
Backer rod comes in different diameters. Know what you need.
Running through asphalt has been problematic for us. The asphalt does not hold up too well, and tends to break off and damage the wire. We've done this in parking lots of C stores, so the asphalt is not of the highest quality (like roadways), and the cable we used is probably not a durable as it should be (manufacturer specified cable).