When using a circular saw to cut asphalt, you'll need a diamond-tooth blade with the proper venting system. The vents between each tooth facilitate the removal of asphalt material as well as provide heat reduction during the cutting process. When cutting masonry material with a circular saw, use a worm drive instead of a conventional saw as working with masonry material can put a high amount of stress on a saw's motor. The worm drive will take some of the torque stress off the saw's electric motor, which may help prolong the tool's lifespan.
Place two marks on the asphalt to indicate the cut line using a brightly colored crayon for easy visibility. Snap a line between the two marks using a chalk box.
Insert a properly vented diamond-tooth saw blade into a circular saw designed to cut asphalt material. Check the circular saw to make sure the housing, cord and all safety features are in proper working order before operating the tool.
Rest the front lip of the circular saw's cutting table onto the ground and align the blade with the indicated cut line. Pull the blade housing back to expose the blade. Squeeze the saw's power trigger and allow the blade to spin to the full rpm.
Gradually swing the blade down into the asphalt. Move the saw in a back and forth motion while making the first plunge cut into the asphalt; doing so will make the hole slightly bigger than the cutting blade, which will help prevent kickback and blade damage.
Stop the circular saw, while the blade is still inside the cut, if you hit dirt or stone. Adjust the circular saw's cutting table by releasing the swing nut at the front and pushing down on the table so that the blade will only cut to the thickness of the asphalt.
Raise the blade out of the cut slightly and squeeze the saw's trigger to allow the blade to spin at the full rpm. Swing the blade back down into the cut and push the saw forward slowly to allow the diamond-tooth blade to cut the asphalt material.
Release the circular saw's power trigger to allow the blade to stop inside the cut once you reach the end of the cut. Raise the saw out of the cut and place it to the side. Avoid any contract with the hot blade housing or blade to prevent burns.