This may or may not help, but for what it's worth... I cut a vent hole for my dryer through a concrete block wall by using cement drill bits and a cold chisel. I drilled a series of holes along the lines I wanted and worked on what remained between the holes with a cold chisel. Since then I realized that a better way would be to use one of those waffle-looking discs on my drill that you can get in a home improvement center. They say they can cut concrete. I haven't used them on concrete but I have cut about 20 ft. of ceramic tile with them. A drill is much lighter than a saw, and for me that's important. Any combination of these methods might work. Good luck.