We have a pool and lots of concrete lines and cracks that grow weeds and grass. I use a cup of brussel sprouts (or cabbage), mashed up well, then I add 1/2 teaspoon liquid dish soap, mix well, add a little water if needed. Every Spring my husband pours this mixture around the pool, walkways and driveway, in every crack and line.
It prevents weeds from growing, no need for poison. Works well.