Bleach is very good for algae. I doubt that it'll do much to weeds growing in the cracks. Herbicide seems a better bet.
Use Full Strength and get 20% if you can find it for better control. http://www.amazon.com/EE-20-Vinegar-Gallon/dp/B0031AY1LA http://maestro-gro.com/vinegar20acidity.aspx http://oregonstate.edu/dept/nursery-weeds/weedspeciespage/acetic_acid_factsheet.pdf