I'm going to cast a 200 (depth) x 100 (height) mm section over 2.3m (length) this is a replacement stooled window cill in concrete. I'm thinking I should use some form of reinforcement. I am concerned about the premature failure of the conventional mild steel rebar so was thinking I would use some 304 stainless steel round bar. What kind of diameter would any of you guys suggest for this size section? I was thinking 1 x 16mm dia over the length......