"Why can’t we use carbon fiber or aluminum or anything that won’t rust?" You can. Stainless steel rebar is a thing and would, largely, solve the problem of sp

"Why can’t we use carbon fiber or aluminum or anything that won’t rust?" You can. Stainless steel rebar is a thing and would, largely, solve the problem of spalling due to rusting steel reinforcements. As you can imagine, stainless steel rebar adds a significant cost.