corrosion of rebar is so significant that there are specs for the acidity of rock used for agregate in the concrete. Older rock that has been "washed" by billions of years of water permiating it , is then used, fetching a premium. Look into it and there are periability numbers for everything, which is how water has gained it's reputation as the universal solven, and granite, hard as it is, is also a bit of a sponge. What is harder to figure is the use of a lot of carbon in rebar, which makes it harder and with a higher tensile stength, but with greater rates of corrosion, somehow the calculation is to not use an ultra low carbon steel with some nickle and larger cross sections along with low acid chemistry in the concrete.