They're close, but not exact. I think concrete on usually given as 13.5 (0.0000135 in/inR), and steel as 11 (0.0000110). It's this difference that reduces RC l

They're close, but not exact. I think concrete on usually given as 13.5 (0.0000135 in/inR), and steel as 11 (0.0000110). It's this difference that reduces RC life expectancy from 100's of years (as advertised by the concrete industry in the early 1900's) to the neighborhood of 10-50 years that we typically see. Whereas glass and platinum, for instance, are generally considered to be exact, and are used for precision measuring and calibration.