The example image there just uses a single instance of Cycles' noise node, which doesn't make the most detailed of varying textures. Start with the mix factor of 0 (just the constant roughness) and increase the mix factor until you start getting a nice breakup in the specular highlights. (overlay does a mix of brightening or darkening within a 0-1 range, so it's well suited to this sort of thing) Often I find it easiest to create this kind of effect by starting with a constant value roughness around where I want for the surface, then blending in some noise or concrete photos using a blend mode like overlay.
(I have a bunch of personal ones I shot at Fort Stevens) You can find these on any stock texture site, or try shooting your own if you find yourself at some place like an abandoned military site. Otherwise (or even with SD!) photographs of dirty concrete usually work wonders. If you have Substance Designer it has some nice noise patterns for this sort of thing. Assuming you're using a PBR shader, that is. It's just a matter of finding some good contrasty and varying detail to put in the roughness map and hitting the right range of values.
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