Maggie's Farm

The Roman concrete recipe, while it grows stronger with time, still does not have near the compressive strength of modern Portland cement. For standard uses, concrete would have around 3,000 psi compressive strength. But for things like bridges and highway spans, it's more like 10,000 psi. And of course un-reinforced Roman cement can accommodate only compressive loads. It's the addition of steel reinforcement that allows modern concretes to withstand repeated load cycles, nominal tensions, and so forth. Now when they lay cement highways, they include threaded rods throughout that are post-tensioned after the cement sets up to make the roads super-strong.

In the oil patch, we pump cement all the time, basically to grout in the steel casings that we run when completing a hole section - it seals the wellbore along the outside of the casing string. It's conventional to use seawater as the mixing water when working an offshore well. Up to a point, the addition of salt (NaCl, CaCl, etc) accelerates the setting reaction, but past certain points, salts will actually retard setting.

It would be a real shame if other people started carrying around rolls of stickers that say something else. Maybe make them slightly larger, but same color, shape, and font - the better to cover with, carrying a different message entirely. What better things can you do while waiting at the gas pump, besides make a contribution to the insurrection?