Concrete is the oldest manmade construction material and the most widely used. Primitive examples of it date back to the ancient Egyptians, and today’s concrete is of course much tougher and more consistent than anything they used. Modern concrete is used to make building foundations and floors, sidewalks, highway overpasses, dams, and more, and average concrete has a strength of about 3,000 psi or so. Some of the strongest concretes even have a strength of 20,000 psi. Still, concrete isn’t indestructible; sometimes, it needs to be lifted, prepped for epoxy, or have its cracks filled in. Fortunately, homeowners and commercial…