How is the strength of concrete measured?
The strength of concrete generally refers to its compressive strength. This is measured by casting cylinders while the concrete is still plastic and crushing them after 28 days. Most concrete has a specified 28 day strength between 20 MPa (3000 psi) and 35 MPa (5000 psi). If cylinders are not made cores can be drilled from the hardened concrete at any age and tested in the same way.
