Strength Testing of Hardened Concrete| Concrete ...
· Beam specimens of concrete, cast per ASTM C31, and hardened in the horizontal position, are used for flexural strength testing. The most common size of beam mold is 6x6 inches and 20 to 21 inches long. As with cylinders, the smallest crosssectional dimension must be at least three times the nominal maximum size of the coarse aggregate.