Strength of Concrete

The compressive strength of concrete, its ability to resist compression, is very high, but its tensile strength, its ability to resist stretching, bending, or twisting, is relatively low. Concrete which must resist a good deal of stretching, bending, or twisting; such as concrete in beams, girders, walls, columns, and the like must be reinforced with steel. Concrete that must resist only compression may not require reinforcement. As you will learn later, one of the most important factors controlling the strength of concrete is the water cement ratio, or the proportion of water to cement in the mix. Another important factor is quality control during the placement of the concrete.