3 new ways to test concrete: (3/3) tensile strength.

Concrete tensile strength is an important parameter in concrete design for several reasons. Concrete tensile strength has a strong and direct influence in the durability and serviceability of reinforced concrete members. In addition, tensile strength of concrete can be considered in the design of plain concrete structures. Nowadays, three methods are commonly used to evaluate concrete tensile strength: direct tension, flexural strength, and splitting tension. Direct tension tests are very difficult to perform because of secondary stresses introduced in the loading process. Flexural tests require the use of beams with rectangular cross sections and the results tend to overestimate concrete tensile strength. The third method is the splitting tension test (sometimes called Brazilian test); the method uses cylindrical specimens but the results tend to overestimate the tensile strength and are influenced by the wood strips attached to the surface of the specimens to apply the loads. With the Nogueira Torsion Test (NTT), using concrete cylindrical specimens without notches, the helical tensile strength f_hel (σ_helical, at maximum applied load P) can be easily calculated using f_hel = P/A, where P is the maximum applied load, A = π·R^2 is the cross sectional area of the cylinder, and R is the radius of the cylinder. When tested with the NTT, concrete cylindrical specimens develop a helical tensile crack, as shown in Fig. 4.