3 new ways to test concrete: (1/3) shear strength.

Shear strength is an important concrete property in research and concrete construction, it is important in structural analysis and design, in the evaluation of failure models, and computational mechanics of concrete. The evaluation of concrete shear strength and concrete behavior under shear stresses can today be considered an open research topic and one of the last frontiers of knowledge in the area of concrete testing and concrete mechanical behavior. Prior to the development of the Nogueira Torsion Test (NTT), concrete shear strength was difficult to evaluate. The NTT allows the application of torques in cylindrical specimens with circumferential notches and a straightforward evaluation of antiplane shear strength. With the NTT device, notched concrete specimens with standardized 4 x 8” (100 x 200 mm ) size can easily be tested. The circumferential notch creates a potential shear fracture circular area. A ratio between the circular notch depth and cylindrical specimen radius of approximately 0.40 can be used to ensure that the antiplane shear crack will initiate and propagate in the notched cross section, preventing crack propagation beyond the circular notch. For the standard 4 x 8” (100 x 200 mm ) concrete cylinders a circumferential notch ¾” (approximately 20 mm) deep can be used. After the notched specimens are placed in the NTT, the vertical load can be applied and the antiplane shear strength, f_sh-ant, calculated using f_sh-ant = (P/A_N)·(R/r), where P is the maximum applied load, and A_N = π·r^2 is the area of the notched cross section (r is the radius). Fig. 2 shows a notched specimen before the test and three specimens after the test.