One device, three ways to test concrete.

The Nogueira Torsion Test (NTT) is a new patented device that allows conducting 3 different procedures to test concrete using cylindrical specimens. The device was initially conceived to apply loads in concrete cylindrical specimens in order to evaluate damage under torsional stresses and antiplane shear using ultrasound. The NTT apparatus was made public in 2016, in a marketing summary (Nogueira Torsion Test for Concrete Cylindrical Specimens – Marketing Summary) and was patented in 2019.  The NTT apparatus can be used with any universal testing machine to apply torsion to concrete cylindrical specimens. Concrete cylinders with dimensions 4 x 8” (100 x 200 mm) and concrete cores - diameter 4” (100 mm) and length 8” (200 mm) or more - can be used. The specimens can be easily inserted in the apparatus and, after the test, removed from it, allowing the tests to be quickly and easily performed. Experiments can evaluate (1) plain concrete shear strength, (2) interface shear strength (across a bonded interface between concrete and a substrate), and (3) helical tensile strength of concrete. The NTT (Fig. 1.a) simultaneously creates helical tensile (and compressive) stresses and shear stresses due to torsion (Fig. 1.b). If there is a circular notch around the cylinder (Fig. 1.c), antiplane shear stresses occur at the notched circular section (Fig. 1). With the application of the vertical force P downwards (using a universal testing machine), the torsional moments T created at the ends of the concrete cylinder are equal to T = (P/2)·R, where R is the radius of the cylinder. The polar moment of inertia of a notched circular cross section under antiplane shear is J = π·r^4/2, here r is the radius of the notched cross section (Fig. 1.c, in the notch, the radius is reduced from R to r). In the notched cross section, antiplane shear strength, f_sh-ant (= τ_max), that occurs at maximum applied load P, can be calculated using the torsion formula, τ = T·r/J, from the applied vertical load P and radii R and r (Eq. 1. Antiplane shear strength in a notched cross section.) Where A_N= π·r^2 is the area of the notched cross section.   If there is no circular notch, the helical tensile strength f_hel (σ_helical at maximum applied load P) can also be calculated from the formula above with r = R (Eq. 2. Helical tensile strength.) Here, A = π·R^2 is the cross sectional area of the cylinder.