Tensile strength of concrete
Concrete has such low tensile strength that tensile stresses are avoided in civil structures. However, tensile strength controls the durability of concrete, so we measure it using the splitting (or, Brazil) test. This loading configuration causes tensile stress between the points of contact (the blue-green hourglass shape in the photo below left).
Splitting test
The clear disk in the photo at left is a special plastic that, when viewed between cross polarizers) clearly shows the stress pattern. The black sticks are applying forxce on the top and bottom, as in the splitting test. The green-blue hourglass pattern shows the region of high tensile stress that pulls the sample apart laterally. The photo on the right shows a cylinder of cement past that was broken in the splitting test. The cracks run perpendicular to the direction of maximum tensile stress.