Testing methods for tensile strength

Direct tension tests of concrete are seldom carried out, mainly because the specimen holding devices introduce secondary stresses that cannot be ignored. The most commonly used tests for estimating the tensile strength of concrete are the ASTM C 496 splitting tension test and the ASTM C 78 third-point flexural loading test (Fig). In the splitting tension test a 15- by 30- cm concrete cylinder is subjected to compression loads along two axial lines which are diametrically opposite. The load is applied continuously at a constant rate within the splitting tension stress range of 0.7 to 1.3 MPa until the specimen fails. The compressive stress produces a transverse tensile stress, which is uniform along the vertical diam-eter. The splitting tension strength is computed from the formula

where T=tensile strengthP=failure loadl=lengthd=diameter of the specimenCompared to direct tension, the splitting tension test is known to overestimatethe tensile strength of concrete by 10 to 15 percent

Source: P. Mehta, Paulo Monteiro Concrete Microstructur