The effect of admixtures of the concrete on flexural tensile strength is studied by Siddiqui (2011) and Amudhavalli and Mathew (2012) . They concluded that optimum amount of silica fume is 10â15% and of fly ash is about 15% for maximum compressive and flexural strength.he deflection and cracking behavior of concrete structure depend on the flexural tensile strength of concrete. Many factors have been shown to influence the flexural tensile strength of concrete, particularly the level of stress, size, age and confinement to concrete flexure member, etc.