Tensile strength plain concrete

For members subjected to bending, the value of the modulus of rupture % rather than tensile splitting strength f is used in design. The modulus of rupture is measured by testing to failure, plain concrete beams 6 in. square in cross-section having a span of 18 in. and loaded at two points, each 16 in. equidistant from the end supports of the beam (ASTM C-78). 

TEPFERS, R., Tensile fatigue strength of plain concrete. J. Amer. Conor. Inst., 1979, 8, 919-33. 

There are less exotic ways of increasing the strength of cement and concrete. One is to impregnate it with a polymer, which fills the pores and increases the fracture toughness a little. Another is by fibre reinforcement (Chapter 25). Steel-reinforced concrete is a sort of fibre-reinforced composite the reinforcement carries tensile loads and, if prestressed, keeps the concrete in compression. Cement can be reinforced with fine steel wire, or with glass fibres. But these refinements, though simple, greatly increase the cost and mean that they are only viable in special applications. Plain Portland cement is probably the world s cheapest and most successful material. 

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