Cylinders which have been subjected only to field curing conditions prior to testing may be used to assess the quality of the concrete as delivered. OA) True B) False The specified compressive strength of a concrete mixture is 30 MPa. If C-2 is chosen

Standard deviation is 3.6 MPa

The flexural strength (fr) of concrete measured from the bending test is always higher than the direct tensile strength (ft). In reality, the stress in the cracked part of the concrete is lower than ft. Also, failure may occur on the compressive side. Assuming NO tension softening (i.e., the stress in the cracked part stays at ft) and infinite compressive strength (i.e., compressive failure will never occur), draw the stress distribution over the depth of the beam at ultimate failure when the curvature of the section is approaching infinity. With this stress distribution, show that the upper bound of fr/ft is equal to 3.   (Hint: On rotating the section, because the compressive stress can increase well beyond ft, the neutral axis will continue to shift upwards.)

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