Uses for Flexural Concrete

Definition

• Flexural strength is defined as a measure of tensile strength, according to the NRMCA's Concrete in Practice publication. By measuring and recording the ability of a slab or beam of unreinforced concrete to resist bending under a specified load, it can be given a number recorded in MR. "MR" stands for modulus of rupture in pounds per square inch.

Procedure

• To determine a concrete's MR, a test slab is used. This beam is 6-by-6 inches, with a length three times its depth/width. It is tested for third-point loading and center-loading capacity. Third-point loading involves splitting the test load in half and placing each half at each third of the beam's length. Center-point loading involves placing the entire load in the center of the beam. The center load indicates a higher strength than when a load is more evenly spread over the beam.

Result

• Traditionally, and especially for paving purposes, concrete strength is tested using the cylinder compression test. In this test, a compression machine is used on cast cylinders of concrete moistened and treated by molten sulfur. Flexural strength tends to equal 10 percent to 20 percent of traditional compressive strength. Flexural concrete is most used for design purposes such as in buildings where the concrete is not the sole load bearer or in decorative walls or fences, fountains and similar applications.

Proper Development

• "Flexural" concrete loses its meaning if the beams tested are not handled properly. Beams that are allowed to dry out on the surface during curing, or that are not soaked in lime water for 20 hours pretesting, may test with a much weaker tensile strength than the same batch of concrete that is handled correctly. In addition, different mixes, or batches, of concrete also test differently, because the recipe ratios change the composition of the concrete. Beams should be cast using the mix to be tested, because a beam sawed off the edge of a formed and cured slab has a significantly reduced strength compared to beams that are cast.