Flexural Strength Essay

2.1.8.4.1 Flexural Strength:

Flexural strength is one measure of the tensile strength of concrete. It is a measure of an unreinforced concrete beam or slab to resist failure in bending, as shown in figure (2.23). It is measured by loading 150 x 150 mm concrete beams with a span length at least three times the depth. The flexural strength is expressed as Modulus of Rupture (MR) in MPa and is determined by two standard test methods: a) the third-point loading test that the half of the load is applied at each third of the span length, b) the center-point loading test which the entire load is applied at the center span. The MR of center-point loading is greater than MR of third-point loading. (ASTM C 78 and ESS 203) Figure (2.23): Test set-up for flexure strength. (ASTM C 293 and ASTM C 78)

The concept of modulus of rupture is

(Russell, 2009) made a comparison of modulus of rupture versus concrete compressive strength shown in figure (2.24) for data by (Shideler, 1957), (Malhotra, 1990), (Hoff, 1992), (Heffington, 2000), (Ramirez, 2000), (Meyer, 2002), (Tasillo, 2004), (Harmon, 2005), (Ozyildirim and Gomez, 2005). These data were for a variety of concrete unit weights, aggregate sources, curing conditions, and specimen sizes. Slate (1986) recommended a modulus of rupture as Eq. (2.19) for compressive strengths from 20 to 60 MPa for moist cured lightweight concretes. MR= 0.21 (fc') 0.5 (2.19)

Where:

MR is the modulus of rupture in MPa; fc' is the cylinder compressive