Flexural toughness

Some contradictory results have been reported concerning the effect of the fiber type on the mechanical performance of fiber cement composites (i.e. enhancements in flexural toughness). 

Fig. 6 Carbon fiber content vs. flexural toughness of artificial woods.

Fiber in FRC Mix Vf Compressive Strength Flexural Strength Flexural Toughness Indices ... 

Method of test for flexural strength and flexural toughness of polymer-modified mortar... 

FIGURE 11. Fracture toughness as a function of alumina content for 10-YS alumina particulate and platelet composites at lOtXPC in air [2, 5, 6]. Flexure toughness of 10-YSZ/alumina particulate composites [2, 5, 6] is included for comparison. Error bars indicate 1.0 standard deviations. The lines represent the best fit... 

The main role of fibres is to bridge the cracks that develop in concrete and increase the ductility of concrete elements. Fibres increase the strain at peak load, as well as provide additional energy absorption ability of reinforced concrete elements and stractures. It was recently reported that they also considerably improve the static flexural strength of concrete as well as its impact strength, tensile strength, ductility and flexural toughness (Shah and Ribakov, 2011 Pacheco-Torgal and Jalali, 2011). 

ASTM C 1018. 2002. Standard Test Method for Flexural Toughness and First-Crack Strength of Fibre Reinforced Concrete. American Society for Testing and Materials, Annual Book of ASTM Standards. 

Brandt, A.M., Glinicki, M.A. (2003) Effects of pozzolanic additives on long-term flexural toughness of HPGFRC , in Proc. Int. Workshop on High Performance Fiber Reinforced Cement Composites HPFRCC-4, A.E. Naaman and H.W. Reinhardt, eds, Ann Arboi Michigan, pp. 399—408. 

A similar method unrelated to any particular beam dimensions, but presented in the form of flexural toughness indices was proposed by ASTM and is discussed by Johnston and Gray (1986). That concept is shown in Figure 10.29 as a load-deflection curve obtained for a third-point loading... 

Figure 10.28 Schematic load-deflection curves for element under bending in calculation of the flexural toughness, after Henager (1978).

Figure 10.29 Schematic curve for determination of the flexural toughness indexes according to ASTM C 1018 (1997).

These features of flexural toughness determination are related to the following two characteristics of fracture behaviour of brittle composites ... 

Figure 10.30 Examples of load-deflection curves with corresponding values of flexural toughness indices.

Johnston, C. D., Gray, R. J. (1986) Flexural toughness and first crack strength of fibre reinforced concrete, using ASTM Standard C1018, in Proc. RILEM Symp. Developments in Fibre Reinforced Cement and Concrete, R. N. Swamy, R. L.Wagstaffee, D. R,Oakley eds, Sheffield paper 5.1. 

ASTMC 1018-97 (1997) Test method for flexural toughness and first-crack strength of fiber-reinforced concrete (using beam with third-point loading). 

ASTM 1550 standard test method for flexural toughness of fibre reinforced concrete (using centrally loaded round panel). 

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