Mechanics of natural fibre reinforced cementitious composites

4 Mechanics of natural fibre reinforced cementitious composites 

Andonian etal. [27] used the composite materials approach, in the form of the rule of mixtures, to account for the strength properties of the composite. They used the same concepts as those described for asbestos-cement composites (Eqs 9.8 and 9.9, Chapter 9), namely, that strength can be calculated as the sum of the effects of the matrix and the fibres the fibre contribution is governed by pull-out and is a function of r /c/, while the matrix contribution is a function of the strength of a void-free matrix, umo, multiplied by its solid content, (1 - Vq). Therefore, For tensile strength  

Fracture mechanics concepts have also been applied to predict the behaviour of natural fibre FRC. Fracture parameters were found to be dependent on the moisture content, with wet composites having higher toughness values [40,51], Wet composites were also found to be notch-insensitive, suggesting that LEFM cannot adequately model the behaviour of such composite [51 ]. This was probably the result of the cracking mode, in which the crack path was tortuous, with some fibres failing by pull-out. 

Flughes and Flannant [52] examined the effects of moisture on the first crack stress, by considering the reduction in the modulus of elasticity of the wet fibre, and using the concepts of crack arrest when the fibre spacing is less than the critical flaw size [52], Their results, assuming a fibre modulus of elasticity of 4 and 40 GPa for wet and dry conditions, respectively, are presented in Table 11.7. If the bond is assumed to remain constant, at about 0.5 MPa (as suggested by Andonian etal. [27]), the matrix failure strain should increase in the wet state. If the bond increases 

Moisture state Fibre modulus (GPa) Bond strength (MPa) Matrix failure strain (%) Maximum fibre stress across a stable flaw (MPa) 

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I 1.4 Mechanics of natural fibre reinforced cementitious composites... 

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