Mechanical effect of fibres in concrete

The mechanism of fibre reinforcement of the cementitious matrix in concrete has been extensively studied in terms of the resistance of the fibres, pullout from the matrix and as a result from the breakdown of the fibre-matrix interfacial bond. Undoubtedly, the knowledge of the individual phases as well as the interface between fibre and matrix is paramount in understanding the mechanical behaviour of FRC. There are a huge number of studies on the mechanical effect of fibres in concrete. The following sections will only 

Romualdi and Batson (1963) have shown that the tensile strength of FRC at the proportional limit is higher than that of the unreinforced matrix. Closely spaced fibres act as crack arrestors and reduce the stress intensity. In other words, the strength is related to the spacing between the fibres, as shown in Fig. 15.2. The average fibre spacing is calculated from Eq. [15.1]  

2 Theoretical and experimental strength ratio as a function of fibre spacing (adapted from Romuaidi and Batson, 1963). 

FRC may be classified in conventional fibre-reinforced concrete (FRC) and high-performance fibre-reinforced concrete (HPFRC). They are composites that present a distinct stress-strain response in tension (Fig. 15.4). The 

3 Structures of long and short fibres controlling crack propagation (adapted from Betterman et a ., 1995). 

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