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FIGURE 15.10 Strain hardening phenomenon of fiber-reinforced concrete.

reaches its tensile strength. The multiple cracking process eventually leads to homogenization of matrix cracks, that is, the end of multiple cracking at which the minimum crack spacing, determined by the interfacial bond properties, is reached.

• In stage 4, no further matrix crack is expected and the additional load is only sustained by the fibers.

To study the multiple cracking and associated interfacial bond behavior, experiments have been conducted on the cementitious composites reinforced with continuous glass, polypropylene, and steel fibers. Three recently developed techniques, laser holographic interferometry, quantitative optical microscopy, and moire interferometry, are being employed in the investigation.

Recent studies have shown that the response of FRCs also depends on the methods of processing. Along this direction, successful applications of pultrusion and extrusion techniques in manufacturing cement composite products are two good examples. Pultrusion is employed to incorporate continuous fibres into the cement matrix. Composites with fiber volume ratio of more than 10% could be produced. Strain hardening type of response is the direct result of a tremendous enhancement in tensile strength. Extrusion can also lead to a strain hardening type of response. It is obvious that special processing compacts matrix with fibers to a low porosity, controls fiber direction and distribution, and improves the interfacial bond between fiber and matrix, which in turn leads to a class of high-performance FRCs with strain hardening.

So far, the application of FRCs in structural components are used for inhibiting cracking, for improving resistance to impact or dynamic loading, and for resisting material disintegration such as airport runway and pavement. This is partly due to high cost. For example, for SFRC, 1% by volume will increase the cost by US$52 per cubic meter.

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