Photo 1: Mode of failure of control beam 0 25 50 75 100 Load / max. load - % 0.00 0.50 1.00 1.50 2.00 Crack width - mm Control Steel fiber: 1.0% Steel fiber: 0.5% 100 mm 100 100 100 Figure 9: Effect of ratio of load / max. load on crack width Photo 2: Mode of failure of polypropylene fibers beam 0 25 50 75 100 Load / max. load - % 0.00 0.50 1.00 1.50 2.00 Crack width - mm Control Polypropylene: 0.5% Polypropylene: 1.0% 100 mm 100 100 100 Figure 10: Effect of ratio of load / max. load on crack width width is not increased so much when the fibers is used. The fibers can restrict the crack propagation under service load even if polypropylene fibers whose Young’s modulus is about one tenth of steel fibers is used. These results can not be explained the flexural toughness factor obtained by Eqn. 1. A number of previous experimental investigations have also established that cyclic loading not only affects the strength but also the serviceability, such as deflection and crack width, of reinforced concrete members [7]. Figures 9 and 10 show the relationship between crack width and load. The result shown in Figures 9 and 10 are obtained by using concrete with steel fibers and polypropylene fibers, respectively. The vertical line of these figures is the ratio between applied load and the maximum load. The crack width was measured at center of specimen. The specimen was made 5 mm raid to introduce the cracking. The control specimen was suddenly broken when the crack width reached at 0.5 mm. However, the concrete with fibers sustained the load of the half of maximum load at 2.0 mm crack width. The relationship between crack width and load of concrete with polypropylene fibers is almost same as that with steel fiber. The crack propagation under cycle service load may depend on the sustaining ability of load after cracking.
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