TABLE1 MIX PROPORTIONS OF CONCRETE Weight per unit volume (kg/m3) 159 350 800 1,040 W C S G SP 1.75 s/a (%) 45.0 W/C (%) 46.0 Max size (mm) 20 Air (%) 2.0 Slump (mm) 150 SP: Superplasticizer The concrete structures are continually subjected to oscillatory loads. The stresses due to the oscillatory loads cause fatigue in such structures. The phenomenon of irreversible and progressive damage in a material subjected to cyclic stress is called fatigue. Generally, concrete structures are designed as the reinforced steel is yielded. The failure of concrete structures by fatigue is also strongly affected by the yield of steel. On the other hand, a crack of concrete can form and then grow by fatigue and concrete structure loses the serviceability before the failure of concrete structure occurred. The growth of fatigue cracking in concrete is attributed to the inherent weakness of concrete in tension. Potentially useful improvements in the mechanical behavior of concrete can be affected by the incorporation of fibers [6]. In this study, the effects of the type of fibers that influence the composite behavior of reinforced concrete have been investigated under cyclic loading conditions. The aim was to quantify the delay in the fatigue crack initiation and further propagation in the concrete matrix due to the addition of fibers. In this study, two types of fiber was used, either polypropylene or steel fibers which are different especially in Young’s modulus. The method to judge the performance of concrete with different types of fiber under service load is investigated. EXPERIMENTAL PROGRAM The proportioning of the concrete mixtures for testing is summarized in Table 1. Superplasticizer admixture was used as 0.5 % of the total cement. All concrete mixtures were prepared with ordinary Portland cement with 3.15 g/cm3 density. The fine aggregate used in concrete was natural river sand with 2.55 g/cm3 density and 2.3 fineness modulus. The coarse aggregate was crushed sand stone with 20 mm maximum size and 2.73 g/cm3 density. Two types of fiber, either polypropylene fibers or steel fibers have generally been used in RC structural members with either 0.5 % or 1.0 % by volume. The fibers were replaced with a part of aggregate. The diameter and length of each fibers are 0.6 mm and 30 mm, respectively. The densities of steel and polypropylene fibers are 7.65 g/cm3 and 0.92 g/cm3, respectively. In the test for flexural static and cyclic loading, four points loading was applied to the specimen. Deflection measurements were obtained using a dial gage accurate to 0.01 mm. Measurements were recorded at midspan. Cracks width was measured at the bottom of specimen using a microscope reading to 0.02 mm. The RC T-Beam tested in flexural cyclic loading is shown in Figure 1. The load fluctuated between 10 % and 60 % of the ultimate load obtained in static flexure test, that is, between 147 kN and 49 kN. The test loads were applied at 300 cycles per minute (5 Hz). The crack width was measured when each T-Beam was loaded up to the upper limit, 147 kN statically. 1,300 mm 500 mm 320 300 200 Figure 1: Set up of RC T-beam
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