This paper presents the findings of an experimental study to investigate the structural behavior of reinforced concrete (RC) beams externally strengthened with various types of kenaf fiber reinforced polymer composite laminates with 50% fiber volume content. The experimental parameters including flexural strength, stress-strain relationship, deflection, tensile stress and young modulus of beams strengthened by different kenaf fiber reinforced polymer composites are discussed. In order to test the flexural strength of the RC beams, a total of eight beams divided into two series were used. In each series, every two of the beams were strengthened with kenaf/epoxy, kenaf/polyester, and kenaf/vinyl ester composite laminates respectively. The remaining two were kept as control specimens. The experimental moment capacity of each beam was calculated using tensile strength and young modulus of the composites. Comparisons were made on the load-deflection, strain behavior and failure mode. Moreover, theoretical moment capacity of each beam was calculated using conventional formulation to verify experimental results. The research findings indicated that all strengthened beams improved structural performance where the maximum flexural strength increase by 40% and maximum deflection reduced by 24%.
This paper presents the experimental results on the effect of nano-CaCO3 on compressive strength development of mor-tars and concretes containing high volume fly ash (HVFA). The effect of various nano-CaCO3 contents such as 1, 2, 3 and 4% (wt.%) as partial replacement of cement on the compressive strength of mortars are evaluated in the first part. The nano-CaCO3 content which exhibited the highest compressive strength above is used in high volume fly ash mor-tars and concretes containing 40% and 60% class F fly ash. The results show that among four different nano-CaCO3 contents, the addition of 1% nano-CaCO3 increased the compressive strength of mortars and concretes. The addition of 1% nano-CaCO3 also increases the early age and 28 days compressive strengths of HVFA mortars and concretes. The X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis results also support the above findings.
This paper reports experimental and analytical results of shear capacity evaluation of concrete beams reinforced by PVA short fibers. Loading tests were carried out on various reinforced concrete beams with PVA short fibers of varying types and content, shear reinforcement ratios, effective depths, and shear span-to-effective depth ratios, a/d. The analysis was carried out using the tension-softening model obtained from the material test to simulate the beam shear tests. >As a result of the investigation, it was confirmed that shear capacity is improved by mixing PVA short fibers in concrete and that the increase in shear capacity is governed by fiber content and beam effective depth. Further, effective fiber behavior was confirmed in beams showing the tied-arch resisting mechanism. As a result of analysis, it was confirmed that the effect of the tension-softening model for diagonal cracks was large in beams with a small a/d, and that the effect of the shear transfer model was large in beams with a large a/d. Based on comparison with experimental results, we recommend the combination of constitutive laws in the evaluation and analysis of the shear capacity of FRC beams.
The body of data about the reaction kinetics of cement has greatly grown in recent years, and in terms of techniques for the prediction of the resulting hydrate formation phases, databases contributing to thermodynamic equilibrium calculations have been developed and are growing increasingly sophisticated. On the other hand, though many studies on cement aim to contribute to concrete engineering and numerical model researchers have pointed out the necessity of shedding light on the relationship between the microstructures generated by hydration and physical properties, such data remains scarce. This study investigated Portland cements using two commonly used water-cement ratios and three types of mineral compositions in the material age range of up to one year. The phase composition in relation to cement hydration was determined by X-ray powder diffraction and Rietveld analysis. In terms of physical properties, compressive strength and Young's modulus were measured through loading tests, and Young's modulus and Poisson's ratio were also obtained from the ultrasonic pulse propagation velocity of longitudinal and transverse waves. Further, water vapor adsorption tests to shed light on moisture behavior were conducted, yielding the BET specific surface area. Thermal conductivity, an important determinant of thermal behavior, was measured using the transient hot wire method. On the premise of the application of these physical properties to numerical calculations, their correlation with the information obtained from the phase composition was considered, leading to the proposal of simple and relatively high-accuracy empirical formulas. Further, background information about raising the correlation of these empirical formulas was also discussed.
The purpose of this study was to compare the fatigue test results of splitting tensile from flexural tensile tests and to develop a probability fatigue models of pavement concretes subjected to splitting tensile fatigue loading. To obtain this goal, splitting and flexural tensile fatigue tests were performed under constant amplitude loadings with three stress levels. Fatigue data analyses, probability distribution analysis of two-parameter Weibull and goodness-of-fit tests with the Kolmogorov-Smirnov method, were performed. The results were as follows: the standard deviations of fatigue life became bigger as the stress levels decreased for both tests. The distribution of fatigue lives for splitting tensile test would be comparable to those for three-point bending test. A guideline for excluding an unexpected fatigue data was proposed in this study: exclude the data either if it is out of bound at 0.9 R2 in S-N regression relationship or if it does not fail to fatigue limit. Fatigue damage was shown to be faster at the splitting tensile test than at the flexural tensile test. From the probability analysis at 5% significance level in each stress level, the probability density function of concrete pavement followed Weibull distribution function. Based on these results, probability fatigue models of pavement concrete subjected to cyclic loadings were proposed.
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