• Journal of the Korea Concrete Institute
• /
• v.14 no.6
• /
• pp.1032-1039
• /
• 2002

Since recycling waste glass as a material for concrete has a great advantage environmentally and economically, the US, Japan and other countries have started recycling waste glass widely and accumulating the technology of manufacturing equipment and its construction. However, there is no practical data on the mechanical property of concrete using waste glass. In this study, the mechanical property of the steel fiber reinforced concrete using waste glass was analyzed in terms of waste glass content(20vo1. ％, 40vo1. ％ as a part of fine aggregate) and steel fiber content(0.5~ 1.5vol.％). The results of this study are as follows : The workability of the concrete including steel fiber and waste glass decreases, as the inclusion rate of waste glass and steel fiber increases. The tensile strength, flexural strength and flexural toughness of the concrete including waste glass increase considerably, as the inclusion rate of steel fiber increases. From the results, the appropriate inclusion rate of steel fiber and waste glass is thought to be 1.0vol. % and 20vo1. ％, respectively.

• Advanced Composite Materials
• /
• v.16 no.4
• /
• pp.299-314
• /
• 2007

In the present study, natural fibers (jute, kenaf and henequen) reinforced thermoplastic (poly(lactic acid) and polypropylene) and thermosetting (unsaturated polyester) matrix composites were well fabricated by a compression molding technique using all chopped natural fibers of about 10 mm long, respectively. Prior to green composite fabrication, natural fiber bundles were surface-treated with tap water by static soaking and dynamic ultrasonication methods, respectively. The interfacial shear strength, flexural properties, and dynamic mechanical properties of each green composite system were investigated by means of single fiber microbonding test, 3-point flexural test, and dynamic mechanical analysis, respectively. The result indicated that the properties of the polymeric resins were significantly improved by incorporating the natural fibers into the resin matrix and also the properties of untreated green composites were further improved by the water treatment done to the natural fibers used. Also, the property improvement of natural fiber-reinforced green composites strongly depended on the treatment method. The interfacial and mechanical results agreed with each other.

• Computers and Concrete
• /
• v.19 no.4
• /
• pp.413-417
• /
• 2017

Concrete is a material popularly used in construction. Due to the load-bearing and external environmental factors during utilization or manufacturing, its surface is prone to flaws, such as crack and leak. To repair these superficial defects and ultimately and avoid the deterioration of the concrete's durability, numerous concrete surface protective coatings and crack repair products have been developed. Currently, studies are endeavoring to exploit the mineralization property of microbial strains for repairing concrete cracks be the repairing material for crack rehabilitation. This research aims to use bacteria, specifically B. pasteurii, in crack rehabilitation to enhance the flexural and compression strength of the repaired concrete. Serial tests at various bacterial concentrations and the same $Urea-CaCl_2$ medium concentration of 70% for crack rehabilitation were executed. The results prove that the higher the concentration of the bacterial broth, the greater the amount of calcium carbonate precipitate was induced, while using B. pasteurii broth was for crack rehabilitation. The flexural and compression strengths of the repaired concrete test samples were the greatest at 100% bacterial concentration. Compared to the control group (bacterial concentration of 0%), the flexural strength had increased by 32.58% for 1-mm crack samples and 51.01% for 2-mm crack samples, and the compression strength had increased by 28.58% and 23.85%, respectively. From the SEM and XRD test results, a greater quantity of rectangular and polygonal crystals was also found in samples with high bacterial concentrations. These tests all confirm that using bacteria in crack rehabilitation can increase the flexural and compression strength of the repaired concrete.

• Structural Engineering and Mechanics
• /
• v.75 no.1
• /
• pp.49-57
• /
• 2020

This paper presents a full-scale experimental test to investigate the flexural behavior of an innovative dovetail ultra-high performance concrete (UHPC) joint designed for the 5^th Nanjing Yangtze River Bridge. The test specimen had a dimension of 3600 × 1600 × 170 mm, in accordance with the real bridge. The failure mode, crack pattern and structural response were presented. The ductility and stiffness degradation of the tested specimens were explicitly discussed. Test results indicated that different from conventional reinforced concrete slabs, well-distributed cracks with small spacing were observed for UHPC joint slabs at failure. The average nominal flexural cracking strength of the test specimens was 7.7 MPa, signifying good crack resistance of the proposed dovetail UHPC joint. It is recommended that high grade reinforcement be cooperatively used to take full advantage of the superior mechanical property of UHPC. A new ductility index, expressed by dividing the ultimate deflection by flexural cracking deflection, was introduced to evaluate the post-cracking ductility capacity. Finally, a strut-and-tie (STM) model was developed to predict the ultimate strength of the proposed UHPC joint.

• Structural Engineering and Mechanics
• /
• v.78 no.3
• /
• pp.231-253
• /
• 2021

Pure bending loading conditions are not frequently occurred in practical engineering, but the flexural researches are important since it's the basis of mechanical property researches under complex loading. Hence, the objective of this paper is to investigate the flexural behavior of concrete-filled rectangular steel tube (CFRT) through combined experimental and numerical studies. Flexural tests were conducted to investigate the mechanical performance of CFRT under bending. The load vs. deflection curves during the loading process was analyzed in detail. All the specimens behaved in a very ductile manner. Besides, based on the experimental result, the composite action between the steel tube and core concrete was studies and examined. Furthermore, the feasibility and accuracy of the numerical method was verified by comparing the computed results with experimental observations. The full curves analysis on the moment vs. curvature curves was further conducted, where the development of the stress and strain redistribution in the steel tube and core concrete was clarified comprehensively. It should be noted that there existed bond slip between the core concrete and steel tube during the loading process. And then, an extensive parametric study, including the steel strength, concrete strength, steel ratio and aspect ratio, was performed. Finally, design formula to calculate the ultimate moment and flexural stiffness of CFRTs were presented. The predicted results showed satisfactory agreement with the experimental and FE results. Additionally, the difference between the experimental/FE and predicted results using the related design codes were illustrated.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.9 no.4
• /
• pp.602-608
• /
• 2021

Recently, research and development has been conducted to impart high performance and functionality to concrete materials by mixing various reinforcing materials into the matrix. Ductile fiber reinforced concrete using a large amount of fibers shows a distributed multiple cracking behavior, and various studies are being conducted on this material. However, research is focused on static behavioral analysis but studies on cyclic behaviors are not sufficient. In this study, beams were made of ductile fiber reinforced concrete with various fiber contents, and static and fatigue flexural tests were performed. As a result, the effect of fiber content on the flexural behavior was analyzed. Also, the applied load level and fatigue life relationship of ductile fiber reinforced concrete was proposed. Concrete with high ductile property could be achieved with a fiber content of 2%. When 0.5% fiber was more added, the maximum flexural strength was similar, but the flexural toughness is nearly doubled. On the other hand, there was no significant difference in the fatigue life of these two mixtures.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.734-737
• /
• 2004

The synthetic fibers such as polypropylene(PP) and polyvilyl-alcohol(PVA) fiber are poised as a low cost alternative for reinforcement in structural applications. It has been reported that synthetic fiber in cement composites can control restrained tensile stresses and cracks and increase toughness, resistance to impact, corrosion, fatigue and durability. High performance fiber reinforced cementitious composite(HPFRCCs) shows ultra high ductile behavior in the hardened state, because of the fiber bridging properties. Therefore, a variety of experiments have being performed to access the performance of HPFRCCs recently. The research emphasis is on the flexural behavior of HPFRCCs made in synthetic fibers, and how this affects the composite property, and ultimately its strain-hardening performance. Three-point bending tests on HPFECCs are carried out. As the result of the bending tests, HPFRCCs showed high flexural strength and ductility. HPFRCCs made in PVA or Hybrid fiber were, also, superior to PP of singleness. On the other hand, effect of sand volume fraction on HPFRCCs made in PP was insignificant.

• Advanced Composite Materials
• /
• v.16 no.4
• /
• pp.283-298
• /
• 2007

Environment-friendly composites reinforced with bagasse fiber (BF), a kind of natural fiber as the remains from squeezed sugarcane, were fabricated by injection molding and press molding. As appropriate matrices for injection molding and press molding, polypropylene (PP) and polycaprolactone-cornstarch (PCL-C) were selected, as a typical recyclable resin and biodegradable resin, respectively. The mechanical properties of BF/PP composites were investigated in view of fiber mass fraction and injection molding conditions. And the mechanical properties and the biodegradation of BF/PCL composites were also evaluated. In the case of injection molding, the flexural modulus increased with an increase in fiber mass fraction, and the mechanical properties decreased with an increase in cylinder temperature due to the thermal degradation of BF. The optimum conditions increasing the flexural properties and the impact strength were $90^{\circ}C$ mold temperature, 30 s injection interval, and in the range of 165 to $185^{\circ}C$ cylinder temperature. On the other hand, as to BF/PCL-C fully-green composites, both the flexural properties and the impact strength increased with an increase in fiber mass fraction. It is considered that the BF compressed during preparation could result in the enhancement in mechanical properties. The results of the biodegradability test showed the addition of BF caused the acceleration of weight loss, which increased further with increasing fiber content. This reveals that the addition and the quantities of BF could promote the biodegradation of fully-green composites.

• Macromolecular Research
• /
• v.11 no.2
• /
• pp.98-103
• /
• 2003

The mechanical properties and failure mechanisms of through-the-thickness stitched plain weave glass fabric/polyurethane foam/epoxy composites were studied. Hybrid composites were fabricated using resin infusion process (RIP). Stitched sandwich composite increased drastically the flexural properties as compared with the unstitched fabrics. The breaking of stitching yarns was observed during the flexural test and this failure mode yielded relatively high flexural properties. Composites with stitched sandwich structure improved the mechanical properties with increasing the number of stitching yarns. From this study, it was concluded that proper combination of stitching density and types of stitching fiber is important factor for through-the-thickness stitched composite panels.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.9 no.6
• /
• pp.170-177
• /
• 2000

Dense $Al_2$O$_3$-30%TiC and Si$_3$N$_4$ ceramic tool materials with various grain size were produced by sintering-HIP treatment and by gas-pressure sintering. The fracture toughness was measured by indentation fracture and indentation strength method for both ceramics with various grain size. The effect of the grain size on the fracture toughness was evaluated, and the correlation between fracture toughness and mechanical properties such as hardness, Young\`s modulus and flexural strength of these ceramic were also investigated. The highest fracture toughness of around 6.7 MPa.m(sup)1/2 was obtained in Si$_3$N$_4$ ceramics with grain size of 1.58${\mu}{\textrm}{m}$. With a larger grain size of $Al_2$O$_3$-30%TiC and Si$_3$N$_4$ ceramics, the fracture toughness was generally increased. The increased fracture toughness of these ceramic also improved the flexural strength although the hardness decreased considerably. Similar results were obtained in grain size and mechanical properties on both $Al_2$O$_3$-30%TiC and Si$_3$N$_4$ ceramic tool materials.