• Geomechanics and Engineering
• /
• v.10 no.5
• /
• pp.677-687
• /
• 2016

Industrialization and urbanization are the two phenomena that are going relentless all over the world. The consequence of this economic success has been a massive increase in waste on one hand and increasing demand for suitable sites for construction on the other. Owing to the surplus raw materials and energy requirement needed for manufacturing synthetic fibers, applications of waste fibers for reinforcing soils evidenced to offer economic and environmental benefits. The main objective of the proposed work is to explore the possibilities of improving the strength of soil using fly ash waste as an admixture and Human Hair Fiber (HHF) as reinforcement such that they can be used for construction of embankments and land reclamation projects. The effect of fiber content on soil - fly ash mixture was observed through a series of laboratory tests such as compaction tests, CBR and unconfined compression tests. From the stress - strain curves, it was observed that the UCC strength for the optimised soil - flyash mixture reinforced with 0.75% human hair fibers is nearly 2.85 times higher than that of the untreated soil. Further, it has been noticed that there is about 7.73 times increase in CBR for the reinforced soil compared to untreated soil. This drastic increase in strength may be due to the fact that HHF offer more pull-out resistance which makes the fibers act like a bridge to prevent further cracking and thereby it improves the toughness which in turn prevent the brittle failure of soil-flyash specimen. Hence, the test results reveal that the inclusion of randomly distributed HHF in soil significantly improves the engineering properties of soil and can be effectively utilized in pavements. SEM analysis explained the change of microstructures and the formation of hydration products that offered increase in strength and it was found to be in accordance with strength tests.

• Journal of the Korea Concrete Institute
• /
• v.18 no.1 s.91
• /
• pp.73-82
• /
• 2006

Nowadays, the general stripping work of form has brought some problems; increase of total constructing cost resulted from the man-dependent form work procedure and environmental issues by wasting the debonded form. In this study, to effectively reduce unnecessary cost and resolve the environmental problems caused by these kinds of reason, a permanent form method using stainless steel fiber was introduced then its material and structural characteristics were evaluated. In the case of material characteristic, the permanent form had a good ductile behavior in the result of flexural test of the permanent form panel and pull-out test of insert bolt which is installed in the permanent form and perfect bonding capacity with a field concrete. In the case of structural characteristic, compressive and tensile behavior of the permanent form was evaluated. It also showed a good structural behavior in the view of load-deflection relationship, crack patterns and additional strengthening effect.

• The Korean Journal of Ceramics
• /
• v.4 no.3
• /
• pp.193-198
• /
• 1998

This paper presents the effects of an initial braking velocity, a braking pressure, and the number of braking stop on the tribological behaviors for the three different C-C composites using an inertia dynamic-friction tester. The C-C composites were prepared through the processes of several cycles of pitch impregnation/carbonization with different friction surface texture such as continuous 8-harness satin fabric (ADD-1), chopped fiber (ADD-2) and chopped fiber (ADD-3) having higher fiber volume fraction on friction than ADD-2 by about 10%. ADD-1 exhibited a higher fraction coefficient (0.41~0.33) than those of ADD-2 and ADD-3 (0.32~0.26) under the various initial braking velocities and braking pressures. The fraction coefficients decreased with increasing the initial velocity and the braking pressures. Wear rate by the thickness change after every 25 stop indicated that ADD-2 and ADD-3 having 1.7~2.7 $\mu\textrm{m}$/stop/pair were much lower than that of ADD-1 showing 5.0~6.5 $\mu\textrm{m}$/stop/pair. All specimens showed a little bit lower wear rate during the middle stage than the initial and latter stages among 100 braking stops. ADD-1 showed higher friction coefficient and wear rate due to the active pull-out of the fibers, evidenced by thicker were film and wear debrises.

• Smart Structures and Systems
• /
• v.17 no.4
• /
• pp.593-610
• /
• 2016

In this study, an innovative and smart glass fiber-reinforced polymer (GFRP) hybrid bar was developed for stronger durability of concrete structures. As comparing with the conventional GFRP bar, the smart GFRP Hybrid bar can promise to enhance the modulus of elasticity so that it makes the cracking reduced than the case when the conventional GFRP bar is used. Besides, the GFRP Hybrid bar can effectively resist the corrosion of conventional steel bar by the GFRP outer surface on the steel bar. In order to verify the bond performance of the GFRP hybrid bar for structural reinforcement, uniaxial pull-out test was conducted. The variables were the bar diameter and the number of strands and pitch of the fiber ribs. Tensile tests showed a excellent increase in the modulus of elasticity, 152.1 GPa, as compared to that of the pure GFRP bar (50 GPa). The stress-strain curve was bi-linear, so that the ductile performance could be obtained. For the bond test, the entire GFRP hybrid bar test specimens failed in concrete splitting due to higher shear strength resulting in concrete crushing as a function of bar deformation. Investigation revealed that an increase in the number of strands of fiber ribs enhanced the bond strength, and the pitch guaranteed the bond strength of 19.1 mm diameter hybrid bar with 15.9 mm diameter of core section of deformed steel the ACI 440 1R-15 equation is regarded as more suitable for predicting the bond strength of GFRP hybrid bars, whereas the CSA S806-12 prediction is considered too conservative and is largely influenced by the bar diameter. For further study, various geometrical and material properties such as concrete cover, cross-sectional ratio, and surface treatment should be considered.

• Structural Engineering and Mechanics
• /
• v.89 no.6
• /
• pp.617-626
• /
• 2024

The study investigated the behavior of plain and fibered Ultra-High Performance Concrete (UHPC) beams under varying loading conditions using integrated analysis of the flexure and acoustic emission tests. The loading rate of testing is -0.25 -2 mm/min. It is observed that on increasing loading rate, flexural strength increases, and toughness decreases. The acoustic emission testing revealed that higher loading rates accelerate crack propagation. Fiber effect and matrix cracking are identified as significant contributors to the release of acoustic emission energy, with fiber rupture/failure and matrix cracking showing rate-dependent behavior. Crack classification analysis indicated that the rise angle (RA) value decreased under quasi-static loading. The average frequency (AF) value increased with the loading rate, but this trend reversed under rate-dependent conditions. K-means analysis identified distinct clusters of crack types with unique frequency and duration characteristics at different loading rates. Furthermore, the historic index and signal strength decreased with increasing loading rate after peak capacity, while the severity index increased in the post-peak zone, indicating more severe damage. The sudden rise in the historic index and cumulative signal strength indicates the possibility of several occurrences, such as the emergence of a significant crack, shifts in cracking modes, abrupt failure, or notable fiber debonding/pull-out. Moreover, there is a distinct rise in the number of AE knees corresponding to the increase in loading rate. The crack mapping from acoustic emission testing aligned with observed failure patterns, validating its use in structural health monitoring.

• Composites Research
• /
• v.12 no.3
• /
• pp.8-16
• /
• 1999

Carbon woven fabric/C/SiC composites were fabricated by multiple impregnations of carbon woven fabric/carbon preform with the polymer precursor of SiC, i.e., polycarbosilane. In addition, two kinds of low density carbon/carbon preforms which had different fiber volume fraction and fiber orientation, i.e., a carbon woven fabric(${\thickapprox}$55 vol%)/carbon and a chopped carbon fiber${\thickapprox}$40 vol%)/carbon composites, were reaction-bonded with a silicon melt at 1$700^{\circ}C$ in a vacuum to fabricate dense carbon fiber/Si/SiC composites. The reaction-bonding process increased the density to ~2.1 g/$cm^3$ from 1.6 g/$cm^3$ and 1.15 g/$cm^3$ of a carbon woven and a chopped carbon preforms, respectively. All of the composites fractured with extensive fiber pull-out. The higher the density the higher the stiffness and proportional limit stress. The mechanical properties obtained from a three-point bend and tension tests were compared. The ratios of the peak tensile stresses to the bending strengths of a carbon woven and a chopped carbon composites were about one-third, respectively. The carbon woven fabric/Si/SiC composites with density of 2.06 g/$cm^3$ showed ~120 MPa of ultimate strength and ~80 MPa of proportional limit in bend testing.

• Macromolecular Research
• /
• v.13 no.2
• /
• pp.81-87
• /
• 2005

Blends of silicone rubber (VMQ) and liquid crystalline polymer (LCP) were prepared by the melt mixing technique. Mechanical, XRD, thermal and dynamic mechanical investigations are reported for the pure silicone rubber and blends. The mechanical properties, viz. the tensile strength, tear strength and elongation at break, of the silicone rubber decreased with the addition of LCP. The SEM study on the tensile fractured surface of the blends revealed that they had a two phase structure, and that the failure was mainly due to fiber pull out, which suggests that the VMQ and LCP are incompatible in all of the proportions examined in this study. However, the FTIR study shows that there was a partial interaction between the VMQ and LCP, but which may not be sufficient to grip the fibrils under the applied load. In the XRD analysis, it was observed that the crystalline structure of the silicone rubber deteriorated in the presence of LCP. The DMA study suggested that the storage modulus of the silicone rubber was improved with the addition of LCP, due to the high modulus of the LCP phase. The thermal stability of the silicone rubber was greatly reduced by the addition of LCP, due to the latter having a thermal stability lower than that of silicone rubber.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10b
• /
• pp.1031-1036
• /
• 2000

In this study, a numerical simulation that can effectively predict the strengthening effect of repaired aged RC structures is developed using the axial deformation link elements. In repaired structures, concrete and interface are modeled as quasi-brittle materials. An elastic-perfectly plastic constitutive relationship is introduced for reinforcing bars. Also, a linear-elastic relationship for repair materials such as FRP or CFS. Structural deterioration in terms of corrosion of steel rebar is considered. The interfacial property between steel and concrete which is reduced by corrosion of steel rebar is obtained by comparing numerical results with experimental results of pull out tests. Obtained values are used in repaired reinforced concrete structures under flexural loading conditions. To investigate strengthening effect of the structures repaired with carbon fiber sheet(CFS), repaired and unrepaired RC structures are analyzed numerically. From analysis, rip-off, debonding and rupture failure mechanisms of interface between substrate and CFS can be determined. Finally, strengthening effect according to the variation of interfacial material properties is investigated, and it is shown that interfacial material properties have influence on the mechanical behavior of repaired structure systems Therefore, the developed numerical method using axial deformation link elements can use for determining the strengthening effects and failure mechanism of repaired aged RC structure.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.4A
• /
• pp.279-286
• /
• 2011

FRP (Fiber Reinforced Polymer) tendons can be used as an alternative to solve the corrosion problem of steel tendons. Material properties of FRP tendons-bond strength, transfer length, development length-must be determined in order to apply to concrete structures. First of all, in case of application for pretension concrete members with CFRP tendons, transfer length is an important characteristic. The bond of the material characteristics should be demanded clearly to apply to PSC structures prestressed with FRP tendons. This paper investigated on the bond characteristics of FRP reinforcements with various surface-type. To determine the bond characteristics of FRP materials used in place of steel reinforcement or prestressing tendon in concrete, pull-out testing suggested by CAN/CSA S806-02 was performed. A total of 40 specimens were made of concrete cube with steel strands, deformed steel bar and 6 different surface shape FRP materials like carbon or E-glass. Results of the bonding tests presented that each specimen showed various behaviors as the bond stress-slip curve and compared with the bond characteristic of CFRP tendon developed in Korea.

• Journal of the Korea Concrete Institute
• /
• v.24 no.6
• /
• pp.761-768
• /
• 2012

The purpose of this study is to investigate bond properties of GFRP used in SFRC (Steel fiber reinforced concrete) and normal concrete. The experimental variables were rebar diameter (D13, D16), steel fiber volume fraction (0~2%) and cover thickness ($1.5d_b$, $5.4d_b$). The experimental results showed a different failure mode depending on the cover thickness. Through the tested specimens, splitting failure occurred for the specimens with small cover thickness and pull out failure occurred in the specimens with large cover thickness. Introduction of steel fiber caused the specimens to have more ductile behavior of bond stresss-lip after peak stress, but they did not increase the bond strength significantly. These failure modes were shown in both steel reinforcement and GFRP. However, from the difference of micro structure of bond failure mechanism between steel rebar and GFRP rebar, more ductile behavior was observed in GFRP-specimens after maximum bond strength was reached.