• Journal of Industrial Technology
• /
• v.17
• /
• pp.145-151
• /
• 1997

This paper presents evaluation results of the tensile behavior of reinforced high strength concrete. The effects of different sizes of reinforcing bar, ranging from D22 to D29, on the formation of cracks was investigated. Two different strength concretes, $270kg/cm^2$ and $550kg/cm^2$, were used in the specimens to investigate the influence if concrete strength on tension stiffening. In the present investigation a method was developed to obtain reliable load-deformation behavior in tension. The experimental results show that (1)high-strength concrete members exhibited larger amounts of tension stiffening than the companion normal-strength concrete members, (2) as the bar diameter increases, the beneficial influence of high-strength concrete on tension stiffening is reduced.

• Computers and Concrete
• /
• v.21 no.3
• /
• pp.231-237
• /
• 2018

A strain-hardening highly ductile composite based on an alkali-activated slag binder and synthetic fibers is a promising construction material due to its excellent tensile behavior and owing to the ecofriendly characteristics of its binder. This study investigated the effect of different types of synthetic fibers and water-to-binder ratios on the compressive strength and tensile behavior of slag-based cementless composites. Alkali-activated slag was used as a binder and water-to-binder ratios of 0.35, 0.45, and 0.55 were considered. Three types of fibers, polypropylene fiber, polyethylene (PE) fiber, and polyparaphenylene-benzobisethiazole (PBO) fiber, were used as reinforcing fibers, and compression and uniaxial tension tests were performed. The test results showed that the PE fiber series composites exhibited superior tensile behavior in terms of the tensile strain capacity and crack patterns while PBO fiber series composites had high tensile strength levels and tight crack widths and spacing distances.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.693-696
• /
• 1999

Reinforced concrete is, in general, known as high durability construction material under normal environments due to strong alkalinity of cement. It is , however, well known that moderate or minor cracks in reinforced concrete should be most serious causes to deteriorate the durability of RC structures. Furthermore, chloride contents penetrating through unexpected cracks in reinforced concrete bridges get to weaken corrosion resistance of reinforcement steel in concrete and than to accelerate the deterioration of concrete durability. The objective of this experimental research is 1) to evaluate the effect of various corrosion protection system for reinforced concrete specimens with moderate or minor cracks which are exposed to cyclic wet and dry seawater, and then 2) to develop effective corrosion protection system for reinforced concrete bridges under the exposure of various detrimental environments such as seawater, deicing and etc.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.533-536
• /
• 1999

The primary purpose of this study is to investigate experimentally the effect of steel fiber reinforcement on the total energy dissipation capacity of R/C flexural members and to make a contribution to the construction of 40~60 story R/C high rise building by developing the new materials and reinforcing details which can improve the seismic performance of high-strength R/C beam-column joints. Experimental research was carried out on 4 type specimen under cyclic loading. Main variables are steel fiber reinforcement, intermediate reinforcements and yield strength of rebars. From the test results, steel fiber reinforcement can improve the ductility of R/C flexural members.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.675-678
• /
• 1999

Rebar corrosion in concrete containing both chloride ions and calcium nitrite inhibitors were investigated by the various electrochemical methods. Rebar corrosion was accelerated by applying the impressed current to the rebar in concrete. Effect of chloride content and inhibitors on rebar corrosion were evaluated. Accelerated corrosion technique is the method to measure the time to the initiation of cracks of reinforced concretes, by applying constant voltage between rebar and the stainless steel cathedes. The increase of concentration of chloride ions in concrete result in the increase in anodic currents and the reduction of time to crack. However addition of inhibitors did not improve corrosion resistance of rebar in concrete. Rebar corrosion in concrete with chloride ions and inhibitors was also analyzed by the immersed tests though the mesurement of corrosion potentials.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.04b
• /
• pp.613-617
• /
• 1998

This study deals with the effect on adhesive strength properties of fiber sheet layer and maintenance position of coccrete structure reinforced using epoxy resin carbon and aramit fiber sheet. Properties of epoxy resin adhesive strength of the concrete bridge slab, tunnel and wall etc. reinforced using fiber sheet under many different environment change according to condition of concrete substrate, temperature, moisture, curing, cleaning, and chemical effects and so on. The purpose of this study is that it makes the estimation value of adhesive strength of concrete substrate and fiber sheet reinforcing layer penetrated epoxy resin under high temperature(9$0^{\circ}C$), chemical attack and condition of curing.

• Carbon letters
• /
• v.14 no.2
• /
• pp.105-109
• /
• 2013

Effects of the amount of nickel powder (Ni) in Ni-carbon fiber (CF) hybrid filler systems on the conductivity(or resistivity) and thermal coefficient of resistance (TCR) of filled high density polyethylene were studied. Increases of the resistivity and TCR with increasing Ni concentration at a given hybrid filler content were observed. Using the fiber contact model, we showed that the main role of Ni in the hybrid filler system is to decrease the interfiber contact resistance when Ni concentration is less than the threshold point. The formation of structural defects leading to reduced reinforcing effect resulted in both a reduction of strength and an increase of the coefficient of thermal expansion in the composite film; these changes are responsible for the increases of both resistivity and TCR with increasing Ni concentration in the hybrid filler system.

• Fibers and Polymers
• /
• v.3 no.1
• /
• pp.24-30
• /
• 2002

Wool yams were coated with conducting Polypyrrole by chemical synthesis methods. Polymerization of pyrrole was caned out in the presence of wool yarn at various concentrations of the monomer and dopant anion. The changes in tensile, moisture absorption, and electrical Properties of the yam upon coating with conductive polypyrrole are Presented. Coating the wool yams with conductive Polypyrrole resulted in higher tenacity, higher breaking strain, and lower initial modulus. The changes in tensile properties are attributed to the changes in surface morphology due to the coating and reinforcing effect of conductive Polypyrrole. The thickness of the coating increased with the concentration of p-toluene sulfonic acid, which in turn caused a reduction in the moisture regain of the wool yin. Reducing the synthesis temperature and replacing p-toluenesulfonic acid by anthraquinone sulfonic acid resulted in a large reduction in the resistance of the yam.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.1003-1008
• /
• 2001

It is recently reported that bond failure can be initiated in the region where maximum bending moment and shear force is acted by accompanying shear deformation after flexural crack in full-scale RC beams strengthened by CFRP. Such a shear deformation effect causing bond failure is relatively little in the case of small-scale specimens. So, additional reinforcing details to the critical beam section where maximum moment and shear were acted is required to prevent the bond failure caused by the shear deformations. The U-type wrapping methods by CFRP to the critical beam section is proposed and tested in this paper. Also, the applicability of design bond strength derived from the tests of small-scale beam was investigated by the full-scale RC beam strengthened by CFRP.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.733-738
• /
• 2001

Although there are strong needs for evaluating statistical characteristics of strengthened reinforced concrete beams under flexure, many researches have been performed mostly on the mechanical properties and failure mechanisms. Different material properties and resulting reinforcing effect could alter the probabilistic values of the strengthened beams. Existing equations suggested for predicting flexural strengthened reinforced concrete beam with CFRP and steel plate are selected and best-fitting one is used in evaluating probability of failure based on Monte-Carlo method. Influential factors are statistically examined and approximate strength reduction factors are suggested. It was found that the factor is more sensitively influenced by predictive equations as well as characteristics and amounts of strengthening materials.