Papers by Author: Hyun Do Yun

Abstract: This paper presents results of experimental investigation to evaluation the effects of compressive strength on flexural behavior of steel fiber-reinforced concrete (SFRC). For this purpose, normal and high strength SFRCs with two different fiber volume fractions of 0.5 and 1.0% were prepared. Compressive strength, modulus of elasticity, flexural strength and toughness were measured with tests on SFRC cylinders and prisms. Test results indicated that steel fiber volume fraction significantly affects the flexural strength and toughness of SFRC. However, the high strength SFRC showed reduction in flexural toughness compared with the normal strength SFRC. It can be concluded that flexural behavior of SFRC depends on both compressive strength and fiber volume fraction.

Abstract: In this paper, an experimental investigation was carried out to evaluate the application of engineered cement composite (ECC) wing wall elements for seismic strengthening of reinforced concrete (RC) buildings with non-ductile reinforcement details. The ECC is mixed with cement, silica fume, fly ash and polyvinyl alcohol (PVA) fiber. The ECC wing wall elements were fitted on three side of RC frame; upper beam, lower beam and column. Two specimens, non-ductile RC bare frame and RC frame strengthened with ECC wing wall, were made for this study. These specimens were made as a third scale for this study. The specimens were loaded through 1,000 kN actuator that consists of two cycles at a displacement level. The test results showed that the seismic strengthening method of ECC wing wall elements had a significant effect to improve seismic performance of non-ductile RC bare frame. As a result, the application of ECC wing wall elements in non-ductile RC bare frame may be effective alternative to seismic retrofit of non-ductile buildings.

Abstract: The purpose of this study is to investigate the compressive and flexural properties of high-strength steel fiber reinforced concrete (SFRC). For this purpose, a total of 5 mixture whose variable is fiber volume fraction, were made and tested in a range of high strength with 70MPa. In case of normal and ultra-high strength, experimental results were collected from existing literatures on the tests conducted in South Korea. Flexural behavior of SFRC is enhanced according to the fiber volume fraction and compressive strength. Experimental and collected data were applied to existing equations, so it was found that the distinctions occurred between experimental or collected data and calculated values. Thus, more efforts are required to predict the flexural behavior of SFRC manufactured in South Korea with respect to the fiber volume fraction.

Abstract: This paper describes the experimental results on compressive and flexural behavior of alkali-activated slag (AAS) concrete reinforced with hooked end steel fiber. Two different fiber volume fractions of 0.5 and 1.0% were used for AAS concrete and Ordinary Portland cement (OPC) concretes were also mixed for comparison. Test results indicated that compressive and flexural performance of AAS concretes with water-to-binder (W/B) ratio of 0.55 are equivalent to those of OPC concrete. The addition of steel fiber to AAS concrete improves more compressive and flexural performance than those of steel fiber reinforced concrete.

Abstract: This paper reports the experimental results to evaluate in-plane shear performance of insulated concrete sandwich panel (ICSP) with glass fiber-reinforced polymer (GFRP) grid shear connectors. The variables considered in this study are the grid size (35 and 53mm) of GFRP shear connectors and the types of insulation (expanded polystyrene, EPS and extruded polystyrene with special slots, XPSS). For loading in-plane shear force to interface between inner and outer wall of ICSP system, the ICSP specimens were supported vertically at the bottom edge of the two concrete outer walls by steel blocks. The test results indicate that ICSP with XPSS developed higher shear flow strengths in ICSP with EPS when 35mm spacing of GFRP grid is used. Also, the test results indicated that as the grid spacing of GFRP shear connector decreases, the shear flow strength of ICSP with XPSS insulation was higher, but the shear flow strength of ICSP with EPS insulation was lower.

Abstract: This study is conducted to evaluate analytically the effect of casting temperature on the heat of hydration in mass concrete foundation with ternary cements and Type IV low heat cement. The mat foundation has the dimension of 15m length, 20m width and 3m depth. Casting temperatures considered for mat foundation consist of 10, 20 and 30C ̊. A commercial software MIDAS/Gen was used to analyze the hydration heat of mass concrete foundation. The maximum adiabatic temperature rise (K), and the coefficient of temperature rise˰˸α˹˰for thermal analysis were drawn from adiabatic temperature rise test. Analytical results show that blended cement PSLB_352 is the most effective to control the heat of hydration in mass concrete foundation and external temperature increases the maximum heat of hydration and crack probability of mat foundation with mass concrete.

Abstract: This paper provides experimental results on the seismic performance of four concrete infill wall elements with test variables of vertical slits and hooked end steel fiber reinforcing. 1/3-scale infill wall elements with height-to-length ratio of 0.55 were manufactured and tested up to failure. Four walls (CIW-N and-S, SCIW-N and-S) are similar to each other except presence of steel fiber reinforcement and vertical slits with the width of 40 mm. All specimens had the same rectangular cross-section of 1,100 mm x 50 mm, with wall panel height of 600 mm. The experimental results showed that concrete infill wall element with vertical slits exhibited more stable hysteretic behavior than solid infill wall element. This phenomenon is remarkable for steel fiber reinforced concrete infill wall element. Inclusion of vertical slits on the normal concrete and steel fiber reinforced concrete infill wall element improve the ductility and energy dissipation capacity but decrease the load-carrying capacity and stiffness of infill walls.

Abstract: In this paper, an experimental investigation was carried out to examine the influence of hooked end steel fiber volume fraction and curing conditions on the compressive performance of concrete produced by using ordinary portland cement (OPC) and alkali-activated slag (AAS). Three different volume fractions of 0.5%, 1.0% and 1.5% were used in OPC and AAS concrete mixtures. Cylindrical specimens with 100 x 200mm were tested for compressive behavior of both concretes at 3, 7 and 28 days of curing age. Test results showed that curing conditions had a significant effect on compressive properties in the hardened OPC and AAS concretes. The addition of steel fibers generated a decrease in compressive strength of OPC while an increase in the compressive strength of AAS concrete was shown with adding steel fiber.

Abstract: This study provides analytical results for heat of hydration in the mat foundation with mass concretes to investigate the effect of lift thickness in the mat foundation on the hydration heat and crack characteristics of mat foundation with mass concrete. Mass concretes were mixed with ternary cement with 1% strontium-based latent heat binder at volume fraction and Type IV low heat cement. The mat foundation has the dimension of 15m length, 20m width and 3m depth. Lift thickness of mass concrete for mat foundation was varied from 1.0m to 3.0m. A commercial software MIDAS/Gen was used to analyze the hydration heat of mass concrete foundation. The maximum adiabatic temperature rise (K), and the coefficient of temperature rise (α) for thermal analysis were drawn from adiabatic temperature rise test. Based on the results of the finite element analysis for mat foundation with different lift thickness, the highest internal temperature and thermal stress increased with increasing with lift thickness of foundation. However, for foundation constructed with premixed strontium based latent heat binder (PSLB) concrete, this phenomenon was less remarkable compared to mass concrete foundation made with low heat cement.

Abstract: This paper provides the results of direct tensile tests for strain-hardening cement composite (SHCC) to investigate the influence of fluosilicate based shrinkage-reducing agent (SRA) on the tensile and cracking behaviors of SHCC material under direct tension. The specified compressive strength of the SHCC material is 50MPa. The adding ratio of fluosilicate based SRA for SHCC material is 2.5 and 5.0%. Two mixitures of SHCC with 2.2% polyvinyl alcohol (PVA) fibers at the volume fraction were mixed; two mixtures with SRA and one mixture of conventional SHCC material. To evaluate the tensile and cracking behaviors of SHCC materials, two dumbbell-shaped tensile specimens for each mixture were manufactured and tested in direct tension. Test results show that the addition of fluosilicate based SRA improved direct tensile and cracking behaviors of SHCC materials with rich mixture. This phenomenon is noticeable for SHCC with higher volume of SRA.