• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.5
• /
• pp.68-74
• /
• 2019

In this study, the mechanical property and durability of improved bond performance mortar shotcrete was investigated. Mortar shotcrete was prepared by replacing coarse aggregate with 100% fine aggregate in the shotcrete mixture proportion proposed in the road construction standard specification. OPC, GGBFS and anhydrite were used as binders, and polymer powder was substituted for 1% and 2% of binder for improving bond property. From the experimental results, it was found that the compressive strength decreased with increasing polymer addition, but the bond strength increased. The addition of polymer to mortar shotcrete also reduced the drying shrinkage and improved the resistance to carbonation. Initial hydration heat of mortar shotcrete decreased with the addition of polymer, and it was judged that the initial compressive strength decreased.

• International Journal of Highway Engineering
• /
• v.7 no.4 s.26
• /
• pp.69-77
• /
• 2005

Joint spacing is a potent influence in increasing the long term performance of jointed concrete pavement slabs through the control of tensile stress, sealant failure and Load Transfer Efficiency (LTE). Internal Joint Spacing is an empirical and fixed method therefore this study will present the optimum joint spacing considerations depending on various climactic conditions. Calculating the optimum joint spacing eliminates random cracking due to the effect of the environmental loads such as the early behavior of drying shrinkage and heat hydration. Optimum joint spacing is calculated so as not to cause pavement distress by the deterioration of LTE by long term pavement movement. This study shows that the provisional joint spacing is 6-8m. Pavement Distress Prediction Models show that pavement distress has no effect on joint spacing of 8m.

• Journal of Korean Society of Disaster and Security
• /
• v.5 no.2
• /
• pp.71-79
• /
• 2012

Recently, in the total railroad construction field, the concrete slab track is adapted, not ballast track. Because the ballast track have the characteristics doing the ongoing maintenance and difficult to handle increasing maintenance costs, eventually the concrete slab track is selected as an alternative. However, owing to the hydration heat reactions and temperature affected shrinkage cracks related to concrete itself, a variety of studies to solve maintenance problems related to concrete slab track are underway. This study analysed characteristics of TQI values evaluating the track irregularity, searched the relationship between crack progress and TQI, and then evaluated of the correlation between the two values. Through this method, there is a need to complete the problems of the current method, only TQI is the main decision making tool in track maintenance, and also the need for the development of evaluation index considering the crack.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
• /
• v.22 no.1
• /
• pp.120-132
• /
• 2009

Objective : Yukmijihwang-tang is one of the important medicines for blood- deficiency and yin-deficiency. Atopic dermatitis usually shows dampness-heat pattern in its acute stage and blood-deficiency or yin-deficiency pattern in its chronic stage. Therefore, I hypothesized that Yukmijihwang-tang is effective on atopic dermatitis and investigated the effects of Yukmijihwang-tang on NC/Nga mice's atopic dermatitis induced by DNCB. Methods : The NC/Nga mice with atopic dermatitis were divided into four groups: three experimental groups and one control group. The experimental groups were respectively put on 2.5g(YM-2.5), 5g(YM-5) and 10g(YM-10) of Yukmijihwang-tang extract per their weight once a day for 10 days while the control group was fed normal saline. After 10 days, I measured TEWL(transepidermal water loss), observed scratching behaviors, conducted a skin biopsy and checked levels of Total IgE, IL-4 and $IFN-\gamma$ on NC/Nga mice. Results : 1. Yukmijihwang-tang significantly suppressed skin dryness. In particular, YM-5 and YM-10 had better skin hydration than YM-2.5. 2. Yukmijihwang-tang significantly suppressed pruritus while there was no significant difference among the experimental groups. 3. Yukmijihwang-tang retained skin structure(epidermis, dermis and subcutaneous fat). 4. Yukmijihwang-tang reduced Total IgE level while there was no significant difference between the control group and the experimental groups. 5. Yukmijihwang-tang did not reduce IL-4(Th2 cytokine) level. 6. Yukmijihwang-tang significantly reduced $IFN-\gamma$(Th1 cytokine) level. In particular, YM-2.5 and YM-5 had lower $IFN-\gamma$ level than YM-10. Conclusion : The results suggest that Yukmijihwang-tang suppresses skin dryness and pruritus, retains skin structure and is effective on chronic atopic dermatitis which is associated with Th1 cytokines in the immune response.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.7 no.3
• /
• pp.210-215
• /
• 2019

Concrete members with wide surface area are vulnerable to cracking due to material behavior such as hydration heat and drying shrinkage. Recently many researches have been performed on improvement of strength and cracking resistance through fiber reinforcement, which are mainly focused on enhancement of tensile strength against cracking due to material behavior. In this paper, CFs(Cellulous Fibers) are manufactured for slurry type, and the engineering properties in cement mortar incorporated with CFs are evaluated for flow-ability, compressive, and flexural strength. Through SEM analysis, a pull-off characteristics of CF in matrix are analyzed. With CF addition of $0.5kg/m^3{\sim}1.0kg/m^3$, flexural strength is much improved and enough toughness of pull-off is also observed unlike plastic fiber containing smooth surface.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.1A
• /
• pp.101-108
• /
• 2009

The performance of high-early strength pavement concrete for large areas is influenced by the physical and chemical environment during service life. Generally, penetration, diffusion, and absorption of harmful materials that exist outside the concrete cause damage to its structure. Thus, we have to use a mixture for durability to keep the required quality for the planned service life. Moreover, in using high-early-strength cement and accelerators, a high heat of hydration to create the initial strength can cause cracks. Based on evaluations from optimal mix proportions of high-early-strength pavement concrete for large areas, we conducted water permeability, abrasion resistance, freeze-thaw, plastic, drying, and autogenous shrinkage tests. Test result showed that a mix of accelerator and PVA fibers showed excellent performance.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.2
• /
• pp.122-129
• /
• 2019

Cracks in concrete structures are inevitable phenomena caused by shrinkage, hydration heat, and external loads. These cracks facilitate the penetration of external harmful ions into the concrete, which greatly reduces its durability. Recently, self-healing concrete has been actively studied. Also, self-healing fiber-reinforced concrete have been studied to control the crack in concrete and to maximize the shelf-healing capability. In this study, mortar specimens containing PVA fiber, fly ash and crystalline admixture were fabricated. The compressive and flexural strength were evaluated. Also, the self-healing performance was evaluated by the absorption test. From the results, it was confirmed that the amount of water absorbed by healing of the crack decreased as time increased. It was also found that PVA fiber is beneficial for the production of calcium carbonate, an additional healing product.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.5
• /
• pp.19-26
• /
• 2014

Concrete guide rail and median barrier are an attached RC member, however they are vulnerable to cracking due to slip form construction and large surface of member. In this study, causes and pattern of cracking are analyzed through assessment and NDT (Non-Destructive Technique) evaluation for concrete guide rail and median barrier on highway structure. For this work, analysis on drying shrinkage and hydration heat are performed considering installation period, and plastic shrinkage is also analyzed considering their environmental conditions. From the evaluation, plastic settlement around steel location, drying/ plastic shrinkage, and aggregate segregation are inferred to be the main causes of cracking in the structures. The crack causes and patterns are schematized and techniques of crack-control are suggested. Furthermore concrete guide rail/ median barrier in the bridge on the sea are vulnerable to cracking at early age so that special attentions should be paid at the stages of material selection and construction.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.661-664
• /
• 2008

The structure which is located in special surroundings like ocean-environment is physically and chemically eroded by seawater or salt damage, and then concrete-structure becomes deteriorated by iron corrosion and swelling pressure which leads to remarkably decline durability due to cracks and exploitation. As a measure against salt damage, it is actively being examined to use the blended cement that controls salt damage and fix chloride in the process of hydration. In this study, therefore, to examine the property of marine concrete added admixture, marine concrete is manufactured by adding high-strength admixture(omega2000) by 0, 5, 10, and 15% to low heat-blended cement. Then it shows that the compressive strength of manufactured marine cement tends to increase and chloride penetration resistance improves.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.445-448
• /
• 2008

It is essential that concrete component is made up with aggregate, cement and water. But today, Public concern is increasing of a variety structure and ocean environmental, resource recycle. Also, According to heat of hydration rising, Concrete is make a causative of concrete-crack. Concrete-crack cause a falling-off in quality of concrete. consequently, High-performance concrete is evaluated by concrete material properties and carbonation resistance with different admixture(fixing fly-ash 20%), granulated blast furnace slag replacement ratio (30%, 45%) different W/B (26%, 30%, 34%) and XRD(X-ray Diffraction) analysis.