• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.733-736
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• 2008

This study, with the purpose for early quality improvement of concrete which used large quantity of fly ash, changed various admixture material type and reviewed the basic characteristics. First off, the flow overall was highest when polycarb onic Acid high early strength AE water reducing agent was displaced, while air amount satisfied target level only in the case of plain, and setting time was shown best by getting 30 more minutes than plain and about 3 more hours than conventional when KOH is displaced. Compressive strength was shown best at age 1 day and 3 days when KOH was displaced, and at age 28 days when fine particle cement was displaced. By and large, this study concludes that concrete quality improvement admixture material that used large amount of fly ash showed worse effects than plain, therefore it is determined that there need be more study for development of concrete early quality improvement admixture material that used large amount of fly ash.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.973-976
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• 2008

Recently, it is increasingly reported that the deterioration of concrete structure under marine environments is due to diffusion and penetration of chloride ions. It is very important to estimate the diffusion coefficient of chloride ion in concrete. Estimation methods of chloride diffusivity by concentration difference is time-consuming. Therefore, chloride diffusivity of concrete is mainly conducted by electrically accelerated method, which is accelerating the movement of chloride ion by potential difference. However, there has not been any proper method for field quality control to closely determine the diffusion coefficient of chloride ion through accelerated tests using potential difference. In this paper, the various test methods for determination of chloride diffusion coefficient in concrete were investigated through comparison accelerated tests. From the results of estimated diffusion coefficient of chloride ion, relationship between the ponding test and acceleration test was examined.

• Resources Recycling
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• v.21 no.6
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• pp.23-31
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• 2012

Removal work about weeds that grow naturally on road and industrial complex is attaining ordinary times but is suffering difficulty in weeding work by strong self-generation power. In the meantime, going side by side with these manual processing and weeding work through construction of weed-proof seat is attaining, but economic performance, limitation of application region and withdrawal processing problem are being blamed for shortcoming. The scope of this study is about the manufacture of weed-proof mortar using eco-friendly industrial byproducts characterized by an economic and simplicity for not limited to loss of function as a product recovered after treatment. After the carried out the various experiments and actual construction for the selection of mixing materials and derivation of appropriate mix, through the comparison and analysis of results, it was investigated the research results of weed-proof mortar for fundamental development.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.51-58
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• 2016

Concrete structure is a construction material with durability and cost-benefit, however the corrosion in embedded steel causes a critical problem in structural safety. This paper presents an evaluation of chloride resistance and pull-off performance with various corrosion level. For the work, OPC(Ordinary Portland Cement) concrete and GGBFS(Ground Granulated Blast Furnace Slag) concrete are prepared with normal steel. Artificially notch induced FRP Hybrid Bar is also prepared and embedded in OPC concrete and accelerated corrosion test is performed. Through the test, FRP Hybrid Bar with notch is evaluated to have insignificant effect on pull-off capacity when corroded steel shows only 21% level of pull-off capacity. Furthermore GGBFS concrete with normal steel shows over 70% level of pull-off capacity due to reduced corrosion currency.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.3
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• pp.152-159
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• 2010

Recently, the public interest in eco-friendly material and structure has been increasing and many Hwang-toh researches are being actively performed. Hwang-toh is one of the traditional environment friendly construction materials used as a construction and plastering material. Hwang-toh has many advantages as construction material due to its high heat storage capacity, auto-purification, antibiotic ability, and infrared ray emission characteristics. But, currently it has not been developed into construction material and used in modern construction due to its low strength and dry shrinkage cracking prone characteristics. According to the recent researches and study results, Hwang-toh can be used as a natural pozzolanic material like fly-ash or pozzolan. In this study, mechanical properties and structural flexure behavior experiments of slag, recycled PET fiber, and Hwang-toh added concrete are carried out. The test results showed that drying shrinkage of concrete mixed with Hwang-toh has lower compressive strength and elastic modulus than those of control cement concrete specimen, but it has the similar flexural behavior in reinforced concrete beams.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.1
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• pp.40-47
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• 2022

In this study, the direction of the steel fibers mixed in the normal mortar and the steel slag mortar was arranged in the circumferential direction by using an electromagnetic field, and a double punch test was performed to evaluate the effect of magnetic filed exposure on tensile strength and on fracture energy. As a result of the experiment, it was confirmed that it is possible to arrange the steel fibers in the circumferential direction. Tensile strength and displacement at failure were also increased according to the arrangement of steel fibers due to exposure to electromagnetic fields. On the other hand, the fracture energy hardly increased. It is considered that there was a limit in resisting crack growth because the area where the arrangement of steel fibers could be adjusted under the electromagnetic field was not deep to center of specimen and the end shape of the steel fibers were straight not hooked. Additional research is needed to address these issues.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.388-395
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• 2016

This paper explores the photocatalytic sensitivity of cement mortar incorporated with recycled $TiO_2$ from waste water sludge. Basically, $TiO_2$ cluster sank down slowly to the bottom of cement mortar specimen before setting and hardening process. This leads the mismatch of $TiO_2$ concentration on the top and the bottom faces of a specimen. This poorly dispersed $TiO_2$-cement mortar naturally exhibits poor NOx removal efficiency especially on the top of cementitious structure. In architectural engineering application such as building or housing structures, one can simply filp over from the bottom so that more $TiO_2$ concentrated surface can be placed outward into the air. However, in highway pavement case, this could not be applicable due to in-situ installation of concrete pavement. Hence, the dispersion of $TiO_2$ cluster inside the cementitous material is getting important issue onto road construction application. To elaborate this issue, according to our results, silica fume, high-ranged water reducer, viscosity agent, blast furnace slag were not enhanced much of dispersion characteristics of $TiO_2$ cluster. The combination of foaming agent and accelerator of hardening with viscosity agent and small grain size of fine aggregate may help the dispersion of $TiO_2$ inside cementitious materials. Even though the enhanced dispersion were applied to the specimen, NOx removal efficiency doest not change much for the top surface of the specimen. This concurrently affected by the presence of tiny air voids and the dispersion of $TiO_2$ in that these voids could easily adsorbed NOx gas with the aid of large surface area.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.2
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• pp.160-169
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• 2015

In this study, experimental research was carried out to improve the seismic performance of reinforced concrete exterior beam-column joint regions using replacing recycled coarse aggregate with hybrid fiber (steel fiber+PVA fiber) in existing reinforced concrete building. Therefore it was constructed and tested seven specimens retrofitting the beam-column joint regions using such retrofitting materials. Specimens, designed by retrofitting the beam-column joint regions of reinforced concrete building, were showed the stable failure mode and increase of load-carrying capacity due to the effect of crack control at the times of initial loading and bridge of retrofitting hybrid fiber during testing. Specimens BCJGPSR series, designed by the retrofitting of replacing recycled coarse aggregate with hybrid fiber in reinforecd beam-column joint regions were increased its maximum load carrying capacity by 1.01~1.04 times and its energy dissipation capacity by 1.06~1.29 times in comparison with standard specimen BCJS. Also, specimen $BCJGPSR_1$ were increased its energy dissipation capacity by 1.33~1.65 times in comparison with specimens BCJS, BCJP and BCJGPR series for a displacement ductility of 9.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.507-515
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• 2014

Although the construction joints of a concrete structure are properly treated with some measures, leakage has frequently occurred. A series of tests on the bond characteristics between new and old concrete were carried out in this study, assuming that the leakage at the construction joints has certain relationship with the bond of concrete. To assess the bond characteristics under various conditions, a number of specimens were made that have an interface between new and old concrete and bond strength, flexural strength and splitting tensile strength were measured. Main test variables are type and amount of mineral admixtures, treatment method of the interface and type of waterstops. In addition, the effects of placing interval between the concrete and of the age of the strength tests were investigated. The test results showed a slightly increased bond strength when applying mineral admixtures, which can be attributed to the interface filled with the calcium silicate hydrate that is formed by pozzolanic reaction. On the other hand, the bond strength was higher when the interface was treated rough and dry, and the roughness of a waterstop affected the bond capacity of the waterstop. Also, an assessment is required that considers the type of strength test because the bond strength varied according to the test methods.

• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.65-73
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• 2015

This study discussed the pozzolanic properties of calcined sewage sludge (CSS) according to calcination and fineness conditions. The chemical and mineralogical analysis of CSS according to calcination temperature and time were carried out and compared with that of the existing pozzolanic materials such as fly-ash, blast furnance slag and meta-kaolin. Various mortars were made by mixing those CSS and $Ca(OH)_2$ (1:1 wt. %), and their compressive strength and hydrates according to experimental factors such as fineness of CSS and curing age were also investigated in detail. The results show clearly the potentiality of calcined sewage sludge (CSS) as an admixture materials in concrete, but the CSS should be controlled by calcination temperature and time, and fineness etc. In this experimental condition, the calcination temperature of $800^{\circ}C$, calcination time of 2 hours and fineness of $5,000cm^2/g$ were optimum conditions in consideration of the mechanical properties and economic efficiency of CSS. The compressive strength of CSS mortars was higher than that of fly-ash mortars and blast furnace slag mortars, especially at the early ages. Then, the utilization of CSS in construction fields was greatly expected.