• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.113-119
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• 2006

It is now established that more than two types of blended aggregate have beneficial effects on quality and supply of concrete in the long run. However, studies on blended aggregate have not widely been progressive and the evaluation method of its most favorable mixture proportion is still needed. Therefore this study investigated the most favorable mixture proportion through the physical experiment of fresh and hardened state's cement mortar, in response to three types of composite ratio, natural fine aggregate(Ns), crushed fine aggregate(Cs) and recycled fine aggregate(Rs). Test showed that increase of blending ratio of Ns and Cs improved fluidity of mot1ar. For the properties of compressive and flexural strength, mortar blending Ns and Cs properly, exhibited similar value to one using only Cs, while mortar mixing Rs showed lower strength value as less as 6% of control one. Mortar using only Rs exhibited the largest drying shrinkage value. In addition, even thought it is not a clear quantitative analysis, technical-imaging-skill presenting the most favorable mixture proportion 3-dimensionally is proposed in this research, in order to notify the proportion easily.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.149-156
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• 2016

It has been well known that concrete structures exposed to chloride and sulfate attack environments lead to significant deterioration in their durability due to chloride ion and sulfate ion attack. The purpose of this experimental research is to evaluate the long-term durability against chloride ion and sulfate attack of the alkali activated cementless concrete replacing the cement with ground granulated blast furnace slag. For this purpose, the cementless concrete specimens were made for water-binder ratios of 40%, 45%, and 50%, respectively and then this specimens were cured in the water of $20{\pm}3^{\circ}C$ and immersed in fresh water, 10% sodium sulfate solution for 28, 91, 182, and 365 days, respectively. To evaluate the long-term durability to chloride ion and sulfate attack for the cementless concrete specimens, the diffusion coefficient for chloride ion and compressive strength ratio, mass change ratio, and length change ratio were measured according to the NT BUILD 492 and JSTM C 7401, respectively. It was observed from the test results that the resistance against chloride ion and sulfate attack of the cemetntless concrete were comparatively largely increased than those of OPC concrete irrespective of water-binder ratio.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.4
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• pp.355-365
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• 2015

This study examined the fluidity and strength properties, water resistance, durability, and freeze-thaw of cementless loess mortar using an eco-friendly hardening agent. The experimental result indicates that 28 days compressive and flexural strength of the loess mortar was increased regardless of the weathered granite soil and loess mixture ratio as the replacement ratio of the hardening agent increases. The strengths were significantly increased until 14 days regardless of the hardening agent, while the effect on the strengths increasement was relatively low after 14 days. Thus, the strength development of loess mortar concrete was found to be faster than that of the normal concrete. In addition, when the hardening agent of 10% was used, the average flexural strength was 1.7MPa which is insufficient compared to the 28-day flexural strength of 4.5MPa for the paving concrete. However, the flexural strengths of the loess mortar concrete using the hardening agents of 20% and 30% were 4.0MPa and 5.3MPa, respectively. Thus, the hardening agent need to be at least 20% so that the loess mortar can be used for paving concrete. The experiment for water resistance shows that the repeated absorption and dry reduced mass regardless of the mixing ratio of the loess. The maximum length change also decreased with increasing the substitution rate loess mixture ratio and the hardening agent. The result of the freeze-thaw resistance test indicates that the relative dynamic modulus of elasticity at 300 cycle freeze-thaw with the hardening agents of 20% and 30% were 75% and 79%, relatively. Thus, the hardening agent of at least 20% is required to obtain the relative dynamic modulus of elasticity of 60% for the loess mortar.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.2
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• pp.248-257
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• 2005

Statement of problem. Cortical bone plays an important role in the primary implant stability, which is essential to immediate/early loading. However, immediate load-bearing capacity and primary implant stability according to the change of the cortical bone thickness have not been reported. Purpose. The objectives of this study were (1) to measure the immediate load-bearing capacity of implant and primary implant stability according to the change of cortical bone thickness, and (2) to evaluate the correlation between them. Material and methods.48, screw-shaped implants (3.75 mm$\times$7 mm) were placed into bovine rib bone blocks with different upper cortical bone thickness (0-2.5 mm) and resonance frequency (RF) values were measured subsequently. After fastening of healing abutment. implants were subjected to a compressive load until tolerated micromotion threshold known for the osseointegration and load values at threshold were recorded. Thereafter, RF measurement after loading, CT taking and image analysis were performed serially to evaluate the cortical bone quality and quantity. Immediate load-bearing capacity and RF values were analyzed statistically with ANOVA and post-hoc method at 95% confidence level (P<0.05). Regression analysis and correlation test were also performed. Results. Existence and increase of cortical bone thickness increased the immediate load-bearing capacity and RF value (P<0.05) With the result of regression analysis, all parameter's of cortical bone thickness to immediate load-bearing capacity and resonance frequency showed significant positive values (P<0.0001). A significant high correlation was observed between the cortical bone thickness and immediate load-beating capacity (r=0.706, P<0.0001), between the cortical bone thickness and resonance frequency (r=0.753, P<0.0001) and between the immediate load-bearing capacity and resonance frequency (r=0.755, P<0.0001). Conclusion. In summary, cortical bone thickness change affected the immediate load-baring capacity and the RF value. Although RF analysis (RFA) is based on the measurement of implant/bone interfacial stiffness, when the implant is inserted stably, RFA is also considered to reflect implant/bone interfacial strength of immediately after placement from high correlation with the immediate load-baring capacity. RFA and measuring the cortical bone thickness with X-ray before and during surgery could be an effective diagnosis tool for the success of immediate loading of implant.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.33-39
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• 2012

With the increase of steel production research interest on the recycling of slag as a by-product also increases steadily. Currently in Korea a lot of researches on blast-furnace slag have been made. However, the researches on the steel slag have been rarely made. Also, a research of steel slag, especially the use of oxidation furnace slag as aggregates for concrete progress, is performing actively, but the research results on the furnace slag are almost nothing. Recently, the research about the furnace slag as backfill material and embankment material confirmed the possibility of the clay soil amendment. Therefore, the object of this study is to review the possibility as civil engineering materials for soil improvement and to find the optimum mixture ratio of furnace slag. This research analyzed the ingredient component of the reduced slag by SEM, XRF, XRD tests and examined the strength increase using unconfined compression tests when the clay and reduced slag are mixed each other. Through this test, the definite strength increase is confirmed according to the mixture of the reduced slag and the possibility of soil improvement is also confirmed based on this result. The object of the study is both utilizing the by-product for civil engineering purpose and effective recycling by the application of the furnace slag for soil improvement.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.837-840
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• 2008

This study was achieved experiment to evaluate effect on fluidity and strength development ratio by slag replacement ratio to $40{\sim}100MPa$ HSC(High Strength Concrete) containing blast furnace slag(GGBS) and fly-ash(FA). Also it was suggested that most suitable replacement ratio of GGBS is effect by strength. The mix plan of concrete used in an experiment was used to the GGBS replacement ratio of 0, 12, 25% as the cement materials, and fly ash was used equally by replacement ratio 15%. According to test results, for use GGBS with fly ash as binder, slump of GGBS replacement ratio 25% is the most superior in 40MPa series, and appeared by thing which slump flow of GGBS 12% is the most superior in 60, 80MPa's series. The other side, was expressed that fluidity is excellent by FA replacement ratio 15% in 100MPa series. In the case of compressive strength 40MPa, it was exposed that the strength revelation is effect in until the GGBS principal parts ratio increases by replacement ratio 25%. Also, it was exposed that GGBS mixing ratio more than replacement ratio 25% is not since fitness in high strength concrete more than 100MPa.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.9
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• pp.749-755
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• 2016

A new method for measuring the 3-axis cutting forces of a pick cutter by substituting costly 3-D load cells is proposed in this paper. The proposed cutting force measurement method is capable of estimating the 3-axis cutting forces through mechanical constraints using four single-axis compressive load cells and shoulder bolts. The feasibility of the proposed method was verified by finite element analysis, and the accuracy of the force measurement of the developed force measurement device was investigated by conducting linear rock cutting tests. The tests showed that the new cutting force measurement method is able to measure 3-axis cutting forces with a relative error of approximately 6%. These results imply that the new method could be a suitable alternative to conventional 3-D load cells. In addition, it will allow a significant reduction of approximately 20-30% in the costs required for measuring the cutting force when compared to conventional 3-D load cells.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.1
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• pp.81-94
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• 2010

This paper deals with the fracture simulation of UHPFRC girder with the interface type model. Based on the existing numerical simulation of quasi-brittle fracture in normal strength concrete, constitutive modeling for UHPFRC I-girder has been improved by including a tensile hardening at the failure surface. The finite element formulation is based on a triangular unit, constructed from constant strain triangles, with nodes along its sides and neither at the vertex nor the center of the unit. Fracture is simulated through a hardening/softening fracture constitutive law in tension, a softening fracture constitutive law in shear as well as in compression at the boundary nodes, with the material within the triangular unit remaining linear elastic. LCP is used to formulate the path-dependent hardening-softening behavior in non-holonomic rate form and a mathematical programming algorithm is employed to solve the LCP. The piece-wise linear inelastic yielding-failure/failure surface is modeled with two compressive caps, two Mohr-Coulomb failure surfaces, a tensile yielding surface and a tensile failure surface. The comparison between test results and numerical results indicates this method effectively simulates the deformation and failure of specimen.

• Journal of the Korea Institute of Building Construction
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• v.14 no.5
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• pp.379-388
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• 2014

The purpose of this study is to investigate the effect of capsulated slurry phase change material (PCM) on the thermal crack in mass concrete by experimental work and FEM analysis. In this study, three conditions of samples were prepared for evaluating the level of hydration heat, i.e., a material condition, a cement paste condition and a concrete condition. Also, a compressive strength test was conducted for FEM inverse analysis. Based on the results of the experiment, exothermic function coefficients of concrete with encapsulated slurry PCM were deducted by the inverse analysis. After that, they applied to FEM analysis of the mass scale concrete structures. From the results of this experiment, $31^{\circ}C$ capsulated slurry PCM had no super cooling phenomenon in the material condition. In the cement condition, hydration heat decreased by 34.61J when PCM of 1g was mixed. In the concrete condition, PCM of 6% was deducted as the best level in hydration heat absorption. In FEM inverse analysis, rate coefficient of reaction gradually decreased when PCM mixing ratio increased. But, temperature-rise coefficient increased when PCM mixing ratio exceeded 6%. For the inversed exothermic function coefficients applying to large scale concrete structures, a thermal cracking index increased by 0.05 when PCM of 1% was mixed.

• Journal of the Korea Institute of Building Construction
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• v.17 no.3
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• pp.227-234
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• 2017

This research analyzes the properties of mortar following the rise in water-cement ratio and applicability as an eco-friendly construction supply by using the mudflats of a dredged arena as a substitute for aggregate. The results of a experiment of the flow showed that the flow value decreases as the amount of mudflats increases. A test for chloride content showed that the chloride content increases with the amount of mudflats. In the compression of specimen mixed with mudflat and the testing of tensile strength, the strength weakened as the addition ratio of mudflats rose. However, with 14-day strength as the standard, most specimen showed more strength than the plain, and 14-day strength was higher than 28-day strength. It appears to be experimental error in the mixing process from the viscosity and cohesion of mudflats, and it is considered that there will be a need for an experiment on mixing methods of mudflats in the future. The compressive strength of this research was the strongest with 70% in water-cement ratio, and the tensile strength was strongest with 80% in water-cement ratio. In the evaluation of surface analysis, 70% water-cement ratio, which is finest in strength, mixing, and compactness, was selected to analyze the roughness of the surface, and the results showed that the surface became smoother as the addition ratio of mudflats increases. In conclusion, it appears that 70% water-cement ratio is the optimal mixing ratio for mortar and 10 to 30% addition ratio of mudflats the optimal ratio. It also appears that the application of interior finishing material like bricks and tiles and interior plastering material using the mudflats are possible.