• Journal of the Korean Wood Science and Technology
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• v.44 no.1
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• pp.40-47
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• 2016

Instead of metal connector generally used on the structural glued laminated timber rahmen joints, the GFRP reinforced laminated plates combining veneer and GFRP (Glass Fiber Reinforced Plastic) and bonded type GFRP rod were used as the connectors. As a result of moment resistance performance evaluation on the joint part applied with these connectors, the yield moment of specimen using the GFRP reinforced laminated plates and GFRP rod pin was measured 4 % lower in comparison to the specimen (Type-1) using the metal connectors, but the initial rotational stiffness was measured 29% higher. Also, the yield moment and rotational stiffness of the specimen using the GFRP-reinforced laminated plates and wood (Eucalyptus marginata) pin showed were measured 11% and 56% higher in comparison to the Type-1 specimen, showing the best performance. It was also confirmed through the failure shape and perfect elasto-plasticity analysis that it showed ductility behavior, not brittle fracture, from the shear resisting force by the pin and the bonding strength increased and the unification of member was carried out. On the other hand, in case of the specimen bonded with GFRP rod, it was impossible to measure the bonding performance or it was measured very low due to poor bonding.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.125-132
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• 2006

Recently, surface finishing and protection materials were developed to restore performance of the deteriorated concrete and inhibiting corrosion of the reinforcing-bar. For this purpose, surface protection agent as well as coatings are used. Coatings have the advantage of low Permeability of $CO_2,\;SO_2$ and water. However, for coatings such as epoxy, urethane and acryl, long-term adhesive strength is reduced and the formed membrane of those is blistered by various causes. Also when organic coatings are applied to the wet surface of concrete, those have a problem with adhesion. On the other hand, surface protection agent penetrates into pore structure in concrete through capillary and cm make a dense micro structure in concrete as a result of filling effect. Furthermore, the chemical reaction between silicate from surface protection agent and cement hydrates can also make a additional hydration product which is ideally compatible with concrete body. The aim of this study is to examine the effect of penetrative surface protection agent(SPA) by evaluating several concrete durability characteristics. The results show that the concrete penetrated surface protection agent exhibited higher durability characteristics for instance, carbonation velocity coefficient, resistance to chemical attack and chloride ion penetration than the plain concrete. These results due to formation of a discontinuous macro-pore system which inhibits deterioration factors of concrete by changed the pore structure(porosity and pore size distributions) of the concrete penetrated surface protection agent.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.677-684
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• 2007

This study investigates the failure mechanism of RC beams strengthened with GFRP (glass fiber reinforced polymer) sheets. After analyzing failure mechanisms, the various methods to prevent the debonding failures, such as increasing bonded length of GFRP sheets, U-shape wrappings and epoxy shear keys are examined. The bonded length of GFRP sheets are calculated based on the assumed bond strengths of epoxy resin. The U-shape wrappings are either adopted at the end or center of the CFRP sheets bonded to the beam soft. The epoxy shear keys are embedded to the beam soft to provide sufficient bond strength. The end U-wrappings and the center U-wrappings are conventional, while epoxy shear keys are new details developed in this study. A total six half-scale RC beams have been constructed and tested to investigate the effectiveness of each methods to prevent debonding failure of GFRP sheets. From the experimental results, it was found that increasing bonded length or end U-wrappings do not prevent debonding failure. On the other hand, the beams with center U-wrappings and shear keys reached an ultimate state with their sufficient performance. The center U-wrappings tended to control debonding of the longitudinal GFRP sheets because the growth of the longitudinal cracks along the edges of the composites was delayed. In the case of shear keys, it was sufficient to prevent debonding and the beam was failed by GFRP sheets rupture.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.645-652
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• 2002

This paper presents the flexural behavior and strengthening effect of reinforced concrete beams bonded with carbon FRP plate. Parameters involved in this experimental study were plate bond length and sheet web anchorage length. Test beams were strengthened with FRP plate on the soffit and anchored with FRP sheet on the web. In general, strengthened beams with no web anchorage were failed by concrete cover failure along the longitudinal reinforcement. On the other hand, strengthened beams with web anchorage were finally failed by delamination shear failure within concrete after breaking of CFRP sheet wrapping around web. The ultimate load and deflection of strengthened beams increased with an increased bond length of FRP plate. Also, the ultimate load and deflection increased with an increased anchorage length of FRP sheet. Particularly, the strengthened beams with web anchorage maintained high ultimate load resisting capacity until very large deflection. The shape of strain distribution of CFRP plate along beam was very similar to that of bending moment diagram. Therefore, an assumption of constant shear stress in shear span could be possible in the analysis of delamination shear stress of concrete. In the case of full bond length, the ultimate resisting shear stress provided by concrete and FRP sheet Increased with an increase of web anchorage length. In the resisting shear force, a portion of the shear force was provided by FRP anchorage sheet.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.617-626
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• 2011

Seven post-tensioned lightweight concrete (LWC) beam specimens were tested under a symmetrical two-point top loading system. The parameters investigated were the amounts of mild longitudinal reinforcement and effective prestressing. The design compressive strength and dry density of the LWC tested were 30 MPa and 1,770 $kg/m^3$, respectively. Similar to post-tensioned normal weight concrete (NWC) beams, the crack propagation and stress increase of the unbonded tendons were significantly affected by the amounts of mild longitudinal reinforcement and effective prestressing. With the increase in the amounts of mild longitudinal reinforcement and effective prestressing, the serviceability and flexural capacity of the beams were enhanced whereas the stress increase in the unbonded tendons decreased. To control the crack width in post-tensioned LWC beams, a minimum amount of mild longitudinal reinforcement specified in ACI 318-08 provision is required. The flexural behavior of post-tensioned LWC beams and stress increase of the unbonded tendons could be rationally predicted by the proposed non-linear two-dimensional analysis. On the other hand, ACI 318-08 flexure provision was too conservative about the post-tensioned LWC beams.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.339-347
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• 2002

An in-situ experiment was performed to evaluate the pullout resistance capacity of chains which is used as a reinforcement of reinforced earth wall. It was also considered that chain was combined with a bar or L-type steel angle by the transverse reinforcement member in the experiment. About 80 pullout tests were peformed with varying the lengths of chain(2.0m, 2.5m, and 3.0m), the combination of each transverse members(chain only, chain＋bar, or chain＋angle), and the vertical placement of reinforcements. In the case that uses a chain only and a chain combined with bar, the maximum displacement was about 150mm and load continuously increased to the ultimate tensile strength of chain, and then tension failure of chains occurred. But in the case of a chain combined with angle, the displacement decreased to about 100mm and so it was expected that this combination can constrain the displacement of chain. On the other hand, comparing the yielding pullout load measured in the field to that calculated by theoretical equation, it is shown that measured values are 1.2~3.0 times greater than those of calculated values according to the length of chain, normal vertical stress, and the combination of chain with transverse members. However, the difference in the increment of yielding pullout load between bar and angle is not clear but it appears almost the same increment. It is expected that chain can be safely used as reinforcements of reinforced earth wall, although a theoretical estimation of the pullout resistance capability of chain is too conservative.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.3
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• pp.173-179
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• 2014

This is an experimental study for recycling coal ash left over from coal use as a potential fine aggregate in concrete. Coal ash is generally divided into either fly ash or bottom ash. Fly ash has been utilized as a substitution material for cement in concrete mixes. On the other hand, bottom ash has the problem of low recycling rates, and thus it has been primarily reclaimed. This study partially substituted fine concrete aggregates with bottom ash to increase its application rate and therefore its recycling rate; its suitability for this purpose was confirmed. The concrete's workability dropped noticeably with increasing bottom ash content when a fixed water-cement ratio of concrete mix was used. Thus, concrete mixes with higher ratio levels are required. To address this problem, concrete was mixed using a polycarboxylate high-range water reducing agent. The fluidity and air entrainment immediately after mixing the concrete and 1 h after mixing were measured, thereby replicating the time concrete is placed in the field when produced either in a ready-mixed concrete or in a batch plant. As a result of this research, the workability and air entrainment were maintained 1 h after mixing for a concrete mixture with approximately 30% of its fine concrete aggregates substituted with the bottom ash. A slight drop in compression strength was seen; however, this confirmed that potential of using bottom ash as a fine aggregate in concrete.

• Korean journal of food and cookery science
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• v.16 no.1
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• pp.1-8
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• 2000

Six Domestic Wheat Tapdong, Eunpa, Kobun, Olgru, Uri, Kumgang cultivars and one standard wheat Dark Northern Spring (DNS) were milled and determined bread-making properties of dough and bread made the wheats. The ash contents of DNS showed 0.54%, on the other hand, domestic wheat flours showed lower contents than DNS, and Kumgang was the lowest. The Protein contents which suggest the flour gluten content showed 11.68% in DNS cultivars, however 13.85% in Kumgang, 12.35% in Eunpa, 12.32% in Kobun. Valorimeter value in Farinograph data for Kumgang, Kobun, Eunpa cultivars which evaluate the dough formation time and stability showed better result than DNS. Resistance rate in Extensograph for Tapdong and Kobun showed higher rate than DNS. Gelatinization temperature in Amylograph for DNS, Tapdong, Eunpa, Kobun, Kumgang revealed 59$\^{C}$, 59$\^{C}$, 58$\^{C}$, 58$\^{C}$, 59$\^{C}$ respectively, but Uri, Olgru cultivars showed upper temperature which suggest the two cultivars was not suitable for bread making. W(gluten strength) in Alveograph data for DNS showed 297, however, 386 for Tapdong, 327 for Kumgang which indicated that the upper domestic wheat cultivars satisfactory the bread-making properties. In the CO$_2$production of straight bread doughs measured with Meissle fermenter for 5hr, Kumgang cultivar showed the highest CO$_2$ as 333 mg per 30 g of dough. The breads prepared with the above domestic wheat flours showed acceptable quality in sensory test for parameters such as volume, color of crust, symmetry of form, crust, evenness, grain, color, texture, aroma, taste, but the bread made DNS seemed to be superior in organoleptic property to the breads made with domestic wheat flours. The sponge dough bread made with Kumgang cultivars showed the best organoleptic quality among the wheat flours tested. These results indicate that the Kumgang seemed to be practical wheat variety for bread-making.

• Tunnel and Underground Space
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• v.18 no.6
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• pp.491-502
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• 2008

A certain range of the original ground around the tunnel should be preserved to ensure structural safety of the tunnel when other structures are made around the tunnel, and thus this range is defined as safety zone of the tunnel. The main points to ensure the stability of an existing tunnel when constructing a new tunnel in an inter-crossing area are distance between two tunnels, size of the new tunnel, excavation method for the new tunnel, ground condition around the tunnel, and lining type of the existing tunnel etc. When the new tunnel is excavated above the existing tunnel, the existing tunnel is likely to suffer deformation at a crown zone, damage of arching effect, and live load of the new tunnel etc. On the other hand, when the new tunnel is excavated below the existing tunnel, the existing tunnel is likely to be damaged due to settlement. This study has been made on the behavior of the existing tunnel by means of model test and numerical analysis when the new tunnel is excavated below the existing tunnel. Safety zone of the tunnel was estimated by the results of strength/stress ratio obtained from numerical analysis, and the movement of ground was estimated by the model test. The results of earth pressure, ground displacements, and convergence of the tunnel obtained from model test were compared with those of numerical analysis, and show a similar trend.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.105-112
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• 2005

Stabilizing and rousing sludge water generated from washing truck mixer and batcher plant can resolve inconsistency in quality and improve strength, therefore it is essential to review how to utilize it. This research conducted experiments and studied on solids of sludge water to find out the types of stabilizing agents available in conditions of producing ready mixed concretes in Korea. The result showed that oxy carboxylic acid retarder dedicated for stabilizing sludge water was most effective in decreasing solid. However, the setting time of cement paste was retarded due to surplus reactants, but it did not impede application of ready mixed concretes. When we left the sludge water mixed with stabilizing agent, it has been noted that initial retard effect recovered to the level using just service water in 7${\~}$8 days and that it is effective to use stabilized sludge water in 2${\~}$3 days. On the other hand, saccharic type super retarding agent was also outstanding in applicability by showing similar effect. The sludge water stabilizing agents currently marketed depend on imports, therefore it is necessary to locally manufacture usable stabilizing agents and to review its usability with multi-dimensional view.