• Journal of the Korean GEO-environmental Society
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• v.9 no.5
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• pp.29-36
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• 2008

The shotcrete is a NATM technique as a major tunnel support for ground stability after tunnel excavation. Instead of a general concrete lining method, it is a trend for curtail of construction periods and reduction of construction expenses that required to use of the permanent shotcrete lining. This high-strength shotcrete is required to use as a permanent shotcrete lining. This brought out the solution of environmental pollution and harmfulness to human. Accordingly, in this study specimens for strength measurement were made to develop shotcrete possible to develop materials in early with cement mineral accelerator as NATM method construction. It was compared with existing shotcrete material, unconfined compression test, flexural strength test, antiwashout underwater test were experimented. The fish poison test was experimented to evaluate an influence of environment. As a results of the test, unconfined compressive strength and flexural strength were equivalent with 28-curing day strength of existing material. An antiwashout of research subject material was revealed excellently in antiwashout Underwater test. As a results of the fish poison, an evaluation research subject material was founded more environmentally friendly than existing shotcrete.

• Journal of the Korea Institute of Building Construction
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• v.15 no.4
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• pp.367-373
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• 2015

In this study, fundamental properties of cement were reviewed to apply high fineness cement at low temperature environment. The classified high fineness cement has large proportion of particles below $10{\mu}m$ which affects early hydration: an overall reaction of cement hydration faster. As a result of using high fineness cement, setting time of concrete was reduced and compressive strength was higher than OPC at all ages. Especially, compressive strength was more than double its value compared with OPC after three days curing in low temperature. Faster reaction and higher heat of hydration was verified by calorimetry early and maximum heat of hydration was analyzed by adiabatic temperature raising test. The analysis of this study confirmed that high fineness cement can be suitable to be used in low temperature environment.

• Journal of the Korea Concrete Institute
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• v.13 no.1
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• pp.69-76
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• 2001

Foamed concrete for cast-in-site, which shows excellent lightweight, thermal insulation, noise insulation, constructability and cost efficiency, has been applied as thermal insulation or filling material for On-dol. However, the technology is too insufficient to obtain the high level of quality, and serious problems often occur in quality control at sites. It, thus, is necessary to establish the proper and reasonable quality control method for ensuring the required quality, based on the investigation on the physical properties and their reciprocal relation. This study aims to settle the quality control method in case of applying FA foamed concrete replacing 40% by weight with fly-ash as the filling material for On-dol. The results of the study include the correlation among flow, as-placed density and foam ratio of fresh foamed concrete, the correlation between physical properties before hardening and after 28-day, provision of an equation to estimate 28-day compressive strength early with 7-day compressive strength, and suggestion of quality criteria for the revision of KS on foamed concrete for cast-in-site.

• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.3
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• pp.51-60
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• 2007

This study was performed to evaluate void ratio, compressive and flexural strengths, and pH properties according to the content ratio of rice husk ash, aggregate size, and neutral treatment time of porous concrete with content of rice husk ash produced as an agricultural by-product. The SEM results for cement mortar with a 5% rice husk ash for the weight of cement formed more C-S-H hydrates due to the $SiO_2$ of rice husk ash. In the XRD test, cement mortar with a 5% rice husk ash for the weight of cement registered a higher peak point of approximately $2{\theta}=20{\sim}25^{\circ}$ compared to cement mortar without rice husk ash. According to the results of the XRD and SEM tests, the $SiO_2$ that was a major chemical element of rice husk ash generated a large amount of calcium hydroxide in the early stage of the hydration process of cement leading to the formation of ettringite. The void ratio of porous concrete with rice husk ash decreased with increasing content ratio of rice husk ash. In addition, the void ratio of porous concrete with rice husk ash decreased compared to porous concrete without rice husk ash. The compressive and flexural strength of porous concrete with a 5% and 10% content ratio of rice husk ash slightly increased compared to concrete without rice husk ash. The pH value of porous concrete rapidly decreased immediately after neutral treatment. Then, it gradually increased and decreased again after 14 days. However, the pH value was nearly the same regardless of neutral treatment time in 28 curing days. Also, for neutral treatment, the pH value of porous concrete showed appropriate pH levels (less than 9.5) in all mixtures for planting at 28 curing days.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.105-108
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• 2008

For the early seismic isolation design in Korea, foreign products of isolation bearings were used. But these days, the application of domestic products of isolation bearings is increasing. However various experimental studies can be found very seldom on the extreme and lonr term behaviors of isolation bearings. In this study, we considered the laminated rubber type isolation bearings that have many application cases in Korea and we evaluated their shear strength, long term characteristics such as aging and creep affecting shear strength of bearings in long term period. For the reality of experiments, fabricated isolation bearing specimens are designed for a real structure and shear loading was applied under design compressive loads. To evaluated aging effect, the specimens were exposed to high temperature environment for certain period and their shear properties were measured to compare with their original values. Also we measured creep amount of isolation bearings under constant compressive load for 1,000 hours and estimated creep amount after 60 years compatible with general life cycle of bridges.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.2
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• pp.99-107
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• 2014

In this study, the effects of curing procedures on the mechanical properties of recycled aggregate concrete (RAC) were investigated. The replacement ratios by recycled coarse aggregate were 0, 25, 50, 75 and 100% by mass of natural coarse aggregate. Steam curing was adopted to all recycled aggregate concrete mixtures. Compressive and split tensile strength, water porosity, chloride ions penetration resistance and drying shrinkage measurements were carried out to determine performance of the RACs. From the test results, it was found that the mechanical performance of RAC decreased as the recycled aggregate contents increased. Furthermore, steam curing reduced the compressive and split tensile strength, water porosity and total charge of RAC, especially at the early ages. However, at the later ages, the beneficial effect of steam curing was less prominent. This study clearly showed that initial steam curing could be one of practical methods to improve performance of RAC with higher replacement ratio of recycled aggregate.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.1
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• pp.44-54
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• 2012

The structural designs of RC flat plates that have no flexural stiffness by boundary beams may be governed not by strength conditions but by serviceabilities. Specially, since over-loading and tensile cracking in early-aged slabs significantly increase the immediate and long-term deflections of a flat plate system, a construction sequence and its impact on the slab deflections may be decisive factors in designs of flat plate systems. In this study, the procedure of calculating slab deflections with considering construction sequences, concrete cracking, and long-term effects is proposed. Using the proposed method, the parametric study for deflections of flat plates is performed. With various conditions for slab construction cycle, the number of shored floors, tensile or compressive reinforcement ratio, compressive strength of concrete, construction live load, and slab thickness, the immediate deflection during construction and long-term deflections after completion are analyzed. The calculated results are compared with the serviceability limits offered by the structural design code.

• Structural Engineering and Mechanics
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• v.50 no.5
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• pp.635-652
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• 2014

Creep and shrinkage behaviour of an ultra lightweight cement composite (ULCC) up to 450 days was evaluated in comparison with those of a normal weight aggregate concrete (NWAC) and a lightweight aggregate concrete (LWAC) with similar 28-day compressive strength. The ULCC is characterized by low density < 1500 $kg/m^3$ and high compressive strength about 60 MPa. Autogenous shrinkage increased rapidly in the ULCC at early-age and almost 95% occurred prior to the start of creep test at 28 days. Hence, majority of shrinkage of the ULCC during creep test was drying shrinkage. Total shrinkage of the ULCC during the 450-day creep test was the lowest compared to the NWAC and LWAC. However, corresponding total creep in the ULCC was the highest with high proportion attributed to basic creep (${\geq}$ ~90%) and limited drying creep. The high creep of the ULCC is likely due to its low elastic modulus. Specific creep of the ULCC was similar to that of the NWAC, but more than 80% higher than the LWAC. Creep coefficient of the ULCC was about 47% lower than that of the NWAC but about 18% higher than that of the LWAC. Among five creep models evaluated which tend to over-estimate the creep coefficient of the ULCC, EC2 model gives acceptable prediction within +25% deviations. The EC2 model may be used as a first approximate for the creep of ULCC in the designs of steel-concrete composites or sandwich structures in the absence of other relevant creep data.

• Steel and Composite Structures
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• v.31 no.1
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• pp.1-12
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• 2019

Steel-concrete composite walls have been proposed and developed for applications in various types of structures. The double-skin profiled composite walls, as a natural development of composite flooring, provide structural and architectural merits. However, adequate intermediate fasteners between profiled steel plates and concrete core are required to fully mobilize the composite action and to improve the structural behavior of the wall. In this research, two new types of fasteners (i.e., threaded rods and vertical plates) were proposed and three specimens with different fastener types or fastener arrangements were tested under axial compression. The experimental results were evaluated in terms of failure modes, axial load versus axial displacement response, strength index, ductility index, and load-strain relationship. It was found that specimen with symmetrically arranged thread rods sustained more stable axial strain than that with staggered arranged threaded rods. Meanwhile, vertical plates are more suitable for practical use since they provide stronger confinement to profiled steel plate and effectively prevent the steel plate from early local buckling, which eventually enhance the composite action and increase the axial compressive capacity of the wall. The calculation methods were then proposed and good agreement was observed between the test results and the predicted results.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.1
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• pp.72-81
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• 2024

In this study, DEIPA was used for enhancing cementitious performance of bottom ash replaced cement. By applying the partial or no-known crystal structure method to X-ray diffraction data, the amounts of amorphous bottom ash and calcium silicate hydrate(C-S-H) could be separated and quantified. In the sample without DEIPA, the bottom ash hardly reacted, resulting in low compressive strength. However, the addition of DEIPA not only altered the hydration behavior of the cement but also enhanced the pozzolanic reaction between bottom ash and calcium hydroxide, leading to the generation of additional C-S-H. This resulted in high compressive strength not only in the early stages but also in the later stages. Therefore, with the addition of DEIPA during the pulverization of the bottom ash, the reactivity of the bottom ash was significantly improved. Hence, there is potential in the development of bottom ash replacement cement.