• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.4298-4307
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• 2015

The expenses of maintenance and reinforcement for aged concrete structures are significantly on the increase as their durability and general performance has been naturally degraded. Due to this reason, interests on concrete crack reduction technology are growing but more researches are required to fulfill such fast growing demands. Particularly in the underground power facilities, it is difficult to maintain the quality of aging concrete spheres for underground power as their deterioration caused by long-term operation is on-going. In recent years, many studies have been made to overcome the issues and now it is determined that the shrinkage reducing technology which can dramatically reduce the crack at the design stage is one of the most effective solutions. In this study, the test investigated fundamental propertiesof concrete using various shrinkage reducing materials to develop low shrinkage mortar. According to results of experimental study, for mortar and concrete, glycol based material showed excellent shrinkage property and compressive strength. For the later study to generic application of the shrinkage reducing materials, performance reviews on the shrinkage reducing materials with variable factors and various materials such as changes in the amount and type of materials should be followed.

• Smart Structures and Systems
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• v.18 no.3
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• pp.405-423
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• 2016

In this study, the feasibility of using telecommunication single-mode optical fiber (SMF) as a distributed fiber optic strain and crack sensor was evaluated in concrete pavement monitoring. Tensile tests on various sensors indicated that the $SMF-28e^+$ fiber revealed linear elastic behavior to rupture at approximately 26 N load and 2.6% strain. Six full-scale concrete panels were prepared and tested under truck and three-point loads to quantify the performance of sensors with pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). The sensors were protected by precast mortar from brutal action during concrete casting. Once air-cured for 2 hours after initial setting, half a mortar cylinder of 12 mm in diameter ensured that the protected sensors remained functional during and after concrete casting. The strains measured from PPP-BOTDA with a sensitivity coefficient of $5.43{\times}10^{-5}GHz/{\mu}{\varepsilon}$ were validated locally by commercial fiber Bragg grating (FBG) sensors. Unlike the point FBG sensors, the distributed PPP-BOTDA sensors can be utilized to effectively locate multiple cracks. Depending on their layout, the distributed sensors can provide one- or two-dimensional strain fields in pavement panels. The width of both micro and major cracks can be linearly related to the peak strain directly measured with the distributed fiber optic sensor.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.101-110
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• 2014

Expansion agent is a very effective admixture for prevention of cracking due to autogenous/drying shrinkage and this can induce internal chemical prestress to embedded reinforcement. In this paper, tension-softening and hardening in cement mortar with steel and CSA expansion agent are experimentally evaluated. Cement mortar with steel reinforcement is prepared and tensile strength test is performed for evaluation of cracking and tensile behavior. In spite of slightly reduced strength and elasticity in CSA mortar, significantly increased tension-hardening behavior is evaluated in CSA mortar with induced chemical prestress. Furthermore previous tension softening models are compared with the test results and improvement are proposed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.11a
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• pp.71-74
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• 2007

With the changes of times the building materials tend to extend the demand for application under the special environment. Since high-ductile mortar is developed, the building materials show excellent performance like toughness, compression, tensile, and bending, etc. in the general concrete from the existing brittle point. And, recently they are widely used as repairing and reinforcing materials both at home and abroad because they are recognized as excellence like durability and fire-resistance. However, it is in a situation of creating problems in durability because it frequently happened deterioration of buildings that have already repaired and reinforced at a time when it requires reconstruction of recently deteriorated construction structure recently. Therefore, in this study improved with a more repair Material development and reinforcement of the second high-ductile mortar products for a variety of basic materials were presented want, research plans used include traditional repair materials and the newly developed PCM (polymer cement mortar) structural reinforcement type indicated that comparison. PCM analysis in order to present a rate depending on the types fiber 0, 1.2 and 2.0(%) at three levels and mixture water according to ratios of weight to Plain in the 2.0 and 1.85(kg) at two levels is set, the results were as follows. 1) This study has shown that PCM had excellent strain hardening behavior at the same time that the bending stress increased according to the fiber contents. 2) This study has shown that it had the durability performance due to the high substance transmission according to the fiber contents.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.137-140
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• 2009

Nowadays, the high performance composite materials are famous for the new construction materials as the construction buildings are bigger and higher. Out of them of all, the fiber reinforced concrete and mortar have been studied to develop and strengthen the performances of concrete, such as tensile strength, durability and the resistibility of crack. Also, it is considered that precast concrete is important alternatives of dry process for saving time, upgrading the material's quality and the productivity. Thus, PC panel is being produced for the use of dry wall as well as exterior finishing materials and it requires lots of tests and studies to be conducted to meet the various functional conditions. According to this study, it is considered that PVA fiber might be more effective than nylon fiber for developing the exterior PC panels.

• Computers and Concrete
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• v.4 no.5
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• pp.347-362
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• 2007

Due to heterogeneities at all scales, concrete exhibits significant variability in mechanical behavior from sample to sample. An understanding of the fundamental mechanical performance of concrete must therefore be embedded in a stochastic framework. The current work attempts to address the connection between a two-dimensional concrete mesostructure and the random local material properties associated within that mesostructure. This work builds on previous work that has focused on the random configuration of concrete mesostructures. This was accomplished by developing an understanding of the effects of variations in the mortar strength and the mortar-aggregate interfacial strength in given deterministic mesostructural configurations. The results are assessed through direct tension tests that are validated by comparing experimental results of two different, pre-arranged mesostructures, with the intent of isolating the effect of local variations in strength. Agreement is shown both in mechanical property values as well as the qualitative nature of crack initiation and propagation.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.329-331
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• 2013

The salt damage resistance of waterproofing membrane was evaluated on the cracked mortar substrate. The types of specimens are urethane, acrylic waterproofing membrane, and no coating mortar substrate. After these specimens were cured by water curing for 4 weeks, they were cured by atmospheric curing at 20±2Co for 8 weeks. The salt water immersion test was carried out by following KS F 2737, and the penetration depth of chloride ion into substrate was measured in 1, 4, 8, and 13 weeks. As a result, in the case of non coating specimen, the chloride ion penetrated within one week. In the coated specimens, a regardless of the membrane type, the chloride ion did not penetrate during 13 weeks-tests on condition that the cracked width of substrate is less than 0.3mm. Also, the penetration speeds of the coated specimens were lower than that of non coating specimen. Therefore, our results reached a conclusion that waterproofing membrane has high salt damage resistance.

• The Journal of Engineering Geology
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• v.4 no.1
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• pp.1-12
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• 1994

In general there are many cracks in rocks. In this study, we are concerned with the mechanical effect on cracks on the behavior of rocks. For this purpose, we used spedmens rnade of mortar having one crack set which has a constant length and same direction. Orientafion of this set was varied with respect to the loading axis. We did a number of uniaxial experiments and observed propagafion of the crack set to understand the effect set of the geometry of the crack set and its location on the mechanical behavior of the rocks with distributed crack sets. Finally, we analysed our experiments by FEM elastic analyses and Homogenization theory.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.365-366
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• 2009

Humidity curing of the concrete after placing is significant to ensure the crack resistance, strength, and durability. Generally, there are watering and sheet curing methods as humidity curing methods to the upper part of slab concrete, therefore this study investigates effects of these curing methods to preservation of humidity on the cement mortar.

• Magazine of the Korea Concrete Institute
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• v.5 no.1
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• pp.145-155
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• 1993

본 연구에서는 표면부를 에폭시 폴리머 모르터로 하고 , 중심부를 발포 폴리스티렌으로 하는샌드위치 패널을 제조하여, 표면부를 용접철강으로 보강한 경우와 보강하지 않은 경우에 대하여 4강 단순지지 조건에서의 정적 차 통해 하중-처짐, 휨모멘트-변형률, 파괴양상 등을 구명하였다. 단위중량, 극한가중, 휨모멘트는 중심부의 두께보다 표면부 두께에 더 큰 영향을 받으며 극한처짐은 보강안된 경우 표면부 보다 중심부 두께의 영향이 월등히 컸으마 보당된 경우는 표면부나 중심부 두께의 영향이 비슷하였다. 그러나 용접철망의 보강은 샌드위치 패널의 처짐억제 보다 인성증가에 기여도가 높은 것으로 나타났다. 샌드위치 패널의 파괴양상은 보강하지 않은 경우 선형파괴가 일어난데 비해 보강한 경우에는 방사상의 파괴가 일어났다.