• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.12
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• pp.915-923
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• 2018

A concrete embedded antenna design is proposed for probing the durability of a building at an industrial scientific medical band of 902~908 MHz. The proposed antenna is designed with a stacked slot patch structure for lower impedance variation to a dielectric constant of concrete, as a dielectric constant difference is derived from the moisture content. The proposed structure has a wider bandwidth when a parasitic patch structure is used, which reduces antenna performance degradation resulting from the moisture content of concrete. The measured voltage standing wave ratio of the proposed structure is less than 2 and the beam width is approximately $80^{\circ}$, whereas the gain is greater than 7 dBi. The proposed antenna is fabricated with a rectangle-type concrete block, which is simulated and measured for return loss and antenna gain.

• Composites Research
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• v.21 no.3
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• pp.24-30
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• 2008

Durability problems may arise in the concrete, which is one of the major construction materials, used in the construction field. Bridge piers and foundation piles are usually made with concrete and they are exposed to the moisture and hence the durability of the concrete reduced significantly due to oxidization of re-bar and icing of concrete. To mitigate such problems, FRP tube has been developed and the concrete filled FRP tube (CFFT) has been investigated to find the confinement effect which is provided additionally. It was reported that if the concrete is wrapped with FRP, strength and chemical resistance are improved significantly. In order to apply such a member in the construction field, structural behavior and applicable design guideline or design criteria must be thoroughly investigated. In the experimental investigation, the results are compared with the previous research results and the relationship which can predict the ultimate strength and strain is suggested. In addition, some comments found at the compression tests are given briefly.

• Journal of the Korea Institute of Building Construction
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• v.23 no.1
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• pp.11-22
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• 2023

In this work, a depth-by-depth evaluation on the deterioration of concrete is suggested by utilizing disk shaped concrete specimens. Dynamic elastic modulus of cylindrical concrete was measured using a free-free resonance column method and compared with dynamic elastic modulus of disk-shaped concrete measured by impulse excitation technique(IET) and impact resonance(IR). According to the results of the experiment, both IET and IR methods showed a smaller difference in dynamic elastic modulus with smaller deviation in data when thickness of the disk specimen was increased. This trend was more evident from dynamic elastic modulus measured by IR method compared to that measured by IET. Variation in data was also smaller with the IR result. To increase the accuracy of the data, it is recommended to use the IR method for disk specimen with a diameter of 100mm and a thickness of 25mm.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.829-839
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• 2003

Recently, the corrosion of reinforced concrete structures has received great attention related with the deterioration of sea-side structures, such as new airport, bridges, and nuclear power plants. In this regards, many studies have been done on the chloride attack in concrete structures. However, those studies were confined mostly to the single deterioration due to chloride only, although actual environment is rather of combined type. The purpose of the present study is, therefore, to explore the influences of carbonation to chloride attack in concrete structures. The test results indicate that the chloride penetration is more pronounced than the case of single chloride attack when the carbonation process is combined with the chloride attack. It is supposed that the chloride ion concentration of carbonation region is higher than the sound region because of the separation of fixed salts. Though the use of fly ash pronounces the chloride ion concentration in surface, amounts of chloride ion penetration into deep region decreases with the use of fly ash. The present study allows more realistic assessment of durability for such concrete structures which are subjected to combined attacks of both chlorides and carbonation but the future studies for combined environment will assure the precise assessment.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.77-78
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• 2017

Although many waterproofing materials and techniques have been developed and applied, there is still a leakage in concrete structures. The main reason for the failure of waterproofing is due to the lack of consideration of the environmental conditions and the inconsistent performance requirement of the waterproofing materials in response to the complexity of the environmental conditions., and materials that are unsuitable to the environment are still being selected for usage due to their low price. Moreover, there is no valid test assessment for waterproofing materials to be used prior to actual application in the construction site. The development of a testing method and apparatus that can evaluate the composite waterproofing method is proposed in this paper and an interpretation method that can analyze the results of the evaluation.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.11a
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• pp.189-190
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• 2018

KS standards mostly relate to single component material evaluation, so in cases of underground structure environments, most cannot predict the existing composite forms of deterioration, resulting in the applied waterproofing materials becoming unable to respond to these damaging factors. Current domestic waterproofing market in Korea mainly uses single-ply waterproofing materials comprised of coatings or waterproof sheets and two or more-ply composite waterproofing methods. In order to evaluate these types of composite waterproofing systems, a new test equipment and method that incorporates various deterioration conditions (joint displacement, chemical exposure, water pressure etc) was developed. In a comparison testing, the results showed that flexible type materials have higher response performance towards joint displacement than the hardened material.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.2
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• pp.136-143
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• 2013

In the sewage structures and wastewater facilities, concrete is exposed to hydrogen sulfide ($H_2S$) which acts as an acid material in a solution, and a strongly acidic sulfate ion ($SO{_4}^{-2}$) is generated by a sulfuric bacteria. Hence, a degradation of concrete with biochemical corrosion would be accelerated. Finally, durability of concrete and concrete structures may be greatly reduced. In this study, in order to remove the hydrogen sulfide which is used by the sulfuric bacteria organic-biologically, the antibiotic metal and metallic salt powders were mixed to concrete, and a suppressing performance of the sulfate ion was assessed. For the sulfuric acid bacteria, a comparative evaluation of antimicrobial performance on neutralized concrete specimens were carried out, also by a rapid chloride penetration test, chloride penetration depths and diffusion coefficients were measured for antibiotic concrete in accordance with the amount of metal and metallic salt-based antibacterial agents. Eventually, by an observation of the biochemical state of the surface of concrete specimens exposed outdoors, the performance and applicability of antibiotic concrete were confirmed.

• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.377-384
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• 2014

Recently, the trend toward larger architectural structures continues and accelerates demand for Ultra High Strength Concrete (UHSC) which satisfies structural performance. However, UHSC has weakness in fire and the performance tests are required. In this paper, the change of mechanical properties of 100 MPa grade UHSC exposed to high temperatures ($20^{\circ}C{\sim}800^{\circ}C$) was observed to develop high temperature material model of UHSC: residual compressive strength, modulus of elasticity, property of stress-strain on monotonous loading and property of stress-strain on cyclic loading. In addition, TG/DTA and SEM Images analyses were performed to investigate chemical and physical characteristics of UHSC, and the results of this research were compared with those of previous studies. As a result, UHSC at the heating temperature of $300^{\circ}C$ showed a sharp decrease of residual compressive strength and modulus of elasticity. And It was shown that UHSC had a plastic behavior at more than $400^{\circ}C$ on the cyclic loading and revealed a same tendency in both monotonous and cyclic loading of all heating temperatures. In addition, through TG/DTA and SEM images analyses compared with those from previous studies, it was shown that the deterioration of concrete inner tissue, water evaporation and chemical reaction caused the decrease of residual compressive strength and modulus of elasticity.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.19-27
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• 2010

Aging and severe environments are major causes of damage in reinforced concrete (RC) structures such as buildings and bridges. Deterioration such as concrete cracks, corrosion of steel, and deformation of structural members can significantly degrade the structural performance and safety. Therefore, effective and easy-to-use methods are desired for repairing and strengthening such concrete structures. Various methods for strengthening and rehabilitation of RC structures have been developed in the past several decades. Recently, FRP composite materials have emerged as a cost-effective alternative to the conventional materials for repairing, strengthening, and retrofitting deteriorating/deficient concrete structures, by externally bonding FRP laminates to concrete structural members. The main purpose of this study is to investigate the effectiveness of adaptive neuro-fuzzy inference system (ANFIS) in predicting behavior of circular type concrete column retrofitted with FRP. To construct training and testing dataset, experiment results for the specimens which have different retrofit profile are used. Retrofit ratio, strength of existing concrete, thickness, number of layer, stiffness, ultimate strength of fiber and size of specimens are selected as input parameters to predict strength, strain, and stiffness of post-yielding modulus. These proposed ANFIS models show reliable increased accuracy in predicting constitutive properties of concrete retrofitted by FRP, compared to the constitutive models suggested by other researchers.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.107-113
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• 2001

This study was conducted preliminarily to develop the crack source location technique for plain concrete beam using acoustic emission(AE). Before the main experiment, the test of virtual An source location was achieved in plain concrete block. The sensor layout was mutually compared between triangular layout and rectangular layout. As the results of test, AE source location by triangular layout was evaluated more effective than that by rectangular layout. The specimen to apply he source location technique was man in total nine specimens (each three in 40 %, 50%, 60% of W/C ratio) which the experiment variable was the compressive strength level(W/C ratio). The bending loading method is selected by cyclic loadings to evaluate the degree of concrete damage. It is seen that Kaiser effect and Felicity effect exists through analysis of AE parameters in coming failure experiment. As a result of analyzing the felicity ratio(FR) values, it is shown that this values can be used for evaluating the degree of concerto damage. AE activity is started highly at the 70% of failure load without the compressive strength level. Thus considered by a index in constructing the system of the failure warning at application of the field structure. And the results compared the real cracking location with the source location has perceived by AE monitoring before it is appeared the primary crack by visual observation.