• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.27 no.1
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• pp.38-45
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• 2017

Objectives: Radon may be second only to smoking as a cause of lung cancer. Radon is a colorless, tasteless radioactive gas that is formed via the radioactive decay of radium. Therefore, radon levels can build up based on the amount of radium contained in construction materials such as phospho-gypsum board or when ventilation rates are low. This study provides our findings from evaluation of radon gas at facilities and offices in an industrial complex. Methods: We evaluated the office rooms and processes of 12 manufacturing factories from May 14, 2014 to September 23, 2014. Short-term data were measured by using real-time monitoring detectors(Model 1030, Sun Nuclear Co., USA) indoors in the office buildings. The radon measurements were recorded at 30-minute intervals over approximately 48 hours. The limit of detection of this instrument is $3.7Bq/m^3$. Also, long-term data were measured by using ${\alpha}-track$ radon detectors(${\alpha}-track$, Rn-tech Co., Korea) in the office and factory buildings. Our detectors were exposed for over 90 days, resulting in a minimum detectable concentration of $7.4Bq/m^3$. Detectors were placed 150-220 cm above the floor. Results: Radon concentrations averaged $20.6{\pm}17.0Bq/m^3$($3.7-115.8Bq/m^3$) in the overall area. The monthly mean concentration of radon by building materials were in the order of gypsum>concrete>cement. Radon concentrations were measured using ${\alpha}-track$ in parallel with direct-reading radon detectors and the two metric methods for radon monitoring were compared. A t-test for the two sampling methods showed that there is no difference between the average radon concentrations(p<0.05). Most of the office buildings did not have central air-conditioning, but several rooms had window- or ceiling-mounted units. Employees could also open windows. The first, second and third floors were used mainly for office work. Conclusions: Radon levels measured during this assessment in the office rooms of buildings and processes in factories were well below the ICRP reference level of $1,000Bq/m^3$ for workplaces and also below the lower USEPA residential guideline of $148Bq/m^3$. The range of indoor annual effective dose due to radon exposure for workers working in the office and factory buildings was 0.01 to 1.45 mSv/yr. Construction materials such as phospho-gypsum board, concrete and cement were the main emission sources for workers' exposure.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.1
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• pp.1-29
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• 2019

Related to the previous paper on the typical crack pattern of tunnel lining with NATM, the characteristic defects in reinforced cement concrete lining of NATM tunnel have analyzed with the precise inspection with safety and diagnosis (PISD) by KISTEC. Depending on the reinforcing materials, steel rebar, steel fiber, and glass fiber have been implemented to reinforcing lining in various NATM tunnel constructions. Reinforcing lining with rebar are prevailed on NATM tunnel to countermeasure the weak geological circumstances, to pursuit the economical tunnel sections, and to resist the risk of tunnel deterioration. By the special act on the safety control of public facilities, the reinforced NATM tunnels for more than 1 km length are scrutinized closely to characterize defects; crack, reinforcement exposure, and lack of lining. Crack resistance by reinforcing is shown in comparison with the normalized crack to the length of tunnel. Typical exposed reinforcements in lining have exemplified with various sections. The lack of lining due to the mal-construction, spalling, fire, earthquake and leaching has been analyzed. The cause and mechanism with the field inspections and other studies has also been verified. Detailed cases are selected by the above concerns as well as the basic information from FMS (Facilities Management System). Likewise the previous paper, this study provides specialized defects in reinforced lining of NATM and it can be widely used in spreading the essential technics and reporting skills. Furthermore, it would be advised and amended for the detail guideline of Safety Diagnosis and PISD (tunnel).

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.2
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• pp.1-8
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• 2022

The corrosion of reinforcement is the main reason for the performance degradation of concrete structures. The pre-rusted parts of rebar in concrete structures are vulnerable to the corrosion, especially if the structure is exposed to wet or chlorinated environments. In this study, effects of different curing solution on corrosion behavior of the pre-rusted rebars in the cement composites were investigated. HCl(3%) and CaCl₂(10%) solution were utilized to accelerate the pre-rust of the rebar, and each pre-rust condition rebar including reference (RE) were placed in mortar cylinder. Three kinds of samples then were cured in CaCl₂ (3%) solution and tap water respectively for 120 days. Electrochemical polarization and half-cell potential measurement were used to monitor the influence of curing water on the corrosion behavior of pre-rusted steel bar in cement composite. The surface morphology and composition of corroded steel bar were analyzed by scanning electron microscope and energy dispersive X-ray diffraction. The results show that the corrosion rates of pre-rusted samples in both curing water are higher than that of non-pre-rusted samples. The corrosion rates of RE, CaCl₂ and HCl pre-rusted samples in salt water were 8.14, 4.48, 13.81 times higher than those in tap water respectively, on the 120th day.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.105-111
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• 2020

The present study examined the effect of the silica-based accelerating agents on the setting time and compressive strength gain of biomimetic glycocalix coating materials that has been developed for protecting the substrate of concrete exposed to chemical and microbiological attacks. The accelerating agent contents varied from 10mL/L to 40mL/L in the mixtures of glycocalix coating materials determined for shotcrete and lining techniques. Test results showed that the setting time of coating materials containing accelerating agents was affected by the contents of the bacteria carrier. When the accelerating agent content was 40mL/L, the final setting time was 80 minutes for shotcrete mixtures and 318 minutes for lining mixtures. Meanwhile, the compressive strength gain of coating materials with accelerating agents tended to be lower than that of counterpart materials without accelerating agents.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.46-52
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• 2017

Recently durability design based on deterministic or probabilistic method has been attempted since service life evaluation in RC(Reinforced Concrete) structure exposed to chloride attack is important. The deterministic durability design contains a reasonable method with time effect on surface chloride content and diffusion coefficient, however the probabilistic design procedure has no consideration of time effect on both. In the paper, a technique on PDF(Probability of Durability Failure) evaluation is proposed considering time effect on diffusion and surface chloride content through equivalent surface chloride content which has same induced chloride content within a given period and cover depth. With varying period to built-up from 10 to 30 years and maximum surface chloride content from $5.0kg/m^3$ to $10.0kg/m^3$, the changing PDF and the related service life are derived. The proposed method can be reasonably applied to actual durability design with preventing conservative design parameters and considering the same analysis conditions of the deterministic method.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.4
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• pp.307-313
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• 2014

Recent interest in the increased structural performance and durability evaluation of this concrete structure in a salt damage environment is increasing. The most secure and reliable method of accelerated corrosion test is a method to carry out the rebar corrosion monitoring can be exposed directly to the marine test site exposure. However, long-term exposure testinghas the disadvantage that a long period is necessary. So, a lot of research on RC of salt damage environment have beenpromoted as alternatives to replace this. However, accelerated corrosion test, in the short term only is appropriate and is but an accelerated test method to evaluate the critical chlorine concentration, there is a difficult problem that you still get the answer. It is one of the correlation problems accelerated test correspond to a certain period of exposure environment. Therefore, in this study, to clarify the differences rebar corrosion beginning, through the actual corrosion accelerated test in corrosion time and laboratory test chamber of the structure of the marine environment results in both environments, it is an object of correlation coefficient derived.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.139-149
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• 2017

The maintenance, repair, and reinforcement projects and structural stability assessments of Seokguram have primarily focused on examining the condition of stone members of Seokguram and the concrete dome structure for Seokguram. However, a 12 m-high rock slope located behind Seokguram raises a concern of slope failure and rockfall, which may reduce stability of Seokguram. It is also unclear whether the soil slopes and masonry wall at the side and the front of Seokguram have sufficient long-term stability against localized heavy rains and earthquakes, which have been frequent in recent years. The present study investigates the ground and the slopes around Seokguram using detailed field survey to identify geographical and geological risk factors, and assess structural stability of the exposed rock mass behind and the slope in front of Seokguram and the masonry wall using stability analysis.

• Journal of the Korean GEO-environmental Society
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• v.8 no.6
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• pp.5-12
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• 2007

Mudstone has characteristics that it has high enough strength and stiffness in a dry condition, but the strength and stiffness decrease in a wet condition with groundwater infiltration. The sliding of cut slope frequently encountered in Pohang area has been reported due to the rapid reduction of shear strength in mudstone after being exposed to the air. The study in this paper shows that mudstone having enough strength in a boring stage has lost the strength after installing PRD (percussion rotary drill) steel pipe pile inducing an insufficient bearing capacity. Field test has been performed to investigate the most favorable method for increasing a pile bearing capacity in mudstone with various methods such as MSG (Micro Silica Grouting) around the tip and side of a pile, the perimeter grouting combined with Micro pile reinforcement, and concrete filling after tip reinforcing grouting. MSG has been turned out to be the most favorable method for increasing a pile bearing capacity in mudstone, confirmed by the static load test.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.259-268
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• 2016

The service life evaluation in RC(Reinforced Concrete) structure exposed to chloride attack can be classified into deterministic and probabilistic method, and it significantly varies with design parameters. The present work derives PDF (Probability of Durability Failure) and the related service life considering time-dependent diffusion coefficient and internal parameters such as reference diffusion coefficient, critical chloride content, and time-exponent. When critical chloride content increases to 133.3%, the changing ratios of service life are 134.0~145.4% for deterministic method and 149.2%~152.5% for probabilistic method, respectively. In the case of increasing time-exponent to 200%, they increase to 323.8% for deterministic method and 346.0% for probabilistic method. Through adopting time-diffusion coefficient for probabilistic method, reasonable service life evaluation can be achieved, and it is also verified that increasing time-exponent through mineral admixture is very effective to extension of service life in RC structure.

• Fire Science and Engineering
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• v.25 no.1
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• pp.63-71
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• 2011

When it comes to slim floor using asymmetric H-beam, it was designed that the steel member is embedded in concrete with relatively low thermal conductivity so as to minimize the deterioration of rigidity of steel member in fire. But given the bottom flange of asymmetric H-beam is directly exposed to the fire, the measure of applying the fireproof coating to improve the fire rate performance of slim floor beam was sought. The test was aimed at comparing the fireproof performance by adjusting the load ratio of 0.4 and 0.3, and The test was carried out to identify the 3-hour fire performance by reinforcing the beam as well as applying the fireproof coat, In the wake of comparing the specimen depending on variation of load ratio, lowering load ratio by 0.1 resulted in difference of 12 minutes and deflection was 39 mm. It was able to improve 12 minutes by reinforcing the beam and up to 102.4 mm in deflection.