• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.3
• /
• pp.92-99
• /
• 2021

In the case of precise safety inspection and precise safety diagnosis of a building, a condition evaluation must be conducted to determine the safety grade. Since 2004, an evaluation method using fuzzy theory has been introduced for quantitative condition evaluation,and the relationship and importance of reinforced concrete members using fuzzy theory have been applied. Generally, fuzzy theory is a method used to deal with ambiguous expressions with unclear correlations, but at the time of development, it seems that it was developed by applying fuzzy theory as an alternative in a situation where inspection and diagnosis result data were insufficient. Therefore, it is necessary to verify the relationship and importance of evaluation items derived based on the current fuzzy theory using actual inspection and diagnosis result data.In this study, the correlation between the evaluation items was derived by using the results of 19 precision safety inspections and 9 precision safety inspections and the performance score function formula, and using this, a reasonable durability score calculation formula of the member was presented.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.2
• /
• pp.172-179
• /
• 2016

For an evaluation of service life in RC(Reinforced Concrete) structures, deterministic method and probabilistic method considering random variables of design parameters are usually adopted. In the work, surface chloride contents which vary with distance from sea shore and height are investigated from the previous research literature surveys, and they are considered for service life estimation. Through the analysis, the probabilistic method shows much lower results, which is due to variations of design parameters and very low intended durability failure. In the deterministic method, the structures within 250m and higher than 60m are evaluated to be free from chloride attack. In the probabilistic method, those higher than 60m in all the region and higher than 40m and 250m from sea shore are evaluated to satisfy the service life.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.4
• /
• pp.220-227
• /
• 2021

PCT (Power Cable Tunnel) and UT (Utility Tunnel), which are non-transport underground infrastructures, are mostly RC (Reinforced Concrete) structures, and their durability decreases due to the deterioration caused by carbonation over time. In particular, since the rate of carbonation varies by use and region, a predictive model based on actual carbonation data is required for individual maintenance. In this study, a carbonation prediction model was developed for non-transport underground infrastructures, such as PCT and UT. A carbonation prediction model was developed using multiple regression analysis and deep neural network techniques based on the actual data obtained from a safety inspection. The structures, region, measurement location, construction method, measurement member, and concrete strength were selected as independent variables to determine the dependent variable carbonation rate coefficient in multiple regression analysis. The adjusted coefficient of determination (Ra2) of the multiple regression model was found to be 0.67. The coefficient of determination (R2) of the model for predicting the carbonation of non-transport underground infrastructures using a deep neural network was 0.82, which was superior to the comparative prediction model. These results are expected to help determine the optimal timing for repair on carbonation and preventive maintenance methodology for PCT and UT.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.4
• /
• pp.479-499
• /
• 2019

State assessment of an operational tunnel is usually done by performing visual inspection and durability tests by following the detailed guideline for safety inspection (SI) and/ or precision inspection for safety and diagnosis (PISD). In this study, 12 NATM tunnels, which have been operational for more than 10 years, were inspected to figure out the cause of longitudinal cracks for the purpose of modifying the scoring items in the state assessment NATM tunnel related to the longitudinal crack and the thickness of concrete lining. All investigated tunnels were classified into four groups depending on the shape and usage of each tunnel. The causes of longitudinal crack occurrence were analyzed by investigating the correlations between the longitudinal crack and the following four factors: the patterns of ground excavation; construction state of primary support system; characteristics of material properties of the concrete lining; and thickness of lining which was obtained by Ground Penetration Radar (GPR) tests. It was found that influencing factors causing longitudinal cracks in the lining were closely related with the construction condition of the primary support system, i.e. shotcrete, rockbolt, and steel-rib; crack occurrences were not much affected by the excavation patterns. As for the properties of concrete lining materials, occurrence of the longitudinal crack was mostly affected by the following three items: w/c ratio; contents of cement; and strength of lining. When estimating the lining thickness of the concrete lining by GPR tests and taking thickness effect into account in the statement assessment, it was concluded that increase of the index score by an average of 0.03 (ranging from 0.01 up to 0.071) is needed; a more realistic way of state assessment should be proposed in which the increased index score caused by lack of lining thickness should be taken into account.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.3
• /
• pp.83-91
• /
• 2019

The purpose of this study is to assess a fire-damaged concrete structure using a digital camera and image processing software. To simulate it, mortar and paste samples of W/C=0.5(general strength) and 0.3(high strength) were put into an electric furnace and simulated from $100^{\circ}C$ to $1000^{\circ}C$. Here, the paste was processed into a powder to measure CIELAB chromaticity, and the samples were taken with a digital camera. The RGB chromaticity was measured by color intensity analyzer software. As a result, the residual compressive strength of W/C=0.5 and 0.3 was 87.2 % and 86.7 % at the heating temperature of $400^{\circ}C$. However there was a sudden decrease in strength at the temperature above $500^{\circ}C$, while the residual compressive strength of W/C=0.5 and 0.3 was 55.2 % and 51.9 % of residual strength. At the temperature $700^{\circ}C$ or higher, W/C=0.5 and W/C=0.3 show 26.3% and 27.8% of residual strength, so that the durability of the structure could not be secured. The results of $L^*a^*b$ color analysis show that $b^*$ increases rapidly after $700^{\circ}C$. It is analyzed that the intensity of yellow becomes strong after $700^{\circ}C$. Further, the RGB analysis found that the histogram kurtosis and frequency of Red and Green increases after $700^{\circ}C$. It is analyzed that number of Red and Green pixels are increased. Therefore, it is deemed possible to estimate the degree of damage by checking the change in yellow($b^*$ or R+G) when analyzing the chromaticity of the fire-damaged concrete structures.

• Korean Journal of Construction Engineering and Management
• /
• v.23 no.1
• /
• pp.46-53
• /
• 2022

The railway platform is an important facility closely related to the safety of passengers, trains, and images of railway facilities, and requires thorough facility management. However, the problem that the finishing material (plastering mortar) for the joint finishing of dissimilar materials (concrete+granite) falls off in the direction of the track at the platform podium is occurring multiple times across the country. Since these problems threaten the safety of train operation and the safety of passengers, immediate and continuous management is required. This study tried to derive improvement plans through the analysis of the drop-off problem of finishing materials occurring at the platform podium. The status of missing finishing materials for the platform podiums of about 200 railway stations and the related design and construction standards of the Korea National Railway were investigated. After that, the cause of the drop-off of the finishing material was analyzed, and as a result, it was found that the main cause was the boundary between the roadbed and the architectural process that occurred during construction. Subsequently, in connection with the derived causes and design, construction standards, (1) improvement of finishing materials or construction methods, (2) design of finishing materials that are easy to adjust height, (3) design of separate finishing methods, (4) improvement methods and durability were suggested.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.4
• /
• pp.57-65
• /
• 2013

The development of the oil refining industry has resulted in an annual 120 million tons of sulphur, which is a by-product of the desulphurization process. To exploit this abundance, the applications of sulphur must be expanded. as excellent durability of reuse of leftover sulphur which has high potential for utilization in construction materials, the study is actively in progress. Meanwhile, there has been active research on semi-rigid pavements that draw on the strengths and overcome the weaknesses of asphalt and concrete pavements. Acrylate is used to prevent cracking but involves a high cost, thus, an alternative material is required. As such, this study presents methods on the reuse of leftover sulphur and examines the engineering performance of grout containing sulfur polymer emulsion (SPE) for use in semi-rigid pavements. Our analysis shows that grout in which 30% of acrylate is replaced with SPE has superior properties in terms of time of flow and strength compared to regular grout. However, performance declined when more than 50% of acrylate was replaced by SPE, indicating that the optimum replacement level is 30%. Through SEM analysis, we found that grout with utra harding cement in this study at three hours had similar hydration properties to that of Type 1 Ordinary Portland Cement (OPC) at seven days, and maintained the properties regardless of grout containing SPE. OPC and grout with a replacement level of 30% displayed similar levels of chloride invasion resistance, whereas grout without SPE was far less resistant. Within the scope of this paper, the optimum replacement level of acrylate with SPE was found to be 30% in consideration of various properties such as time of flow, strength, and chloride invasion resistance.

• Journal of the Korea Institute of Building Construction
• /
• v.11 no.4
• /
• pp.345-352
• /
• 2011

The purpose of this study was to investigate the expansion of alkali-activated mortar based on ground granulated blast furnace slag containing reactive aggregate due to alkali-silica reaction. In addition, this study was particularly concerned with the behavior of these alkaline materials in the presence of reactive aggregates. The experimental program included expansion measurement of the mortar bar specimens, as well as the determination of the morphology and composition of the alkali-silica reaction products by using scanning electron microscopy(SEM), and energy dispersive x-ray(EDX). The experiment showed that while alkali-activated ground granulated blast furnace slag mortars showed expansion due to the alkali-silica reaction, the expansion was 0.1% at Curing Day 14, showing that it is safe. After the accelerated test, SEM and BEM analysis showed the presence of alkali-silica gel and rim around the aggregate and cement paste. According to the EDX, the reaction products decreased markedly as alkali-activated ground granulated blast furnace slag was used. In addition, for the substitutive materials of mineral admixture, a further study on improving the quality of alkali-activated ground granulated blast furnace slag is needed to assure of the durability properties of concrete.

• Journal of the Korea Institute of Building Construction
• /
• v.17 no.2
• /
• pp.149-155
• /
• 2017

In this research, the surface covered curing method using the double-layered bubble sheet was evaluated. This double-layered bubble sheet has outstanding insulating performance with its low heat conductivity and high economic feasibility with its high durability. However, in the case of wall-typed building construction, the area of exposed rebar is curious on curing performance with the double-layered bubble sheet in spite of the double-layered bubble sheet showed favorable performance for slab. Therefore, in this research, regarding the actually constructed wall-typed apartment building, the most efficient curing method was suggested based on the evaluation of curing performance depending on temperature distribution depending on various location of covered or exposed rebar. As a result, the D method was determined as the most efficient curing method without any concern of early-age frost damage. However, by considering easiness of construction, the B method of covering the pieced double-layered bubble sheet on gap between rebars can be another option of desired result.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.1D
• /
• pp.91-98
• /
• 2011

Recently, the usage of elastic paving using EPDM Chip instead of pedestrian sidewalk blocks or permeable concrete used mostly for pedestrian walk, trails and in parks has been increassed as it can absorb impact during walking and produce wide range of colors and designs. However, the properties of EPDM Chip including elasticity and durability are decreased when exposed to ultraviolet ray and scenic paving functions through various colors are lowered due to the yellowing phenomenon. In this study, ultraviolet ray accelerated weathering test has been conducted to analyze the color changes in EPDM Chip and polyurethane resin, which are the main ingredients of elastic paving, when exposed to ultraviolet ray. The color differences are quantitatively analyzed through the color value coordination of the colored space by using the color difference scheme. The experimental results show that the color changes in BL polyurethane resin which is used most frequently at present was larger than that of EPDM Chip. Moreover, the total color difference, ${\Delta}E$, of BC polyurethane resin are 3.162 on the $14^{th}$ day of commencement of acceleration, which is 6 times greater color change resistance against ultraviolet ray than that of BL polyurethane resin with total color difference of 20.639. Therefore, the usage of BC polyurethane resin, which is manufactured to have chain-type molecular structure by using the isocyanate as the HMDI at the time of producing polymer, as binder in elastic paving with EPDM Chip is found to be a highly efficient method of restraining the color changes due to the ultraviolet ray.