• Journal of Korean Association for Spatial Structures
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• v.23 no.4
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• pp.81-88
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• 2023

Numerous factors contribute to the deterioration of reinforced concrete structures. Elevated temperatures significantly alter the composition of the concrete ingredients, consequently diminishing the concrete's strength properties. With the escalation of global CO2 levels, the carbonation of concrete structures has emerged as a critical challenge, substantially affecting concrete durability research. Assessing and predicting concrete degradation due to thermal effects and carbonation are crucial yet intricate tasks. To address this, multiple prediction models for concrete carbonation and compressive strength under thermal impact have been developed. This study employs seven machine learning algorithms-specifically, multiple linear regression, decision trees, random forest, support vector machines, k-nearest neighbors, artificial neural networks, and extreme gradient boosting algorithms-to formulate predictive models for concrete carbonation and thermal impact. Two distinct datasets, derived from reported experimental studies, were utilized for training these predictive models. Performance evaluation relied on metrics like root mean square error, mean square error, mean absolute error, and coefficient of determination. The optimization of hyperparameters was achieved through k-fold cross-validation and grid search techniques. The analytical outcomes demonstrate that neural networks and extreme gradient boosting algorithms outshine the remaining five machine learning approaches, showcasing outstanding predictive performance for concrete carbonation and thermal effect modeling.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.1-7
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• 2018

As part of a research dedicated to the field evaluation of the durability of concrete subjected to freezing-thawing, this study analyzes the relationship between the surface roughness and the relative dynamic elastic modulus through image analysis. Four mix compositions with water-to-binder ratios (W/B) of 40%, 50%, 60% and 70% and without AE agent were considered to provoke early freezing. The basic physical properties of the mixes including the relative dynamic elastic modulus and the compressive strength were first evaluated experimentally according to W/B. Then, tests were performed to measure the surface roughness followed by photographs and SEM image analysis. The measured surface roughness tended to increase with larger number of freezing-thawing cycles regardless of W/B. The relative dynamic elastic modulus appeared to increase gradually with the number of cycles for the relatively denser mixes with W/B of 40% and 50%. Besides, the surface roughness increased only at rupture for the mixes with W/B of 60% and 70%. Moreover, the analysis of the photographs of the surface of the mixes with W/B of 40% and 50% revealed that the degradation progressed gradually from the surface with the freezing-thawing cycles. However, for the mixes with W/B of 60% and 70%, apparent change of the surface remained very insignificant until rupture at which damage like cracking could be observed. Consequently, the analysis of surface photograph or the measurement of the surface roughness presented some limitation in assessing the degree of freezing-thawing-induced degradation in case of relatively porous specimens. On the other hand, the photograph and surface roughness appeared to be sufficient for assessing such degradation for the mixes with W/B of 40% and 50%. Accordingly, the image of the surface and the surface roughness are potentially applicable on site for the assessment of freezing-thawing damages in relatively dense mixes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.57-62
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• 2020

Among the sewage pipes installed in Korea, the length of concrete pipes exceeding 20 years is 66,334 km (42.5%). Deteriorated concrete sewer pipes need to be repaired due to the leakage of internal sewage, which causes problems such as sink holes by expanding the cavity around the pipeline. In this study, we tried to apply anti-washout underwater mortar with ultra rapid hardening cement and segregation reducing agent to sewage pipe repair. As a result of the setting time test, the final set time was delayed by up to 172% by incorporating segregation reducing agent. In the test for measuring the degree of mortar segregation in water, it was measured at pH 12 or less under all mixing conditions. In addition, the suspension amount was measured to be 50 mg / l or less to satisfy the KCI-AD102 standard by incorporating a segregation reducing agent. In terms of the average value of mortar compressive strength, by incorporating segregation reducing agent, the strength of the specimens produced in air was more than 80% of that of the specimens produced in water. Conversely, the bond strengths of the specimens produced in water were measured to be higher than those of the specimens produced in air. Water resistance was evaluated by measuring water absorption and water permeability. Water absorption and water permeability were reduced by 42.6% and 36.6%, respectively, by mixing segregation reducing agent.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.220-227
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• 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 the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.122-129
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• 2019

The movement of deterioration agents such as a chloride ion, etc. in concrete varies with loading conditions and micro-structure developed by age effect. In this paper, the carbonation behavior by accelerated carbonation test is evaluated considering curing periods(28 days, 91 days, and 365 days) and loading conditions. Carbonation velocity coefficients are obtained referred to KS F 2584. In the control case without loading condition, carbonation velocity coefficient of 91 days decreases to 50.0 % level and that of 365 days decreases to 44.8 % level than that of 28 days curing condition. In 28 curing days, carbonation velocity coefficients changed level of 103.9 ~ 108.8 % in tensile region and 91.9~104.6 % in compressive region by loading conditions. Carbonation velocity coefficients in the 30 % and 60 % tensile loading case at 28 days decreases to 47.3 % and 52.5 % level compared to control case after 1 year. Furthermore, 45.8 % and 44.9 % level of carbonation velocity coefficients are evaluated for 30 % and 60 % compressive loading conditions compared to control case after 1 year. Carbonation velocity coefficient decreases in the 30 % compressive loading level due to effective pore compaction and it increases afterwards due to micro-cracking. In the tensile loading condition, unlike the behavior of compressive region, it linearly increases with increasing loading level.

• Journal of the Korean Geosynthetics Society
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• v.19 no.4
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• pp.41-50
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• 2020

Since cracks in concrete structures expedite corrosion of reinforced concrete over a long period of time, regular on-site inspections are essential to ensure structural usability and prevent degradation. Most of the safety inspections of facilities rely on visual inspection with naked eye, so cost and time consuming are severe, and the reliability of results differs depending on the inspector. In this study, a portable measuring device that can be used for safety diagnosis and maintenance was developed as a device that measures the width and length of concrete cracks through image analysis of cracks photographed with a camera. This device captures the cracks found within a close distance (3 m), and accurately calculates the unit pixel size by laser distance measurement, and automatically calculates the crack length and width with the image processing algorithm developed in this study. In measurement results using the crack image applied to the experiment, the measurement of the length of a 0.3 mm crack within a distance of 3 m was possible with a range of about 10% error. The crack width showed a tendency to be overestimated by detecting surrounding pixels due to vibration and blurring effect during the binarization process, but it could be effectively corrected by applying the crack width reduction function.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.69-78
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• 2008

In this study, in order to verify the reinforcement effects of the cracked concrete tubes and culverts, static load test was conducted. After the load carrying capacity of the original concrete tubes (nominal diameter 0.8 m, 1.0 m, 1.5 m) and box culverts (inner width 2.0 m. 2.5 m) was reduced by the cracking test, the cracked concrete specimens were strengthened by installing profile with steel stiffener and high strength mortar. And then, the maximum load tests were conducted the renewal concrete tubes and box culverts. According to the method application, the load carrying capacity increased 1.66~3.50 times than it of the original tubes before applying the method. In case of the original box culverts, the load carrying capacity increased 1.66~3.10 times than the case before installing profile and high strength mortar. Also non-linear analysis was carried out by using the commercial FEM program of ABAQUS 6.6. Solid (C3D8R) elements and concrete damage plasticity option was applied to the analysis. For reflecting confined reinforcing bars in the analysis, the composite material properties were used.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.130-136
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• 2017

The present work is for an evaluation of tension behavior and surface deterioration of FRP Hybrid Bar due to UV exposure and freezing/thawing(F/T) actions. For the work, FRP Hybrid Bar is subjected to UV exposure test, then F/T test is performed successively to 180 cycles. In FRP Hybrid Bar, no significant surface deterioration is evaluated after UV exposure. Tension hardening performance, a unique engineering advantage of FRP Hybrid Bar, is still maintained after F/T test. The performance in FRP Hybrid Bar exposed to UV is still effective. FRP Hybrid Bar exposed to UV have almost similar tension behavior of FRP Hybrid Bar without UV exposure. Although F/T cycles increase to 180, steel rebar, FRP Hybrid Bar, and FRP Hybrid Bar exposed to UV show no significant changes in tension behavior. In the work, UV exposure and F/T actions are evaluated to have little negative effect on surface deterioration and tensile performance in FRP Hybrid Bar, however spalling of silica coating due to impact should be considered since it affects bonding strength to outer concrete.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.59-64
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• 2018

The damages to the reinforced earth retaining wall are divided into the front wall, foundation, drainage and upper slope. Damage of reinforced earth retaining wall is mainly caused by damage caused by drainage problem in the field. Recently, damage caused by snow removal materials have been occurred. Recently, the amount of snow removal materials used in winter is increasing due to abnormal weather. This chlorides degrades the concrete structure, where the reinforced earth retaining wall was no exception. There has recently been a case in which the front wall of the reinforced earth retaining wall deteriorates due to the chlorides introduced into the back filling portion through the drainage passage. Therefore, in this study, the cause of damages of reinforced earth retaining wall constructed in bridge abutment was analyzed, and an analytical study was conducted on the countermeasure. As a result, it was found that chlorides, which was introduced through the drainage system in the expansion joint of the bridge shift part or the upper structure, is infiltrated into the back part of the reinforced earth retaining wall and damaged. Therefore, it is suggested to improve the drainage system and restored the stiffness of the front wall.

• Magazine of the Korea Concrete Institute
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• v.7 no.3
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• pp.187-198
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• 1995

This paper develops practical and reallstic reliabllity models and methods for the evaluation of system rehability and system rellabllity based ratlng of R.C box glrder bridge superstructures. The precise prediction of reberved carrying capacity of bridge as d system is extremely difficult especially when the brldges are highly redundant and slgnlficantly deter 1or;itcd or dainagetl. Thls papel proposes a nt2w approach for the evaluation of reseived system c,drrying capaaty of br~dges in terms ot equ~vdleiit system strength, which may b~ ddcflned as a brtdge system strength correipcmdlng tu the system rehability of the bridge. This cm be ticrAvcd from an Inverse process bami or1 the con~ept of FOSM(F1rst Order Second Moment) form of system reliabihty index. The sf rength llmt state models for K C box girder br~dges suggested In the paper dre based on the basi~ bending and shear strength And thc system reliatxllty pro,~lerri of box gritier super structure 1s formuldted as parallel serles models obtalncd f ~ o m thc FMA(Fdilure blode Rp proath) based on major failure mc>clmusrns or c~itlcal fdure ,>tatcs of each nuder .WOSM(Ad-vanced First Order Second Moment) and IST(1mportance Sampling Technique) simulation algorithm are used for the reliability analysis of the proposed models.