https://doi.org/10.4334/JKCI.2026.38.3.275

서동희(Donghui Seo) ; 이태민(Taemin Lee) ; 우욱용(Ukyong Woo) ; 목지욱(Ji-wook Mauk) ; 최하진(Hajin Choi)

This study presents a non-destructive evaluation technique utilizing ground penetrating radar (GPR) to identify interlayer boundaries and quantitatively assess the thicknesses of floor system components. The proposed method employs time-series electromagnetic signals acquired through GPR antennas, incorporating time-zero correction and hyperbola removal to enhance measurement accuracy. Validation was performed using mock-up specimens, with GPR-derived depths compared against those obtained via core drilling. The estimated thicknesses of the finishing mortar and autoclaved lightweight concrete (ALC) layers achieved accuracies of 95.8 % and 99.9 %, respectively. A multilayer depth extraction method, which independently applies the relative permittivity of each layer, yielded deviations of only ?0.10 mm and 0.26 mm from the core drilling results. Field implementation in apartment buildings confirmed the applicability of the method, with average measured thicknesses of 45.08 mm and 43.85 mm for the finishing mortar and ALC layers, respectively. These findings demonstrate the effectiveness of the proposed GPR-based multilayer evaluation technique for verifying construction quality and assessing the performance of floor impact sound insulation systems.

https://doi.org/10.4334/JKCI.2026.38.3.285

최승국(Seung-Guk Choe) ; 정현우(Hyun-Woo Jung) ; 김창혁(Changhyuk Kim)

This study addresses the limitations of the structural safety evaluation program (SafetyMan) currently used for detailed safety inspections of buildings. To achieve this, three main improvements are proposed: (1) simplifying the user input process, (2) introducing a new concrete strength estimation formula based on domestic structural data, and (3) quantifying qualitative evaluation criteria. Regression analyses using data provided by the Korea Authority of Land & Infrastructure Safety (KALIS) revealed that an exponential regression model performed best, achieving a mean error rate of 12.56 % and reducing estimation errors by up to 75.6 % compared with existing Japanese formulas. Furthermore, qualitative judgment factors, such as “minor damage,” appearing in the assessment of strength ratio, concrete strength, displacement, and deflection were redefined into numerical ranges, thereby enhancing consistency and objectivity. Application of the improved program to case studies demonstrated that, while overall safety grades remained unchanged, sub-indicators reflected more rational and consistent evaluation outcomes. These improvements are expected to enhance the reliability of safety diagnostics for aging buildings and to support systematic maintenance practices.

https://doi.org/10.4334/JKCI.2026.38.3.293

민근형(Geunhyeong Min) ; 김기환(Kihwan Kim) ; 정유석(Yoseok Jeong) ; 김우석(WooSeok Kim)

Concrete is widely used in structures for its cost-effectiveness, strength, and durability. However, concrete structures experience deterioration such as cracks or spalling, requiring sectional repair works. This study investigated repair performance based on different deterioration removal methods, application of saturated surface dry conditions, coarse aggregate inclusion in the repair material, and curing agent application. Field experiments were conducted, and performance was evaluated through bond strength measurements. The results indicated that the use of water jetting for deterioration removal, utilizing polymer cement concrete as the repair material, and the application of a curing agent each contributed to improved bond strength, indicating enhanced repair performance.

https://doi.org/10.4334/JKCI.2026.38.3.301

김민서(Min-Seo Kim) ; 백선우(Seon-Woo Baek) ; 박상우(Sang-Woo Park) ; 김창수(Chang-Soo Kim)

This study proposes an analysis-based blast-resistant design framework for nonstructural components attached to the interior surface of reinforced concrete (RC) walls subjected to blast loading. The blast response of a blast-resistant RC wall was evaluated using both SDOF and FEM analyses, and the maximum acceleration transmitted to the attached nonstructural component was evaluated. Based on the resulting acceleration demand and the mechanical capacity of the nonstructural component, its structural response and potential modes were assessed. The results indicate that, even when the RC wall is designed to satisfy the required blast-resistant performance, the attached nonstructural component may lose its functionality and become detached, posing significant life-threatening hazards. These findings demonstrate that blast-resistant design of nonstructural components is required independently of the blast performance of structural elements. Accordingly, protection levels for nonstructural components were established based on allowable damage states, and corresponding blast-resistant design approaches for Protection Levels A, B and C were proposed.

https://doi.org/10.4334/JKCI.2026.38.3.313

손운호(Un-Ho Son) ; 이승훈(Seung-Hoon Lee) ; 김한수(Han-Soo Kim)

We examined the influence of irreversible material behavior during the cooling phase on the fire resistance of reinforced concrete columns. While conventional fire resistance assessments primarily focus on the heating phase, this research incorporated both the thermal and mechanical characteristics that arise during cooling. Four material models were developed by combining reversible and irreversible material properties based on EN 1992-1-2, and seventy-four column specimens were evaluated using the Duration of Heating Phase index. The analysis revealed that additional structural degradation occurs during the cooling phase, with mechanical irreversibility exerting the most significant influence on the reduction in fire resistance. These findings highlight the need to incorporate irreversible material behavior into post-fire structural evaluations in order to avoid overestimating residual structural capacity.

https://doi.org/10.4334/JKCI.2026.38.3.321

강인규(In-Gyu Kang) ; 김건우(Geon-Woo Kim) ; 안태윤(Tae-Yun An) ; 신상철(Sang-Chul Shin) ; 김진만(Jin-Man Kim)

The formwork striking time is primarily governed by the early age strength of concrete and directly influences structural safety, construction efficiency, and overall project economics. This study evaluates the early strength development of concrete incorporating high early strength chemical admixtures (poly naphthalene sulfonate (PNS) and polycarboxylate (PC)) and quantitatively assesses their effectiveness in accelerating formwork removal using the maturity method. To reflect the wide temperature fluctuations experienced in Korea, curing temperatures of 5, 10, and 20 °C were adopted, and design strengths of 24, 27, and 30 MPa, commonly used in domestic construction, were examined. The test results indicate that high early strength admixtures substantially accelerate early cement hydration, resulting in improved early age strength development, with PNS exhibiting the greatest enhancement. The maturity based analysis further confirmed that these admixtures significantly reduce the time required to achieve the formwork removal strength thresholds of 5 MPa (vertical) and 14 MPa (horizontal). This reduction effect was particularly pronounced under low temperature curing conditions, demonstrating that high early strength admixtures can serve as an effective method for shortening construction duration and improving economic feasibility during cold or transitional seasons.

https://doi.org/10.4334/JKCI.2026.38.3.335

이규찬(Gyu-Chan Lee) ; 황지원(Ji-Won Hwang) ; 양근혁(Keun-Hyeok Yang)

We investigated the fundamental performance of a composite carbon-neutral mortar that combines physical carbon adsorption by biochar with biological carbon sequestration by photosynthetic bacteria. Rhodopseudomonas palustris, which captures CO2 via the Calvin cycle, was selected as the biological agent and immobilized in porous expanded vermiculite. The immobilized bacteria were incorporated by replacing 0~20 % of the fine aggregate volume. Biochar produced by pyrolysis of livestock manure at temperatures above 650 °C was used as a partial cement replacement at levels ranging from 0 to 20 % by mass. The experimental results indicate that the compressive strength development, stress-strain behavior, and splitting tensile strength of the carbon-neutral mortar are comparable to those of conventional mortar. In contrast, the CO2 capture capacity of the carbon-neutral mortar was up to 2.4 times higher at 91 days, with the performance enhancement becoming more pronounced over time. Overall, the proposed carbon-neutral mortar shows strong potential as a sustainable construction material capable of continuous CO2 capture under ambient environmental conditions.

https://doi.org/10.4334/JKCI.2026.38.3.343

박산하(San-Ha Park) ; 권승희(Seung-Hee Kwon) ; 이정수(Jung-Soo Lee) ; 김형기(Hyeong-Ki Kim)

This study proposes an improved prediction model for the autogenous (or basic) shrinkage of concrete, specifically focusing on the correlation between the water-to-binder ratio (w/b) and the theoretical ultimate shrinkage. Autogenous shrinkage is a complex phenomenon influenced by internal relative humidity changes and early-age creep; however, these aspects are not sufficiently reflected in current Korean design codes. To address this, more than 200 sets of experimental autogenous shrinkage data were collected from Korean literature published between 1990 and 2024. The data-driven parameter analysis revealed that the theoretical ultimate autogenous shrinkage was primarily governed by the w/b, while no clear trend was identified for the parameters controlling the rate of shrinkage development. Based on these findings, a simplified autogenous shrinkage model was developed in which the ultimate shrinkage is defined as a function of w/b and the rate-related parameters are assigned average values. Validation results showed that more than 95% of the experimental data fell within +20% of the model predictions, indicating that the proposed model achieves a level of accuracy suitable for practical applications.

https://doi.org/10.4334/JKCI.2026.38.3.355

여남구(Nam-Goo Yeo) ; 하니프, 무함마드 로샹(Muhammad Roshaan Hanif) ; 서수연(Soo-Yeon Seo) ; 윤현도(Hyun-Do Yun) ; 최원창(Won-Chang Choi) ; 석승욱(Seung-Wook Seok)

This study experimentally investigated the shear strength of reinforced concrete beams incorporating wood-based biochar as a partial replacement for cement. Four specimens were fabricated with biochar replacement ratios of 0 % and 5 % and shear span-to-depth ratios of 1.5 and 2.5. Experimental results showed that the porous structure of the biochar reduced the compressive strength of the concrete, thereby reducing the shear strength of the beams. Shear testing of beams without shear reinforcement resulted in shear failures in all specimens, with shear crack angles ranging between 30 and 40 degrees. When compared with design standard prediction values, the current standard equations were found to appropriately predict the experimental strengths of specimens.

https://doi.org/10.4334/JKCI.2026.38.3.363

이현호(Hyun-Ho Lee)

This study experimentally investigates the influence of steel damper installation location on the seismic performance of reinforced concrete (RC) frame structures. Cyclic loading tests were conducted on three specimens: an unstrengthened RC frame (BF), a frame strengthened with steel dampers installed at the upper part of the frame (SFD), and a newly developed specimen with dampers installed at the lower part of the frame (RS2). The experimental results showed that the damper strengthened specimens exhibited improved strength, energy dissipation capacity, and ductile behavior compared to the unstrengthened frame. In particular, the RS2 specimen demonstrated stable post-peak behavior due to the rocking mechanism induced by the hinge installed at the lower steel plate. The results provide useful experimental data for understanding the structural behavior of RC frames strengthened with steel dampers and for developing practical seismic retrofit strategies.

https://doi.org/10.4334/JKCI.2026.38.3.373

김희선(Hee Sun Kim) ; 김민희(Min-Hee Kim) ; 이채은(Chae Eun Lee) ; 김나은(Na Eun Kim)

This study evaluates thermal and structural behaviors of heated glass fiber reinforced polymer (GFRP) reinforced concrete beams compared to those with reinforced concrete (RC) beam. To this end, transient heat transfer and structural analyses were conducted using finite element method and validated with previously reported test results for temperature distributions and load-bearing capacities of RC beam. The predicted results of temperature distributions showed that the temperature ranges in GFRP rebars were greater than those in steel rebars, while there was not much difference in concrete temperatures regardless of rebar type. In addition, the strength reduction ratio of the heated concrete beams with GFRP rebars was greater than that of heated concrete beam with steel rebars. As the heat exposure duration increased, the strength of GFRP reinforced concrete beams decreased almost linearly. The findings of this study are expected to serve as a reference for establishing testing and evaluation methods, as well as performance-based fire resistance design guidelines for GFRP reinforced concrete beams.

https://doi.org/10.4334/JKCI.2026.38.3.381

채경훈(Kyoung-Hun Chae) ; 박태원(Tae-Won Park) ; 허무원(Moo-Won Heo)

As buildings become taller and larger, the structural safety of envelope systems has increased the demand for cast-in anchor channels owing to their installation flexibility and superior performance. Due to the lack of domestic standards in South Korea, European specifications (EAD and EN) are currently utilized. This study evaluates the structural reliability of a domestically developed hot-rolled anchor channel system to establish characteristic resistance values for structural design. Following the EAD 330008-04-0601 protocol, static tension and shear tests were conducted. The results confirmed robust structural integrity under ultimate loads without sudden strength degradation, facilitated by a stable load transfer mechanism through the bolt-lip-profile-anchor sequence. Furthermore, coefficients of variation (COV) below 5 % across all series demonstrated high quality, with characteristic strengths closely approximating mean failure loads. This enables more economical design by minimizing the required strength reduction factors. These findings provide a standardized engineering foundation for the development of future domestic design standards. Subsequent research on seismic and fatigue performance is expected to further enhance the structural safety of domestic building envelope systems.

https://doi.org/10.4334/JKCI.2026.38.3.391

김성수(Seong-Soo Kim) ; 정보선(Bo-Sun Jung) ; 주혁진(Hyeok Jin Ju)

This study experimentally evaluated the effects of amine-based organic corrosion inhibitors on the physical properties of concrete and the corrosion inhibition performance of reinforcing steel. The primary variables included the water to cement ratios (W/C 35 %, 45 %, and 55 %), the typs of inhibitor (nitrite-based and amine-based), and their respective contents. The experimental results indicated that the addition of corrosion inhibitors had a negligible impact on the slump, air content, and compressive strength of the concrete; these physical properties were predominantly governed by the W/C ratio rather than the type of inhibitor. Air content remained stable within the range of 4.1 % to 4.8 % for all mixtures, and the 28-day compressive strength maintained a level similar to the plain specimens, generally within ±2 MPa. According to the accelerated corrosion tests conducted per ASTM G109, the time to reach the cumulative charge threshold of 150 C was delayed by more than 20?50 days in specimens containing inhibitors compared to the plain specimens. Even under the relatively unfavorable condition of W/C 55 %, the use of inhibitors showed a substantial delay in the time to reach 150 C. Regression analysis confirmed a high linear correlation between inhibitor content and the time to reach 150 C. At standard contents, amine-based inhibitors exhibited equivalent or slightly superior performance compared to nitrite-based inhibitors, suggesting their potential as a viable alternative for enhancing the durability of reinforced concrete structures.

https://doi.org/10.4334/JKCI.2026.38.3.401

전시우(Siwoo Jeon) ; 모바헤디 나스타란(Nastaran Movahedi) ; 주민관(Minkwan Ju) ; 박경수(Kyoungsoo Park)

This study compared the pull-out behavior of concrete anchors as predicted by the cohesive zone model (CZM), the concrete damage plasticity model (CDPM), and the ACI and KDS design codes. The results demonstrated that the ACI and KDS design equations generally underestimate anchor pull-out strength, while the numerical analyses successfully capture the change in pull-out strength with respect to fracture energy. Additionally, a parametric study was conducted to investigate the effects of element size, tensile strength, dilation angle, and failure angle on the load?displacement response. The CZM provided converged results regardless of element size. Since most CZM parameters are obtained directly from fracture tests, the model is less sensitive to subjective calibration of the load?displacement curve. In contrast, CDPM results vary slightly with mesh density and exhibit high sensitivity to the choice of dilation angle, which cannot be directly obtained through experimental testing. These findings suggest that, while design codes offer a practical baseline for pull-out strength evaluation, the characteristics of the chosen analysis model should be carefully considered, and fracture mechanics?based approaches may be employed when a more detailed assessment of pull-out behavior is required.