Due to seismically deficient details, existing reinforced concrete structures have low lateral resistance capacities. Since these building structures suffer an increase in axial loads to the main structural element due to the green retrofit (e.g., energy equipment/device, roof garden) for CO2 reduction and vertical extension, building capacities are reduced. This paper proposes a machine-learning-based methodology for allowable ranges of axial loading ratio to reinforced concrete columns using simple structural details. The methodology consists of a two-step procedure: (1) a machine-learning-based failure detection model and (2) column damage limits proposed by previous researchers. To demonstrate this proposed method, the existing building structure built in the 1990s was selected, and the allowable range for the target structure was computed for exterior and interior columns.

Many older reinforced concrete (RC) buildings were constructed and designed with only gravity loads in mind. Columns in those buildings have insufficient reinforcement details that do not satisfy the requirements specified in current seismic design standards. This study aims to develop drift-based fragility functions for lightly RC columns. For this purpose, a database of 193 lightly RC columns was constructed to determine central and dispersion values of drift ratios for individual damage states. Additionally, to develop more accurate fragility functions of the columns, the failure mode of RC columns was incorporated into fragility functions. The classification procedure for column failure mode is proposed in this study. Fragility functions for older RC columns are constructed according to four different damage states. The main variables of the fragility functions proposed in this study are column properties and failure mode.

손상된 콘크리트 구조물은 적절한 보수 및 보강을 통해 성능과 기능을 회복시켜야 한다. 장기간 공기 중에 노출된 콘크리트는 동결융화 작용으로 균열 및 박리를 일으켜 내부 철근의 부식을 유발하게 되는 주요 요인이 된다. 본 연구에서는 동 결융해 손상을 입은 콘크리트 교각의 FRP 보강의 연성에너지 증가 효과를 분석하였다. 보강 FRP 재료와 보강 높이, 보강 겹수 에 따라 동결융해 손상 콘크리트의 푸쉬오버 매개변수 해석을 수행하여 모멘트 곡률의 연성에너지를 비교 분석하였다. FRP 보 강 높이는 소성 힌지 이상의 높이 보강은 비효율적이며, 동결융해 손상이 커질수록 FRP 보강으로 인한 연성에너지 증가량은 커 지는 것을 확인하였다. 보강으로 인한 연성에너지 증가를 위해서는 고강도 FRP 재료보다는 높은 탄성계수를 갖는 FRP 재료가 효율적으로 나타났다. 또한 각 FRP 재료의 특성에 따라 일정 보강 겹수 이상에서 보강 효과가 나타나는 것을 확인하여 FRP 보 강으로 인한 손상된 콘크리트 교각의 연성에너지를 비교 분석하였다.

PURPOSES : Recently, interest in maintaining aged concrete pavements has been increasing. An asphalt overlay is generally used for pavement maintenance, and a tack coat is used to secure interlayer adhesion. Particularly, aged concrete pavements are required for higher adhesion performance of tack coats for attaching interlayers to materials with different properties. Insufficient interlayer adhesion could cause pavement damage, such as slippage, rutting, shoving, corrugation, and pothole. In this study, we examined the performance of interface adhesion by applying a tack coat material developed for maintaining aged concrete pavement. METHODS : In this study, we examined the effect of adhesion performance at the pavement interface, using a tack coat material developed for the maintenance of aged concrete pavement. RESULTS : The developed tack coat not only accomplished the performance objectives but also improved the results by more than 12 to 43%, compared to commonly used materials. CONCLUSIONS : The use of developed tack coat is expected to improve the interlayer adhesion and reduce the delay of the maintenance process in aged concrete pavement.

PURPOSES: This study determines the life of asphalt overlay over old concrete pavements for various times of overlay, using the actual 30- year performance history of the Jungbu Expressway. The results from this study can be used as the basis for decisions on the proper time for overlay, and can also provide information for life cycle cost analysis. METHODS : The maintenance history of the Jungbu Expressway and traffic database 30 years after construction were analyzed. The durations between the first overlay and subsequent overlay for each section of the pavement were analyzed for the entire Jungbu Expressway. The durations were analyzed in terms of both years and the ESAL traffic volumes. RESULTS : 1. The life of the asphalt overlay over the old concrete pavements depended on the time of overlay in terms of both age and cumulative ESALs. A strong correlation was observed between the overlay life and the cumulative ESALs at the time of overlay. 2. The life of the second overlay at the same section was significantly shorter than the first overlay. For JCP, the average lives of the first and second overlays were 6.1 and 2.4 years, respectively. For CRCP, they were 4.8 and 2.7 years, respectively. The main reason for the shorter life of the overlay for CRCP may be that the overlay time was generally later than that for the JCP. 3. The life of the overlay was analyzed according to its materials. SMA exhibited the best performance, followed by CRM. CONCLUSIONS: Life of the overlay reduced with the time of overlay especially in terms of cumulative ESALs, and the life of the second overlay at the same section was significantly shorter than the first overlay. The results can be used in the decision making of the time of overlay and in the life cycle cost analysis.

PURPOSES : The purpose of this paper is to develop an evaluation method for aged reclaimed asphalt pavements using RAP mortar specimen and FTIR method. METHODS: To evaluate the low-temperature behavior of aged reclaimed asphalt pavements, an indirect tensile strength test was adopted with an RAP mortar specimen. The RAP mortar specimen without a rejuvenator was fabricated with two fine aggregate types as a function of passing sieve sizes. The fabricated RAP mortar specimen was frozen for 24 h at -20℃. The indirect tensile strength was measured as a function of different absolute viscosities. The indirect tensile strength and displacement were varied as functions of the dosage of the rejuvenator. The spectroscopy analysis of four asphalt binders was performed under attenuated total reflection. The four asphalt binders comprised of a virgin binder, two extracted RAP binders, and a mixed virgin and extracted RAP binder. To evaluate the oxidation of the binder, the carbonyl index was calculated. RESULTS : The four extracted RAP binders were measured with an extremely wide range of absolute viscosity from 30,000 poise to 170,000 poise. The indirect tensile strength of the RAP mortar decreased as the absolute viscosity increased. This means that at lower temperatures, the indirect tensile strength can indicate the oxidation of RAP. Also, the indirect tensile strength and displacement changed sensitively as the dosage of the rejuvenator was changed. Based on the FTIR principle, a good relation was observed between the dosage of the rejuvenator and the FTIR absorbance peak. It can be used to estimate the dosage of the rejuvenator in hot reclaimed asphalt mixture. Also, the carbonyl index of the RAP binder was calculated to evaluate asphalt oxidation using the FTIR principle. CONCLUSIONS : There is a good relation between the indirect tensile strength of RAP mortar and its absolute viscosity. This indicates that RAP mortar can be used to estimate the properties of aged RAP. Also, the usage of rejuvenator can be evaluated with both the indirect tensile strength and FTIR absorbance peak. The carbonyl index can be used to predict asphalt oxidation.

PURPOSES: The purpose of this study is to determine the effective maintenance method for a deteriorated jointed plain concrete pavement by evaluating the long-term performance of the repaired concrete overlay sections. METHODS: Long-term performance evaluation was conducted for the test section at the intersection between SeoPa and IlDong in National Road No. 37. Firstly, the distress conditions of the concrete pavement, which was constructed in December 2003, were evaluated by referring to the existing report. Secondly, the results of pretreatment, material properties, and initial performance evaluation were analyzed for the overlay test conducted in 2011. Finally, a field survey was carried out using visual inspection and nondestructive testing with a FWD in August 2018, and long-term performance evaluation was conducted for about seven years after maintenance. RESULTS: Visual inspection of the old concrete pavement showed severe damage such as joint spalling and asphalt patching. The cores taken from the old concrete had indirect tensile strength of 2.6-3.8 MPa. It is difficult to determine the freeze-thaw resistance because the average amount of air was only 1.6-2.2%, and spacing factor values were over 400㎛ regardless of location. During maintenance, overlay and partial depth repair were performed by applying three types of overlay materials which are typical in Korea. On the material side, high compressive strength (over 40 MPa) and chlorine ion penetration resistance (less than 1,000 coulomb) at 56 days were achieved. In August 2018, seven years after maintenance, visual inspection and nondestructive testing using FWD were conducted for long-term performance evaluation. Regardless of the maintenance materials, surface deficiencies such as spalling and map cracking occurred extensively near the joint. CONCLUSIONS: In conclusion, if the strength and durability index of aged concrete pavement is low, then it was determined that partial depth repair at the joint is not an effective maintenance alternative. In the case of overlay, the durability of the overlay material is considered the most important factor. In the absence of adequate reinforcement at the joint of the distressed concrete pavement, freeze-thaw damage caused by moisture penetration through the joint and failure of the old concrete are repeated, making it difficult to ensure long-term durability.

국내 고속도로는 1970년을 시작으로 많은 발전을 이루었으며, 콘크리트 포장은 아스팔트 포장에 비해 시공비가 저렴하고 일정기간 동안 유지보수가 필요하지 않은 이점을 가지고 있어 고속도로 포장에 본격적으로 적용되었다. 국내 고속도로의 콘크리트 포장은 약 60% 이상을 차지하고 있으며, 그 중 설계수명을 지난 콘크리트 포장이 증가하는 추세이며 향후 10년 내에 6배까지 증가할 것으로 예측되고 있다. 포장 파손에 대해 일시적인 보수를 실시하고 있으며, 이러한 단편적인 보수는 2차 파손을 야기하는 비효율적인 모습을 보이고 있다. 그리하여 리모델링이라는 대대적인 보수 방법을 적용하기 위하여 본 연구에서는 리모델링 지수를 개발하고 동질성 구간을 선정하여 리모델링 우선순위를 결정하고자 한다. 한국도로공사의 HPMS(Highway Pavement Management System) 자료, 기상청의 기상자료, 본 연구를 통해 개발된 RMI지수를 이용하여 동질성 구간을 선정하고자 한다. 본 연구에서는 각 노선의 행선에 따라 노후 고속도로 포장 구간을 구분하였다. 리모델링 지수의 기준에 따라 그림과 같이 시각화된 자료를 통해 리모델링이 필요한 구간을 정성적으로 선정하고 RMI의 평균값이 7이상되는 구간을 선정한다. 동질성 구간의 최소 연장은 5km로 하며, 콘크리트 포장 이외의 구간은 실무자의 판단 하에 포함 여부를 결정할 수 있도록 하였다. 실무자가 엑셀 Sheet를 이용하여 동질성 구간을 분할 할 수 있도록 하였으며, 그에 필요한 매뉴얼 또한 개발하여 실무자의 편의를 도모하고자 하였다. 본 연구를 통해 동질성 구간을 선정하여 리모델링 우선순위를 결정하는데 도움을 주고자 하였다.

국토교통부의 도로보수현황에 따르면 2016년 말 기준 전국 고속국도 유지보수연장은 75,766km에 달하며, 보수비용으로 4,019억 원이 사용되었다. 이 중 약 30% 금액에 해당하는 1,237억 원이 포장 보수비용에 해당하며, 포장보수로 대부분 소파보수와 덧씌우기와 같은 단면보수가 적용되었다. 하지만 이러한 소규모의 국부적인 보수는 2차 파손을 반복적으로 야기하고 있어서 유지관리 측면에서 비효율적인 모습을 보이고 있다. 따라서 본 연구에서는 리모델링 지수(Remodeling Index;RMI)를 개발하여 노후 콘크리트 포장의 리모델링 우선순위를 결정하고자 한다. 한국도로공사의 HPMS(Highway Pavement Management System) 자료와 기상청의 기상자료를 수집·분석하여 패널레이팅을 위한 대표구간을 선정하였으며, 패널레이팅을 실시하여 RMI 개발을 위한 종속변수를 획득하였다. 패널레이팅을 통해 획득한 각 대표구간의 RMI를 종속변수로 하고 포장 파손, 교통, 환경 인자를 독립변수를 하는 RMI 회귀모형을 개발하였다. RMI 모형의 독립변수별 민감도 분석을 수행했으며, RMI 모형으로 예측한 결과와 측정된 RMI 결과를 비교하여 모형의 정확성을 검증하였다.

PURPOSES: The objective of this study is to verify the effect of fiber grid reinforcement on the long-term performance of asphalt pavement overlaid on old concrete pavement by performing field investigation, laboratory test, and finite element analysis. METHODS : The reflection cracking, roughness, and rutting of fiber grid reinforced overlay sections and ordinary overlay sections were compared. Cores were obtained from both the fiber grid reinforced and ordinary sections to measure bonding shear strength between the asphalt intermediate and asphalt overlay layers. Fracture energy, displacement after yield, shear stiffnesses of the cores were also obtained by analyzing the test results. Finite element analysis was performed using the test results to validate the effect of the fiber grid reinforcement on long-term performance of asphalt pavement overlaid on the old concrete pavement. The fatigue cracking and reflection-cracking were predicted for three cases: 1) fiber grid was not used; 2) glass fiber grid was used; 3) carbon fiber grid was used. RESULTS : The reflection-cracking ratio of fiber grid reinforced sections was much smaller than that of ordinary sections. The fiber grid reinforcement also showed reduction effect on rutting while that on roughness was not clear. The reflection-cracking was not affected by traffic volume but by slab deformation and joint movement caused by temperature variation. The bonding shear strength of the fiber grid reinforced sections was larger than that of the ordinary sections. The fracture energy, displacement after yield, and shear stiffnesses of the cores of the fiber grid reinforced sections were also larger than those of the ordinary sections. Finite element analysis results showed that fatigue cracking of glass or carbon fiber grid reinforced pavement was much smaller than that of ordinary pavement. Carbon fiber grid reinforcement showed larger effect in elongating the fatigue life of the ordinary overlay pavement compared to glass fiber grid reinforcement. The binder type of the overlay layer also affected the fatigue life. The fiber grid reinforcement resisted reflection-cracking and the carbon fiber grid showed the greater effect. CONCLUSIONS: The results of field investigation, laboratory test, and finite element analysis showed that the fiber grid reinforcement had a better effect on improving long-term performance of asphalt pavement overlaid on the old concrete pavement.