PURPOSES : The performance of pavements is decreased by reduced bearing capacity, deterioration, and distress due to complex loading conditions such as traffic and environmental loads. Therefore, the proper maintenance of pavements must be performed, and accurate evaluation of pavement conditions is essential. In order to improve the accuracy of the heavy weight deflectometer (HWD), which is a nondestructive evaluation method, the correlation between HWD test results and temperature factors were analyzed in this study. METHODS : The HWD test was conducted five times for one day on airport concrete pavement, and the ambient temperature, surface temperature, and slab internal temperature were collected. Since the slab internal temperature was nonlinear, it was replaced by the equivalent linear temperature difference (ELTD). The correlation between the HWD test results and each temperature factor was analyzed by the coefficient of correlation and coefficient of determination. RESULTSAND: The deflection of the slab center, mid edge, and corner, and impulse stiffness modulus (ISM) showed significantly high correlation with each temperature factor, especially the ELTD. However, the load transfer Efficiency (LTE) had very low correlation with the temperature factors. CONCLUSIONS : It is necessary to analyze the effect of aggregate interlocking on LTE according to the overall temperature changes in slabs by conducting seasonal HWD tests. It is also necessary to confirm the effect of seasonal temperature changes on deflection and ISM.

Airport concrete pavement slabs show contraction and expansion behavior due to environmental factors such as temperature and humidity. Among the various environmental factors, temperature is the most influential factor in the concrete slab. However, it is inadequate to consider air temperature or surface temperature as influential factors especially for airport concrete slabs with very large thicknesses. Therefore, this study intends to utilize the equivalent linear temperature difference calculated from the data of the thermometer embedded in 5 depths(50mm, 150mm, 250mm, 350mm, 450mm) on the airport concrete slab. Equivalent linear temperature difference is the temperature difference between the uppermost and lowermost part of the concrete slab, which shows the same behavior due to actual temperature. Since the upper part of the concrete slab is more affected by air temperature than the lower part, the daily temperature range is large. Therefore, the equivalent linear temperature difference increases during the day and decreases at night, and concrete slabs show curl-down during the day and curl-up at night. This daily variation of curling behavior causes a difference in HWD experimental results. The HWD(Heavy Weight Deflectometer) test is mainly performed to investigate the condition of the pavement. And the calculated values are deflection, ISM(Impact Stiffness Modulus), LTE(Load Transfer Efficiency). The equivalent linear temperature difference represents the behavior of the concrete slab by the environmental load, and the calculated values by the HWD test represent the behavior. Therefore, the purpose of this study is to investigate the behavior of concrete slab by combined load including environmental load and traffic load through correlation analysis between these values. This study was supported by Incheon International Airport Corporation(BEX00625) and Korea Airports Corporation.

Airport concrete slabs behave by combined loads including environmental loads and traffic loads. To analyze the behavior of concrete slabs by combined load, the dynamic strain gages were embedded at 2 depths(50mm, 450mm) and 3 locations(corner, Center and Mid-Edge). And the thermometers were embedded at 5 depths(50mm, 150mm, 250mm, 350mm, 450mm) in actual airport concrete slabs. HWD(Heavy Weight Deflectometer) is a device to measure the deflection by applying an impact load. The values calculated by the HWD test are deflection, ISM(Impact Stiffness Modulus), LTE(Load Transfer Efficiency). Concrete slabs tend to expand during the summer when the temperature is high, and contract during the winter when the temperature is low. In addition, the drying shrinkage occurs as age increases. Field HWD test were conducted in March, May, August, and November to examine seasonal and age-specific changes. Furthermore, the temperature difference between top and bottom of concrete slabs causes the curl-up and curl-down behavior. The test was conducted 3 times at 12o`clock, 16o`clock, 21o`clock, 3o`clock, 7o`clock to examine temporal changes. The strain of the slab at HWD strike was measured 500 times per second because the strain occurred instantaneously, and the temperature was measure 1 times per 10 minutes. The calculated values and the measured values varied according to environmental loads. In order to examine these values in various angles, the equivalent linear temperature difference obtained by converting the temperature by depth into the uppermost lowermost temperature difference, the temperature of the slab which changes seasonally as a whole, and the drying shrinkage which occurs as the age increases are considered. Therefore, the purpose of this study is to clarify the behavior of concrete slabs by combined load considering long - term drying shrinkage, annual variation of temperature, and daily variations. This study was supported by Incheon International Airport Corporation(BEX00625) and Korea Airports Corporation.

공항 콘크리트 포장 슬래브는 온도와 습도 등 환경요인의 복합적인 영향으로 수축과 팽창을 반복한다. 하지만 슬래브 상·하부간의 비선형적인 온도구배로 인해 깊이에 따른 열팽창률이 다르며, 슬래브 표면에서의 증발로 인한 수분 손실로 인해 부등건조수축이 발생하여 위아래로 뒤틀리는 컬링(Curling)거동을 야기한다. 이처럼 환경요인에 의한 슬래브의 거동은 단기적으로 일주기의 대기 온도변화에 의한 거동특성을 보이며, 장기적으로 건조수축 및 계절적인 온도변화에 의한 거동특성을 보인다. 본 연구에서는 인천국제공항 현장에서의 HWD실험을 통하여 단기 및 장기적인 콘크리트 포장 슬래브의 거동을 예측하고자 하였다. 본 연구를 위해 2016년 11월부로 인천국제공항의 4단계 건설사업 중 3단계 건설사업이 진행중인 여객계류장 현장에 정적 및 동적 계측기를 설치하였으며, 상시적으로 정적변형률을 계측함과 동시에 정기적으로 HWD실험을 통해 동적변형률을 계측하였다. 계절별 거동특성을 분석하기 위해 2017년 3월, 5월, 8월 3차례에 걸쳐 HWD실험을 실시하였으며, 일주기 거동특성을 분석하기 위해 매 실험마다 3시, 7시, 11시, 15시, 21시에 걸쳐 총 5회의 실험을 실시하였다. HWD 실험을 통해 그림 1과 같이 슬래브의 중심, 모서리, 우각부의 내측 및 외측을 대상으로 타격하였으며, 처짐량, 충격강도계수(ISM), 하중전달률(LTE), 포장체 내 변형률, 역산 탄성계수를 조사하여 분석하였다. 현재까지의 HWD실험을 통해 슬래브 거동특성을 분석한 결과 초기상태의 슬래브는 부등건조수축으로 인한 Curl-up이 발생하며, 우각부와 보조기층이 분리된 것으로 예측되었다. 하지만 재령이 지날수록 일정한 Curl-up상태를 유지한 체 보조기층의 침하가 동반되어 Curl-up이 완화되는 거동이 예측되었다. 본 연구진은 추후 추가적인 HWD실험을 실시하여 슬래브 거동 예측결과를 검증 할 예정이다.

The Joint Load Transfer (LTE) is important for both design and evaluation of concrete pavements. Numerous researches have been published to determine different factors that affect the load transfer efficiency through Finite Element Method (FEM) and field measurements. Most of these researches are using static analysis. Previous study pointed out the weakness of the assumption of this analysis and successfully differentiate the dynamic stress-based LTE with static stress-based LTE through FEM. Usually deflection based LTE(w) is being evaluated in the field through Heavy Weight Deflectometer (HWD). This test is a dynamic test which typically uses peak displacement and assumed to be static displacement when similar amount of static loading is applied. The calculation of LTE(w) in the field involves the ratio of the peak displacement of unloaded to loaded slab. Using this LTE(w) calculation, there were instances that high values were obtained from spalled joints and joints with wider opening. This study attempts to provide a better characterization of the condition of the joint. A time-based LTE(t) using the time delay were investigated and correlated with the current LTE(w) using a 24 hour measurement of deflection from asphalt and concrete pavement, with a 3-hour interval done in Gimpo International Airport. Wider values of LTE(t) were obtained while the deflection-based LTE(w) shows almost similar values. The time-based LTE(t) shows better relationship with the physical condition of the joint than LTE(w). It shows that LTE(t) can characterized the condition of the joint. This result will be used for further study to improve the measurement of load transfer efficiency of concrete pavement joints