# Behavior of Airport Concrete Pavement Slabs
## 1 Introduction  
Environmental factors, such as variations in temperature and moisture, cause the deformation of concrete pavement slabs that leads to the development of various stresses. Thermal expansion or contraction of a concrete slab occurs owing to temperature changes; the slab shrinks continuously as it dries over a prolonged period [1; 2; 3]. Sufficient time is required for temperature to be transferred to the bottom of a slab, and the temperature changes continuously with daily and yearly cycles. Consequently, the top of the slab periodically contracts or expands more than the bottom of the slab. In addition, the top of the slab dries faster than the bottom, resulting in differential drying shrinkage because the slab surface is in direct contact with the ambient air [4; 5; 6]. Therefore, slab curling occurs, wherein the slab bends upward or downward owing to the difference in contraction and expansion between the top and bottom of the slab [3; 7; 8; 9].  
Stress develops in a concrete slab when the slab contracts or expands owing to weather conditions; this stress depends on factors such as the friction with the sublayer, weight of the slab, and dowel bars. Distress can occur in a concrete slab because of an environmental load that exceeds the strength of the slab [10]. In contrast, most design guidelines for airport pavements, including FAAFRIELD (the Federal Aviation Administration's (FAA) newest airport pavement thickness design program), do not consider the effect of environmental loading despite it having a significant impact on slab behavior and distress. [PERSON] et al. [11] reported that the coefficient of thermal expansion (CTE) of a concrete slab mustbe considered when designing airport pavements to minimize distress. [PERSON] et al. [12] analyzed the influence of temperature gradient on the curling behavior of concrete pavement slabs by measuring the temperature and strain according to the slab depth. In addition, [PERSON] et al. [13] reported that the efficiency of load transfer between adjoining slabs could vary according to the temperature gradient, resulting in an increase of up to 0.5 inches in the design slab thickness. The drying shrinkage of a concrete slab due to moisture evaporation was also analyzed because most prior studies focused only on the temperature effect.  
The AC 150/5320-6D [14] was developed by the FAA in the 1990s and was used until the 2000s. This is an empirical guide for airport pavement design using nomographs. This design guide was upgraded to the AC 150/5320-6E [15] and AC 150/5320-6F [16] guidelines, which are mechanistic empirical design guides that utilize finite element analysis (FEA), but they also do not consider environmental loading. The mechanistic empirical pavement design guide (MEPDG) was developed by the American Association of State Highway and Transportation Officials (AASHTO) for road pavements and considers the curling of concrete slabs caused by temperature variations. Additionally, it uses empirical values for other environmental factors, such as differential drying shrinkage and creep [17]. Therefore, there is a need for the development of an airport pavement design method that simultaneously considers the effects of temperature and moisture, which are the major meteorological factors that have the highest influence on the behavior of concrete slabs.  
Figure 1 presents a flow chart of this study. First, temperature sensors and strain gauges were installed at the concrete pavement construction site in Incheon International Airport (IIA). The temperature and strain data were collected from the concrete slabs, and the real and shrinkage strains were calculated according to the slab position and depth. The short- and long-term behaviors of the concrete slabs were investigated using the calculated strains. This study explains the effects of environmental factors on the behavior of a concrete slab to design airport concrete pavements more reasonably and accurately.