# Behavior of Airport Concrete Pavement Slabs
## 3 Data Collection
### Material Properties of the Concrete Slab  
The concrete specimens were molded at the construction site to test the material properties of the concrete slabs in the laboratory. The CTE of the specimens was tested according to the TxDOT standard, and the other material properties were tested according to the American Society for Testing and Materials [19; 20; 21]. The elastic modulus, Poisson's ratio, modulus of rupture, and CTE were measured for the concrete specimens that had been cured in water for 28 days, and they were also measured after aging for 90 days (Table 2). The modulus of rupture satisfied the designed flexural strength required by the IIA Corporation. The elastic modulus, Poisson's ratio, and CTE were in the general range required for a concrete pavement slab [22].  
Figure 6: Weather data over a two-year period: (**a**) ambient temperature and ambient relative humidity and (**b**) solar radiation and wind speed.  
The final setting times at which the concrete slabs hardened and began to resist tensile stresses were determined according to the slab position and depth using the maturity obtained from a mortar penetration test. The results were designated as the zero points of the measured strain [23]. Maturity is a unique characteristic of concrete and is expressed by multiplying the temperature and time, as given below.  
\[M=\sum_{0}^{t}(T-T_{0})\Delta t \tag{1}\]  
M: Maturity after time t from the placement of concrete (\({}^{\circ}\)C h);  
T: Average temperature for a time interval \(\Delta t\) (\({}^{\circ}\)C);  
\(T_{0}\): Datum temperature (-10 \({}^{\circ}\)C);  
\(\Delta\)t: Time interval (h).  
Maturity refers to the hardening of concrete depending on the material and mixture properties [24; 25; 26]. Thus, the setting times of the concrete slabs with the same materials and mixture proportions under different curing temperature conditions could be estimated using maturity.  
The maturity was 336 \({}^{\circ}\)C h at the final setting time, when the penetration resistance of the mortar extracted from the concrete slab mixture was 28.0 MPa, as shown in Figure 7. The time corresponding to the maturity of 336 \({}^{\circ}\)C h could be found according to the slab depth for use as the zero points of the strain using the concrete temperature measured from the placement of the concrete slab. Figure 8 presents the temperature gradient of each slab at the final setting time. The trends of the temperature gradients are typically the same; however, there was a slight difference according to the construction time.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Test Item**} & \multirow{2}{*}{**Test Method**} & \multicolumn{2}{c}{**Test Results**} & \multirow{2}{*}{**Criteria/General Range**} & \multirow{2}{*}{**Note**} \\ \cline{3-3} \cline{5-6}  & & **28 Days** & & **90 Days** & \\ \hline Flexural strength (MPa) & ASTMC78 & 4.94 & 5.10 & 4.50 & \\ Elastic modulus (GPa) & ASTM C469 & 26.2 & 28.1 & 28.0–30.0 & \\ Poisson’s ratio & ASTM C469 & 0.178 & 0.193 & 0.176\(\sim\)0.182 & \\ CTE (\({}^{\circ}\)C) & TEX-428-A & \multicolumn{2}{c}{\(9.92\times 10^{-6}\)} & (8.6–12.3) \(\times 10^{-6}\) & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Material properties of a concrete slab.  
Figure 7: Maturity at final setting obtained by the mortar penetration test.