## 4 Impact of CTE on Concrete Pavements
[34] examined the impact of CTE on jointed concrete pavement cracking. According to reports, more cracking was visible in pavements with CTE value greater than 9.9 \(\times\) 10\({}^{-6}\)/\({}^{\circ}\)C.  
Similarly, in research carried out to understand the horizontal cracking in continuously reinforced concrete pavement, it was found that concrete with a higher CTE has a greater potential to crack horizontally [39]. This is because higher CTE causes more volume change in the concrete due to temperature fluctuations, which, when limited by the longitudinal steel, results in substantial stress [39]. Similarly, results from field and laboratory analysis carried out in continuously reinforced concrete pavement in Texas found that concrete with a higher thermal expansion coefficient experienced greater shear and normal stresses, particularly at depths where steel bars are present, which contribute to the development of horizontal cracks [40]. The CTE of concrete has a substantial impact on the behavior of continuously reinforced concrete pavement, influencing volumetric changes and stress levels caused by thermal variations. While low-CTE aggregates are desirable since using hard and angular aggregates with lower CTE can enhance load transfer and improve crack behavior, local materials can be used to offset the disadvantages of greater aggregate CTE values by adjusting steel composition, bar size, and optimizing construction procedures [41]. It is advised  
Figure 1: Portland cement concrete slab curling effect during day and night. to use the coarse aggregate type that provides lower CTE and elastic modulus values in continuously reinforced concrete pavement [39]. In a study on optimized aggregate gradation for concrete pavement to understand the gradation effect on CTE, the in situ test results showed that optimized aggregate gradation in concrete showed 14% lesser CTE compared to normal aggregate gradation, which is attributed to larger coarse aggregate volume [42]. Mechanistic-Empirical Payement Design Guide is the first design methodology to directly include the CTE as an input parameter in concrete pavement design. In addition to all other inputs, such as traffic, climate, and material, Mechanistic-Empirical Payement Design Guide also considers CTE values, concrete's elastic modulus and the modulus of rupture for rigid pavement design, and pavement performance evaluation [14]. [PERSON] et al. [43] stated that \"The Mechanistic-Empirical Payement Design Guide possesses three hierarchical levels: Level 1 from actual tests resulting in higher accuracy, Level 2 from less than optimal testing or by calculations considering the individual CTE of the aggregates and the cement paste, and Level 3 from the agency database, user-selected default values, typical averages for the region, or a default value based on type of coarse aggregate\". Moreover, the integration of CTE considerations into Mechanistic-Empirical Payement Design Guides has been shown to enhance the predictive accuracy regarding pavement performance. The data obtained from level 1 are found to be more reliable than those from level 2 and level 3 since they are project-specific CTE testing data; however, the data are costly. [PERSON] et al. [44] investigated the prediction of concrete's mechanical properties, including its CTE, using machine learning. The study results showed that machine learning models, specifically random forest models trained with just 50% of the dataset, were more accurate in predicting CTE than level 2 and level 3 methods of the Mechanistic-Empirical Payement Design Guide suggesting that machine learning could be used to accurately predict the CTE of concrete.