Thermal Behavior of Plain and Fiber-Reinforced Rigid Concrete Airfield Runways
The environmental condition and temperature gradient are important factors resulting in concrete airfield runways cracking during the time. Rigid concrete airfield runways experience different thermal gradients during the day and night due to changes in air temperature. Curling and thermal expansion stresses are the main consequences resulting in various types of cracking over the surface and thickness of concrete airfield runways and increasing maintenance costs. The curvature of concrete slabs increases with an increase in the temperature gradient which is amplified when runways open to traffic. Additionally, the combination of the curling and shrinkage stresses, in rare circumstances, can be highly adequate that it cracks before the pavement is exposed to any traffic loading. In addition, the movement of vehicles and increasing stresses increase the depth of cracks and thus the separation of parts of the airfield runways. Therefore, the reconstruction requires the destruction of the previous concrete airfield runways which is very time-consuming and costly. Conversely, the size effect including the dimension of concrete segments and concrete material characteristics plays the main role in controlling the curling and thermal stresses in rigid concrete airfield runways which have not been comprehensively considered by previous investigations, up to now. Previous studies only examined the effect of a limited number of influential factors, and no solution has been provided to mitigate the thermal behavior of rigid concrete slabs, and needs a comprehensive study on the curling and thermal behaviors. Therefore, there is a knowledge gap in mechanistic quantification of the damages imparted on rigid concrete airfield runways exposed to thermal stresses. Thus, this study was designed to bridge this gap by classifying the influence of various geometric characteristics, materials properties, environmental conditions, and boundary situations on the thermal and curling stresses of rigid concrete airfield runways and provide a solution to mitigate the negative influence of this type of environmental impact. The primary goal of this study was to mechanistically quantify the damages and structural responses imparted on rigid concrete slabs due to thermal and curling stresses. To achieve the research objectives, initially, a comprehensive evaluation was carried out to measure the influence of various geometric characteristics and materials properties on the curling and thermal stresses of slabs exposed to various temperature gradients. For this aim, a total of 8213 numerical models have been carried out to consider the effect of slab dimensions, modulus of rupture, compressive strength, and thermal coefficient of concrete on the structural responses of rigid slabs. The secondary aim of this research was to provide a solution to mitigate the negative influence of thermal stress utilizing polypropylene fibers (PF) results to provide further insights on necessary improvements in rigid concrete slabs. For this aim, different PF fractions were incorporated in a combination of various geometric and concrete material properties to control the thermal behavior of rigid concrete slabs. Then, the author utilized the ultrasonic imaging evaluation to simulate the non-destructive test using wave propagation over the thickness and surface of rigid concrete slabs. Ultrasonic imaging is a powerful nondestructive evaluation technology for examining the condition of concrete structures through focused images obtained with the Synthetic Aperture Focusing Technique. Therefore, the results of this evaluation provide a comprehensive opportunity to measure the influence of material properties and geometric characteristics on the strength of rigid concrete slabs using wave propagation. The author then developed a theoretical concept named “advanced zero-stress assessment” to measure the depth of cracks through the slab’s thickness. This impression provides a comprehensive overview of the cracking in rigid slabs due to the curvature under the influence of curling stress. For this purpose, the influence of wide-range variables on the depth of cracking and their propagation was assessed. Clearly, the results of this projected theory might be used by many businesses to create models, and DOTs could use them to construct robust concrete slabs that better account for improving the curling and thermal stresses. Then, a finite element method formulation was developed for measuring the curling stress in rigid concrete slabs considering all effective variables. The relevant information on curling and thermal stresses considering material properties and geometric characteristics was incorporated into a finite element modeling for developing a formulation to measure the curling-buckling behavior in rigid slabs under thermal stresses. The developed finite element method provides an inclusive evaluation to consider the effect of boundary conditions and fiber incorporation as well as the effect of base layer stiffness on the curvature, deformation, and buckling in rigid concrete slabs exposed to the temperature gradient. Another noteworthy finding of this study was providing a highly accurate practical formula using a multi-layer genetic programming machine learning approach to predict the curling stress in rigid concrete airfield runways. Previously proposed equations showed a low accuracy and the lack of some main parameters’ consideration. As a result, providing a new highly accurate formula including all effective geometric and material variables is necessary. This proposed theory's findings will undoubtedly be put to use by many firms to develop models, and DOTs and concrete pavement designing standards may use them to build sturdy concrete slabs that better take into consideration the curling and thermal stresses. Additionally, a methodologically sound and robust protocol was developed using various artificial neural networks for the mechanistic characterization prediction of the curling and thermal stress impacts on transportation infrastructure. The devised multilevel prediction approach consists of the following analysis procedures: quantification of cracking, (2) pavement curling and thermal resistances, the potential of buckling resistance, and deformation. The multi-layer framework developed in this study gives engineers and agencies to have a comprehensive view of the thermal behavior of rigid concrete slabs for future construction. Ultimately, findings were also employed in the risk analysis for pavement failure. The Rackwitz-Fiessler method introduces an analysis that takes into account the probability model of each variable. These reliability analysis methods will be used to verify how the structure would perform under loading and analyze the reliability index of determinate and indeterminate rigid concrete slabs and their failure probability under the effect of temperature variation considering a wide range of variables. As a result, the probabilistic study can give a broad view of the properties of the influence of various parameters on the curling and thermal behaviors of the rigid concrete slabs for engineers and DOTs. The synthesized results of this research can provide insights to improve current protocols for the analysis and design of plain and fibers-reinforced rigid concrete airfield runways subjected to thermal and curling stresses.
Civil engineering|Artificial intelligence|Materials science
Karimi Pour, Arash, "Thermal Behavior of Plain and Fiber-Reinforced Rigid Concrete Airfield Runways" (2023). ETD Collection for University of Texas, El Paso. AAI30424703.