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The dynamic stress response of concrete pavements subjected to moving tandem-axle loads of constant amplitude and harmonic and arbitrary variations was investigated. The concrete pavement was modeled using a plate of infinite extent on a viscoelastic foundation. Formulations were developed in the transformed field domain using ( a) a double Fourier transform in space and moving space for moving loads of constant amplitude and for the steady-state response to moving harmonic loads and ( b) a triple Fourier transform in time, space, and moving space for moving loads of arbitrary variation. The effects of viscous damping, velocity, load frequency, and phase between front- and rear-axle loads on the maximum stress and the stress distribution were analyzed. Without viscous damping, the effects of velocity and frequency, within practical ranges, on the stresses are negligible; however, with viscous damping, those effects are significant. Since materials used in various pavement layers possess damping characteristics, wheel load stresses can vary considerably because of velocity and load frequency. The increase in wheel load variations and corresponding concrete stresses can be significant if the roughness of the pavement surface is not controlled. The difference in the phase angles between front- and rear-axle loads can considerably increase the maximum stress; therefore, the use of tandem-axle loads and dynamic analyses is necessary to obtain the accurate stresses because the phase effect cannot be obtained with single-axle loads or static analyses.

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The coefficient of thermal expansion (CTE) of concrete has substantial effects on the behavior and performance of portland cement concrete (PCC) pavement. The CTE is one of the input variables with significant effects on PCC pavement performance in the newly developed Mechanistic–Empirical Pavement Design Guide. Currently, the most advanced and accepted evaluation method for the CTE is the provisional AASHTO TP60. In this test method, concrete specimens are saturated before and during the testing. It has been recognized that the CTE of cement paste is influenced by the relative humidity (RH) within the specimen. Results from previous research studies were nearly consistent: the maximum CTE value occurs at about 70% RH and its value is almost twice the value at 100% RH. Laboratory evaluations were conducted to quantify the effects of RH on CTEs in cement paste and concrete. In the testing program, target RH levels within the specimens were 45%, 60%, 70%, 80%, and 100%. RH sensors were installed within the specimens during their preparation. The specimens were fabricated and cured in 23°C (73°F) and 50% RH conditions for 6 weeks. Subsequently, the specimens were placed in the environmental chamber until the internal RH values reached the target RH levels. Then CTE testing was conducted by changing temperatures while evaluating displacements with externally mounted vibrating wire gauges. The results showed some effects of RH on the CTE of cement paste and concrete, with maximum values at about 70% to 80% RH. The effect was larger for cement paste than for concrete. Considering the small effects of RH on the concrete CTE, AASHTO TP60 appears to provide adequate CTE values for PCC pavement analysis for environmental stresses.

Continuously reinforced concrete pavement (CRCP) performance depends primarily on early-age cracks that result from changes in temperature and drying shrinkage. Presented is the behavior of the CRCP due to the temperature change obtained by using a three-dimensional finite element model. The nonlinear effects of the bond-slip between concrete and steel and between concrete and base have been studied. Modeling for the curling effect and for the viscoelastic material characteristics also has been considered. The results from the two-dimensional and three-dimensional models have been compared to verify the possibility of using a two-dimensional model. From this study, it was found that crack width and concrete stress are dependent on the transverse steel arrangement near the edge (longitudinal joint), but they are almost independent in the interior of the slab. The tensile stress occurring at the top of the edge on the transverse steel location can be higher than that occurring at the top of the slab center. This represents the possibility of forming a transverse crack from the edge on the transverse steel location. The twodimensional model with the plane stress element gives results very close to those of the three-dimensional model, except near the edge.

The coefficient of thermal expansion (CTE) of concrete has a significant effect on the performance of portland cement concrete pavement. Concrete with a higher CTE is more prone to cracking, additional warping, and spalling. To improve PCC pavement performance, several districts of the Texas Department of Transportation (TxDOT) currently limit the CTE of concrete. To support this policy, efforts have been made to improve the accuracy and repeatability of the testing procedures for CTE. The current AASHTO Test Method TP 60 has been evaluated, its shortcomings identified, and improvements made. The improvements include CTE determination from regression analysis of temperature and displacement measurements. The effects of a number of variables on concrete CTE were investigated. The effect of the rate of heating and cooling is negligible. Concrete age and specimen size also have a negligible effect. Coarse aggregate content in the concrete mix has an effect on the test results. This test procedure was used to evaluate coarse aggregates from 32 sources in Texas. The results show that coarse aggregate type has a significant effect on concrete CTE. The proposed testing procedure for concrete CTE provided more accurate results than the AASHTO TP 60. TxDOT plans to implement this test procedure and to develop appropriate steel design standards for continuously reinforced concrete pavement and other construction-related requirements such as different curing methods for concrete with varying CTEs. This implementation should result in better concrete pavement performance.