A Half-analytical Elastic Solution for 2D Analysis of Cracked Pavements

International audienceThis paper presents a half-analytical elastic solution convenient for parametric studies of 2D cracked pavements. The pavement structure is reduced to three elastic and homogeneous equivalent layers resting on a soil. In a similar way than the Pasternak's modelling for concrete pavements, the soil is modelled by one layer, named shear layer, connected to Winkler's springs in order to ensure the transfer of shear stresses between the pavement structure and the springs. The whole four-layer system is modelled using a specific model developed for the analysis of delamination in composite materials. It reduces the problem by one dimension and gives access to regular interface stresses between layers at the edge of vertical cracks allowing the initial debonding analysis. In 2D plane strain conditions, a system of twelve-second order differential equations is written analytically. This system is solved numerically by the finite difference method (Newmark) computed in the free Scilab software. The calculus tool allows analysis of the impact of material characteristics changing, loads and locations of cracks in pavements on the distribution of mechanical fields. The approach with fracture mechanic concepts is well suited for practical use and for some subsequent numerical developments in 3D

Impact of Equivalent Young’s Modulus Ratio Values between Material Layers on Pavement Structural Fracture Performance

International audienc

Influence of sliding interfaces on the response of a layered viscoelastic medium under a moving load

This article presents a method to compute the response of a viscoelastic layered half-space to a moving load when interlayer slip is considered. The Navier equations of equilibrium are solved for each layer in the frequency domain. The solution in the spatial coordinate system is subsequently obtained by means of Fast Fourier Transform and quadrature rules applied to integrable singularities. Following the global solution technique, the developed method compiles all the interface and the boundary conditions within a global matrix and it solves a unique linear system per couple of wave numbers. This method proves to be effective and is validated in an elastic case by comparison with the ALIZE-LCPC software that implements the Burmister axisymmetric solution. The influence of the interface sliding condition on the response of a layered viscoelastic medium is studied through an application to pavement structures. In this application, the effect of the load speed on vertical and horizontal profiles of the longitudinal strain and the normal stress is analyzed. It is shown, inter alia, that the maximum extension in the medium is not systematically observed at the location of an interface and that, as expected, low speeds and interlayer slip are more damaging to the structure when either a strain or a stress criterion is considered

Development of an Analysis System for Discontinuities in Rigid Airfield Pavements.

The response of the rigid pavement slab-joint-base structural system is complex, and accurately predicting the response of such a system requires a significant degree of analytical sophistication. The research reported in this dissertation has defined some essential features required to adequately model the system and has demonstrated a technique to develop a comprehensive three-dimensional (3D) finite element model of the rigid pavement slab-joint-foundation structural system. Analysis of experimental data from the 1950s confirms that explicit modeling of dowels is not required to model the structural response of the system. Additional experimental data gathered as a part of this research indicates that joint response depends upon the presence and condition of a stabilized base. The presence of cracking in the base and the degree of bonding between the slabs and stabilized base course influences the structural capacity and load transfer capability of the rigid pavement structure. The finite element models developed in this research indicate that a comprehensive 3D finite element modeling technique provides a rational approach to modeling the structural response of the jointed rigid airport pavement system. Modeling features which are required include explicit 3D modeling of the slab continua, load transfer capability at the joint (modeled by springs between the slabs), explicit 3D modeling of the base course continua, aggregate interlock capability across the cracks in the base course (again, modeled by springs across the crack), and contact interaction between the slabs and base course. The contact interaction model feature should allow gaps to open between the slab and base, and, where the slabs and base are in contact, transfer of shear stresses across the interface via friction should be modeled

EFFECTS OF COEFFICIENT OF THERMAL EXPANSION ON UNBONDED CONCRETE OVERLAY DESIGN AND PERFORMANCE

With the deterioration of highway pavements across the country, more emphasis is being laid on the rehabilitation of existing pavements. Unbonded concrete overlay (UBCO) is a cost-effective technique used to rehabilitate damaged concrete pavements. The design and performance of UBCO rely on various properties of concrete, of which coefficient of thermal expansion (CTE) is an important one. Concrete CTE has a direct impact on the design and performance of rigid pavements and overlays. CTE regulates the magnitude of curling and related stresses that impact the performance of overlays with regards to cracking, faulting and pavement roughness. Previous research revealed that thermal expansion of concrete is caused by re-distribution of water between capillary pores and gel pores in the cement paste with a change in concrete temperature. The volume of these pores changes with the ongoing hydration process in the cement paste and thus the CTE of concrete also changes with age progression. Several researchers worked on the effects of concrete age on CTE but found different conclusions with some researchers opined that CTE decreases with age, some said that CTE increases with age, and some said that CTE remains constant. Almost all of the previous studies had some limitations i.e. use of old test method, short term CTE testing, and not following the test protocol. With the above in view, it is a necessity to study the effects of age progression on the CTE of paving concrete. The present study involved testing of 7 concrete paving mixes for long term CTE ranging from 7 days to 360 days to obtain accurate laboratory test data for further analysis. These concrete mixes were collected from different districts of New Mexico (NM), prepared from different coarse aggregates with varying mineralogy. The CTE value of these mixes varies over a fairly large range i.e. from 3.71 to 5.95 μԐ/˚F. The long term CTE test data showed significant effects of age progression on CTE value of paving concrete with CTE increasing in the range of 0.33 μԐ/˚F to 0.55 μԐ/˚F with a percent increase of 6.4% to 12.6% between 28 days and 360 days. The increase in CTE is different for different paving mixes which can be attributed to the difference in mix design proportions and different (mineralogy) coarse aggregates being used. This variation in CTE may affect the performance of UBCO and use of 28 days CTE may give inaccurate design. The impact of coarse aggregate mineralogy on the CTE value was also evident from the test data in this study. The CTE values of CA-ID-1, 2, 4, and 7 i.e. granite, dolomite, and quartzite are consistently higher than that of CA-ID-3 and 5 which are limestone mixes. This confirms the previous research/literature that concrete with limestone aggregate has the lowest CTE value as compared to other minerals. The effects of aged CTE on the design and performance predictions of UBCO were evaluated by conducting simulations in Pavement ME (Mechanistic-Empirical) Design software version 2.3. Time series data for concrete mechanical properties including compressive strength, elastic modulus and modulus of rupture (MOR) were obtained by laboratory testing of the beam and cylindrical specimens at the age of 7 days to 90 days. Inter-conversion models were developed to convert compressive strength to elastic modulus and MOR. Analysis showed that these models work better for NM paving mixes as compared to the Pavement ME default models. The effects of aged CTE were quantified by conducting UBCO design simulations incorporating time series data and using 28 days CTE value for each mix and then repeating the process with 360 days CTE value with other design variables. The results show that there is a significant impact of CTE variation on the performance of UBCO with regards to transverse cracking with a percent increase of 1.6 to 9.7% while the percent increase of joint faulting is 10% to 19.9%. Further analyses were conducted to determine the reduction of overlay service life with an increase in CTE from 28 days to 360 days. It is shown that the reduction in overlay service life ranges between 4 to 13 years. It is evident from these results that a UBCO designed with 28 days CTE value may not be able to perform up to the designed service life as the distresses increase with an increase in CTE value which may result in the early failure of overlay pavement. A prediction model was developed to determine long term CTE incorporating mixture volumetrics, concrete strength properties, concrete age and 28 days CTE value. The analysis of the developed model showed that the model worked well in predicting aged CTE when compared with long term CTE test data. This model can be incorporated in Pavement ME Design software to better predict pavement performance and enhance the effectiveness of UBCO design. A temperature gradient exists between the top and bottom of the concrete pavement slab which results in thermal curling, producing thermal stresses in the pavement. Previous practice was to assume a linear temperature gradient in the pavement slab, but later researchers found that the thermal gradient is non-linear. In the present study, numerical modeling was conducted in finite element software ABAQUS 6.14 to evaluate the impact of aged CTE on the stresses in pavement slab incorporating nonlinear temperature gradient. As an initial step, pavement slab was modeled with a linear temperature gradient with constant CTE value to determine the state of bending stresses through the thickness of the pavement slab. The results were compared with previous analytical and numerical studies and good match was found. With this analysis, it was deduced that the FE idealization used in this study works well and can be further used for nonlinear thermal modeling. As a next step, the pavement slab was modeled with a nonlinear temperature gradient and the results of bending stresses through the thickness of the slab were determined. These results were again compared with the previous studies and matched well with the stress profiles. FE modeling was conducted to evaluate the effects of aged CTE (at 360 days) in comparison to CTE at 28 days on the stress profiles in concrete pavement slab with a nonlinear thermal gradient. The FE idealization used earlier was re-employed for this purpose. The results showed that the longitudinal bending stresses at the top and bottom of the pavement slab increase significantly with an increase in CTE values. The increase in stress values ranges from 6.4% to 12.5%. This increase in stresses may result in increased distresses and early deterioration of concrete pavements and UBCOs. It became evident from these results that UBCO designed with CTE value at 28 days may not perform well through its designed service life

Doctor of Philosophy

dissertationCracking and debonding are important considerations for pavement maintenance because they are linked with the service life of pavement structures. Concrete overlay pavements are expected to have reduced crack widths and reduced debonding rates when the concrete mixture contains fibers. The age-dependent changes in flexural and fracture properties of fiber-reinforced concrete (FRC) between 3 and 90 days were experimentally investigated. Compared to plain unreinforced concrete, steel and polymeric macro-FRC of up to 1% by volume of fibers were confirmed to have no significant effects on compressive strength, free drying shrinkage, or coefficient of thermal expansion. For both steel-fiber-reinforced concrete (SFRC) or polymeric-fiber-reinforced concrete (PFRC) mixtures, fracture properties as used in the FEA model were found, through wedge splitting testing, to increase with age. However, the property currently used in the FRC overlay pavement design is the residual strength ratio, which was found to decrease with age for both SFRC and PFRC. A simple crack width equation was developed to predict the crack width of thin FRC overlays based on the addition of fibers to the concrete. The predicted crack widths were validated against data from a field project on variable joint spacing and subjected to temperature and humidity variations. Both the tensile and shear bond between an aged concrete and a newly cast fiber-reinforced mortar were investigated. The tensile interfacial energy between the fiber-reinforced mortar cast against the aged and sand-blasted concrete was higher than that of plain unreinforced mortar. It was found that this tensile interfacial energy was proportional to the physical number of fibers located near the interface surface, particularly because some of the fracture path went through the mortar layer and was bridged by these fibers. No statistical trend could be found between the peak strengths associated with either the tensile or the shear bond and the addition of fibers in the overlay mixture. In addition, a performed finite element analysis (FEA) study indicated that, as expected, crack width, vertical liftoff, and debonding length all decreased as the fracture energy of the FRC increased or as the interfacial tensile bond increased. The developed crack width equation and finite element model were found to predict the crack widths within 0.19 mm (or 26%) compared to actual pavement. The previously developed FEA model was modified to resemble 150 mm thick pavement in order to to compare FRC pavement responses to that of unreinforced concrete containing dowels. Compared to completely unreinforced pavement, it was found that dowel reinforcement reduced crack widths by 3 times, while a typical 0.5% volume fraction of PFRC reduced crack widths by only 1.3 times. Dowel bars are used only in thick pavements rather than thin pavements, so among thin overlays, FRC is a good option to reduce crack width, debonding length, and vertical deflection

Optimización del diseño estructural de pavimentos asfálticos para calles y carreteras

gráficos, tablasThe construction of asphalt pavements in streets and highways is an activity that requires optimizing the consumption of significant economic and natural resources. Pavement design optimization meets contradictory objectives according to the availability of resources and users’ needs. This dissertation explores the application of metaheuristics to optimize the design of asphalt pavements using an incremental design based on the prediction of damage and vehicle operating costs (VOC). The costs are proportional to energy and resource consumption and polluting emissions. The evolution of asphalt pavement design and metaheuristic optimization techniques on this topic were reviewed. Four computer programs were developed: (1) UNLEA, a program for the structural analysis of multilayer systems. (2) PSO-UNLEA, a program that uses particle swarm optimization metaheuristic (PSO) for the backcalculation of pavement moduli. (3) UNPAVE, an incremental pavement design program based on the equations of the North American MEPDG and includes the computation of vehicle operating costs based on IRI. (4) PSO-PAVE, a PSO program to search for thicknesses that optimize the design considering construction and vehicle operating costs. The case studies show that the backcalculation and structural design of pavements can be optimized by PSO considering restrictions in the thickness and the selection of materials. Future developments should reduce the computational cost and calibrate the pavement performance and VOC models. (Texto tomado de la fuente)La construcción de pavimentos asfálticos en calles y carreteras es una actividad que requiere la optimización del consumo de cuantiosos recursos económicos y naturales. La optimización del diseño de pavimentos atiende objetivos contradictorios de acuerdo con la disponibilidad de recursos y las necesidades de los usuarios. Este trabajo explora el empleo de metaheurísticas para optimizar el diseño de pavimentos asfálticos empleando el diseño incremental basado en la predicción del deterioro y los costos de operación vehicular (COV). Los costos son proporcionales al consumo energético y de recursos y las emisiones contaminantes. Se revisó la evolución del diseño de pavimentos asfálticos y el desarrollo de técnicas metaheurísticas de optimización en este tema. Se desarrollaron cuatro programas de computador: (1) UNLEA, programa para el análisis estructural de sistemas multicapa. (2) PSO-UNLEA, programa que emplea la metaheurística de optimización con enjambre de partículas (PSO) para el cálculo inverso de módulos de pavimentos. (3) UNPAVE, programa de diseño incremental de pavimentos basado en las ecuaciones de la MEPDG norteamericana, y el cálculo de costos de construcción y operación vehicular basados en el IRI. (4) PSO-PAVE, programa que emplea la PSO en la búsqueda de espesores que permitan optimizar el diseño considerando los costos de construcción y de operación vehicular. Los estudios de caso muestran que el cálculo inverso y el diseño estructural de pavimentos pueden optimizarse mediante PSO considerando restricciones en los espesores y la selección de materiales. Los desarrollos futuros deben enfocarse en reducir el costo computacional y calibrar los modelos de deterioro y COV.DoctoradoDoctor en Ingeniería - Ingeniería AutomáticaDiseño incremental de pavimentosEléctrica, Electrónica, Automatización Y Telecomunicacione