Roberto Soares

A Computational Model for Predicting the Effect of Tire Configuration on Asphaltic Pavement Life

ABSTRACT This paper proposes a model for predicting the mechanical behavior and performance life of asphalt pavements subjected to various tire configurations, layer thickness, and material properties. A viscoelastic two-dimensional finite element model was developed and utilized in order to predict pavement life depending on different combinations of these design variables. The effects of truck loads on the pavement performance were studied by simulating three tire configurations: two types of the new generation wide-base single tire and one conventional dual tire configuration. Also, two different types of hot mix asphalt (HMA) and three variations of the HMA layer thickness were evaluated. Results showed that the use of conventional dual tires produces approximately 50 per cent longer asphalt service life when compared to the use of wide tires. The service life is shown to increase by increasing the HMA layer thickness. In fact, simulation results suggest that a 200 mm thick HMA layer provides a 15 per cent longer life than a 100 mm thick layer. Asphalt material results also suggest that the quality of materials can significantly affect pavement performance and service life. Furthermore, service life is significantly reduced when a poor quality material is combined with a thin asphalt layer. The simulation model presented here will be useful for future pavement design and material selection.

Multi-scale computational model for design of flexible pavement – part II: contracting multi-scaling

Abstract A computational multi-scale procedure for designing flexible pavements is developed in this, the second of a three-part series. In this study, computational analyses are performed on sequentially smaller length scales, termed contracting multi-scaling. The model is constructed by utilising the finite element method on each length scale, thereby creating a one-way coupled multi-scale algorithm that is capable of accounting for the effects of cyclic loading on the initiation and evolution of cracks on multiple length scales within the roadway. For example, the algorithm can be utilised to predict the effects of small-scale design variables such as aggregate volume fraction, as well as the effects of large scale design variables such as asphalt concrete thickness on pavement cracking due to external loading. The model for predicting roadway cracking is briefly described herein, including the experimental properties required to deploy the cracking model within a computational framework. The article concludes with demonstrative examples intended to elucidate the power of this predictive technology for the purpose of designing more sustainable roadways.

Multi-scale computational model for design of flexible pavement – part III: two-way coupled multi-scaling

Abstract A computational multi-scale procedure for designing flexible roadways is developed in this part, the third of a three-part series. In this study, a two-way coupled multi-scale algorithm was developed and utilised to predict the effects on pavement performance caused by variations in local and global design variables. The model is constructed by utilising the finite element method at two simultaneous and two-way coupled length scales, thereby creating a multi-scale algorithm that is capable of accounting for the effects of variations in design parameters on both length scales. Energy dissipation mechanisms such as viscoelasticity in the asphalt mastic, plasticity in the base layer and crack propagation in the asphalt concrete are incorporated within the model for the purpose of predicting permanent deformations in typical roadways subjected to cyclic tyre loadings. The algorithm is briefly described herein, including the experimental properties required to deploy the computational scheme for the purpose of pavement design. The algorithm is subsequently utilised to predict the effects on pavement performance of variations in design variables on the global length scale (metres) such as asphalt concrete layer thickness and base layer yield point as well as design variables on the local length scale (centimetres) such as aggregate volume fraction and asphalt mastic fracture toughness. These demonstrative examples elucidate the power of this new technology for the purpose of designing more sustainable roadways.

Modeling the Structural Response of Urban Subsurface Drainage Systems

In recent years, many City of Saskatoon (COS), Canada, roads have experienced premature failures. High water tables, increased precipitation, and poor surface drainage have caused increased moisture infiltration in road structures. Further deterioration of these aged pavements is attributable to heavy year-round loadings in urban traffic. To address these issues, COS piloted subsurface drainage and strain dissipation layers in some roads. These drainage systems were constructed with crushed portland cement concrete (PCC) rock and conventional virgin crushed rock. Given the empirical nature of conventional road design methods currently used by COS, the structural benefits of drainage systems are difficult to quantify. Therefore, a reliable method that directly incorporates recycled materials, substructure drainage systems, and diverse field conditions is needed. A mechanistic analysis of the drainage systems was piloted in rehabilitated COS pavement structures with a three-dimensional (3-D) nonlinear orthotropic computational road structural model. The 3-D mechanistic model was used to predict peak surface deflections and normal and shear strains in the structure. Modeling results showed that constructing pavement structures with a substructure drainage layer of crushed PCC rock improved the structural performance of the road system in terms of strains under applied traffic loads. The road model provided primary response predictions that correlated with deflections measured by a heavy weight deflectometer, before and after construction. Therefore, the road model used is a reliable pavement engineering analysis tool able to predict the in-field structural behavior of various road structures under diverse field state conditions.

Modeling In Situ Performance of Cement-Stabilized Granular Base Layers of Urban Roads

This study used a three-dimensional nonlinear orthotropic computational road model to measure the performance of reclaimed and recycled portland cement concrete (PCC) aggregates and reclaimed asphalt pavement (RAP) aggregates stabilized with cement as a base layer in a typical local road structure in the city of Saskatoon, Saskatchewan, Canada. The pavement structure was composed of 45-mm hot-mix asphalt concrete on a 225-mm granular base built directly over an in situ subgrade. The cross section was analyzed with a conventional granular base layer as a baseline and PCC and RAP base layers with 2% cement stabilization. The cement-stabilized PCC and RAP base layers showed improved shear strain and horizontal strain behavior when compared with the conventional granular base layer (which was not cement stabilized). This improvement con-firmed that cement stabilization of reclaimed PCC and RAP materials provided an enhanced primary response. This study demonstrated that typical thin Saskatoon pavement structures were highly dependent on the constitutive properties of base layer material. Stabilizing the PCC and RAP base layers with 2% cement reduced the maximum shear strains at the edge of the pavement structure by 12% and 25%, respectively, compared with the unstabilized conventional granular base layer. It was believed that the increased fracture and cohesion of the residual cementitious materials inherent to recycled granular base, as well as the cementitious binder added, improved structural performance.

A Computational Multiscale Investigation of Failure in Viscoelastic Solids

Accurate predictions of the mechanical response of heterogeneous viscoelastic solids is a complex task. An even more challenging task is the prediction of failure in structural components made from this class of materials. One of the primary recognized failure modes for heterogeneous solids is the development of new internal boundaries in the form of cracks. In this form of failure multiple cracks of widely varying length scales can interact in such a way as to produce sufficient energy dissipation to cause total destruction of the component. On the other hand, many structural parts can undergo significant damage, and can continue to perform their intended tasks for many years. Furthermore, components that possess multiple length scales happen often in nature, such as composite materials used in aircraft industry, geologic media, tank armor and asphaltic roadways. Finally, experimentally based design procedures are extremely costly, suggesting the need for improved models. Therefore, models that can accurately predict the evolution of damage and the ultimate failure event, though complex, would appear to be useful for design purposes.