No description available.

A large proportion of the U.K. highway network constructed in the 1960's and 1970's contains lean concrete roadbase with bituminous surfacing. Pavements containing relatively high strength lean concrete have rarely required structural maintenance (thick overlay or reconstruction) but have required maintenance because of reflection cracking where the surfacing cracks above cracks in the lean concrete. The time of appearance of this cracking is very variable (2-20 years). Field observations indicate that roadbase transverse crack spacings are often greater than 5m. Reflection cracking at these long spacings can be caused by thermal stresses, This project identifies conditions under which ther<ral reflection cracking will occur and develops a predictive model that allows estimation of the combined effect of thermal and traffic stresses. Finite element analyses indicate that initial crack development is likely to be caused by thermal stresses and final cracking will be assisted by traffic stresses. A temperature model has been developed to determine roadbase daily temperature range and surfacing temperature on a mean monthly basis. Thermal reflection cracking is considered to result from daily cycle fatigue rather than an extreme low temperature mechanism. A test rig has been developed to apply cyclic crack opening movements and simulative tests have been accelerated to 0.1Hz by using a "bitumen stiffness" fatigue criterion., Finite element results, displacements recorded during tests and tensile creep tests to determine mix stiffness, enable dc/dN and K 1 values and material constants (A, n) to be determined. This fracture mechanics interpretation of test results serves as the basis of the predictive model for thermal reflection cracking that is consistent with observations from an untrafficked road. The combined estimate of thermal and traffic stresses cannot however explain reflection cracking at<5m spacings. This cracking apparently initiates at the surface and is probably influenced by other mechanisms.

Este trabalho investiga os efeitos das solicitações do tráfego sobre o desempenho de pavimentos. Dentre vários fatores de tráfego analisados preliminarmente, são selecionados a carga por eixo, a pressão de enchimento dos pneus, o tipo de rodagem, o tipo de pneu e a distribuição da pressão de contato pneu-pavimento. Visando investigar em maior profundidade os efeitos desses fatores, inclusive os de suas interações, efetua-se uma programação fatorial de simulações determinísticas, que inclui também 8 estruturas de pavimento e 5 respostas estruturais: deflexão superficial, deformação horizontal de tração e deformação vertical de compressão na fibra inferior do revestimento asfáltico, deformação vertical de compressão no topo do subleito e tensão horizontal de tração na fibra inferior da camada tratada com cimento, calculadas por 2 programas computacionais (ELSYM5, para análises elástico-lineares, e ILLI-PAVE, para análises elástico-não-lineares). Da análise estatística dos resultados das simulações são obtidos modelos empírico-mecanísticos para cálculo dos Fatores de Equivalência de Cargas. Com esses Fatores de Equivalência de Cargas e mediante utilização do programa de Gerência de Pavimentos HDM III são calculados os impactos econômicos dos fatores de tráfego selecionados sobre as parcelas de custos rodoviários (construção, manutenção e operação). Faz-se análise crítica dos fatores de equivalência de cargas adotados pelas normas brasileiras e internacionais e apresentam-se sugestões para a incorporação dos resultados deste trabalho aos métodos de dimensionamento de pavimentos e de dosagem de misturas asfálticas. No que diz respeito à regulamentação técnica de pesos e dimensões dos veículos rodoviários de carga e à alocação dos custos, investigam-se, em detalhe, as implicações do uso de pneus extralargos em substituição às rodas duplas convencionais, a utilização de pneus com elevadas pressões de enchimento, vários cenários de sobrecarga e a utilização de veículos combinados longos (VCLs). / The effects of traffic loading factors on the pavement performance are studied in this work. Several loading factors are analyzed and the most important ones (axle load, tire inflation pressure, wheel type, and tire-pavement contact pressure distribution) are selected for a more detailed investigation. lt is performed a factorial experiment of deterministic simulations that includes other complementary factors: 8 pavement structures and 5 structural responses (deflection at the top of the surface, horizontal tensile strain and vertical compressive strain at the bottom of the surface, vertical compressive strain at the top of the sub grade, and horizontal tensile stress at the bottom of the cement-treated layer), obtained from 2 computer programs (ELSYM5, for linear elastic analysis, and ILLI-PAVE, for non-linear elastic analysis). Empirical-mechanistic Load Equivalency Factors (LEF) are obtained from the statistic analysis of the factorial experiment. The economic impacts of the selected loading factors on the highway costs (construction, maintenance, and utilization) are calculated using those LEF as input for the Highway Design and Maintenance Standard Model (HDM Ill). The LEF used by Brazilian methods of pavement design are analyzed. Suggestions are made aiming to incorporate the results of this study to the asphalt mix and structural design of pavements, technical regulations and cost allocation procedures. It is discussed the implications of the use of super single tires instead of dual wheels, tire inflation pressures above the values recommended by the tire industry, various scenarios of overloaded trucks, and the traffic of Long Combination Vehicles (LCVs) in Brazilian highways.

No description available.

Este trabalho investiga os efeitos das solicitações do tráfego sobre o desempenho de pavimentos. Dentre vários fatores de tráfego analisados preliminarmente, são selecionados a carga por eixo, a pressão de enchimento dos pneus, o tipo de rodagem, o tipo de pneu e a distribuição da pressão de contato pneu-pavimento. Visando investigar em maior profundidade os efeitos desses fatores, inclusive os de suas interações, efetua-se uma programação fatorial de simulações determinísticas, que inclui também 8 estruturas de pavimento e 5 respostas estruturais: deflexão superficial, deformação horizontal de tração e deformação vertical de compressão na fibra inferior do revestimento asfáltico, deformação vertical de compressão no topo do subleito e tensão horizontal de tração na fibra inferior da camada tratada com cimento, calculadas por 2 programas computacionais (ELSYM5, para análises elástico-lineares, e ILLI-PAVE, para análises elástico-não-lineares). Da análise estatística dos resultados das simulações são obtidos modelos empírico-mecanísticos para cálculo dos Fatores de Equivalência de Cargas. Com esses Fatores de Equivalência de Cargas e mediante utilização do programa de Gerência de Pavimentos HDM III são calculados os impactos econômicos dos fatores de tráfego selecionados sobre as parcelas de custos rodoviários (construção, manutenção e operação). Faz-se análise crítica dos fatores de equivalência de cargas adotados pelas normas brasileiras e internacionais e apresentam-se sugestões para a incorporação dos resultados deste trabalho aos métodos de dimensionamento de pavimentos e de dosagem de misturas asfálticas. No que diz respeito à regulamentação técnica de pesos e dimensões dos veículos rodoviários de carga e à alocação dos custos, investigam-se, em detalhe, as implicações do uso de pneus extralargos em substituição às rodas duplas convencionais, a utilização de pneus com elevadas pressões de enchimento, vários cenários de sobrecarga e a utilização de veículos combinados longos (VCLs). / The effects of traffic loading factors on the pavement performance are studied in this work. Several loading factors are analyzed and the most important ones (axle load, tire inflation pressure, wheel type, and tire-pavement contact pressure distribution) are selected for a more detailed investigation. lt is performed a factorial experiment of deterministic simulations that includes other complementary factors: 8 pavement structures and 5 structural responses (deflection at the top of the surface, horizontal tensile strain and vertical compressive strain at the bottom of the surface, vertical compressive strain at the top of the sub grade, and horizontal tensile stress at the bottom of the cement-treated layer), obtained from 2 computer programs (ELSYM5, for linear elastic analysis, and ILLI-PAVE, for non-linear elastic analysis). Empirical-mechanistic Load Equivalency Factors (LEF) are obtained from the statistic analysis of the factorial experiment. The economic impacts of the selected loading factors on the highway costs (construction, maintenance, and utilization) are calculated using those LEF as input for the Highway Design and Maintenance Standard Model (HDM Ill). The LEF used by Brazilian methods of pavement design are analyzed. Suggestions are made aiming to incorporate the results of this study to the asphalt mix and structural design of pavements, technical regulations and cost allocation procedures. It is discussed the implications of the use of super single tires instead of dual wheels, tire inflation pressures above the values recommended by the tire industry, various scenarios of overloaded trucks, and the traffic of Long Combination Vehicles (LCVs) in Brazilian highways.

Graduation date: 1995

Thesis (Ph. D.)--University of Washington, 1982. / Vita. Includes bibliographical references.

Perpetual pavement design philosophy provides a long-life pavement design alternative. The ability of a pavement design to perform as long-life pavement is subjected to several technical constraints. Throughout the past 10 years, perpetual asphalt pavement designs have been under investigation in several parts of the world. The Canadian climate represents an additional challenge to the success of long-life pavement performance. This project investigated the construction and performance of three pavement test sections that were constructed on Highway 401 in Southern Ontario. The construction phase of this project was completed in 2010. The test sections were equipped with various sensors to monitor the structural performance. The test section included two perpetual pavement sections and one conventional pavement section. The two perpetual pavement designs were identical with the exception of the bottom asphalt layer, which was constructed as a Rich Bottom Mix (RBM) layer in one of the perpetual sections. The three pavement sections were evaluated from a structural point of view through the analysis of the in-situ tensile strain collected from asphalt strain gauges installed at the bottom of asphalt layers under the wheel path. In addition, asphalt material laboratory characterization was undertaken by testing asphalt samples collected during construction of the three test sections. The laboratory testing was performed at the Centre for Pavement and Transportation Technology (CPATT) at the University of Waterloo. The laboratory experimental matrix in this research included dynamic modulus testing, resilient modulus testing and Thermal Stress Restrained Specimen Testing (TSRST). The correlation between various laboratory test results and the collected in-situ tensile strain was evaluated. Several linear regression models were developed to correlate the laboratory test results and the field asphalt temperature with the in-situ tensile strain. Overall, it was found that the perpetual pavement with RBM section had the lowest tensile strain at the bottom of asphalt layers. Also, various models were developed that predict tensile strain at the bottom of asphalt layers by using laboratory test data. An economic analysis was implemented to evaluate the perpetual and conventional pavement designs including a Life Cycle Cost Analysis (LCCA). Furthermore, a sustainability assessment for both design philosophies was executed to evaluate the environmental benefits of perpetual pavement designs. The perpetual pavement designs were shown to provide many benefits over the conventional asphalt pavement designs for usage on Canadian Provincial and Interstate Highways in similar climatic zones with similar traffic loading. The advantages of perpetual pavement design philosophy are not limited to structural benefits, but also extended to economic and environmental benefits in the long term.

An inverted base pavement is a new pavement structure that consists of an unbound aggregate base between a stiff cement-treated foundation layer and a thin asphalt cover. Unlike conventional pavements which rely on upper stiff layers to bear and spread traffic loads, the unbound aggregate inter-layer in an inverted base pavement plays a major role in the mechanical response of the pavement structure. Traditional empirical pavement design methods rely on rules developed through long-term experience with conventional flexible or rigid pavement structures. The boundaries imposed on the unbound aggregate base in an inverted pavement structure change radically from those in conventional pavements. Therefore, current empirically derived design methods are unsuitable for the analysis of inverted base pavements. The present work documents a comprehensive experimental study on a full-scale inverted pavement test section built near LaGrange, Georgia. A detailed description of the mechanical behavior of the test section before, during and after construction provides critically needed understanding of the internal behavior and macro-scale performance of this pavement structure. Given the critical role of the unbound aggregate base and its proximity to the surface, a new field test was developed to characterize the stress-dependent stiffness of the as-built layer. A complementary numerical study that incorporates state-of-the-art concepts in constitutive modeling of unbound aggregates is used to analyze experimental results and to develop preliminary guidelines for inverted base pavement design. Simulation results show that an inverted pavement can deliver superior rutting resistance compared to a conventional flexible pavement structure with the same fatigue life. Furthermore, results show that an inverted base pavement structure can exceed the structural capacity of conventional flexible pavement designs for three typical road types both in rutting and fatigue while saving up to 40% of the initial construction costs.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains viii, 79 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 52-54).