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There is a growing interest for the use of mechanistic procedures and analytical methods in the design and evaluation of pavement structure rather than empirical design procedures. The mechanistic procedures rely on predicting pavement response under traffic and environmental loading (i.e., stress, strain, and deflection) and relating these responses to pavement field performance. A research program has been developed at the Center for Pavement and Transportation Technology (CPATT) test track to investigate the impact of traffic and environmental parameters on flexible pavement response. This unique facility, located in a climate with seasonal freeze/thaw events, is equipped with an internet accessible data acquisition system capable of reading and recording sensors using a high sampling rate. A series of controlled loading tests were performed to investigate pavement dynamic response due to various loading configurations. Environmental factors and pavement performance were monitored over a two-year period. Analyses were performed using the two dimensional program MichPave to predict pavement responses. The dynamic modulus test was chosen to determine viscoelastic properties of Hot Mix Asphalt (HMA) material. A three-step procedure was implemented to simplify the incorporation of laboratory determined viscoelastic properties of HMA into the finite element (FE) model. The FE model predictions were compared with field measured pavement response. Field test results showed that pavement fully recovers after each wheel pass. Wheel wander and asphalt mid-depth temperature changes were found to have significant impact on asphalt longitudinal strain. Wheel wander of 16 cm reduced asphalt longitudinal strains by 36 percent and daily temperature fluctuations can double the asphalt longitudinal strain. Results from laboratory dynamic modulus tests found that Hot Laid 3 (HL3) dynamic modulus is an exponential function of the test temperature when loading frequency is constant, and that the HL3 dynamic modulus is a non-linear function of the loading frequency when the test temperature is constant. Results from field controlled wheel load tests found that HL3 asphalt longitudinal strain is an exponential function of asphalt mid-depth temperature when the truck speed and wheel loading are constant. This indicated that the laboratory measured dynamic modulus is inversely proportional to the field measured asphalt longitudinal strain. Results from MichPave finite element program demonstrated that a good agreement between field measured asphalt longitudinal strain and MichPave prediction exists when field represented dynamic modulus is used as HMA properties. Results from environmental monitoring found that soil moisture content and subgrade resilient modulus changes in the pavement structure have a strong correlation and can be divided into three distinct Seasonal Zones. Temperature data showed that the pavement structure went through several freeze-thaw cycles during the winter months. Daily asphalt longitudinal strain fluctuations were found to be correlated with daily temperature changes and asphalt longitudinal strain fluctuations as high as 650 [mu]m/m were recorded. The accumulation of irrecoverable asphalt longitudinal strain was observed during spring and summer months and irrecoverable asphalt longitudinal strain as high as 2338 [mu]m/m was recorded.
Abstract : This study aimed to investigate the use of wide base tires (WBT) in Michigan to quantify the effect of different percentages of WBT loads on flexible and rigid pavements. Surveys and field investigations were conducted to quantify the WBT usage in Michigan. The JULEA (for flexible pavements) and Illislab (for JPCP) software programs were used to calculate the mechanical response between dual tire (DT) and WBT loads, while the Mechanical-Empirical (ME) pavement design process was utilized for damage accumulation and pavement distress analysis. Investigation results rationalized the assumption of WBT proportion for design purposes as 10% currently and up to 25% in the future for Michigan with the majority of axles load still employing DT assemblies. WBT loads were found to increase pavement distress mechanistically using this process, with fatigue cracking for flexible pavement and faulting for JPCP most critical. Thicker asphalt concrete (AC) layers were beneficial in reducing WBT impact on fatigue cracking, while rutting was much less impacted by the thickness of the AC layer under WBT using the ME design process. Thicker concrete slabs helped reduce WBT impacts on both transverse cracking and faulting for JPCP. It was also found that WBT loads did not affect the international roughness index (IRI) significantly for both flexible and JPCP using a process adapted from the Pavement ME analysis. Based on analysis results, the WBT impact on pavement structures with 5-12" AC layers or 6-13" PCC slabs were quantified for up to 25% WBTs, with the respective adjusted Pavement ME and AASHTO 93 design threshold and recommendation for implementation.
This textbook lays out the state of the art for modeling of asphalt concrete as the major structural component of flexible pavements. The text adopts a pedagogy in which a scientific approach, based on materials science and continuum mechanics, predicts the performance of any configuration of flexible roadways subjected to cyclic loadings. The authors incorporate state-of the-art computational mechanics to predict the evolution of material properties, stresses and strains, and roadway deterioration. Designed specifically for both students and practitioners, the book presents fundamentally complex concepts in a clear and concise way that aids the roadway design community to assimilate the tools for designing sustainable roadways using both traditional and innovative technologies.
The project represents a coordinated study involving a laboratory investigation, theoretical analysis and field measurements of stresses induced in flexible pavements by moving wheel loads. The laboratory tests indicated that the modulus of resilience is virtually independent of stress intensity and number of load repetitions provided the boulder clay samples are preconditioned. The theoretical (finite) element program was developed to the stage where either linear or nonlinear material properties in any combination can be handled in pavement structures of one to four layers. Results of trial problems indicate that the finite element program is working correctly and yields realistic answers to pavement deflections. Results are presented. (Author).
This book summarizes research being pursued within the Research Unit FOR 2089, funded by the German Research Foundation (DFG), the goal of which is to develop the scientific base for a paradigm shift towards dimensioning, structural realization and maintenance of pavements, and prepare road infrastructure for future requirements. It provides a coupled thermo-mechanical model for a holistic physical analysis of the pavement-tire-vehicle system: based on this model, pavement structures and materials can be optimized so that new demands become compatible with the main goal – durability of the structures and the materials. The development of these new and qualitatively improved modelling approaches requires a holistic procedure through the coupling of theoretical numerical and experimental approaches as well as an interdisciplinary and closely linked handling of the coupled pavement-tire-vehicle system. This interdisciplinary research provides a deeper understanding of the physics of the full system through complex, coupled simulation approaches and progress in terms of improved and, therefore, more durable and sustainable structures.