Stress Intensity Failure Rate Propagators Of Flexible Pavement

Abstract

A responsive pavement management infrastructure is essential for providing durable pavement infrastructure. This need has been accentuated by the quest for sustainability through the adoption of Road Traffic Management System (RTMS) patterns as employed by the various Departments of Transportation (DOT) in South Africa. It can be summarised that increasing humidity/moisture content resulting in percentage increase in saturation content of the underlying base, subbase or subgrade layers will significantly result to a reduction of the Resilient Modulus (MR) of the entire pavement structure weather flexible or rigid. However, this scenario poses a great threat to the structural carrying capacity of the pavement structure. Therefore, it is imperative to provide a solution to such critical problems as they occur and when there is no control to avert them. This can, only be made possible by identifying the exact cause of the problem and providing a feasibly efficient and achievable solution. In the design of roads, flexible pavement has overtime experienced associated distress failure modes resulting in potholes, loss of skid resistance, and reduction in riding quality, noise and road surface ponding. Many of these have being tackled by research, both in the past and currently. The structural collapse of pavement is as a result of distress modes caused by human factors, construction error, excessive traffic loading, environmental factors, cumulative design and geometric errors results to unnecessary loss of strength and stability during the estimated design pavement service life. The objective of this current study is to develop stress intensity failure rate propagators induced by the factors of distress earlier mentioned in order to develop performance functions of asphaltic pavement model using the finite element method followed by a semantic stream-web data analysis (JAVA Expert System Shell analysis JESS). Multivariable transfer functions are generated in order to assess the different modes of failure for Mode I where the onset of crack begins to develop. Moisture sensors are embedded into the pavement in other to determine the real time failure modes populated under service loading and environmental conditions. Damage models are obtained to evaluate the evolution of crack growth and the strain energy release rate for failure mode I (crack initiation). The analysis of this study is further modelled in Abaqus CAE 6.13 as well as a proposed web-based computation analysis of pavement failure (JESS). The FE model indicates that at 20% moisture ingress, the vertical deformation of the subgrade is stable with a value 6.65 E-05. With further increase in moisture, the pavement stiffness reduces and the deformation increases with a failure rate value of 9.68 E-05. The difference indicates that there is a high percentage correlation between moisture content or saturation content increase in pavement and the resilient modulus of the pavement (Stiffness coefficient). Further subjecting the pavement to the same load or increasing load cycles will result in gradual delamination and further yield to total deformation. The results are as presented and discussed as the data obtained from the sensor probes are discretised for analysis in the workbench. A network level pavement management system to contribute to the development of a framework for evaluating pavements’ quality index (PQI) and service life capacity with varying environmental and climatic conditions is presented. The results indicate variation of stiffness with increasing moisture content. Increase in moisture propagation increased saturation of the unbound granular base which reduced the elastic modulus of the subbase layer and reduced the strength of the pavement leading to formation of bottom-up cracks and cracking failure. The horizontal tensile strain (E11) at the asphalt layer at 20% was 69.57x10-4, which increased to 140.8x10-4 at 60% moisture content. The horizontal deformation (E22) reduced, assuming that the material is experiencing work-hardening and no further stress can result to any significant damage. The damage remained at a constant value of 96.8 x 10-4 at 60% saturation. Consequently, the performance of the pavement is affected by temperature gradient. This implies that increasing temperature gradient results in reduction in stiffness of the asphalt layer. In tropical regions, this can result to immediate rutting failure of the asphalt layer, which overtime leads to formation of top-down cracks and potholes with increasing moisture content, even if it is a newly constructed road less than two years old. The web data architecture analysis provides deflection values for failure occurring within the pavement underlying layers. The findings indicate that there is a high correlation between Environmental Condition and road pavement (Asphalt Concrete). The result indicates that increasing temperature gradient of the pavement reduces the fracture energy of the pavement, which results in delamination and collapse over a longer period of time. On the contrary, reduced temperature gradient increases the fracture Energy, making the pavement stiffness high and resistant to failure, but at very low temperatures a compromise is reached and the strength is breached resulting in a brittle material (glass). Although the failure is not visible at the onset of crack propagation, but continual exposure to increasing temperatures as well as increasing moisture content will lead to failure of the pavement before the design life is reached. There is also a surge in the relationship between Pavement Fracture Energy and the Pavement Resilient Modulus. Further, it is found that, the higher the temperature, the higher the rate of deflection and the lower the temperature, the lower the deflection.