|Title:||The effects and causes of oxidative aging of compacted asphalt mixtures|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Asphalt emulsion mixtures
Asphalt -- Additives
|Pages:||xiii, 183 pages : color illustrations|
|Abstract:||Asphalt mixture is a widely used material for the construction of road, airfield, and parking lot pavements. Asphalt binder in asphalt mixture is subjected to oxidative aging, which causes asphalt to become stiffer and more brittle and leads to higher asphalt stress that makes the pavement more susceptible to cracking under a given deformation. Existing studies mainly focus on the aging-related issues of asphalt binder per se. It remains unclear how asphalt binder aging drives the mechanical property changes of asphalt mixtures and what factors affect asphalt binder aging in asphalt mixtures. The overall goal of this research is to (1) quantify the relationships between the aging-induced chemical and physical changes of recovered asphalt binder and the property changes of compacted asphalt mixture, and (2) identify the key factors that affect the aging of asphalt binder in asphalt mixtures. The overall research goal consists of four specific objectives: (1) Development of a new method to simulate the long-term aging for compacted asphalt mixtures, (2) Quantification of the relationship between the aging of asphalt binders and asphalt mixtures, (3) Determination of the oxygen transport efficiency and possible oxygen consumption of asphalt mixtures, and (4) Identification of critical factors that affect the aging susceptibility of asphalt binders in compacted asphalt mixtures. To achieve the research objectives, two new pieces of equipment were developed. One piece of equipment was developed to more realistically simulate the long-term aging of compacted asphalt mixtures. The newly developed equipment was subsequently used to age a variety of compacted asphalt mixture types. The dynamic modulus values of compacted asphalt mixtures at different aging states were tested. Based on the results, the quantitative relationship between the rheological properties of asphalt binder and the dynamic modulus of compacted asphalt mixtures were examined. The other new piece of equipment was developed to measure the oxygen diffusion and consumption coefficients of compacted asphalt mixtures, along with test procedures for making the measurements. The methods to calculate the oxygen diffusion and consumption coefficients of compacted asphalt mixtures were also assessed. The relationship between oxygen diffusion coefficients and mixtures' volumetric parameters were examined.|
The following major findings are made through this research. (1) The newly developed aging method can efficiently simulate the long-term aging of compacted asphalt mixtures without impairing the integrity of the mixtures during the aging process. (2) The dynamic modulus values of compacted asphalt mixtures are well related to the aging states of asphalt binders. (3) The accuracy and robustness of six models for predicting the dynamic modulus of compacted asphalt mixtures vary with mixture types and aging states, and the Improved Hirsch's Model has higher accuracy and robustness in predicting the dynamic modulus of compacted asphalt mixtures for different asphalt mixture types. (4) It is feasible to use the developed apparatus and test procedure to measure the oxygen diffusion coefficients of compacted asphalt mixtures. Additionally, oxygen consumption can be neglected at room temperature. (5) Oxygen diffusion coefficients of compacted asphalt mixtures vary greatly and are affected by the volumetric characteristics of the compacted asphalt mixtures. (6) The oxygen diffusion coefficient provides a good indication of the aging susceptibility of compacted asphalt mixtures. It is believed that this study contributes to the body of knowledge in pavement engineering by having developed new methods and gained new insights into compacted asphalt mixture aging. The findings will also have significant implications for pavement engineering practices.
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