Abstract
In this study, cellulose and basalt fiber were introduced simultaneously to stone mastic asphalt (SMA) to investigate the effects of hybrid modification on performance improvement of asphalt mixture. The study consists of three parts. The first part investigated material properties of cellulose and basalt fiber, including microscope electrical scanning. The second part conducted a series of tests to evaluate the effects of different combinations of cellulose and basalt fiber on performance. With a total addition of fiber 0.4% by the weight of mixture, five different cellulose-basalt fiber ratios, 0 : 4, 1 : 3, 2 : 2, 3 : 1, and 4 : 0, were introduced to the asphalt mixtures. A series of tests including draindown, permanent deformation, low temperature bending, beam fatigue, and moisture damage resistance were conducted. In the final part, a benefit-cost ratio was designed to help determine the optimum cellulose-basalt fiber combination in the economic aspect. Results show that material properties of the two fibers are very different, including thermostability, modulus, surface, and microstructure, especially oil absorption. In general, all samples with fibers outperformed the control group in all the performance tests. Specifically, cellulose fiber improved draindown, ductility, and fatigue more significantly, whilst basalt fiber has more influence on improving permanent deformation, deflection strength, and stress sensitivity. Equal portion of cellulose and basalt fiber has the best moisture damage resistance. The mechanisms of the two fibers are different, resulting in different performance improvements on asphalt mixtures. Overall, an appropriate combination of the two fibers would produce paving materials with more balanced performance in an economical way.
Highlights
Asphalt mixture is made of bitumen, aggregates, and filler, of which the properties are very sensitive to many factors including temperature, load-time, moisture, and stress level
Researches have stated that fibers can significantly improve asphalt mixture performances in one way or another [1]. e finely divided fiber provides a high surface area per unit weight so that mixtures with fiber showed an increase in the optimum binder content [2]
B value increases first and declines. is would bring in conflicts when performances with opposite B trends are needed at the same time, e.g., a fiber combination that achieves higher B value in permanent deformation would result in a lower B value in fatigue
Summary
Asphalt mixture is made of bitumen, aggregates, and filler, of which the properties are very sensitive to many factors including temperature, load-time, moisture, and stress level. Cellulose was not as stable as basalt fiber in high temperature, and the mass loss was much higher, about 5% at 165°C for 2 h. E relative high mass loss in cellulose raises the consciousness of strict temperature control during the production of asphalt mixtures with fiber. Test results showed that pH of water with cellulose was 7.24, and pH of water with basalt fiber was 7.92. High absorption of cellulose is a very good complement for basalt fiber to help hold asphalt and solves problems like draindown and bleeding in SMA. Similar tests were done with distilled water, and the absorption was 510% and 96% for cellulose and basalt fiber, respectively. Cellulose has better absorption of and stronger bond with asphalt material, while basalt fiber demonstrates better thermal stability and mechanical behavior (higher elastic modulus and higher tensile strength). It is preliminarily hypothesized that the introduction of both fibers will complement each other and leads to more balanced performances of asphalt mixture than only one fiber
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