Fatigue Behaviour of Jute fiber reinforced asphalt concrete

Varma, Kamila Rohit and Saride, Sireesh (2019) Fatigue Behaviour of Jute fiber reinforced asphalt concrete. Masters thesis, Indian institute of technology Hyderabad.

Text
Mtech_Thesis_TD1541_2019.pdf
Restricted to Repository staff only until 23 July 2021.
Download (5MB) | Request a copy

Abstract

Flexible pavements fail majorly due rutting and fatigue. These failures compromise the quality of the road by causing discomfort to the passengers and requires periodic maintenance which is inefficient and uneconomical. Although flexible pavements are the most popular pavements, their life is much lower generally ranging between 15- 20 years. After the life of the pavement is over pavement has to be entirely reconstructed or temporary measures may be taken which are not that effective. Many modifiers are being used to improve the performance of the asphalt concrete mixes. Fatigue failure happens when vehicular loads repeatedly applied on the pavement layer lead to bottom up cracking in the asphalt layer. Vehicular loads induce micro cracks at the bottom of the asphalt layer which accumulate over time to develop into macro cracks and lead to the fatigue fracture of the pavement layers. Many techniques are being employed to enhance the performance of asphalt concrete like asphalt binder modification using polymers and reinforcing the asphalt mix with fibers of high tensile strength. Fiber reinforcement of asphalt mixes has gained considerable attention during the past decade due to its effectiveness in improving the fatigue performance of the asphalt. Out of these mostly synthetic fibers like polypropylene fibers, polyester fibers etc., and mineral fibers are used. Natural fibers like cellulose, wool, jute and coir are also studied by some researchers. But the fatigue behavior of these fibers is not very well understood. It is observed in the existing literature that jute fiber possesses a great potential as an alternative for synthetic fibers which are much costlier and not easily available in all the places. Most of the literature focused on marshall mix design of the jute fiber asphalt concrete. A limited number of studies are available to understand the fatigue performance of the jute fiber reinforced asphalt concrete. It is also observed that most of the test methods employed are not representative of the field conditions. In this context the present study aims to evaluate the fatigue performance of the jute fiber reinforced asphalt concrete based on repetitive load tests conducted on beams in four point beam bending mode. In addition attempt has been made to understand the mechanism of the jute fiber reinforcement in the asphalt beams. In order to achieve these goals a two stage experimental program was designed in which three jute dosages are used 0%, 0.1%, 0.25% and 0.45% to understand the effect of the fiber content on various parameters. These percentages were chosen based on the literature. In these tests jute fiber are mixed thoroughly with the asphalt ensuring randomness in fiber distribution and then compacted to make slabs which were eventually cut into beams. Static and repetitive four point bending tests were conducted on these beams in load controlled mode at a constant temperature of27°C. 50% (120N) of the strength obtained from the static tests is taken as amplitude for the load controlled testing in repetitive tests. In the first stage the effectiveness of the jute fiber reinforced asphalt concrete is studied by analyzing the load-deflection data. The initial stiffness values, dissipated energy during crack propagation, peak loads of the beams were obtained from this data. Further to understand the fatigue behaviour of jute fiber reinforced asphalt concrete images were captured during the test and were analyzed using DIC technique. All the fiber contents have improved the performance of the asphalt mixes by improving the strength and crack resisting potential of the asphalt mixes. Among these specimens 0.25% jute fiber reinforced specimens have shown best performance based on all parameters. 0.25% JFR has shown an increase in peak load by 65%, initial stiffness by 31% and reduction in tensile strain at 245N load by 33% as compared to control section. DIC technique employed was effective in obtaining vertical deflections and tensile strains. In addition to static tests, it is necessary to evaluate the behaviour of the asphalt mixes in repetitive fatigue loading. Load controlled repetitive tests were conducted with 120N amplitude and 10Hz frequency. DIC technique as employed to study the strain mobilization and crack initiation. The effectiveness of the jute fiber reinforcement in the asphalt beams is evaluated using the vertical deflections, tensile strains and normalized complex modulus values obtained from load deflection data and DIC data. All the jute fiber reinforced beams have showed improved results in all the above mentioned parameters. 0.25% jute fiber reinforced specimen has performed better than other specimens. At lower reinforcement percentages not enough fibers are present to reinforce the tension zone. But when the fiber content increases beyond a point the fibers start clumping thus reducing the effectiveness of the jute fibers. This was observed to be the reason behind the reduction in performance of the 0.45% jute fiber reinforced asphalt mix. The control section has failed at 15900 cycles. At 15900 cycles the reinforced specimens have not failed and have shown promising performance. Especially the 0.25% reinforced specimens has shown no fatigue cracks and the maximum tensile strains at this cycle were reduced by 30%.

[error in script]

IITH Creators: