Use of Lime as Anti-Strip Additive for Mitigating Moisture Susceptibility of Asphalt Mixes Containing Baghouse Fines.

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Title: Use of Lime as Anti-Strip Additive for Mitigating Moisture Susceptibility of Asphalt Mixes Containing Baghouse Fines.
Author: Shidhore, Aniruddha Vilas
Advisors: Dr. N. Paul Khosla, Committee Member
Dr. Akhtarhusein A. Tayebali, Committee Chair
Dr. Michael L. Leming, Committee Member
Abstract: Recent NCDOT research suggests that baghouse fines with gradation similar to the natural and manufactured fines passing #200 sieve seems to have beneficial effect on stiffness and rutting characteristics of the asphalt mix. However, these studies conclude that mixes containing baghouse fines were highly moisture susceptible, and recommended that baghouse fines be metered into the mix to create a uniform percentage throughout the mix. This study assesses the effectiveness of hydrated lime as an anti-strip additive in mixes containing excess baghouse fines. Comparison of test results of the mixes containing hydrated lime versus the mixes containing organic anti-stripping additive (LOF 6500) was also done. Two different types of baghouse fines, one from Boone, NC and one from Enka, NC, were used in HMA mixtures in the amounts of 1.5, 5.5 and 6.5-percent. Modifications were made to the available JMF and specimens were prepared in the laboratory and several different tests were performed. Wet sieve analysis was first done to check the gradation of materials. Using this gradation and the available JMF, aggregate proportioning was done to satisfy NCDOT mix design criteria. Moisture susceptibility of mixes was determined by performing TSR tests on mixes with different proportions of BHF, and with or without lime. TSR testing showed that moisture susceptibility was dependant on both the concentration of baghouse fines and anti-strip additive. Presence of hydrated lime in mixes increased the resistance to moisture damage. Specimens were also tested using the SST machine. Samples were compacted and sawed and one half of the specimens were moisture conditioned. The FSCH and RSCH tests were then performed on the samples to determine the material properties as well as the rutting resistance and fatigue life. In general, the test results indicate that addition of lime enhances the mix performance - |G*| values are higher, rut depths are lower, and fatigue resistance is higher. Based on the results of this study, it may be concluded that, addition of 1-percent hydrated lime to asphalt mixtures with up to 5-percent additional BHF (total of 6.5-percent) enhances the mix performance. Addition of lime also helped in the mitigation of moisture susceptibility of asphalt mixes. It is thus recommended that NCDOT should consider addition of 1-percent hydrated lime (by weight of dry aggregates) to mixes which are expected to have excess BHF content.
Date: 2005-11-10
Degree: MS
Discipline: Civil Engineering

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