Presently, in North Carolina the bag-house materials used in hot-mix-asphalt (HMA) are purged intermittently into the AC mixtures rather than being stored in a silo and added to the mixture as mineral filler in a uniform, controlled manner. Previous studies have shown that the volumetric properties of asphalt mixtures are greatly influenced by the source and gradation of the baghouse fines. Due to this reason, several states require contractors to waste baghouse fines. However, there is some environmental concern in wasting the fines.
Recent NCDOT research suggest 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 research proposes to conduct a laboratory study of moisture sensitivity of asphalt mixes containing controlled percentages of Boone and Enka baghouse fines in the amount of 0, and 4-percent. In this study, lime will be used as an anti-strip agent to determine its effectiveness in mitigating moisture damage. The results of this study will complete, and support the outcome of the previous NCDOT studies that investigated mitigation of moisture susceptibility of mixes containing baghouse fines with organic anti-strip additives. The recommendations based on results of this study should enable NCDOT to formulate specifications with regards to the use of baghouse fines in NCDOT mixes. Three possible outcomes that may be pursued are: 1) waste baghouse fines all together; 2) require use of baghouse fines in uniform controlled manner; 3) require use of lime as anti-strip additive in lieu of the use of organic anti-strip additives.
The objective of this research will be to evaluate the use of lime as anti-strip additive for mitigating the moisture susceptibility of asphalt mixes containing baghouse fines. Two baghouse fines - Boone and Enka that has been used in prior NCDOT studies [2, 3] will be evaluated. This will allow direct comparison of the same mixes containing organic liquid anti-strip with those containing lime as anti-strip.
The anticipated results of this research study will be a clear understanding of the significance of the use of baghouse fines in asphalt mixes used in the state of North Carolina, vis-à-vis comparison between mixes containing lime and organic anti-stripping agent.
