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Performance of Lime in Hot Asphalt Mixtures
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The pavement community has recognized that moisture damage of hot mixed asphalt (HMA) mixtures has been a serious problem since the early 1960s. Numerous additives have been evaluated with the objective of reducing the potential of moisture damage in HMA mixtures. Lime has been one ofthe most common additives used to reduce the potential of moisture damage. The Nevada Department of Transportation (NDOT) has been using lime in HMA mixtures since the mid 1980s. The objective of this research is to quantify the improvements in pavement performance that have been realized through the addition of lime to HMA mixtures. The research used two methodologies: 1) quantify the effectiveness of lime on NDOT's HMA pavements through the evaluation of field pavements and 2) evaluate the various techniques of adding lime to HMA mixtures through laboratory testing. The evaluation offield pavements consisted of evaluating field samples and pavement performance data from untreated and lime-treated pavements. The evaluation of various techniques to add lime into HMA mixtures conducted laboratory evaluation of laboratory-mixed-laboratory-compacted HMA mixtures treated with lime using different techniques. The properties of untreated and lime-treated mixtures from field projects in the southern and north-western parts of Nevada indicated that lime treatment of Nevada's aggregates significantly improves the moisture sensitivity of HMA mixtures. The study showed that lime-treated HMA mixtures become significantly more resistant to multiple freeze-thaw than the untreated mixtures. The long term pavement performance data indicated that under similar environmental and traffic conditions, the lime-treated mixtures provided better performing pavements with less requirements for maintenance and rehabilitation activities. The analysis of the impact of lime on pavement life indicated that lime treatment extends the performance life of HMA pavements by an average of 3 years. This represents an average increase of 38% in the expected pavement life. The laboratory portion of the study showed that lime improves the tensile strength and resilient modulus properties of the HMA mixtures after single and multiple freeze-thaw cycling. The portion of the laboratory study dealing with the evaluation oflime application indicated that all methods of application can produce similar results 80% of the time. In the other 20% of the time, the NDOT process for 48-hours marination showed to be the most effective. Based on the data generated in this experiment, the addition of lime on wet aggreagtes with 48-hours marination would be the most desirable method of lime application because it provides effective results and it is less susceptible to field problems than the addition of lime to wet aggregates without marination.