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Laboratory and field tests were conducted to evaluate the use of hydrated lime as an antistrip additive in hot mix asphalt concrete. Batch and drum mix plants were used to prepare the paving mixtures. Lime was added dry and in slurry form. Individual aggregates and the total aggregate were separately treated with lime slurry and allowed to age for different time periods from a few minutes to 30 days before mixing with asphalt. Laboratory mixed and plant mixed asphalt concrete was tested using indirect tension and resilient modulus before and after moisture conditioning. Results indicate that lime is effective in reducing moisture susceptibility and that it is most effective when applied in the presence of moisture. In addition, a time delay after application of lime to aggregate is unnecessary. There are no significant differences in mixtures produced in batch and drum plants.
This synthesis will be of interest to pavement designers, construction engineers, maintenance engineers, and others interested in avoiding or limiting moisture damage in asphalt concrete. Information is provided on physical and chemical explanations for moisture damage in asphalt concrete, along with a discussion of current practices and test methods for determining or reducing the susceptibility of various asphalt concrete components and mixtures to such damage. Moisture damage in asphalt concrete is a nationwide problem which often necessitates premature replacement of highway pavement surfaces. This report of the Transportation Research Board describes the underlying physical and chemical phenomena responsible for such damage. Current test methods used to determine the susceptibility of asphalt concretes, or their constituents, to moisture damage are described and evaluated. Additionally, current practices for minimizing the potential for moisture damage are examined.
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The benefits of using hydrated lime as an additive in asphalt concrete are well known. When added to asphalt concrete mixtures hydrated lime shows the beneficial effects of filler, while also improving resistance to moisture damage. This study presents findings from four studies into the impact of hydrated lime, the impact of lime introduction method on the volumetric optimums, and the performance evaluation of unmodified and lime-modified hot mix asphalt (HMA) mixtures at varying asphalt contents using Simple Performance Tests developed from the NCHRP projects 9-19 and 9-29 and the viscoelastic continuum damage (VECD) finite element analysis. The performance characteristics evaluated in this study include fatigue cracking and rutting behavior in both dry and moisture-conditioned states. Test methods adopted in this evaluation are: the dynamic modulus test for stiffness characterization; the triaxial repeated load permanent deformation test for rutting characterization, and the direct tension test for fatigue cracking characterization. From the experimental investigation it is found that the method of lime introduction can have an important effect on the optimum volumetric asphalt content. Regarding dynamic modulus it is found that hydrated lime has a minimal impact on the mixtures in this study. However, the findings from this study support conventional understanding of the effects of asphalt content, lime modification, and moisture conditioning on the fatigue cracking and rutting performance of HMA mixtures. That is, as asphalt content increases, the resistance to fatigue cracking improves and rutting performance worsens. Another accepted fact is that lime modification reduces the susceptibility for moisture damage in terms of both fatigue cracking and rutting. The contribution of this paper, therefore, is to demonstrate advanced test methods and models that can be used in the performance evaluation of various mixtures. With additional validation and calibration.