Taslima Khanum

Comparison of Pavement Design Using AASHTO 1993 and NCHRP Mechanistic- Empirical Pavement Design Guides

The new Mechanistic-Empirical Pavement Design Guide (MEPDG) provides methodologies for mechanistic-empirical pavement design as opposed to the empirical methodology used in the 1993 American Association of State Highway and Transportation Officials (AASHTO) pavement design guide. The objective of this study was to compare the pavement designs obtained using the 1993 AASHTO and the new MEPDG methods for typical Portland Cement Concrete (PCC) and Asphalt Concrete (AC) pavements in Kansas. Five in- service Jointed Plain Concrete Pavement (JPCP) projects were reanalyzed as equivalent JPCP and AC projects using both approaches at the same reliability level. The results show that the new MEPDG analysis yielded thinner AC sections for all projects than those obtained from the 1993 AASHTO design guide analysis. Four of the PCC sections, designed using the 1993 AASHTO design guide, were thicker than the sections obtained with MEPDG. The MEPDG analysis resulted in thicker PCC slab for the fifth project. Effect of change in performance criteria on the thickness of AC and PCC sections has also been investigated. It has been found that AC sections are more sensitive to change in performance criteria as compared to PCC sections using MEPDG versions 1.0 and 1.1. In general, difference in thickness using both versions is not significant for all practical purposes.

Effect of Quarry Production Process on Specific Gravities of Aggregates

The combined bulk specific gravity of aggregates is a basic input in the Superpave asphalt mixture volumetric design. In order to identify and quantify the factors affecting the aggregate specific gravity values, tests methods similar to AASHTO T84 and T85 were conducted on aggregate samples collected from four different quarries in Kansas. All test results were analyzed statistically to find the significance of the factors—top size and fine loss of the aggregates during replicate testing—used in the experimental program. The results show that the bed from which the aggregates are produced has a significant effect on the specific gravities. However, different aggregate products obtained from the same bed in a quarry may have dissimilar specific gravities. The analysis also shows that the aggregate production process affects the specific gravities significantly when the aggregates are softer, such as soft limestone in Kansas. Fine loss during replicate testing does not affect the results for harder aggregates.