Daba S. Gedafa

Performance-Related Specifications for PCC Pavements in Kansas

Statistical specifications for highway construction provide the means to measure important quality control attributes and ensure their compliance. The pay adjustments in these specifications reflect the amount of pay reduction and the optimized risk distributed between the owner agency and the contractor. The Kansas Department of Transportation (KDOT) has built a comprehensive database of as-constructed properties of materials for Portland cement concrete (PCC) pavements from the tests required as part of the quality control/quality assurance (QC/QA) program. Currently, KDOT pays incentives/disincentives for thickness and strength for PCC pavements. A practical performance model and composite index that include these two quality characteristics (thickness and strength) and air content for durability are needed to reflect the combined effect on the performance of PCC pavements. The main objectives of this study were to investigate the effect of levels of significance and lot size and to develop a practical performance model and composite index for PCC pavements in Kansas. Thirteen projects from four administrative districts of KDOT were selected for this study. Statistical analysis software was used for statistical analysis. Microsoft Excel was used to develop the performance models. Lot-wise comparison showed that QC means are significantly different in most of the cases. These cases increase with an increase in significance level. A practical performance model and composite index using quality characteristics (thickness, strength, and air content) have been proposed as an integral part of performance-related specifications in Kansas.

Network Level Testing for Pavement Structural Evaluation Using a Rolling Wheel Deflectometer

Structural evaluation can be very useful at the network level of pavement management for project prioritization purposes. However, due to expenses involved in data collection and analysis, pavements are not tested for structural capacity at the network level. Rolling wheel deflectometer (RWD), which measures surface deflections at highway speed, is an alternate, faster method of pavement deflection testing for network level data collection. This study was initiated to assess the feasibility of using RWD for network level pavement deflection measurements. RWD deflection data was collected under an 80-kN axle load and at about highway speed on non-interstate highways in northeast Kansas in July 2006. Falling-wheel deflectometer (FWD) data on these roads, collected from 1998 to 2006, were also used for comparison. The computed effective structural numbers from both FWD and RWD deflection data were compared. The results show that the deflections measured by RWD and the center (first sensor) deflections from FWD are statistically similar. The effective structural numbers computed from the FWD and RWD deflection measurements are also statistically similar. Thus RWD appears to be a valuable tool for structural capacity evaluation of pavements at the network level.

Comparison of Moduli of Kansas Superpave Asphalt Mixes

Currently, hot-mix asphalt (HMA) mixture design and pavement structural design are not fully integrated, although Superpave® asphalt mixture design is somewhat project specific. The objective of this study was to compare elastic moduli assumed during structural design of pavements with the backcalculated moduli of HMA layers obtained from the falling weight deflectometer (FWD) tests and the dynamic modulus values measured in the laboratory. Five newly built Superpave pavements, designed by using the 1993 AASHTO Design Guide, were selected as study sites in this research. Deflection data were collected with a Dynatest 8000 FWD on a 1,000-ft test section at each site. The HMA layer moduli were then backcalculated by using an elastic-layer analysis program. Full depth cores were taken from each section and tested in the laboratory for dynamic moduli. The results showed that backcalculated and laboratory moduli were somewhat comparable for all practical purposes. The laboratory dynamic moduli increased with the loading frequency, indicating the need for consideration of vehicle speeds in the HMA pavement structural design. HMA design moduli, assumed by the Kansas Department of Transportation during pavement structural design, are lower than both backcalculated and laboratory dynamic moduli. Thus, current HMA design moduli are achievable in the field through Superpave mixture design, despite the fact that the pavement structural design and mix design processes are not integrated.

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.

Performance-Related Specification for Superpave Pavements in Kansas

Statistical specifications for highway construction provide the means to measure the important quality control attributes and ensure their compliance. The pay adjustments, part of these specifications, reflect the amount of deduction or bonus and the optimized risk distributed between the owner and the contractor. The Kansas Department of Transportation (DOT) has built a comprehensive database of as-constructed material properties for Superpave® pavements from the tests required in the quality control–quality assurance (QC-QA) program. Currently, Kansas DOT pays incentives or disincentives for mixture air voids and in-place density of Superpave pavements. A practical performance model and a composite index that includes air voids, in-place density, asphalt content, and voids in mineral aggregate are needed to reflect the factors that affect the performance of Superpave pavements. The main objectives of this study were to investigate the effect of levels of significance and lot size and to develop practical performance models and a composite index for Superpave pavements in Kansas. Thirty-five projects from six administrative districts of Kansas DOT were selected in this study. Lot-by-lot comparison showed that QC-QA means were significantly different in most cases. The number of cases with a significant difference in means increased with an increase in significance level. A practical performance model and composite index from multiple quality characteristics have been proposed as an integral part of performance-related specifications (PRS) for Superpave pavements in Kansas. The performance model can be used to better understand the consequences of either exceeding or falling short of the desired quality levels and will provide a logical and defensible basis for the adjusted pay schedules that are an integral part of PRS.