Doseung Lee

DEVELOPMENT OF NEW PROFILE-BASED TRUCK DYNAMIC LOAD INDEX

A new roughness index called the dynamic load index (DLI) is developed for the purpose of identifying pavement profiles that are likely to generate high dynamic truck-axle loads. The DLI is calculated as a weighted index of variances of the profile elevation in the frequency ranges of 1.5 to 4 Hz and 8 to 15 Hz. The first frequency range corresponds to truck body bounce, and the second frequency range corresponds to axle bounce. The analysis showed a very good relationship between the DLI and dynamic load. The DLI was tested on a range of road profiles from in-service pavements, and it was found that for any particular value of ride quality index (RQI), the DLI can cover a wide range of values, and this variation in DLI was found to correlate well with dynamic load, as predicted by a truck simulation program. This was not the case for the international roughness index, which gave a low coefficient of correlation with dynamic load for the same range of profiles. Therefore, the new index can differentiate between profiles that generate high dynamic loads and those having the same RQI but generating low dynamic loads. Most importantly, the use of the DLI negates the need for running a truck simulation program. This makes it possible for a state highway agency to decide whether a particular pavement with a given surface profile needs smoothing (to extend its service life) based on the DLI value.

USE OF DISTRESS AND RIDE QUALITY DATA TO DETERMINE ROUGHNESS THRESHOLDS FOR SMOOTHING PAVEMENTS AS A PREVENTIVE MAINTENANCE ACTION

In this discussion, 462 pavement sections from 37 projects in Michigan were analyzed to investigate the interaction between pavement surface roughness and distress. The main hypothesis of this research is that an increase in roughness leads to higher dynamic axle loads, which in turn can lead to a tangible acceleration in pavement distress. If this relationship is established, then it will be possible to plan a preventive maintenance (PM) action to smooth the pavement surface. Such a PM action is bound to extend the service life of the pavement by several years. The objective of the research presented was to develop such roughness thresholds. The selected projects include 13 rigid, 15 flexible, and 9 composite pavements. The ride quality index (RQI) and distress index were used as measures of surface roughness and distress, respectively. To get a good relationship between distress caused by dynamic loading and surface roughness, dynamic-load-related distress types were extracted. The analysis showed very good relationships between distress and roughness for rigid and composite pavements (R2 = 0.739 and 0.624). However, for flexible pavements there was significant scatter (R2 = 0.375), reflecting the higher variability in flexible pavement distresses. A logistic function was used to fit the data, and roughness thresholds were determined as the RQI-values corresponding to peak acceleration in distress. These were determined to be 64 [international roughness index (IRI) = 1.99 m/km or 124 in./mi] for rigid pavements and 51 (IRI = 1.43 m/km or 89 in./mi) for composite pavements.

DEVELOPMENT OF A PREVENTIVE MAINTENANCE STRATEGY FOR MINIMIZING ROUGHNESS-RELATED PAVEMENT DAMAGE

The Michigan Department of Transportation (MDOT) uses several measures of pavement performance in managing its pavement network, including the distress index (DI) and the ride quality index (RQI). Currently, decisions on when and where to take rehabilitation or preventive maintenance action are mainly based on the DI. The RQI is used only in a passive or reactive fashion: When DI reaches the threshold for poor ride quality, a decision to rehabilitate the road is made. MDOT is currently funding a research study to develop RQI thresholds for each pavement type (rigid, flexible, or composite) aimed at retarding pavement damage caused by roughness-generated, dynamic (impact) loading. These thresholds correspond to the RQI value at which pavement damage is accelerated by high dynamic loads. Given these new RQI thresholds, extending the service life of the pavement by taking preventive maintenance action in the form of smoothing of the pavement surface (by way of milling, grinding, or adding a thin overlay) becomes possible. New RQI thresholds are proposed in a proactive fashion in the context of preventive maintenance: The objective is to determine the opportune time and locations for applying relatively light maintenance to smooth the pavement surface, thereby minimizing dynamic (impact) loads and extending the pavement service life at minimal cost. For this purpose, a reliability-based model for selecting the optimal timing (or planning period) for such preventive maintenance action was developed using the new RQI-threshold and actual RQI-growth rates from in-service pavements. This model can be an effective tool to use in the context of preventive maintenance of pavements.

Development of Roughness Thresholds for Preventive Maintenance Action Aimed at Reducing Dynamic Loads

In this discussion, roughness threshold values and corresponding life extensions are determined using relative damage and reduction in pavement life concepts. Using the fourth power law the following were calculated and plotted for 333 sections: relative damages from the 95th percentile dynamic load at different roughness index values and the corresponding percent reduction in life. A newly developed roughness index, the dynamic load index (DLI), was used for this purpose. Estimates of pavement life extension resulting from smoothing its surface were then generated for different remaining service life (RSL) values. The results were presented in tables showing the expected life extension for a range of RSL and DLI values. These tables would enable a highway agency to determine when a particular pavement needs to be smoothed to obtain a given (desired) life extension. The analysis was done for the three pavement types (rigid, flexible, and composite). RSL values were calculated for 805-m (0.5-mi) sections using actual distress growth over time. The results showed that for rigid pavements, 17% to 51% of sections would have life extensions of more than 3 years depending on roughness level. For composite pavements, none of the sections would have life extensions of 3 years or more. For flexible pavements, 9% to 34% of sections would have life extensions of more than 3 years depending on roughness level. These results indicate that preventive maintenance by smoothing action is best suited for rigid pavements.