Arash Rezaei

Probabilistic Approach to Life-Cycle Cost Analysis of Preventive Maintenance Strategies on Flexible Pavements

Preventive maintenance (PM) is recognized as a potentially useful tool to reduce pavement network operation costs. To identify the lowest-cost maintenance and rehabilitation strategies to keep pavement conditions at their desired levels, agencies need to predict conditions on the network accurately. This need presents a challenge because pavement deterioration is a complex mechanism that involves not only structural damage but also the effects of interactions between traffic, material, environment, and time. Earlier studies have based cost analyses on deterministic pavement deterioration prediction models, even though these models lack the capability to capture the random part of true pavement field behavior. An alternative approach is to use probabilistic models, which are built on the basis of observations of in-service facilities and allow a more realistic representation of pavement performance. In this research study, pavement crack initiation models were developed on the basis of stochastic hazard rate modeling techniques. Significantly, model development included data from the California Department of Transportation Pavement Condition Survey so that the effects of a wide range of facilities and environmental conditions could be represented. This study also compared several pavement maintenance scenarios with the use of rehabilitation only as the control case. The studys performance results were then coupled with available cost information to develop life-cycle cost comparisons. The research results confirmed that, compared with rehabilitation alone and maintenance at advance levels of cracking pavement, PM practices significantly reduced long-term costs of roadway maintenance.

Effects of Milling and Other Repairs on Smoothness of Overlays on Asphalt Pavements

The application of asphalt overlays on existing pavements comprises a significant percentage of the maintenance activities undertaken to restore asphalt pavement condition. The improvement of surface smoothness from overlay construction is gaining increasing attention because smoother overlays are likely to have longer lives as a result of decreased dynamic loading and to provide fuel economy benefits and greater comfort to road users. This paper presents a study in which the California Department of Transportation (Caltrans) Pavement Condition Survey (PCS) data were used to investigate the effects of repairs, preoverlay condition, and surface and binder type on initial overlay (postoverlay) smoothness. Linear mixed-effect models were used in the analysis to take into account the variation across random-effect variables. The smoothness of overlays was measured in terms of the international roughness index (IRI). The analysis indicated that the pavement preoverlay condition (IRI) was the most important variable to affect overlay smoothness: pavements with lower preoverlay IRIs were smoother than those with higher preoverlay IRIs. An increase in overlay thickness also was found to have a significant effect on the smoothness when the preoverlay condition was poor. In terms of preoverlay repairs, analysis of the Caltrans PCS data showed that pavements with digouts (milling and patching in the wheelpaths) performed better than did pavements whose entire surface was milled before the overlay. The effects of surface type (dense- or gap-graded versus open-graded) and binder type (rubberized or not rubberized) depended on the preexisting pavement condition, other factors, or both. Possible reasons for differences between this study and previous ones are offered.