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4 CHAPTER 1 INTRODUCTION PROBLEM STATEMENT In addition to funding and institutional issues, there are the not-so-insignificant problems of determining what treatment In many state highway organizations recognition of the to apply to a pavement, when in the life of the pavement to importance of maintenance and particularly preventive main- apply this treatment, and what measurable improvement is tenance is rapidly changing. During the decades of Interstate obtained by the application of this treatment in comparison expansion (from the 1960s through the 1970s), SHAs were with other alternatives, including doing nothing. Although organized around construction. By the 1980s, the majority of all are critical issues, the first step is the acceptance that pre- the Interstate system was constructed and emphasis gradually ventive maintenance is an effective approach in preserving shifted toward rehabilitation activities. In recent years, how- the agency's pavement investment. ever, increased emphasis was placed on pavement preserva- When applied to the right pavement at the right time, proper tion and preventive maintenance concepts and programs (1). preventive maintenance treatments are a cost-effective means Many factors contributed to this changing paradigm. Prob- of obtaining the desired life and performance of the pave- ably the single largest factor was the realization that available ment. Treatments applied too soon add little benefit and treat- funding levels--and doing business in the usual way--did ments applied too late are ineffective, failing to prolong the not result in pavements that perform at the level of service life of the pavement. Considering the annual magnitude of demanded by the traveling public. The analyses of perfor- highway investments, the potential savings from following a mance data in pavement management systems have helped to cost-effective approach to meeting an agency's performance prove that point, as agencies could see the impact of allocat- objectives for pavements are significant. ing the limited available funds to pavement projects on a Unfortunately, little guidance is available about timing of worst-first basis (i.e., funding and treatments are provided for the application of pavement maintenance treatments. Agen- pavements in the worst condition) (2). The result, in most cies at both the state and national levels have conducted cases, has been a gradual decline in the number of miles an research on whether preventive maintenance is an appropri- agency could treat each year and a decrease in the overall ate pavement preservation strategy; however, the wide range condition of the pavement network. of chosen treatment timings has raised questions about the The inability to provide an acceptable level of service to the effectiveness of preventive maintenance. For example, some public has been confirmed through public surveys. National agencies have applied preventive maintenance treatments at studies and statewide surveys have consistently shown a the end of a pavement's life because funds were not available desire for longer lasting, safer roads, with fewer disruptions for the required rehabilitation. Preventive treatments are effec- from continual road work (3, 4, 5). For example, the results tive when applied to relatively young pavements in good con- from a survey in Arizona have shown that the public would dition. However, the poor performance of treatments applied even be willing to pay higher taxes to meet improved levels of at inappropriate timings could lead to the erroneous conclu- maintenance service, and spend more money now to save sion that preventive maintenance does not work. Fortunately, money on maintenance in the long term (6); public opinion many agencies believe preventive maintenance works and surveys in Washington State revealed similar findings (4). have developed schedules to apply preventive maintenance As it has become evident that rehabilitating pavements treatments, although they do not claim to have identified the when they are near failure is not a cost-effective pavement "optimal" timing for treatment applications. Such examples management technique, the need for a better approach to illustrate the importance of determining the window of time optimize pavement condition and minimize the associated in which preventive maintenance treatments perform as they costs was recognized. The concept of "preventive mainte- are intended. nance," which refers to the application of one or more treat- This project is based on the premise that preventive main- ments to a pavement to retard or delay the development of tenance is effective and there is a "best" time to perform it-- pavement deterioration, subsequently emerged. an idea that is easy to accept. All pavements begin to deteri- There are several difficulties associated with moving away orate as they are exposed to traffic and environmental forces. from the worst-first approach used by most highway agencies. For bituminous-surfaced (flexible) pavements, this deteri-