Effectiveness of Highway Pavement Seal Coating Treatments

Seal coating is a preventive maintenance technique typically applied to low volume asphaltic concrete pavements to defer the need for major rehabilitation. Past research on seal coating effectiveness has generally indicated that both short- and medium-term benefits are associated with this treatment. Regarding the relationship between short-term effectiveness and initial pavement condition, results of past studies have been equivocal: some studies found that lower levels of initial pavement condition are associated with lower effectiveness after seal coating treatment, while results of other studies were to the contrary. This paper, in developing seal coating effectiveness models, explains the findings of both schools of thought. The paper finds that the direction of seal coating effectiveness in relation to the initial pavement condition depends on the measure of effectiveness used: pavements in relatively poor condition were generally associated with higher performance jumps but lower reductions in their rates of deterioration. This implies that the greater benefits of seal coating on relatively good pavements, compared to relatively poor pavements, are observed particularly when considered over an extended period of time. On the other hand, pavements in relatively good condition were generally associated with lower performance jumps but greater reductions in their deterioration rates. In the course of the study, the paper selects appropriate measures of seal coating effectiveness, calculates values of each measure using data on Indiana pavements that received this treatment, determines the statistical significance of such effectiveness values, and finally estimates seal coating effectiveness as a function of pavement and/or treatment attributes. In the computation of effectiveness values, due cognizance is given to the critical issue of relative timing between the application of the seal coating treatments and annual performance monitoring.