Evaluation of pavement surface friction subject to various pavement preservation treatments

This study compared the effectiveness of preservation treatments on pavement surface friction and investigated the long-term variation of friction using the data collected in the Specific Pavement Studies-3 (SPS-3) of the Long Term Pavement Performance (LTPP) program. The SPS-3 focuses on the effect of four preservation treatments (thin overlay, chip seal, crack seal, and slurry seal) on pavement performance under five design factors (traffic, precipitation, temperature, existing pavement condition, and subgrade type). Both the simple ranking method and statistical methods (boxplot and Fisher's Least Significance Difference test) were used to compare the effectiveness of preservation treatments on friction improvement. The statistical analysis results indicate that slurry seal causes significantly greater friction number compared to the control section; and the ranking from high to low based on the average friction number among four preservation treatments is: slurry seal, chip seal, thin overlay and crack seal. Among the five design factors, subgrade type and existing pavement condition show less influence on pavement friction compared to climate and traffic factors. Stepwise regression analysis was conducted to quantify the influence of various factors (material, traffic, temperature, precipitation, and freezing index) on the long-term variation of pavement friction within the monitoring period. It was found that the application rate of slurry seal and chip seal affected the friction variation and temperature showed negative correlation with friction. In addition, pavement roughness was found having certain correlation with friction for the control sections and the sections with crack seal.