| Abstract: | In Research Project 0-6615, Use of Fine Graded Asphalt Mixes, a preliminary evaluation was made of the newly developed ultra-thin slurry seal (UTSS). The slurry is a combination of fine aggregates and emulsion that is rapidly sprayed onto the pavement surface. Some issues were raised about durability of the product, but the Texas Department of Transportation (TxDOT) wanted to evaluate its potential for both shoulder and main lane applications. Areas of interest included clearly demarcating and sealing shoulders, prolonging the life of raveling pavements, and blacking out existing markings in reconstruction projects. In this study, the researchers evaluated existing projects constructed in three TxDOT districts, namely Beaumont, San Antonio, and Fort Worth. In these evaluations, the researchers found that UTSS introduced an unacceptable drop in skid resistance on high-speed roadways. Lab studies were then conducted, and a new formulation was introduced with substantially higher aggregate content. In the lab, skid measurements were made with the dynamic friction tester on treated slabs undergoing polishing with the Texas A&M Transportation Institute's three-wheel polisher. A significant improvement in skid was noted over the preliminary design. The modified design was pilot tested on a highway in the Bryan District. Unfortunately, it was found that the initial improvements in skid did not last more than 2 months. The slurries were also found to not be effective in stopping reflection cracks. For now, TxDOT should continue using this product for shoulder demarcation and sealing and not for main lane applications. However, the manufacturers have changed the methods used to place the product--replacing the spray application with a spreader box--which will provide opportunities to redesign this product to address the critical skid issues in the future. |
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