Pavement Preservation Journal - Spring 2013 - (Page 38)

Optimum Time for Slurry Seal Depends on Original Build Date By Elie Y. Hajj, Ph.D., Luis Loria and Peter E. Sebaaly, Ph.D., P.E. L ocal agencies and the Regional Transportation Commission (RTC) in northern Nevada use slurry seal as a main preventive maintenance for their flexible pavements. However, due to the lack of a standard specification, the timing of slurry application to asphalt pavements has been according to the project engineer’s standard of practice, which resulted in an inconsistency in the timing of application between and even among the agencies themselves. Thus, recognizing the significance of optimal time at which a roadway would most benefit from a preventive maintenance treatment, in 2010 the RTC sponsored a research study at the University of Nevada-Reno (UNR) to evaluate and assess the optimum time of slurry seal application on asphalt pavements within the RTC region. This objective was achieved by evaluating the long-term pavement performance and the cost-effectiveness of slurry seals applied to new and existing flexible pavements within the Washoe County, Nev., region with respect to the time of slurry seal application. Exiting pavements were generally dense graded hot-mix asphalt (HMA) with AC-20, AR4000 or PG 64-22 unmodified asphalt binders. Slurry seals were designed in accordance with guidelines contained in International Slurry Surfacing Association (ISSA) Publication A105. In general, emulsion asphalts consisted of latex modified cationic quick set with a minimum of 3 percent latex rubber by weight of the binder following agencies requirements. A total of 2,700 pavement sections from minor arterials, collectors and residential streets were evaluated in this study, with the latter having by far the highest number of pavement sections. 38 Effect of slurry seal on the performance of a newly constructed pavement when applied at three or seven years after construction Only pavement sections that were slurry sealed once during their intended performance life were evaluated and were grouped as follows: • Do-nothing: a slurry seal was not applied to the pavement • Slurry seal applied immediately after construction, and • Slurry seal applied at: one, three, five, seven and nine years after construction. The figure illustrates the effect of slurry seal on the performance of a newly constructed pavement when applied at three or seven years after construction. The slurry seal performance life and the extension in pavement service life were determined for the various slurry seal applications. In this study, the slurry seal performance life ranged from two to four years, except when applied at years zero and one (ranged from zero to one years). The pavement service life was extended in only few cases by one-half to two years. The study also evaluated the costeffectiveness of applying slurry seals at various years following construction activities. Based on the relative benefit and benefit-cost-ratio observations, user satisfaction and agency cost effectiveness were maximized when slurry seals were applied as follows: • Year three for newly constructed arterials and newly constructed residential streets • Years three and five for newly constructed collectors, and • Years three and five for arterials, collectors and residential streets with overlays. The application of a single slurry seal immediately after or one year after construction of the asphalt layer is not effective in terms of both the benefit to the users and the benefit-cost ratio for the agency. For uniformity purposes, it is recommended that the agency apply slurry seal three years after the construction of the asphalt layer for both new and overlay constructions. Hajj is research assistant professor, Loria is graduate research assistant, and Sebaaly is director and professor, Western Regional Superpave Center, University of Nevada-Reno View past issues of the Pavement Preservation Journal online at www.naylornetwork.com/fpp-nxt http://www.naylornetwork.com/fpp-nxt

Table of Contents for the Digital Edition of Pavement Preservation Journal - Spring 2013

President’s Message
MAP-21: Pathway to Preservation at the Federal Funding Level
Cold-in-Place Recycling, Fiber Membrane and Seal Preserves Desert Highway
NCPP: New Online Tool Helps Measure Road Network Health
NCAT UPDATE: Axle Loads, Mileage Begin to Accumulate on NCAT Tests
NEPPP: Ribbon Cuttings Shine Spotlight on New Hampshire Pavement Preservation
TPPC: Micro Surfacing Training Offered at Texas Center
MnROAD Studies Pavement Preservation
Enlist News Media in Battle for Pavement Preservation
HIR Solves Cost Challenge to Runway Reconstruction
Shale Gas Boom Drives Town’s Bridge Renovation
Optimum Time for Slurry Seal Depends on Original Build Dat
Index of Advertisers

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