Slurries and Micro-Surfacing Mixes Have Their Place
Emulsion industry veteran tells when and why
It's been said that for every dollar spent today on pavement preservation and maintenance, at least eight dollars will be saved over the next five years, says International Slurry Surfacing Association (ISSA) executive director John Fiegel. He reports that ISSA is working very closely with the Federal Highway Administration (FHWA) and the Foundation for Pavement Rehabilitation and Maintenance Research (FPRMR) to strengthen the emphasis on preventive maintenance. Slurry seal and micro-surfacing are two of the most versatile, low-cost, long-term pavement maintenance solutions, adds Fiegel.
In an effort to determine just when slurry surfacings should be used, questions as to its applications and its costs were asked of Jeff Reed, president of Sacramento, Calif.-based Valley Slurry Seal Co. (VSS). VSS supplies slurry/micro-surfacing paving machines, emulsion plants, raw materials and technology transfer and consulting to contractors and government agencies worldwide.
Q: When should slurry surfacings be used and when not?
Reed: Slurry seals and micro-surfacings may be used for preventive maintenance or rehabilitation. Neither type may be used as crack treatments where cracks are active. Surface cracks caused by aging of the existing asphalt may be filled to no more than (0.12 inches) 3mm.
Slurry surfacings should be used as an overlay at the point where worn pavements are just starting to ravel, show age cracking and where water is starting to penetrate the base. This technology should not be used on streets and surfaces wherethere was no base or on which a base failure has already occurred. A good base is especially important when slurry surfacings are used as the only asphalt surfacing.
Slurry seals are suitable to renew the surface, and micro-surfacing is used where surface irregularities need to be taken out, ruts filled, or where traffic needs to go back on to the surface quickly.
Q: Why not use hot mix asphalt (HMA) instead of slurry surfacings in this situation?
Reed: HMA mixes are normally applied in layers of 2 inches (50 mm) or more. However, special mixes have been laid at down to 1 inch (25 mm). For hot mix to perform correctly, it must be compacted. In addition, a 1-inch (25-mm) overlay of hot mix costs more, has practically the same structural resistance as a slurry surfacing, and uses up curb depth.
Q: How do slurry surfacings differ from chip coats?
Reed: Slurry surfacings are designed in a lab, are proportioned by the slurry machine, and laid down and cured so the asphalt-to-aggregate ratio is maintained at the optimum value to assure uniform aggregate coating and adhesion. Slurry surfacing thicknesses can vary automatically during laydown to smooth out depressions up to ? times the normal thickness of the overlay. Chip coats provide no such leveling.
Q: How do slurry surfacing costs compare with other resurfacing?
Reed: Slurry seal is usually less per square yard (sq. m) than chip coats. The minimum 0.125-inch (3-mm) thickness of slurry seals is about 55 to 65 cents per square yard (sq. m.) in the U.S. One-quarter inch (6.35 mm) slurry in severe winter regions of the U.S., or in areas of high traffic or where steel stud tires are used, costs 80 to 90 cents per square yard (sq. m.), or slightly more. Micro-surfacing is about $1.20 to $1.50 per square yard (sq. m), while HMA overlays can cost from $4 to $6, or more, per square yard (sq. m).
Q: From your perspective, what are the overall benefits of slurry surfacings?
Reed: As well as being highly cost-effective, slurry surfacings use large fractions of fines material down to less than 75 µ (#200). This gives a very high surface area and a lot of micro structure, leading to a sand-paper surface and a high skid resistance, while maintaining a smooth finish. The relatively higher asphalt content and low voids lead to a blacker, more durable surface and as a result, markings stand out. The higher binder content and smaller stones also eliminate large flying stones and give a much quieter surface.
It's been said that for every dollar spent today on pavement preservation and maintenance, at least eight dollars will be saved over the next five years, says International Slurry Surfacing Association (ISSA) executive director John Fiegel. He reports that ISSA is working very closely with the Federal Highway Administration (FHWA) and the Foundation for Pavement Rehabilitation and Maintenance Research (FPRMR) to strengthen the emphasis on preventive maintenance. Slurry seal and micro-surfacing are two of the most versatile, low-cost, long-term pavement maintenance solutions, adds Fiegel.
In an effort to determine just when slurry surfacings should be used, questions as to its applications and its costs were asked of Jeff Reed, president of Sacramento, Calif.-based Valley Slurry Seal Co. (VSS). VSS supplies slurry/micro-surfacing paving machines, emulsion plants, raw materials and technology transfer and consulting to contractors and government agencies worldwide.
Q: When should slurry surfacings be used and when not?
Reed: Slurry seals and micro-surfacings may be used for preventive maintenance or rehabilitation. Neither type may be used as crack treatments where cracks are active. Surface cracks caused by aging of the existing asphalt may be filled to no more than (0.12 inches) 3mm.
Slurry surfacings should be used as an overlay at the point where worn pavements are just starting to ravel, show age cracking and where water is starting to penetrate the base. This technology should not be used on streets and surfaces wherethere was no base or on which a base failure has already occurred. A good base is especially important when slurry surfacings are used as the only asphalt surfacing.
Slurry seals are suitable to renew the surface, and micro-surfacing is used where surface irregularities need to be taken out, ruts filled, or where traffic needs to go back on to the surface quickly.
Q: Why not use hot mix asphalt (HMA) instead of slurry surfacings in this situation?
Reed: HMA mixes are normally applied in layers of 2 inches (50 mm) or more. However, special mixes have been laid at down to 1 inch (25 mm). For hot mix to perform correctly, it must be compacted. In addition, a 1-inch (25-mm) overlay of hot mix costs more, has practically the same structural resistance as a slurry surfacing, and uses up curb depth.
Q: How do slurry surfacings differ from chip coats?
Reed: Slurry surfacings are designed in a lab, are proportioned by the slurry machine, and laid down and cured so the asphalt-to-aggregate ratio is maintained at the optimum value to assure uniform aggregate coating and adhesion. Slurry surfacing thicknesses can vary automatically during laydown to smooth out depressions up to ? times the normal thickness of the overlay. Chip coats provide no such leveling.
Q: How do slurry surfacing costs compare with other resurfacing?
Reed: Slurry seal is usually less per square yard (sq. m) than chip coats. The minimum 0.125-inch (3-mm) thickness of slurry seals is about 55 to 65 cents per square yard (sq. m.) in the U.S. One-quarter inch (6.35 mm) slurry in severe winter regions of the U.S., or in areas of high traffic or where steel stud tires are used, costs 80 to 90 cents per square yard (sq. m.), or slightly more. Micro-surfacing is about $1.20 to $1.50 per square yard (sq. m), while HMA overlays can cost from $4 to $6, or more, per square yard (sq. m).
Q: From your perspective, what are the overall benefits of slurry surfacings?
Reed: As well as being highly cost-effective, slurry surfacings use large fractions of fines material down to less than 75 µ (#200). This gives a very high surface area and a lot of micro structure, leading to a sand-paper surface and a high skid resistance, while maintaining a smooth finish. The relatively higher asphalt content and low voids lead to a blacker, more durable surface and as a result, markings stand out. The higher binder content and smaller stones also eliminate large flying stones and give a much quieter surface.
Last Updated (Saturday, 18 July 2009 18:45)