When you have 250 centerline miles of paved streets to maintain, finding the most economical way to keep those roads in good condition is paramount when making prudent decisions in managing the dollars allocated for street maintenance. That's the reality for Tom Conti, a project engineer for the City of Santa Barbara's Department of Public Works' Engineering Division.
"From year to year we look at what's (maintenance/preservation products/processes) out there, what has been proven to work, and if it looks like it might be the best cost-effective approach for what we want to accomplish, we'll give it a try," Conti says.
Santa Barbara has taken a proactive approach to pavement preservation for the past 15 years, according to Conti, who has been leading the charge for the past four years.
"Back in the mid-80s our PCI (Pavement Condition Index) was in the 50s' range, meaning that approximately 50% of our roads were in poor condition," Conti notes. "So, we began to inject a substantial amount money into improving our road network and bringing it up into the 70-80 range (good condition).
City streets are currently managed and maintained on a rotating zone bases - five residential and two arterial (main commuter routes and heavily traveled business areas). Residential streets receive a preservation treatment every seven to eight years, while arterial roads receive a preservation treatment every five to six years.
"Since we invested a lot to bring our streets up to a good quality service level and implemented our current zone management process a few years ago, we're now able to maintain a 71 PCI rating of our entire network," Conti says.
Preservation efforts have focused primarily on spot repairs and slurry seals. Last year (2009) was the first time Santa Barbara used the polymer-modified asphalt surface sealer (PASS) CR (chip retention) scrub cape seal process. In researching other agencies' asphalt preservation work, the city determined the PASS CR process would be worth exploring.
Flowers & Associates Inc., a civil engineering services provider, has worked closely with the City of Santa Barbara in recommending the most cost-effective road preservation solution that extends the life cycle of the municipality's road network. Flowers' Eric Flavell, principal engineer, and Allan Chierici, project engineer, both explain the city's intent to evaluate in-place pavement preservation solutions, and have focused most of its efforts on slurry treatments as a viable solution.
"We researched the County of Santa Barbara's usage of the scrub cape seal process and how that particular product (PASS CR) and application process delivered good results, and determined that it would suit the needs of the city," Flavell notes.
The one-step crack-filling, sealing and rejuvenating application is designed to be used on moderately distressed asphalt surfaces. On the Santa Barbara streets, Western Emulsions' PASS CR formula was used to bond a chip seal application to the existing surface before a final slurry seal application was put down.
According to Chierici, two-thirds of the Santa Barbara streets treated during the 2009 preservation program received the cape seal process - with the rejuvenating emulsion applied first with a distributor truck, followed by the chip application, and then covered with Type II slurry. The remaining one-third of the streets in the preservation program received a slurry treatment only.
Western Emulsions' PASS CR Scrub Seal is designed for asphalt surfaces showing signs of cracking, raveling or more severe surface deterioration. The highly polymerized emulsion adds flexibility, toughness and durability to a road surface, while providing exceptional chip binding and rejuvenating qualities. The chemistry of the PASS emulsion along with the broom scrubbing application helps to mitigate reflective cracking. The chip seal application further mitigates reflective cracking when forced into the emulsion filled surface cracks during the application process.