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.
On the Santa Barbara application, the PASS Scrub Seal followed by a chip seal application served as a Stress-Absorbing Membrane Interlayer (SAMI) with final slurry seal being applied.
According to Conti, Santa Barbara just started using the PASS Cape Seal preservation process in 2009.
"The rejuvenating agent and the chips (aggregate spread over the sealer) rolled into the emulsion seemed to be good approach to filling cracks and minimizing reflective cracking since the voids were being filled with structural material," Conti explains. "And by giving the rejuvenating sealer (with chip application) three to seven days to fully cure before applying the slurry seal, it also provided the best conditions for the rejuvenating emulsion and chips to fully bond with the surface areas of the cracks."
After the scrub cape seal cured, a final Type II slurry seal was applied to the road surface.
"We placed 4 million square feet of cape and slurry seals during our 2009 street preservation work and we're happy with how the cape sealed streets look and perform," Conti says. "The cape seal process costs approximately 20 cents more per square foot over a standard slurry seal process, but we believe the combination of applying a rejuvenating seal with a chip application followed by a slurry seal will minimize reflective longitudinal and alligator cracking longer. We have an annual preservation budget of $2 million, and we believe this particular solution will help us maximize our investment by maintaining the quality of those roads treated for a longer period of time."
As Flavell and Chierici point out, slurry applications require a lot of prep work, like crack filling for example, and the scrub cape seal process eliminates that prep work. For the 2 million square feet of cape seal application, the engineers specified a ¼-inch black aggregate to maintain a dark surface look long after the top slurry seal begins to oxidize.
"If you have to perform spot repairs on 15% or more of road surface before applying a surface preservation treatment, it's almost more cost-effective to mill and fill the entire project," Flavell notes. "But by using the rejuvenating cape seal process, you heal those surface deformations with very little spot repair required. And that approach is at a cost that's approximately 40% of what a mill and fill approach would run.
"The rejuvenating chip seal process has been a beneficial tool in providing the city with a cost-effective alternative to a double slurry seal application," he continues. "We still use the double slurry seal on some streets, but when you have a process that can eliminate a lot of prep work and provide some structural integrating in the process, it's a good option to consider based on the condition of the road surface, the traffic volume, and the public's desire for the type of road surface they want."
Both Flavell and Chierici are confident the scrub cape seal application will extend the service life of the roads treated for another eight years before additional preservation work will be required.
Conti and others in his department agree and they're anxious to monitor the performance characteristics of the cape seal process. The pavement management report city street engineers conduct every two years to evaluate 30 to 40% of the road network's condition will, according to Conti, provide a better analysis of the preservation work conducted in 2009.
"We're always evaluating different approaches in an effort to maximize the return on investment we continue to make to keep our system in good order," Conti says.
Since 91% of the city's streets are asphalt pavements, you can be sure Conti and other street officials want to keep those pavements in the 70-80 range of good quality pavements.
And you can also be sure the City of Santa Barbara will continue to add new preservation solutions to maintain the value of community's road network.