|Written By: Joe Romer, RGS Inspector for City of Rocklin
Great Job Holbrook Asphalt…Blair
The City of Rocklin, always open to new products to maintain city streets and different strategies for pavement maintenance, applied High Density Mineral Bond (HDMB) treatment to residential streets this past summer. Richard Lawrence, Public Works Supervisor, became interested in HDMB after a webinar session on pavement maintenance products and applications. The City of Rocklin is no stranger to pavement maintenance projects. Slurry seal, crack sealing, micro surfacing and cape seals have been regular components of the city’s maintenance programs.
According to Mark Beatty, Senior Vice President at IPS / Holbrook Asphalt, “The City of Rocklin, was the first California agency to apply a new classification in pavement preser- vation known as a High Density Mineral Bond. With a 14-year performance history in other states, the product minimized any agency risk commonly associated with a first-time project. The surfacing couples a preservation treatment with a track record of performance with high aesthetics that residents embrace.”
Figure 1. HDMB Surfacing
HDMB has triggered intense interest and use nationally based solely upon its performance record. HDMB is a proprietary product of emulsion, polymer additives and very fine aggregates.
Figure 2. Spray Application of HDMB
It is spray-applied, similar to some seal coats, in a two application process. Rocklin’s research verified the performance history of HDMB. Over 200 million square feet have been installed throughout the U.S. The history of the product dates back to pilot installations in 2002.
It is a preservation treatment intended to keep good pavements in good condition by minimizing oxidative damage from moisture and from UV rays.
“Even though the application was new to California, we were anxious to get it on the ground because it had over a decade of prov- en performance,” stated Rocklin’s Richard Lawrence.
As Tregg Holbrook, founder and CEO of IPS / Holbrook Asphalt, puts it, “As we advised community leaders managing pavement assets, we would steer decision makers to treatments with a known level of functioning, such as slurry, micro surfacing, or chip seals. The feed- back from residents was that they were often displeased with these types of surface treatments after they were installed.
Figure 3. Valve Covers Masked Before Spray Application of HDMB
Suggesting that agencies use pavement sealers that are considered to have better aesthetics, such as fog seals or parking lot emulsion sealers, which both turn roads black and are believed to look good post-installation, was always an option, but the performance longevity was recognized as a considerable weakness.”
As the inspector on this project, and hearing of this product for the first time, there were many questions to be answered. For example; What is it? How is the product applied? How do you measure the application rate? What is the product supposed to look like after application?
After the first day of application, these questions were quickly answered. The “HA- 5” HDMB product was installed by Holbrook Asphalt in July, 2015, working as subcontractor to Sierra Nevada Construction. Dipping the tank on the spreader truck before and after solved the application rate question. The HDMB left the roads a deep black color. This product is applied in two applications per street, requiring a 24-hour closure for the applications to fully cure. Each application consisted of one spreader truck “cutting in the gutters” by hand wand and shield, and the second spreader truck spraying the streets with the spray bar. This procedure was repeated a second time, after the first application had time to break. The average total application rate was 0.35 gallons per square yard. Street closures were planned such that residents were able to park a short distance from their homes. Phone calls were minimal after the residents were able to see the finished product.
There were many lessons learned from this project. Interestingly, it was found that after the HDMB was installed, surface temperatures, anticipated to be higher due to the darker col- or alone, were actually 5 to 10 degrees cooler as compared to adjacent pavements that either had no previous treatment or that had a micro or slurry installed years earlier.
Figure 4. “Cutting in the Gutters” by hand wand and shield
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