TEXTILES.ORG
By Ray Myers
Background
Cameron Airpark Estates, about 20 miles east of Sacramento, Calif., is a unique residential community and airport. In 1950, Larry Cameron, a former champion rodeo rider and successful auto dealership entrepreneur, envisioned a place where residents could play golf, swim in a lake, and even enjoy the benefit of their own private airport.
He began his dream by purchasing 5,000 acres of land that the trailblazer originally used for ranching purposes. Over the years, the land was slowly divided into ranch-sized properties and varying other parcels were designed for medium- and high-density residential neighborhoods.
Eventually named Cameron Park, the community today contains a mixture of single-family homes, apartments, large ranches, horse properties, and various businesses. It also boasts a fine country club and a championship golf course worthy of the most challenge-starved golfer. In addition, Cameron Park has a community center and pool complex, a recreational lake that covers approximately 10 acres, and then, of course, the Cameron Airpark Estates.
Streetways
Cameron Airpark Estates includes a diverse group of residents: airline pilots, retirees, and others who commute by private plane to the San Francisco Bay area, Tahoe, Vegas, or other destinations.
The airpark homes—approximately 200 of them—are built on 90-ft-wide street/taxiways (hence, “streetways”), where pilots taxi their private planes from their own oversized garage/hangers to the 4,000-ft runway.
Over the years, crack-seal and other minor upkeep procedures were used to maintain the approximately 1 million sf of asphalt at Cameron Airpark. However, when the pavement could no longer be maintained with minor repairs, the homeowner’s association decided that it should consider appropriate options. Several vendors were invited and each proposed its own particular plans for the streetways, ranging from simple sealing to complete reconstruction.
Three problems
The homeowners wisely engaged the professional services of Jeff Crovitz, P.E. of MGE Engineering in Sacramento. Crovitz reviewed the existing pavement thoroughly and determined that there were three separate problems.
First of all, he concluded that subsurface water was causing significant cracking and overall structural failure of the streetways. Crovitz said it was obvious that underdrains should be installed to control the flow of the multiple areas of perched groundwater under the asphalt.
Second, the vast areas of flat pavement needed a moisture barrier to prevent water from passing through the asphalt to the base.
And third, MGE Engineering determined that an asphalt overlay would be necessary to increase the load-bearing capacity of the pavement section.
Drainage
Engineer Crovitz also recommended that a geotextile fabric interlayer should be used to mitigate future reflective cracking, while simultaneously creating a moisture barrier. He then designed more than 1,100 lineal ft of subsurface drainage for specific areas to capture subsurface water.
This drainage system required a shallow system because there was little elevation change to work with throughout the project worksite. MGE’s answer was to use a thin, tall geocomposite drainage system. This particular drainage system was selected because of its ease of installation, high flow capacity, high compressive strength, and overall long-term life projections.
The work was planned to start in the summer of 2008. However, the assessment was put to a vote and it was defeated by the residents. After another year of pavement deterioration and distress, it was clear to the homeowners that major maintenance could be postponed no longer.
The one-year wait proved to be a benefit because the recession brought much lower construction costs as well as more advantageous financing. Bids went out in 2009 and estimates for the 9,000-tons-of-asphalt project came in surprisingly low. This time the assessment passed.
Granite Construction Co.. of Sacramento was the low bidder and the first action Granite officials took was to approach the homeowners with one more money-saving proposal. Granite recommended the use of warm mix asphalt concrete (WMAC), which would save thousands compared to the conventional hot mix asphalt concrete typically used in projects of this type.
In addition to the savings, homeowners responded enthusiastically to the overall “green” benefits that would be realized. WMAC meant that material could be mixed and installed at lower temperatures. Since reductions of as much as 50°–100° are common, the obvious benefits include: cutting fuel consumption, decreased production of greenhouse gases, better overall compaction, and the ability to haul the paving mix longer distances. This warm mix asphalt was placed on this project at temperatures from 250°–260°F.
Crovitz, the engineer with MGE, still was not concerned about how well the geotextile interlayer would work with the lower temperature asphalt mix even though detractors were. Crovitz maintained that with close monitoring of the geofabric laydown with the WMAC that a successful result could be achieved.
Western Oil Spreading Services of Sacramento was subcontracted to install the interlayer fabric. The conventional 4.1–oz., nonwoven polypropylene geotextile was specified and was bonded with PG 70-10 liquid asphalt. The interlayer was installed using a truck-mounted laydown unit. The binder was applied at a rate in concurrence with Asphalt Interlayer Association (AIA) specifications of 0.25 gal/sy +/- 0.03. (The binder always goes under the geotextile fabric layer.)
Upon project completion, Granite Construction drilled cores to verify that all required aspects of the WMAC were met. Granite officials also wanted to verify competent bonding of the geofabric interlayer. Dan Ridolfi, P.E., and quality manager for Granite, reported the following: “The density of the mat averaged 97% of maximum theoretical specific gravity and laboratory examination of the cores drilled from the jobsite indicated the paving fabric was well-bonded to both the existing asphalt and the new WMAC. Furthermore, the bond between the asphalt interlayer and warm mix was the same as we would expect with hot mix.”
Crovitz went a step further and removed a small section of the completed pavement section and attempted to separate the lifts. Using a 3-in. chisel and 2-lb. sledge, he was unable break the bond between the fabric and the WMAC. He said he was confident that his many years of personal asphalt construction and inspection would eliminate any potential problems. This project certainly confirmed his position. The warm mix was sealed with a double-coat fog seal in the summer of 2010.
In the end, the homeowners of Cameron Airpark Estates received a well-engineered, top quality, new pavement solution. Granite Construction will benefit as well, with a quality WMAC showcase project under its belt.
It is probably safe to say that Larry Cameron would be proud of the airstrips that continue to befit his legacy for years to come.
Ray Myers is the executive director of the Asphalt Interlayer Association.
Ron Bygness, editor of Geosynthetics, also contributed to this article.
For more information on this project, contact Granite Construction at its Sacramento office (+1 916 921 6195) or Jeff Crovitz at jcrovitz@mgeeng.com.
For additional information on geotextile interlayers, contact Ray Myers at the Asphalt Interlayer Association (+1 916 933 9140).