Maintaining Long-Term Success with Interlocking Concrete Pavers

Oracle’s headquarters near San Francisco includes over 35,000 sf of concrete pavers.

The 66-acre campus for Oracle’s U.S. headquarters next to San Francisco Bay offers more than just office space for its employees in eleven campus buildings. Built on the San Francisco Bay, the office buildings, conference and fitness centers are embraced by a synthetic lake, trails and concrete paver walkways.

Oracle began building in 1989 with eventual campus completion in 2002. Because aesthetic features were an important factor in the original design, special attention was given to landscaping and hardscaping to ensure the campus was visually appealing to employees and visitors. “Hardscape makes up 5.13 acres of our campus and interlocking concrete pavers represent between 15 and 20 percent of the hardscape,” says George Denise, Director of Operations and Director of Sustainability.

Willow Walk, a half-mile, paver path around the campus lake, continues providing a relaxing ambiance for employees and visitors.

In addition to patio areas, pavers are used for three driveways, walkways connecting the building and the Willow Walk, a half mile, 6 to 8-foot wide walkway around the lake, he explains. Willow Walk expanded about 12 years ago with additional features such as large sandstone blocks forming a low wall along the walkway. “The combination of the hardscape, landscape and water creates a pleasant area for employees to walk and enjoy being outside during the workday,” explains Mr. Denise.

Water also presents a challenge, especially in the Willow Walk area, says Mr. Denise. “We should have a base with 1-inch of sand but there are areas of the walkway where we have only silt. The base has washed away.” The combination of a high-water table and improper cleaning with a power washer contributed to the disappearance of the pavers’ base, he says. “It’s amazing that it has lasted 12 years.”

European Paving Designs in San Jose, California anticipates repairing one of the driveways and sections of the Willow Walk for Oracle. “One of the challenges with long-term interlocking paver installations in a campus setting is improvement in technology over the years,” says Randy Hays, CEO and founder of the firm. Advances in manufacturing that enables consistent paver joint sizes, technical research leading to guidelines helps ensure the best performance. In addition, development of new materials can be applied to new projects and repairs.

Besides developing a maintenance plan, Oracle maintenance staff switched from power washing to a rider/scrubber machine to maintain walks, driveways and the plaza shown here.

ASTM C144 jointing sand is an example of a material that European Paving Designs will use in the Oracle repairs that was not available 25 years ago. “Plaster sand was used, which doesn’t meet today’s guidelines,” says Mr. Hays. Plaster sand is finer than C144 sand (also known as mason sand). Plaster sand doesn’t encourage interlock among pavers and tends to wash out easily, and more so from power washing. To meet ICPI guidelines for aspect ratio (i.e., length divided by thickness), pavers for the driveway repair will be 4 x 8 x 3 1/8-inch thick pavers with a 4-inch thick compacted, crushed aggregate base under 1 inch of bedding sand. This provides more support than the current installation, he adds this is also the minimum base thickness recommended by ICPI.

A soil engineer assisted in the assessment of Oracle’s existing paver installations to ensure that the contractor and owner knew exactly what repairs were needed to avoid future failures. “We don’t typically work with soil engineers in all projects because we typically enter at the bid stage rather than the design stage,” explains Mr. Hays. “When we handle design-build projects that start two years before construction, we include engineering reports as part of educating the team of owners and architects involved in the project to make sure everyone understands the importance of developing specifications that take all factors into account including soil, water issues, landscape features and the specific use of the pavement.”

Maintenance is a key issue for long-term installations of interlocking concrete pavers, points out Mr. Denise. “As we renovate areas, we want to make sure they are properly maintained, which includes regular preventive maintenance,” he says. “This will prevent the need for extensive repairs in the future.” He is developing a plan to ensure that all areas are evaluated for bedding sand replacement over the next three years.

“We do have a major cleaning challenge because we have a resident population of Canadian geese that necessitates cleaning Willow Walk regularly,” explains Mr. Denise. “For a long time, a power washer was used to clean the area, which washed away the sand and crushed rock under the pavers.” The purchase of a rider/scrubber that uses a water spray and rotating brush to clean the pavers, and suctions excess water from the surface for reuse not only cleans the pavers, but does not wash away sand and base material.
“We recommend inspections of all pavers at least twice each year,” suggests Mr. Hays. “Look at the pavement in early spring to identify areas that need attention and make repairs before any big change in weather.” In some areas of the country, that might be a rainy or winter season, he points out. After these, check the pavement again for any damage that needs to be corrected. He adds, “With proper installation and maintenance, an interlocking concrete paver installation should last for generations.”