Masonry Magazine April 2007 Page. 51
Small is Beautiful
DESIGNERS, CONTRACTORS AND HOMEOWNERS OFTEN ASK WHAT THE MAXIMUM SLOPE IS FOR A DRIVEWAY CONSTRUCTED WITH CONCRETE PAVERS. The best example of a steeply sloped project is a street in Colma, Calif., with an 18-percent grade. While there might be driveways and streets with steeper slopes, the Colma project provides the current upper limit in North America at 18 percent (see Figure 1).
Of course, higher slopes have been achieved. Figure 2 shows a Costa Rican road with a maximum slope of 25 percent that leads to a mountain hotel on the Papagayo Peninsula. Likewise, moving into South America, Figure 3 shows a street and pedestrian walkway with a 14-percent slope just after construction was completed in Medellin, Colombia.
For embankment applications without vehicles, the limiting factors are the angle of repose of the bedding sand, base and soil subgrade and, most importantly, the resistance to soil and base sliding under compaction equipment. The angle of repose can be as steep as 35 degrees, or about 70 percent; however, the tendency of soil and base to slide during compaction will reduce this limit.
Adequate performance of interlocking concrete pavements on slopes greater than 7 percent depends on careful design considerations and proper execution of construction details. Experience with steep sloping streets and embankments next to bridges have demonstrated that stationary edge restraints, consistent and tight paver joints, and herringbone patterns will.
The brick walls provide a surface for capturing and reflecting the gentle sounds from a small fountain in one of the planters.
No backyard is too small for a makeover, not even the Old Town Alexandria, Va, townhouse of Randy Lindner, president of Bostrom Corporation, the company that manages the Interlocking Concrete Pavement Institute.
Like thousands located in historic Old Town, the four-story brick townhouse has the typical brick wall-enclosed, brick-and-mortar-over-concrete patio consisting of no more than 700 square feet (70 m²). While not particularly unattractive, the existing patio presented an opportunity to take it to the next lifestyle design level. The results renewed the home's character through the colors and textures in concrete pavers and segmental concrete retaining walls.
The revamped rear entrance includes full-length steps with bullnose coping and tumbled concrete pavers overlaying the concrete stoop. Replacing the patio entrance doors created space for two chairs; the entrance was further opened by removing the old wrought iron railing. This transformed the stoop to a mini-patio, allowing for a dry area during wet weather.
Existing at-grade planting areas along the brick wall hold shrubs and tall trees that provide a delightful, soft canopy roof. The planting areas were raised and enclosed with segmental concrete walls filled with soil. Their low height creates additional seating for overflow entertainment situations, while the enlarged planting area provided space for a small fountain with the calming sounds of softly running water. Lighting in the planters highlights the fountain, as well as sculpture and plants.
The existing clay brick and mortar were replaced with 2-3/8-inch (60 mm) thick tumbled concrete pavers in a random pattern over one inch (25 mm) of bedding sand. As the weak link in rigid clay paving, the mortar was beginning to crack and degrade from weather. Whether clay or concrete units, a sand-set system provides a more durable and maintenance-friendly approach since it enables immediate replacement of cracked or stained units, if the need arises.
"The space is wonderfully transformed into a place that accommodates everyday living and entertaining friends," Lindner said. "While there was some Initial concern about the concrete pavers and wall products visually clashing with the brick walls, they actually work quite well together.
"While my neighbors were somewhat skeptical about introducing concrete pavers and segmental wall systems into a traditional brick English patio, it is now the envy of the neighborhood," he continued.
An Interlocking Concrete Pavement Institute Certified Concrete Paver Installer assisted with the design ideas and construction. Even in a small backyard, concrete pavers and walls transform its mood and delight the senses while fitting into the existing textures and architectural style that distinguish historic Old Town.