Big precast concrete blocks provide big advantages.
By Fernando Pagés Ruiz
Bob Hampton builds neighborhoods with rolling hills, trees, meandering streams and small ponds. Sculpting these bucolic subdivisions requires extensive use of retaining walls, shore liners and detention cells. Faced with a choice between masonry walls that may not hold up to erosion and unattractive alternatives, Hampton searched for a better option.
He wanted something aesthetically pleasing that would fit the landscape and experimented with treated wood and small-block masonry systems. Neither could withstand the scouring of waves along waterways, washing out during Nebraska’s frequent and intense downpours. The small blocks required backbreaking labor to erect and seemed undersized and artificial against the backdrop of a large lake or hillside. Hampton sought something massive to fit the scale of his projects and strong enough to bear up without maintenance. He found it, along with unexpected cost savings in a precast concrete building block system.
In 1999, while walking the floor of an industry trade show, Hampton spotted an exhibit of large, precast concrete blocks that promised to resolve his dilemma. The oversized blocks looked like chiseled stone and appeared to provide enough weight and mass to resist erosion.
Hampton’s consultants liked the big-block concept, too. It mimicked the structural qualities of concrete retaining walls while providing design flexibility. Using modular blocks actually made the engineering a little easier. “You can turn a tight radius and create serpentine patterns with modular, precast concrete block that are hard to achieve in a poured or masonry block wall,” says Dan Thiele, owner of Thiele GeoTech in Omaha, Neb. This meant that instead of imposing straight and level walls on an irregular world, Hampton could apply the natural appearance and flexible design armaments available with precast building blocks to celebrate the sensual contours of his subdivision landscapes – without sweating the cost.
Precast concrete products also provide dependable strength and consistency. “You can rely on the manufacturer’s specifications with an engineered precast product and save hours of structural engineering and uncertain quality control on site,” says Thiele.
After reviewing several products, Hampton decided to use Stone Strong, a hollow precast block with unit sizes available from 6 (24 by 36 inches) to 24 square feet (96 by 36 inches). This relatively lightweight product provided the look, price and stability Hampton needed for his development projects, along with a host of unexpected benefits.
Hampton’s engineers determined they could stack the blocks 9 feet high without geo-grid or other tiebacks, making it possible to assemble these oversized blocks directly against a property line or utility easement. Later, they found the product could handle heavy loads, such as bridge columns and abutments.
Hampton was delighted when he saw a three-man crew could lay about 2,000 square feet of block in a day – nearly six times the production of a small-block installation. This helped with project schedules and reduced labor costs.
Installation is easy and quick
After excavating a 60-inch-wide trench 9 inches deep, workers added 1½ inches of compacted limestone, then stacked the first course of block and leveled it to assure proper line and grade. The cast-in handles made it easy to hoist the blocks and act as alignment pins for stacking successive lifts.
Made with ordinary 4,000-psi air-entrained concrete, Stone Strong blocks come in 24-, 6- and 3-square-foot sizes to accommodate large and small structures. The blocks interlock precisely and feature built-in steel handles that make it easy to lift and place each 5,600-pound unit with a standard excavator or loader.
One of Hampton’s newest subdivisions, Thompson Creek in Lincoln, Neb., features extensive use of precast big-block retaining walls and shore protection. Because these oversized building-block walls won’t wash out in a storm or deteriorate in detention cells, Hampton feels better about handing over maintenance to a fledgling homeowner’s association. The stability of the precast concrete block makes it easy to maintain the landscape around water features and prevents silt from building up in ponds.
Because it looks natural, Hampton plans on using a prominent Stone Strong retaining wall as a project monument, engraving the neighborhood moniker right on the block. While few retaining wall products provide the level of aesthetics needed to create a neighborhood marker, these large building blocks resemble chiseled rock. Hampton is understandably pleased to welcome future residents with a touch of precast concrete magic.
The big-block revolution
You can see large, precast blocks rising all over the country because they provide an easy-to-erect alternative to site-poured concrete for large retaining walls, shoreline protection, bridge approaches and abutments, overpasses and underpasses, storm sewer outlets, stream channel walls and drop structures.