While unit masonry block dominates the North American retaining wall market, engineers, architects, builders, municipalities, transportation departments and homeowners are discovering the benefits of the large “wet-cast” block alternative.

According to Stan Hamilton, president of ReCon Wall Systems in Minneapolis, these blocks offer the aesthetics of natural stone (or any special texture the customer may desire) while providing the durability to resist deterioration caused by continual freezing, thawing and exposure to deicing compounds. Large precast blocks, he adds, are less expensive than cast-in-place options; and, unlike quarried limestone, granite or boulder walls not subject to engineering, they can be designed to safely achieve greater wall heights.

Construction options for tall retaining walls and abutments have been limited in the past to mostly cast-in-place structures, which at $40-$50 per square foot can be costly despite improved durability and aesthetic appeal added by means of a decorative form liner. Now that large, high-slump precast blocks have been introduced, municipalities and transportation agencies have what Re-Con notes is an option offering the durability of cast-in-place concrete and the affordability of segmental retaining wall units.

The company underscores the durability aspect of wet-cast blocks, noting that departments of transportation have shown an interest in such technology for retaining walls along many North American thoroughfares regularly exposed to road salts. “DOTs need something that can stand up to those conditions,” says Mike Gresser, one of ReCon's founders and also owner and president of Gresser Companies, Inc., a second-generation concrete and masonry contractor based in Minnesota's Twin Cities. He adds that because the large blocks are placed into position with a skid steer or backhoe, road builders are spared the back-breaking manual labor involved in the installation of the smaller blocks, some of which weigh 100 lbs.

While the look of a natural limestone or granite wall is often deemed preferable, such walls cannot be engineered to meet standards for holding back earth at greater heights. Traditional, small dry-cast block walls exceeding four feet in height generally require geo-grid reinforcement; necessary excavation behind the wall adds to installation cost, may create property encroachment issues, and raises the prospect of removing trees and features behind the structure, Re-Con officials contend. In contrast, large-block walls can go as high as 10 ft. 8 in. without geo-grid reinforcement, they add, saving trees and easing lot-line concerns for property owners.

Those who have worked with large-block walls generally attest that this new technology bridges the gap between the look of natural stone and the convenience of a segmental block retaining wall. “When we made the decision to modify our stadium and add a new elevated viewing platform for special events,” says Aaron Koski of the Minnesota Amateur Sports Commission, “we found that ReCon Block not only met our structural requirements, but its size, natural stone texture and ability to match our existing stadium color pattern have dramatically enhanced the appearance of our stadium complex.” Gresser affirms, “If customers require engineering or cost efficiencies, large wet-cast block walls are the aesthetically pleasing, engineered, durable, and in many cases, cost-effective alternative.”

In early 1999, the concept of wet-cast blocks was developed after Gresser board member Tony Phillippi of Truck Crane Co. noted the versatility, durability and aesthetic possibilities of wet-cast concrete during the pour for a decorative cast-in-place wall. He pondered the possibility of a demand for decorative large-block modular retaining walls produced with the same technology. Gresser and Phillippi took the idea to Matt Barron of Hardscape Construction, Inc. After a year of research and development, the company launched its large wet-cast blocks in 2001.

Experiencing steady growth in production since that debut, ReCon now has eight licensed producers across the U.S. and Canada. Wall sales in 2003 exceeded 40,000 sq. ft. in the company's immediate market.

Information on licensing or additional technical and engineering details can be obtained from ReCon Wall Systems, 612/374-1113; www.reconwalls.com

LARGE BLOCK BENEFITS

• Size — Placing one block provides 5.33 sq. ft. of retaining wall (16-in.-tall × 48-in. on the face).
• Engineering — The block features a locking system that in combination with the mass of the unit (1,400-2,500 lbs./block) permits walls as high as 10 ft. 8 in. without geo-grid support.
• Durability — The block is made from wet-cast, air-entrained concrete of minimum 4,000 psi.
• Aesthetics — The block has a natural stone-texture face, available in granite and limestone finishes or custom-finished to specification on large projects.
• Modular dimensions — Easily substituted for small block wall designs.
• Taller gravity walls — The massive size and weight of the block enable the construction of taller unreinforced retaining walls than can be accomplished with smaller blocks. The time and cost associated with excavation and soil replacement when reinforcing geo-grid is required are thus eliminated.
• Engineered and tested — The block's modular dimensions and tested geo-grid pull-out and shear performance allow the wall to be professionally engineered, providing a measure of wall performance not generally available with natural stone walls. Engineering support is included for producers and installers.