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During the past ten years, concrete segmental retaining wall (SRW) units have evolved into a significant part of the product mix of many concrete masonry manufacturing operations. The history and background of the growth of concrete segmental retaining wall units provide a blueprint for producers to use as they strive to improve company profitability by identifying future market trends and potential.

Mortarless modular units and soil reinforcement elements were used 2500 to 3000 years ago by Ancient civilizations to realize their architectural dreams. One of the Seven Wonders of the World, the pyramids in Egypt were built using large modular units held together without the use of mortar. Tall structures called Ziggurats, such as the Leaning Tower of Babel, were built using modular facing units and soil reinforcing elements of woven reeds. Researchers have discovered that portions of the Great Wall of China use soil reinforcement elements made of tamarisk branches. The survival of these ancient structures proves that civilizations before us understood how reinforced soils functioned; time has proven the long-term strength of the structures.

The emergence of segmental concrete retaining wall units produced on concrete products machines occurred in Canada in the early- to mid-1970s. Marketed under the name Pisa Stone, it was sold in Canada and the United States. The system still enjoys international popularity today. Less than a decade later, Keystone® introduced its system in the United States and the growth of the industry began in earnest. By the end of the 1980s there were several proprietary segmental wall systems being licensed around the world.

Although there are not any firm industry statistics that measure the growth or market share of segmental retaining walls, it is generally accepted that from the late 1980s segmental retaining wall use grew at a rate of 20 to 25% annually. In 1998 the National Concrete Masonry Association (NCMA) organized a meeting of over 30 stakeholders in the segmental wall industry. The group consisted of concrete products producers, licensors, material vendors, engineers and others with interest in the SRW market. The consensus of the group after approximately six hours of discussion was that use of segmental retaining walls will double by 2003.

Why does the use of segmental retaining wall systems continue to grow? The logical answer to that question is that the systems are environmentally friendly, easy to construct, aesthetically pleasing and economical, and offer flexibility of design. The most compelling of these attributes are aesthetics and economy of the systems to build. In June 1998, Drexel University in Pittsburgh, Pennsylvania published Geosynthetic Research Institute Report #20, titled "Earth Retaining Wall Costs in the USA," authored by Dr. Robert M. Koerner, Jamie Koerner and Dr. Te-Yang Soong, which documents the relative cost of various styles of retaining wall systems.

Concrete segmental retaining walls are clearly the most economical.

Initially ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units, was used as the governing specification for segmental retaining wall units. This seemed appropriate since most units were manufactured on concrete products machines. Recognizing that segmental retaining walls have performance requirements more stringent than regular concrete masonry units, industry leaders, under the leadership of the NCMA, pursued development and adoption of a new ASTM specification exclusively for segmental retaining wall units. The proposed specification was adopted in 1997 as ASTM C1372, Standard Specification for Segmental Retaining Wall Units. The specifications are similar to ASTM C90 except that ASTM C1372 requires a higher minimum compressive strength (3000 psi vs.
1900 psi) and requires freeze/thaw testing of units that will be used in areas where repeated freezing and thawing in saturated condition can occur. The specification also defines pass/fail performance criteria for the segmental retaining wall units.

ASTM C1372, which requires high compressive strengths and good performance in freeze/thaw durability testing, challenges producers.

Production variables such as concrete mix and machine adjustments are critical to the production of high quality segmental retaining wall units. The mix design must contain the correct amounts of cement, aggregates and water to achieve the physical properties dictated by the specification. When developing a mix design, the quality of aggregates, including their sieve analysis, should be carefully considered. The cement content for the concrete mix should be higher than for producing architectural concrete masonry units and must be determined through testing of the SRWs. Machine settings and operation of the machine becomes more important and must be monitored more closely than when making standard concrete masonry units. Your Besser representative will provide assistance in developing mix designs and operational guidelines to achieve required product standards.

As you carefully consider the extra effort needed to produce units that meet ASTM C1372, keep in mind that there is a significant opportunity for increased profitability. Segmental retaining wall units are a high-end value added product providing generally high margins.

The ongoing success of the SRW portion of the concrete products industry is a direct result of the investment of the major licensors into multi-faceted marketing efforts. This is the fuel that drives the industry. From education and design guides to Home and Garden television and exhibits at trade shows, these significant financial and human resources maximize the popularity of SRWs.

The success of SRWs is a blueprint that can be followed for all aspects of our business. Blending attractive, quality products with qualified people, and investing in strong marketing efforts, add up to long-term financial gains and industry growth.