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Fueled by concerns about masonry's continued viability as an economic construction method, engineers from the U.S. Army Construction Engineering Research Laboratories, Champaign, Ill., initiated a Cooperative Research Development Agreement to design a better building unit. "The goal of the CRDA was to find a way to help increase worker productivity and thus lower capital construction costs," says Steve Sweeney, the CERL research structural engineer who coordinated the project. This CMU had to be compatible with a producer's existing block-making equipment. The result was a smooth, uniformly-textured lightweight CMU that weighs about 19 pounds, has an average compressive strength of 4000 psi and is more durable than a standard unit. Researchers developed mix designs for high-strength lightweight block that provided good texture along with durability. Their final election of the mix designs was based upon workability. Researchers finally had to develop data to convince producers and contractors of the benefits of the A-Block. While contractors paid higher initial costs for the redesigned A-Block, the study indicated that they would lower their ultimate construction costs by 3.8%. In addition to ultimate cost reductions, researchers believe lighter blocks should help contractors in other intangible ways such as reduced labor-related losses due to injuries and workers' compensation and disability claims. The masons who participated in the field tests found that workers place more units during each shift and lessen muscle wear and tear. The new shape also offers producers intangible savings from potential lower transportation costs. With a different shape, operators may need to change standard cubing arrangements. Even so, lighter block can increase delivery truck utilization because trucks can carry more CMUs on each trip. The research results, including mix-design and mold-design information, are available from the U.S. Army Construction Engineering Research Laboratories. Keywords: A-block, University of Nebraska, enhancer, lightweight block