The Story of Lightweight Concrete Masonry Units

Shortly after World War I, F. J. Straub pioneered the so-called “cinder block,” a manufactured concrete masonry unit using coal cinders as the aggregate. Then, in 1923, Dan F. Servey of Kansas City introduced the first masonry block employing lightweight expanded shale as the aggregate and expanded shale aggregate quickly achieved popularity among both block manufacturers and users of the end product.

The general characteristics of the lightweight masonry unit were that it provided a high degree of insulation, lightweight, nominal shrinkage and a uniform compressive strength equal to a heavyweight block with equal cement content. The block manufacturers found that the lightweight aggregate produced a block which was easier to sell to architects and engineers and, from a practical point of view, the blocks were slightly more than half the weight of the normal weight concrete blocks of the time, so that transportation costs to the job were radically reduced.

Their high degree of insulation against heat, fire and sounds made the expanded shale blocks particularly attractive to architects and engineers, as did their structural integrity, and contractors favored them because the light weight enabled greater productivity of crews. Individual masons found the lightweight blocks much less tiring to work with; in an average day, they might lift 4,000 pounds less than they would with normal weight concrete blocks!

Lightweight concrete masonry units can be found in every type of building – from barns and other farm building to homes, commercial, and industrial structures, schools, theaters, multiple story building, warehouse, recreation buildings and churches. The choice of lightweight concrete masonry is often driven by its fire resistance, but there are many other advantages to using lightweight units. The productivity advantages mentioned above mean lower installed wall costs. Increased productivity doesn’t come from speeding up the mason; rather, the lightweight units enable the mason to maintain his or her normal pace throughout the day, everyday until the end of the project. In the end, more units have been placed in less time. At the same time, less fatigue and fewer injuries mean a sustainable workforce and lower workers compensation insurance ratings.

The same thermal properties that give lightweight units their fire resistance also make them more energy efficient. With energy codes becoming more stringent, this is an important issue for building owners, as well as the concrete masonry industry itself. The combination of lightweight concrete with thinner face shells and smaller and fewer webs now permitted by ASTM C90, Specification for Loadbearing Concrete Masonry Units, makes integral insulation for concrete masonry walls much more efficient, resulting in high R-values that couldn’t be achieved just a few years ago.