Sources: National Concrete Masonry Association, Herdon, Va.; CP staff
A new provision allowing a single web of ¾-in. minimum thickness invites an array of alternatives to the three-web configuration of 8x8x16 block meeting requirements of ASTM C90 Standard Specification for Loadbearing Concrete Masonry Units.
Advancing C90 changes through ASTM C15.03 Committee on Concrete Masonry Units, NCMA noted how the single-web configuration, compared to legacy product designs, reduces by up to 75 percent the material connecting 8×16 face shells. The revised standard holds the potential to a) lower products’ mass and transportation costs; b) increase masons’ productivity through lighter units, while reducing fatigue and injury associated with heavier block handling; c) ease rebar congestion and grout placement in reinforced wall assemblies; and, d) boost wall R-values by a factor of 3 to 4.
Amid ASTM Committee C meetings in Tampa, C15.03 members approved what NCMA calls one of the most substantive changes to C90 in decades. The single-web provision revises requirements that have been a defining concrete masonry unit characteristic—three webs, two cells—for nearly a century. It does not require block shapes or sizes to be reconfigured, but offers concrete masonry producers and their customers more flexibility in how webs are arranged to meet evolving building code requirements and marketplace demands. Other C90-prescribed unit properties remain, including face shell thicknesses and minimum unit compressive strength.
NCMA anticipates the revised standard to be published in January, and plans online meetings this winter to help industry stakeholders present the new web-thickness provisions to architectural, engineering and construction interests.