Work Item
ASTM WK89380
Revision of C90-23 Standard Specification for Loadbearing Concrete Masonry Units
Rationale
ASTM C90 defines ‘solid’ vs. ‘hollow’ masonry units based on the threshold of having a actual cross-sectional area of 75% of the total cross-sectional area.
This definition has roots that extend back more than 80 years to when ASTM had two separate standards:
C90 – Hollow Loadbearing CMU and C145 – Solid Loadbearing CMU.
ASTM C145 was withdrawn in 1990 and C90 was rewritten to apply to all loadbearing CMU (hollow and solid).
Distinguishing between solid and hollow CMU did have implications under the empirical design method, which based loads and stresses on the gross cross-sectional area (out-to-out dimensions) and did not account for the void area of the cells. Empirical design has been removed from current masonry codes and standards. Today, structural masonry analysis follows an engineering design approach that accounts for the open area of the cells and assembly.
At this point, there is little value in having 75% solid units defined as ‘solid’ and few, if any, producers manufacture them. It also causes some confusion in architects, specifiers and users. This ballot item proposes to remove the non-intuitive definition such that ‘solid’ CMU will now be required to be 100% solid.
Work Item Status
Date Initiated: 01-24-2024
Technical Contact: Nicholas Lang
Item: 000
Ballot:
Status: