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NCMA Commentary Discussions to
ASTM C90-09
Standard Specification for Loadbearing Concrete Masonry Units
Last Revised June 9, 2010
How to use this Commentary to ASTM C90:
This document provides background information and discussion on the requirements of ASTM
C90 that may be useful to designers, contractors, producers, or specifiers of manufactured
concrete masonry products. The provisionsof ASTM C90 are shown shaded, with each section
followed by commentary discussion related to the provisions of that section. Where appropriate,
the reader is referred to additional discussion provided within other documents or resources for
further information on a particular topic.
1. Scope
1.1 This specification covers hollow and solid (see 5.3 and 5.4) concrete masonry units made
fromhydraulic cement, water, and mineral aggregates with or without the inclusion of other
materials. There are three classes of concrete masonry units: (1) normal weight, (2) medium
weight, and (3) lightweight. These units are suitable for both loadbearing and nonloadbearing
applications.
Section 1.1 Commentary Discussion
General Requirements
Prior to reviewing the provisions and requirementsthat are included in ASTM C90, it is
worth discussing what requirements are not covered by ASTM C90. Because ASTM
C90 is a minimum product specification, it only addresses those physical attributes that
are common to, or necessary in, the majority of applications in which these units are
used. As a result, designers and specifiers must often stipulate requirements in addition
to compliance withASTM C90 if particular features or properties are desired for a unique
application. A few such attributes include:
• Aesthetics – While ASTM C90 does include minimum finish and appearance
requirements, these provisions are oriented toward minimum chipping and
cracking common to all exposed units and do not address aesthetically-driven
considerations such as color, texture, or architecturalfeatures, which must be
specified separately by the purchaser. Refer to the commentary discussion
provided under ASTM C90 Section 7 for additional discussion related to finish
and appearance.
• Fire Resistance – Concrete masonry units are inherently noncombustible; indeed
they are used in many applications where direct exposure to heat and flame are
anticipated. Different concrete masonryunits, however, will have varying fire
resistance ratings determined in accordance with ASTM E119, Standard Test
Methods for Fire Tests of Building Construction and Materials, or calculated in
accordance with ACI 216.1/TMS 216, Standard Method for Determining Fire
Resistance of Concrete and Masonry Construction Assemblies. (The provisions
of the ACI 216.1/TMS 216 standard are referenced by andidentical to the
calculated fire resistance requirements contain in recent editions of the
International Building Code, Section 721 “Calculated Fire Resistance”.)
Commentary to ASTM C90 – Standard Specification for Loadbearing Concrete Masonry Units
Last Revised June 9, 2010

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Concrete masonry assemblies have fire resistance ratings that can vary from 1hour to 4 hours or more depending upon the type of aggregate(s) used in
production, the volume of concrete in the unit, and whether the cells of hollow
units are filled with a material that is: 1) recognized by ACI 216.1/TMS 216 (or
the International Building Code); or 2) evaluated in accordance with ASTM E119
or an equivalent to this testing procedure. When a specific fire resistance rating isdesired, it should be specified separately. For more information on fire resistance
ratings of concrete masonry assemblies see NCMA TEK 7-1C, Fire Resistance of
Concrete Masonry Assemblies.
Water Penetration Resistance – Refer to the commentary discussion provided in
Appendix X1.
Crack Control – Refer to the commentary discussion provided in Appendix X2.
Admixtures – Additives and...