These standards reflect the expert opinion of researchers, concrete masonry manufacturers, designers, contractors and others with an interest in quality standards for concrete masonry. Consequently, concrete masonry units chosen for testing should be randomly sampled. Choosing units from one portion of a pallet, or choosing the most or least desirable units may misrepresent the properties of the lot. Although a shipment may consist of several different unit configurations, samples for testing should all have the same configuration and dimensions.
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These ASTM standards contain minimum requirements that assure properties necessary for quality performance. These requirements include items such specified component materials, compressive strength, permissible variations in dimensions, and finish and appearance criteria.
Currently, seven ASTM standards apply to units intended primarily for construction of concrete masonry walls, beams, columns or specialty applications see Table 1.
The letter and first number of an ASTM designation is the fixed designation for that standard. The number immediately following indicates the year of last revision i. A date in parentheses after the last revision date is the reapproval date. Because significant changes can be introduced into subsequent editions, the edition referenced by the building code or by a project specification can be an important consideration when determining specific requirements.
Also note that it may take several years between publication of a new ASTM standard and its subsequent reference by a building code. Code officials will commonly accept more current editions of ASTM standards than that referenced in the code, as they represent state-of-the-art requirements. The bulk of these revisions are editorial, although two recent major changes are discussed here. In , web thickness requirements were significantly revised.
Additionally, equivalent web thickness, a measure of the width of web per foot of wall length was used to determine if sufficient web was present to transfer shear loads. The equivalent web thickness was replaced with a normalized web area, a measure of the area of web contact with the face shells per square foot of wall see Table 2. The designations were withdrawn because they were difficult to effectively use and enforce, and because of newly developed concrete masonry crack control provisions.
The new crack control guidelines are based on anticipated total volume changes, rather than on the specified moisture contents that formed the basis for Type I requirements.
Control joint criteria can be found in References 5 and 6. For more detailed information on removal of the Type designations, see the Frequently Asked Question on this topic here. D Minimum normalized web area does not apply to the portion of the unit to be filled with grout. The length of that portion shall be deducted from the overall length of the unit for the calculation of the minimum web cross-sectional area. Physical Requirements Physical requirements prescribed by ASTM C90 include dimensional tolerances, minimum face shell and web thicknesses for hollow units, minimum strength and maximum absorption requirements, and maximum linear shrinkage.
Exceptions are faces of split-face units and faces of slump units which are intended to provide a random surface texture. In these cases, consult local suppliers to determine achievable tolerances. Minimum face shell and web thicknesses are those deemed necessary to obtain satisfactory structural and nonstructural per- formance.
Note that although there are some unique face shell thickness requirements for split-faced units see Table 2 footnote B , ground-face units i. In addition to minimum permissible web thicknesses for individual webs, the specification also requires a minimum total web contact area with face shells per square foot of wall area. When evaluating this normalized web area, the portion of a unit to be filled with grout is exempted.
This provision avoids excluding units intentionally manufactured with reduced webs, including bond beam units and open-end block, where grout fulfills the structural role of the web. Minimum face shell and web thicknesses are not prescribed for solid units.
Gross and net areas are shown in Figure 1. Net area compressive strength is used for engineered masonry design, taking into account the mortar bedded and grouted areas. Gross area compressive strength is still used for empirically designed masonry IBC Section Maximum permissible water absorption is shown in Table 3. Absorption is a measure of the total water required to fill all voids within the net volume of concrete.
It is determined from the weight-per-unit-volume difference between saturated and oven-dry units. Aggregates with relatively large pores, such as some lightweight aggregate, have a greater absorption than dense, nonporous aggregates, given the same compaction.
As a result, lightweight units are permitted higher absorption values than medium or normal weight units. Because concrete masonry units tend to contract as they dry, C90 limits their potential drying shrinkage to 0. For units which will be exposed, the presence of objectionable imperfections is based on viewing the unit face s from a distance of at least 20 ft 6.
Five percent of a shipment may contain chips not larger than 1 in. The specification requires that color and texture be specified by the purchaser. In , the grades were removed and requirements for concrete brick used in veneer and facing applications were moved into a new standard: C see below. ASTM C55 now only applies to concrete masonry units with: a maximum width of 4 in.
Requirements for C ref. Finish and appearance criteria only address defects which might affect placement or permanence of the resulting construction.
Compression and absorption requirements are listed in Table 4. Both C and C55 refer to C ref. These units are not suitable for exterior walls subjected to freezing cycles unless effectively protected from the weather. These units must be clearly marked to preclude their use as loadbearing units. Minimum net area compressive strength requirements are psi 3. Two grades are included: Grade SW—Brick intended for exposures below freezing in the presence of moisture.
Minimum compressive strength requirements are 4, psi 31 MPa for an individual unit and 5, psi Grade MW—Brick intended for exposure to temperatures below freezing, but unlikely to be saturated with water.
Minimum compressive strength requirements are 3, psi Facing requirements in C include: resistance to crazing, surface burning characteristics, adhesion, color permanence, chemical resistance, cleansability, abrasion, and dimensional tolerances.
Units are required to be at least 5 in. References International Building Code. International Code Council, , , Reported by the Masonry Standards Joint Committee, ASTM International, National Concrete Masonry Association, TEK
ASTM C426 PDF
Want this as a site license? Changes from the previous issue A redline edition is available for this document, with all changes visible. Ask Document Center Inc. Scope 1. Both procedures are intended for use in determining the effects of variations in the properties of concrete on the resistance of the concrete to the freezing-and-thawing cycles specified in the particular procedure.
SAMPLING AND TESTING CONCRETE MASONRY UNITS
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ASTM SPECIFICATIONS FOR CONCRETE MASONRY UNITS