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// CODE SNIPPET

21-4 Hollow and Solid Load-Bearing Concrete Masonry Units

Los Angeles Existing Building Code > Referenced Standards > 21-4 Hollow and Solid Load-Bearing Concrete Masonry Units
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Based on Standard Specification C 90—95 of the ASTM International.
Extracted, with permission, from the
Annual Book of ASTM Standards, copyright
ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428

Note: See Appendix Chapter A1, Section A106, California Existing Building Code

Section 21.401 — Scope

This standard covers solid (units with 75 percent or more net area) and hollow load-bearing concrete masonry units made from portland cement, water and mineral aggregates with or without the inclusion of other materials.

Section 21.402 — Classification

21.402.1 Types

Two types of concrete masonry units in each of two grades are covered as follows:

21.402.1.1 Type I, Moisture-Controlled Units

Units designated as Type I shall conform to all requirements of this standard including the moisture content requirements of Table 21—4-A.

21.402.1.2 Type II, Nonmoisture-Controlled Units

Units designated as Type II shall conform to all requirements of this standard except the moisture content requirements of Table 21—4-A.

21.402.2 Grades

Concrete masonry units manufactured in accordance with this standard shall conform to two grades as follows:

21.402.2.1 Grade N

Units having a weight classification of 85 pcf (1360 kg/m3) or greater, for general use such as in exterior walls below and above grade that may or may not be exposed to moisture penetration or the weather and for interior walls and backup.

21.402.2.2 Grade S

Units having a weight classification of less than 85 pcf (1360 kg/m3), for uses limited to above-grade installation in exterior walls with weather-protective coatings and in walls not exposed to the weather.

Section 21.403 — Materials

21.403.1 Cementitious Materials

Materials shall conform to the following applicable standards:

  1. Portland Cement—ASTM C 150 modified as follows:

    Limitation on insoluble residue—1.5 percent maximum.

    Limitation on air content of mortar, Volume percent—22 percent maximum.

    Limitation on loss on ignition—7 percent maximum.

    Limestone with a minimum 85 percent calcium carbonate (CaCO3) content may be added to the cement, provided the requirements of ASTM C 150 as modified above are met.

  2. Blended Cements—ASTM C 595.
  3. Hydrated Lime, Type S—UBC Standard 21-13.

21.403.2 Other Constituents and Aggregates

Air-entraining agents, coloring pigments, integral water repellents, finely ground silica, aggregates, and other constituents, shall be previously established as suitable for use in concrete or shall be shown by test or experience to not be detrimental to the durability of the concrete.

Section 21.404 — Physical Requirements

At the time of delivery to the work site, the units shall conform to the physical requirements prescribed in Table 21—4—B. The moisture content of Type I concrete masonry units at time of delivery shall conform to the requirements prescribed in Table 21—4-A.

At the time of delivery to the purchaser, the linear shrinkage of Type II units shall not exceed 0.065 percent.

Section 21.405 — Minimum Face-Shell and Web Thicknesses

Face-shell (FST) and web (WT) thicknesses shall conform to the requirements listed in Table 21—4-C.

Section 21.406 — Permissible Variations in Dimensions

21.406.1 Precision Units

For precision units, no overall dimension (width, height and length) shall differ by more than 1/8 inch (3.2 mm) from the specified standard dimensions.

21.406.2 Particular Feature Units

For particular feature units, dimensions shall be in accordance with the following:

  1. For molded face units, no overall dimension (width, height and length) shall differ by more than 1/8 inch (3.2 mm) from the specified standard dimension. Dimensions of molded features (ribs, scores, hex-shapes, patterns, etc.) shall be within 1/16 inch (1.6 mm) of the specified standard dimensions and shall be within 1/16 inch (1.6 mm) of the specified placement of the unit.
  2. For split-faced units, all non-split overall dimensions (width, height and length) shall differ by no more than 1/8 inch (3.2 mm) from the specified standard dimensions. On faces that are split, overall dimensions will vary. Local suppliers should be consulted to determine dimensional tolerances achievable.
  3. For slumped units, no overall height dimension shall differ by more than 1/8 inch (3.2 mm) from the specified standard dimension. On faces that are slumped, overall dimensions will vary. Local suppliers should be consulted to determine dimension tolerances achievable.

Note: Standard dimensions of units are the manufacturer's designated dimensions. Nominal dimensions of modular size units, except slumped units, are equal to the standard dimensions plus 3/8 inch (9.5 mm), the thickness of one standard mortar joint. Slumped units are equal to the standard dimensions plus 1/2 inch (13 mm), the thickness of one standard mortar joint. Nominal dimensions of nonmodular size units usually exceed the standard dimensions by 1/8 inch to 1/4 inch (3.2 mm to 6.4 mm).

Section 21.407 — Visual Inspection

All units shall be sound and free of cracks or other defects that would interfere with the proper placing of the unit or impair the strength or permanence of the construction. Units may have minor cracks incidental to the usual method of manufacture, or minor chipping resulting from customary methods of handling in shipment and delivery.

Units that are intended to serve as a base for plaster or stucco shall have a sufficiently rough surface to afford a good bond.

Where units are to be used in exposed wall construction, the face or faces that are to be exposed shall be free of chips, cracks or other imperfections when viewed from 20 feet (6100 mm), except that not more than 5 percent of a shipment may have slight cracks or small chips not larger than 1 inch (25.4 mm).

Section 21.408 — Methods of Sampling and Testing

The purchaser or authorized representative shall be accorded proper facilities to inspect and sample the units at the place of manufacture from the lots ready for delivery.

Sample and test units in accordance with ASTM C 140.

Total linear drying shrinkage shall be based on tests of concrete masonry units made with the same materials, concrete mix design, manufacturing process and curing method, conducted in accordance with ASTM C 426 and not more than 24 months prior to delivery.

Section 21.409 — Rejection

If the samples tested from a shipment fail to conform to the specified requirements, the manufacturer may sort it, and new specimens shall be selected by the purchaser from the retained lot and tested at the expense of the manufacturer. If the second set of specimens fails to conform to the specified requirements, the entire lot shall be rejected.

TABLE 21—4-A

MOISTURE CONTENT REQUIREMENTS FOR TYPE I UNITS

LINEAR SHRINKAGE, PERCENTMOISTURE CONTENT, MAX. PERCENT OF TOTAL ABSORPTION (Average of 3 Units)
Humidity Conditions at Job site or Point of Use
Humid1Intermediate2Arid3
0.03 or less454035
From 0.03 to 0.045403530
0.045 to 0.065, max.353025
  • 1Average annual relative humidity above 75 percent.
  • 2Average annual relative humidity 50 to 75 percent.
  • 3Average annual relative humidity less than 50 percent.

TABLE 21—4-B

STRENGTH AND ABSORPTION REQUIREMENTS

COMPRESSIVE STRENGTH, MIN, psi (MPa)WATER ABSORPTION, MAX, lb./ft. (kg/m) (Average of 3 Units)
Average Net AreaWeight Classification—Oven-dry Weight of Concrete, lb./ft. (kg/m)
Average of 3 UnitsIndividual UnitLightweight, Less than 105 (1680)Medium Weight, 105 to less than 125 (1680-2000)Normal Weight, 125 (2000) or more
1900 (13.1)1700 (11.7)18 (288)15 (240)13 (208)

TABLE 21—4-C

MINIMUM THICKNESS OF FACE-SHELLS AND WEBS

NOMINAL WIDTH (W) OF UNIT (inches)FACE-SHELL THICKNESS (FST) MIN., (inches)1,4WEB THICKNESS (WT)
Webs1 Min., (inches)Equivalent Web Thickness, Min., In./Lin. Ft.2
× 25.4 for mm× 83 for mm/lin. m
3 and 43/43/415/8
61121/4
811/4121/4
1013/811/821/2
11/43
1211/211/821/2
11/43
  • 1 Average of measurements on three units taken at the thinnest point.
  • 2 Sum of the measured thickness of all webs in the unit, multiplied by 12 (305 when using metric), and divided by the length of the unit. In the case of open-ended units where the open-ended portion is solid grouted, the length of that open-ended portion shall be deducted from the overall length of the unit.
  • 3 This face-shell thickness (FST) is applicable where allowable design load is reduced in proportion to the reduction in thicknesses shown, except that allowable design load on solid-grouted units shall not be reduced.
  • 4 For split-faced units, a maximum of 10 percent of a shipment may have face-shell thicknesses less than those shown, but in no case less than 3/4 inch (19 mm).

Related Code Sections


21-4 Referenced Standards, Hollow and Solid Load-Bearing Concrete Masonry Units
with 75 percent or more net area) and hollow load-bearing concrete masonry units made from portland cement, water and mineral aggregates with or without ...
Los Angeles Existing Building Code > Referenced Standards > 21-4 Hollow and Solid Load-Bearing Concrete Masonry Units
Section 21.409 Referenced Standards, — Rejection
in thicknesses shown, except that allowable design load on solid-grouted units shall not be reduced. 4 For split-faced units, a maximum of 10 ...
Los Angeles Existing Building Code > Referenced Standards > 21-4 Hollow and Solid Load-Bearing Concrete Masonry Units > 21.409 — Rejection
Section 21.404 Referenced Standards, — Physical Requirements
of Type I concrete masonry units at time of delivery shall conform to the requirements prescribed in Table 21—4-A. At the time of delivery ...
Los Angeles Existing Building Code > Referenced Standards > 21-4 Hollow and Solid Load-Bearing Concrete Masonry Units > 21.404 — Physical Requirements
Section 21.403 Referenced Standards, — Materials
, and other constituents, shall be previously established as suitable for use in concrete or shall be shown by test or experience to not be detrimental ...
Los Angeles Existing Building Code > Referenced Standards > 21-4 Hollow and Solid Load-Bearing Concrete Masonry Units > 21.403 — Materials
Section 21.405 Referenced Standards, — Minimum Face-Shell and Web Thicknesses
Face-shell (FST) and web (WT) thicknesses shall conform to the requirements listed in Table 21—4-C ...
Los Angeles Existing Building Code > Referenced Standards > 21-4 Hollow and Solid Load-Bearing Concrete Masonry Units > 21.405 — Minimum Face-Shell and Web Thicknesses
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