Masonry Magazine May 1976 Page. 15
NCMA-TEK
An Information series from National Concrete Masonry Association
Concrete Brick
Design Considerations
Introduction
Concrete brick offer a wide variety of choices of natural faces and finishes for walls. Variation in texture, color and size, along with choices in bonding patterns and joint treatment, make concrete brick an excellent choice for exterior and interior walls in residential and non-residential buildings. In addition, concrete brick offers the designer and builder a structural or non-structural wall material which is economical, durable, easy to maintain, and fire-resistant. Availability of particular sizes, colors, and textures of concrete brick should be determined from local producers.
ASTM
Requirements
ASTM Standard Specification C55 covers requirements for concrete brick and similar solid units (units not less than 75 percent solid) made from portland cement, water, and suitable mineral aggregates with or without the inclusion of other materials. The requirements in ASTM C55 are also applicable to solid concrete veneer and facing units larger than brick size, such as split block.
Two types of concrete brick in each of two grades are covered in the ASTM C55 specification. Grade N is for use as architectural veneer and facing units in exterior walls and for use where high strength and resistance to moisture penetration and severe frost action are desired. Grade S is for general use where moderate strength and resistance to frost action and moisture penetration are required. Concrete brick designated as Type 1 (Grades N-I and S-I) are moisture controlled units and are required to conform to the moisture content requirements of Table 1. Concrete brick designated as Type II (Grades N-11 and S-11) are nonmoisture-controlled units and are required to conform to all the requirements in ASTM C55 except the requirements of Table 1.
At the time of delivery to the work site, concrete brick should conform to the physical requirements prescribed in Table 2. ASTM C55 also requires that no over-all dimension (width, height, or length) shall differ by more than 1/8 in. (3.2 mm) from the specified standard dimensions. When particular concrete brick features are desired, such as weight classification, high compressive strength, surface textures for appearance or bond, finish, color, fire resistance, insulation, acoustical properties, or other special features, such properties should be specified separately by the purchaser. However, local suppliers or manufacturers should be consulted as to the availability of concrete brick having the desired features.
Structural Design
Structural design requirements for load-bearing concrete brick walls are contained in "American Standard Building Code Requirements for Masonry," ANSI A41.1-1953(R 1970), and "Specification for the Design and Construction of Load-Bearing Concrete Masonry," NCMA-1970. As defined in the HUD Minimum Property Standards, nonreinforced masonry that is designed in accordance with empirical requirements and limitations (i.e., ANSI A41.1-1953 Standard) is considered as "conventional masonry construction." Nonreinforced or reinforced masonry, which is designed in accordance with an engineering analysis (i.e., NCMA-1970 Standard), is defined as "engineered masonry construction."
Conventional Masonry Construction
Allowable compressive stresses for concrete brick masonry, which are contained in the ANSI A41.1 Standard are given in Table 3.
If the wall is constructed of concrete brick and other structural members composed of different kinds or grades of units or mortars (i.e., composite wall), the maximum compressive wall stress cannot exceed the allowable stress for the weakest of the combination of units and mortars of which the wall is composed. For example, if the wall is constructed of concrete brick, hollow concrete block and Type M mortar, the maximum allowable compressive stress is limited by the A41.1 Standard to 85 psi for solid walls and to 70 psi for hollow walls.
Lateral support and thickness requirements specified in ANSI A41.1 for concrete brick walls are the same as those specified for other types of solid masonry unit walls (see NCMA TEK 73, "Empirical Design of Concrete Masonry Walls").