Masonry Magazine August 1995 Page. 20
sizes, other unit heights, lengths, and thicknesses may be available from local concrete masonry producers.
Standard Specification for Load-Bearing Concrete Masonry Units, ASTM C 90 (ref. 4) is the most frequently referenced standard for concrete masonry units. ASTM C 90 includes minimum face shell and web thicknesses for the different sizes of concrete masonry units as listed in Table 1. Overall unit dimensions (height, width, or length) are permitted to vary by in. (3.2 mm) from the dimensions specified by the manufacturer. Where required, units may be manufactured to closer tolerances than those permitted in ASTM C 90. ASTM C 90 also defines the difference between hollow and solid concrete masonry units. The net cross-sectional area of a solid unit is at least 75% of the gross cross-sectional area.
In addition to the "standard" sizes listed above, concrete brick is available in typical lengths of 8 and 16 in. (203 and 406 mm), nominal 4 in. (102 mm) width, and a wide range of heights. They may be 100% solid, or may have two or three cores. Like ASTM C 90, Standard Specification for Concrete Building Brick, ASTM C 55 (ref. 3), permits overall unit dimensions to vary +s in. (3.2 mm) from the dimensions specified by the manufacturer. Nominal dimensions of modular concrete brick equal the actual dimensions plus % in. (9.5 mm), the thickness of one standard mortar joint. However, nominal dimensions of nonmodular sized concrete brick usually exceed the standard dimensions by 1/s to 1/4 in. (3.2 to 6.4 mm).
SHAPES
Concrete masonry unit shapes have been developed for a wide variety of applications. The most common shapes are shown in Figure 2. Typically, the face shells and webs are tapered on concrete masonry units. Depending on the core molds used in the manufacture of the units, face shells and webs may be tapered with a flare at one end, or may have a straight taper from top to bottom. The taper provides a wider surface for mortar and easier handling for the mason.
The shapes illustrated in Figure 3 have been developed specifically to accommodate reinforcement. Open-ended units allow the units to be threaded around reinforcing bars. This eliminates the need to lift units over the top of the reinforcing bar, or to thread the reinforcement through the masonry cores after the wall is constructed. Bond beams in concrete masonry walls can be accommodated either by saw-cutting out of a standard unit, or by using bond beam units. Bond beam units are either manufactured with reduced webs or with "knock-out" webs, which are removed prior to placement in the wall. Horizontal bond beam reinforcement is easily accommodated in these units. Lintel units are similar to the U shaped bond beam units. Lintel units are available in various depths to carry appropriate lintel loads over door and window openings. The solid bottom confines
Open end, or
"A" shaped unit
Double open end unit
Lintel unit
Stretcher unit
Single corner unit
Concrete brick
Corner return unit
Double corner or
plain end unit
Figure 2-Typical Concrete Masonry Units
Bond beam units
Pilaster units
Figure 3-Shapes to Accommodate Reinforcement
grout to the lintel. Pilaster and column units are used to easily accommodate a wall-column or wall-pilaster interface, allowing space for vertical reinforcement in the hollow center.
Figure 4 shows units developed for specific wall applications. Sash block have a vertical groove molded into one end to accommodate a window sash. Sash block can be laid with the grooves adjacent to one another to accommodate a preformed control joint gasket. Control joint units are manufactured with one male and one female end to provide lateral load transfer across control joints. An all-purpose or kerf unit contains two closely spaced webs in the center, rather than the typical single web. This allows the unit to be
20 MASONRY-JULY/AUGUST, 1995