Masonry Magazine August 1973 Page. 20
Variety of weights manufactured is reflected by the latest ASTM Specifications for load-bearing concrete masonry units. Two categories of lightweight units are listed: units having a density of less than 105 lb/ft³: a "medium weight" category includes units having a density of 105 to 125 lb/ft³; units weighing 125 lb/ft³ or more fit into the category of "normal weight". Maximum water absorption permitted depends upon weight category, recognizing the fact that lightweight aggregates contain pores which can absorb water even though the concrete of which they are made is well compacted.
For load-bearing hollow concrete masonry. Table 1 lists the minimum face shell and web thickness requirements as related to the width, or thickness of the unit. Although these thicknesses may vary slightly from plant to plant the minimum values can be used to estimate properties for preliminary design. Table 2 shows estimated net area of block, and section modulus for various wall thicknesses.
Although the industry has standardized on exterior dimensions of modular units, differences in thickness of face shells and webs, and size and number of cores for the same size hollow unit may exist between manufacturers. As an example, the 8 x 8 x 16 hollow unit may range from about 50% to 63% solid, depending upon the size and number of cores. These variations may result from the need to obtain properties such as fire resistance, sound insulation, and the like.
Oversize Units
Costs of mortar and labor can both be reduced by the use of oversize units. One type of oversize unit that has been made commercially has a face 12" high and 16" long. Another type has a face 8" high and 24 long. Each is thus 50 percent larger than a standard unit. They have been produced from aggregate that is sufficiently light in weight so that a single 8" thick unit weighs only about 33 lb. Consequently each block can be laid about as rapidly as a standard block, but wall construction is about 50 percent faster. The dimensional proportions of both block shapes in the finished walls are pleasing.
FIGURE 1-Typical functional shapes
Screen Block
Open-faced block of many patterns are available for decorative uses, or for the purpose of partially screening walls or yards from either the sun or outside viewers. These screen block are made in a wide variety of patterns and are useful, both indoors and out, for such uses as fences and carport walls, sun screens, curtain walls, room dividers, and veneers and friezes. Only a limited number of patterns may be available in a single locality but arrangements can often be made for special production runs of other patterns made with rented molds.
Floor and Roof Block
Floor and roof block offer the means of rapid but inexpensive construction of concrete floors, combined with excellent resistance to fire and sound. Such floors function as diaphragms and transmit wind loads or seismic loads through the walls to the foundation. Floor and roof block are of two types: filler block for joists and block for making plank.