Making Concrete Blocks
Concrete masonry units commonly referred to as concrete blocks, are commonly used in building foundations and basement walls.
Concrete block was once called cinder block because it contained the cinders left after burning coal. Today, a concrete block is constructed using other materials such as sand and gravel.
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Making the blocks …
Water is added to Portland cement, filler materials such as sand and gravel, and special additives known as admixtures. (Admixtures affect the color and other properties of the cement, such as freeze resistance, weight, and speed of setting.)
Molding and curing the blocks …
The block is machine-molded into shape. It is compacted in the molds and cured, typically using live steam.
After curing the blocks …
After curing, the blocks are dried and aged. The moisture content is checked. It must be a specified minimum amount before the blocks can be shipped for use.
Concrete Blocks: Sizes
A concrete block is typically 8” x 8” x 16”, with a hollow core. Blocks come in modular sizes and colors determined by their ingredients.
A variety of surface and mixing treatments can give the blocks varied and attractive surfaces. Newer finishing techniques can give blocks the appearance of brick, rough stone, or cut stone.
Like clay masonry units, blocks can be placed in structural pattern bonds. Blocks takes up more space than other building units, so fewer are needed. Block bed joints usually need mortar only on the shells and webs, so there is less mortaring as well.
Concrete Blocks: Weights
Concrete block comes in three weights: normal, lightweight, and aerated.
1) Normal-weight blocks can be made of concrete with regular, high, and extra-high strengths. The last two are made with different aggregates and curing times. They are used to limit wall thickness in buildings over ten floors high.
2) Lightweight blocks are made with light-weight aggregates. The load bearing and appearance qualities of the first two weights are similar; the major difference is that lightweight blocks are easier and faster to lay.
3) Aerated blocks are made with an admixture that generates gas bubbles inside the concrete for a lighter block.
More Information About Concrete Blocks
Common hollow units have two or three cores. The hollow cores make it easy to reinforce concrete block walls.
Grout alone, or steel reinforcing rods combined with grout, can be used to fill the hollow cores.
Reinforcement increases load bearing strength, rigidity, and wind resistance.
Load-bearing blocks are used as a backing for veneer walls, bearing walls, and all structural uses. Both regular and specially shaped blocks are used for paving, retaining walls, and slope protection.
Nonstructural blocks are used for screening, partition walls, and as a veneer wall for wood, steel, or other backing.
Both kinds of blocks come in a variety of shapes and modular sizes.