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Written by GJ Stott
CMU stands for concrete masonry unit, which is the 8x8x16-inch concrete block that makes up CMU concrete block walls. CMUs have been improving in materials and mixtures since 1882, but their general size and purpose remains the same. Popularly used as a standard building material, CMUs are simply precast concrete blocks, meaning that they have been molded to a specific shape and size to build a block or rock retaining wall.
Made from cement, aggregates and water, CMUs are formed in molding equipment and allowed to cure. Curing implies that the concrete CMU does not dry as it hardens but rather retains moisture as it strengthens. Retaining water is part of what gives the concrete block wall its integrity.
In addition to the ingredients listed above, CMU mixtures may include a host of optional admixtures created to enhance or change the finalized CMU block’s characteristics, which shows on the concrete block wall. By adding such ingredients, the manufacturer may be able to strengthen, air-entrain, color, accelerate curing speed, retard or plasticize the CMU. For example, air bubbles disperse in concrete (know as air-entraining) to protect against freezing and thawing conditions. Plasticizers help make concrete more workable while forming it.
As they are manufactured, CMUs are generally formed in a concrete forming machine that takes moist concrete and quickly pours it into the desired block dimensions. Placed in chambers that have extremely high temperatures, the CMU blocks undergo accelerated curing. Finally, they are stored for a specific period of time to promote further curing prior to shipment. These CMU blocks are designed to ultimately be the core for concrete block walls and buildings that need to be fabricated economically, efficiently and for fire-resistance.
As the finalized CMU blocks are identical, they provide a good material to build a solid concrete block wall. The CMU blocks are stacked in layers with mortar between each block. This process allows for flexible and versatile concrete masonry, but the cost of time and money to build concrete concrete block walls can be high. Other types of walls, such as ones offered by Stonetree®, are better alternatives.
CMUs are formed for many different purposes and include various masonry unit types including split face concrete block, slotted and glazed CMUs. Split face CMUs are formed as one unit and then split revealing the rough aggregate texture. Slotted CMUs offer high sound absorption in places where a sound barrier concrete block wall may be needed. Glazed CMUs are primarily used when an aesthetically pleasing finish is desired. AFTEC Precast Concrete Block Walls and stone columns offer each of these benefits in one double-sided textured wall.