Concrete blocks are a popular building material used to construct walls, floors and foundations. Also known as concrete masonry units (CMUs), they can be made in a wide variety of shapes and sizes, which makes them suitable for construction projects of all types. The basic block is typically constructed from a mixture of powdered portland cement, water, sand and gravel. The mixture is pressed into a mold to form the shape of the finished block. It is then fired in a kiln to cure and harden. Some block manufacturers offer variations on the basic block to achieve unique visual effects or provide desirable structural features for specialized applications.
The process of manufacturing concrete blocks is highly automated, with plants capable of producing up to 2,000 blocks per hour. The basic block is available in a range of standard shapes and sizes, such as single bullnose blocks that look like wide goggles when viewed from straight-on. The blocks can also be made with different finishes, such as a textured finish that is attractive to the touch and provides some extra slip resistance.
Hollow concrete blocks are usually gray in color, but some manufacturers make them in a range of colors. The blocks can also be coated with a baked-on glaze that adds aesthetic appeal and protection against chemical attack. The concrete mixture used to make the block may contain a variety of chemicals, called admixtures, that alter curing time or increase the strength and workability of the finished block.
While the basic concrete block remains an extremely versatile and cost-effective building material, engineers and designers continue to experiment with new designs that promise to make construction faster and more efficient while increasing the durability and energy efficiency of buildings. Developing block shapes and sizes that can accommodate more plumbing and electrical conduits is one of the main challenges, but there are other potential innovations as well.
Some block manufacturers offer a variety of lightweight versions of the basic concrete block to reduce its weight and make it easier for masons to handle and place. The lightweight blocks are made by replacing the sand and gravel with materials such as expanded clay, shale or slate. Expanded blast furnace slag and natural volcanic materials, such as pumice or scoria, are sometimes used as well.
A number of progressive block manufacturers also offer a wide variety of modifications on the basic concrete block to achieve unique visual effects or provide desirable architectural and structural features for specialized applications. For example, one manufacturer offers a block that is designed to resist the penetration of water through exterior wall surfaces. The block incorporates a special water repellent admixture to reduce the concrete’s absorption and permeability, a beveled upper edge to shed water away from the horizontal mortar joint and a series of internal grooves that direct the flow of any crack-induced leakage. The block also incorporates a low-vapor emission technology to prevent moisture from damaging the interior of the building.
