Knowledge

Concrete Block

Types and Sizes

Concrete masonry units (CMU) are made from a combination of cementitious materials, aggregate, admixtures, and water. Materials are mixed at the block plant, placed into molds, and vibrated. Very dry mixes are used to permit rapid mold stripping. Concrete masonry units are cured at the block plant to ensure proper hydration of cementitious materials. CMU may include pigments for color variations or integral water repellents.

Concrete masonry units are manufactured in a wide range of sizes and configurations, to be used for masonry veneers and load bearing or reinforced masonry construction. Hollow units for reinforced masonry have a standardized length of 16 inches and a height of either 4 or 8 inches. Through-the-wall thicknesses are manufactured to be 4, 6, 8, 10, or 12 inches. Actual CMU sizes are slightly less than the listed nominal sizes to account for a 3/8” mortar joint thickness.

Colors, Surface Textures

A wide range of colors and surface textures are available for architectural variation. Colors range from the standard “cement gray” to white, from tan to red to dark brown and black. Most block manufacturers will mix a pigment into the concrete mix, creating a color consistent through the entire unit thickness.

Split-face or “rock-face” units are especially popular. Other surface finishes include smooth ground-face, ribbed units, and scored units.
Contact your local supplier for availability in your area.

ASTM Requirements for Concrete Block

ASTM contains a series of specifications for different concrete masonry units. Most common is ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units, which contains requirements for strength, absorption, dimensions, and durability properties.

Concrete Block Tests

ASTM C140, Test Methods for Sampling and Testing Concrete Masonry Units, contains a series of test methods used to measure CMU strength, absorption, dimensions, and durability properties.

Specifying Concrete Block