ASTM C90 is a standard specification for load-bearing concrete masonry units. According to ASTM C90, solid and hollow masonry units are defined as follows:
Solid masonry units: These are concrete blocks that are made from solid concrete and have no cores or voids. Solid masonry units are designed to provide strength and stability to masonry walls and are often used in load-bearing applications.
Hollow masonry units: These are concrete blocks that have one or more cores or voids that are not filled with mortar. The cores or voids can be arranged in various patterns, such as a single rectangular core or multiple square cores. Hollow masonry units are used in non-load-bearing applications, such as interior walls or decorative features. They are also used in load-bearing applications, where the cores or voids are filled with grout or concrete to provide additional strength and stability.