What Is the Load Bearing Capacity of Different Sized Concrete Blocks?

The Problem

• Determining the load bearing capacity of a concrete block proves more or less impossible without context. Concrete blocks come in myriad sizes, numerous shapes and contain a variety of ingredients. In addition to material considerations, the structural context of a concrete block heavily affects its load bearing capacity. To determine the load bearing capacity of a block, which can run a gamut of hundreds, if not thousands, of pounds, you must test the actual block in its context.

Structural Context

• A number of structural factors affect how much weight a concrete block can hold. For instance, weight applied to a concentrated point on a block via a support column exhibits greater stress than weight spread over a wide area. Because of this, a block used to support a column can bear less weight than the same block used to support a slab. Furthermore, blocks in a weight distribution network can support more weight than those used individually as load bearing units. For instance, a wall of blocks, particularly one reinforced with steel beams, can bear heavier loads than the sum load bearing capacity of each individual block.

Material Considerations

• The material used in the construction of a concrete block affects its load bearing capacity. For instance, a 10-by-8-by-16-inch concrete block made with stone dust may support more weight than a 15-by-12-by-24-inch block made with sand, because stone dust exhibits greater weight and strength than sand. Also, some concrete blocks exhibit holes, while others comprise solid slabs of material. A large block with large holes can bear less weight than a smaller block with no holes. A large block distributes weight over a great area, however, and potentially serves as a better means of weight distribution, despite its load bearing capacity.

Standards

• As per standards published in 2003 by ASTM, an international building standards non-profit, all concrete blocks must support at least 1,700 pounds of weight per square inch (PSI). This standard only describes minimum requirements, however. A small block may support more weight than a large block if it exhibits a high enough pounds per square inch load bearing capacity. Determining a PSI rating requires applying weight to a block until it cracks and dividing the pressure that made the block break by the total square inches in the block. This is more complicated than it seems because three-dimensional shapes, such as concrete blocks, measure in cubed, not square, units.