Lightweight Concrete Block

Lightweight concrete blocks are made of expanded aggregate to reduce the density and weight compared to standard concrete blocks.

Description:

A lightweight concrete block is an engineering control that may help reduce heavy lifting and carrying. The lightweight concrete block is a concrete masonry unit (CMU) made of expanded aggregate to reduce the density and weight compared to standard concrete block.  Weights vary significantly, but are less heavy than CMUs' with denser aggregates.  
 

A lightweight concrete block is a concrete masonry unit (CMU) made of expanded aggregate to reduce the density and weight compared to standard concrete block.  Weights vary significantly, but are less than when denser aggregates are used.  Where structurally feasible, lighter weight block should be used to reduce strains/loading on the masons' backs and resultant injury.  For masons laying block, back injuries commonly represent half of the cost of workers' compensation.
 
Lightweight or ultra lightweight may also be applied to a different technology known as aerated autoclaved cement (AAC) block.  AAC block entrains air/gas in the concrete and produces a much lighter block (variable density 1/2 to 2/3 weight reduction compared to standard concrete).  AAC block is most commonly used for interior walls and structures of two stories or less.  This may also be used in large panels, and has improved insulating characteristics.

Lightweight Block

Figure 1. Variety of lightweight concrete blocks 

Risks Addressed:

Heavy lifting and carrying can cause low back disorders, such as muscle strain or a disc herniation (“slipped disc”), which is bulging of disc material possibly pressing on the spinal cord or nerves that go into the leg.  The lightweight concrete blocks can help reduce heavy lifting and carrying by minimizing the weight of the concrete blocks that must be lifted and carried during brick-laying tasks. 

How Risks are Reduced:

Using lightweight concrete block reduces strain and loading on mason's backs. Risk of low back pain is related to heavy lifting. If the weight of the materials being handled is reduced, then workers' risk of developing low back pain is also reduced.

Lower weight decreases the forces exerted on the spine and other parts of the skeleton during lifting, carrying and laying the block.  Independent studies have shown a reduction in exposure to known risk factors for low back pain.  The Construction Safety Association of Ontario analyzed masonry activities to determine their potential for causing musculoskeletal disorders.  The study revealed that working with standard concrete blocks (12 x 24 x 6 inches, 35-45 pounds) can expose masons to a high risk of low back injury.  The study found that reducing the weight of the block reduced back stress (see below) . The study also showed that adding grips to the block reduced stress as well.

                 Graph: Force on back for various weights of concrete block with and without use of grips.

Figure 3: Mean low-back moment while participants lift solid concrete block. A "moment" (or torque) is defined as the tendency of a force applied to an object to cause the object to rotate, twist or bend about a point, axle or axis. The higher the moment of force, the higher the stress on the lower back.

Another study found that muscle activity was slightly lower when masons were laying lightweight block compared to standard weight block. Fatigue would be reduced by performing the same task with less muscle activity.  

There have not been independent published studies measuring the effect of using light weight block on reducing low back pain. Regardless, health and safety experts believe that masons will be less likely to develop low back problems if they are able to substitute light weight block for standard weight block due to reduced exposure to known risk factors.

Effects on Productivity:

Masons are able to lay more block in less time using lightweight block compared to standard weight block.

Additional Considerations:

Aggregates differ by region of the country, and lightweight block is not available everywhere.  The actual weight of a "lightweight" CMU can be as high as 30 lbs, so a contractor should check the weight with his supplier to get the most reduction possible.

Effective implementation of interventions such as lightweight block may be more effective if architects, engineers, and building owners are aware that by using lighter weight block there may be a decrease the risk of work-related muscle and joint problems among masons.

Contributors:

Dan Anton, PT, PhD, ATC and Alysha Meyers, PhD – University of Iowa

Hazards Addressed: