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 as well as lighter weight.
Manual material handling (heavy lifting)
Using lightweight concrete block reduces strain and loading on mason's backs. Risk of low back pain is related to heavy lifting. In general, muscle activity was 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. Workers lifting, carrying, and laying concrete blocks frequently suffer from low back injury. This is from a combination of fatigue or overexhaustion, repetitive lifting, twisting of the torse while lifting and working part of the timie above the shoulders or below the knees.
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.
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.
Masons are able to lay more block in less time using lightweight block compared to standard weight block.
Manufacturers of light weight aggregate report a 15-30% increase in productivity.
Health and safety experts believe reducing the risk of developing musculoskeletal disorders may lead to increased productivity because: 1) masons can lay block for longer periods with fewer breaks and less fatigue, and 2) there may be a reduction in lost time injuries.
Because of the repetitive nature of block laying it is relatively easy to calculate differences in productivity by simply measuring square feet or pallets/blocks used. As a result work sampling data is more prevalent than for less repetitive tasks.
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.
Dan Anton, PT, PhD, ATC and Alysha Meyers, PhD – University of Iowa
This solution is also referenced in: Albers, James T., and Cheryl F. Estill. Simple Solutions: Ergonomics for Construction Workers. DHHS(NIOSH) Pub. No. 2007-. http://www.cdc.gov/niosh To view other solutions in this document go to http://www.cpwr.com/simple.html. Please send requests for copies of this publication to firstname.lastname@example.org reference number 2007-122.
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