Information on this page is drawn from "Simple Solutions: Ergonomics for Construction Workers" published by NIOSH
The Problem
A regular concrete block (also called a concrete masonry unit, or CMU) can weigh up to 50 pounds, depending on size. For masons and mason tenders, lifting and placing CMUs can cause fatigue and put strain on the low back, hands, and arms. If you do this work often, you may be at risk of a serious muscle or joint injury.
The risk depends on how many units you handle, how heavy they are, how often you work with them, how low they are stored, and how high you have to reach to place them on the course. You have even more risk if you twist your body when lifting or holding CMUs, or if you lift or hold them with one hand.
One Solution
Use lightweight concrete block. Units weigh 30-40% less than regular block without sacrificing strength or performance. Working with lightweight block can improve your output during the day and still decrease the total weight you lift. Less weight means you will be less tired and there will be less stress on your back, hands, and arms.
Light weight Concrete Masonry Units (CMU) are made with aggregates that make it more porous. The use of light weight CMU has been shown to reduce the risk of MSDs among masons. 1
How It Works
The aggregate used for lightweight block is made from shale, clay, and/or slate. These materials are expanded in a rotary kiln at temperatures over 1000° C.
The block is structurally strong, stable, and durable, yet also light in weight and a good insulator. The block density is only 40-50 pounds per cubic foot. An ordinary block made from rock and sand has a density of regular heavy concrete block (American Society for Testing and Materials (ASTM)C 90 Standards Specifications for Load-bearing Concrete masonry Units).
Benefits for the Worker and Employer
Laying lightweight CMUs reduces a worker's fatigue and lowers stress on the back and arm muscles. One study looked at how concrete block of different weights affects muscle stress. Masons built two walls. One used lightweight CMUs and the other regular CMUs. When workers built the lightweight CMU wall, they had less back and arm muscle stress. The difference was greatest when lifting the block to the top of high walls.
There can also be a gain in productivity. According to the National Concrete Masonry Association (NCMA),
Approximate Cost
Lightweight block costs slightly more per unit than standard block. However, since masons and mason tenders can work faster and better, there should be a reduction in labor cost. This can account for up to 80% of the finished wall cost. Shipping and handling costs may be lower as well.
Resources
1 The information in this section is from "Innovations to Reduce Injuries in Masonry Workers" by Jennifer Hess and Marc Weinstein.
For More Information
- Products related to this solution are described at CPWR's Supplement to NIOSH's Simple Solutions.
- Local contractor tool and equipment suppliers or rental companies may be another source of information on products.
- For general information on this solution, check CPWR's Construction Solutions Database and eLCOSH - Electronic Library of Occupational Safety and Health. The Expanded Shale, Clay, and Slate Institute (ESCSI) in Salt Lake City, UT also has more information.
