According to a recent bulletin by the American Society of Concrete Contractors, the free fall of concrete directly over rebar or at high slumps may not reduce strength or cause segregation, as originally thought.
Published June 16, ASCC’s bulletin titled “Free Fall of Concrete” observes the results of three different free-fall tests, which cover the results of concrete hitting rebar, the effect of slump and mixing soil with concrete.
While it is common for site inspectors to dictate the maximum free fall distance of concrete, the results of the test found that it may not be necessary. According to the study, “The free fall of concrete from heights of up to 150 feet, directly over rebar or at high slumps, does not cause segregation or reduce strength.” The bulletin also states that restricting the free-fall heights does decrease concrete production and increases owner costs, without necessarily increasing the quality of the concrete.
The ASCC’s technical bulletin #3 is available to members and non-members. For more information or to order, call 1-866-788-2722 or click on the link to the right.
