Lean concrete and flowable concrete are terms used to describe low-grade concrete slurry that is used in a variety of construction projects. In some ways the two terms are interchangeable, both describing concrete made with lesser ingredients, but there are some differences in how the two are used. Lean concrete tends to be more long-lasting than flowable concrete, which is often temporary.
Lean concrete is made with low cementitious material content. This means that it does not have many of the heavy, high-density rock and sand elements that normal concrete has. Instead, it can use a mixture of standard concrete materials, reclaimed and crushed concrete, discarded sand and recycled ash. This makes lean concrete very cheap in nature and simple to make and use.
Lean concrete is primarily poured through chutes, conveyors buckets or pumps. It is used primarily in areas where support and strength are not critical. Contractors may simply need to fill the areas for appearance or continuity. This can help reduce costs for overall construction projects. The mixture is also highly liquid compared to real concrete and is self-leveling, two features that make it ideal for saving time.
Flowable concrete, or flowable fill, is similar in composition to lean concrete. It is a type of slurry that can be used to quickly and easily fill cavities. It has low strength and self-leveling capabilities, with a late-age strength of between 30 and 150 pounds per square inch. It may be used instead of dry fill or backfill in some construction projects.
Like lean concrete, flowable concrete or flowable fill is used for sub-bases and subfooting as well as abandoned wells and cavities. But flowable concrete is more associated with backfill projects where the concrete will be removed in several months when projects are completed. Because it will be taken away, it may be made of cheaper and less durable materials than lean concrete.