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What Is the Difference Between Lean Concrete and Flowable Concrete?

by TRP Ready Mix on March 11, 2020

Multi level concrete structure

Exploring the Key Features of Lean & Flowable Concrete

The terms lean and flowable concrete are often used interchangeably, but there are key features offered in both. To help you better understand how they differ from one another, we’ll explore the main differences and benefits that both lean and flowable concrete have to offer.

What is Lean Concrete?

Lean concrete does not contain many of the heavy, high-density rock and sand elements which are present in normal concrete. A mixture of standard concrete materials, reclaimed and crushed concrete, discarded sand, and recycled ash make lean concrete far less expensive and simple to make and use than standard concrete.

Main Uses

Lean concrete is made up of low cementitious material content. It is primarily poured through chutes, conveyor buckets, or pumps. It is used in various areas where support and strength are not critical. The mixture is highly liquid when compared to real concrete and is self-leveling, making it ideal for saving time. Its main function is to provide a uniform surface to the foundation and to prevent the direct contact with the soil. It provides a level surface to allow the placement of a main foundation and acts as a barrier for moisture or other chemicals in soil, such as sulphates which can attack concrete and weaken it.

Pros of Lean Concrete

Lean concrete is good for use under foundations. It can provide a flat bottom in uneven dirt or terrain. Because it contains a lower level of cement in it, it is mostly used for fillings or under foundations to keep them protected from the soil. It is also used to provide a level surface where main foundation can be placed. Moisture and/or other chemicals in soil, such as sulphates, can attach concrete and weaken it. Lean concrete can protect the main foundation from the soil below it. Lean concrete is recommended where quality foundation is required.

Cons of Lean Concrete

Careful preparation of lean concrete is crucial. If not applied or mixed to the proper specifications, it can crack over time. It is not suitable for projects which require more than 2 inches of sub-base or ground clearance.

What is Flowable Concrete?

Flowable concrete, which is also sometimes referred to as flowable fill, is similar in nature to the composition of lean concrete. It can be used to quickly and easily fill cavities. Its low strength and self-leveling capabilities contain strength of between 30 and 150 lbs per square inch. It may be used instead of dry fill or backfill in some construction projects.

Main Uses

The main use of flowable concrete is for sub-bases and sub footing, along with abandoned wells and cavities. It is associated with backfill projects where concrete will be removed in the near future when projects are completed. It is typically made of materials that are of a lesser quality and less durable than lean concrete, due to its more temporary nature.

Pros of Flowable Concrete

Flowable concrete can offer many benefits, such as reduced costs for labour and equipment, minimized settlement. It is also easily removable, durable, and versatile. Plus, it offers year-round availability and does not require compaction. Additionally, it is self-leveling and can be colour-coded for utility identification.

Cons of Flowable Concrete

As with lean concrete, flowable concrete also has its disadvantages. The testing of flowable fill is usually done seven days after the mix has been used. Since installation is likely to have been completed, any problem revealed during testing could be difficult to correct, since pipes have typically already been overfilled by then. Flexible pipe products can be impacted due to their dependence on the strength of pipe zone material, which carries the external loads.

Although flowable concrete is easier to place, it takes approximately two to four hours to set. This means that overfilling cannot be completed until the initial set is accomplished.

Flowable fill is also not waterproof and requires equal volumes of material on both sides of a pipe to prevent movement or extra stresses to the pipe.

Which Should You Choose

Lean concrete tends to be a longer-lasting material than flowable concrete, which is often a temporary solution. Both lean and flowable concrete can be used to fill sub-bases and sub footing as well as abandoned wells and cavities, however, flowable concrete is more associated with backfill projects in which concrete will be removed soon after the project is completed. Because it will be disposed of, it is made of cheaper and less durable materials than lean concrete.

The Deciding Factors

The nature of your project is the determining factor when it comes to selecting flowable vs. lean concrete. Having reviewed the pros and cons to both and understanding the varying aspects of the work you will be completing, the choice should be clear. Your local concrete supplier is best equipped with the knowledge to assist you in making an informed decision about the best material selection.