What is Lean Concrete?

PCC in foundation

Concrete is a mixture of Cement, Sand and Coarse Aggregate mixed in water in a specified ratio. To know more about Concrete, please read our previous article What is Concrete? Basically depending upon the cement content, a concrete is decided whether it is a rich concrete or lean concrete. Concrete having ratio 1:2:4 and above, are known as rich concrete. Rich concrete is used in structural elements where strength is prime objective. Whereas concrete have ratio 1:3:6 and below, are known as lean concrete.  Here we will read about lean concrete.

Normally 1:3:6, 1:4:8 and 1:5:10 mixes are used for lean concreting. It has very low strength as compared to rich concrete but still it is very important in construction activities. Its role in building a structure is very limited but cannot be overlooked. Here are the main two reasons for which lean concrete is used.

  1. Leveling course: In Shallow foundation, leveled surface is required to erect the footings of columns. During excavation, the soil becomes undulated. Hence to provide a level surface to the foundation, lean concrete is used. Similarly for flooring also, lean concrete provides a leveled surface, upon which Tiles, Marbles, Granite, Kota Stone etc can be laid easily.
  2. Separator: It is not desirable that the foundation of a structure come in direct contact with the soil. Here lean concrete acts like a separator. A layer of 75mm or 100mm not only provides uniform surface but also separates foundation from soil.

PCC in foundation

Method of concreting:

The method of laying lean concrete is very simple. The concrete mixture is mixed in a mechanical mixture machine and laid in the foundation area over the soil. Since the cement is very low, hence for compaction iron rammers are used instead of needle vibrators.

Hence for a stable and strong foundation, lean concrete should be used invariably.

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