Difference between Lean concrete and Plain Cement concrete(PCC)?

Lean concrete

Lean concrete is a mix where the amount of cement is lower than the amount of liquid present in the strata.

The higher the Aggregate/cement ratio, the leaner the concrete. In lean concrete, less quantity of paste is available for providing lubrication, per unit surface of aggregate and hence the mobility of aggregate is restricted .

Lean Concrete is ‘not Rich’, in other words the ratio of cement to water and of course to aggregate would be low.

 

Casting of lean in concrete in site

 

Example

M5 GRADE OF CONCRETE → 1:5;10 (CEMENT:SAND:AGGREGATES) {5mpa}

M7.5 GRADE OF CONCRETE→1:4:8 (CEMENT:SAND:AGGREGATES) {7.5mpa}

Main purpose of lean concrete
  1. Main function of the lean concrete is to provide the uniform surface to the foundation concrete and to prevent the direct contact of foundation concrete from the soil.
  2. Lean concrete is used under the foundations. 
  3. It is good for providing a flat bottom in uneven or dirt terrain.
  4. Lean concrete has a lower level of cement in it, which is why it’s mostly used for fillings or under the foundations, to keep it protected from the soil.
  5. Lean concrete is used to provide a level surface , where main foundation (raft, isolated or any other type) can be placed.
  6. Another purpose is protection of main foundation from soil below, as moisture or other chemicals in soil like sulphates may attack concrete and can weaken it.

If you need a quality foundation and the entire structure as a whole, then use lean concrete.

Plain Cement Concrete

The mixture of cement, fine aggregate (sand) and coarse aggregate is called plain cement concrete (PCC) .

 

Casting of PCC

 

Example

M10 GRADE OF CONCRETE → 1:3:6 (CEMENT:SAND:AGGREGATES) {10 mpa}

M15 GRADE OF CONCRETE→1:2:4 (CEMENT:SAND:AGGREGATES) {15 mpa}

Main Purpose of PCC
  1. It is used as a protective layer for the RCC above so that water from the RCC is not absorbed by the earth below.
  2. Moisture available in soil should not absorbed by R.C.C footings which causes corrosion of reinforcement.
  3. PCC provides a base for the concrete and also helps workers to set out the structure above in a easier way.
  4. It provides a flat base for upcoming foundation rather than undulated base.
  5. The effective depth of RCC member is achieved as the form-works can be easily and sturdily fixed.
  6. As the Grade of concrete of PCC and Foundation is different it also provide material difference for ground bacterial effect on foundation.
  7. Act as a cover to reinforced cement concrete i.e. resist corrosion of steel bars in footings.
  8. Some time it can decrease the stresses to the soil.

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