Lean Mix Concrete- Specifications and Uses of lean mix concrete

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What is lean mix concrete?

Lean mix concrete is a mix in which the amount of cement present in the strata is lower than that of liquid. This is used as a base layer where other types of concrete are placed on the top.

Concrete with more water content is known as lean because of a lower concentration of cement compared to other kinds of paving and building materials of that class.

Lean Mix Concrete- Specifications and Uses of lean mix concrete
Lean Mix Concrete

It is mostly used between the bricks or other pieces of infrastructure as a plaster to create a tight seal. It cracks over time when it is not mixed properly or mixed to the right specifications.

In this method, less quantity of paste is available for providing lubrication, per unit surface aggregate. Hence the mobility of concrete is restricted. In lean mix concrete, the ratio of cement to water and of course aggregate would below.

Lean concrete mix ratio

M5 grade of concrete (1:5:10)

(Cement, Sand, Aggregate) => {5 mpa}

M7.5 grade of concrete (1:4:8)

(Cement, Sand, Aggregate) => {7.5 mpa}

Purposes of concrete

  1. The main function of lean mix concrete is to prevent the foundation from the direct contact of soil and to provide the same surface to the foundation concrete.
  2. It is used under foundations.
  3. It is good for providing a flat bottom in dirt terrain or uneven.
  4. It is mostly used for falling or under the foundations, to keep it protected from the soil because of the lower level of cement.
  5. It also provides a level surface, where the main foundation can be placed.
  6. Another purpose is to protect the main foundation from the soil below, as moisture or other chemicals that lie in the soil like sulfates may attack concrete and can weaken it.

Specifications

  1. M.D.D: As per trial
  2. OMC: AS per trial and 1% above during execution
  3. Cement:
  4. Ordinary Portland cement
  5. Portland pozzolana cement (PPC)
  6. Portland slag cement
  7. The minimum thickness should not be less than 150 mm
  8. Water absorption of aggregate should not be more than 3%.
  9. The maximum size of aggregate should not be more than 26.5 mm.
  10. Mineral admixtures: Fly ash, 15-30 percent or ground granulated blast furnace slag (GBFS), 25-50 percent by weight of cementitious material may be used in concrete as partial replacement of ordinary Portland cement, and in such case, the ordinary Portland cement shall not be less than 100 Kg/m3 of concrete.
  11. Mix proportion: The concrete mix shall be proportioned with a maximum aggregate cement ratio of 14:1 where OPC is used and 12:1 where PPC or PSC is used.
  12. Atmospheric temperature and finishing time: Final finishing of the same shall not exceed 90 minutes when the concrete temperature is between 25 and 300C and if less than 250 times can be up to 120 minutes.
  13. Trial length: Minimum 60 m and the full length of pavement
  14. Density: Average 97% with 200 mm dia. 3 density hole. The densities achieved at the edges i.e. 0.5 m from the edges shall not be less than 95 percent.
  15. Minimum cement content:  140 Kg/m3
  16. Concrete compressive strength: The average compressive strength of each consecutive group of five concrete cubes should not be less than 7 Mpa at 7 days. In addition, the compressive strength of any individual concrete cube shall not less than 5.5 Mpa at 7 days.

Difference between lean mix and PCC concrete

The main difference between lean mix concrete and PCC concrete is that lean mix concrete contains lea amount of cement as compared to water content which is present in it. This means, when compared to plain cement concrete, the ratio of cement to water has smaller in lean mix concrete.

Lean mix concrete is used to provide plain surface steel and maintaining slope whereas PCC is provided to act as a surface to withstand the load.

The bearing capacity of lean mix concrete is not the main thing whereas, in PCC, it enhances the bearing capacity of subgrade.

The thickness of PCC is generally more than lean mix.

Uses of lean mix concrete

  1. It is used to provide a uniform surface.
  2. It is used to fill an uneven floor to make even/smooth.
  3. It is used as a base layer where other types of concrete are placed on top.
  4. It is used to prevent direct contact of foundation concrete from the soil.

I hope this article remains helpful for you.

Happy Learning – Civil Concept

Contributed by,

Civil Engineer – Pradip Thakur

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