Lean Concrete - Base - Mix Design - Strength - Purpose - Uses

Lean concrete mixes is a concrete mix with low cement content and high percentages of aggregates, it is used in several works such as the blinding concrete under foundations and as leveling course below footings or in mass concrete such as dams.

Lean concrete is a mixture where the amount of cement used is less than the amount of liquid present in the strata. Lean concrete is that concrete which has high aggregates to cement ratio.

In technical terms ,if the cement content of the mix falls out to be lesser than 10 percent than the mix is called as lean concrete mix.

The higher the aggregate / cement ratio, the more the concrete bends. In lean solids, less amount of paste is available to provide smoothness, aggregates per unit surface and therefore mobility of aggregates is restricted.

In India the current practices of the construction of rigid pavement require a layer of dry lean concrete abbreviated as (DLC). This course takes the work of a base course over which pavement quality concrete slabs rests.

Even the Municipal's concrete roads including white-topping are being constructed using DLC base course. DLC is mostly manufactured with ordinary Portland cement as per Indian Road Congress specification SP-49: 1998. IRC SP-49: 1998, advocates the use of Portland pozzolana cement (PPC) and portland slag cement (PSC) also in the manufacture of DLC. PPC is widely available in market all over the India, however, PPC has properties significantly different from OPC.

Purpose of Lean Concrete

· A layer of lean concrete, usually 5 to 10 cm thick, placed on soil to seal it and provide a clean and level working surface to build the foundations of a wall, or any other structure.

· An application of fine material e.g. sand, to fill voids in the surface of a pavement or earthworks layer.

·

Mix Ratio of Lean Concrete

As far as Civil construction is considered, the ratio of concrete is 1: 3: 6 (M-10) and below, which is called lean concrete.

Generally 1: 3: 6, 1: 4: 8 and 1: 5: 10 mixes are used for lean concrete mixes.

Examples:-

Grade of concrete (M-5) → 1: 5; 10 (cement: sand: aggregates)

M-5 grade concrete will give a total characteristic strength of 5 MPa.

Grade of concrete ( M-7.5 )→ 1: 4: 8 (cement: sand: aggregates)

M-7.5 grade concrete will give a total characteristic strength of 7.5 MPa.

Grade of concrete ( M-10)→ 1: 3: 6 (cement: sand: aggregates)

M-10 grade concrete will give a total characteristic strength of 10 MPa.

Advantages of lean concrete: -

• · Lean concrete provides a uniform surface to the foundation surface and prevent direct contact of the foundation concrete with the soil.
• · Lean concrete is used under the foundation.
• · It forms a solid concrete bed where the placing of steel reinforcement is easily done for the foundation works.
• · It prevents the direct contact of foundation concrete from the soil.
• · It provides the protection of the main foundation from the soil below, because moisture or other chemicals in the soil such as sulfates can attack the concrete and weaken it.

Construction Methodology

Before placing lean concrete, compact underlying surface to within 13 mm 1/2in of finish grade and elevations shown in drawings. Wet underlying material in advance of placing lean concrete to ensure a firm, moist condition at time lean concrete is placed. Do not permit equipment, other than lean concrete delivery or paving equipment on prepared underlying material. In cold weather, protect underlying material from frost. Do not use chemicals to eliminate frost.