Lime concrete is a composite mixture of lime as binding material, sand as fine aggregate, and gravel as coarse aggregate in appropriate proportions. Lime concrete mix ratio depends on the type of construction, but in general, it can be taken up to a 1:2:3 ratio for lime, sand, and coarse aggregate, respectively.
Lime concrete had broad applications in construction before the trend of using cement as binding material got prevalent. Nowadays, lime concrete is also used as a capillary break by laying it on top of the insulation base, which is vapor permeable.
In this article, we shall discuss the proportioning, mixing, placing, and curing of lime concrete.
Lime shall be classified into two types :
- Class A – Eminently hydraulic lime used for structural purposes.
- Class B – Semi hydraulic lime used for lime concrete.
Proportioning of Lime Concrete
- The proportions of aggregate to lime mortar shall be done by volume.
- Generally, lime is prepared by mixing 100 parts of 40 mm nominal size graded stone aggregate, gravel, or brick aggregate as specified and 40 parts of lime mortar of the specified mix.
Mixing of Lime Concrete
Lime concrete shall be mixed in a mechanical mixer. In exceptional circumstances, hand mixing shall be allowed. Before mixing, brick aggregate shall be well soaked with water for a minimum period of 24 hours, and stone aggregate or gravel shall be washed with water to remove dirt, dust or any other foreign materials.
1. Machine Mixing
- Mixing shall be done by pouring the measured quantity of coarse aggregate and wet ground mortar in the mixer’s drum while it is revolving.
- The quantity of materials loaded in the drum shall not exceed the rated capacity of the mixer.
- The water shall be added gradually up to the required quantity, and the wet mixing of a batch shall be continued for at least two minutes in the drum till concrete of uniform color with uniformly distributed materials and consistency is obtained.
- The consistency of the lime concrete shall be such that the mortar does not tend to separate from the coarse aggregate.
- If there is segregation after unloading from the mixer, the concrete should be removed.
- The entire batch of concrete shall be discharged before the materials for the new batch are poured into the drum.
- Before suspending the work, the mixer shall be cleaned by revolving the drum with plenty of water each time.
2. Hand Mixing
- When hand mixing is specifically permitted, it shall be done on a clean and watertight masonry platform of sufficient size to provide adequate mixing space.
- The specified wet lime mortar shall be laid on the top of the aggregate. Turning shall be done repeatedly with the addition of the necessary quantity of water until a uniform mix of required consistency is obtained.
- The consistency of the lime concrete shall be such that the mortar shall not tend to separate from the coarse aggregate.
Placing and Compaction
- The lime concrete shall be laid in layers while it is fresh.
- Each layer of the lime concrete shall be thoroughly rammed and consolidated before the succeeding layer is placed.
- Consolidated thickness of each layer shall not exceed 15 cm. Joints where necessary shall be staggered in different layers unless otherwise specified.
- Ramming shall be done by heavy iron rammers of 4.5 kg to 5.5 kg and the area of the rammer shall not be more than 300 sq. cm.
- Ramming shall be continued till a skin of mortar covers the surface of the laid lime concrete completely.
- Concrete laid on a particular day shall be consolidated thoroughly on the same day before the work is stopped.
- Freshly laid concrete shall be protected from rains by suitable coverings.
Curing of Lime Concrete
- Once the concrete has begun to harden, i.e., about 24 hours after its placing and compaction, the curing shall be done by keeping the concrete damp with moist gunny bags, sand, or any other method for a minimum period of 7 days.
FAQs on Lime Concrete
Lime concrete is a composite mixture of lime as binding material, sand as fine aggregate, and gravel as coarse aggregate in appropriate proportions.
Lime concrete mix ratio depends on the type of construction, but in general, it can be taken up to a 1:2:3 ratio for lime, sand, and coarse aggregate, respectively.
The properties of lime concrete are-
1. Lime concrete provides good workability and has desired plasticity.
2. It prevents subsoil dampness due to a certain level of waterproofing property.
3. It resists weathering effects.
4. Bases constructed with lime concrete bears sufficient loads.
5. It needs more time for the setting.
6. It attains significantly less compressive strength at the initial stage of setting.
7. Lime concrete is environmentally friendly as it requires less energy for the production of lime and emits less carbon dioxide through the carbonation process compared to conventional Portland cement.