PREPARATION AND PROPERTIES OF LIME CONCRETE
Manufacturing of lime
Lime is usually manufactured by burning limestone, in the process driving off carbon dioxide leaving the clinker of calcium oxide and quick lime. When quick lime is slaked with water, it disintegrates into fine grained powder depending on the volume of water added. The pure slaked lime formed in this way is said to be as fat lime. It can be used for construction of masonry but it hardens quickly in air. Masonry buildings that were built in the past by with fat lime are now demolished as there strength is very less than the strength when lime concrete was placed.
Hydraulic lime is one of the advanced form of fat lime. It is manufactured by addition of fat lime with surkhi (clay rich in silicates).Hydraulic lime can be made into satisfactorily mortar that achieves strength similar to that of cement mortar.
Lime concrete is 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 1:2 ratio for lime, sand respectively and up to 1:3 ratio for lime, coarse aggregate respectively.
Lime concrete had wide applications in construction before the trend of using cement as binding material. Now-a-days Lime concrete is also used as a capillary break by laying on top of insulation base which is vapor permeable.
Preparation of lime concrete
The main ingredient of this concrete is slaked lime as binding material. The slaked lime is obtained in various forms as hydrated lime powder, lime putty, slaked lime slurry that is prepared by grinding in suitable Grinding Mills. Slaked lime is first mixed with sand to prepare lime mortar which is then further mixed with coarse aggregates, in suitable proportion. For preparation of lime concrete, first hard impervious level base is prepared by stones or brick pitching.
Then quantity of sand is spread as the horizontal base. Generally lime & sand are taken in ratio of 1:1 to 1:3 by volume. Measured quantity of slaked lime is then added to sand and then mixing is done. In this mixing, water is sprinkled continuously to make the whole mass plastic.
Then the whole mass is allowed to mature for 1 to 3 days. After that coarse aggregates of desired type are used to lay on the prepared hard impervious level surface. After that lime mortar which is made with sand & lime is introduced into the base. Sufficient water is sprinkled over the base and it is cut into the layers and then is turned upside down with the help of spade or shovel until the whole assembly has become uniform.
Properties of Lime Concrete
- Lime concrete provides good workability and has desired plasticity.
- It prevents subsoil dampness due to certain level of waterproofing property.
- It resists weathering effects.
- Bases constructed with lime concrete bears sufficient loads.
- It needs more time for setting.
- It attains very less compressive strength at the initial stage of setting.
- Lime is cheaper and available easily.
- Lime concrete is environment-friendly as it requires less energy for production of lime and emits less carbon dioxide through carbonation process compared to conventional Portland cement.
Drawbacks of Lime concrete
- Hydraulic lime usually gains strength in time greater than the time in which cement concrete gains same value of strength.
- Lime cement takes a long time to cure, and while the ancient world had lots of time, today time is money.
- Lime cement does not harden in water but stays soft. So there are situations where it cannot be used.
Uses and precautions
- Lime concrete is very widely used for foundation bases of load bearing walls, columns, and under layers of floors.
- Due to its flexibility it adjusts very well with the underneath base ground and upper construction of cement base.
- For better quality of lime concrete it is important to compact & cure concrete properly. Lime causes rashes on human skin so the persons which are dealing lime concrete should be provided with suitable rubber gloves.
- Persons should use oil on their skin to avoid rashes and cracking of their skin due to reaction of lime.
- To achieve good quality lime concrete, certain admixtures, fibers etc can be used