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close this book Small Scale Production of Lime for Building
close this folder 1. General Information
View the document 1.1 Geological description of limestone
View the document 1.2 Chemical composition of limestone
View the document 1.3 Physical characteristics of limestone
View the document 1.4 Classification of limestone
View the document 1.5 Chemical reactions in the production of lime
View the document 1.6 Common uses of lime in developing countries

1.6 Common uses of lime in developing countries

1.6.1 Use of lime in building construction

1.6.2 Soil stabilization in road construction

1.6.3 Lime in agriculture

1.6.1 Use of lime in building construction

Lime is used in buildings in one of two forms, either as dry slaked lime powder or as putty. The choice of whether to use one or the other form depends on the preference of the builders, the availability of water at the production site and the available means of transport. There is little difference in terms of quality between the two.

The properties which make lime an excellent cementitious building material are the shape and fineness of the particles, which provide the plasticity necessary for a good workable mortar or plaster, and its chemical properties which are the mechanical, strength giving characteristics.

Historically, lime was used for building in such places as ancient China and Greece and, although since the discovery of portland cement its relative use has decreased. it is used in mortars and plasters in combination with cement in most countries of the world.

Good mixing proportions are:

lime

cement

sand

1

1

6

1

2

9

The first mix is used where greater strength and resistance to weather are required and the second where these properties are unnecessary.

In situations where the sand to be used is very fine and/or not well graded, a mix of 1:1:7 can be used. Where the use of cement is limited in one way or another a small proportion of cement will suffice or none need be used at all. The use of such mortars or plasters is however limited since they are susceptible to weathering. They are best used on internal walls, external walls which are well protected from the rain, and in dry climates. The mix suitable under such circumstances is 1:2/3, i. e. 1 part lime to 2 or 3 parts sand. The same mix proportions are used for mortars and plasters. Special care must be taken where the' lime is of low quality (relatively low hydroxide content) and the sand badly graded and fine.

Limewash as an external and sometimes internal wall coating is used in many countries today. Its advantages are that it is relatively cheap, easy to apply and gives a clean white finish, whilst its disadvantage is that it rubs off easily.

The durability of limewashes can be improved by adding small amounts of common salts or stearates. The recipes given by Bessey are:

"Quicklime

1 kg

Tallow

60 g

Water

2.5 Iitres"

Quicklime is broken into small lumps and tallow is placed in shreds over it. Enough water is then added to slake the quicklime. Once slaking is complete the remaining water is added and then the slurry is screened to remove any lumps and remaining shreds of tallow.

If only hydrated lime is available, powdered calcium stearate and water are added to it to produce a slurry. The recipe is:

"Hydrated lim

1 kg

powdered calcium stearate

50 g

Water as required"

 

Lime in combination with pozzolanic material can be used as an alternative cementitious material to portland cement. This type of cement can be used successfully for most purposes other than structural concrete work, i.e. in plaster, mortar, production of building blocks, screeds etc. Some types of pozzolanic materials are: pulverized fuel ash, blastfurnace slag, volcanic ash, diatomatious earth, under-fired clay bricks, porcellanite and others. Each has a particular form in which it is most effective as a pozzolana.

1.6.2 Soil stabilization in road construction

The construction of roads in tropical and sub-tropical regions in areas where the soil is clay or laterite will require the use of a soil stabilizer. Lime, like portland cement, reacts chemically with certain constituents of the clay and acts as a binder. The effectiveness of lime as a soil stabilizer is increased in warm climates where its rate of strength development will be faster than in cooler areas. 2 - 5 % hydrated lime is mixed with soil from the road and spread over the road surface for compaction. The quantities required will depend on the compaction density, width and thickness of sub-base or base designed, and also on the proportion of available lime in the lime hydrate. For a road 11 m wide, sub-base 200 mm thick and a compaction density of 1500 kg/m3, where 4 % lime is to be added, 130 tonnes lime per kilometer of road will be required.

For an existing limework with a low output (up to 15 tonnes), the implications of such a demand are:

-A long period of warning will be required to develop stockpiles, the development of which will require special financing arrangements since the stockpiling will cause excessive strain on cashflow.

- The accent will be placed on the quantity rather than the quality produced. It should be noted however, that the higher the quality the lower the quantities of lime required. The economic effects on transport cost, sales prices, etc. need to be carefully considered.

-A dry hydrate needs to be produced.

The possibility of installing a small limeworks near the road works, if possible in a situation where its operation will be continued after the completion of the road, must be considered as it may be more economic than transporting large quantities over long distances.

1.6.3 Lime in agriculture

Lime and limestone are used in agriculture to neutralize the acidity of the soil and to promote effective use of added fertilizers. Crushed limestone, dolomite, chalk, etc. are preferred as they are slower acting than lime and therefore last longer.

Other uses are:

-water purification,

-sugar refining,

-tanning,

-neutralizing acid mine water,

-oil well drilling,

-wire drawing,

-paper and pulp production,

-sewage treatment,

-metallurgical processing,

-petroleum refining,

-calcium silicate brick production,

-pains production

and others.