Iron and steel
In many countries, lime is used more for iron and steel making than for construction and building. Most of the lime used is for removing impurities in the basic oxygen steelmaking (BOS) process. The BOS process is now used for 70% of the worlds steel production, with the remainder being in electric arc furnaces (EAF).
Iron and steel are used extensively in the construction of roads, railways, infrastructure and buildings. Most large modern structure, such as stadiums, skyscrapers, bridges and airports, are supported by a steel skeleton. The most famous of examples include the construction of Wembley Football Stadium in London, and the Eiffel Tower in Paris.
The construction and building industry are the major use of lime products: in 1994, for example, it used 36% of the 19 million tonnes of lime sold in the European Union, compared with 38% used in iron and steelmaking.
Lime currently plays an important part in the following areas:
- In the drying, improvement and stabilisation of soils to provide a platform for heavy construction (as explained below).
- As a component of mortars, exterior rendering and interior plasters.
- As an anti-stripping agent in the production of asphalt and tarmac for road construction.
- As a binder in the productions of bricks, aircrete, fire resistant board and concrete.
Overall the use of lime provides numerous environmental benefits, as well as a superior aesthetic appeal to that of normal cheaper materials.
Although widely known as Soil Stabilisation, there are a number of distinct processes which can be carried out by the addition of quicklime to waterlogged, clay bearing or contaminated land. Improvement is the first process step, which is the drying out of water bearing material by the heat generating reaction with quicklime, this also converts some of the free water to hydrated lime. Using this process, it is possible to convert an unworkable site into a solid working platform providing a base for construction development, or alternatively as a potential area for agricultural use.
Find out more in the technical section.
Hydrated lime can be used as an additive to hot mix asphalt used for road surfacing. The addition of lime increases the resistance of the asphalt to water stripping, allowing it to maintain strength and provide good resistance to heavy stress i.e. for road surfaces prone to regular traffic or congestion. Lime also acts as a mineral filler which increases the viscosity of the binder, increasing the stiffness, tensile strength, compressive strength and resistance to water stripping.
Asphalt is currently used for the majority of road networks throughout the world. Infrastructure is often dependent on the quality of road surfaces, and without its superior materialistic properties, roads would be more hazardous and all types of vehicles would be prone to damages and accidents
Find out more in the technical section.
Aerated concrete blocks
Quicklime is mixed with cement, sand, water and aluminium powder to give a slurry which rises and sets to form honeycomb structured blocks which have excellent thermal and sound insulation properties.
The heat generated when quicklime reacts with water and the alkaline conditions combined with aluminium powder generates hydrogen bubbles which cause the blocks to rise. The heat generated subsequently causes the slurry to set. The blocks are then heated in an autoclave, which promotes reactions between calcium and silicates in the sand or PFA and gives extra strength. Dolomite lime and/or modified quicklime can be added to reduce excessive shrinkage or cracking, an issue which is increasingly useful for highly stressed materials, such as busy road junctions.
Current cement-lime mixes provide the most efficient mix in regards to possessing both good 'soft' properties as well as controlled strength. The benefits of using lime and lime-cement mortars can be divided into two categories; 'soft' and 'hard' characteristics. They are as follows:
- They have high workabilities
- Their water retentivities are very high, making them particularly suitable for use with absorptive units.
- The set times and 7 day strengths of lime-cement-sand mortars can be controlled by the amount and type of cement.
- The compressive strength of lime-cement mortars can be adjusted to the required level by the selection of the mix design.
- Incorporating lime in mortar improves adhesion and reduces rain penetration.
- The presence of lime can often increase the resistance of mortar to attack by sulphate.
- It confers the healing of cracks, which reduce the strength of the masonry unit and increase water penetration.
- Mortars containing lime absorb carbon dioxide from the atmosphere which dissolves within any water present in the mortar, and reacts with the lime to produce carbonate crystals. These crystals form in available spaces such as cracks and grow, thereby sealing the cracks. This 'self healing' characteristic reduces water penetration and increases durability.
Mortar is essential in the construction industry, without it we would have nothing to hold the bricks together that form our houses, offices and other buildings.
Internal plastering is used to cover up differences in level and to provide a surface which is suitable for the final decorative finish. The use of lime with cement nowadays provides a quick, strong and easily applied process of coating durable plaster. Other benefits are described as follows:
- The high water-retentivity of lime based plasters, coupled with their high workability, ensures a good bond to the background material.
- The ability of lime to promote the healing of cracks helps to ensure its durability by reducing water penetration.
- The high alkalinity of the plaster inhibits the growth of mould and the corrosion of iron and steel.
In general the benefits raised from the addition of lime in the plaster, far outweigh the small increase in raw material costs.
Lime concrete or "limecrete" is made by mixing controlled amounts of sand, aggregate, binder and water.
Portland Cement is normally used as the binder, although nowadays hydraulic lime or hydrated lime can also be used. This type of concrete is used all over the world, including almost every type of transport surface from roads, runways, bus and rail tracks to the construction of buildings and even large dams.
Limewash is a traditional method of painting walls with a colour base that allows the masonry to breathe, providing both protection and aesthetic appeal.
Limewash is also widely used in agricultural buildings due to its germicidal qualities coupled with its extreme ease of application and low cost.
Conservation / heritage
Buildings pre 1900 would not have been built with cement but with a lime mortar. Therefore in order to conserve these buildings it is essential to use similar materials when doing so. To introduce cement or cementitious mortar would cause decaying due to the difference in chemical composition of cement and inevitably result in irreversible damage. Hydraulic lime mortars, hydraulic lime plasters and renders and lime putty are therefore all used for the restoration of the UK and the majority of Europe's built heritage. The restoration of these buildings is often important for surrounding communities, providing them with lasting historical and cultural heritage, prolonging the buildings use as a tourist attraction, and often even increasing the aesthetic appeal of the local area.
Hydrated lime is widely used in the production of oil additives for lubricants specifically sulphonates, phenates and salicylates. The oil additives are used as detergents and improve the life of engines in cars, ships and other vehicles.