Specialist products used in a number of applications…
Building, Construction and Civil Engineering
For information on how our lime products can be used in Building, Construction and Civil Engineering, click here
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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.
Initially lime was the main material used for the production of concrete, but was replaced towards the end of the 19th Century by a superior binder known as Portland Cement. Cement had many advantages over lime-based products, being produced from a wide range of raw materials, giving much greater strength, and being more consistent than natural hydraulic limes,
However, lime still plays an important part in the following areas:
- In the drying, improvement and stabilisation of soils
- 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 a range of autoclaved calcium silicate products (including bricks, aircrete, fire resistant board and concrete).
Lime treatment for soils, often involves the use of quicklime, or slaked lime, either as powdered hydrated lime, or as milk of lime. The effect of adding lime to soils can be divided into three distinct stages; drying, modification, and stabilisation.
- Drying – occurs when quicklime is used. The quicklime hydrates, absorbing water and generating heat, which in turn causes some of the water to evaporate. Total water moisture loss can be up to double that required to hydrate the quicklime. The drying process occurs almost immediately with reactive quicklimes.
- Modification – occurs with both quick and slaked lime, which rapidly enter into the physio-chemical reactions with any clay minerals present. The resulting changes include ion exchange and can occur within 6 hours, dramatically reducing the plasticity of the soil but increasing its workability and improving its compaction characteristics.
- Stabilisation – is often a much slower, occurring overall several months it involves the reaction of lime with the siliceous and aluminous components of the soil. The addition of lime raises the pH of the soil to above 12, resulting in the formation of calcium silicates and aluminates. These are believed to form initially as gel, which coats the soil particles, and subsequently crystallises as calcium silicate/aluminate hydrates. Those hydrates are cementitious products, similar in composition to those found in cement paste. The resulting gain in strength is progressive.
After the drying and modification stages, water is added to obtain required moisture content for consolidation. The soil is then compacted to reduce the level of air voids to no more than 5%, ensuring that the stabilisation reaction proceeds in the compacted state and results in a homogenous, impermeable and stable layer. The stabilised layer has a low and acceptable shrink-swell potential, and improved compressive, tensile and flexural strengths. It also reduces the susceptibility of the stabilised layer to frost damage.
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.
Building and conservation lime
Buildings pre 1900 would not have been built with cement (with few exceptions in the late 19th century) 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. Lime mortars, 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
Singleton Birch can produce a wide range of quality construction aggregate from high-density Lincolnshire chalk. Materials can be produced to highways series 600 specifications in large volumes.