Lime (material)

Lime is a calcium-containing inorganic mineral composed primarily of oxides, and hydroxide, usually calcium oxide and/ or calcium hydroxide. It is also the name for calcium oxide which occurs as a product of coal seam fires and in altered limestone xenoliths in volcanic ejecta.[1] The word lime originates with its earliest use as building mortar and has the sense of sticking or adhering.[2]

These materials are still used in large quantities as building and engineering materials (including limestone products, cement, concrete, and mortar), as chemical feedstocks, and for sugar refining, among other uses. Lime industries and the use of many of the resulting products date from prehistoric times in both the Old World and the New World. Lime is used extensively for wastewater treatment with ferrous sulfate.

The rocks and minerals from which these materials are derived, typically limestone or chalk, are composed primarily of calcium carbonate. They may be cut, crushed, or pulverized and chemically altered. Burning (calcination) of these minerals in a lime kiln converts them into the highly caustic material burnt lime, unslaked lime or quicklime (calcium oxide) and, through subsequent addition of water, into the less caustic (but still strongly alkaline) slaked lime or hydrated lime (calcium hydroxide, Ca(OH)2), the process of which is called slaking of lime.

When the term is encountered in an agricultural context, it usually refers to agricultural lime, which is crushed limestone, not a product of a lime kiln. Otherwise it most commonly means slaked lime, as the more dangerous form is usually described more specifically as quicklime or burnt lime.

Limestone quarry
Limestone quarry in Brønnøy, Norway

Production

In the lime industry, limestone is a general term for rocks that contain 80% or more of calcium or magnesium carbonates, including marble, chalk, oolite, and marl. Further classification is by composition as high calcium, argillaceous (clayey), silicious, conglomerate, magnesian, dolomite, and other limestones.[3] Uncommon sources of lime include coral, sea shells, calcite and ankerite.

Limestone is extracted from quarries or mines. Part of the extracted stone, selected according to its chemical composition and optical granulometry, is calcinated at about 1,000 °C (1,830 °F) in different types of lime kilns to produce quicklime according to the reaction:

.

Before use, quicklime is hydrated, that is combined with water, called slaking, so hydrated lime is also known as slaked lime, and is produced according to the reaction:

.

Dry slaking is when quicklime is slaked with just enough water to hydrate the quicklime, but remain as a powder and is referred to as hydrated lime. In wet slaking, a slight excess of water is added to hydrate the quicklime to a form referred to as lime putty.

Because lime has an adhesive property with bricks and stones, it is often used as binding material in masonry works. It is also used in whitewashing as wall coat to adhere the whitewash onto the wall.

Cycle

The lime cycle
The lime cycle for high-calcium lime

The process by which limestone (calcium carbonate) is converted to quicklime by heating, then to slaked lime by hydration, and naturally reverts to calcium carbonate by carbonation is called the lime cycle.[4] The conditions and compounds present during each step of the lime cycle have a strong influence of the end product,[5] thus the complex and varied physical nature of lime products.

An example is when slaked lime (calcium hydroxide) is mixed into a thick slurry with sand and water to form mortar for building purposes. When the masonry has been laid, the slaked lime in the mortar slowly begins to react with carbon dioxide to form calcium carbonate (limestone) according to the reaction:

Ca(OH)2 + CO2 → CaCO3 + H2O.

The carbon dioxide that takes part in this reaction is principally available in the air or dissolved in rainwater[6] so pure lime mortar will not recarbonate under water or inside a thick masonry wall.

The lime cycle for dolomitic and magnesium lime is not well understood[5] but more complex because the magnesium compounds also slake to periclase which slake more slowly than calcium oxide and when hydrated produce several other compounds thus these limes contain inclusions of portlandite, brucite, magnesite, and other magnesium hydroxycarbonate compounds. These magnesium compounds have very limited, contradictory research which questions whether they "...may be significantly reactive with acid rain, which could lead to the formation of magnesium sulfate salts."[7] Magnesium sulfate salts may damage the mortar when they dry and recrystalize due to expansion of the crystals as they form which is known as sulfate attack.

Building materials

Lime used in building materials is broadly classified as "pure", "hydraulic", and "poor" lime;[8] can be natural or artificial; and may be further identified by its magnesium content such as dolomitic or magnesium lime. Uses include lime mortar, lime plaster, lime render, lime-ash floors, tabby concrete, whitewash, silicate mineral paint, and limestone blocks which may be of many types. The qualities of the many types of processed lime affect how they are used. The Romans used two types of lime mortar to make Roman concrete, which allowed them to revolutionize architecture, sometimes called the Concrete revolution.

Lime has many complex qualities as a building product including workability which includes cohesion, adhesion, air content, water content, crystal shape, board-life, spreadability, and flowability; bond strength; comprehensive strength; setting time; sand-carrying capacity; hydrolocity; free lime content; vapor permeability; flexibility; and resistance to sulfates. These qualities are affected by many factors during each step of manufacturing and installation, including the original ingredients of the source of lime; added ingredients before and during firing including inclusion of compounds from the fuel exhaust; firing temperature and duration; method of slaking including a hot mix (quicklime added to sand and water to make mortar), dry slaking and wet slaking; ratio of the mixture with aggregates and water; the sizes and types of aggregate; contaminants in the mixing water; workmanship; and rate of drying during curing.[9]

Pure lime is also known as fat, rich, common, air, slaked, slack, pickling, hydrated, and high calcium lime. It consists primarily of calcium hydroxide which is derived by slaking quicklime (calcium oxide), and may contain up to 5% of other ingredients. Pure lime sets very slowly through contact with carbon dioxide in the air and moisture; it is not a hydraulic lime so it will not set under water. Pure lime is pure white and can be used for whitewash, plaster, and mortar. Pure lime is soluble in water containing carbonic acid, a natural, weak acid which is a solution of carbon dioxide in water and acid rain so it will slowly wash away, but this characteristic also produces autogenous or self-healing process where the dissolved lime can flow into cracks in the material and be redeposited, automatically repairing the crack.

Semi-hydraulic lime, also called partially hydraulic and grey lime, sets initially with water and then continues to set with air. This lime is similar to hydraulic lime but has less soluble silica (usually minimum 6%) and aluminates, and will set under water but will never harden.[10]

Hydraulic lime is also called water lime. Hydraulic lime contains lime with silica or alumina and sets with exposure to water and can set under water.[11] Natural hydraulic lime (NHL) is made from a limestone which naturally contains some clay. Artificial hydraulic lime is made by adding forms of silica or alumina such as clay to the limestone during firing, or by adding a pozzolana to pure lime.[10] Hydraulic limes are classified by their strength: feebly, moderately and eminently hydraulic lime. Feebly hydraulic lime contains 5-10% clay, slakes in minutes, and sets in about three weeks. It is used for less expensive work and in mild climates. Moderately hydraulic lime contains 11-20% clay, slakes in one to two hours, and sets in approximately one week. It is used for better quality work and exterior walls in freezing climates. Eminently hydraulic lime contains 21-30% clay, slakes very slowly, and sets in approximately a day. It is used in harsh environments such as damp locations and near saltwater. Hydraulic lime is off-white in color. "The degree of hydraulicity of mortars will affect many characteristics. By selecting an appropriate ratio of clay to limestone mortars that carbonate or set hydraulically to a varying extents can be designed for particular application requirements such as setting time, strength, colour, durability, frost resistance, workability, speed of set in the presence of water, vapour permeability etc."[11]

Poor lime is also known as lean or meager lime. Poor lime sets and cures very slowly and has weak bonding. Poor lime is grey in color.

Magnesium lime contains more than 5% magnesium oxide (BS 6100) or 5-35% magnesium carbonate (ASTM C 59-91).[12] Dolomitic lime has a high magnesium content of 35-46% magnesium carbonate (ASTM C 59-91).[12] Dolomitic lime is named for the Dolomite Mountains in the Italian and Austrian Alps.[13]

In the United States the most commonly used masonry lime is Type S hydrated lime which is intended to be added to Portland cement to improve plasticity, water retention and other qualities. The S in type S stands for special which distinguishes it from Type N hydrated lime where the N stands for normal. The special attributes of Type S are its "...ability to develop high, early plasticity and higher water retentivity and by a limitation on its unhydrated oxide content."[14] The term Type S originated in 1946 in ASTM C 207 Hydrated Lime for Masonry Purposes. Type S lime is almost always dolomitic lime, hydrated under heat and pressure in an autoclave, and used in mortar, render, stucco, and plaster. Type S lime is not considered reliable as a pure binder in mortar due to high burning temperatures during production.

Kankar lime, a lime made from kankar which is a form of calcium carbonate.

Selenitic lime, also known as Scotts' cement after Henry Young Darracott Scott is a cement of grey chalk or similar lime, such as in the Lias Group, with about 5% added gypsum plaster (calcined gypsum).[10] Selenite is a type of gypsum, but selenitic cement may be made using any form of sulfate or sulfuric acid.[15] Sulfate arrests slaking, causes the cement to set quickly and stronger.

Roman concrete

The Romans made concrete by mixing lime and volcanic ash to create a pozzolanic reaction. If this was mixed with volcanic tuff and placed under seawater, the seawater hydrated the lime in an exothermic reaction that solidified the mixture.[16]

See also

References

  1. ^ "Lime in Handbook of Mineralogy" (PDF). Retrieved 24 April 2017.
  2. ^ "Online Etymology Dictionary". Retrieved 24 April 2017.
  3. ^ Lazell, Ellis Warren. Hydrated lime; history, manufacture and uses in plaster, mortar, concrete; a manual for the architect, engineer, contractor and builders. Pittsburgh: Jackson-Remlinger Printing Co., 1915. 21. Print.
  4. ^ "The Lime Cycle". 27 October 2011. Retrieved 24 April 2017.
  5. ^ a b Krzysztof Kudłacz, "Phase Transitions Within the Lime Cycle: Implications in Heritage Conservation" Thesis. April, 2013. University of Granada.
  6. ^ British Lime Association
  7. ^ Heather Hartshorn, "Dolomitic Lime Mortars: Carbonation Complications and Susceptibility to Acidic Sulfates" Thesis. May 2012. Columbia University
  8. ^ Rajput, R. K.. Engineering Material: (Including Construction Materials). 3rd ed. New Delhi: S. Chand & Co. Ltd. 2006. 74. Print
  9. ^ "S. Pavia and S. Caro, "Petrographic Microscope Investigation of Mortar and Ceramic Technologies for the Conservation of the Built Heritage"". Retrieved 24 April 2017.
  10. ^ a b c Heath, A. H.. A manual on lime and cement, their treatment and use in construction.. London: E. & F.N. Spon;, 1893. 6. Print.
  11. ^ a b "John W Harrison, "Carbonating and Hydraulic Mortars - the difference is not only in the binder. Aggregates are also important."" (PDF). Retrieved 24 April 2017.
  12. ^ a b Hewlett, Peter C.. Leaʼs chemistry of cement and concrete. 4. ed. Amsterdam: Elsevier Butterworth-Heinemann, 2004. 27. Print.
  13. ^ Heather Hartshorn, "Dolomitic Lime Mortars: Carbonation Complications and Susceptibility to Acidic Sulfates" Thesis 2012 Columbia University
  14. ^ ASTM C 207 quoted in Margaret L. Thomson, "Why is Type S Hydrated Lime Special?". International Building Lime Symposium 2005. Orlando, Florida, March 9 -11, 2005
  15. ^ Smith, Percy Guillemard Llewellin. Notes on building construction: arranged to meet the requirements of the syllabus of the Science & Art Department of the Committee of Council on Education, South Kensington .... 2nd ed. London: Rivingtons, 1879. Print.
  16. ^ "Roman Seawater Concrete Holds the Secret to Cutting Carbon Emissions". Berkeley Lab. Retrieved 14 June 2013.

Further reading

  • J.A.H. Oates, Projet de. Lime and Limestone – Chemistry and Technology, Production and Uses. Wiley-VCH, ISBN 3-527-29527-5 (1998)
  • US Geological Survey

External links

Biota of Tokyo Imperial Palace

The biota of Tokyo Imperial Palace grounds, especially of the Fukiage Garden, consists of enriched and distinct flora and fauna found in Tokyo, Japan. An untouched, vast open space in the middle of Tokyo hosts diverse species of wildlife which have been catalogued in field research. For comparison, this article also covers biodiversity in other open spaces in the central districts of Tokyo.

Calcium carbonate

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which is a type of sedimentary rock consisting mainly of calcite) and is the main component of pearls and the shells of marine organisms, snails, and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous.

Calcium oxide

Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "lime" connotes calcium-containing inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate. By contrast, quicklime specifically applies to the single chemical compound calcium oxide. Calcium oxide that survives processing without reacting in building products such as cement is called free lime.Quicklime is relatively inexpensive. Both it and a chemical derivative (calcium hydroxide, of which quicklime is the base anhydride) are important commodity chemicals.

External render

An external render is, in its most basic form, a coating applied to the walls of a building, to provide a protective coating which would prevent rain penetration. It also acts as a decorative finish to enhance the appearance of a building.

Lime plaster

Lime plaster is a type of plaster composed of sand, water, and lime, usually non-hydraulic hydrated lime (also known as slaked lime, high calcium lime or air lime). Ancient lime plaster often contained horse hair for reinforcement and pozzolan additives to reduce the working time.

Traditional non-hydraulic hydrated lime only sets through carbonatation when the plaster is kept moist and access of CO2 from the air is possible. It will not set when submersed in water. When a very thick layer or several layers are applied, the lime can remain soft for weeks.

The curing time of lime plaster can be shortened by using (natural) hydraulic lime or adding pozzolan additives, transforming it into artificially hydraulic lime. In ancient times, Roman lime plaster incorporated pozzolanic volcanic ash; in modern times, fly ash is preferred. Non-hydraulic lime plaster can also be made to set faster by adding gypsum.

Lime production for use in plastering home-made cisterns (in making them impermeable) was especially important in countries where rain-fall was scarce in summer. This enabled them to collect the winter run-off of rain water and to have it stored for later use, whether for personal or agricultural needs.

PPC Ltd.

PPC Ltd, a leading supplier of cement, lime (material) and related products in southern Africa, PPC has 11 cement factories and a lime manufacturing facility in six African countries including South Africa, Botswana, Democratic Republic of Congo, Ethiopia, Rwanda and Zimbabwe. The recent commissioning of PPC’s milling depot, located in Harare, Zimbabwe and new plants in the DRC and Ethiopia bring PPC’s capacity to around eleven and a half million tons of cement products each year, compared to 8 million tons in 2015.PPC’s Materials business, consisting of Pronto Holdings (including Pronto Building Materials, Ulula Ash and 3Q Mahuma Concrete), forms part of the company’s channel management strategy for southern Africa. PPC’s footprint in the readymix sector has grown to include 29 batching plants across South Africa and Mozambique and also has the capacity to produce half a million tons of fly ash. PPC also produces aggregates in South Africa and Botswana.

PPC Lime, one of the largest lime producers in the southern hemisphere, produces metallurgical-grade calcitic and dolomitic lime and sinter stone used mainly in the steel and related industries.

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