These materials are still used in large quantities in the manufacture of steel and as building and engineering materials (including limestone products,cement,concrete, andmortar), as chemical feedstocks, forsugar refining, and 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.[citation needed] Lime is used extensively forwastewater treatment withferrous sulfate.
The rocks and minerals from which these materials are derived, typicallylimestone orchalk, are composed primarily ofcalcium carbonate. They may be cut, crushed, or pulverized and chemically altered.Burning (calcination) of calcium carbonate in alime kiln above 900 °C (1,650 °F)[4] converts it into the highlycaustic and reactive materialburnt lime,unslaked lime orquicklime (calcium oxide) and, through subsequent addition of water, into the less caustic (but still stronglyalkaline)slaked lime orhydrated lime (calcium hydroxide, Ca(OH)2), the process of which is calledslaking of lime.
When the term lime is encountered in an agricultural context, it usually refers toagricultural lime, which today is usually crushed limestone, not a product of a lime kiln. Otherwise it most commonly meansslaked lime, as the more reactive form is usually described more specifically asquicklime orburnt lime.
Limestone is extracted fromquarries ormines. Part of the extracted stone, selected according to its chemical composition andoptical granulometry, iscalcinated at about 900 °C (1,650 °F) inlime kilns to produce quicklime according to the reaction:[6]
Before use,quicklime ishydrated (combined with water,slaking). Hydrated lime is also known as slaked lime, and is produced according to the reaction:
Dry slaking is slaking quicklime with just enough water to hydrate the quicklime, but to keep it as a powder; it is referred to as hydrated lime. Inwet slaking, a slightexcess of water is added to hydrate the quicklime to a form referred to as lime putty.
Lime is commonly used as a bindingmortar in masonry due to its adhesive properties with bricks and stones. It is also used in whitewashing as a wall-coat to allow the whitewash to adhere the wall.
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 thelime cycle.[7] The conditions and compounds present during each step of the lime cycle have a strong influence of the end product,[8] 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 formmortar 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[9] 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[8] and more complex because the magnesium compounds also slake topericlase which slake more slowly than calcium oxide and when hydrated produce several other compounds. Thus, these limes contain inclusions ofportlandite,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."[10] Magnesium sulfate salts may damage the mortar when they dry and recrystallize due to expansion of the crystals as they form, which is known assulfate attack.
Lime formed to piping bringing thermal water to Katlanovo spa, North Macedonia.
Lime used in building materials is broadly classified as "pure", "hydraulic", and "poor" lime;[11] can benatural orartificial; and may be further identified by its magnesium content such as dolomitic or magnesium lime. Uses includelime mortar,lime plaster,lime render,lime-ash floors,tabby concrete,whitewash,silicate mineral paint, andlimestone blocks which may be of manytypes. The qualities of the many types of processed lime affect how they are used. The Romans used two types of lime mortar to makeRoman concrete, which allowed them to revolutionize architecture, sometimes called theConcrete 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; hydraulicity; 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 withaggregates and water; the sizes and types of aggregate; contaminants in the mixing water; workmanship; and rate of drying during curing.[12]
Pure lime is also known as 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 containingcarbonic acid, a natural, weak acid which is a solution of carbon dioxide in water andacid 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 solublesilica (usually minimum 6%) andaluminates, and will set under water but will never harden.[13]
Hydraulic lime is also calledwater lime. Hydraulic lime contains lime with silica or alumina and sets with exposure to water and can set under water.[14]Natural hydraulic lime (NHL) is made from a limestone which naturally contains someclay.Artificial hydraulic lime is made by adding forms of silica or alumina such as clay to the limestone during firing, or by adding apozzolana to pure lime.[13] Hydraulic limes are classified by their strength:feebly,moderately andeminently 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 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."[14]
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).[15]Dolomitic lime has a high magnesium content of 35-46% magnesium carbonate (ASTM C 59-91).[15] Dolomitic lime is named for theDolomite Mountains in the Italian and Austrian Alps.[16]
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 improveplasticity, 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."[17] 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, andplaster. 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 afterHenry Young Darracott Scott, is a cement of grey chalk or similar lime, such as in theLias Group, with about 5% addedgypsum plaster (calcinedgypsum).[13]Selenite is a type of gypsum, but selenitic cement may be made using any form ofsulfate orsulfuric acid.[18] Sulfate arrests slaking, causes the cement to set quickly and stronger.
The Romans madeconcrete by mixing lime andvolcanic ash to create apozzolanic reaction. When this was mixed withvolcanic tuff and placed under seawater, the seawater hydrated the lime in an exothermic reaction that solidified the mixture.[19]
^Pasero, Marco; et al. (May 2022)."The New IMA List of Minerals – A Work in Progress"(PDF).The New IMA List of Minerals.IMA – CNMNC (Commission on New Minerals Nomenclature and Classification).Archived(PDF) from the original on 10 May 2022. Retrieved7 June 2022.
^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.
