Hydraulic lime (HL) is a general term for
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 ...
, a variety of
lime
Lime commonly refers to:
* Lime (fruit), a green citrus fruit
* Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide
* Lime (color), a color between yellow and green
Lime may also refer to:
Botany ...
also called quicklime, that sets by
hydration Hydration may refer to:
* Hydrate, a substance that contains water
* Hydration enthalpy, energy released through hydrating a substance
* Hydration reaction, a chemical addition reaction where a hydroxyl group and proton are added to a compound
* ...
. This contrasts with
calcium hydroxide, also called slaked lime or air lime that is used to make
lime mortar
Lime mortar or torching is composed of lime and an aggregate such as sand, mixed with water. The ancient Egyptians were the first to use lime mortars, which they used to plaster their temples. In addition, the Egyptians also incorporated various ...
, the other common type of lime mortar, which sets by
carbonation
Carbonation is the chemical reaction of carbon dioxide to give carbonates, bicarbonates, and carbonic acid. In chemistry, the term is sometimes used in place of carboxylation, which refers to the formation of carboxylic acids.
In inorganic ch ...
(re-absorbing carbon dioxide (CO
2) from the air). Hydraulic lime provides a faster initial set and higher compressive strength than air lime, and hydraulic lime will set in more extreme conditions, including under water.
The terms 'hydraulic lime' and 'hydrated lime' are quite similar and may be confused but are not necessarily the same material. Hydrated lime is any lime which has been slaked whether it sets through hydration, carbonation, or both.
Calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
reacts in the lime kiln with the clay minerals to produce
silicates
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name i ...
that enable some of the lime to set through hydration. Any unreacted calcium is slaked to
calcium hydroxide which sets through carbonation. These are sometimes called 'semi-hydraulic lime' and include the classifications feebly and moderately hydraulic lime, NHL 2 and NHL 3.5.
Types
There are two basic types of hydraulic limes:
Natural hydraulic lime (NHL)
Natural hydraulic lime (NHL) is produced by heating (calcining)
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
that naturally contains
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
and other impurities: no materials may be added to create the hydraulicity. In the United States NHL may be called 'hydrated hydraulic lime' (HHL) per ASTM C-141 Standard Specification for Hydrated Hydraulic Lime for Structural Purposes.
[Michel Couvreux, "Selecting A Natural Hydraulic Lime: What To Look For" ''The Last Straw'' No. 62, Spring 2014. 8-10. Print.]
/ref>
Artificial hydraulic lime (AHL)
Artificial hydraulic lime (AHL) or artificial lime (AL) becomes hydraulic when hydraulic and/or pozzolan
Pozzolans are a broad class of siliceous and aluminous materials which, in themselves, possess little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide (Ca(OH)2) ...
materials are added either before or after burning in a lime kiln. Artificial limes are more specifically identified as 'hydraulic lime' (HL), as defined European Norm
European, or Europeans, or Europeneans, may refer to:
In general
* ''European'', an adjective referring to something of, from, or related to Europe
** Ethnic groups in Europe
** Demographics of Europe
** European cuisine, the cuisines of Europe a ...
459 (EN-459), "Consists of lime and other materials such as Portland cement
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th c ...
, blast furnace slag, fly ash, limestone filler and other suitable materials."; 'formulated lime' (FL) (EN-459) consists of "...mainly of hydrated lime and or NHL with added hydraulic and/or pozzolanic material. It is identical to HL but its composition must be declared on the CE marking.". 'Pozzolanic hydraulic lime' (PHL) (ASTM C-1707)is "very similar to HL or FL. Consists mainly of hydrated lime with one or more pozzolans with possible inclusion of inert filler. When Portland cement, even traces, is present (can be up to 20% of binder weight), it has to be labeled as 'PHLc'."
Characteristics
Hydraulic lime is a useful building material for the following reasons:
* It has a low elastic modulus
An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is ...
.
* There is no need for expansion (movement) joints.
* It allows buildings to "breathe", and does not trap moisture in the walls.
* It has a lower firing temperature than Portland cement
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th c ...
, and thus manufactured consuming less energy.
* Stone and brickwork bonded with lime is easier to re-use.
* Lime acts sacrificially in that it is weaker and breaks down more readily than the masonry, thus saving weaker stone such as sandstone and limestone from the harmful effects of temperature expansion and mortar freeze.
* It is less dense than cement, thus less cold bridging.
* Lime re-absorbs the carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
(CO2) emitted by its calcination (firing in a kiln), thus partially offsetting the large amount emitted during its manufacture. The more hydraulic a lime, the less CO2 is reabsorbed during set, for example, 50% of CO2 is reabsorbed by NHL 3.5 during the set, compared to 100% of CO2 being reabsorbed by pure calcium hydroxide (fat lime putty).
Hydraulic lime concrete
Hydraulic lime concretes have been in use since Roman times, either as mass foundation concretes or as lightweight concretes using tufa
Tufa is a variety of limestone formed when carbonate minerals precipitate out of water in unheated rivers or lakes. Geothermally heated hot springs sometimes produce similar (but less porous) carbonate deposits, which are known as travertine. ...
or pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...
as aggregates and a wide range of pozzolans to achieve different strengths and speeds of set. This meant that lime could be used in a wide variety of applications including floors and even vaults or domes. An example is the Pantheon
Pantheon may refer to:
* Pantheon (religion), a set of gods belonging to a particular religion or tradition, and a temple or sacred building
Arts and entertainment Comics
*Pantheon (Marvel Comics), a fictional organization
* ''Pantheon'' (Lone S ...
in Rome, which has survived for nearly two thousand years. The dome's diameter is equal to its height from the floor. It is constructed from six different lime mixes, which change the properties and lightness of the material.
Classification
Natural hydraulic lime (NHL) is classified for different uses the first two of which are sometimes called semi-hydraulic lime because they initially set with water but continue to set in contact with carbon dioxide in the air.
Feebly hydraulic lime
Feebly hydraulic lime (NHL 2) is used for internal work and external work in sheltered areas.
Feebly hydraulic lime contains up to 10% clay / clay mixed with other impurities. It might take one week or more to set after the addition of water. Setting is the process of permanently taking the shape into which lime has been moulded.
Moderately hydraulic lime
Moderately hydraulic lime (NHL 3.5) can be used for external work in most areas.
Moderately hydraulic lime contains clay in the range of 11% to 20%. This type of lime sets (assumes given shape) within a few days after the addition of water.
Eminently hydraulic lime
Eminently hydraulic lime (NHL 5) is used for external work in exposed areas, such as chimneys and for floor slabs/underpinning.
Eminently hydraulic lime contains clay in the range of 21% to 30%. Properties of eminently hydraulic lime are close to those of cement. Eminently hydraulic lime sets within one day after the addition of water.
Benefits
* Hydraulic limes gain strength over time hence providing flexibility and avoiding the need for expansion joints.
* Considered to be more environmentally friendly than portland cement as they are burnt at a lower temperature and uniquely re-absorb some of the carbon dioxide given off during burning as they cure/carbonate in/on the wall.
* Enable building components to be reclaimed and reused as they are 'softer' than cement.
* Set under water hence making them ideal for applications in contact with the sea, canals, rivers etc.
See also
*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 ...
*Lime mortar
Lime mortar or torching is composed of lime and an aggregate such as sand, mixed with water. The ancient Egyptians were the first to use lime mortars, which they used to plaster their temples. In addition, the Egyptians also incorporated various ...
*Hempcrete
Hempcrete or hemplime is biocomposite material, a mixture of hemp hurds ( shives) and lime, sand, or pozzolans, which is used as a material for construction and insulation. It is marketed under names like Hempcrete, Canobiote, Canosmose, Isochan ...
References
{{Reflist
External links
The Technology and Use of Hydraulic Lime, by John Ashurst
The National Lime Association (US & Canada)
How to use hydraulic lime and PDF application fact sheets
The Scottish Lime Centre
Building materials