Term: Hydraulic lime

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– Natural hydraulic lime (NHL) is produced by heating limestone naturally containing clay and impurities.
– In the United States, NHL may be called hydrated hydraulic lime (HHL) per ASTM C-141.
– Artificial hydraulic lime (AHL) becomes hydraulic by adding materials before or after burning.
– Formulated lime (FL) consists mainly of hydrated lime with added materials like Portland cement.
– Pozzolanic hydraulic lime (PHL) consists mainly of hydrated lime with pozzolans and possible inert filler.

– Hydraulic lime has a low elastic modulus.
– Buildings using hydraulic lime do not need expansion joints.
– Lime allows buildings to breathe and prevents moisture trapping.
– It has a lower firing temperature than Portland cement, consuming less energy.
– Lime re-absorbs carbon dioxide emitted during its calcination process.

Hydraulic lime concrete:
– Hydraulic lime concretes have been used since Roman times.
– Lime can be used in a variety of applications due to its versatility.
– The Pantheon in Rome is an example of the longevity of lime concrete.
– Lime mixes can be adjusted to change properties and lightness of the material.
– Lime concrete can be used for floors, vaults, and domes.

– Feebly hydraulic lime (NHL 2) is used for internal and sheltered external work.
– Moderately hydraulic lime (NHL 3.5) is suitable for most external work.
– Eminently hydraulic lime (NHL 5) is used for exposed areas like chimneys and floor slabs.
– These classifications are based on the amount of clay present in the lime.
– Properties of eminently hydraulic lime are similar to cement.

– Hydraulic limes gain strength over time, avoiding the need for expansion joints.
– They are considered more environmentally friendly than Portland cement.
– Hydraulic lime enables reclamation and reuse of building components.
– It can set under water, making it suitable for applications in contact with water bodies.
– The unique properties of hydraulic lime make it ideal for various construction applications.

Hydraulic lime (Wikipedia)

Hydraulic lime (HL) is a general term for calcium oxide, a variety of lime also called quicklime, that sets by hydration. This contrasts with calcium hydroxide, also called slaked lime or air lime that is used to make lime mortar, the other common type of lime mortar, which sets by carbonation (re-absorbing carbon dioxide (CO2) 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.

Smeaton's Eddystone Lighthouse. John Smeaton is credited with pioneering hydraulic lime in the 18th century, which led to the development of Portland cement and thus modern concrete. Painting by John Lynn.

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 reacts in the lime kiln with the clay minerals to produce silicates 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.

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