Lime (material)

Building lime is a binder that is used in the construction industry as a building material. It is used for the production of lime mortar, which is used as bricks and plaster. In the field of ground improvement in construction industry can be used for soil stabilization. Furthermore, it is added to certain types of cement in order to change its properties. Pure lime mortar in the hardened state has a lower strength than cement mortar.

When dealing with Baukalken is important to note that these materials are highly alkaline and can cause skin burns. Quicklime can lead to blindness if it gets into your eyes.

  • 4.1 setting process
  • 4.2 Baukalkprodukte

Production

Quicklime is produced from limestone (calcium carbonate), which at about 900 ° C calcined ( burnt lime ) and then deleted ( slaked lime ) is. When burning the carbon dioxide escapes and you get calcium oxide. To delete the calcium oxide is added to water, making it converts to calcium hydroxide, releasing large amounts of heat. This manufacturing process is part of the technical Kalkkreislaufes - the Wiedererhärtung of Baukalks takes place when the calcium hydroxide then again under water delivery (see " Dry Living" ) to the carbon dioxide of the air to form calcium carbonate.

Forms and naming of the lime

Quicklime was formerly usually supplied in the form of chunks ( lump lime ) and deleted on site to obtain lime paste, which was then mixed with sand. In some cases the lump lime for mortar preparation was added before the sand, should lead to better mortar properties and probably the most violent fighting reaction mitigates somewhat.

Improve the properties of the slaked lime with the time duration of the " Einsumpfens " ( slaked lime, fat lime ), which is particularly important when the lime will not be used for the preparation of mortar, but as a lime paint. This happened earlier in lime pits that were widely missing. The milk of lime must be stored during the always to soak under a water layer. Otherwise the lime would begin to react with the carbon dioxide in air. Deleted limestone ( calcium hydroxide ) are used for mortar production today, today mainly powdered, "dry" steam used. Depending on the purity of the limestone is called white lime or Graukalk or black chalk, the latter has shares in carbons, resulting in better curing. Dolomitic lime is burnt dolomite, namely high white, but magnesian.

Pure Kalkbrände be called quicklime. You can confirm with simultaneous air, because carbon dioxide in the air combines with water to carbonic acid, which is used for carbonation of the calcium hydroxide only in a humid environment.

Hydraulic curing binders are usually harder than Luftkalke.

With weak hydraulic lime hydraulic curing limestones were formerly known, which were fired below 1250 ° C from argillaceous limestone ( calcareous marl ). They harden by carbonation and hydration.

Hydraulic limes are mixtures of calcium hydroxide and so-called Hydraulefaktoren such as calcium silicates and calcium aluminates. The proportion of the hydraulic binder to harden, even under water, since no ingress of carbon dioxide is necessary. Instead, allow reactive oxides such as silicates (eg SiO2), aluminates (eg Al2O3) and iron oxides (eg Fe2O3) the hardening by hydration. To obtain a hydraulically hardening binder is lime mixed ( Trasskalke, volcanic ash or fly ash ), for example with cement (hydraulic), brick dust, blast furnace slag ( latent hydraulic) or pozzolans. The method of manufacture of hydraulic building lime from limestone and volcanic soil has been known since ancient times.

Nomenclature according to DIN

In Germany, a basic distinction is in accordance with standard Baukalken between quicklime and hydraulic lime. Luftkalke continue to be distinguished in white lime (abbreviated CL) and dolomite (abbreviation DL).

The hydraulic limes (abbreviated HL ) nor the subset of the natural hydraulic limes is added (abbreviated NHL). In the case of an admixture of the hydraulic substance pozzolan material shall be known as natural hydraulic lime with pozzolanic additives (abbreviated NHL -Z).

Lime putty versus hydrated lime

Traditional lime was stored for up to 3 years as slaked lime prior to use. Today, slaked lime is at least a few weeks, but better to soak months. Too short bearing lime putty may contain unquenched particles, which are noticeable during processing to plaster mortar or lime paint.

By to soak the plasticity of the limy improved. The reason for this is probably the altered morphology and size of the calcium hydroxide crystals.

With dry slaked hydrated lime in powder form, however, a one-day storage, water is sufficient. After that, no further change obviously occurs more.

A chemistry book explains the processes as follows: " In the quenching of fire limestones with water creates calcium hydroxide, which is in the form of a hydrogel, which is why more water is required for deletion, as is clear from the stoichiometric ratio. This hydrogel causes the hydroxide is much more reactive than the crystalline hydroxide, which is produced by evaporation of lime. The same hydroxide occurs probably when deleting quicklime with water vapor for the manufacture of hydrated lime.

Lime hydrate forms by previously soaking no hydrogel, but the slurry is improved. "

Use

Setting process

When Luftkalkmörtel is a slow setting of particular importance to ensure that a clean microcrystalline structure can form. A coated or direct sunlight on highly absorbent ground exposed lime plaster can " burn up ", ie it dries out before it has set sufficiently. Even hardened lime only at temperatures above 4 ° C clean and " freezes " in frost. In both cases, loose crystals form without bond, so that the plaster or chalk crumbles. Luftkalkmörtel is more elastic than others and mortar may be slight movements in the underground, caused for example by thermal stresses due to the swelling and shrinkage on exposure to moisture or subsidence, compensate to some extent without tearing. The strength of Luftkalkmörteln still rising slightly in the first few years. Since lime is slightly soluble in water, the binder so that fine cracks in the plaster over long time periods stored in pressurized by rain plaster facades slowly, again " grow " can. Reiner Luftkalkmörtel has been in commercial use largely replaced by mortars with additives of hydraulic limes, cement or synthetic resins, as quicklime long must be kept moist, the strength is slow to develop, and the mortar only be strengthened if the ingress of carbon dioxide is guaranteed, so that mortar has often not yet set in the interior of thick walls after years.

With the technical names of the materials shows the Kalkkreislauf in the following form:

Baukalkprodukte

Depending on the amount of water transfer is called whitewash, lime or lime sludge; These are used as a white color for the liming of walls.

Are you the fat lime, hydrated lime or sand Hydraulkalk and optionally gravel ( aggregate ), one obtains lime mortar, one of the oldest building materials in general. Slaked lime combines the grains of sand and consolidate the mass of cheap sand provides the necessary compressive strength and reduces the amount of required lime. Crushed sand from limestone is less pressure resistant than quartz sand, but the lime crystallizes directly to the successful glued surface and not only mechanically with the surcharge.

Norms and Standards

  • DIN 459-1 VEN - Building lime
  • DIN 1060 -1
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