In construction lime was well-known long ago and has been being used as an astringent for preparation of masonry and finishing mortars and of lime paints.
Common lime is manufactured by the way of moderate calcining (without bringing till boiling) of lime-magnesia soils, containing 8% of impurities maximum (clay, quartz sand etc.)
The burned lime has the name of "lump lime". I t consists of lumps of 2 - 15 sm. by size and by phase composition it is mainly a calcium oxide and in smaller dosage - magnesium oxide, partially undecomposed calcium carbonate and also has some small quantity of calcium aluminates and ferrites. Lump lime is a semi-product for production of lime astringent.
Powder-like astringents are produced of lump lime by two ways: milled quicklime is produced by fine pounding and is similar to lump lime by its' chemical and phase composition. The hydrated lime is produced by the way of slaking of lump lime by appropriate quantity of water. It consists mainly of hydrate of lime Ñà(OH)2 as well as magnesium hydroxide Mg(OH)2 and some impurities. The lime paste is produced by slaking of lump lime till forming of paste (with content of physical and adsorption-combined water of 45-50%).
In dry construction mixtures for plasters, fillings, trowellings, laying compositions the hydrated lime is used as one of mineral astringents. Technical requirements, applied to construction lime, as well as the test methods of lime astringents are regulated by GOST 9179-77 and GOST 22688-77.
Hydrated lime is qualified according to following features:
1. Content of active CaO+MgO, which is qualified by chemical method. In hydrated lime of the first grade it should be 76% min, in that of the second grade - 60% min.
2. The presence in lime of non-decomposed carbonate soils and CO2 content.
3. Humidity, which should not exceed 5%.
4. Dispersibility, sizing on sieves ¹2 and ¹ 008. The remainder on sieves should be respectively 2,5% and 15% max.
5. Absence of unevenness of volume change. The test is done on the flats, produced out of lime-cement paste by way of evaporation during two hours.
But for complete evaluation of lime quality the above-mentioned tests are not enough.
Main features of lime astringents, which determined their successful use as a part of paints, fillings and plasters, are plasticity and high water-retaining ability. Water-retaining ability of lime is 75-95% and that of portland-cement solutions is 50-60%. In GOST of construction lime there are no tests, characterizing above features. Standards of USA, England and other countries include the tests for plasticity, water-retaining ability, unevenness of volume change, by several methods, as well as the tests for lime aptitude in plasters, determination of dispersibility and so on.
This features are especially significant in compounding of CCC, where it is expedient to use such construction-technical quality of lime as sand-capacity.
In practice the high-plastic types of lime are called "greasy" and low-plastic ones are called "poor". "Greasy" types of lime have a sand-capacity of 3-4 mass parts of sand to 1 mass part of lime.
Water-requirement of water may be determined by several methods, which are based on the measurement of plastic properties of lime paste. So, according to Standard ASTMC 110-98 the water-requirement is determined as the quantity of tempering water, necessary for reaching of standard consistence. Standard consistence conforms to such plasticity of a mixture at which the slightly modified Vika pistil (P 12,5 mm) after 30 seconds from the moment of hydrate lime tempering by water sinks to a ring, filled up by paste to 20 + 5 mm.
In the old German Standard TGL 28110-03 the water-requirement of hydrate lime was determined as the quantity of water, which was necessary to insert into lime paste in order to get the spread value of 180 + 2 mm. after 15 jogs of a sample, produced in a standard conic mould for determination of a normal consistence of lime mixtures.
In order to save high plasticity of lime paste it is necessary to prevent the agglomeration of particles. It is assured by inserting of dispersants into mixtures. The high-performance dispersants of hydrated lime are sodium polyacrylates. They do the job significantly if their content in a mixture is 0.2%.
The other means of influence on stability of hydrate lime particles are the protective colloids, which depending on the length of chains may make better or worse the stability of dispersions.
The use of high-molecular types of methylcellulose (Thylose MH30000) reduces the stability of suspensions. Low-viscosity types of cellulose (Thylose MH200) do not divide particles enough effectively. The best results are achieved after use of ethers with a middle length of chains (Thylose MH4000). Its content in dispersions of hydrated lime is 0,2%.
According to Standard ASTMC 110-98, the plastisity of lime paste can be determined with the help of plastometer.
One of the important features of lime is the unevenness of volume change. After our experience, the methods of tests for unevenness of volume change according to GOST 22688 do not always allow to determine this feature. The absence of regulations for cement specifications (activity in early period of solidification, content of additives in cement and others) leads to mistaken valuation of this feature. Cement in a mixture with lime, is used for producing of samples-flats. It was not seldom that the samples of hydrate lime, testes successively according to GOST 22688 after some time of storage in air conditions revealed the
showings of unevenness of volume change (after 1 - 1,5 months). The reliable method of determination of unevenness of volume change during solidification is done in Standard ASTMC 110-98 "Bursting and Separation", according to which the mixtures of construction gypsum with lime are tested by boiling. Standard ASTMC 110-98 contains also the autoclave method of lime enlargement test.
Main functions, which the hydrate lime acts as a part of CCC together with imparting of durability to mixtures in the process of aquation and carbonization, is promoting of high plasticity and workability. Besides, hydrated lime in the process of mixing with water because of recrystallization of hydrate of lime reduces the shrinkage during solidification of mixtures in dry-air conditions. Adding of hydrated lime (2-3%) into CCC for self-aligning floor plays the part of accelerator for the formation of potassium ettringit and hexagonal aluminates, i.e neoplasms, promoting formation of durability in early period (hours after the beginning of mixing with water) and restrain the shrinkage deformation.
Main requirements to the quality of hydrated lime, used as a part of CCC, are to be as follows:
- lime must be a calcium one, have small content of magnesium oxide, because high content of MgO reduces plasticity of hydrated lime, makes worse the durability of lime coverings.
- hydrated lime must not contain particles of size 0,6 mm, because the coarse fractions make worse the quality of lime coverings and in the content of trowellings cause the scratching of facing slab and become the reason of uneveness of volume change in material.
- The content of unslaked granules of magnesium oxide and calcium oxide should not exceed 1% and 2-3% respectively, because the presence of unhydrated oxides may cause a retarded slow slaking in product as well as formation of cracks in the result of bulking.
- humidity of hydrated lime should not exceed 5% in order to prevent the caking of dry mixture.
There are several basic compoundings, containing hydrated lime.
Dry mixture for cement filling (% mass):
1. Portland cement ÏÖ500-ÄÎ - 40.0
2. Hydrated lime - 8.0
3. Quartz sand (0,1-0,3 ìì) - 49.0
Dry mixture for cement filling (% mass)
1. Portland cement ÏÖ500-ÄÎ - 40.0
2. Hydrated lime - 8.0
3. Quartz sand (0,1-0,3 mm) - 49.0
4. Roximat PAV 22 - 3.0
5. Walocell MKX15000PP25 - 0.15
Dry mixture for vertical and horizontal use (% mass):
1. Portland cement - 20.5
2. Hydrated lime - 2.5
3. Quartz sand (0,08-2 mm) - 75.0
4. Drycryl ÄÐ-2904 - 2.5
5. Aluminum sulfate - 0.5
Mixture for self-aligning floor (% mass)
1. Portland cement ÏÖ500-ÄÎ - 36.0
2. High alumina cement - 9.0
3. Hydrated lime - 4.5
6. Quartz sand (0-0,5 ìì) - 30.0
7. Lo-Wate -18.0
8. Water-retaining additive - 0.5-2.0
Filling based on lime and cement (% mass)
1. Portland cement - 10-20
2. Hydrated lime 5-10
3. Quartz sand or Lo-Wate - 70-85
- plaster for inner works - 0-0.8 ìì
- plaster for external works - 0-2.0 ìì
4. Bermokoll E411FQ - 0.04-0.16 Bermokoll CCA203 - 0.04-0.16
Mineral paint based on cement and lime (% mass):
1. Portland cement - 12-16
2. Hydrated lime - 10-20
3. Limestone flour < 0.1mm - 45-60
4. Inorganic pigment - 0.3
5. Tylose ÌÍ30000ÓÐ2 or ÌÍ6000ÓÐ2 - 0.3-0.8
6. Movilit ÄÌ2010Ð or ÄÌ1140Ð - 4-8
7. Genaool PF80P - 0.01-0.3
8. Oil wetting agent (stearates/oleates) - 0.3-0.6
9. Anti-frothing agent - 0.15-0.30
Investigation of quality of hydrated lime, produced by different manufacturers, showed that many samples of lime contain the coarsely dispersed particles of > 0.6 mm. Content of unslaked oxides reaches the level of 3-4% of MgO and 15-17% of CaO, humidity of some samples of hydrated lime can be up to 25%. Among the investigated samples of lime the best qualitiy had the lime, produced by Uglovsky lime factory and hydrated lime, produced by the way of slaking of lump lime at the factory of KZHBI 211 (Sertolovo village of Leningrad Region).
The example of phase content of hydrated lime, produced by Uglovsky lime factory ( after the results of petrography test) is as follows: main phase - Ca(OH)2; Mg(OH)2 - 4-5%; undecomposed CaCO3 - 2-3%; repeated CaCO3 - 10-12%; CaO - in the center Ca(OH)2 - äî 1%; MgO - almost absent, impurities - quartz, ferric oxides, mica, b - C2S, CA2 - S 3-4%.
Taking into consideration the important part of hydrated lime in the CCC of numerous types of functions, it is necessary to revise the working standard or to work out the standard-technical documentation for hydrated lime in the dry construction mixtures within the limits of the Union of dry construction mixtures producers and also to point out the methods of its' quality tests.