Ancient Greeks used to build buildings in the 8th century BC, and China began using lime in the 7th century BC. Lime is still a widely used building material. Lime has quicklime and slaked lime (ie slaked lime), which can be divided into calcareous lime and magnesia lime according to its magnesium oxide content (limited to 5%). Due to its wide distribution of raw materials, simple production process and low cost, in the lime slurry formed by the extensive use of quicklime in civil engineering, the lime particles form a colloidal structure of calcium hydroxide, and the particles are extremely fine (particle size is about 1 μm), specific surface area. It is very large (up to 10 ~ 30 m2 / g), its surface is adsorbed by a thick layer of water film, which can absorb a large amount of water, so it has a strong ability to retain moisture, that is, good water retention. It is blended into cement mortar and blended into a mortar to significantly improve the workability of the mortar.
Lime is hardened by dry crystallization and carbonization. Because the carbon dioxide content in the air is low, and the hard shell formed by carbonization prevents carbon dioxide from penetrating into the interior, it also prevents the water from evaporating outward, so the hardening is slow and the strength after hardening is not High, 1:3 lime mortar 28 d compressive strength is only 0.2 ~ 0.5 MPa. When in a humid environment, the moisture in the lime does not evaporate, the carbon dioxide cannot penetrate, and the hardening will stop; plus the calcium hydroxide is easily soluble in water, and the hardened lime will dissolve and dissipate in contact with water. Therefore, lime should not be used in long-term wet and water-soaked environments.
During the hardening process of lime, a large amount of water is evaporated, causing a significant shrinkage of the volume, which is prone to dry shrinkage cracks. Therefore, lime should not be used alone, generally with sand, paper ribs, hemp knives and other materials to reduce shrinkage, increase tensile strength, and save lime.
Lime has a strong basicity, and reacts with glassy active silica or activated alumina at room temperature to form a hydraulic product, resulting in cementation. Therefore, lime is an important raw material in the building materials industry.
Lime quality requirements
The cementitious component of lime is effective calcium oxide and magnesium oxide, and its content is the main indicator for evaluating the quality of lime. The content of effective calcium oxide and magnesium oxide in lime can be directly determined, and can also be reflected by the total amount of calcium oxide and magnesium oxide and the content of carbon dioxide, the requirement of raw lime and undigested residue content; the fine powder has the requirement of fineness; The hydrated lime powder also has requirements for volume stability, fineness and free water content.
The national building materials industry divides the construction of quicklime, building lime powder and architectural slaked lime powder into three grades of superior and qualified products. However, in the transportation department, JTJ 034-2000 "Technical Specifications for Highway Pavement Base Construction" still divides quicklime and slaked lime into three grades according to the original national standard (GB1594-79).
Lime application
Lime has a wide range of applications in civil engineering. The main uses are as follows:
(1) Lime milk and mortar slaked lime powder or lime paste is mixed with a large amount of paint. Lime mortar or slaked lime powder can be used to prepare lime mortar or cement-lime mixed mortar for masonry or plastering works.
(2) Lime stabilized soil The slaked lime powder or quicklime powder is mixed into various crushed or loose soils. The mixture obtained after mixing, compacting and curing is called lime stabilized soil. It includes lime soil, lime stabilized gravel soil, lime gravel soil, and the like. Lime stabilized soil has a certain strength and water resistance. It is widely used as the foundation of buildings, the cushions of the ground and the pavement base of roads.
(3) Silicate products with lime (calcium ash or quicklime powder) and siliceous materials (sand, fly ash, volcanic ash, slag, etc.) as the main raw materials, after the ingredients, mixing, molding and curing can be made of bricks , blocks and other products. Because the internal gelling substance is mainly hydrated calcium silicate, it is called silicate product, and commonly used are lime sand brick, fly ash brick and the like.
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