Quicklime is obtained by calcining natural rocks mainly containing calcium carbonate at high temperature, and its main component is calcium oxide (CaO). During calcination, due to uneven fire or temperature control, underfire lime or overfire lime is often contained. Underfire lime has a small yield, poor quality, low utilization rate, and no harm. The hydration rate of overfired lime is greatly slowed down, and hydration reaction with water occurs after hardening, resulting in a large volume expansion, causing local bulging and cracking on the surface of hardened lime, which is called "ash exploded" in engineering. . "Burning dust" is one of the common problems of construction engineering quality.
The process of the interaction of quicklime and water with quick-ripened lime (Ca(OH)2) is called slaked. In engineering, quicklime is added with a large amount of water (2 to 3 times the quality of quicklime) to slake into lime milk, then flow into the ash storage tank through a screen and "aged" for at least two weeks to eliminate the harm of overfired lime, and remove it by precipitation The paste obtained from the excess water is lime paste. It is also possible to pour a block of quicklime every half meter high with appropriate water (60% to 80% of the amount of quicklime), and the powder obtained by sintering is called slaked lime powder. The amount of water added should be slightly moistened with slaked lime powder, but not agglomerated.
Basic performance and application
Lime has good water retention and plasticity. It is often used in engineering to improve the water retention of mortar to overcome the shortcomings of poor water retention of cement mortar. Lime has a slow setting and hardening speed, low strength, and poor water resistance. Lime has a large drying shrinkage, so it should not be used alone except for painting.
The main uses of lime in construction are:
A. Lime milk paint The thin slurry obtained by adding a large amount of water to lime is called lime milk. Mainly used for indoor painting that is not demanding.
B. Mortar Lime paste or slaked lime powder can be used to make lime mortar or cement-lime mixed mortar for plastering and masonry.
C. Lime soil and clay soil The slaked lime powder and clay are called lime soil, and sand, stone chips, slag, etc. are added to form three clay. Lime soil and sandstone are widely used for foundations of buildings and cushions for roads.
D. Silicate concrete and its products use lime and siliceous materials (such as quartz sand, fly ash, slag, etc.) as the main raw materials, after grinding, batching, mixing, forming, and curing (steam curing or pressure steam curing) ) Artificial stone obtained by other processes. Commonly used silicate concrete products include various fly ash bricks, lime-sand bricks, blocks and aerated concrete that are cured by steam curing and pressure steam curing.
E. Carbonized lime board is made of ground quicklime, fibrous fillers (such as glass fiber) or lightweight aggregates added with water and stirred into a green body, and then carbon dioxide is introduced for artificial carbonization (about 12-24 hours). Lightweight board. It is suitable for non-load-bearing internal partitions, ceilings, etc.
Quicklime blocks and quicklime powder must be transported and stored under dry conditions, and should not be stored for too long. It should be kept under closed conditions for long-term storage, and should be moisture-proof and waterproof.
Lime has a wide range of applications in civil engineering, and the main uses are as follows:
(1) Lime milk and mortar Add a lot of slaked lime powder or lime paste to paint. Lime paste or slaked lime powder can be used to prepare lime mortar or cement-lime mixed mortar for masonry or plastering projects.
(2) Lime stabilized soil The mixture obtained by mixing slaked lime powder or quicklime powder into various crushed or originally loose soils, after mixing, compacting and curing, is called lime stabilized soil. It includes lime soil, lime stabilized gravel soil, lime gravel soil and so on. A small amount of active silica and alumina on the surface of the clay particles react with calcium hydroxide to generate hydraulic calcium silicate hydrate and calcium aluminate hydrate, which improves the clay's impermeability, compressive strength, and water resistance. It is widely used as the foundation of buildings, the cushion of the ground and the pavement base of roads.
(3) Silicate products use lime (slaked lime powder or quicklime powder) and siliceous materials (sand, fly ash, pozzolan, slag, etc.) as the main raw materials, and can be made into bricks after batching, mixing, molding and curing. , Blocks and other products. Because the internal gelling material is mainly hydrated calcium silicate, it is called silicate products. Commonly used are lime sand bricks and fly ash bricks.