MindMap Gallery Air-hardening cementitious materials
Civil engineering materials - air-hardening cementitious materials, which introduce cementitious materials, lime, gypsum, sodium silicate, quartzite, etc. I hope this mind map will be helpful to you.
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This is a mind map about bacteria, and its main contents include: overview, morphology, types, structure, reproduction, distribution, application, and expansion. The summary is comprehensive and meticulous, suitable as review materials.
This is a mind map about plant asexual reproduction, and its main contents include: concept, spore reproduction, vegetative reproduction, tissue culture, and buds. The summary is comprehensive and meticulous, suitable as review materials.
This is a mind map about the reproductive development of animals, and its main contents include: insects, frogs, birds, sexual reproduction, and asexual reproduction. The summary is comprehensive and meticulous, suitable as review materials.
Air-hardening cementitious materials
cementitious material
definition
After a series of physical and chemical changes, it can solidify and harden, and the block or powdery materials can be cemented together to form a whole material.
Classification
Inorganic cementitious materials
Air-hardening cementitious materials (lime, gypsum, water glass) Lime ≠ limestone (mainly calcium carbonate)
Can only condense and harden in the air
Hydraulic cementitious materials (cement)
Can condense and harden in both air and water
Organic cementitious materials (asphalt, polymers)
lime
Lime production
Raw material CaCO3
Production process - calcination The lime production process is a limestone calcination process. According to the degree of calcination, it can be divided into underfired lime, normalized lime and overfired lime.
Types of lime
①Lumpy quicklime
②Grind quicklime powder
③Slaked lime powder
④Lime paste
⑤Milk of lime
Lime paste, hydrated lime powder, quicklime powder
Excludes limestone blocks
Ripening
The slaking process of lime: quicklime water = slaked lime
Characteristics of the aging process include the release of a large amount of heat Volume expansion 1.5-3.5 times
Lime slaking method
Lime paste is formed after quicklime is slaked with water. It cannot be used immediately to prepare masonry mortar for wall masonry.
Treatment of over-fired lime and under-fired lime
Things to note during the aging process
·Chen Fu for more than 2 weeks: →Purpose: To prevent the harm of burnt lime.
·Prevent lime carbonization:→Measures: Keep a layer of moisture on the surface of the ash tank.
hardening
hardening process
·Ca(OH)2 precipitates from the saturated solution, and the crystals are interconnected and symbiotic, thereby improving the strength.
Drying and hardening
. Ca(OH)2 reacts with CO in the air to form CaCO, which gradually increases the strength of lime.
Carbonization hardening
The hardening process includes two simultaneous processes: drying hardening (crystallization) and carbonization hardening (carbonization) (anhydrous hardening)
Carbonization hardening proceeds slowly "from the outside to the inside" → After the mortar joints of masonry mortar and plastering mortar harden, there is still uncarbonized Ca(OH)2 component.
Thinking: Why is lime mortar plastering prone to cracking, shelling, and peeling in an environment that has been exposed to moisture for a long time? Under the action of moisture in a humid environment, the uncarbonized and hardened Ca (OH)2 dissolves in water, resulting in a reduction in the strength of the structure → resulting in mortar cracking, shell jumping, peeling and other phenomena.
Technical properties and applications of lime
Lime quality grade
Construction quicklime, construction quicklime powder, and construction slaked lime powder are based on the effective CaO MgO content. It can be divided into three levels: superior product, first-class product and qualified product.
Properties of lime
1. Good plasticity;
In engineering, (lime paste) is often added to cement mortar to improve its plasticity.
2. Quicklime has strong hygroscopicity and good water retention
3. Slow hardening and low strength;
4. The volume shrinks greatly after hardening and is easy to crack.
5. Poor water resistance.
6. The characteristics of the aging process are that a large amount of heat is released, and the volume expands 1.5-3.5 times, that is, slight expansion.
7. The condensation and hardening process can only be carried out in an air environment (air-hardening cementitious materials)
Application of lime
Prepare lime mortar and lime milk; ·Prepare lime soil (slaked lime clay) and Sanhe soil (slaked lime clay sand); ·Production of carbonized lime boards;
·Production of silicate products (such as lime (slaked lime powder or quicklime powder) and siliceous materials (sand, fly ash, volcanic ash, slag, etc.) As the main raw material, various products such as bricks and blocks can be made after batching, mixing, shaping and curing);
·Reinforce the foundation.
lime storage
·Do not mix, store or transport with flammable, explosive and other dangerous liquid items.
·The storage time of quicklime should not be too long, generally no more than one month. Achieve "change as you go".
·Hydrated lime must be aged for more than two weeks before use to prevent the damage caused by burnt lime to the building.
Quicklime should be stored in a dry warehouse to protect it from water and moisture. When the storage time is long, it is best to digest it into lime paste in the ash tank, and cover the surface with a permanent film to isolate the air and prevent carbonization.
plaster
Raw materials, production and varieties of gypsum
The production of gypsum cementitious materials is usually made by calcining, dehydrating and then grinding dihydrate gypsum at a certain temperature and pressure.
·Under different calcination temperatures, the products obtained are different. The specific process is as follows:
·Building gypsum is commonly used in construction projects; high-strength gypsum is used to produce building gypsum products.
Setting and hardening of building gypsum
Condensation of building gypsum: it is a process of dissolution, reaction, precipitation and crystallization;
Gypsum hardening: It is the formation process of the crystal structure network between the dihydrate gypsum crystals.
(Crystals intersect with each other to form a network structure; as the reaction continues, The crystal structure network gradually becomes denser, causing the gypsum crystals to gradually harden. )
Technical requirements for building gypsum
Properties and applications of gypsum
Technical properties of construction gypsum
·Condensation and hardening quickly;
The volume expands slightly during condensation;
·Large porosity→low apparent density and low strength; Low thermal conductivity, good thermal insulation performance, and good sound absorption performance; Strong hygroscopicity, poor water resistance and frost resistance; generally not used for outdoor decoration
·Has good fire resistance
9. The reason why gypsum products have good fire resistance is ().
Gypsum products have high porosity
The large amount of crystal water contained in it can absorb a large amount of heat during the evaporation process
CaSO4·2H20 dehydrates during fire and forms a water film on the surface
Good processability.
Application of Gypsum
·Indoor plastering and painting;
·Production of construction gypsum products;
·Added to cement as a retarder during cement production.
Gypsum products can be used for ().
Interior wall insulation materials, non-load-bearing partition panels, ceiling materials, perforated veneer panels for theaters and lecture halls
The strength of ordinary building gypsum is low. This is because the amount of water added when preparing the slurry during the construction process is (much larger than) the theoretical amount of water added. The evaporation of excess water leads to the formation of a large number of capillary pores inside.
water glass
Production of water glass
Silicate modulus of water glass
·The modulus n of water glass: refers to the ratio of the number of molecules of silicon oxide and sodium oxide in sodium silicate (Na, OnSiOz), which is generally between 1.5 and 3.5.
Formulate heat-resistant concrete or serve as a setting accelerator for cement
n=3.3~3.5 is appropriate
for foundation grouting
n=2.6~2.8 is appropriate
For painting material surfaces
n-2.7~3.0 is appropriate
hardening of water glass
Liquid water glass absorbs carbon dioxide in the air to form an amorphous silicate gel, which gradually dries and hardens. The specific reaction formula is as follows:
In order to accelerate the hardening of water glass, it can be heated or mixed with 13% to 15% of the hardening accelerator sodium fluorosilicate.
Properties and applications of water glass
Properties of water glass
① Strong adhesion ② Good acid resistance ③ Good heat resistance
Application of water glass
①·Brush or impregnate the material to improve its weather resistance (but it is prohibited to use it on the surface of gypsum products);
②·Prepare heat-resistant mortar and heat-resistant concrete;
③·Prepare acid-resistant mortar and acid-resistant concrete;
④·Prepare waterproofing agent for repairing cracks and plugging leaks;
⑤·Calcium chloride strengthens the foundation. Na0· nSi02 CaCl2 .xHl,O= 2NaC1 nSi0(x—1)H.O Ca(OH),
Water glass can be used to paint the surface to improve its water resistance.
Cement concrete, clay bricks, silicate products, stone
Rhododendron
Magnesium bicarbonate is produced by calcining magnesium bicarbonate at high temperature, and its composition is magnesium oxide.
Directly add water and mix: Mg(OH) is generated, → loose and has no cementing ability. Add magnesium chloride solution and mix: it will coagulate and harden quickly, and the strength of the reaction product after hardening can reach 40~60MPa. (In engineering, two magnesium compounds, magnesium oxide and magnesium chloride, are sometimes used as the main raw materials to produce cement, which is called "magnesium oxychloride cement", also known as "double magnesium cement")
The hydration and hardening product of Lingkushi has poor gelling properties, but its strength is higher after being mixed and hardened with magnesium chloride aqueous solution.
The hardening process of caltropite will produce micro-volume expansion; after hardening, it becomes weakly alkaline, has a certain strength, strong hygroscopicity, and poor water resistance; it has a corrosive effect on steel bars.