Sulphoaluminate cement
Sulfoaluminate cement series is a new type of cement, which is mainly composed of calcium sulphoaluminate and dicalcium silicate. Developed and invented independently by China Institute of Building Materials Science.
Sulfur (iron) aluminate cement series can be used alone or mixed with ZB-type sulfur (iron) aluminate cement special admixture, which is widely used in emergency repair construction projects, prefabricated components, GRC products, low-temperature construction projects, seawater corrosion resistance projects and so on. ;
① It has the characteristics of early strength and high strength, and its 3-day strength is equivalent to the 28-day strength of portland cement with the same grade, which is suitable for emergency repair construction;
(2) Because the strength of this cement series can be rapidly developed, the application in prefabricated components can save the energy cost of steam curing;
③ The PH value of low-alkali aluminate slurry is less than 10.5, which is especially suitable for glass fiber products (GRC);
④ Good frost resistance, widely used in low-temperature construction projects in winter;
⑤ The impermeability and seawater corrosion resistance are far superior to portland cement, and it is suitable for marine construction projects;
⑥ It has excellent performance, such as being particularly effective for curing hazardous wastes, and is suitable for curing hazardous and toxic wastes.
In 1970s, China invented sulphoaluminate cement. In 1980s, the industrial production of aluminoferrite cement began. If silicate cement series products are generally called the first series cement, aluminate cement series products are generally called the second series cement. Then, we can call sulphoaluminate cement, ferric aluminate cement and other cement varieties derived from them the third series cement. The mineral composition of this series of cement is characterized by containing a large number of C4A3 minerals. This is different from other series of cement. It also constitutes the basic characteristics of the third series of cement, such as early strength, high strength, high impermeability, high frost resistance, corrosion resistance, low alkali and low production energy consumption.
Main composition of cement: The main composition is silicate. There are many kinds of cement, and the composition is different. Name and chemical formula of main components of ordinary cement: tricalcium silicate, dicalcium silicate and tricalcium aluminate: 3CaO? SiO2，2CaO？ SiO2，3CaO？ Alumina.
Cement can also be divided into many kinds according to its composition: portland cement, ordinary portland cement, slag cement, pozzolanic cement and fly ash cement. Our commonly used cement is ordinary portland cement and portland cement. Ordinary portland cement is generally used, and the weight of ordinary bags is 50kg.
In April of 20001year, the state formulated a new cement labeling standard. The new general cement standards are: GB 175- 1999 portland cement, ordinary portland cement, GB 1344- 1999 slag portland cement, pozzolanic portland cement and fly ash portland cement, and GB12958-65439. Six cement standards implement the strength grade expressed in MPa, such as 32.5, 32.5R, 42.5R, 42.5 r, etc. Therefore, the value of strength grade is the same as the lowest value of 28-day compressive strength index of cement. The new standard also plans the strength grade of cement in China. Portland cement is divided into three strength grades and six types, namely 42.5, 42.5R, 52.5, 52.5R, 62.5R and 62.5r. The other five cements are also divided into three grades and six types, namely 32.5, 32.5R, 42.5R, 52.5r and 52.5r respectively. ..
After testing, the State Building Materials Bureau concluded that the strength grade of the new cement standard and the cement grade of the old cement standard have the equivalent relationship in the following table:
GB 175-92 GB 175- 1999
725(R) 62.5(R)
625(R) 52.5(R)
525(R) 42.5(R)
425(R) 32.5(R)
Second, sand.
Sand, also called sand, is an essential material in cement mortar. If there is no sand in cement mortar, the setting strength of cement mortar is almost zero.
Sand can be divided into fine sand, medium sand and coarse sand according to specifications. Sand with a particle size of 0.25-0.35 mm is fine sand, medium sand with a particle size of 0.35-0.5 mm and coarse sand with a particle size of more than 0.5 mm. Generally, medium sand is recommended for home decoration.
Sand can be divided into sea sand, river sand and mountain sand from the source. In building decoration, the state prohibits the use of sea sand. Although the sea sand is clean, its salinity is high, which has a great influence on the engineering quality. Distinguishing whether it is sea sand mainly depends on whether the sand contains tiny shells of the sea. Because of the rough surface of mountain sand, the cement bonding effect is good, but the composition of mountain sand is complex, and most of them contain organic impurities such as soil. Therefore, it is recommended to use river sand in general decoration projects. The surface roughness of river sand is moderate, relatively clean and less impurities. Generally, the sand purchased from the market must be screened with a net before use.
Third, additives.
The purpose of cement mortar additive is to enhance its cohesiveness and elasticity. The main varieties are:
1) 107 glue (polyvinyl formal), because 107 glue contains poison and pollutes the environment, at present, some cities in China have begun to ban the continued use of 107 glue.
2) White latex (polyvinyl acetate emulsion) has better performance than 107, but its price is relatively high.
Four, the deployment of cement mortar
Generally speaking, the proportion of cement mortar in home decoration is about 1:3 (cement: sand), and the amount of water added should be determined according to the visual feeling of the site, neither too dry nor too thin. The proportion of additives shall not exceed 40%.
Verb (abbreviation of verb) red brick
Red bricks are generally made of red clay, and their colors are not exactly the same according to the soil quality in different places. Generally speaking, bricks made of red soil and cinder are stronger.
Because clay is needed to make red bricks, which will destroy farmland or natural vegetation to some extent, coupled with the problem of structural bearing, the country has now begun to ban the use of red bricks in buildings, but the author has reservations about the practice of using hollow bricks in kitchen and bathroom interior walls, because the problems caused by this are endless.
The plane of red brick is 225* 105*70mm (tolerance 5 mm).
Six, hollow brick
Hollow brick is the main wall material widely used in construction industry in recent years. Because of its advantages of light weight and low consumption of raw materials, it has become the first choice recommended by the Ministry of Construction. Like red bricks, the common raw materials of hollow bricks are clay and cinder ash, and the general specification is 240 *115 * 90 mm.
Seven, caulking agent
Color joint filler is a one-component cement-based polymer modified dry-mixed mortar. Showing off powder is usually sold in small bags in China. Although it was listed earlier abroad, it is still a new thing in China. It is durable, waterproof and compressive, and it is a substitute for ordinary joint filling material white cement. It can be used in advanced decoration projects and can fill the gaps of various stones and tiles. There are two deployment methods:
1, proper amount of water (about 5.5 ~ 6.5 liters), and fully stir until it is even and paste-free.
2. First, add water into the bucket, then slowly add the powder, and keep stirring until it is even without particles and becomes paste. Then let it stand for 5 ~ 10 minutes, and stir it a little before use.
The gap of joint sealant should not be less than 1mm, preferably1-5 mm. There is also a wide joint practice, that is, the gap is 6-12 mm.
Aluminate cement
It is a hydraulic cementing material made of bauxite and limestone by calcining to obtain clinker with calcium aluminate as the main component and alumina content of about 50%, and then grinding. Aluminate cement is often yellow or brown, and some are gray. The main mineral of aluminate cement becomes monocalcium aluminate (CaO? Aluminate such as Al2O3, abbreviated as CA), and a small amount of dicalcium silicate (2CaO? SiO2), etc.
According to the national standard (GB201-2000), the density and bulk density of aluminate cement are similar to those of ordinary portland cement. Its fineness is specific surface area ≥300m2/kg or 45μm sieve residue ≤20%. Aluminate cement is divided into four types: CA-50, CA-60, CA-70 and CA-80. The setting time and strength of each cement shall not be lower than the standard.
Aluminate cement has a rapid solidification and hardening speed. The strength of 1d can reach more than 80% of the highest strength, and it is mainly used in emergency projects, such as national defense, roads and special emergency repair projects.
Aluminate slurry has high hydration heat and concentrated heat release. The hydration heat released in 1d accounts for 70% ~ 80% of the total, which makes the internal temperature of concrete rise relatively high. Even if it is constructed at-10℃, aluminate cement can quickly set and harden, which can be used in winter construction projects.
Under ordinary hardening conditions, aluminate cement has strong sulfate corrosion resistance, because cement stone does not contain tricalcium aluminate and calcium hydroxide and has high density.
Aluminate cement has high heat resistance. If refractory coarse aggregate and fine aggregate (such as chromite, etc. ) Heat-resistant concrete with service temperature of 1300 ~ 1400℃ can be prepared.
However, the long-term strength and other properties of aluminate cement tend to decline, and the long-term strength decreases by about 40% ~ 50%. Therefore, aluminate cement is not suitable for long-term load-bearing structures and projects in high temperature and high humidity environment. It is only applicable to emergency military projects (road construction and bridge construction) and emergency repair projects (plugging, etc.). ), temporary works and preparation of heat-resistant concrete.
In addition, when aluminate cement is mixed with portland cement or lime, it not only causes flash coagulation, but also cracks or even destroys concrete due to the formation of high alkaline calcium aluminate hydrate. Therefore, it should not be mixed with lime or portland cement during construction, nor should it be used in contact with unhardened portland cement.
There are many cement production enterprises, and the technical requirements of these two kinds of cement are not high. The quality of cement is graded according to your needs. Generally, it is best to choose cement from nearby materials to save freight. In other words, where there are many developments, the cement industry is bound to flourish.