Compared with the general cement used in civil and architectural engineering, special cement refers to cement varieties that have certain unique properties, apply for specific purposes, or play a special role and give buildings special functions, including characteristic cement and dedicated cement. For example, expansive cement with expansive properties, oil well cement is specially used for cementing oil and gas wells, etc.
Cement manufacturing, cement plant and cement equipment
No matter what type of cement you want, most of them require similar cement manufacturing process and cement plant. As we all know, a complete cement plant generally includes cement raw material production, clinker production, cement grinding, finished cement production, etc. Related cement equipment is selective for different needs.
- Cement raw material production: raw materials of cement should be crushed by cement crusher such as jaw crusher, cone crusher, impact crusher or mobile crushing plant into certain sizes and pre-blending, then cement mill will grind them into the raw material of cement, next, stacker and reclaimer will homogenize raw meal for preparation of cement clinker burning;
- Clinker production: to improve the working efficiency of whole clinker plant, cyclone preheater will process raw meal before feeding into cement kiln, after preheating, cement kiln will calcine raw meal into cement clinker. There is two typical cement kiln for clinker production: cement rotary kiln and shaft kiln. In this step, cement dryer and clinker cooler also paly vital roles.
- Cement grinding: the cement clinker and other materials are grounded into finished cement by cement grinding plant that is grouped by cement ball mill, cement roller press or vertical cement mill.
- Finished cement production: finally, finished cement can be packed or stored in cement silo according to real needs.
Types of special cement
By mineral content, special cement can be classified into six types, including silicate cement (also called Portland cement, except for general cement), aluminate cement, sulphoaluminate cement, iron aluminate cement, fluoraluminate cement, others (clinker-free cement, low-clinker cement).
Rapid hardening Portland cement
The early strength of rapid hardening Portland cement is high, the 1d compressive strength is 30%-35% of that of 28d, and the later strength shows a continuous growth trend. The setting time is normal, generally, the initial setting time is 2-3h, the hydration heat of cement is high, and the early dry shrinkage rate is also large.
Mainly apply for emergency repair, military engineering, and prestressed concrete parts.
The manufacturing process of rapid hardening Portland cement
- Design reasonable mineral composition;
- Properly increase the specific surface area;
- Increase the gypsum content appropriately.
Rapid hardening sulphoaluminate cement
Calcining clinker proper cement raw materials into clinker with the main mineral components of anhydrous calcium sulphoaluminate and dicalcium silicate, adding the appropriate amount of gypsum and 0-10% of limestone, grinding mixture into hydraulic cementitious materials with high early strength, called rapid sulphoaluminate cement. The labels of fast sulphoaluminate cement are expressed as 3d compressive strength, divided into 425,525,625,725.
Long-term strength is stable, even rose, good low-temperature performance, when the temperature is above – 5 ℃, the construction can be run normally without any special measures,
Mainly apply for emergency repair engineering, such as juncture, plugging, express, to repair the runway, highway, etc., suitable for winter construction engineering, underground engineering, the preparation of expansion concrete and self-stressing cement and glass fiber mortar, etc., but not suitable for environments above 100 ℃.
- Specific surface area is not lower than 350㎡/kg；
- Initial setting time is more than 25mins, and final setting time is less than 3h;
- The strength of each age should be higher than the national standard(in China).
Rapid hardening fluoraluminate cement
The main minerals of rapid hardening fluoraluminate cement include calcium fluoride aluminate, alite, belite, and calcium ferric aluminate solid solutions.
Rapid hardening fluoraluminate cement sets quickly and hardens quickly. It can be used in emergency repair works, used as jet cement for shotcvete and anchorage. Because its hydration product -ettringite is rapidly dehydrated and decomposed at high temperature, it can be used as sand cement for the foundry industry.
Rapid hardening iron aluminate cement
Rapid hardening iron aluminate cement is made from the clinker of iron phase, anhydrous sulphoaluminate, and calcium silicate, the right amount of limestone and gypsum, grinding mixture into hydraulic cementitious material high early strength.
It has advantages of high early strength, good frost resistance, good corrosion resistance, and high anti-permeability. Apply for winter construction engineering, emergency repair engineering, preparation of shotcrete and production of precast components.
By function or uses of cement, special cement includes rapid hardening cement, hydraulic engineering cement, oil well cement, decoration cement, expansive cement, white cement, colored cement, road cement, acid-resisting cement(typically include sulfate resistant cement), eco-cement, etc.
Sulfate resistant cement
The production process of sulfate resistance cement is basically similar to Portland cement manufacture, except for the clinker minerals. For sulfate-resistant cement clinker, due to the low KH value, high n value and low p-value, the formation heat of clinker are lower than that of the Portland cement clinker.
Sulfate-resistant cement has good corrosion resistance, is mainly used for sulfate-eroded seaports, water conservancy, underground, tunnels, water diversion, roads and bridge foundations.
White cement is white Portland cement, belongs to decoration cement. It is characterized by convenient use, low price, and good durability.
Refractory cement, also known as high-temperature resistant cement, is widely used in the industrial kiln lining of petroleum, metallurgy, chemical, electric power and building materials industries.
Expensive cement refers to hydraulic cementitious materials with expansibility manufactured by grinding Portland cement clinker, high aluminum cement clinker, sulphoaluminate cement clinker, and appropriate amount of gypsum and other natural or granulated blast furnace slag, such as fly ash, gypsum and other materials.