第1个回答 2024-06-28
Cement, known as "cement" in English, is a powdery hydraulic inorganic cementitious material. When mixed with water, it forms a slurry that can harden in air or water, and can firmly bond materials such as sand and stone together. Cement is an important building material, and the mortar or concrete made from cement is strong and durable, widely used in civil engineering, water conservancy, and defense projects.
The term "cement" originated from the Latin word "caementum", meaning broken stone and slab. The history of cement can be traced back to the lime and volcanic ash mixtures used in ancient Roman architecture. In 1796, the British J. Parker produced a brown cement called Roman cement or natural cement by burning marlstone. In 1824, the British J. Aspdin produced cement by burning limestone and clay, and the color of the hardened cement resembled the stone used for building on the Isle of Portland in England, named Portland cement, and obtained a patent. By the early 20th century, with the improvement of people's living standards, the requirements for architectural engineering were increasing, and a series of special cement for special architectural engineering were developed while improving Portland cement, such as high-alumina cement and special cement, and the types of cement have developed to more than 100.
The production process of cement mainly uses limestone and clay as raw materials, and the raw materials are ground into raw materials, fed into the cement kiln for calcination into clinker, and then mixed with an appropriate amount of gypsum (sometimes also mixed with admixtures or admixtures) and ground into cement. According to the use and performance, it is divided into three categories: 1. General purpose cement, used in general civil engineering projects, such as portland cement (a general term for cement with calcium silicate as the main mineral composition, internationally known as Portland cement, including ordinary portland cement, slag, volcanic ash, fly ash, and composite portland cement, etc.). 2. Special purpose cement, used for certain special projects, such as oil well cement, foundry sand cement, etc. 3. Special cement, used for engineering projects with special requirements for concrete properties, such as rapid hardening cement, hydraulic cement, sulfate-resistant cement, expansive cement, autogenous stress cement, etc. The performance of cement must meet the indicators specified in the national standard, such as fineness, setting time, stability, strength, specific gravity, hydration heat, impermeability, frost resistance, shrinkage and expansion, heat resistance, and corrosion resistance.
Cement is named according to its main hydraulic mineral, admixture, use, and main characteristics, and strives to be concise and accurate. If the name is too long, abbreviations are allowed. General purpose cement is named with the main hydraulic mineral name, mixed material name, or other appropriate name. Special purpose cement is named according to its specific use, and may be crowned with different types. Special cement is named with the main hydraulic mineral name, crowned with the main characteristics of the cement, and may be crowned with different types or mixed material names. Cement with volcanic ash or potential hydraulic materials and other active materials as the main components is named with the main component name and active material name, and may also be named with characteristic name, such as gypsum slag cement, limestone volcanic ash cement, etc.
The main types of cement include: 1. Portland cement, also known as portland cement; 2. Aluminate cement; 3. Sulfoaluminate cement; 4. Ferrite aluminate cement; 5. Fluoroaluminate cement; 6. Cement with volcanic ash or potential hydraulic materials and other active materials as the main components. Cement is classified according to the main hydraulic material name and the main technical characteristics that need to be indicated in the cement name, which can be divided into: 1. Fast setting: divided into fast setting and ultra-fast setting; 2. Hydration heat: divided into medium heat and low heat; 3. Sulfate resistance: divided into medium sulfate corrosion resistance and high sulfate corrosion resistance; 4. Expansive: divided into expansive and autogenous stress; 5. High temperature resistance: the high temperature resistance of aluminate cement is graded according to the content of alumina in the cement.
The main types of cement kilns and their functions include: 1. Rotary kiln: The kiln body is horizontally placed (with a slight slope) and can rotate, also known as rotary kiln or rotary kiln. 2. Vertical kiln: The kiln body is vertically placed and does not rotate, also known as vertical kiln.
The types and characteristics of vertical kilns used in China include: 1. Ordinary vertical kiln: manual feeding and unloading or mechanical feeding, manual unloading; 2. Mechanical vertical kiln: mechanical feeding and unloading. Mechanical vertical kilns are continuous operations, and their production, quality, and labor productivity are higher than those of ordinary vertical kilns. According to the requirements of building materials technology policy, small cement plants should use mechanized vertical kilns to gradually replace ordinary vertical kilns.
The main technical performance indicators of cement include: 1. Specific gravity and bulk density: The specific gravity of ordinary cement is 3:1, and the bulk density is usually 1300 kg/m3. 2. Fineness: Refers to the coarseness of cement particles. The finer the particles, the faster the hardening and the higher the early strength. 3. Setting time: The time from mixing cement with water to the start of setting is called initial setting time. The time from mixing cement with water to the completion of setting is called final setting time. The initial setting time of portland cement should not be earlier than 45 minutes, and the final setting time should not be later than 12 hours. 4. Strength: The strength of cement should meet the national standard. 5. Volume stability: Refers to the uniformity of volume change of cement during hardening. If there are more impurities in cement, uneven deformation will occur. 6. Hydration heat: Cement and water will produce a heat-releasing reaction when they react. The heat released during the hardening of cement is called hydration heat.
Common types of cement include: 1. Portland cement: Portland cement clinker with calcium silicate as the main component, mixed with an appropriate amount of gypsum and ground into a hydraulic cement. 2. Ordinary Portland cement: Portland cement clinker, mixed with an appropriate amount of gypsum and admixtures and ground into a hydraulic cement. 3. Slag Portland cement: Portland cement clinker, mixed with an appropriate amount of granulated blast furnace slag and gypsum and ground into a hydraulic cement. 4. Volcanic ash Portland cement: Portland cement clinker and volcanic ash materials, mixed with an appropriate amount of gypsum and ground into a hydraulic cement. 5. Fly ash Portland cement: Portland cement clinker and fly ash, mixed with an appropriate amount of gypsum and ground into a hydraulic cement. 6. Composite Portland cement: Portland cement clinker, mixed with two or more specified admixtures and an appropriate amount of gypsum and ground into a hydraulic cement. 7. Medium heat Portland cement: Portland cement clinker with appropriate composition, mixed with an appropriate amount of gypsum and ground into a hydraulic cement with medium hydration heat. 8. Low heat blast furnace slag Portland cement: Portland cement clinker with appropriate composition, mixed with an appropriate amount of gypsum and ground into a hydraulic cement with low hydration heat. 9. Rapid hardening Portland cement: Portland cement clinker mixed with an appropriate amount of gypsum and ground into a cement with high early strength, with 3-day compressive strength as the grade. 10. Sulfate resistant Portland cement: Portland cement clinker mixed with an appropriate amount of gypsum and ground into a cement with good resistance to sulfate corrosion. 11. White Portland cement: White Portland cement clinker mixed with an appropriate amount of gypsum and ground into a white cement. 12. Road Portland cement: Portland cement clinker for road construction, mixed with 0-10% active admixtures and an appropriate amount of gypsum and ground into a hydraulic cement, also known as road cement. 13. Masonry cement: Active admixtures, mixed with an appropriate amount of Portland cement clinker and gypsum, ground into a low-strength cement mainly used for masonry mortar. 14. Oil well cement: Portland cement clinker with appropriate mineral composition, mixed with an appropriate amount of gypsum and admixtures, ground into a cement suitable for oil and gas well casing engineering in certain well temperatures. 15. Gypsum slag cement: Ground cement with granulated blast furnace slag as the main component material, mixed with an appropriate amount of gypsum, Portland cement clinker, or lime and ground into a cement.
The main changes in the new and old Chinese cement standards include: 1. Adopt GB/T 17671-1999 "Cement mortar strength test method (ISO method)" instead of the current GB17