An assistant engineer from a new construction materials company in a second- and third-tier city has summarized some notes about her career change in January, which can help everyone understand this industry. I also ask for your advice. .
1. What is ready-mixed concrete? What is the main raw material composition? How is the rebound of concrete determined?
It is produced in the mixing station and sent to the place of use through the conveying equipment. Concrete is supplied as a mix.
The main raw materials of concrete include concrete, large and small asphalt mixtures (gravel, river pebbles, sand), water, admixtures and mineral admixtures (coal ash, mineral powder)
Concrete rebound levels are divided into C10, C15, C20, C25, C30, C35, C40, C45, C50, C55, C60, C65, C70, C75, C80, C85, C90, C95, C100
2. What are the basic properties of concrete?
(1) Characteristics of concrete mixtures: fluidity, cohesion, water solubility, bulk density, air content
(2) Characteristics of hardened concrete: physical properties, volumetric reliability, usability, thermal properties
3. What are the compressive strengths of concrete?
Concrete compressive strength, concrete water Ash ratio, quality of other constituent raw materials, construction methods, maintenance methods, experimental methods, etc.
11. What are the commonly used admixtures for concrete? What are the common admixtures for concrete at this stage?
Commonly used admixtures:
(1) Pumping agent: In pumping concrete, it can significantly improve the adhesion and cohesion of concrete, reduce the friction between concrete and pipelines, and reduce slump damage.
(2) Concrete antifreeze: an admixture that can harden concrete at negative temperatures and exceed expected properties under required maintenance standards. This is a chemical substance that can prevent moisture in raw materials from freezing at ultra-low temperatures.
(3) Water-reducing agent: Water-reducing agent is a concrete admixture that can reduce the mixing water requirement while maintaining the slump of the concrete. Most belong to anionic surfactants. After adding concrete mixture, it has a dispersing effect on concrete particles, which can improve its workability, reduce the water demand of the enterprise, improve the circulation of the concrete mixture; or reduce the amount of concrete used by the enterprise and save concrete.
(4) Retarder: slow down the setting time of concrete without significant harm to the compressive strength in the middle and late stages.
(5) Expansion agent: used to compensate for the shrinkage of the material during the hardening process and prevent cracking
(6) Air-entraining agent: can improve the fluidity of concrete and ductility, reducing bleeding and concrete segregation, and increasing the compressive strength by 12% to 30%. The thermal diffusion and thermal conductivity of concrete mixed with this agent are reduced, and the volumetric stability of concrete and the aging resistance of various outdoor structures are sufficiently improved. Air-entraining agents are commonly used in road concrete to extend the service life of the road surface.
(7) Retarder: Concrete retarder refers to an admixture that can increase the initial compressive strength of concrete and has no obvious harm to the compressive strength in the middle and later stages.
(8) Waterproof coating: significantly improves the moisture-proof effect of the concrete impermeability level, the impermeability level reaches about P25, and has the functions of retarding, early strength, water reduction, crack resistance, etc., and can improve fresh mix The bonding properties of cement mortar (fluidity, cohesion, water solubility): it can replace lime paste. It is very suitable for concrete for rural bungalow roofs, large-volume waterproof concrete, hydraulic concrete, waterproof coatings, etc. It can completely eliminate roof leaks, wall moisture, and road leaks. It is a cheaper, ideal, and reliable choice of raw materials in China at this stage
(9) Accelerated setting agent: When added to concrete, it can Admixtures that make concrete quickly solidify and harden.
(10) Retarding high-efficiency water-reducing agent: high water-reducing rate, significant improvement effect, can greatly improve the fluidity and workability of concrete, and retard setting before initial setting The actual effect is remarkable, and the early strength effect after final setting is remarkable. It can greatly improve the compressive strength of concrete at all ages and is widely integrated into concrete types. It has no rust on building steel bars and can be mixed with silica powder or mineral fine admixtures to form high-strength concrete below C80.
4. What is concrete segregation in concrete?
It refers to the separation of multiple components of the concrete mixture, resulting in unevenness and loss of sustainability.
5. What is the bleeding of concrete?
It refers to the mixing and other processes of the concrete mixture. During the solidification and hardening process, the granular materials move downward. The problem of part of the mixing water floating to the surface of the concrete is called bleeding.
11. What factors will lead to the loss of concrete? (1) The design value of the mortar mix ratio deviates greatly from the actual value (2) Incorrect measurement and verification (3) During production Improper adjustment and preparation, immediate water depletion without taking measures to replenish other raw materials (4) Extravagant and wasted concrete during the concrete pouring process (5) Concrete remaining outside the pipe (6) Concrete stuck in the inner cavity of the mixer, tank truck Internally bonded concrete.
6. What is winter construction? What aspects does winter construction include? What is the minimum mold entry temperature? The standard for winter construction deadline zoning is that when the outdoor daily average temperature continues to be lower than 5 days for 5 days, 5 degrees means winter construction will begin. When the outdoor daily average value is higher than 5 degrees for 5 consecutive days, winter construction will be cancelled. Winter installation costs include concrete antifreeze, boiling water, central heating, and insulation.
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