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One hundred knowledge of concrete ask how much do you know (1)
2018-7-27 13:11:13 Source: JunGong mixer truck manufacturer

This article is mainly based on the requirements of national standards, specifications and procedures, combined with many years of practical experience, for positions such as experimenter, production controller, dispatcher, weigher, transporter driver, loader driver and pumping operator. The general knowledge of the commercial concrete involved was briefly discussed, and some problems were sought to be explained from the mechanism and reason, so that the employees who had just entered the industry had some understanding.

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1. What is commercial concrete?
Answer: According to the requirements of the purchaser, use cement, water, sand, stones, admixtures, and mineral admixtures in a certain proportion, measured at the mixing station, sold after mixing, and use a mixing truck, within the specified time Concrete mixes transported inward to the delivery side of the purchaser.
2. Which are general products?
Answer: The strength grade is not greater than C60, the slump is not greater than 180mm, and the maximum stone particle size is 20-40mm. There is no other requirement for commercial concrete.
3. Which are special products?
Answer: Any one of the indicators is beyond the scope of general commodity regulations or commodity concrete with special requirements. Such as fine stone concrete, pile foundation concrete, impervious concrete, antifreeze concrete, etc.
4. What is the delivery place?
Answer: The concrete transfer site, which is the construction site, determined by the supply and demand parties in the contract.
5. What is factory inspection?
Answer: Inspection of the quality of commercial concrete before it leaves the factory. Such as sampling to detect slump, making strength test blocks, visually checking slump, workability, etc.
6. What is delivery inspection?
Answer: At the place of delivery, both the supplier and the purchaser and the supervisor carry out an inspection of the commercial concrete. Such as detecting slump, making test blocks, visually checking slump, workability, etc.
7. What is cement? How many types of cement are commonly used?
Answer: Any hydraulic cementitious material made of Portland cement clinker, a reasonable proportion of mixed materials, and a proper amount of gypsum is called cement. Commonly used cements are: Portland cement, ordinary Portland cement and composite cement. Silicate cement is divided into P • Ⅰ and P • Ⅱ types, with strength grades of 52.5 and 62.5. Ordinary portland cement is divided into ordinary type and early strength type, code is P • O, strength grade is 42.5, 42.5R, 52.5, 52.5R. The composite cement code is P • C, and the strength grades are 32.5, 32.5R, 42.5, 42.5R.
8. What are the items of cement re-inspection?
Answer: Setting time, stability, strength, fineness (specific surface area).
9. What is aggregate? There are several types of aggregates
Answer: The material that plays the role of skeleton in concrete is called aggregate (also called aggregate). The stone is called coarse aggregate, and the sand is called fine aggregate. The stones are divided into pebbles and crushed stones, and are divided into limestone crushed stones and granite crushed stones according to the stone quality. Sand can be divided into river sand, sea sand, mountain sand, artificial sand and so on.
10. How many kinds of sand are divided according to their fineness modulus?
Answer: Sand is divided into coarse sand (3.1 ~ 3.7), medium sand (2.3 ~ 3.0), and fine sand (1.6 ~ 2.2) according to its fineness modulus.
11. Why is medium sand preferred for pumping concrete?
Answer: Because the gradation of the medium sand is reasonable, the content of particles below 0.3mm can reach about 15%. This part of the particles in the mortar of the concrete is close to the pipe wall in the pump pipe, and the friction resistance is small, which is conducive to pumping. Coarse sand has high friction resistance, which is not conducive to pumping. Fine sand has a large surface area, and more cement is used at the same strength, which has a high probability of cracking.
12. How many types of granules are there?
Answer: Single grain and continuous grain. The single-grain grades are: 10-20, 16-31.5, 20-40. The continuous grain grades are: 5-10, 5-16, 5-25, 5-31.5, 5-40.
13. Why should continuous grain grade stones be preferred for pumping concrete?
Answer: Because the porosity of the single-grained grade is larger than the porosity of the continuous-grained grade when the maximum particle size of the stones is the same, the large porosity needs to be filled with mortar. The surface area of aggregate in each cubic meter of concrete under the same conditions: the use of single-grained stones is larger than the continuous-grained stones, and the corresponding amount of cement is also required. And because continuous grain stone is better than concrete mixed with single grain stone, it is good for pumping construction. Therefore, priority is given to continuous-grain stones.
14. What are the main requirements for the quality of good stones?
Answer: There are mainly the following:
(1) The particle size meets the requirements, and the particle size is continuous particle size;
(2) There are no yellow-skinned (mud on the surface) mud eggs, large mud blocks, and large-grain stones;
(3) The smaller the content of acicular and flake particles, the better (the content of acicular particles of pumping concrete stones should not exceed 10%);
(4) The less shale content, the better (because the strength of shale is low and the content of flaky particles is increased).
15. What are the requirements for the quality of good sand?
Answer: There are the following:
(1) The particle size distribution meets the requirements of medium sand;
(2) The particle size is medium sand, the content of particles larger than 10mm is less, and the maximum is not more than 10%;
(3) No mud eggs, large mud cakes, and the mud content does not exceed 3%;
(4) No debris such as tree roots, grass roots, sludge, plastic bags.
16. What is fly ash?
Answer: Fly ash is the fine powder collected by the dust removal equipment in the flue gas of the pulverized coal furnace of the power plant.
17. Fly ash is divided into several levels according to its technical requirements? Where does each apply?
Answer: It is divided into three grades; grades I, II, and III; grade I is applicable to C40 and above concrete, grade II is applicable to C15 ~ C40 concrete, and grade III is applicable to cement admixtures.
18. Why should fly ash be added to pump concrete?
Answer: Because the microstructure of fly ash is spherical particles, the fineness is finer than cement, it also has a certain activity, and mixing it into cement can replace part of the cement, and can increase the fluidity of the concrete mixture, greatly The pumpability of the pumped concrete is improved, and the post-strength and durability of the concrete are also improved.
19. What items should be inspected when fly ash enters the plant?
Answer: The fineness of fly ash and the water demand ratio should be checked. The key item is the water demand ratio. If the fineness slightly exceeds the standard and the water demand ratio reaches the level II requirement, this ash is available, otherwise it is not available.
20. What is concrete admixture?
Answer: The additive used to improve the performance of concrete is called concrete admixture.

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