What is "concrete"?
Engineering students, especially those who study civil engineering, as well as those engaged in the design, construction, supervision, and budget and final accounts of civil engineering projects, often have to deal with the word "tong". Speaking of this "concrete" word, it is really a bit of a head.
"Concrete" is synonymous with "concrete"; it is pronounced "tóng" (as is the word "copper"). "Concrete" usually refers to cement, sand, gravel and water mixed in a certain proportion and hardened after the construction material. The only meaning of "concrete" is "concrete", so it cannot be an ancient word, and "cement" was not invented or produced in ancient China (although volcanic eruptions may produce natural cement), and the application of "concrete" cannot be discussed. Therefore, its invention can only belong to the "modern and modern inventions". The invention of the word "concrete" can be regarded as a big invention, because it can replace "concrete" in many occasions and play the role of "three words at the top of one word", which is amazing: you think, write the three words of "concrete", with a total of 30 strokes, and use the word "concrete" to write only 10 strokes; this will provide great convenience for students who need to take notes when listening to lectures, and a large number of technical cadres, managers, workers, etc. who write this word repeatedly every day. In the preparation of relevant drawings, technical documents and materials, the three words "concrete" will be encountered frequently. How much will a replacement save technicians, as well as supporting personnel such as cartographers? Especially in the days when computers and computer-aided design were not yet born or popularized. The inventor of the character "concrete" is named Cai Fangyin, who was an early Tsinghua student. He invented the word in 1953 and soon became popular among engineering technicians and college students. This new word is very cleverly created, and it is also very reasonable: the word "concrete" is broken into three words, which becomes "people, workers, and stones", indicating that concrete is artificial stone; if it is broken down into two words, it is "TongShi", and "Tong" is a variant of "Tong", and "Tongshi" can be understood as the main properties of concrete and natural stone are roughly the same. In 1955, the Terminology Office of the Compilation and Publication Committee of the Chinese Academy of Sciences explicitly recommended the use of the terms "concrete" and "concrete" in the book "Structural Engineering Terms" approved and promulgated. Since then, "concrete" has been widely used in various civil engineering books. The scope of civil engineering is very wide, including houses, roads, bridges, railways, tunnels,, seaports, municipal health, farmland water conservancy, civil air defense engineering, etc., so the impact of this matter in the engineering community is not small. In 1985, the Chinese Character Reform Commission officially approved the legal status of "concrete" synonymous with "concrete" and used together, making it a "special word for engineering" in the mainland. Later, in the drawings and technical documents, the word "钅仝" (next to the golden character, a "仝" character on the right) was popular to replace the five words "reinforced concrete". However, this word, the reason for creating a word is not sufficient, so it has not been officially approved and promoted, and this illegal word cannot be found in the dictionary.
Brief introduction of the inventor of the word "concrete"
Cai Fangyin (1901-1963) was a native of Nanchang, Jiangxi. Specialist in civil building structures. After graduating from Tsinghua University in 1925, he entered the Department of Architecture of the Massachusetts Institute of Technology in the United States and obtained bachelor's and master's degrees. In 1928, he worked as a design engineer at the New York Architectural Company. After returning to China, he was recruited as a professor in the Department of Architecture of Northeastern University. He teaches courses in shading and architectural engineering theory. After the "918" incident, he successively served as a professor at Tsinghua University and Southwest Union University. After 1949, he successively served as a consulting engineer of the Ministry of Heavy Industry, and the vice president and chief engineer of the Institute of Building Science of the Ministry of Construction Engineering. He has been engaged in the teaching and research of building science for a long time, and has achieved great achievements in engineering structural mechanics, especially variable section rigid structure analysis and truss rigid structure analysis. His monographs include "General Structural Science", "Analysis of Variable Section Rigid Structure", "Prefabricated Wedge Stranded Rigid Frame" and so on. In 1955, he was elected an academician of the Chinese Academy of Sciences.
Invented the word "concrete". It was a major invention that reduced "concrete" to "artificial stone": "concrete". This artificial stone is divided into different strength grades.
How is the strength of concrete accepted?
Start by making a test block
A mold is required to make a test block
1Why is the concrete compressive test block square and the impermeable test block round?
A: The compressive test block is to test the strength of concrete, the impermeability test block is to test the waterproof performance of concrete, the impermeability test is to inject water from the middle and pressurize, the shape of the penetration is round, so the shape of the test block is also cylindrical.
Before making the test block, brush the inner surface of the test mold with a layer of cleaning oil as a barrier agent.
2Can edible oil be used as a barrier agent?
A: The main role of the isolating agent is not to let the concrete stick to the mold, and cooking oil is also OK. Then follow these 6 steps to carefully vibrate the compact.
3 The upper layer of the test block made out has a very thick layer of scum, and the scum has no strength at all, why?
A: Now most of the concrete is pumped concrete, the sand rate (the proportion of sand) is very large, and the upper layer of scum is caused by the sinking of the stone after vibration. The cause of this is excessive vibration. Solution: After the test block is pounded, select a few stones from the mixed concrete (no dry stones can be added) and add them.
4 site test block has not done parallel inspection, the company to check, let us do parallel inspection, parallel inspection of the test block to maintain how many days? How to be notified?
A: Parallel inspection is a supervision method, and the supervision method is divided into side stations, inspections and parallel inspections. The parallel inspection here means that the construction unit does the test block, and the supervisor also does the test block, and each takes it to test the pressure to see if the construction unit has falsified when doing the test block. The method of the test block test and the construction unit are completely consistent. However, this method is rarely used because it is tiring to do so.
5 This is a question of preventing human cheating, how can concrete test blocks be intelligently and low-cost to prevent being dropped during the production process?
A: The simplest way is to bury the chip under the supervision of the supervisor when the trial block is made. Each set of test blocks is 3 blocks, and the standard maintenance is 28 days.
6 Test block soaked in water is not OK? Is it okay to be buried in the sand?
A: The standard maintenance test block requires constant temperature (20 °C±2 °C) constant humidity (95% humidity), the humidity in the water is too large, the temperature is not necessarily 20 °C±2 °C, the standard maintenance test block is generally carried out in the standard maintenance room or the standard maintenance box.
7 Will the maintenance of concrete test blocks in the water reduce the strength?
A: This is not true, because the process of cement hardening is a chemical reaction with water. Take it for testing on day 28 until the test block is crushed. At this time, the force recorded by the test machine, divided by the area (225 square millimeters), is the strength of this test block.
What is the strength of 3 test blocks in group 1? This is how it needs to be calculated.
8In the strength test of concrete test blocks, are there any requirements for the temperature and humidity of the laboratory?
A: No, the temperature and humidity requirements are put forward for the maintenance of the test block.
9 Is the compressive test block the longer the time, the higher the strength?
A: Yes, but the strength of concrete is growing very quickly and then it is getting slower.
10How to do if the holiday test block of the Spring Festival testing company is overdue?
A: Experimental studies have shown that after 28 days, the intensity increase is very slow, but it is still growing. If the purpose of the test is not to engage in scientific research, but to test the strength of concrete, the impact of a few days overdue is not too large. However, this intensity is not a 28-day standard maintenance intensity after all, and cannot participate in the assessment.
11Why is the 100×100×100 test block and the 150×150×150 test block do the compression test, and the results can be equivalent?
A: Correct your mistake, when sampling, you can do 100×100×100 cube test blocks, you can also do 150 × 150 × 150 test blocks, the compressive strength obtained by the test should be multiplied by the conversion coefficient of 0.95, and the data obtained is the compressive strength of the test block.
Every pouring of concrete does not mean that only one set of test blocks is done, it requires many groups.
12 Concrete pouring pile concrete test block retention standard culture or the same conditions? Which one is regulated?
A: Concrete pouring pile concrete test block instead of standard culture or the same conditions? Which one is regulated?
13Do masonry construction columns need to be indwelled with test blocks? How many groups are liened if needed?
A: Each inspection batch of masonry construction columns is not less than 1 group of test blocks, and a total of not less than 3 groups of test blocks.
Just talked about the standard breeding test block, in addition, but also to make the same condition maintenance test block.
The same condition maintenance test block should be maintained to the day when the cumulative 600 ° C.
How many sets of trial blocks with the same conditions? What's the point?
14Why should I leave the demo demo demo test block?
A: The mold removal test block is mainly used to judge whether the strength of the concrete meets the strength requirements of the formwork demolition, and it also needs to be maintained under the same conditions. The collapse of the construction platform of the cooling tower of Jiangxi Fengcheng Power Plant is caused by the low strength of the concrete when the mold is disassembled, and if the demotion test block test is done seriously, such a safety accident can be completely avoided.
15What is the significance of retaining more than one 7-day compressive strength test block?
A: Sometimes we consciously do more test blocks, mainly in case of unexpected situations. For example, if the test pressure does not reach the strength, it is necessary to dismantle the template a few days later, and then wait a few days to take the spare test block to test the pressure.
16Can the same condition concrete test block expire? Which specification is indicated?
A: In the 600 °C day to test the pressure, more than 600 °C days is overdue.
17How to do the concrete critical test block?
A: Critical strength is the minimum strength that must be achieved before the concrete poured in winter is frozen. The critical strength test block is also a kind of maintenance test block under the same conditions, which is used to determine whether the concrete can be removed from insulation.
18The difference between the delivery inspection test block and the standard culture test block?
A: The delivery inspection test block is not equal to the opening appraisal test block. Concrete is a special commodity, and when the concrete mixing plant is delivered, it is impossible to judge whether the concrete can achieve strength. After delivery, if the maintenance conditions of the site are poor, it will also affect the strength of the concrete. Once the strength problem occurs, the two sides are prone to quarrels. When the concrete is delivered, a set of test blocks are made, maintained according to the standard and then tested to prove whether the concrete sent by the mixing station is qualified.
19 Concrete with the same conditions of maintenance test block and standard breeding test block has a kind of unqualified, how to assess conformity?
A: There are two methods for concrete strength assessment: more than 10 groups, and non-statistical methods within 10 groups of statistical methods. It is not difficult to tell you the following method:
20 Some test blocks are too strong, is it a fake test block?
A: It is some construction units that are cheating. The high strength of the test block is outrageous, and there is indeed a suspicion of fraud. There are local standards in various places, for example, we think that the strength of the test block is 2 levels higher, and it is judged that the test block is fake.
21C45 concrete test block pressure resistance in batches of unqualified?
A: If many test blocks are unqualified, the final assessment of such concrete will definitely be unqualified.
22C35 Underwater Concrete Should the minimum strength of the test block be greater than 35MPa or should it be greater than 40MPa?
A: In order to ensure the quality of underwater pouring, the mix ratio of underwater concrete is one level higher than that of conventional concrete for trial matching, acceptance or according to the design strength, or 35MPa.
23 According to the specification, the sample capacity of a test batch should be three consecutive sets of test pieces, if there is only one set of concrete test blocks, how to evaluate?
A: If there is only one set of test blocks, it must be greater than the design strength. For the evaluation of concrete strength, it is first necessary to make standard maintenance test blocks, and also to leave test blocks with the same conditions. In the case of unqualified test blocks under the same conditions, it can rebound and detect. If the rebound test is still unqualified, it needs to be sampled for drill core, and if it is still unqualified, it is necessary to:
24 What should I do if the rebound strength of the concrete is insufficient and the strength of the test block is qualified?
A: The data obtained by the rebound method to detect the strength of concrete is conservative. There are two possibilities for this result: 1. The strength is qualified, and 2. The test block is counterfeited.
25 What if there is a group of excavated piles that have not been sent to the test block but the superstructure has been constructed for 2 floors?
A: In this case, there is no way to rebound, and there is no way to drill the core to sample, which is really difficult. If it is continuously poured concrete, it seems that there is no basis for inference. If you must know whether the pile is qualified, doing a load test may be the best solution.