Qin Haijuan also became more and more energetic the more she spoke, and simply talked about those advanced theories again.

I saw her say confidently: "Manager Wu, that's right, I hope we can cooperate happily in the future." ”

Hearing Qin Haijuan say this, Manager Wu knew that at least the technical quality department had passed, and the hope of success was much greater.

Manager Wu also stretched out his hand, shook hands with Qin Haijuan warmly again, and said with a smile: "Director Qin, that's a great point!" We also need your support and help! In the future, I must always ask you about the knowledge of concrete, if you don't learn, you can't do it! ”

Qin Haijuan said with a smile: "There is no problem, we will also hold some technical training for suppliers." Now people who are engaged in engineering also know that the strength performance of ordinary concrete is mainly determined by the ratio of cement strength to water-cement. Due to the high strength of cement and aggregate compared with ordinary concrete, the failure of cement stone and aggregate generally does not occur, and the failure mainly occurs at the interface of cement stone and aggregate. Modern observation technology has found that in the process of setting and hardening ordinary concrete, due to the constraints of aggregate, the volume change of cement binder is uneven, and cement stone will produce great tensile stress, and when the tensile stress is large, microcracks will be formed at the interface between cement stone and aggregate, and these microcracks have existed before the concrete is loaded. When the concrete is loaded, stress concentrations will occur at these micro-cracks, and the cracks will begin to extend and develop, and communicate with each other, leading to the failure of the concrete structure. This is the failure mechanism of ordinary concrete. ”

"In particular, the strength properties of high-strength concrete are different from those of ordinary concrete. The strength of high-strength concrete cement is higher, and the active mineral admixture is added, the aggregate particle size is smaller, the particle shape is more uniform, the water cement is smaller, and the cement stone is deformed evenly in the process of coagulation and hardening, and there are fewer micro-cracks. Due to the small particle size of the aggregate, the concrete material is uniform and the internal stress distribution is uniform. The failure mechanism is that under the action of load, the coarse aggregate around the larger particles produces bonding cracks, and according to the fracture mechanics criterion and the inclination angle of the interface of the second stone relative to the compression axis, the crack extension may stop and no penetrating crack is formed. As the load increases, it is possible for the stress to penetrate the stone directly, creating new cracks. Due to the lack of crack concentration, when the failure load is reached, the individual cracks develop rapidly, and the stress concentration specimen is instantaneously formed, showing a brittle failure form, which is the failure form of high-strength concrete. Therefore, the key influencing factors of high-strength concrete are cement strength, mineral admixture fineness and activity, aggregate quality and particle shape and particle size. ”

Manager Wu said seriously: "It seems that we should also strengthen our learning as a sand and gravel supplier." It turns out that there is so much truth in ordinary sand stone. ”

Qin Haijuan said with a smile: "The mud content and mud content of the aggregate are also very important. When the mud content of the sand is too large, it will adsorb part of the admixture and make the concrete mixture collapse too small, and the formula of the admixture must be adjusted to meet the requirements of the materials used. What's more, it will affect the strength of concrete, so our concrete batching plant will try to use sand with less mud content. When the mud content of the stone is too large, it will also adsorb part of the admixture, so that the concrete mixture will collapse too little, and the formula of the admixture must be adjusted to meet the requirements of the materials used. It is also to try to choose stones with less mud content. When the shale content in the stone is too large, some admixtures will be adsorbed to make the concrete mixture collapse too small, which is mainly caused by the large water absorption rate of shale. Therefore, we require that all kinds of impurities in the stone should not exceed the standard. ”

Qin Haijuan continued: "Under the condition that the superplasticizer and cementitious material system have good adaptability, the main influencing factors of sand and gravel aggregate quality in normal production are gradation and needle flake content, fineness modulus, mud content or stone powder content, water absorption, etc. The quality control of aggregate is first of all the source control, the quality of single-source aggregate is relatively stable, and the multi-source aggregate is used at the same time, without suitable measures, it will cause changes in the indicators of these factors, making the concrete construction performance worse. ”

Manager Wu nodded and said, "Then what work do we need to do well?" ”

Qin Haijuan said with a smile: "One is the control of gradation and needle flake content, whether it is the gradation of fine aggregate or coarse aggregate, the broken file or uneven distribution of fine and coarse particles, such as the lack of fine particles below 0.16mm or the lack of intermediate files such as 0.315mm, will make the workability of concrete suddenly deteriorate." The needle-like content of crushed stone increases, the aggregate porosity increases, and the concrete construction performance deteriorates. ”

"The second is the control of the fineness modulus. Different concrete strength grades have different requirements for the fineness modulus of fine aggregates. The fineness modulus of low-strength grade concrete is 2.4~2.6, and the mixture above 2.7 is easy to cause poor water leakage and wrapping; Medium and high strength grade concrete is suitable for 2.7~2.9, and the workability of concrete above 3.0 will also deteriorate. Therefore, we hope that the fineness modulus of the sand on the field is between 2.4 and 2.7, and if it exceeds 3.0, we will not accept it. ”

Manager Wu nodded and said, "We can guarantee this." ”

Qin Haijuan smiled: "This is very good. Let's talk about the control of mud content or stone powder content. The aggregate often contains clay, limestone gravel is stricter, and the clay has a strong adsorption of the superplasticizer, which is about 50 times that of cement, which has a strict impact on the working performance of concrete. The adsorption capacity of stone powder in crushed stone to superplasticizer is comparable to that of cement, indicating that too high stone powder content will affect the workability of concrete when preparing concrete. For example, river sand with a mud content of less than 0.5% or a fineness modulus of 2.6~2.8, and crushed stone with a stone powder content of less than 1% are more beneficial to improving the workability of concrete. When the time comes, we will have a specific indicator requirement. ”

Manager Wu nodded and said, "Well, you go on." ”

Qin Haijuan said: "Another is that the aggregate water absorption rate has a great impact on the workability of concrete, the greater the water absorption, the higher the water demand, and the greater the slump sensitivity." The water absorption rate of different varieties of sand and coarse aggregate is different, in the water absorption rate of different varieties of sand, river sand is the smallest, mountain sand is the largest, and the water absorption rate of machine-made sand processed by crushed stone due to the strength of the base metal itself is also different, the minimum is about the same as river sand, and the maximum may exceed 3 times of the water absorption rate of river sand; In coarse aggregates, the higher the strength of the base metal, the smaller the water absorption. If the water absorption rate of aggregate exceeds 1%, the water consumption and slump loss of concrete will change greatly. Therefore, we will attach great importance to the aggregate water absorption rate, and hope that the aggregate water absorption rate sent by the supplier is as small as possible, and we will also have a control index. ”

Manager Wu sighed: "I really don't know if I don't learn, I am shocked when I learn, it turns out that there are so many theories of sand and gravel aggregates!" In the future, I also let the people in our company learn more. Director Qin, let's have dinner together tonight, how about students inviting teachers? (To be continued.) )