Qin Haijuan said: "Li Liangfeng, learn more!" Our Mr. Li is an expert in the concrete industry, as the saying goes, there are no weak soldiers under the strong general, we can't lose face to the boss, right? Okay, let's hurry up and continue. After determining the amount of water to be used, it is time to calculate the amount of cement and fly ash, and you can continue to calculate. “

Li Liangfeng nodded and began to continue calculating on the paper.

First, the water consumption of 187 kg was divided by the water-cement ratio of 0.71, and the cement dosage of 255 kg was obtained, which is the amount of cement when fly ash is not added, and after the fly ash is added, the appropriate fly ash dosage must be selected according to the regulations. Of course, for concrete like C15, it is generally used as non-structural parts of unreinforced concrete, so there is no requirement for the amount of fly ash and the total amount of rubber, so the range of possible values of fly ash content is very large, and the maximum can reach 50%.

Li Liangfeng didn't know how much to take, after all, he had no experience. So Li Liangfeng looked at Qin Haijuan and whispered: "Director Qin, I don't know how much to take for the amount of fly ash to be used, you can give me a guide!" ”

Qin Haijuan smiled: "Didn't Mr. Li say it just now?" Our C15 concrete is a kind of low-strength concrete, to meet the requirements of pumping, it is necessary to make the amount of cementitious material as much as possible to reach 280 kg or even more than 300 kg, you think about how much you should take. ”

Li Liangfeng took a look, yes, the amount of cement is now 255 kilograms, to make the amount of rubber to reach 300 kilograms, it is necessary to add 45 kilograms, and the excess coefficient is the largest 1.4, so the amount of cement to be replaced must exceed 100 kilograms, and the final amount of cementitious materials can reach 300 kilograms.

So Li Liangfeng began to calculate on paper, and if he took 40 percent, it was just about the same.

Li Liangfeng said with understanding: "Director Qin, I should be able to choose 40% of the fly ash content, right?" ”

Qin Haijuan smiled: "No problem. However, when it comes to the C20 or higher level, it is necessary to pay attention to the requirements of the specification. The higher the content of fly ash, the better. Well, you calculate! ”

Li Liangfeng calculated on the paper that 40 percent of the fly ash content was replaced, and the amount of cement replaced was 102 kilograms. According to the excess coefficient of 1.4, multiply the phases to calculate the amount of fly ash, 143 kg. The amount of cement used was 255 kg minus 102 kg, resulting in 153 kg. The total amount of cementitious material is 143 kg plus 153 kg, which is 296 kg, which is basically close to the 300 kg of rubber material mentioned by Li Ruoyu.

Li Ruoyu nodded frequently on the side, and Xie Zili also nodded, they all felt that this Li Liangfeng was still a material that could be made.

The next step is to choose the sand rate of the concrete mixture, which is also a very critical parameter, which will affect the working performance and concrete strength of the concrete. If the sand rate is too low, the workability of the concrete will become very poor, that is, the mortar is insufficient, and the gap between the stones cannot be filled well. And if the sand rate is high. It will cause the concrete water consumption to exceed the design water consumption, and at the same time, due to the more sand, the total specific surface area of the whole aggregate increases, and more paddles are needed to wrap it, so in the case of no increase in the slurry, the concrete working performance will also become worse, and the concrete strength will be reduced.

Of course, there are two ways to choose the sand rate, one is the empirical method, and the other is selected from the table in the procedure. For a newcomer like Li Liangfeng. Naturally, it is better to choose from the table.

So Li Liangfeng selected the sand rate from the table according to the method of the design procedure. According to the water-cement ratio, bone variety and maximum particle size, Li Liangfeng chose a sand rate of 42%.

Li Ruoyu also said at this time: "The selection of sand rate must be determined through the guò test. Now you just refer to the preliminary results of the selection based on the table. But in practice, sometimes the requirements are often not met. Because the concrete slump, the thickness of the sand, the gradation of the gravel and other factors have not been taken into account, so in the end, the sand rate must be adjusted to find out the best sand rate. Okay, let's calculate the amount of sand and gravel! If it's simpler, let's use the assumed bulk density method. ”

Li Liangfeng said suspiciously: "What is the hypothetical bulk density method?" ”

Qin Haijuan smiled and said, "Actually, let's assume the weight of a cubic of concrete. Generally speaking, the density of ordinary concrete is between 2350 kg per cubic meter and 2450 km per cubic meter, of course, there are many factors that affect the density of concrete, for example, the higher the strength grade of concrete, the more cement used, the higher the density of concrete. In addition, the lower the water consumption of concrete, the higher the density of concrete. In addition, the density of various raw materials also affects the density of concrete, for example, concrete using granite and basalt is denser than concrete using limestone. In addition, the air content of concrete has a relatively large impact on the density of concrete. If the air entrainment is too high, it will lead to a decrease in the density of concrete, and if the air content is too high, more than a certain degree, it will cause a significant decrease in the strength of the concrete, and even cause a quality accident. Generally speaking, the air content of concrete should be less than 3%, and not more than 5% at most. ”

Li Liangfeng nodded and said, "I understand." So how much is the bulk density of our C15 concrete now? ”

Qin Haijuan said with a smile: "You can take it lower, first, the water consumption you calculated just now is 187 kilograms, which is relatively high, and the amount of fly ash is also relatively large, so the bulk density of concrete will be relatively low." Of course, this is only a preliminary calculation, when the concrete mix ratio is finally determined, it is necessary to pass the guò test matching, and use the concrete out of the trial to determine the bulk density of concrete, that is, the density, if the error with the theoretical calculation results is within the range of two percent, it can not be corrected, but if it exceeds two percent, it must be corrected. That is to say, if you set the bulk density of 2350 kg now, and the actual bulk density of the concrete tested reaches 2400 kg, the relative error between the two is more than 2 percent, then you need to calculate the amount of each material in the mix ratio you are now calculating, multiplied by the correction factor. We'll talk about this later, now you calculate the amount of sand and gravel according to the assumed bulk density of 2350 kilograms per cubic meter, before calculating this, you also have to remember to count the admixture, which can not be missed. ”

Li Liangfeng nodded, and began to bury his head in the calculations again. The first is to calculate the dosage of admixture, according to the manufacturer's recommended dosage range, Li Liangfeng chose 1.8% of the dosage, multiplied by the amount of glue material 296, the result is 5.33 kg. (To be continued.) )