Although China’s economy is stronger than that of Europe and the United States in terms of growth rate, however, after all, we are a developing country, there is a big gap between the economic strength and developed European and American countries, especially in the per capita purchasing power gap is greater, water conservancy and hydropower projects in Europe and the United States has been very perfect, but China belongs to the development stage, in order to reduce the gap with the developed countries in Europe and the United States, so China must firmly implement scientific and Contribute to the sustainable development of water conservancy and hydropower projects.
Only in this way can the people’s lives continue to improve, and China’s comprehensive national power can be enhanced. The successful completion of a water conservancy and hydropower project cannot be achieved without the support of technology and construction materials, especially the quality of concrete, which is an important part of the entire water conservancy and hydropower construction project, and the cost of using concrete accounts for about 60% of the total cost of the entire water conservancy and hydropower project. The importance of concrete requires that we must pay sufficient attention to both the selection and use of concrete.
1 The current situation of concrete management in China’s water conservancy and hydropower construction projects
1.1 The gap of management concept
The construction of water conservancy and hydropower construction projects is an important part of the realization of socialist modernization. Although we are in a leading position in the world in the technical field of water conservancy and hydropower engineering, however, there is no complete system for the management of concrete, and the construction personnel tend to have different attitudes towards concrete management according to the size of water conservancy and hydropower projects, and the concrete management of projects with large construction volume will The construction of a large volume of projects, concrete management will pay attention to the small volume of the project, in terms of concrete management will be easy to ignore, such a management concept is certainly wrong.
It cannot be ignored because of the small volume of the project, because the use of water conservancy and hydropower projects is very long, a project will usually serve several generations.
1.2 Lack of management knowledge
In water conservancy and hydropower projects, lack of management knowledge is also the main reason affecting concrete management. Although there is no gap between our construction technology and Europe and the United States, and even in some aspects to be ahead of Europe and the United States, however, there is a gap in knowledge about concrete management, Europe and the United States construction personnel are better educated, in concrete management, there is a high level of knowledge, China’s construction people, especially the most grass-roots personnel, the general level of education is not very high, and thus lack of concrete management.
1.3 Lack of machines
Concrete management is not only the responsibility of the construction personnel, the management of the machine is also an important reason, the degree of dilution of concrete can be observed by the naked eye, the degree of acidity and alkalinity of concrete must be done with the help of measuring instruments, the degree of acidity and alkalinity of concrete determines the degree of corrosion resistance, has a certain impact on the surrounding environment, especially the water at the bottom of the dam and the concrete pH gap is too large, it will accelerate the corrosion of concrete . The use of machines is very important in managing concrete.
2 The key points of concrete selection for hydropower construction projects
Concrete refers to: cement, sand, stone and other admixtures mixed in a certain proportion to become a composite building material. There are many types of concrete, which can appear according to the different mixing materials. For example: inorganic gel concrete, organic gel concrete, gypsum concrete and metal concrete, etc. The construction of hydraulic and hydroelectric construction projects are different, so we can choose the concrete that is beneficial to the project to use. But the most basic materials we must choose well.
2.1 The choice of cement
In the choice of cement, we must choose the first-class cement that meets the national standard, such as silicate cement, which has very good water retention and can still maintain good viscosity during long-distance transportation. If the water conservancy and hydropower project is built in the cold weather areas such as northeast and northwest, we must choose the cement with good anti-freezing property. We should also pay attention to the purchase amount, don’t buy too much cement because of the large amount of project construction, the normal use period of cement is 3 months, more than 3 months of cement in use, will lose the use effect.
2.2 Selection of sand
The choice of sand is also important, to choose yellow sand with less mud, when the sand contains more mud, once the concrete is set, the strength of the mud is lower than the mix, which will form small hollow holes, which will affect the quality of the entire project, reducing the use of the dam time, resulting in very serious consequences.
2.3 Selection of stones
The use of concrete, the use of stone is equally important to the strength of concrete, and the use of stone in the same project can not be the same standard, in the construction of the dam base, often choose a larger stone. This will increase the weight of the dam footing and increase the strength of the footing. When building the surface of the dam, use smaller stones, which can increase the degree of fit between the concrete, reduce the hollow between the concrete, choose concrete materials containing smaller stones, when building the dam, can make the surface of the dam more smooth, reduce the friction of the water has the dam, delay the service life of the dam.
3 problems and causes of the use of concrete in hydraulic and hydropower construction projects
3.1 Surface drying and cracking
In many water conservancy and hydropower construction projects, due to some construction errors, after the concrete has set, it will more or less dry cracking phenomenon, the main causes of dry cracking are the following: First, the concrete in the process of gradually becoming dry, the concrete due to the loss of moisture on some deformation, when the degree of concrete deformation is greater than the aggregate deformation, the aggregate will be under pressure, resulting in aggregate surface dry cracking, cracks etc. Second, improper concrete proportioning will also cause dry cracking, the amount of cement or poor cement specifications, concrete in such cases will also appear dry cracking. Third, the improper construction of workers, after the construction, the concrete has not been set in time, the construction workers remove the fixed mold, so that the concrete will also appear dry cracking situation.
In the construction process of water conservancy and hydropower projects, the situation of honeycomb is not uncommon, honeycomb refers to: the concrete after the condensation of the stone exposed situation. Such a surface is very loose. The main reasons are the following.
First, the content of concrete in the concrete is small. In the concrete, stones, sand and other aggregates mainly support the strength of the concrete, while cement and other additives mainly play a coagulation role, once the proportion of cement in the concrete is less, sand stones and other aggregates coagulation will be smaller, thus leading to the concrete in the solidification out of the school surface loose honeycomb situation.
Second, the stone diameter is larger. The stone in the concrete is too large, in the process of pouring the dam will appear in the case of aggregate separation, which will also lead to the concrete honeycomb situation.
3.3 Exposure of reinforcement
In water conservancy and hydropower projects, the situation of exposed reinforcing steel, also occurs from time to time. This is very harmful to the overall water conservancy and hydropower projects, mainly because: in the process of pouring concrete, reinforcing steel because of construction and other reasons of displacement, or in the construction process, the construction personnel in the location of the reinforcing steel in the amount of concrete used is not enough. When the situation of exposed reinforcement, the construction steps must be repeated so as to reduce greater losses.
4 hydropower construction project how to use the correct concrete
The mixing standard of concrete must conform to the previously designed specifications. In the process of mixing, the ratio of cement, sand, stone and other aggregates must be weighed using weighing tools, so as to ensure the effect of concrete use. The water used for mixing concrete is also very important. Before mixing the concrete, the pH value of the water should be measured to see if there is a chemical reaction between the acidity of the water and the composition of the concrete. In terms of mixing methods, concrete mixing, divided into manual mixing and machine mixing, manual mixing is less efficient rarely used, water conservancy and hydropower projects will take machine mixing.
In the construction of water conservancy and hydropower projects, while requiring high technology, but also to ensure the quality of concrete, construction technology is the soul of the entire project, and the use of concrete is the foundation of the entire project, if a project is compared to a person, technology is his education and skills, concrete is his physical health.