Construction of water conservancy projects starts with understanding concrete construction!
What is hydraulic concrete?
In order to achieve the purpose of flood control, irrigation, power generation, water supply, shipping, etc., it is usually necessary to build different types of buildings for water blocking, flood discharge, water delivery, sand discharge, etc. These buildings are called hydraulic structures.
The concrete used in these buildings is called hydraulic concrete. Hydraulic concrete is often used in water, underwater and water level change areas.
According to the size of hydraulic structures, it can be divided into large-volume concrete (such as dam concrete) and general concrete. Mass concrete is divided into internal concrete and external concrete.
Hydraulic concrete has different technical requirements due to its different uses: when it is often in contact with environmental water, it generally requires good impermeability; in cold areas, especially in areas with varying water levels, it requires higher resistance Freezing; when in contact with aggressive water, good corrosion resistance is required; when used in large-volume structures, in order to prevent the appearance of temperature cracks, heat resistance and low shrinkage are required; when washed by high-speed water It is required to have anti-erosion, abrasion resistance and cavitation resistance when used in the parts. Hydraulic concrete is the main building material in water conservancy projects, especially large-scale water conservancy projects.
What types of hydraulic concrete are there?
Hydraulic concrete can be divided into the following categories according to its working conditions:
1. Classified according to the relationship between buildings and water level
The ones that are often located in the water are called underwater concrete; those in the water level change area are called water level change area concrete; those above the water level change area are called water level soil.
2. Classification by volume and location
According to the volume of the concrete building and its position in the large-volume building, it can be divided into three categories: large-volume internal concrete (small cross-section with a size of more than 2.5 m), large-volume external concrete and non-bulk concrete .
The so-called large-volume concrete refers to any large-scale cast-in-place concrete, that is, the concrete is large enough to take measures to properly deal with the heat generated and the subsequent volume changes, and requires reducing cracks to a small degree.
3. Classification according to whether it bears water pressure
According to the condition of bearing water pressure, it can be divided into two types: hydraulic concrete and non-hydraulic concrete.
The difference between hydraulic concrete and construction concrete
The structures and buildings of water conservancy projects, such as dams and water transportation terminals, have to bear the pressure of water. They are huge, ranging from tens of thousands of cubic meters to hundreds of thousands or even tens of millions of cubic meters. Most of the concrete used is large Volumetric concrete. Controlling the temperature rise of concrete and preventing temperature stress cracks are the keys to the success of construction. Therefore, it is necessary to make efforts to reduce the amount of cement during the preparation to reduce the adiabatic temperature rise of concrete and improve the crack resistance of concrete.
The construction concrete, that is, the ordinary concrete structure is relatively small in volume and densely reinforced. Because the pumping construction is mainly used, the fluidity of the concrete is required to be high (generally 100 ~ 220 mm). In addition, the concrete strength range used in ordinary concrete structures is much larger, C30 to C50 are commonly used, and the high ones may reach C70 and C80.
Construction characteristics of hydraulic concrete
Due to different uses of hydraulic concrete, its technical and quality requirements are different from those of general industrial civil construction concrete. In addition to strength requirements, it also meets the requirements of impermeability, crack resistance, frost resistance, tensile resistance, and tensile resistance according to the location and working conditions. Design requirements such as impact resistance, weathering resistance and corrosion resistance.
Hydraulic concrete construction generally has the following characteristics:
(1) Large engineering volume and long construction period: The amount of concrete used in large and medium-sized water conservancy and hydropower projects is usually hundreds of thousands to several million cubic meters. It usually takes 3 to 5 years from the start of pouring concrete to the completion of the project to store water To complete. In order to ensure the quality of the concrete and speed up the construction progress, it is necessary to adopt comprehensive mechanized construction methods and choose advanced and economically reasonable construction schemes.
(2) Strong seasonal construction: The construction of hydraulic concrete is often unable to achieve continuous and balanced construction due to factors such as temperature, precipitation, construction diversion and flood control, and irrigation and domestic water.
(3) Strict temperature control requirements: Most of the large-volume concrete or large-area concrete in hydraulic concrete usually needs to be split and divided for pouring. In order to prevent the temperature cracks of concrete (especially the concrete at the foundation restraint site) and the surface freezing damage (especially large-area thin concrete), and to ensure the integrity of the building, strict temperature control and surface protection must be adopted for the concrete according to the local temperature And seam grouting.
(4) Complex construction technology: due to different uses and working conditions of hydraulic structures, the general structure is complex and diverse, and various grades of concrete are often used. In addition, concrete pouring often crosses the foundation excavation, treatment and part of the installation works, and because of the many types of work procedures and mutual interference, there is great conflict.