The concrete construction of water conservancy projects has been one of the key points of water conservancy construction, because the concrete is for the overall body to play a supporting role, the main building materials of China’s water conservancy projects are steel and concrete, but usually the characteristics of concrete in the water is not good, can not meet the requirements of the technology, which requires the addition of crushing technology in the construction of concrete to enhance the quality of concrete.
1 Project Overview
The main function of a water conservancy and hydropower project is to generate electricity, the total capacity of the reservoir is 26.51 million m3, the total length of the river is 50km, the rain-collection area is 320km2, and the width of the dam roof is 5.5m. The project is mainly composed of the diversion tunnel, the crushed concrete gravity dam, the power transmission tunnel, the power house, the booster station and other buildings, and the annual power generation capacity of the project is 2988.6kW per hour.
The material of the crushed concrete gravity dam is mainly divided into five zones: the upstream surface is made of secondary with crushed metamorphic concrete (1m thick C9020), the inside of the dam is made of tertiary with crushed normal concrete (C9010), the downstream water level change zone is made of secondary with crushed metamorphic concrete (1m thick C9020), the dam foundation is made of tertiary with normal concrete (1.5m thick C9015), the top of the dam and other casting zones are made of tertiary with normal concrete (C9030). The total amount of concrete for the dam body is 106,000 m3.
2 Concrete crushing construction plan
In the concrete construction program to be based on the construction of the weather conditions, temperature, air humidity, etc. to do a good job of monitoring and evaluation of merit, in the construction of concrete is in accordance with different conditions to choose a different construction program, according to the construction program can also choose a different concrete ratio to improve the quality of concrete.
Before the construction according to the characteristics of the concrete, should choose a reasonable way. According to the construction requirements of the dam to complete the concrete pouring work. Therefore this requires the concrete construction to first investigate the site of construction first.
3 Construction technology of compacted concrete
3.1 Mixing concrete construction method
Mixing concrete construction method is the concrete construction is, now the raw materials of concrete together into the mixer, and then the mixer for mixing, through the mixing and crushing technology, the raw materials will be evenly distributed, because of this way the concrete solidification time is later, so the tightness of the concrete but often in the concrete for pouring because of the mixing tank and pouring the zone of high distance, the concrete appears segregation This seriously affects the quality of concrete, so the general requirement of the vertical drop of concrete does not exceed 1.5m is better.
In order to ensure the quality of the dam, it is necessary to have strict control measures on the discharge of the mixing vehicle, the location of the pouring, and the concrete segregation test data. Therefore, this causes the construction is more complex, bad management and other phenomena.
3.2 Laying crushed construction concrete technology
Because the main body of the dam is in the water, it is necessary to ensure the compactness of the concrete construction, the management of concrete quality after the concrete construction is very important.
In many cases, if there are certain gaps between the various layers of concrete construction, on land such gaps may not affect much, but in the water, water will gradually immerse in these gaps, through the flow of water and pressure, resulting in gaps continue to increase, eventually leading to the phenomenon of inter-layer shedding, bringing great harm to the safety of the dam.
So the concrete construction in the dam to do two issues, one is to prevent the bond layer gaps, the other for the prevention of water infiltration. This requires some good techniques to complete the construction of the concrete body. To improve the quality between the bonding layer, its main method includes the construction of a new concrete layer quickly when the concrete is first set, which can make the concrete bonding tight and prevent the formation of cracks at the same time.
When the area of construction is too large, the method of pouring with the aid of steps or laying flat is used. Such a construction method is also susceptible to the construction site, if the construction site is small, it is necessary to use other techniques, usually according to the shape of the dam and then use the construction method of inclined layer pushing paving. This construction method not only conforms to the unique shape of the dam, but also solves the problem of water accumulation by constructing from the bottom up.
But to meet the technical requirements requires good rolling technology, to ensure that the concrete and the bottom layer of a tight connection without air bubbles, water, gaps, etc.. Therefore, the aspects to be controlled include the strength of rolling, the thickness of rolling, the frequency of rolling, etc. In the location of the overflow of the dam because of the high water level, so the highest standard of concrete construction is required.
3.3 Control the temperature of crushed concrete
During the construction of crushed concrete, cracks often appear on the concrete due to improper arrangement of concrete temperature control measures and unfavorable operation. If the temperature of concrete is not controlled in the specified range, cracks will easily appear in the process of rising concrete temperature, resulting in a reduction of the impermeability and quality of concrete.
In order to improve the quality of crushed concrete construction, the temperature control measures for mass concrete should be done during construction. In this project, two main methods are used to control the temperature by increasing the heat dissipation rate of concrete and reducing the heat generation of concrete.
Most of the concrete used in this project is proportioned by three-stage proportioning, and the particle diameter of concrete aggregate is 45-85 mm. in the process of construction, in order to effectively reduce the temperature of the concrete into the warehouse and prevent the appearance of cracks, the construction is not carried out during the time when the temperature is too high at noon.
3.4 Construction technology of rolling and paving mixes
In order to make the concrete paving quality to be effectively guaranteed, paving operations generally use asphalt pavers for construction, in order to ensure that the paving work can be carried out smoothly, to ensure that the leveling reference point to choose, to ensure that the effect of rolling can meet the requirements of the provisions of the project, to keep the pavers can continue to be in a more efficient working condition.
In the paving process, if the paving speed is too fast, the quality of concrete paving is not guaranteed, if the paving speed is too slow, it will affect the efficiency of construction.
Therefore, the operating speed of the paver should be controlled, which is generally based on the power of the paver and the transportation efficiency of the concrete. In the process of paving, reversing or emergency stopping is not allowed, and after the paving work is finished, the mixture should be rolled.
3.5 Maintenance of concrete
After the completion of the paving and rolling operation, to ensure the quality and strength of the concrete, it is necessary to maintain it as soon as possible. The maintenance of concrete is mainly in the following aspects.
(1) To ensure that the moisture and cement have enough time to react, the concrete should be maintained for a sufficient time.
(2) after the paving and rolling of the mix is completed, the surface of the concrete should be covered with materials that have a moisturizing effect, more commonly used moisturizing materials such as plastic film, etc. In order to make the surface of the concrete can continue to be in a wet state, to use water to spray the surface.
(3) In cutting the shrinkage joints, first of all, to ensure that the strength of the concrete to meet the requirements of the cut, in cutting in accordance with the design requirements to cut.
In the concrete construction work of water conservancy and hydropower projects, first of all, it should be clear that the concrete underwater is always subject to strong water pressure, in the construction of concrete so to improve the corresponding quality. Water is a permeable function, very easy to penetrate in the gap between the concrete layer, after the role of scouring lead to structural problems.
Therefore, the technique of rolling is used in construction to help eliminate gaps and improve the degree of compactness during the construction of concrete. The factors affecting the construction site need to be controlled in concrete construction. For example, water, humidity. Temperature, etc. After the completion of the construction, the maintenance of concrete is also very important, do a good job of sprinkling water maintenance work to ensure that the full reflection of cement and water end, do a good job of cutting joints in the concrete body, to prevent the concrete heat up and cold shrinkage on the safety of the dam has a greater impact.