According to the data of the multi-year average temperature in the Three Gorges Dam area, the temperature is relatively high from April to October every year, especially from May to September. The average outside temperature is as high as 29°C. Therefore, the Three Gorges Corporation will set the summer period from April to October as the summer construction phase. During the concrete construction in the summer construction period, the temperature control of concrete has always been a matter of concern to everyone and a technical problem that is difficult to control. For this reason, the owners, design, supervision, and construction units all attach great importance to the temperature control of concrete.
The tender documents for the second phase of the Three Gorges Project put forward strict requirements for the temperature control of the Three Gorges Project. It is required that the exit temperature of the concrete should not exceed 7°C (7°C concrete) during the summer construction period, and that the temperature required for pouring the concrete should not exceed 14°C. At the same time, the construction unit is required to take the necessary measures to ensure that the maximum temperature inside the concrete does not exceed the design allowable value. The most effective method is to pre-cool the aggregates and add ice when the concrete is mixed to ensure that the exit temperature and pouring temperature of the concrete meet the requirements of the tender, supplemented by water cooling, concrete surface water flow, spray curing, and other measures. In order to achieve the purpose of reducing the maximum temperature of concrete.
1Concrete storage number and cement usage Basic situation The left bank non-overflow dam No. 18 dam foundation construction base surface elevation is EL86.0m, and the warehouse surface is an upstream low and high downstream slope. The area of ​​the warehouse is about 500m. 3. Within the range of 1m around the orifice of the row of sand holes, there is R 400 impact and abrasion resistant concrete, and the rest is R 300 concrete. In order to facilitate the construction and reduce the construction interference, the warehouse number shall be prepared in the process of the construction of the tank number by one-time pouring to the bottom EL 90. 0m. However, the concrete in this area is located in the strong boundary of the foundation, surrounded by the old concrete surface and bedrock, and it is also poured in the higher temperature season. Therefore, the temperature control technology problem is particularly prominent.
Concrete No. 18 of No. 525 No. 514 Jingmen No. 525 No. 525 No. 525 No. 525 No. 525 No. 525 No. 525 No. 525 No. 525 No. 525 No. 525 No. , The maximum cement dosage is 344 kg/m 3, the minimum cement dosage is 3, there are a small amount of Grade II and Grade IV concrete, and the cement dosage is 230kg/m respectively. 3. Due to the early strength of the cement, the heat of hydration rises quickly. The characteristics, together with the high concrete content of the poured concrete, are important for controlling early concrete temperatures.
This warehouse number is densely packed with steel mesh, and the pouring method can only be used for warehousing with the MQ2000 type door machine. The door machine runs at a slow speed and the pouring speed is relatively slow. The left side of the warehouse number is the exposed bedrock, and the right and the back are preceded by block concrete with a height difference of more than 10m. The 18th dam section of the non-overflow dam on the left bank is enclosed by a product type, and the construction surface is complex. It is difficult for machinery and equipment to operate quickly.
2 Concrete temperature control measures 2.1 Decrease the concrete pouring temperature a. Control of the concrete outlet temperature. Because this site is very important, and in the second phase of the Three Gorges Project, it was the first time encountered a high-grade concrete such as an intake. Therefore, before pouring the warehouse number, the owner, design, supervision, and other units conducted a special project on this part of the pouring program. discuss. After discussion, it is believed that the temperature of the concrete exit should be controlled firstly. The temperature of the concrete exit should not exceed 7°C, and the pouring temperature must be controlled at 10°C to ensure 11°C. After the adoption of appropriate measures, the standard for the concrete exit temperature does not exceed 6 °C. The construction company strictly follows the requirements of the Three Gorges Corporation and takes corresponding measures to control the temperature of the concrete exits to be below 6°C. According to this requirement, the aggregates are first pre-cooled and iced while the concrete is being mixed (the cooling system of the mixing building is designed at 7°C concrete). From the field measured data, the concrete outlet temperature is up to 5 °C, and the average concrete outlet temperature is about 4 °C. It can be seen that the capacity and system operation of the cooling system of the mixing plant can meet the special temperature control requirements of various concretes. The normal operation of the mixing building has provided the most basic guarantee for the quality of high-grade concrete after pouring.
b. Controlling temperature rise during transport and storage of concrete.
The warehouse number was placed on a plate at 2:20 on April 29, 1999 and closed at 8:50 on May 1. The door machine is used for warehousing. The distance from the material receiving port of the mixing building to the door hopper is about 250 m, and the transportation time is about 1.5 min. The hopper of the concrete transport vehicle is equipped with awnings to prevent the excessive temperature of the concrete caused by solar radiation. Pick up. From the transportation time point of view, the temperature of the concrete temperature rise is relatively small, but the site is densely packed with steel, it is difficult to vibrate by hand, and the pouring speed is slow. Therefore, there is a pressing phenomenon of the pressing car, so that the concrete temperature has a certain rise, but all satisfy the concrete. Storage temperature requirements. In order to reduce the temperature rise of the concrete caused by the inconvenience of the pouring speed, the pouring unit allocates a large amount of labor force, strengthens the vibrating force of the concrete, increases the pouring strength, and avoids the pressing phenomenon of the pressing car as much as possible. Therefore, the temperature rise rate of concrete during transportation and warehousing is relatively small. The average concrete storage temperature measured during pouring is 4.4°C, and the recovery rate is 10, which is far less than the entrancing of the concrete from the exit from the tender. 25 recovery rate.
c. Strengthen the insulation of the warehouse surface to reduce the temperature loss during the pouring process.
In the pouring process, especially in the daytime, if any concrete is exposed to the sun, the temperature of the concrete will rise linearly, and the concrete pouring temperature will hardly meet the requirements. The temperature control measures adopted in the pouring process include heat preservation materials such as straw-covered mats, EPE sheets, etc. to keep warm and reduce the temperature loss of the concrete. From the actual measurement of the site temperature and pouring temperature of the concrete can be seen, covering the mat and EPE sheet insulation materials, the effect is remarkable. The actual measured temperature of the concrete in the warehouse is up to 7°C, and the average storage temperature is 4. 4°C. The highest casting temperature was 11°C, and the average pouring temperature was 6.9°C. The control of concrete pouring temperature has achieved satisfactory results, which has played a significant role in controlling the maximum temperature rise inside the concrete.
d. Manually reduce the outside temperature and reduce the loss of concrete temperature.
From the pouring time point of view, most of the concrete control is poured at night when the temperature is low, so the concrete temperature control reduces some of the burden. During the pouring process, the highest measured outside temperature was 28°C, the lowest was 13.5°C, and the average temperature was 19.9°C. During the pouring process, the daily temperature from noon to 17:00 pm is relatively high, and it is easy for the concrete to cause excessive temperature rise. The main measure is to adopt the method of aerial spraying around the top of the warehouse number, and use a high-pressure nozzle or a gun to spray water mist on the first-placed blocks on both sides of the block A of the non-overflow dam No. 18 of the left bank. The method of using air spray is effective for reducing the outside air temperature. The higher the air temperature, the greater the reduction. The field measurement data is: When the outside temperature is 28°C, the temperature of the warehouse (under direct sunlight) can be reduced by about 2°C by cooling the spray, and the temperature within the mist can be reduced (in the sun's dark side). 4°C. It can be seen that the method of using air spray to reduce the outside air temperature is very effective, and it is very helpful for reducing the concrete temperature.
2.2. Decrease the heat of hydration of the cementitious material a. Cool the concrete by cooling water. Due to the severe temperature control situation in this area, and the rapid rise in the temperature of the concrete hydration, the opening of the warehouse number began to pass 6 ~ 8 °C cooling water cooling to reduce the heat of hydration temperature. In view of the fact that the cement hydration heat rises quickly and high, in the early stage of water cooling, the method of increasing the flow rate of water is used to control the maximum temperature of the concrete within 30°C so as to ensure that the maximum temperature difference between the cooling water and the concrete is not Exceeds the design limit of 25°C. After 4 days of water flow, the maximum temperature inside the concrete was 27.9°C, but it did not rise to 30°C and the control was ideal. After that, the temperature inside the concrete began to fall. At this time, it began to reduce the flow of water to 20-25 L/min, and accordingly increase the inlet temperature of 7-8 °C, to ensure that the cooling rate is not greater than 1 °C / d. In the water cooling After 7 days, the maximum temperature inside the concrete has dropped below 24°C. In order to avoid temperature stress caused by excessive cooling, the cooling of concrete is stopped at this time. After analyzing the temperature change for 7 consecutive days after water stoppage, the internal temperature of the concrete slowly rises after the water is stopped. In the early stage of water stoppage, the temperature will rise by about 0.3°C per day, and the temperature will not rebound too much.
b. Surface water conservation cooling. The concrete number on the storage floor is R 400. The heat of hydration rises. To reduce the internal temperature of the concrete and prevent cracks on the concrete surface, the water mixture of cooling water and system water is used to start the concrete after 25 hours of the warehouse closing. Surface water conservation. From the measured concrete surface temperature, the measured concrete surface temperature is 2~3°C lower than the ambient temperature, which plays a significant role in reducing and controlling the internal temperature of the concrete.
3 temperature control detection methods In order to facilitate the inspection and understanding of the concrete internal temperature conditions, take the necessary measures to control the internal temperature of the concrete in a timely manner, in the water inlet bottom plate center line two marking areas choose a representative location buried two thermometers CT181 and CT182, The buried elevations were Y = 48 091 .25. A cooling water pipe with a spacing of 1.5 m x 1.0 m was placed at 50 cm at the bottom of the two instruments. According to the results measured in the first two weeks of the two instruments, the entire temperature can be seen. The change process is smooth and there is no mutation. The temperature rose after cooling stopped, indicating that the temperature control measures adopted were reasonable, and the temperature-controlled cooling measures were also implemented well.
in. Then, after the test section wall reached a certain age, the cores were drilled at different depths at the stations 7 057 and 7 051. After testing, the compressive strength of the test blocks was 2.95-7.39 MPa. The coefficient is cm/s to meet the design requirements. At the same time, the selected parameters are reasonable.
2.3. Control of construction quality After completion of the test, complete construction shall be carried out according to the test parameters. The construction axis shall be arranged on the side of the embankment of the embankment. The distance between the two shall be 6 m. The construction shall begin with the downstream station number 7 084 and end with the upstream station number 6 834. , Full length 250m. From the whole process, the construction progressed smoothly, but there are also some problems, such as: encountered a hard layer (gravel clay) in the pile 6854 ~ 6834, hole depth 8 ~ 16m, difficult to sink The die-to-design depth was dealt with in a timely manner due to mechanical failures, blackouts, and other reasons.
In the construction process, strict implementation of the three inspection system, according to the characteristics of the project and process, the continuity, verticality, slot depth and slurry preparation as the focus of control.
a. Continuity. When inserting the second slot segment, it must overlap with the first slot segment by 0.2 - 0.3m. At the same time, a 0.55m guide plate is installed on the side of the end of the steel mold, which overlaps with the first slot tile and serves as a guide and connection. .
b. Verticality. Before the steel mold is inserted, level the pile chassis with a horizontal ruler, hang a vertical ball on the pile frame, and adjust the length of the diagonal pull rod to ensure that the upper vertical guide frame is vertical. The inclination does not exceed the planned 0.3.
c. Slot depth. According to the geological survey data and the speed of vibration of the vibration board, the lower limit depth of the impervious wall is determined.
d. Slurry. The materials used must meet the requirements of the relevant national regulations and no damp and agglomerated cement shall be used. The ratio is determined by tests. When the slurry is stored for more than 4 h, it should be treated as spent pulp, and the mixture must be sieved and perfused.
After construction, cores were taken at different depths at stations 7 081 and 7 045, respectively. The compressive strength of the test piece was 2.76-3.6 MPa, and the coefficient of permeability cm/s all met the design requirements.
3 Conclusion The cut-off wall as a new type of anti-seepage wall technology has been successfully applied in the embankment anti-seepage reinforcement project in Huizhou. The principle of wall forming is simple, the construction is convenient, the mold sinking, draft drawing, vibrating, wall forming speed, high efficiency, good quality, thin wall, low cost, easy to ensure the integrity and quality of the impervious body. This technology is suitable for the soil layer, sand layer, and gravel layer with less gravel, and should be used with caution when the gravel content is large and the grain size is large or the treatment depth reaches a new level (above 25 m).
4 Conclusion a. The left bank non-overflow dam No. 18 dam block A sand steel inlet plate in the pouring process of the various aspects of the temperature control measures such as reducing the concrete exit temperature, speed up the concrete pouring speed, strengthen the storage number, reduce Outside air temperature, artificial cooling water cooling, concrete surface water flow maintenance, etc. are all implemented better, and the effect is obvious, indicating that these experiences are worthy of promotion.
b. The temperature control of Block A at the No.18 block of the non-overflow dam on the left bank is better because of several favorable conditions, such as the short distance between the warehouse and the mixing plant, and relatively low outside temperature. However, the temperature control of Block A at the No.18 dam of the non-overflow dam on the left bank has obvious deficiencies. For example, the flow rate of water in the early stage is too large, and its cooling effect is not very good, and it may cause disadvantages in concrete deformation. When artificially reducing the outside temperature, the scope of spray of water mist is too small, the degree of atomization of water is not ideal, and the extent of reduction of outside air temperature still needs to be improved. According to the analysis of measured data, artificially reducing the range of external air spray, the degree of atomization of water is large, and the reduction in outside air temperature will also increase.
c. In the hot season construction, the difficulty of concrete temperature control will gradually increase. What is worth noting in the future is that all measures must be put in place. Only the above measures may not necessarily ensure the concrete temperature control of the inlet of the unit, and further tests and studies of new methods and measures for temperature inspection are required. ? Newsletter?
The growth of wind power installed capacity in the world's three largest wind power installations in recent years Wind power generation is a kind of sustainable development of green energy. In recent years, it has developed rapidly in the world, especially in Germany, the United States and Denmark, and has become the world’s largest installed wind power. Countries. The growth of wind power installations in recent years is shown in Table 1.
Year wind power installed capacity in each country / 10,000 kW Germany, the United States Denmark, the average annual growth rate for five years can be seen from Table 1: 1 these three countries in the recent five years, wind power installed capacity has doubled, with an installed capacity of 2 million kW the above. India and Spain ranked far behind are ranked far behind, and the gap with Denmark has expanded to over 1 million kW. 2 From the perspective of development speed, Germany ranks first, with an average annual growth rate of 40.1 over five years, which is more than one times higher than that of the United States. In 1997, the number of installed wind power units surpassed that of the United States and ranked first in the world. In the following three years, the development momentum continued unabated, further widening the gap. According to reports, the annual power generation of wind power in Germany can reach 100 million kW under normal conditions. h , accounting for the total annual power generation in Germany (Wu Gao's contribution)
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