Polyurethane insulation moisturizing test on concrete dam surface Du Bin Ren Zongshe 2, Zhou Bingliang 2 (1. Yichang Tianyu Technology Co., Ltd., Yichang, Hubei 443002; 2. Yellow River Hydropower Company Laxiwa Construction Branch, Qinghai Guide 811700) The dam of the Lijiaxia Hydropower Station, which is close to the natural climatic conditions, conducts the spraying test of polyurethane foam under natural environmental conditions, and investigates the spraying of concrete under different spraying schemes of different colors, different thicknesses of polyurethane foam and surface grouting cement in low temperature environment. Insulation and moisturizing effect, and observation and analysis of prototypes for up to 2 months by thermometer and hygrometer embedded in the polyurethane insulation layer. The test results show that compared with the conventional insulation materials, the spray polyurethane foam construction process is simple, the product performance is stable and reliable, and has good economy. The spray polyurethane foam can satisfy the heat preservation and moisturizing effect under various test conditions.
Patent project: Patent of National Intellectual Property Office (L012590649)-), male, Sichuan Nanchong, senior engineer, master, engaged in water conservancy and hydropower engineering new technology, new materials research uE-mailtianyuduHfevip.sinacom two / 62Amr Guangshuili hydropower technology progress, 2007 The 27(2)1Te/Laxiwa Hydropower Station is located in the alpine region of northwest China, and is located in the mid-latitude inland plateau, which is a typical continental climate. In winter, the extreme temperature is low, dry and the temperature difference between day and night is large, the cold wave is frequent and often accompanied by strong winds. The average annual temperature is 7.2Â°C, the average monthly minimum temperature is 0.3, the minimum temperature is 23.8Â°C, the average annual rainfall is 259mm, the evaporation capacity is 2004mm, the cold wave frequency is 10.2 times, and the annual freezing and thawing cycle is 117 times. The average temperature of the temperature difference greater than 15 Â°C is 190d. The long-term thermal insulation technology of the dam in the alpine region is complicated, and there are many control links and uncertain factors. In order to meet the thermal insulation requirements of the construction of high concrete arch dams in the alpine region, the Laxiwa Hydropower Station Before the dam begins to pour concrete, it is necessary to select suitable dam insulation and moisturizing measures, so it is necessary to carry out the dam insulation moisturizing test in advance.
Since the Laxiwa Hydropower Station is still in the stage of foundation pit excavation, the conditions for spraying polyurethane test on the dam concrete structure are not available. Therefore, the Lijiaxia Hydropower Station, which is close to the geographical location and natural conditions of the Laxiwa Hydropower Station, is selected for testing.
The Lijiaxia Hydropower Station is located in the hinterland of the inland plateau and has typical continental climate characteristics. It is long and cold in winter, cool in summer, with large daily temperature difference, short frost-free period and strong solar radiation. The winter is controlled by cold and high pressure, the weather is dry and cold, and there is often a cold wave intrusion. The average maximum temperature in January is 2 73 Â°C, the average minimum temperature is 125 Â°C, the extreme minimum temperature - 19.8 spring is slow, the temperature rises slowly, the rainfall is small; the summer and autumn are short and cool, the dam area is dry and the annual precipitation is low. The average annual precipitation is 331mm and the evaporation capacity is 1881mm. The test site is selected to be 2059.0~2087.0m elevation at the No. 9 dam section behind the dam of Lijiaxia Hydropower Station. Considering that the Lijiaxia Hydropower Station was built in the 1990s, the temperature and humidity inside the dam have been basically stable. Therefore, this test mainly studies the effect of spraying different thickness of polyurethane materials on the surface temperature and humidity of the dam under natural environmental conditions. The effects of temperature and humidity inside the concrete are not considered.
The main purpose of the test is: 1 For the construction requirements of the Laxiwa Hydropower Station, the selection of the spraying polyurethane equipment and the modification of the construction equipment can meet or meet the construction conditions; 2 The original shape observation of the construction of the thermal insulation material of the Laxiwa Hydropower Project Obtain the data on the moisturizing effect of polyurethane foam in low temperature environment; 3 Observe and analyze the thermal insulation of colored polyurethane and polyurethane surface with cement slurry protection surface while understanding the material properties.
1 Test materials For many years, the thermal insulation and crack prevention of dam projects generally use foamed plastic sheets or cardboard, or foamed plastic sheets with polyvinyl chloride film and polystyrene foam plastic sheets, as well as insulation quilts, polyethylene air cushion films, and polyethylene. Foam plastics are waiting. These materials have complicated construction techniques and unstable insulation effects during use, which provides a new way for crack resistance of dam concrete.
1.1 Polyurethane foam material Polyurethane is the abbreviation of urethane high polymer, which has high tear strength, tear strength, wear resistance and outstanding impact resistance, and has good decorative properties and excellent resistance. Chemical corrosion properties, therefore, people often use it as a film-forming material to synthesize protective coatings, widely used in the field of decoration and anti-corrosion. In recent years, with the development of reactive spray molding technology and mature polyurethane, it has the advantages of no pollution to the environment, no heating, energy saving, rapid curing, and short construction period. See the physical and chemical properties of polyurethane.
In the foaming process of polyurethane foam, the material reaction is carried out simultaneously at a relatively fast speed. In the presence of a catalyst, some of the reaction can be largely completed in a matter of seconds, and finally a high molecular weight and a polyurethane having a certain degree of crosslinking is formed.
1. The color of polyurethane foam Because the color of polyurethane foam is yellow, it will gradually turn into brown under the influence of long-term sunshine, which affects the beauty of the dam. In order to solve this problem, the author's company has completed a series of experimental research, has completed the preparation of color rigid foam insulation moisturizing material, while achieving good color effect, without any adverse effect on the strength and density of polyurethane foam, the product is in Good performance in terms of dimensional stability and chemical resistance.
Dimensional stability. When the polyurethane foam is heated or frozen, its size and volume will change. The rate of change is related to the foam type, structure, density, molding conditions, foaming agent type and environment. Polyurethane foam does not change significantly in temperature below 100 Â°C, and has low temperature resistance during long-term low temperature. The polyurethane foam has a dimensional change rate of less than or equal to 1% in a temperature range of 24 to 35 Â° C. Chemical resistance. Polyurethane foam is resistant to a wide range of organic solvents. In some highly polar solvents, swelling occurs, and in concentrated acids and oxidants, decomposition occurs. The chemical resistance of polyether type colored polyurethane foam is shown in Table 1. Table 1 Chemical resistance of polyether type colored polyurethane foam Resistant chemical resistance Reagent type Resistant chemical resistance Gasoline good brine (0%) Excellent diesel Excellent turpentine excellent kerosene good motor oil excellent toluene excellent benzene good hydrochloric acid (0%) good hydrochloric acid (concentrate) reaction sulfuric acid (concentration) reaction 2 spraying process spraying polyurethane material process, the author has obtained the national utility model patent P. construction Before the test, the climatic conditions of the construction site, the characteristics of the polyurethane foam, and the process of spraying the polyurethane material were analyzed in detail. The problems encountered during the construction of the sprayed polyurethane rigid foam were estimated, and the following principles were formulated and followed: in principle. When spraying polyurethane rigid foam material, it should be constructed according to the top-down or bottom-up order principle to effectively control the spray quality.
Layered spray principle. Layered spraying is the main construction process in spray application. When spraying polyurethane foam, the thickness of one spray should not exceed 15, which ensures that the polyurethane can get enough space when it reacts. If the spray is too thick at one time, the foam may perforate, and a good closed cell ratio is not obtained, which directly leads to foam quality problems.
The principle of uniform dispersion. In the spraying construction, the sprayed polyurethane rigid foam material should be evenly dispersed. The spray gun and the spray gun nozzle should be correctly selected before spraying. Generally, the flat spray is mainly used for flat spray or round spray gun nozzle. If it is not evenly dispersed during the spraying process, the foam formed after spraying will be uneven, affecting the aesthetics and quality of the dam, and wasting polyurethane material.
Constant temperature principle. The polyurethane rigid foam is required to be thermostated within the optimum reaction temperature range of the material after it is extracted from the raw material tank by the primary pump until the spray gun is ejected.
Safety principle. During the construction process, the construction personnel should be in contact with the chemicals. At the time of spraying, a certain pressure and temperature must be maintained. Therefore, the principle of â€œsafety firstâ€ must be followed at all times.
3 Test Arrangement 3.1 Test Division The test was divided into 4 sections, and the sections and sprayed materials of each section were as shown. The spraying test construction period is from January 2 to 7, in which the A zone is selected to be constructed at a relatively low temperature, in order to test the moisturizing effect, durability and appearance quality of the polyurethane foam and the sprayed cement surface in a cold temperature environment.
The polyester foam is sprayed with fine spray. 5111 thick polyester foam sprayed 5cm thick / color polyester foam poly 05 foam spray polyurethane foam test zone schematic. 2 On-site temperature measurement and humidity instrument installation Two or three sets of thermometers and hygrometers are embedded in each test area, each consisting of three thermometers and one hygrometer. Install 3 thermometers in Zone D and Zone B, and install 2 hygrometers in Zone A.
The thermometer is a resistance type thermometer. When it is buried, it is close to the concrete surface. After the thermometer is covered by the insulation material and sprayed to the required thickness, the temperature measurement starts, and the temperature measurement time is 2 months. The embedding of thermometer and hygrometer is shown in Table 2. 4 Test results analysis Through the long-term observation of the thermometer and hygrometer buried under the polyurethane insulation layer, a large amount of temperature and humidity data were obtained, and the measured temperature and Measured humidity analysis.
4.1 Measured temperature analysis The temperature measurement period is from January 3 to March 16, 2006. During these two and a half months, three typical phases occurred, namely the daily temperature change phase, the temperature rise phase, and the temperature dip phase, as shown.
During the ~16 days, the number of temperature measurements per day was 4 times, and the temperature at 9:20:00 was close to the lowest temperature and the highest temperature in the whole day.
For the convenience of analysis, the concrete surface thermal insulation coefficient is defined as K, and the calculation formula is as follows: Here, the temperature variation refers to the daily variation. The smaller the K value, the better the insulation measures will be.
It can be seen from the data that the K value of the A region is 0.22B, and the K value is 0. 28, the K value of the C region is 0. 28, and the average value of the D region is 0.24. It is the K zone of concrete surface insulation coefficient of A various schemes, followed by zone D, and the heat preservation effect of zone C is about the same as that of zone B.
4.1.2 Temperature rise stage Table 2 Test equipment embedding at different depths Instrument name No. 1 instrument concrete surface No. 2 instrument concrete concrete inside 15cm3cm3 instrument concrete 5cm4 instrument concrete surface No. 5 instrument concrete 1.5cm6 instrument concrete Inside 5cm7 instrument concrete surface No. 8 instrument concrete 15cm9 instrument concrete 5cm thermometer Tp1 shows spraying 5cm thick color polyurethane; 1 means adding 1 No. 3 instrument, 2 means adding 1 No. 4 instrument.
As shown in the temperature rise phase, from 23 February to March 10, the temperature rises from 23 Â° C to 23 Â° C for 23 d. It shows the advantages and disadvantages of various schemes and the daily temperature change phase. The results are consistent, that is, on the concrete surface, the temperature rise in the D zone and the A zone is the least, the C zone is the second, and the surface temperature of the B zone rises the most.
The temperature variation of concrete at different depths shows that the temperature gradient of the concrete surface is 1.5cm deep, and the concrete temperature changes slowly within the depth range of 1.5~5.0cm.
It can be seen that the concrete surface should be the focus of temperature stress analysis.
The surface temperature of the concrete in the 1Â°QB area increased by 45. The surface thermal insulation coefficient K was 0.37, which was much larger than the surface thermal insulation coefficient of the daily temperature change stage of 0.28. The results of other schemes were similar, which indicated the thermal insulation effect and temperature change effect of the thermal insulation measures. Time is relevant, and attention should be paid to the time factor when evaluating the insulation effect of insulation materials.
4.13 On the 12th day of the sudden temperature drop, it experienced 1 cold wave. The temperature dropped from 995 Â°C to 1.9 Â°C in 2d, and the average daily temperature dropped by 6 Â°C. During the temperature dip, the internal temperature of concrete at different depths changed. It is roughly equivalent to the temperature rise phase (see). The main difference is that the cold tide lasts for a short time, so the surface thermal insulation coefficient is similar to the daily temperature change phase. The K in zone B is 0.28, and the K in zone D is 0.23. The temperature change of concrete at different depths during cold wave 4.2 The measured humidity is the concrete in zone B. The humidity change process line, the average humidity of the dam site area varies between 30% and 60%, and the average value is 43.2%. If there is no moisturizing measure, the concrete surface will have a large dry shrinkage stress.
It shows that after spraying polyurethane foam, the humidity of the concrete gradually rises and stabilizes quickly, maintaining between 74% and 78%, which is basically not affected by the change of external humidity. The difference between the concrete surface and the depth of 3cm is also from the beginning. 20% dropped to 2%, indicating that the moisturizing effect of polyurethane foam is very significant.
5 Conclusion Through the analysis, it can be seen that due to the low thermal conductivity of the polyurethane material itself, the polyurethane foam and the dam surface have good bonding ability when using the spray application process, regardless of which scheme of A, BC, D is adopted, in the cold Under the dry condition, the polyurethane foam has good heat preservation and moisturizing effect, which satisfies the requirements of heat preservation and moisturization of the concrete dam surface.
Polyurethane foam has a remarkable moisturizing effect, and a 1.5cm thick polyurethane foam can be used to obtain a good moisturizing effect.
When the spray thickness is the same, the heat preservation and moisturizing effect of the colored polyurethane foam insulation layer is slightly inferior to the natural color polyurethane foam; the surface of the polyurethane foam plus spray cement has a certain effect on improving the heat preservation and moisturizing effect of the concrete, but the effect is not significant.
Compared with other insulation and moisturizing processes applied in water conservancy and hydropower engineering, polyurethane foam materials can save bonding costs and laying man-hours due to the use of spraying technology, and have high material utilization rate and good comprehensive economic benefits.
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