Mixed condensation
land
China National Core Journal of Building Science
Study on durability of buildings under severe acid rain environment
Chen Jianxiong 1, Wu Jiancheng 1, Chen Hanbin 2.
(1 Department of Materials Science and Engineering, Chongqing University Campus B, Chongqing 400045; 2 PLA Logistics Engineering College, Chongqing 40004 1)
[Abstract] In view of the serious acid rain pollution in southwest China, taking Chongqing as the investigation object, a lot of research has been done on the factors affecting the durability of buildings in Chongqing.
Data collection and field investigation. The results show that acid rain has different effects on the durability of buildings in Chongqing. The field investigation results of buildings in different ages further confirm this conclusion.
[Keywords:] durability; Acid rain; corrode
[China Library Classification Number] TU528 33 [Document Identification Number] A [Document Number]1002-3550 (2001)1-0044-04.
1 preface
Acid rain has been widely regarded as one of the factors that have a serious impact on the ecological environment at home and abroad. Due to the restriction of geographical environment, industrial structure and energy consumption structure, southwest China has become the most serious acid rain area. Among them, Chongqing in the southwest of Sichuan Basin and Guiyang in the middle of Guizhou are typical. As a new municipality directly under the Central Government, Chongqing is the largest industrial city in the southwest of China. Since the reform and opening up, the economy has developed rapidly, among which the industry has grown rapidly. However, with the development of economy, the problem of environmental pollution has become increasingly prominent, especially the air pollution caused by the energy structure mainly burning high-sulfur raw coal and specific natural environmental conditions is very serious, which leads to high precipitation acidity, high acid rain frequency and poor precipitation quality in Chongqing. This has become one of the factors that can not be ignored affecting the durability of buildings in Chongqing.
The degree increases. Compared with 1988+098 1, 1 increased by 0.5 times. Fuel consumption and pollutant emissions have also increased accordingly. After Chongqing became a municipality directly under the central government, this number has increased. The sulfur content of Chongqing coal is as high as 3%~5%, the ash content is about 25%, and the combustible volatile matter is 30%. It consumes more than 6.5438+0.5 million tons of coal every year, and emits more than 800,000 tons of sulfur dioxide and 200,000 tons of smoke and dust to the atmosphere, which is unique among cities in China. According to calculation, 60% of sulfur dioxide is converted into sulfuric acid [3]. The molecular weight of sulfuric acid (H2SO4) is 98, so 736,000 tons of sulfuric acid fell to Chongqing and its surrounding areas in various forms every year in 1980s. According to meteorological analysis [4], the frequency of still wind and breeze in Chongqing is above 50% all year round, and the atmospheric structure is very stable. Therefore, only 1/3 of SO2 discharged from Chongqing leaves the city through the atmospheric conveyor belt, and 2/3 is deposited in the city in dry state (gaseous and granular) and wet state (rain, fog, snow and dew) [5].
The air pollution in Chongqing is mainly manifested in the high concentration of sulfur dioxide pollution in the air. According to the monitoring data of Chongqing Environmental Protection Bureau [2], from 198 1 994 to 1994, the annual average range of sulfur dioxide in urban air is (0.26 ~ 0.49) mg/m3, which is 3 ~ 7 times higher than the national secondary standard (0.06 mg/m). The annual average is 0.30 mg/m, and 12 years exceeds the standard by more than 4 times. See figure 1 for details. There are few cities with such a high concentration of sulfur dioxide in China and even in the world. two
three
three
2 air pollution
2 1 concentration and change trend of major air pollutants
According to the statistics of1985 ~1988 [1], the industrial coal consumption in Chongqing accounts for more than 65% of the city's coal consumption. Annual coal consumption in Chongqing
5,000 t ~110,000 t large-scale pollution source enterprises 6 1 family, and the total coal consumption reached 42.6110,000 tons. The number of motor vehicles in Chongqing is also 14%.
Figure 1 Changes of Ambient Air Quality in Chongqing
[date of receipt] 200 1-09- 17
The seasonal variation of sulfur oxide concentration in a year has a certain law, which is usually high in cold season (autumn and winter) and low in warm season (summer and spring). The regional distribution is that urban areas are higher than suburban areas, and counties and towns are higher than rural areas, showing the characteristics of sulfur dioxide emission centered on cities. 2 2 Comparison of air quality between Chongqing and some cities at home and abroad
According to the national environmental protection bureau 1988 published in 23 cities in China.
According to the statistics of SO2 concentration and the comparison of SO2 concentration between Chongqing and some cities in the world [6], the SO2 level in Chongqing is relatively high at home and abroad, as shown in Figure 2. According to the standard of World Health Organization (WTO) (SO2 is 0.06 mg/m3). Chongqing has become one of the representative areas of acid rain pollution in China and even the world.
Fig. 265438-0988 SO2 concentration in ambient air of 23 cities in China.
3 acid precipitation
The acid rain in Chongqing is directly related to the atmospheric SO2 pollution mentioned above. The variation and regional distribution of rainfall acidity and main pollutant concentration are also related to the distribution and pollution of SO2 in the atmosphere. Chongqing is one of the earliest cities in China to carry out acid rain monitoring. In pure air, the pH value of rainfall is about 5.65 because CO2 in the atmosphere is dissolved in rainwater. When the atmosphere contains acid oxides such as sulfur dioxide and nitrogen oxides, the pH value of rainfall will be less than 5.6. According to the monitoring data of Chongqing Environmental Protection Bureau [7], it is severe from 198 1 to 1994.
The range of pH annual rainfall weighted average of precipitation (including rain and snow) is
4 09~4 70。 The frequency of acid rain is above 70%. During 1999, the pH value of precipitation in the main urban area of Chongqing ranged from 3.64 to 7.84, with an annual average of 4.88 and 4.55, and the frequency of acid rain was 38. 1%. See Figure 3 for details. In the first quarter of 2000, the pH value of precipitation ranged from 3.75 to 7.60, the seasonal average value was 4.46, the seasonal average value of acid rain was 4. 1.7, and the acid rain frequency was 34.7%. In the precipitation of Chongqing, sulfate is the main pollution anion, and its concentration accounts for more than 75% of the measured anions, thus forming the characteristics of acid rain erosion with sulfuric acid as the main component, which is different from the situation abroad. See the comparison between Figure 4 and Figure 5 for details.
For more than ten years, the annual change trend of acid rain in Chongqing is not obvious, but the spatial change is worrying. According to the survey, 65! During this period, the coverage area of acid rain below 4.5 is about 1000km2, which will reach the seventh five-year plan! And with
After that, the coverage area of acid rain below pH 4.5 expanded to about 20000km2 in the whole city. The spread of acid rain is very alarming.
4 Acid rain corrosion of concrete mortar
According to the suggestion of Cembureau (European Association of Cement Statistics and Technology), when evaluating the chemical erosion degree of concrete by water and soil containing aggressive substances, the pH value of 6.5 ~ 5.5 is weak erosion; Moderate erosion occurs when the pH value is between 5.5 and 4.5; Strong erosion occurs when the pH value is between 4.5 and 4.0; pH value
Because the hydration products of cement are mainly alkaline silicate, aluminate and a considerable amount of free CaO, the acidic medium first reacts with lime, which drastically reduces the alkalinity of concrete medium. Part of the corrosion products of cement stone are dissolved, and the other part remains in the original reaction place.
Its reaction formula
[8]
As follows:
Calcium hydroxide+sulfuric acid? Calcium sulfate 2H2O
mCaOnSiO2 aq+mH2SO4+H2O？ Manganese sulfate aqueous solution+sodium siliconitrate
In view of the obvious influence of acid deposition on non-metallic building materials and cultural relics in recent years, Cai Yongtai 1988, the former chongqing jianzhu university, conducted comparative tests on mortars with different proportions in the laboratory with simulated accelerated corrosion tests close to the acidity of natural rainfall. The influence of simulated acid rain on the appearance, quality and volume of corroded mortar was studied. The test results show that acid rain has obvious influence on the appearance of mortar. Generally, with the increase of erosion time, its appearance gradually turns from gray to dark. Turn yellow? A gradient of whitening. Corrosion products delaminate and peel off. With the increase of acidity of acid rain,
The neutralization depth of concrete and mortar is also increasing.
[9]
Photo 1 corrosion of telephone poles in Yangjiaping Street
Photo shows the surface corrosion of the old cable car concrete foundation at Tianmen Wharf in Chaochao.
This result is consistent with the appearance of buildings corroded by acid rain observed in Chongqing. The scope of investigation is mainly concentrated in the main urban area of Chongqing, and a large number of buildings built in different periods are investigated and counted. The results show that the surface of buildings built earlier can be eroded by acid rain to varying degrees. In particular, a number of poles produced in the 1950s are seriously corroded. See Table 2 for the survey statistics of poles near Yangjiaping main street highway 1956. From the photo of Yangjiaping main street 1, it can be seen that the surface concrete has become loose due to long-term erosion and erosion, and the surface concrete has peeled off under the load, leaving the steel bars exposed on the surface. Acid rain accelerated the corrosion of steel bars. Photo 2 shows that the concrete foundation surface of the old cable car at Chaotianmen Wharf, which was built in 1950s, was eroded by acid rain. Due to various factors, the cable car has stopped using. The investigation results show that the damage of the main structure of the cable car is obviously affected by environmental factors. The rail surface of the cable car has been peeled off layer by layer due to corrosion, and the concrete at the bottom of the beam has also fallen off in large quantities, and the steel bars have been seriously corroded. It can be clearly seen from photo 2 that with the constant reaction of H+ with cementitious materials in concrete and the scouring of rain, the cementitious materials on the concrete surface have been washed away, and the coarse aggregate is completely exposed on the concrete surface, similar to the water brush stone structure. After careful observation, concrete with limestone as coarse aggregate not only
Cement slurry was corroded by acid rain, and some limestone was also affected by acid rain. Because the old cable car of Chaotianmen Wharf was built earlier, the high water-cement ratio and construction quality of concrete at that time were the factors that caused acid rain to corrode concrete and destroy the structure.
Table 1 pole erosion statistics table
Erosion degree
Slight erosion amount 24
Percentage/%
20
Moderate erosion amount 60
Percentage/%
50
Number of severe erosion 36
Percentage/%
30
Note: Slightly eroded # # surface turns yellow and coarse aggregate is exposed; Medium erosion # # # coarse aggregate exposed, small area of steel bar exposed; Severe corrosion # # # Large area steel bars are exposed and severely corroded.
5 conclusion
A large number of field investigation results show that acid rain has seriously affected the durability of buildings in Chongqing. Acid rain has become one of the factors that cannot be ignored in the durability design of key projects in Chongqing. For a long time, the durability and service life of various buildings and infrastructure projects in China have not been paid enough attention. This has led to a lot of economic losses, waste of resources and various social problems caused by insufficient durability. Therefore, it is suggested to investigate the necessary durability influencing factors of key projects all over the country in combination with local actual conditions.
[References]
[1] Chen Guiyuan. Pollution sources in Chongqing and their influence on acid rain [J]. Chongqing Environmental Science, 199 1, 13 (5): 2-5.
[2] Zhou Baixing, Yu Xu. Acid rain in Chongqing and its control countermeasures [J]. Chongqing Department of Environmental Science
Xue, 1996, 18 (2): 1-4.
[3] Yoshio Noi. Lime? Environment # Purification and Preservation [J]. Gypsum? Lime, 1999, (9):27 1-279.
[4] Richard Dai, et al. Meteorological causes and control countermeasures of sulfur dioxide pollution in Chongqing. China and Japan.
Proceedings of the Symposium on Air Pollution Prevention and Control [J]. Chongqing: Chongqing Environmental Protection Bureau. International Research Group of Japanese Ministry of Education,1992.6438+037-143.
[5] Yu Xu, et al. Analysis of precipitation trend of atmospheric sulfur and rainwater acid in Chongqing. Acid rain
The formation and influence of [R]. Beijing: Environmental Science Information Network of China Academy of Sciences, 1987.257-267.
[6] World Resources Institute (USA), Wang Zhijia et al. World Resources Report (1988~
1989)[R]。 Beijing: China Science Press, 1990.
Chen Guiyuan, Xu Fang, Frida Meng. Acidic sediment # Rain fog dew acidification pollution group.
Chongqing Distribution Law [J]. Chongqing Environmental Science, 1993, 15(5):
25-29.
Zhou Yan, Di Tan Xiao, et al. Guide for durability design of CEB concrete structures [M]. First
Second edition, 1989.63-64. [9] Cai Yongtai. Effect of acid rain on durability of building mortar [D]. chongqing jianzhu university
Postgraduate thesis, 1988, 6:29-35.
[Author Brief Introduction] Chen Jianxiong (1963-) is engaged in the study of concrete durability. Department of Materials Science and Engineering, Campus B, Chongqing University (400045) [Tel] 023-68707274; E-Mail:Jacob.wu@263.net
Building durability survey
Xiong, Cheng, Bin
(College of Materials Science and Technology, Chongqing University, Chongqing, China 400045) Abstract: For the severe rain pollution in southwest China, taking Chongqing as an example, the investigation report provides some data and results related to the building durability factors in Chongqing. The results show that many buildings in Chongqing are aging in different degrees due to the influence of acid rain. Acid rain; corrode
5438+00 Production, sales, storage and price of cement enterprises in China in June this year
This month, there were 0/06 cement enterprises/kloc-0 (an increase of 0/6 compared with the same period of last year), producing 0/0465800 tons of cement, an increase of 0/310% compared with the same month of last year, and the cumulative production of cement was 93219.
It decreased by 3.2%, and the cumulative sales of cement was 9399 1.8 million tons, up by 1.59% year-on-year. This month, the sales rate of cement was 65,438+000.76%, which was 4,654.38+06 percentage points lower than that of last month, and the cumulative sales rate was 65,438+000.83%, which was 2.77 percentage points higher than that of the same period last year. At the end of the month, the cement inventory was 3.2710.4 million tons. (Compared with the same period, excluding new enterprises)
.
In the same month last year, cement production increased, and sales exceeded production. Enterprises with sales exceeding output accounted for 46% of the reported enterprises, and they were distributed in 3 enterprises in North China, 5 enterprises in Northeast China, 6 enterprises in East China/KLOC-0, 3 enterprises in Central South China/KLOC-0, 5 enterprises in Southwest China and 7 enterprises in Northwest China. Road, slag and low-alkali special cement are the leading products of infrastructure construction in the future.
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