Concrete carbonation analysis

1、concrete carbonation analysispick to: building of concrete carbonation, has great influence on its durability, serious when make concrete crack, flake, protective destruction, which eventually led to the structures destroyed. this paper mechanism and influencing factors of concrete carbonation is an

2、alyzed, and puts forward the induction of concrete carbonation simple test methods and preventing measures. the management on the hydraulic structure concrete maintenance and prevent aging are to have the certain reference value.keywords: concrete carbonation analysisbuildings in concrete structure,

3、 and the concrete structure composed more than the bad climate environment is, the sediment, waters, physics, chemistry, temperature, etc many influential factors. concrete destruction to carbide, freeze-thaw damage, which is a common in many buildings running life is much shorter, causing tremendou

4、s waste. it is necessary to further explore of concrete carbonation hydraulic structures, freeze-thaw failure mechanism and preventive measures. 2 concrete carbonation, freeze-thaw failure mechanism analysis1. the mechanism of concrete carbonation in three silicate minerals cement calcium and calciu

5、m content more, two silicate about 75% of the total weight, cement hydration, completely the hydration calcium silicate gel generation accounts for 50% of the total volume, about 25% of calcium hydroxide, mainly depends on the strength of the cement paste.the hydration calcium silicate, the content

6、of water shutoff in concrete accounted for 25% of the total volume. concrete has the characteristics of capillary - pore structure, these capillary - pore including concrete molding remained on the cement paste.the bubble, the wool stoma and gel hole, and cement stone and aggregate contact place cai

7、ties which act, etc. in addition, still may exist because the cement paste.the drying shrinkage and temperature deformation caused by micro cracks. ordinary concrete porosity of general no fewer than eight - 10%. concrete carbonation refers to the first carbon dioxide in the atmosphere permeates the

8、 pores in concrete, and then dissolved in water, and the wool stoma cement hydration process produces hydration calcium silicate and calcium hydroxide etc hydration products generate calcium carbonate interactions, such product. so, concrete carbonation is due to concrete exists in pore, filled with

9、 water and air, the gas phase in concrete, liquid and solid phase on a very complicated physical and chemical continuous process multiphase. concrete strength of concrete carbonation have increased the function and reduce the permeability, it could be because the moisture out carbide cement hydratio

10、n and calcium carbonate to promote the precipitation reduced the reason cement paste.the pore. but, after the concrete carbonation, speed up the alkaline reduce corrosion of reinforcement. concrete carbonation is the concrete was a chemical corrosion. the co2 gas in the air in concrete, permeate rea

11、cts with alkaline substances generated carbonate and water, after the process of concrete alkalinity reduce concrete carbonation, called again called neuter, the chemical reaction is: ca (oh) 2 + co2 = caco3 + h2o. cement hydration process in the form a calcium hydroxide, make concrete filled the ga

12、p, the saturated alkaline medium calcium hydroxide solution of reinforced good protective effect, make steel surface generating the undissolved fe2o3 and the fe3o4, called purification membrane. after carbide concrete alkalinity reduce carbonization of concrete, when more than in water and protectiv

13、e air existence condition, can make of reinforced concrete lose a protective effect, reinforced began to rust. visible, concrete carbonation generally not the direct causes of its performance degradation, for conerete, carbonization and enhance the durability of concrete effect, but for reinforced c

14、oncrete speaking, carbonation can make concrete alkalinity lower, at the same time, increase concrete hole solution hydrogen ions quantity, thus makes the protective effects of reinforced concrete abate. the frost resistance of concrete by physical function is concrete and temperature variation (dro

15、ught-wet change, freeze-thaw changes, etc) on the one hand, the durability of concrete is a reflection of the important indexes. the frost resistance of concrete couldnt only understand the nature of freeze-thaw for resistance in cold region, not only the concrete buildings have anti-freeze requirem

16、ents, tepid area by concrete buildings will also be dry, wet, cold, hot alternate damage, experience time long will occur surface peeling, structure phenomena, such as osteoporosis or damaged, zhejiang province of hunan province of fuchunjiang hydropower station, reservoir, etc make has happened dif

17、ferent degrees of freeze-thaw damage. so for the research of concrete freeze-thaw destruction becomes especially important. on concrete freeze-thaw damage mechanism of the current understanding is not completely consistent, according to accepted by the high degree owerse american scholar, t.c.p prop

18、osed expansion pressure and osmotic theory, bibulous saturated concrete in the process of its freeze-thaw, suffer damage stress mainly consists of two parts. one is when concrete in a negative the wool stoma water temperature changes by found happened under water turns into ice, volume dilatancy 9%,

19、 by wool stoma wall constraints, thus forming inflationary pressure in the microstructure of the holes produce around tensile stress; the second is when wool stoma ice frozen water by gel in concrete hole supercooled water microcosmic structure of migration and weight distribution of permeability ca

20、used pipe voltage. due to the effect of surface tension, concrete wool stoma freezing water as aperture gaps and decrease of reduced. gel hole formed the temperature of the water ice nucleation below in - 78, and by ice and water of saturated steam pressure differential between the salt water and mo

21、isture transfer caused by poor concentration formed osmotic pressure. another gel increasing inflationary pressure, to form larger, when concrete, the two whostillhave pressure will damage the concrete internal microstructure, only when after repeated freeze-thaw cycle, the damage accumulating after

22、 expanding constantly, develop into each other, make connecting cracks of concrete strength gradually reduce, finally even completely lost. from practice, it is easy to see in dry conditions of concrete obviously does not exist freeze-thaw damage problem, so saturated state is concrete occur one of

23、the essential requirements of freeze-thaw destruction, another prerequisite is plus or minus outside temperature change, make pore water in the concrete natural freeze-thaw cycle, the repeated episodes of two necessary condition, decided the concrete freeze-thaw damage from the concrete surface laye

24、r of erosion damage began. 3 concrete carbonation, freeze-thaw destructive influence and control2. concrete carbonization influence factors of concrete carbonation hydraulic structures more, have internal factors affecting factor, have external factors. 2.1 influence the internal factors of concrete

25、 carbonation 2.1.1 cement different cement, its mineral composition, mixed material quantity, and admixture, raw chemical composition, the direct impact on different cement activity and concrete alkalinity, has an important influence of carbonization speed. generally speaking, cement clinker is more

26、, the slower the carbonization of concrete. admixtures (water-reducer, air-entraining agent) general all can improve penetration-proof quality, abate carbonization speed, but chlorine salt anti-freeze, early strength agent, it will seriously accelerate corrosion of reinforcement, should strictly con

27、trol of dosage. 2.1.2 aggregate varieties and grading aggregate gradation different varieties and, its inner pore structure difference is very big, the direct impact on course aggregates of concrete. material dense gradation solid and better aggregate concrete, its carbonation more slowly. 2.1.3 gri

28、nding fine mineral admixtures varieties and quantity has active rigid materials such as water, it is not the admixtures to atherosclerosis, but can and cement hydration precipitation of calcium hydroxide or and join formed the lime interaction with steady strong cementing material, make concrete alk

29、alinity reduced. in water cement ratio unchanged under the condition of using isometric substitute, mixing with the feed replace cement, concrete carbonation speed faster. 2.1.4 dosage of cement increase dosage of cement, on the one hand, can change the concrete workability of concrete, improve cour

30、se aggregates; on the other hand, still can increase concrete alkaline reserves, make its carbonation performance increase, with the dosage of cement carbide speed decreases. 2.1.5 water-cement ratio in the dosage of cement certain conditions, increase water cement ratio, concrete adds, its density

31、of porosity, permeability increase reduced, moisture from the air and harmful chemicals more immersed concrete concrete carbonation, speed up inside. 2.1.6 construction quality performance for the poor quality of construction ofnon-vibrating imperfect, causing the strength of concrete is low, cellul

32、ar, pits and empty for carbon dioxide in the atmosphere, the infiltration moisture content and create conditions of concrete carbonation, accelerate. 2.1.7 maintenance quality concrete forming, must be suitable environment for their maintenance. maintenance good concrete, have gelled good, high stre

33、ngth, light and within the reality erosion resistance, and a strong ability to prevent moisture in the air and carbon dioxide invades inside, delaying carbonization speed. concrete carbonation 2.2 influence of external factors 2.2.1 acidic medium acidic gas (such as co2) into concrete pore dissolved

34、 in the liquid of concrete and cement stone formed acid, the hl, portland, aluminate and other compounds, leading to the neutralization reaction happens gradually metamorphism, concrete cement paste.the reduce alkalinity, this is the cause of concrete carbonation directly responsible. experimental s

35、tudy of concrete carbonation already proof, speed and carbon dioxide concentrations is proportional to the square root of concrete carbonation speed coefficient, namely, with the increase of carbon dioxide concentrations accelerated. corrosion of reinforcement in concrete another important and commo

36、n cause are chlorine ion (cl -) function. liquid chlorine ion in concrete with calcium hydroxide formation hydrochloric acid, calcium chloride, calcium chloride transamination with high hygroscopic, in its concentration and humidity high, can damage violently reinforced passivation membrane happened

37、, crushing another sexual rusted steel. laws 2.2.2 temperature and light concrete temperature pelter, its surface contraction produce tension, once more than concrete, the tensile strength of concrete surface will craze, resulting in the formation, cracks or gradually fall off to carbon dioxide and

38、moisture infiltration created conditions, accelerate concrete carbonation. the sun concrete temperature is high, the concrete temperature back positive aspect of the diffusion coefficient of carbon dioxide in the air for its larger, with calcium hydroxide reaction provides favorable conditions, dire

39、ct sunlight, accelerate its chemical reaction and carbonization speed. 2.2.3 moisture content and relative humidity of relative humidity surrounding media content and carbonization of concrete directly affect the size of the speed coefficient. excess humidity (such as 100%), make concrete pore fille

40、d with water, carbon dioxide easily spread to cement, low humidity activity (such as 25%), the pores in not enough water to make carbon dioxide generated carbonation are not easily, carbonate; when the relative humidity surrounding media for 50 to 70 percent, concrete carbonation fastest. therefore,

41、 concrete carbonization of concrete still depends on the speed of the water and the surrounding media relative humidity. in practical engineering concrete structure of carbonization degree is the upper light, is mainly the result of humidity affects. 2.2.4 freeze-thaw and leakage in concrete saturat

42、ed or water soaking parts, due to temperature changes, variations of concrete pore water alternately flabby, and thawing frozen inflation caused by large loose flake or concrete cracks, lead to concrete carbonation. the seepage can make concrete calcium hydroxide erosion, in the concrete surface for

43、m calcium carbonate crystallization, cause the decomposition of the concrete hydration products, the result is severely reduces the strength of concrete and alkalinity, worsening rebar corrosion condition.3. the simple test concrete carbonation by chemical testing method. the first, then cut off con

44、crete cover drip or daub phenolphthalein agent, see whether discoloration (carbonization of concrete), if found to have carbonigation condition, can be rapidly tested its carbonation depth. 3.1 phenolphthalein agent, according to practical test results compound obtained with 99% of alcohol, add 1% o

45、f phenolphthalein fluid, prepared by a light color; phenolphthalein agent use 96% of alcohol add 4% phenolphthalein liquid, which is brunet prepared phenolphthalein agent. both of these can be used to test the carbonization of concrete. 3.2 concrete carbonation depth detection first will judge and n

46、eeded to cut the concrete surface play testing necessary test depth to clean the surface, then, daub or drip into the has made good phenolphthalein agent. when phenolphthalein agent drops into the concrete swab or within 1 2 minutes later and then have a reaction. if the concrete, the concrete not b

47、ecome red carbonization; if the concrete discoloration, is already carbonization of concrete. because phenolphthalein agent contains a lot of alcohol, easy to volatile, so in testing and observe, faster in concrete carbonation as soon as measured with the carbonization interface size in order to get

48、 accurate carbonation depth. 3.3 obtain concrete carbonation assessment of concrete structure due to hydraulic structure which is different, its carbonation degree part is endless also and same concrete carbonation, so in testing, must be measured a few times more, with its average assessment for co

49、ncrete carbonation. 3.4 test of concrete carbonation digging in concrete carbonization test work processing after completion of concrete carbonation, the detection of the cut surface applied epoxy mortar or epoxy concrete for fill closed processing.4. concrete carbonation concrete carbonation preven

50、tion measures with concrete cancer say, the key is to prevent measures should be taken. 4.1 design according to the structure of hydraulic structures of different forms and different environmental factors of concrete protective covering respectively, adopt different thickness, should try to avoid sh

51、all be by 2-3cm. 4.2 construction of concrete quality stand or fall, construction is the key. one is to choose seriously building materials. cement choose carbonation ability of silicate cement; aggregate gradation for breaking dormancy and choose texture of good sand and stone; construction in addi

52、tion to sieve, sand stone to wash, but also pay special attention to eliminate aggregate of hazardous substances. second, in the concrete can be mixed high-quality appropriate additive, such as water reducing agent, etc, in order to improve the water resistance of concrete certain performance, impro

53、ve its strength and close-grained sex, penetration-proof quality, frost resistance. three is to strictly control the water-cement ratio of concrete, the requirement is low water-cement ratio during solidification, low collapsbillity, to put the dosage of the water control in meet the minimum ingredi

54、ents and construction need within the scope of concrete, minimize the free water. four is vibrating and maintenance, vibrating must fully and strictly according to the prescribed standards and, when necessary, surface treatment; maintenance must promptly, once the concrete to initial setting, it sha

55、ll immediately maintenance, and insist on different cement required time conserve, good control of environmental temperature and humidity, in order to make concrete in suitable environment for their maintenance. five is reinforced concrete cover depth, when construction will use prefabricated good b

56、eforehand reinforced cushion block high standard mortar pad, allowing reinforced concrete cover depth and meet the design requirements. six is construction joints to do less leave or not, must want to leave, should make juncture of processing. 4.3 use in use for the hydraulic structures do not chang

57、e the original design of the conditions of use. because the hydraulic structures using conditions change, directly related to the outside air, temperature and humidity changes caused by factors of concrete certain conditions change, particularly for concrete component parts, more easily collision sh

58、all set up angle and layer between the protection. 4.4 management of concrete component for hydraulic structure of management, mainly is regular inspection, strengthen maintenance. for easy to produce the carbonization of concrete component, it should send periodic basis observation and testing temp

59、erature, humidity, check the cracks circumstances and carbonation depth, and make the detailed record. if discover the concrete surface crack, flake phenomenon, should be timely use protective coating of concrete surface closed or take make concrete surface and atmospheric isolation measures, never allowed its crack continue to expand and, when necessary, be concrete reinforcing treatment. 5.1 concrete freeze-thaw destruction affecting factors and prevention 5.1.1 factors affecting concrete freeze-thaw destroy the influence factors of concrete freeze-thaw destruction are v