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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 prevention 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,
