Abstract
The crack problem of concrete is a widespread existence but again difficult in solve of engineering actual problem, this text carried on a study analysis to a lttle bit familiar crack problem in the concrete engineering, and aim at concrete the circumstance put forward some prevention, processing measure.
Keyword: Concrete   crack   prevention   processing
Foreword
Concrete's ising 1 kind is anticipate by the freestone bone, cement, water and other mixture but formation of the in addition material of quality brittleness not and all material. Because the concrete construction transform with oneself, control etc. a series problem, harden model of in the concrete existence numerous tiny hole, spirit cave and tiny crack, is exactly because these beginning start blemish of existence just make the concrete present one some not and all the characteristic of quality. The tiny crack is a kind of harmless crack and accept concrete heavy, defend Shen and a little bit other use function not a creation to endanger. But after the concrete be subjected to lotus carry, difference in temperature etc. function, tiny crack would continuously of expand with connect, end formation we can see without the aid of instruments of macro view the crack be also the crack that the concrete often say in the engineering.
Concrete building and Gou piece usually all take sewer to make of, because of crack of existence and development usually make inner part of reinforcing bar etc. material creation decay, lower reinforced concrete material of loading ability, durable and anti- Shen ability, influence building of external appearance, service life, severity will threat arrive people's life and property safety. A lot of all of crash of engineering is because of the unsteady development of the crack with the result that. Modern age science research with a great deal of of the concrete engineering practice certificate, in the concrete engineering crack problem is ineluctable, also acceptable in certainly of the scope just need to adopt valid of measure will it endanger degree control at certain of scope inside. The reinforced concrete norm is also explicit provision: Some structure at place of dissimilarity under the condition allow existence certain the crack of width. But at under construction should as far as possible adopt a valid measure control crack creation, make the structure don't appear crack possibly or as far as possible decrease crack of amount and width, particularly want to as far as possible avoid harmful crack of emergence, insure engineering quality thus.
Concrete crack creation of the reason be a lot of and have already transformed to cause of crack: Such as temperature variety, constringency, inflation, the asymmetry sink to sink etc. reason cause of crack; Have outside carry the crack that the function cause; Protected environment not appropriate the crack etc. caused with chemical effect. Want differentiation to treat in the actual engineering, work° out a problem according to the actual circumstance.
   In the concrete engineering the familiar crack and the prevention
1.Drying shrinkage crack and prevention
Drying shrinkage crack much appear after the concrete protect be over of a period of time or concrete sprinkle to build to complete behind of around a week. In the cement syrup humidity of evaporate would creation stem Suo, and this kind of constringency is can't negative. Stem Suo crack of the creation be main is because of concrete inside outside humidity evaporate degree dissimilarity but cause to transform dissimilarity of result: The concrete is subjected to exterior condition of influence, surface humidity loss lead quick, transform bigger, inner part degree of humidity variety smaller transform smaller, bigger surface stem the Suo transform to be subjected to concrete inner part control, creation more big pull should dint but creation crack. The relative humidity is more low, cement syrup body stem Suo more big, stem the Suo crack be more easy creation. Stem the Suo crack is much surface parallel lines form or the net shallow thin crack, width many between 0.05-0.2 mm, the flat surface part much see in the big physical volume concrete and follow it more in thinner beam plank short to distribute. Stem Suo crack usually the anti- Shen of influence concrete, cause the durable of the rust eclipse influence concrete of reinforcing bar, under the function of the water pressure dint would creation the water power split crack influence concrete of loading dint etc.. Concrete stem the Suo be main with water ash of the concrete ratio, the dosage of the composition, cement of cement, gather to anticipate of the dosage of the property and dosage, in addition etc. relevant.
   Main prevention measure: While being to choose to use the constringency quantity smaller cement, general low hot water mire and powder ash from stove cement in the adoption, lower the dosage of cement. Two is a concrete of stem the Suo be subjected to water ash ratio of influence more big, water ash ratio more big, stem Suo more big, so in the concrete match the ratio the design should as far as possible control good water ash ratio of choose to use, the Chan add in the meantime accommodation of reduce water. Three is strict control concrete mix blend with under construction of match ratio, use of concrete water quantity absolute can't big in match ratio design give settle of use water quantity. Four is the earlier period which strengthen concrete to protect, and appropriate extension protect of concrete time. Winter construction want to be appropriate extension concrete heat preservation to overlay time, and Tu2 Shua protect to protect. Five is a constitution the accommodation is in the concrete structure of the constringency sew.
2.The plasticity constringency crack and prevention
plasticity constringency is the concrete is before condense, surface because of lose water quicker but creation of constringency. The plasticity constringency crack is general at dry heat or strong wind the weather appear, crack's much presenting in the center breadth, both ends be in the centerthin and the length be different, with each other not coherent appearance. Shorter crack general long 20-30 cm, the longer crack can reach to a 2-3 m, breadth 1-5 mm. It creation of main reason is: The concrete is eventually almost having no strength or strength before the Ning very small, perhaps concrete just eventually Ning but strength very hour, be subjected to heat or compare strong wind dint of influence, the concrete surface lose water to lead quick, result in in the capillary creation bigger negative press but make a concrete physical volume sharply constringency, but at this time the strength of concrete again can't resist its constringency, therefore creation cracked. The influence concrete plasticity constringency open the main factor of crack to have water ash ratio, concrete of condense time, environment temperature, wind velocity, relative humidity...etc.
Main prevention measure: One is choose to use stem the Suo value smaller higher huo sour salt of the earlier period strength or common the Huo sour brine mire. Two is strict the control water ash ratio, the Chan add to efficiently reduce water to increment the collapse of concrete fall a degree and with easy, decrease cement and water of dosage. Three is to sprinkle before building concrete, water basic level and template even to soak through. Four is in time to overlay the perhaps damp grass mat of the plastic thin film, hemp slice ...etc. keep concrete eventually before the Ning surface is moist, perhaps spray to protect etc. to carry on protect in the concrete surface. Five is in the heat and strong wind the weather to want to establish to hide sun and block breeze facilities, protect in time.
3.Sink to sink crack and prevention
The creation which sink to sink crack is because of the structure foundation soil quality not and evenly, loose soft or return to fill soil dishonest or soak in water but result in the asymmetry sink to decline with the result that; Perhaps because of template just degree shortage, the template propped up to once be apart from big or prop up bottom loose move etc. to cause, especially at winter, the template prop up at jelly soil up, jelly the soil turn jelly empress creation asymmetry to sink to decline and cause concrete structure creation crack. This kind crack many is deep enter or pierce through sex crack, it alignment have something to do with sinking to sink a circumstance, general follow with ground perpendicular or present 30 ° s-45°Cape direction development, bigger sink to sink crack, usually have certain of wrong, crack width usually with sink to decline quantity direct proportion relation. Crack width under the influence of temperature variety smaller. The foundation after transform stability sink to sink crack also basic tend in stability.
   Main prevention measure: One is rightness loose soft soil, return to fill soil foundation a construction at the upper part structure front should carry   on necessity of Hang solid with reinforce. Two is the strength that assurance template is enough and just degree, and prop up firm, and make the foundation be subjected to dint even. Three is keep concrete from sprinkle infusing the foundation in the process is soak by water. Four is time that template tore down to can't be too early, and want to notice to dismantle a mold order of sequence. Five is at jelly soil top take to establish template to notice to adopt certain of prevention measure.
4.Temperature crack and prevention
Temperature crack much the occurrence is in big surface or difference in temperature variety of the physical volume concrete compare the earth area of the concrete structure .Concrete after sprinkling to build, in the hardening the process, cement water turn a creation a great deal of water turn hot, .(be the cement dosage is in the 350-550 kg/m 3, each sign square the rice concrete will release a calories of 17500-27500 kJ and make concrete internal thus the temperature rise to reach to 70 0C or so even higher)Because the physical volume of concrete be more big, a great deal of water turn hot accumulate at the concrete inner part but not easy send forth, cause inner part the temperature hoick, but the concrete surface spread hot more quick， so formation inside outside of bigger difference in temperature, the bigger difference in temperature result in inner part and exterior hot the degree of the bulge cold Suo dissimilarity, make concrete surface creation certain of pull should dint. When pull should dint exceed the anti- of concrete pull strength extreme limit, concrete surface meeting creation crack, this kind of crack much occurrence after the concrete under construction period. In the concrete of under construction be difference in temperature variety more big, perhaps is a concrete to be subjected to assault of cold wave etc., will cause concrete surface the temperature sharply descend, but creation constringency, surface constringency of the concrete be subjected to inner part concrete of control, creation very big of pull should dint but creation crack, this kind of crack usually just in more shallow scope of the concrete surface creation.
   The alignment of the temperature crack usually none settle regulation, big area structure the crack often maneuver interleave; The size bigger structure of the beam plank length, the crack run parallel with short side more; Thorough with pierce through sex of temperature crack general and short side direction parallelism or close parallelism, crack along long side cent the segment appear, in the center more airtight. Crack width the size be different, be subjected to temperature variety influence more obvious，winter compare breadth, summer more narrow. The concrete temperature crack that the heat inflation cause is usually in the center the thick both ends be thin, but cold Suo crack of thick thin variety not too obvious. The emergence of the this kind crack will cause the rust eclipse of reinforcing bar, the carbonization of concrete, the anti- jelly which lower concrete melt, anti- tired and anti- Shen ability etc..
   Main prevention measure: One is as far as possible choose to use low hot or medium hot water mire, like mineral residue cement, powder ash from stove cement.. etc.. Two is a decrease cement dosage, cement dosage as far as possible the control is in the 450 kg/m 3 following. Three is to lower water ash ratio, water ash of the general concrete ratio control below 0.6.Four is improvement the bone anticipate class to go together with, the Chan add powder ash from stove or efficiently reduce water etc. to come to reduce cement dosage and lower water to turn hot. Five is an improvement concrete of mix blend to process a craft, lower sprinkle of concrete to build temperature. Six is the in addition that the Chan add a have of fixed amount to reduce water and increase Su, slow Ning etc. function in the concrete, improvement the concrete mix to match a thing of mobility, protect water, lower water to turn hot, postpone hot Feng of emergence time. Seven is the heat season sprinkle to build can the adoption take to establish to hide sun plank etc. assistance measure control concrete of Wen Sheng, lower to sprinkle temperature of build the concrete. Eight is the temperature of big physical volume concrete should the dint relate to structure size, concrete structure size more big, temperature should dint more big, so want reasonable arrangement construction work preface, layering, cent the piece sprinkle to build, for the convenience of in spread hot, let up control. Nine is at great inner part constitution of the physical volume concrete cool off piping, cold water perhaps cold air cool off, let up concrete of inside outside difference in temperature. Ten is the supervision which strengthen concrete temperature，adopt to cool off in time, protection measure.11 is to reserve temperature constringency to sew.12 is to let up to control, sprinkle proper before building concrete in the Ji rock and old concrete top build a 5 mm or so sand mat a layer or usage asphalt etc. material Tu2 Shua.13 is to strengthen concrete to protect, the concrete after sprinkle build use moist grass Lian in time, hemp slice's etc. overlay, and attention sprinkle water to protect, appropriate extension protect time, assurance the concrete surface be slow-moving cool off. At the cold season, concrete surface should constitution heat preservation measure，in order to prevent cold wave assault.14 is the allocation be a little amount in the concrete of reinforcing bar perhaps add fiber material concrete of temperature crack control at certain of scope inside.
5.Crack and prevention that the chemical reaction cause
Alkali bone's anticipating the crack that reaction crack and reinforcing bar rust eclipse cause is the most familiar in the reinforced concrete structure of because of chemical reaction but cause of crack.
   The concrete blend a future reunion creation some alkalescence ion, these ion with some activity the bone anticipate creation chemical reaction and absorb surroundings environment in of water but the physical volume enlarge，make concrete crisp loose, inflation open crack. ln this kind of crack general emergence concrete structure usage period, once appear very difficult remediable, so should at under construction adopt valid the measure carry on prevention. Main of prevention measure: While being to choose to anticipate with the alkali activity small freestone bone. Two is the in addition which choose to use low lye mire with low alkali or have no alkali. Three is the Chan which choose to use accommodation with anticipate to repress an alkali bone to anticipate reaction.
Because the concrete sprinkle to build, flap Dao bad perhaps is a reinforcing bar protection layer thinner, the harmful material get into concrete to make reinforcing bar creation rust eclipse, the reinforcing bar physical volume of the rust eclipse inflation, cause concrete bulge crack, the crack of this kind type much is a crack lengthways, follow the position of reinforcing bar appear.
Usually of prevent measure from have: One is assurance reinforcing bar protection the thickness of the layer. Two is a concrete class to go together with to want good. Three is a concrete to sprinkle to note and flap Dao airtight solid. Four is a reinforcing bar surface layer Tu2Shua antisepsis coating.
   Crack processing
The emergence of the crack not only would influence structure of whole with just degree, return will cause the rust eclipse of reinforcing bar, acceleration concrete of carbonization, lower durable and anti- of concrete tired, anti- Shen ability. Therefore according to the property of crack and concrete circumstance we want differentiation to treat, in time processing, with assurance building of safety usage.
   The repair measure of the concrete crack is main to have the following some method: Surface repair method，infuse syrup, the Qian sew method, the structure reinforce a method, concrete displacement method, electricity chemistry protection method and imitate to living from heal method.
   Surface repair the method be a kind of simple, familiar of repair method, it main be applicable to stability and to structure loading the ability don't have the surface crack of influence and deep enter crack of processing. The processing measure that is usually is a surface in crack daubery cement syrup, the wreath oxygen gum mire or at concrete surface Tu2 Shua paint，asphalt etc. antisepsis material, at protection of in the meantime for keeping concrete from continue under the influence of various function to open crack, usually can adoption the surface in crack glue to stick glass fiber cloth etc. measure.
1.infuse syrup, the Qian sew method
Infuse a syrup method main the concrete crack been applicable to have influence or have already defend Shen request to the structure whole of repair, it is make use of pressure equipments gum knot the material press into the crack of concrete, gum knot the material harden behind and concrete formation one be whole, thus reinforce of purpose. The in common use gum knot material has the cement the syrup, epoxy ,A Ji C Xi sour ester and gather ammonia ester to equalize to learn material. The Qian sew a method is that the crack be a kind of most in common use method in, it usually is follow the crack dig slot, the Qian fill plasticity in the slot or rigid water material with attain closing crack of purpose. The in common use plasticity material has PVC gum mire, plastics ointment, the D Ji rubber etc.;/n common use rigid water material is the polymer cement sand syrup.
2.the structure reinforce a method
When the crack influence arrive concrete structure of function, will consideration adopt to reinforce a method to carry on processing to the concrete structure. The structure reinforce medium in common use main have the following a few method: The piece of enlargement concrete structure in every aspect accumulate, outside the Cape department of the Gou piece pack type steel, adoption prepare should the dint method reinforce, glue to stick steel plate to reinforce, increase to establish fulcrum to reinforce and jet the concrete compensation reinforce.
3.concrete displacement method
Concrete displacement method is processing severity damage concrete of a kind of valid method, this method be first will damage of the concrete pick and get rid of, then again displacement go into new of concrete or other mate rial. The in common use displacement material have: Common concrete or the cement sand syrup, polymer or change sex polymer concrete or sand syrup.
4.the electricity chemistry protection method
The electricity chemistry antisepsis is to make use of infliction electric field in lie the quality of electricity chemical effect, change concrete or reinforced concrete the environment appearance of the place, the bluntness turn reinforcing bar to attain the purpose of antisepsis. Cathode protection method, chlorine salt's withdrawing a method, alkalescence to recover a method is a chemistry protection method in three kinds of in common use but valid method. The advantage of this kind of method is a protection method under the influence of environment factor smaller, apply reinforcing bar, concrete of long-term antisepsis, since can used for crack structure already can also used for new set up structure.
5.imitate to living from legal more
Imitate to living from heal the method be a kind of new crack treatment, its mimicry living creature organization secrete a certain material towards suffering wound part auto, but make the wound part heal of function，join some and special composition(such as contain to glue knot of the liquid Xin fiber or capsule) in the concrete of the tradition the composition，at concrete inner part formation the intelligence type imitate to living from heal nerve network system, be the concrete appear crack secrete a parts of liquid Xin fiber can make the crack re- heal.
Conclusion
The crack is widespread in the concrete structure existence of a kind of phenomenon, it of emergence not only will lower the anti- Shen of building ability, influence building of usage function, and will cause the rust eclipse of reinforcing bar, the carbonization of concrete, lower the durable of material, influence building of loading ability, so want to carry on to the concrete crack earnest research, differentiation treat, adoption reasonable of the method carry on processing, and at under construction adopt various valid of prevention measure to prevention crack of emergence and development，assurance building and Gou piece safety, stability work.