Abstract: elaborated the common surface defects in concrete ( porosity, cracking, stress cracking, honeycomb, misalignment, drop, Yanshuang, aggregate is disclosed and pollution prevention and treatment methods of identification ).
Key words: concrete; defect; identification; prevention; treatment
1cited words
When a block of buildings or structures from the surface of the concrete structure, high quality appearance has become the design, specification and construction process should be considered one of the main factors. A measure of project quality, not just to consider its applicability, economy and safety, for aesthetics requirements also appears increasingly important.
2common concrete surface defect recognition and Prevention
2.1 air holes
Stomatal characteristics: dispersion, separate, less than 10mm stoma.
Reasons: (1) the aggregate gradation unreasonable, excessive coarse aggregate, fine aggregate less;
(2) improper aggregate size, flat-elongated particles content more;
(3) with a large amount of water, high water ash concrete;
(4) vibration is not sufficient;
(5) the use of surface oil brush steel template.
Solution: (1) good materials. Strict control of aggregate size and needle chip particle concentration, preparation should be carefully screened, reject unqualified material;
(2) choice of reasonable gradation of coarse aggregate, fine aggregate ratio and moderate;
(3) to select the appropriate water cement ratio;
(4) highly vibrated concrete;
(5) to ensure that the template hard, apply the appropriate thickness of the mold release agent.
2.2plastic cracking
Its features: crack, usually does not extend, occurs in the top.
Reasons: (1) the temperature shrinkage is the important reason of concrete cracking;
(2) early dry shrinkage crack of concrete is also one of the important reasons;
(3) the concrete before hardening settlement can also cause cracking;
(4) local unevenness can also cause cracking of concrete;
(5) unit to use too much water, cement content mostly too may lead to cracking of concrete.
Solution: (1) strictly control the water cement ratio, reducing the water content of concrete mixture;
(2) selects the suitable cement, sand stone and accurately grasp the qualified ratio;
(3) strengthen the conservation, contraction of the concrete surface, can be used to spray maintenance, in order to increase air humidity and added concrete premature evaporation of moisture. In the concrete is solidified immediately covered bags (or sand, geotextile) and the full water maintenance, to ensure the concrete strength of normal growth, prevent water loss due to excessive and dry shrinkage crack.

2.3stress cracking
Stress cracking performance characteristics: usually long, horizontal distance of the same crack.
Reasons: (1) the hardened concrete temperature variation;
(2) premature bearing;
(3) stripping ( bottom die prematurely ).
Solution: (1) check the structural steel design and construction joint position;
(2) note that casting process;
(3) control the stripping time, preventing structure load.
The 2.4honeycomb
Honeycomb features: the exposed stone and rough surface.
Reasons: (1) concrete mixing material of fine material is not enough;
(2) the coarse aggregate fine aggregate shortage;
(3) vibration is not sufficient;
(4) in construction in template seam or in the bolt connecting hole leak slurry.
Solution: (1) check of cement and sand mixture ratio;
(2) check the coarse aggregate gradation;
(3) full mixing, carefully casting, full vibration;
(4) to ensure that the template does not gel slurry.
2.5( the wrong tooth. )
Misalignment ( staggered ) features: protruding, into a waveform or other types of original design in discrepant cases.
Reasons: (1) the template installation is not accurate;
(2) when pouring, under the action of load or due to template moisture content changes caused by deformation.
Solution: (1) to detect whether the template straight;
(2) to check whether there is sufficient template fixing clamp, template reinforcement is stable and reliable;
(3) detection frequency and number of concrete pouring, to avoid more than the template design bearing capacity;
(4) the use of wooden template, avoid the template in the moisture content is too large.
2.6( fall off angle )
Drop ( drop angle ) features : the hardened concrete.
Reasons: (1) early removal of mould. Advance in construction of formwork, accidentally and the template and concrete structure collision, prone to fall;
(2) the low intensity concrete itself, cannot withstand a collision;
(3) aggregate does not meet the requirements, fragile;
(4) the template surface roughness, release agent coating unevenness, concrete and formwork of adhesion, stripping caused by peeling.

Solution: (1) check whether the stripping strength of concrete strength;
(2) extending the stripping time, particularly in colder weather;
(3) check the template design, clean up and release agent coated case.
2.7 Salt Cream
Features: as Yanshuang chalk shape white powder or precipitate.
Cause: often due to effect of rainwater in the concrete surface to form insoluble calcium carbonate.
Solution: (1) in the casting after the first few days to the attention of rain;
(2) when the air is damp can reduce carbonation, and dry conditions can increase the carbonation.
2.8aggregates revealed (commonly known as the" stone plaques ." )
Aggregate revealed features: similar to the size of dark spots and a coarse aggregate shape.
Cause: in a template with coarse aggregate surface contact between the office due to vibration caused by fine aggregate and combined water segregation.
Solution: (1) template reinforcement is better, reduce the shaking template;
(2) increase the sand content rate;
(3) using the same continuously graded aggregate;
(4) the use of insert type vibrator.
2.9 pollution ( color )
Pollution features: concrete surface rendering and mixture material unrelated to the discoloration; concrete surface is yellow or brown; sometimes exposed sand.
Reasons: (1) by steel bars or joints pollution;
(2) the die plate or release agent in color or dirt contamination;
(3) release agent pollution;
(4) steel formwork surface not clean, in the steel surface rust ( yellow ) directly brush demoulding agent.
Solution: (1) ensure that the form does not pollute the concrete material;
(2) to ensure that the release agent of pure, prevent mould release agent coating template contaminated;
(3) don't wipe the excess release agent in concrete pouring, the day before and release agent.
Indeed, the concrete surface defects are more than above nine. Since appearing on surface defect, the repair work appears especially important.
3concrete surface defect repair
The 3.1deployment of color
The majority of repair work failure is due to failure to use with the surrounding concrete surface with the same mixture ratio of the material caused by the. Even using the same with the original concrete mixture ratio, it is difficult to guarantee that trim part and the original color concrete color consistency. In order to remedy the defect repair, usually for mixture ratio ( there are several specific optimal ratio obtained only through on-site commissioning ):

The white Portland cement ( pure silicon ) + fly ash and water;
The white Portland cement ( pure silicon ) + fly ash and sand and water;
The white Portland cement ( pure silicon ) + Portland cement and sand and water;
The white Portland cement ( pure silica sand ) + + water;
The ordinary cement and sand and water.
The above five kinds of mixture ratio to guarantee repair materials and the original concrete combination can consider building glue.
3.2control absorbent
Cement materials to repair, not in the dry concrete on the surface, this is because the noodles will draw for the repair of the mortar in the water, which will reduce the new and original material on the surface of the concrete bond, will also reduce the quality and durability of repair materials. Trim surface first to soak, the best approach is fully wetted surface, surface humid conditions when the repair effect is good.
3.3 dozen of mill
The leakage caused by the hanging curtain and a template mounting instability caused by misalignment ( concrete surface projections ), can be used directly the angle mould machine ( diamond disc ) on the concrete surface grinding.
3.4 broken edge trimming
Due to the accidental collision or stripping caused by careless corner broken, in the repair should be first corner dressing into quadrilateral, sprinkler wet after use of mortar in repair. In the patch before commissioning mixture color, for repairing concrete and original concrete color consistency.
The 3.5hole of the modified
(1) the need to repair the water wet;
(2) with a trowel will transfer a good mortar is pressed into the hole, at the same time off excess mortar;
(3) attention to maintenance, repair mortar reaches certain strength, the use of angle grinder polishing it again. For the requirements of the higher places available sandpaper polished.
The 3.6honeycomb with rough surface modification
(1) the loose concrete removal, until exposing the hard concrete;
(2) the surrounding dressing into four square, chiseling depth roughly the same;
(3) the need to repair the parts to make it fully wet sprinkler;
(4) according to the chiseling depth decided to use mortar or fine stone concrete, mortar ( or fine stone concrete ) press;
(5) water conservation.
In actual operation, the concrete surface defect treatment method is varied, the author not only lists one one, describes the common processing method.
4node -
For the defects of concrete appearance, just to find out the reasons, propose appropriate solutions, most can be eliminated. On the defects of concrete has emerged, as long as carefully repaired, can fully guarantee the concrete appearance requirements