Concrete appearance of the ills
one cellular
(1) are not allowed to mix measurement, graded sand and gravel well;
(2) mixing uneven;
(3) template slurry leakage;
(4) inadequate or missing vibrator vibration;
(5) soil mixed with a thick pouring, layering unclear, concrete transition is unclear, the quality can not grasp the vibrator;
(6) free fall height of more than dumping provisions, concrete segregation, cast stone heap;
(7) vibrators damage, or when the power failure caused by leakage of vibration monitoring;
(8) vibration time is not sufficient, the bubble has not ruled out.
II, Ma surface
(1) with the
(2) the template does not clean up the net, or early form removal, template adhesions;
(3) mold release or leakage of brushing uneven brush;
(4) wooden model is not water wet, the concrete surface dehydration, starting powder;
(5) pouring too long, the template does not hang too much time cleaning up dust, causing the surface layer is not dense;
(6) vibration time is not sufficient, the bubble has not ruled out.
three holes
(1) the reasons for the same cell;
(2) steel was too dense, too thick concrete aggregate, is not easy under the gray, hard vibrator;
(3) hole, bottom template-free exhaust port, a balloon inside the concrete.
four, exposed tendons
(1) with the
(2) steel frame processing are not allowed, top paste the template;
(3) lack of protective layer pads;
(4) steel too close;
(5) measures targeting non-reinforced, reinforced punch displacement.
V. Langen
(1) plug the gap strict template root slurry leakage;
(2) before pouring concrete mix ingredients are not the same below the same no stone mortar;
(3) poor workability of concrete, water cement ratio is too large stones sink to the bottom;
(4) pouring height is too high, focus on a concrete cutting, concrete or stone to catch the high heap analysis;
(5) vibrator false;
(6)-mold clean up dirty, wet well.
six missing off edge angle
(1) template design does not consider factors that prevent the form stripping off angle;
(2) wooden model is not ahead of moist wood mold after pouring of concrete caused by expansion of crack angle;
(3) template lax joints, leakage pulp;
(4) template is not brushing or brushing poor release agent, resulting in adhesions form removal;
(5) too much too early form removal, improper form removal methods and procedures;
(6) maintenance is not good.
seven hole deformation
(1) mold between the top brace too, the cross section is too small;
(2) mold-free lifter support, lack of rigidity, can not maintain the Founder;
(3) Concrete pouring will die extrusion asymmetric bias;
(4) hole with the main template fixed template is not good, resulting in relative movement.
eight, dislocation
(1) pay-off error is too large;
(2) template displacement deformation, formwork is not required to find direct measures;
(3) tilt or up the top of the lower template model, the formation of the upper reset the template to correct the wrong table;
nine, slab concrete pouring false
(1) slab is too small, too large stones;
(2) sewing templates hanging branch is not strong, deformation, leakage of plasma;
(3) outstanding debris within the joint or joints in piping;
(4) non-small vibrator or vibrating plug vibrator ramming or bad.
ten, crack
(1) water-cement ratio is too large, the surface pores, cracks;
(2) excessive use of cement, shrinkage cracks;
(3) maintenance is not good or not timely, surface dehydration, shrinkage cracks;
(4) slump too, pouring too much too thick, thick liquid floating surface cracking;
(5) early form removal, improper force to pry the concrete cracking;
(6) concrete surface wiping pressure false;
(7) reinforced protective layer is too thin, smooth muscle while the cleft;
(8) lack of stirrups, the temperature of the concrete cracking ribs;
(9) no mass concrete measures to reduce the temperature difference between inside and outside;
(10) applications such as hole concentration at the corner of no steel reinforcement.
(11) Concrete cracks and crack features.
XI sandwich construction joints phenomenon:
combination of bad concrete construction joints, there are gaps or folder with debris, resulting in poor structural integrity. Analysis:
1, the infusion did not seriously addressed before concrete construction joint surface before pouring, tamping is not enough. 2, the infusion of mass concrete structures, often hierarchical sub-construction. Stop often during the construction wood, sawdust and other debris accumulated in the concrete surface, not carefully check the clean-up, concrete when mixed concrete re-infusion, the debris caused by the sandwich construction joints at the preventive measures:
1, continued perfusion in concrete construction joints, such as exceeding the prescribed interval time, press the construction joint in the concrete compressive strength of not less than 1. 2Mpa only when they agreed to continue perfusion.
2, the concrete has hardened concrete surface prior to perfusion, remove the surface cement film and loose gravel or soft concrete layer, and fully wet and rinse the surface of the water left in the concrete to be removed. 3, before pouring, construction joints are advised to shop wiping a layer of cement. Control method: When the surface of the gap smaller, the available water to clean the cracks, wipe after full wet slurry. Careful handling of the sandwich. Reinforcement before reinforcement take temporary support only after the tick chisel. The dissection of the debris and loose concrete removed, rinse with water, fully wet, reperfusion, with increased level of strength grade concrete tamping of fine stone and carefully conserved.
cracks
fracture characteristics
concrete materials
1, cement setting (time) does not normally
larger irregular cracks in the initial concrete setting
2, the cement is not normal expansion
radial network cracks
3, when the concrete setting pulp floating and sinking
concrete pouring one or two hours after the reinforced walls and floor above and the junction of intermittent
4, aggregate in the mud
< p> cracked concrete surface an irregular mesh 5, cement hydration heat
mass concrete pouring 1 to 2 weeks after the rules appear equidistant line cracks, the surface of the also through the
6, concrete hardening, shrinkage
pouring two or three months began to emerge and develop, and the beam-side corner of the window appears inclined cracks in slender beams, floor, wall, etc. equidistant vertical cracks appeared in
7, Jiecha bad
burst from inside the concrete, damp places more
construction aspects of
1, mixing time is too long
an all-mesh and the length of the irregular crack
2, pumping water and cement to increase the amount of time
Easy in and out and long-duration irregular mesh crack
step random reinforcement, reinforced protective layer thinning
occurred along the concrete around the ribs, and along the surface of reinforcement and piping
4, pouring too fast
pouring 1 to 2 hours later, the bar above the wall and the plate, beam and column junction part of the cracks
5, the casting is uneven, not dense
easy to crack the starting point for a variety of
6, template muster
moving in the direction parallel to the template, some of Cracks
7, Jiecha handled properly
Jiecha occurring at the crack of cold crop
8, hardening of the former by the vibration or loading
stress state after hardening cracks
9, the initial maintenance is not good
premature drying
water near the surface of the letter short irregular crack
initial cold
fine cracks. Concrete surface after stripping back to white, hollowing, etc.
10, template pillar sink
end of the beam and the floor above and below the middle of the crack
< p> use and environmental conditions 1, temperature, temperature change
similar to shrinkage cracks, the crack has occurred with the ambient temperature, temperature changes
2, the concrete structures on both sides of the temperature and humidity difference
side at low temperature or low humidity, around the corner prone
3, repeated freezing and thawing
surface air Drums
4, the surface heat of fire
entire surface of the first crack Turtle
5, expansion of steel corrosion Large cracks along the reinforcement, and even falling off, the rust out of the water etc.
Large cracks along the reinforcement, and even falling off, the rust out of water
6, by etching acid and salts
or concrete surfaces subject to corrosion, swelling substances or produce a comprehensive debacle
structure and external influence
1, overloading
beam and floor in the side of a vertical tension crack
2, earthquakes, stacking load
columns, beams, walls, etc. 45 ° inclined crack occurred
3, section steel insufficient
components by a vertical tension crack
4, uneven ground subsidence structure
45 ° Large cracks occurred
second, the phenomenon common problem cause and preventive measures
1,. concrete surface, lack of pulp, rough, uneven, but no exposed steel and stones. 1. Template surface is not cleaned before the concrete pouring, concrete surface is sticky when form removal damage;
2., Not all use of steel formwork, inclusion of other types of templates;
3., The template surface release agent brushing uneven, resulting in concrete form removal occurred when the mucosal;
4,. template closely enough at the patchwork, concrete pouring mortar joints when the outflow of the template;
5., concrete vibrator is not enough , concrete cleaner the air is not excluded. 1. Template seriously clean up the surface, not stained with dry hard cement mortar and other debris;
6,. All use of steel formwork;
7,. Concrete release agent brushing uniform, not a drain brush ;
8., vibration must follow the rules and even vibrated dense layer to prevent leakage pound, hand-in vibrator vibrator only when the master vibration standards: concrete surface, no longer bubbles.
9,. concrete local crisp, almost no mortar between the stones, voids, holes in the formation of honeycomb. 1. Concrete ratio allowed, raw materials, measurement error;
10,. Not to mix concrete, workability is poor, not vibrating compaction;
11., Failure to Practice pouring concrete, improper cutting, the occurrence of segregation caused by separation of stones and mortar.
12,. leakage caused by cellular vibration;
13,. template there are big holes in concrete pouring slurry leakage caused serious when the cell. 1. Measured by electronic automatic mixing station spices, materials are checked out each set workability; concrete mixing time, mixing time should meet the minimum requirements;
14,. Concrete cutting height of more than two meters above the tube or slide should be used to string;
15,. concrete layer thickness of strictly controlled within 30 centimeters; vibrators vibrators move when the radius is not greater than the specified range; vibrated hand lap points Section vibrator, to avoid leakage of vibration;
16,. double-check the template, and the concrete pouring, strengthening on-site inspection.
17,. concrete structure with cavity, there is no concrete local or cellular huge. 1. Steel-intensive, embedded parts, dense, concrete can not enter, can not fill the template;
18., Concrete vibrator out of order, resulting in leakage of vibration;
19, concrete slump too small vibrating compaction;
20,. there are lumps of concrete or other large debris, or other workers, equipment falling;
21,. do not follow the prescribed procedures under the material, or a lower expected too much, Lai Buji vibration caused. 1. The maximum size of coarse aggregate shall meet the specifications;
22,. To prevent the leakage of vibration, personal attendant checks;
23, to ensure mobility of the concrete pouring conditions attached to the scene together, the construction of check each plate to the scene of the concrete, failure to resolutely abandoned;
24., to prevent sand and stone mixed with clay or ice blocks and other debris; to prevent debris falling into the concrete is poured, such as found in complex material should immediately clean up;
many reasons why concrete cracks, a deformation caused by cracks, cracks caused by external loads, there is conservation of the environment caused by chemical action improper and cracks and so on. In the construction should be treated differently, and the actual situation correctly solve the problem. This paper analyzes the reasons for cracks and make some treatment measures.
XIII, shrinkage cracks and treatment
shrinkage cracks in concrete curing and more after the end of a period of time or the week after pouring concrete around the evaporation of water slurry will generate shrinkage. Shrinkage cracks usually affect the impermeability of concrete, causing corrosion of reinforced concrete durability, water pressure will produce hydraulic fracturing under the impact of the bearing capacity of concrete.
main preventive measures: First, choose a smaller contraction of cement, commonly used in low-heat cement and fly ash cement, reducing the amount of cement; Second, the shrinkage of concrete influenced by the water-cement ratio in concrete mix design water-cement ratio should try to control the selection, while adding a suitable superplasticizer; Third, strict control of concrete mixing and construction of the mixing ratio, water of concrete mix design must not be greater than the given water consumption; fourth is to strengthen the early curing of concrete and appropriate to extend the concrete curing time. Winter construction thermal insulation of concrete cover to be extended time and curing agent brushing conservation; fifth is set in the proper concrete contraction joint.
fourth, plastic shrinkage cracks and plastic shrinkage
prevention is before the concrete in the condensation of the surface due to rapid water loss resulting from contraction. Plastic shrinkage cracks is generally hot and dry or windy weather occurs, cracks, mostly wide in the middle and thin on both sides of different lengths, each inconsistent state. Shorter cracks generally 20 to 30 centimeters long, long cracks up to 2 to 3 meters wide, l ~ 5 mm. The main causes are: before the final setting of concrete in almost no strength or intensity is very small, or just the final setting and the strength of concrete is very small, or large wind by the impact of high temperature, excessive water loss of concrete surface, resulting in capillary generated larger volume of negative pressure leaving a sharp contraction of concrete, the strength of concrete at a time when they can not resist the contraction of its own, resulting in cracks. Plastic shrinkage cracking of the main factors water-cement ratio, concrete setting time, temperature, wind speed, relative humidity.
main preventive measures: First, use high early strength and shrinkage value is small or ordinary Portland cement. Second, strict control of water-cement ratio, adding superplasticizer to increase slump and workability of concrete, reduce the amount of cement and water. Third, before the pouring of concrete, water will be evenly wet the grass roots and templates. Fourth, the time covered by plastic film or damp straw, hemp and other films to keep wet concrete surface before the final setting, or curing agent in the sprayed concrete surface for conservation. Five hot and windy weather in the sun and wind to set up facilities, timely maintenance.
fifth and subsidence cracks and cracks to prevent
subsidence due to soil structure, uneven ground, soft, or backfill false or due to flooding caused by uneven settlement; or because of lack of rigidity of the template. Template support or support to ask too much from the bottom as a result of loose, especially in the winter, the template support in the permafrost, the permafrost thaw resulting from differential settlement, resulting in cracks in concrete structures.
main preventive measures: First, soft soil, filling the upper structure of the foundation necessary before construction compaction and consolidation; the second is to ensure that the template has sufficient strength and stiffness, and the solid support, and to force uniform foundation ; Third, the process to prevent concrete poured foundation by water immersion; fourth time the template is not removed too early, and pay attention to the order form removal; erection of five die in the permafrost to take a certain pull to the attention of prevention measures.
sixteen, temperature, and prevention of cracks occurred
temperature cracks in mass concrete surface temperature changes or large areas of concrete structures. Larger temperature difference between internal and external thermal expansion and contraction caused by different levels of some of the concrete surface tensile stress. When the tensile stress exceeds the ultimate tensile strength of concrete, the concrete surface will have a crack, this crack occurred late in the concrete construction. Concrete construction when larger temperature changes, or by the cold wave hit the concrete, the concrete surface temperature will lead to sharp decline in contraction, contraction of the concrete surface of the concrete by internal constraints, resulting in a large tensile stress and cracks, this crack usually only in the context of shallow concrete surface produced. The trend of temperature cracks are usually no fixed rules, often criss-crossing a large area of structural cracks; slab length of a larger size class structure, cracks and more parallel to the short side; depth and temperature through the cracks of the general direction of the short sides parallel or nearly parallel , fracture occurs along the long side of the segment, the middle dense. Crack width sizes, temperature change is more obvious in winter wide, narrow summer. The emergence of such cracks can cause corrosion, carbonation of concrete, reduce the freeze-thaw resistance of concrete, anti-fatigue and anti-permeability capability.
main preventive measures:
1, try to use low heat or in the hot cement, such as slag cement, fly ash cement.
2, to reduce the amount of cement, will try to control the amount of cement of 450 kg / cubic meter.
3, lower water-cement ratio, the general control of the concrete water-cement ratio of 0.6 or less.
4, to improve the aggregate gradation, fly ash or high water reducing agent to reduce the amount of cement to reduce heat of hydration.
5, to improve the concrete mixing process, in the traditional three-technology based on cold air cooling with the second new technology, reduce the temperature of the concrete pouring.
6, in the concrete by adding a certain amount of water, plasticizer, such as the role of retarding admixture to improve the flow of fresh concrete, water retention, reduce heat of hydration, to postpone the appearance of thermal spike time.
7, erection can be used when pouring the hot season the sun visor and other auxiliary measures to control the concrete temperature rise, reducing the temperature of pouring concrete.
8, the temperature of mass concrete structure size-related stress and to arrange the construction process, stratified, block casting, to facilitate cooling, reducing the constraints.
9, set in the internal cooling mass concrete pipes, cold water or air through the cooling, reducing the temperature difference between inside and outside the concrete.
10, reinforced concrete temperature monitoring, timely cooling, protective measures.
11, reserved for temperature contraction joints.
12, reduce the constraints, before pouring concrete in the basement and the old concrete should be laid on sand bedding materials such as brushing or use of asphalt.
13, strengthen the concrete curing, concrete pouring, the timely use of wet straw mat, linen strips, cover, and pay attention to watering conservation, appropriate to extend the curing time. In the cold season, the concrete surface insulation measures should be taken to prevent the cold wave attack.
14, configure a small number of reinforced concrete or fiber materials were mixed, the temperature of the concrete crack control in a certain range.
In summary, prevention should focus on the causes of concrete cracks, and implement the principle of prevention, improve the design and construction and other aspects of strengthening the management of the concrete structure is not as much as possible to minimize the cracks or fractures in order to ensure that the structure Security.
one cellular
(1) are not allowed to mix measurement, graded sand and gravel well;
(2) mixing uneven;
(3) template slurry leakage;
(4) inadequate or missing vibrator vibration;
(5) soil mixed with a thick pouring, layering unclear, concrete transition is unclear, the quality can not grasp the vibrator;
(6) free fall height of more than dumping provisions, concrete segregation, cast stone heap;
(7) vibrators damage, or when the power failure caused by leakage of vibration monitoring;
(8) vibration time is not sufficient, the bubble has not ruled out.
II, Ma surface
(1) with the
(2) the template does not clean up the net, or early form removal, template adhesions;
(3) mold release or leakage of brushing uneven brush;
(4) wooden model is not water wet, the concrete surface dehydration, starting powder;
(5) pouring too long, the template does not hang too much time cleaning up dust, causing the surface layer is not dense;
(6) vibration time is not sufficient, the bubble has not ruled out.
three holes
(1) the reasons for the same cell;
(2) steel was too dense, too thick concrete aggregate, is not easy under the gray, hard vibrator;
(3) hole, bottom template-free exhaust port, a balloon inside the concrete.
four, exposed tendons
(1) with the
(2) steel frame processing are not allowed, top paste the template;
(3) lack of protective layer pads;
(4) steel too close;
(5) measures targeting non-reinforced, reinforced punch displacement.
V. Langen
(1) plug the gap strict template root slurry leakage;
(2) before pouring concrete mix ingredients are not the same below the same no stone mortar;
(3) poor workability of concrete, water cement ratio is too large stones sink to the bottom;
(4) pouring height is too high, focus on a concrete cutting, concrete or stone to catch the high heap analysis;
(5) vibrator false;
(6)-mold clean up dirty, wet well.
six missing off edge angle
(1) template design does not consider factors that prevent the form stripping off angle;
(2) wooden model is not ahead of moist wood mold after pouring of concrete caused by expansion of crack angle;
(3) template lax joints, leakage pulp;
(4) template is not brushing or brushing poor release agent, resulting in adhesions form removal;
(5) too much too early form removal, improper form removal methods and procedures;
(6) maintenance is not good.
seven hole deformation
(1) mold between the top brace too, the cross section is too small;
(2) mold-free lifter support, lack of rigidity, can not maintain the Founder;
(3) Concrete pouring will die extrusion asymmetric bias;
(4) hole with the main template fixed template is not good, resulting in relative movement.
eight, dislocation
(1) pay-off error is too large;
(2) template displacement deformation, formwork is not required to find direct measures;
(3) tilt or up the top of the lower template model, the formation of the upper reset the template to correct the wrong table;
nine, slab concrete pouring false
(1) slab is too small, too large stones;
(2) sewing templates hanging branch is not strong, deformation, leakage of plasma;
(3) outstanding debris within the joint or joints in piping;
(4) non-small vibrator or vibrating plug vibrator ramming or bad.
ten, crack
(1) water-cement ratio is too large, the surface pores, cracks;
(2) excessive use of cement, shrinkage cracks;
(3) maintenance is not good or not timely, surface dehydration, shrinkage cracks;
(4) slump too, pouring too much too thick, thick liquid floating surface cracking;
(5) early form removal, improper force to pry the concrete cracking;
(6) concrete surface wiping pressure false;
(7) reinforced protective layer is too thin, smooth muscle while the cleft;
(8) lack of stirrups, the temperature of the concrete cracking ribs;
(9) no mass concrete measures to reduce the temperature difference between inside and outside;
(10) applications such as hole concentration at the corner of no steel reinforcement.
(11) Concrete cracks and crack features.
XI sandwich construction joints phenomenon:
combination of bad concrete construction joints, there are gaps or folder with debris, resulting in poor structural integrity. Analysis:
1, the infusion did not seriously addressed before concrete construction joint surface before pouring, tamping is not enough. 2, the infusion of mass concrete structures, often hierarchical sub-construction. Stop often during the construction wood, sawdust and other debris accumulated in the concrete surface, not carefully check the clean-up, concrete when mixed concrete re-infusion, the debris caused by the sandwich construction joints at the preventive measures:
1, continued perfusion in concrete construction joints, such as exceeding the prescribed interval time, press the construction joint in the concrete compressive strength of not less than 1. 2Mpa only when they agreed to continue perfusion.
2, the concrete has hardened concrete surface prior to perfusion, remove the surface cement film and loose gravel or soft concrete layer, and fully wet and rinse the surface of the water left in the concrete to be removed. 3, before pouring, construction joints are advised to shop wiping a layer of cement. Control method: When the surface of the gap smaller, the available water to clean the cracks, wipe after full wet slurry. Careful handling of the sandwich. Reinforcement before reinforcement take temporary support only after the tick chisel. The dissection of the debris and loose concrete removed, rinse with water, fully wet, reperfusion, with increased level of strength grade concrete tamping of fine stone and carefully conserved.
cracks
fracture characteristics
concrete materials
1, cement setting (time) does not normally
larger irregular cracks in the initial concrete setting
2, the cement is not normal expansion
radial network cracks
3, when the concrete setting pulp floating and sinking
concrete pouring one or two hours after the reinforced walls and floor above and the junction of intermittent
4, aggregate in the mud
< p> cracked concrete surface an irregular mesh 5, cement hydration heat
mass concrete pouring 1 to 2 weeks after the rules appear equidistant line cracks, the surface of the also through the
6, concrete hardening, shrinkage
pouring two or three months began to emerge and develop, and the beam-side corner of the window appears inclined cracks in slender beams, floor, wall, etc. equidistant vertical cracks appeared in
7, Jiecha bad
burst from inside the concrete, damp places more
construction aspects of
1, mixing time is too long
an all-mesh and the length of the irregular crack
2, pumping water and cement to increase the amount of time
Easy in and out and long-duration irregular mesh crack
step random reinforcement, reinforced protective layer thinning
occurred along the concrete around the ribs, and along the surface of reinforcement and piping
4, pouring too fast
pouring 1 to 2 hours later, the bar above the wall and the plate, beam and column junction part of the cracks
5, the casting is uneven, not dense
easy to crack the starting point for a variety of
6, template muster
moving in the direction parallel to the template, some of Cracks
7, Jiecha handled properly
Jiecha occurring at the crack of cold crop
8, hardening of the former by the vibration or loading
stress state after hardening cracks
9, the initial maintenance is not good
premature drying
water near the surface of the letter short irregular crack
initial cold
fine cracks. Concrete surface after stripping back to white, hollowing, etc.
10, template pillar sink
end of the beam and the floor above and below the middle of the crack
< p> use and environmental conditions 1, temperature, temperature change
similar to shrinkage cracks, the crack has occurred with the ambient temperature, temperature changes
2, the concrete structures on both sides of the temperature and humidity difference
side at low temperature or low humidity, around the corner prone
3, repeated freezing and thawing
surface air Drums
4, the surface heat of fire
entire surface of the first crack Turtle
5, expansion of steel corrosion Large cracks along the reinforcement, and even falling off, the rust out of the water etc.
Large cracks along the reinforcement, and even falling off, the rust out of water
6, by etching acid and salts
or concrete surfaces subject to corrosion, swelling substances or produce a comprehensive debacle
structure and external influence
1, overloading
beam and floor in the side of a vertical tension crack
2, earthquakes, stacking load
columns, beams, walls, etc. 45 ° inclined crack occurred
3, section steel insufficient
components by a vertical tension crack
4, uneven ground subsidence structure
45 ° Large cracks occurred
second, the phenomenon common problem cause and preventive measures
1,. concrete surface, lack of pulp, rough, uneven, but no exposed steel and stones. 1. Template surface is not cleaned before the concrete pouring, concrete surface is sticky when form removal damage;
2., Not all use of steel formwork, inclusion of other types of templates;
3., The template surface release agent brushing uneven, resulting in concrete form removal occurred when the mucosal;
4,. template closely enough at the patchwork, concrete pouring mortar joints when the outflow of the template;
5., concrete vibrator is not enough , concrete cleaner the air is not excluded. 1. Template seriously clean up the surface, not stained with dry hard cement mortar and other debris;
6,. All use of steel formwork;
7,. Concrete release agent brushing uniform, not a drain brush ;
8., vibration must follow the rules and even vibrated dense layer to prevent leakage pound, hand-in vibrator vibrator only when the master vibration standards: concrete surface, no longer bubbles.
9,. concrete local crisp, almost no mortar between the stones, voids, holes in the formation of honeycomb. 1. Concrete ratio allowed, raw materials, measurement error;
10,. Not to mix concrete, workability is poor, not vibrating compaction;
11., Failure to Practice pouring concrete, improper cutting, the occurrence of segregation caused by separation of stones and mortar.
12,. leakage caused by cellular vibration;
13,. template there are big holes in concrete pouring slurry leakage caused serious when the cell. 1. Measured by electronic automatic mixing station spices, materials are checked out each set workability; concrete mixing time, mixing time should meet the minimum requirements;
14,. Concrete cutting height of more than two meters above the tube or slide should be used to string;
15,. concrete layer thickness of strictly controlled within 30 centimeters; vibrators vibrators move when the radius is not greater than the specified range; vibrated hand lap points Section vibrator, to avoid leakage of vibration;
16,. double-check the template, and the concrete pouring, strengthening on-site inspection.
17,. concrete structure with cavity, there is no concrete local or cellular huge. 1. Steel-intensive, embedded parts, dense, concrete can not enter, can not fill the template;
18., Concrete vibrator out of order, resulting in leakage of vibration;
19, concrete slump too small vibrating compaction;
20,. there are lumps of concrete or other large debris, or other workers, equipment falling;
21,. do not follow the prescribed procedures under the material, or a lower expected too much, Lai Buji vibration caused. 1. The maximum size of coarse aggregate shall meet the specifications;
22,. To prevent the leakage of vibration, personal attendant checks;
23, to ensure mobility of the concrete pouring conditions attached to the scene together, the construction of check each plate to the scene of the concrete, failure to resolutely abandoned;
24., to prevent sand and stone mixed with clay or ice blocks and other debris; to prevent debris falling into the concrete is poured, such as found in complex material should immediately clean up;
many reasons why concrete cracks, a deformation caused by cracks, cracks caused by external loads, there is conservation of the environment caused by chemical action improper and cracks and so on. In the construction should be treated differently, and the actual situation correctly solve the problem. This paper analyzes the reasons for cracks and make some treatment measures.
XIII, shrinkage cracks and treatment
shrinkage cracks in concrete curing and more after the end of a period of time or the week after pouring concrete around the evaporation of water slurry will generate shrinkage. Shrinkage cracks usually affect the impermeability of concrete, causing corrosion of reinforced concrete durability, water pressure will produce hydraulic fracturing under the impact of the bearing capacity of concrete.
main preventive measures: First, choose a smaller contraction of cement, commonly used in low-heat cement and fly ash cement, reducing the amount of cement; Second, the shrinkage of concrete influenced by the water-cement ratio in concrete mix design water-cement ratio should try to control the selection, while adding a suitable superplasticizer; Third, strict control of concrete mixing and construction of the mixing ratio, water of concrete mix design must not be greater than the given water consumption; fourth is to strengthen the early curing of concrete and appropriate to extend the concrete curing time. Winter construction thermal insulation of concrete cover to be extended time and curing agent brushing conservation; fifth is set in the proper concrete contraction joint.
fourth, plastic shrinkage cracks and plastic shrinkage
prevention is before the concrete in the condensation of the surface due to rapid water loss resulting from contraction. Plastic shrinkage cracks is generally hot and dry or windy weather occurs, cracks, mostly wide in the middle and thin on both sides of different lengths, each inconsistent state. Shorter cracks generally 20 to 30 centimeters long, long cracks up to 2 to 3 meters wide, l ~ 5 mm. The main causes are: before the final setting of concrete in almost no strength or intensity is very small, or just the final setting and the strength of concrete is very small, or large wind by the impact of high temperature, excessive water loss of concrete surface, resulting in capillary generated larger volume of negative pressure leaving a sharp contraction of concrete, the strength of concrete at a time when they can not resist the contraction of its own, resulting in cracks. Plastic shrinkage cracking of the main factors water-cement ratio, concrete setting time, temperature, wind speed, relative humidity.
main preventive measures: First, use high early strength and shrinkage value is small or ordinary Portland cement. Second, strict control of water-cement ratio, adding superplasticizer to increase slump and workability of concrete, reduce the amount of cement and water. Third, before the pouring of concrete, water will be evenly wet the grass roots and templates. Fourth, the time covered by plastic film or damp straw, hemp and other films to keep wet concrete surface before the final setting, or curing agent in the sprayed concrete surface for conservation. Five hot and windy weather in the sun and wind to set up facilities, timely maintenance.
fifth and subsidence cracks and cracks to prevent
subsidence due to soil structure, uneven ground, soft, or backfill false or due to flooding caused by uneven settlement; or because of lack of rigidity of the template. Template support or support to ask too much from the bottom as a result of loose, especially in the winter, the template support in the permafrost, the permafrost thaw resulting from differential settlement, resulting in cracks in concrete structures.
main preventive measures: First, soft soil, filling the upper structure of the foundation necessary before construction compaction and consolidation; the second is to ensure that the template has sufficient strength and stiffness, and the solid support, and to force uniform foundation ; Third, the process to prevent concrete poured foundation by water immersion; fourth time the template is not removed too early, and pay attention to the order form removal; erection of five die in the permafrost to take a certain pull to the attention of prevention measures.
sixteen, temperature, and prevention of cracks occurred
temperature cracks in mass concrete surface temperature changes or large areas of concrete structures. Larger temperature difference between internal and external thermal expansion and contraction caused by different levels of some of the concrete surface tensile stress. When the tensile stress exceeds the ultimate tensile strength of concrete, the concrete surface will have a crack, this crack occurred late in the concrete construction. Concrete construction when larger temperature changes, or by the cold wave hit the concrete, the concrete surface temperature will lead to sharp decline in contraction, contraction of the concrete surface of the concrete by internal constraints, resulting in a large tensile stress and cracks, this crack usually only in the context of shallow concrete surface produced. The trend of temperature cracks are usually no fixed rules, often criss-crossing a large area of structural cracks; slab length of a larger size class structure, cracks and more parallel to the short side; depth and temperature through the cracks of the general direction of the short sides parallel or nearly parallel , fracture occurs along the long side of the segment, the middle dense. Crack width sizes, temperature change is more obvious in winter wide, narrow summer. The emergence of such cracks can cause corrosion, carbonation of concrete, reduce the freeze-thaw resistance of concrete, anti-fatigue and anti-permeability capability.
main preventive measures:
1, try to use low heat or in the hot cement, such as slag cement, fly ash cement.
2, to reduce the amount of cement, will try to control the amount of cement of 450 kg / cubic meter.
3, lower water-cement ratio, the general control of the concrete water-cement ratio of 0.6 or less.
4, to improve the aggregate gradation, fly ash or high water reducing agent to reduce the amount of cement to reduce heat of hydration.
5, to improve the concrete mixing process, in the traditional three-technology based on cold air cooling with the second new technology, reduce the temperature of the concrete pouring.
6, in the concrete by adding a certain amount of water, plasticizer, such as the role of retarding admixture to improve the flow of fresh concrete, water retention, reduce heat of hydration, to postpone the appearance of thermal spike time.
7, erection can be used when pouring the hot season the sun visor and other auxiliary measures to control the concrete temperature rise, reducing the temperature of pouring concrete.
8, the temperature of mass concrete structure size-related stress and to arrange the construction process, stratified, block casting, to facilitate cooling, reducing the constraints.
9, set in the internal cooling mass concrete pipes, cold water or air through the cooling, reducing the temperature difference between inside and outside the concrete.
10, reinforced concrete temperature monitoring, timely cooling, protective measures.
11, reserved for temperature contraction joints.
12, reduce the constraints, before pouring concrete in the basement and the old concrete should be laid on sand bedding materials such as brushing or use of asphalt.
13, strengthen the concrete curing, concrete pouring, the timely use of wet straw mat, linen strips, cover, and pay attention to watering conservation, appropriate to extend the curing time. In the cold season, the concrete surface insulation measures should be taken to prevent the cold wave attack.
14, configure a small number of reinforced concrete or fiber materials were mixed, the temperature of the concrete crack control in a certain range.
In summary, prevention should focus on the causes of concrete cracks, and implement the principle of prevention, improve the design and construction and other aspects of strengthening the management of the concrete structure is not as much as possible to minimize the cracks or fractures in order to ensure that the structure Security.
No comments:
Post a Comment