Abstract: the construction of concrete engineering, some common quality problems often occur, these quality problems can not be eradicated, in the construction can only be carried out control, this article from the common quality problems causes and prevention of.
Key words: concrete quality common fault prevention and cure
Concrete construction process, some common quality problems often occur, affecting the safety of the structure, how to maximize the eliminating common quality defects, ensure project safety, project management staff needed to master, this paper combined with practical work, on the common quality defects of concrete engineering and control are discussed.
In 1, the honeycomb
1.1phenomenon. Concrete, mortar and less local shortening, stones, stones forming a gap between the similar honeycomb hole.
1.2reasons
(1) improper concrete mix or sand, gravel, cement and water metering allowed, causing less more, stone mortar;
(2) concrete mixing time is not enough, not to mix uniformly, and poor workability, vibrating compaction;
(3) feeding or improper feeding is too high, no collusion to gravel concentration, causing stone mortar segregation,
(4) the concrete not layered material, vibration is not real, or leakage or vibration, vibration time enough;
(5) a template slot is not blocked, slurry erosion;
(6) reinforced dense, using stones size is too large or small slump;
(7) foundation, column, wall of not little intermittent continue to fill the upper concrete.
1.3prevention measures.
(1) careful design, strict control of concrete mixture ratio, often check, accomplish accurate measurement, concrete mixing evenly, slump fits; concrete feeding height more than2m should set the series cylinder or chute: watering should be stratified material, layered tamping, prevent leakage isolation: template seam shall be tight blockage, irrigate, should always check the template support to prevent slurry leakage; foundation, wall, column should be finished in the lower part of the intermittent1 ~ 1.5h, and then poured heavy upper concrete, avoid to appear" sodden neck".
(2) small cellular: wash clean, with1:2or 1:2.5cement mortar screeding compaction; large honeycomb, honeycomb is weak to cut loose particles after wash, brush, formwork with a high level of fine stone concrete careful packing ramming, deep honeycomb, such as removal of difficulty, can be embedded grouting pipe, exhaust pipe, surface plastering mortar or concrete closed, cement grouting,
2, on the
2.1phenomenon. Part of the concrete surface to appear to lack slurry and many small pits, pits, forming a rough surface, but no exposed reinforcement phenomenon.
2.2reasons
(1) the template surface roughness or adhesion slurry slag from cleaning up on the net, during the removal of formwork concrete surface is sticky bad;
(2) template not watering humid or wet enough, member of the concrete surface water to be sucked, so too much on concrete water loss;
(3) touch panel lax flat-fell seam, local leakage;
(4) Die spanner isolated agent brushing unevenness, or local leak brush or failure. The concrete surface and template bonding caused by pitting;
(5) concrete vibrator is not real, bubble not discharged, stopped in the template surface pitting.
2.3prevention measures
(1) the template to face clean, not stick to dry cement mortar and other debris, concreting, template should be watered to fully wet, template slot, application of asphalt felt paper, putty and other blocked, mold plate isolation agent should choose long-acting, uniform coating, can not leak brush; concrete should be stratified homogeneous vibration compacting, to remove air bubbles;
(2) surface to be painted, but no treatment, surface without paint, on the site should be watered fully wet, with the original concrete mix to stone mortar, will and smooth pressure light.
In 3, hole
3.1phenomenon. Concrete structure has internal dimensions bigger gap, local no concrete or honeycomb is particularly large, reinforced the partial or total nudity.
3.2reasons
(1) in the reinforced dense parts or reserved holes and embedded parts, concrete material is a live, without vibration will continue pouring upper concrete;
(2) the concrete mortar separation, segregation, stone piles, serious run slurry, and without vibration.
(3) a concrete feeding too much, too thick, feeding too high, vibrator vibration to form holes, loose;
(4) in concrete, wood, plaster, and so fall with debris, concrete was stuck.
3.3prevention measures
(1) in the dense steel bars and the complex site, using fine stone concrete pouring, the mold plate filled with, carefully layered vibration compacting, reserved holes should be both sides at the same time, feeding, watering gates to prevent leakage of side added, vibration, sand and gravel mixed with clay blocks, template tools and other debris fall into the concrete, should be timely clean;
(2) the void around loose and soft membrane concrete chiseling, pressure rinsed with water, wet high intensity grade fine stone concrete, carefully watering ramming.
4, exposed reinforcement
4.1phenomenon. Concrete internal main reinforcement, stirrups Bureau vice ribs or exposed surfaces of structural elements.
4.2reasons
(1) concrete, reinforced bar protection layer pad displacement or pad too little or drain, causing reinforced snugly template exposed;
(2) structural section is small, too dense steel bars, the stone card in the steel, so that the cement mortar can not fill reinforced around, causing exposed reinforcement;
(3) improper concrete mix, resulting from the fold, rely on template parts missing pulp slurry leakage or template.
(4) a protective layer of concrete is too small or a protective layer of concrete vibration or vibration is untrue; or vibrating rod impingement reinforced or trample the reinforced, steel bar displacement, resulting in exposed reinforcement;
(5) mold plate without watering humid absorbent adhesive. Or release early, during the removal of formwork, lack of edge off angle, lead to leaking tendon
4.3prevention measures
(1) pouring concrete, shall ensure that the thickness of protective layer of reinforced position and correct, and strengthen the check, dense steel bars, should choose a suitable particle size gravel, ensure concrete proportioning accuracy and good workability; irrigating height more than 2m, string, or application of blanking tube chute, to prevent segregation; the template should be fully wet and serious plugging cracks; concrete vibrating impact bar, operation, to avoid trampling reinforced, such as when bending or release, timely adjustment of the real; protective layer of concrete vibration compacting; correctly grasp the release time, prevent premature removal, broken edges.
(2) surface leaking tendon after wash, brush on the surface, in1: 2 or1: 2.5 cement mortar, will be full of leaking tendon site level; leaking tendon deep hole to weak coagulation and prominent granular, wash clean, with more than the original high level of fine stone concrete filling compaction.
In 5, gap, sandwich
5.1phenomenon. Concrete memory in a horizontal or vertical loose concrete sandwich.
5.2reasons
(1) construction joint or deformation joint without joint treatment, removal of the surface film and the loosening of cement stone, not removing the weak layer of concrete and fully moist concrete;
(2) construction joints, sawdust, mud, bricks and other debris is not clear or not clear;
(3) the concrete irrigates the height is too large, not set series Jane, chute, resulting in segregation of concrete;
(4) the underlying junction without irrigation joint seam concrete mortar layer, not very good vibration.
5.3prevention measures
(1) according to seriously construction acceptance norms of construction joints and deformation joint surface; the seams sawdust, clay bricks and other sundries shall be clean and wash; concrete pouring height is greater than 2m shall be set the series cylinder or chute, the seams to irrigate before pouring50 ~100mm thick raw mix without stone mortar, for the benefit of combination good, and strengthen the seams of the vibration compacting concrete.
(2) gap dissection is not deep, can be loosely concrete chisel, wash clean, with1:2or 1:2.5cement mortar filling compaction; joint interlayer is deep, should remove loose parts and inclusion, with pressure water rinse after the mold, pouring fine stone concrete or the closed surface after grouting
In 6, missing edge off angle
6.1phenomenon. Structural components or the corner of concrete falling, irregular, angular defect
6.2reasons
(1) the wood formwork is not fully watering humid or wet enough, after pouring concrete maintenance is not good, cause dehydration, low strength, or template expansion will corner crack, stripping, edges and corners were sticking out;
(2) low temperature construction of premature removal side non-load-bearing template;
(3) removal, edge angle of external force or impact, or is not well protected, edges and corners were knocked off;
(4) template not brushing isolation agent, or uneven brushing.
6.3prevention measures
(1) the wood formwork in the concrete should be sufficient moisture, after pouring concrete should be carefully watering and maintenance, demolition side non-load-bearing template, concrete should have more than 1.2MPa strength; mould stripping, pay attention to the protection of the edges and corners, to avoid excessive force hastily; hoisting template, prevent the impact angle, transport, will finished corner with bags such protection is good, so as not to damage the.
(2) missing edge off angle, the loose particles can be removed, washed fully wet, as the extent of damage with1:2or 1:2.5 cement mortar plastering to complete the whole, or used for the formwork than the original high level concrete mended, careful maintenance.
7, surface roughness
7.1phenomenon. Concrete surface is uneven, or plates of different thickness, the surface is uneven.
7.2reasons
(1) after pouring concrete surface with a spade, only beaten flat, not with a trowel leveling pressure light, causing the surface rough rough;
(2) template is not supported in hard soil, or bearing surface defects, or supporting loose, water, cause new concrete early stage occurs when the uneven subsidence of;
(3) the concrete not achieves certain intensity, one operation or transport of the material, so that the surface pitting uneven or impression
7.3prevention measures
In strict accordance with the construction of standardized operation, concrete pouring, should according to the level of control markers or wire with a trowel leveling, pressure light, after the final setting water conservation; template should have enough strength, stiffness and stability, should be supported on a solid foundation, have enough bearing area, and to prevent flooding, to ensure that it does not occur sinking; in pouring concrete, strengthening inspection, strength of concrete can reach more than 1.2MPa, before walking on cast structure.
8, not intensity, heterogeneity difference
8.1phenomenon. The same batch of concrete compressive strength average value lower than the design strength level.
8.2reasons
(1) the cement expired or damp, activity decreased; sand, stone aggregate gradation is not good, large voids, large amount of mud, debris, admixture used improperly, volume is not accurate;
(2) improper concrete mix, inaccurate measurement, construction of free water, make water cement ratio increasing;
(3) the concrete feeding order, mixing time, mixing unevenness;
(4) winter construction, form removal too early or early by chen;
(5) the concrete block production without vibration compacting, maintenance management, or curing conditions do not meet the requirements, in the same condition, early dehydration or destroyed by outside force.
8.3prevention measures
(1) the cement should have factory certification, fresh without agglomeration, expired cement by the test only; sand, gravel size, gradation, mud content should comply with the requirements, and strictly control the concrete mix, to ensure accurate measurement, concrete should be sequentially mixing, ensure the mixing time and mix; prevent concrete early frost winter construction, with ordinary cement concrete, strength reached more than 30%, slag cement concrete, strength reached more than 40%, only then can suffer from freezing, according to the requirements of construction specification carefully produced concrete test block, and to strengthen the management and maintenance of test piece.
(2) when the concrete strength is low, available non destructive methods (such as the rebound method, ultrasonic method ) to determination of the structure of actual strength of concrete, if still can not meet the requirements, according to the actual strength of the safety degree of the structure, research solutions, take corresponding the reinforcing measures.