CPC

Concrete prevents carbonization

time:2018-12-06 source:维特编辑部browse:73

混凝土防碳化
Concrete prevents carbonization
Concrete carbonization prevention measures
Concrete carbonization resistance is an important index to measure durability. If CO2 in the air penetrates through the capillary channels inside concrete and generates CaCO3 in the body prematurely, the protective effect of alkaline medium on steel reinforcement will be lacking, and the strength growth cycle due to concrete will be shortened, which will have an impact on the strength of solid and the durability of structure.
Through the comprehensive analysis of concrete carbonization test and strength growth curve, we suggest the following carbonization prevention measures in the construction process:

1. Prevention and cure of template surface cleaning and demoulding agent coating.
Usually, the template will be used repeatedly, in the process of mold support should be considered: (1) before the use of the impurities on the surface of the template to eliminate clean, prevent impurities adsorption demolding agent, no isolation effect;
(2) brush demulsifier coating to evenly brush all in place, to prevent part of the concrete and formwork adhesion, the removal of the mold should occur in the presence of peeling, pitting and other phenomena, expand the concrete internal capillary channel, accelerate the carbon dioxide on the concrete surface depth.
2. Prevention and treatment of reasonable vibration frequency to enhance compactness.
Concrete pouring is usually the first concrete tank to the designated parts before vibration, so the concrete transmission process is to control the discharging speed of the material, not too much accumulation or break the material, can play a uniform sinking role;
And timely and uniform vibration, to prevent under-vibration, leakage vibration or vibration, take the size of slump to choose the vibration time.
Generally, the vibration time when the slump is 150mm is 10-15 seconds, the vibration time with small slump is longer, and the vibration time with large slump is shorter, which can prevent the concrete from not compacting to expand the internal capillary holes and increase the carbonization depth.
3. Prevention and cure of carbonization by secondary drawing and pressing on floor and board surface.
First, concrete vibrate after a little sinking, should be timely to supplement concrete, before the initial setting for the first time to wipe out, wipe out the excess water;
Second, before the final condensation of the wool or calendering, the application of certain pressure, surface cracks can reduce the formation of capillary channel, can effectively isolate CO2 on the concrete surface infiltration.
4. Prevention and cure of carbonization by extending curing time.
At present, the main maintenance of concrete surface for water retention, curing agent spraying or wet cover, is to solve: (1) ensure the hydration process of cement temperature increase required water, Ca(OH)2 activity growth time can be extended;
(2) make the concrete surface has a layer of water film, can isolate CO2 direct contact with the concrete surface;
(3) in the process of concrete growth can inhibit the formation of cracks after concrete drying shrinkage.
So extend concrete to protect wet curing time had better have 14 days above.
5. Prevention and cure of carbonization by extending the mold removal time.
After pouring, vibrating and final setting of concrete, mold removal and maintenance are generally carried out according to the strength, but premature mold removal will also affect the infiltration of CO2 on the concrete surface.
The performance is: (1) early cancellation of the surrounding template tightening side pressure, directly affect the concrete in the growth process of expansion and contraction of concrete to reduce the compaction of concrete, forming a lot of capillary holes in the concrete;
(2) after the removal of mold concrete surface can not guarantee the moisture state, will increase CO2 and concrete surface contact.
Therefore, the extension of mold removal time can not only ensure the surface smoothness of concrete, but also prevent CO2 infiltration, preferably in more than 5 days, the appropriate extension of winter.

Construction technology of epoxy thick paste coating against carbonization

(1) material configuration: the main material required for the project is h52-s4 epoxy thick paste coating.
(2) check the corrosion joints, stressed joints, honeycomb, pitted surface, damage and other situations of steel bars on the surface of components and make records to observe the width of stressed joints
(3) the surface of the concrete components will be the first dust, dust, moss, rust spots, oil removal, oil pollution is serious to use organic solvents repeatedly live spirit immersion scrub.
Use steel wire brush to brush roughness to the surface, burnish with sandpaper, go out concrete surface float, float dust.
Use chisel and shovel to remove uneven concrete and slurry residue during pouring, so that the concrete surface is flat;
Clear loose layer, on the surface of concrete pitting, honeycomb, cracks and other defects with putty repair, exposed steel reinforcement to rust, the larger area, the deeper part of the concrete shed with high grade concrete repair, wipe with cotton yarn, so that the concrete surface to keep clean and dry.
(4) apply brush.
H52 - S4 high build epoxy coating by the main agent and curing agent preparation, party a and party b two groups and packing, preparation in the a: b = 7:1 preparation, high temperature, curing agent, low temperature, curing agent, more appropriate ratio of specific visual actual temperature a little floating up and down, permissible error less than 20%, coating increases with the increasing use, with less frequently, specialist is responsible for the work is, one with a nucleus.
Concrete surface requirements of clean, dry, flat, dense no debris, divided into three times of painting, each time is completely dry on the surface of the case, and strive to paint uniform, to prevent the flow hang, wrinkle phenomenon.
For the first time, apply a layer of epoxy base solution. After the application, stop for about 40 minutes and draw the wire by hand. Then apply epoxy mortar.
The second time the prepared epoxy mortar with a spatula according to the design requirements of the thickness of 2~4mm daub on the base surface of the brushed base solution, the thickness of the daub does not exceed the original concrete surface layer shall prevail, daub as far as possible in the same direction of continuous amortize, and pay attention to the joint compaction exhaust.
Side daub, side compaction leveling, surface pulping.
After the coating compaction pulp, interval of about 2 hours, wipe again.
;
The third appearance treatment, epoxy slurry and silver powder a certain proportion of preparation, as the final process, so that the appearance of the structure to maintain uniform color, and a certain degree of carbonization strengthening.
Each process shall be subject to quality inspection and acceptance, and shall be operated in strict accordance with the requirements. Only when qualified can the next step be carried out to ensure quality.
(5) after the epoxy coating is applied, the construction area shall be isolated for maintenance. The maintenance period is 28 days. During the maintenance period, attention shall be paid to prevent the epoxy mortar surface from being soaked by water, trampled by personnel or hit by heavy objects.
When curing environment temperature below 15 ℃, will need a heating heater thermal curing.
(6) matters needing attention.
The interval time between coating and brushing construction layers shall be determined according to the temperature, generally not less than 6 hours, and the non-stick hand of the above layer shall prevail before each coating;
Encounter hemp pit, honeycomb, crack, when besmear brushs the first time, want to rub repeatedly, freely besmear brushs, along seam daub, make coating infiltrates flaw place adequately;
Brush is to pay attention to safety, do not smoke.

Construction technology of cement mortar carbonization prevention

Cement mortar material is better sealed.
Because it and base course belong to same kind of material, grain knot is firm, be inspired by the construction method of ground of building cement mortar, take seriously "ferrification treatment" working procedure, namely the calendering working procedure between initial setting and final setting of concrete.
The advantage of this treatment method is that it is cheap.
2. Simple construction technology, easy to master;
3 the material and concrete composition of the same material, combined with good, convenient maintenance in the future 4 protection cycle, long service life.

The construction technology

(1) materials.
Cement :P1O3215 (or P1O4215) silicon cement.
Yellow sand: natural medium sand with good gradation and hard texture shall be sifted and washed.
(2) surface cleaning.
Use wire brush to remove dirt and attachments on the surface, rinse with water and dry.
(3) gouge.
Use a chisel to remove the peeling and loose parts of the surface, leaving the hard stones in place and the edges visible.
This procedure requires dense uniform, do not leak chisel, do not hurt the deep concrete.
Then rinse the surface with a water pump and let dry.
(4) plastering.
Prior to plastering with cement paste foundation, horizontal and vertical evenly brush the cement slurry once.
The action of this procedure is to increase the bond force with the original concrete.
After the initial setting of cement slurry, 1 :2 cement slurry is used to divide the bottom layer and the second layer of the surface layer for plastering, each layer is about 5 ~ 7 mm thick.
Cement mortar should strictly control water-cement ratio.
(5) iron treatment.
Press light four times.
The first time after the surface layer mortar laid, so that the surface layer mortar uniform, flat, close;
The second time should be carried out after the initial setting of cement (generally 1 ~ 2 h after mortar mixing, according to the specific water-cement ratio, temperature, according to the hand according to no obvious sag), the role is to eliminate surface bubbles, pores, increase the compactness of mortar;
The third, fourth should be in the cement before the final coagulation, mainly to block mortar pores, further improve the compactness, make the surface smooth.
When calendering to force, such as plastering surface appear sand, can be used after the iron plate with water pressure.
(6) maintenance.
The last pressure light 3 hours or so, with grass curtain cover sprinkler maintenance, maintenance time is more than 15 days.

conclusion

(1) epoxy thick-grouted coating is a new type of anticorrosive material with good anticorrosive effect, moderate cost, wide application range and simple construction technology. Its successful application in the carbonization prevention treatment of concrete in many practical projects provides experience for the anticorrosive treatment of hydraulic concrete and has wide application value.
(2) practice has proved that the anti-carbonization treatment effect of cement mortar is good, and the economic analysis is also cost-effective.
This provides an economical and practical way to carbonize similar concrete.
This treatment method is suitable for large planar parts, and it is difficult to guarantee the quality of scattered parts.

Key words: concrete anti-carbonization bridge bearing replacement
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