Present a larger amount of pumping concrete in order to ensure pumpability of concrete pumping, concrete pumping often adding an appropriate amount of air entraining agent, the performance of various air-entraining agents are quite different, so rendered in concrete state are not the same, and some of AEA in concrete form larger bubbles, and low surface energy, connectivity is easy to form large bubbles, if coupled with unreasonable vibration, large bubbles can not be completely discharged, and will definitely to the surface of hardened concrete caused by Honeycomb.
b, improper concrete mix, concrete is too thick, vibration is difficult to discharge when the bubble is caused by the surface structure of hardened concrete reasons for Honeycomb.
as improper concrete mix, such as cementing material ones, sand ratio is too large, too small amount of water, there are unreasonable thickening additive components, will be led to fresh concrete is too thick, When the concrete in the mixing will be wrapped into a large number of bubbles, even if rational bubbles in the viscous vibrator in the discharge of concrete is also very difficult, leading to the surface of hardened concrete structure Honeycomb.
c, the poor workability of concrete, resulting in segregation bleeding. In order to prevent the concrete layers, concrete and afraid to adequately vibrated into the mold, a large number of bubbles did not break out, can lead to hardening of the surface of concrete structures Honeycomb.
d, there are some cement to increase the fineness of cement, but also take into account energy conservation, often include some time in the mill grinding aids, such as wood calcium, diethylene glycol, triethanolamine, propylene glycol and other substances, some of which aids are cited as gas, and the introduction of non-uniform and larger bubbles, the surface will result in a hardened concrete structure Honeycomb.
2, external causes
a, gb/t10-95 high, due to air bubbles travel too long, even if the vibration of the time required to reach a point of order, the bubble can not be completely discharged, it will also result in a hardened concrete surface, Honeycomb.
b, irrational use of release agents is caused by hardening the surface of concrete structures the main reason for Honeycomb.
release agent market is chaotic now, good and bad, the product can be divided into the following categories:
(1) mineral oils, such as oil, diesel, kerosene, diesel oil increases, oil plus kerosene, light oil,
virtuemart template, transformer oil increases.
(2) emulsified oil, light oil and water together with the quantitative formation of oil in water emulsion emulsion.
(3) the water quality categories, namely, saponification of animal and vegetable oils, and then diluted with water liquid.
(4) polymer classes, namely, paraffin, liquid paraffin, turpentine and other substances generated and then adding organic solvent solution, due to higher costs with less. To mineral oil release agent, the viscosity of different grades of oil are not the same, even with the label of the oil, the ambient temperature is not the same with different viscosity, low viscosity at high temperatures, low temperatures dipped degree high. When the temperature is low, the oil attached to the template than the stick, the surface layer of fresh concrete structure once the bubble come into contact with viscous oil, even though it is difficult to reasonable vibrated bubble rising along the template discharge, a direct result of the surface of concrete structures Honeycomb appears. Some units fully aware of this, add in the part of the diesel oil, release agent used to reduce the viscosity, this can play a role, but still can not achieve satisfactory results.
water, milk release agent on the market now are more, but some products are made of relatively high emulsifier with gas will cause the surface layer to the concrete structure Honeycomb.
animal and vegetable oils for lipid problems of the release agent more, the reason cited is the product gas contains relatively large emulsifiers and thickeners, concrete surface will bring great effects.
3, the template material with different surface layer of concrete structures will also appear different state
contact solution and will form a variety of different solid contact angle, cement paste is no exception, the smaller the contact angle of a liquid, the stronger focus on the dressing (can be explained with the law of cosines),
prestashop templates, with water and the following material contact, for example, were measured:
PTFE Polypropylene 102.0 109.2
q235 iron 68.2
commonly used in daily life, practice, we all know, in the other conditions under the same premise, the use of urea-formaldehyde bamboo tree refers to the suppression of the template shape of the concrete or wood surface quality than the iron surface layer of concrete forming the template significantly improves the quality. 4, the ambient temperature on the surface quality of concrete structure is particularly evident
containing the gas inside the bubble, bubble volume change and therefore particularly sensitive to ambient temperature, ambient temperature is high volume of larger bubbles, the bubble becomes smaller capacity, easy to burst. Low temperature bubble volume becomes smaller, larger capacity, not easy to form Unicom bubbles. Even if the concrete surface bubbles, bubbles are very small, little effect on the appearance of concrete structures,
virtuemart templates, which bring to mind the summer and winter surface layer of concrete structures is better than spring and autumn.
spring and autumn, the larger temperature difference between day and night, so deposited with the surface of the concrete structure of the bubble volume change is also great, when the concrete surface layer is less than the strength of cement paste strength of the bubble, the bubble volume changes with temperature changes in cement paste around bubbles also change, over time increasing the strength of cement paste, when the bubble reaches a certain intensity of the surrounding cement paste, the changes do not change with the bubble volume, and if this time is to catch When the bubble diameter, is bound to leave holes in the surface layer of concrete.
Second, the elimination of negative factors within the method of concrete
1, choose to use high-quality air-entraining agent
quality of AEA in concrete bubble diameter should be introduced in the 10-200μm, a relatively high surface energy of the bubble, bubbles in the concrete more evenly distributed (average distance of less than 0.25μm), the author has test 11 kinds of air-entraining agent for concrete air content, compressive strength, setting time, and when the air entrained air content by the loss of agents such that the tannic acid and pinene as the main raw materials, better overall performance air entraining agent. 2, lower viscosity of concrete
appropriate adjustments concrete water-cement ratio, sand ratio, the amount of cementing material and the admixture of components to improve the viscosity of concrete, but also can improve the quality of the surface layer of concrete structures.
3, control of the workability of fresh concrete, if the bleeding of concrete segregation, strict control of vibration time, must be timely revival.
4, if the air-entraining cement containing component, in which the mixing of concrete should be added defoamer, such as adding the right amount of tributyl phosphate resin, silicone defoamer, defoaming polyether agent and the surface tension of less than 30dny/cm many additives, which can eliminate air bubbles.
Third, adverse external factors to solve the method of concrete
1, in strict accordance with gb/t10-95
2, choose to use high-quality release agent.
has a factory in Hebei, animal and vegetable oils obtained after saponification of the release agent, oil, oil + diesel, Japanese flower Wang Li Shi -50 (water in oil type), Beijing - thermal power plant and auxiliary works jointly developed by Tianjin ra (water in oil type), rb (water in oil type, which add defoamer), rc (water in oil type, which add defoamer and brightener) and other seven release agent test, the same as in other conditions conditions, the 50 × 50 × 10cm3 of iron, respectively, brushing twice the mold release agents, concrete form removal observed 24h after molding, the template brushing Lai Shi -50 and r series was better than the concrete surface layer good, especially the template brushing pieces of the best rc release agent, and the price is only Lai Shi -50/1/3-1/4.
3, with a mean suppression of urea-formaldehyde bamboo tree, wood template forming the surface layer of concrete was significantly better than the iron template, priority should be given a conditional use under the tree refers to the suppression of urea-formaldehyde bamboo, wood template.
4, revival is to remove the surface layer of concrete structures Honeycomb one of the most effective way.
South Fourth Ring Road in Beijing, the site found that six concrete bridge surface of the lower flat smooth stone block, the more bubbles the more up, bubble up to the top of a stone block with the same batch of concrete bridge, and even concrete with the same car, but up and down the same template, the results show a different state, check the main reason is vibrated when the second layer of concrete and vibrated unconsciously the first layer, the vibrator does not consciously third layer and the second layer and the vibrator the first layer, press the lower part of the concrete practice of bridge stone block is equal to many times by the vibrator, so the outside surface of the pier to the upper layer from the next bubble is gradually increasing.
Although gb/t10-95 , the actual operation of the unit so small, should lead to the construction management attention.
IV Conclusion
concrete surface Honeycomb appears there are two main reasons, first, their own reasons for concrete, one concrete external causes, according to different reasons put forward solutions and precautions.
br br a, concrete excessive gas virtuemart templat
miraculous elision
Linear Mode
