The extensive usage and promotion of commercial concrete, significantly enhanced the building speed and constructing quality, and promote the vigorous advancement of industrial concrete innovation.
The resulting early cracking of commercial concrete, however till the end has actually not been a reliable solution to the quality of building projects in recent years is the focus of controversy and complaints, has actually triggered excellent issue to the market and society.
The cause of fractures in industrial concrete is of course complex and complex
The absence of understanding of making use of commercial soil and inappropriate maintenance, is the main reason for the frequency of fractures in business concrete, this paper on the cracking of business concrete and upkeep issues to discuss the views.
Second, the value of the beginning of the upkeep time to manage the early shrinkage of industrial concrete
1, for common concrete not mixed with water-reducing agent, early shrinking is small, early sprinkler maintenance is primarily to make the cement completely hydrated to make sure the development of concrete strength, therefore, China’s concrete structure construction quality acceptance specifications, the start of concrete maintenance time is within 12 hours after putting.
2, for a large number of contemporary commercial concrete blended with water-reducing representative, it is shown by appropriate tests that the shrinking increases sharply within 8 hours after initial setting, and in the actual project, the most a great deal of large volume of floor fractures mainly appear within a couple of hours after initial setting of concrete, for that reason, a good grasp of the starting treating time is the essential to control the early shrinkage of commercial concrete cracks.
If we continue to wait 12 hours after putting and after that spray upkeep, we will lose the very best time to manage early shrinking fractures, and in regards to early shrinkage crack control, we will lose any role. Many of the present building and construction unit is still accustomed to the standard construction maintenance experience, not according to the qualities of the present business concrete, that is, in the concrete just initial set (before the surface area water loss), on the adoption of sensible maintenance measures, successfully decrease shrinkage, minimize breaking.
Third, The requirement for prompt and appropriate wetting of commercial concrete maintenance
1, The so-called prompt treating is primarily: to treating the concrete prior to the surface does not lose water.
In the real operation, it is hard to master timely treating, but it needs to be figured out according to the performance of the concrete mix and the climate, and so on (Generally, wet curing must be performed when the concrete is first set), and if water loss has actually happened on the surface throughout curing, the problems caused by water loss should be dealt with prior to curing to ensure the effect of treating
2, the so-called full treating, generally: to guarantee that in the entire given maintenance period, concrete can not lose water, no water loss is the complete curing; Otherwise, water loss is insufficient treating.
Concrete treating the more appropriate, then the presence of concrete defects is less; concrete treating is not sufficient, then the existence of concrete problems more. However, the majority of the current building system of the concrete upkeep remain in the pouring of the next day after the start of watering, 2-5 times a day, so that the maintenance is neither timely nor appropriate, leading to a great deal of cracks.
4th, damp treating 7-day period, the effect of the various stages of business concrete curing.
1, according to the test information and production experience, the 7d strength of industrial concrete is probably 28d strength (65% ~ 85%), so the specification needs wet treating 7 days is reasonable, it is best to keep 7 days without water loss.
According to our production experience, in these 7 days, the earlier the time, the much easier it is for the concrete to lose water, the more likely to form problems, the more important it is to prevent water loss.
2, 3-d strength is about 28d strength (45% ~ 60%), so the very first 3 days to prevent water loss is particularly important. If the first 3 days do not lose water, then continue to water and moisturize to 7 days, from the project in fact, the outcomes are excellent.
3, the very first day is very critical, if the very first day excessive water loss, the flaws brought on by the future might be challenging to repair.
4, we found that some websites, the first day do not focus on maintenance, the next day before the start of water conservation, upkeep is over, the board still has a lot of cracks, the analysis of its causes: because the very first day has actually been a fracture, which indicates that the very first day of the non-maintenance of the fairly coarse pores have been formed, it is challenging to heal.
7 days of damp upkeep, the key is the very first 3 days, the most crucial is the very first day, so we have to make sure that the very first day is not water loss, no matter what kind of maintenance we use.
Fifth, The importance of secondary concrete troweling.
1 Smoothing in one go. Immediately smooth the surface area with a wood trowel, known as « main smoothing ».
, known as « secondary wiping ». This is called « secondary cleaning ».
The primary function of secondary wiping has 3 points.
( 1) Eliminate surface area problems, internal secretory channels (i.e., capillary channels) and early plastic cracks in concrete.
( 2) Improve the density of the concrete surface area layer.
( 3) Improve the surface area compaction, slow down the migration and evaporation of water in concrete, and improve the anti-cracking ability of concrete.
3 From the first smoothing to the 2nd smoothing, it is the procedure of gradual initial setting of concrete.
4 The formation of fractures. In an extended period of time, as long as the relative humidity of the environment is listed below 100%, the concrete surface will lose water, the development of internal flaws – capillary channels. These flaws are not gotten rid of, in the case of ongoing water loss on the concrete surface, the pore will be additional deepened, the further expansion of fractures, cracking, severe cases will cause permeating cracks, leading to flooring leakage.
5we found that in the damp treating is appropriate and not timely (such as standard wet treating), only a smoothing without secondary erasure, concrete breaking will be very major.
With secondary troweling, the degree of splitting is considerably reduced. Unless the implementation of instant treating, so that the concrete surface area can not create water loss defects, otherwise the secondary wiping process is needed.
6the traditional trowel manual trowelling. In the secondary wiping process, now often utilized to trowel manual cleaning, not only ineffective, not strong enough, when the defect from the surface and inside the advancement of much deeper, it will be tough to get rid of
7 Disc type power trowel: the best secondary cleaning using disc type concrete trowel machine, the removal of surface flaws (and concrete internal secretion channels) and compressed surface area than the trowel, the role of much better, high effectiveness.
There are two types of power trowel: stroll behind power trowel and ride on trowel, that makes the secondary trowel more efficient and more accurate. Much better finish the ground leveling.
8 concrete losing water again, just in this way, can ensure the early hydration of concrete, enhance the quality of solidified concrete, and lay an early quality structure for the enhancement of concrete toughness.
Sixth, early membrane curing is extremely essential.
Practice has actually revealed that the use of membrane curing after concrete putting is a efficient and easy way of treating. Specifically in the huge northern areas, high temperature, wind speed, dry air, water loss quickly, making use of membrane curing, you can quickly seal the concrete wetness in the interior, and in the membrane and the concrete surface to form a long-term damp curing environment, after the final set concrete surface temperature level cracks, survival tidy and cool.
The membrane curing building requires to focus on the timeliness, and need to finish the membrane lamination before the initial setting of concrete. Movie and concrete surface should be carefully bonded without bubbles, no space between the membrane and the membrane cover, no large location overlap, and do a great job of later surface area watering maintenance, keep the membrane surface area moist.
In the aspect of movie coating maintenance, Weinan Hongji Da did an excellent task in the construction of Purple Emperor House and other tasks, and accomplished the extensive movie coating upkeep of concrete putting, no structural concrete cracking phenomenon, which guaranteed the quality and safety of concrete structure and lovely image.
To sum up, as long as the construction is performed strictly according to the building and construction requirements, the concrete surface is secondary smoothed, and enough and timely membrane wetness preservation is carried out, the cracks of concrete can be lowered to a large degree, so that the concrete cracks can be efficiently managed.