These two erroneous practices have not been corrected.
So, will the concrete crack after a long time? Judging from the situation of their sidewalks, they may not crack: (the sidewalks in the United States are basically made of concrete, and few are paved with floor tiles.
Source: business cooperation between engineering construction standards and practice.
It is almost a common practice in Xi’an to add water to the concrete arbitrarily; In addition, during the secondary calendering, a small bucket is also carried, and a large amount of water is sprinkled while wiping and pressing.
The fastest time in China is two days to complete all the above processes.
There is a hydraulic system under the discharge chute, and the tanker driver can manipulate the discharge chute to swing left and right up and down to deliver the concrete to the designated place.
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The height of the top surface of the formwork shall be level with the ground, so as to facilitate the control of the surface height of the ground: after the formwork is erected, the concrete shall be poured: note that their tank car is unloaded in front; The discharge chute extends for more than 5m.
This does not include the time for concrete curing.
The plane size of the site is 12 × 7.8m: ground construction process includes: site leveling; Sand cushion; Site compaction; Supporting the formwork around the ground; Placing concrete; Troweling and compaction of concrete surface; Settlement joints and contraction joints shall be reserved on the ground.
At the same time, the quality of concrete ground is often unsatisfactory: the surface is uneven, and even footprints are left.
They use a small loader and manual operation: after the site is leveled and the sand cushion is paved, the vibrating compactor is used for compaction: compared with the frog compactor, the vibrating compactor is convenient to turn around and turn; Do not rely on the power supply, and accidentally get an electric shock.
No cracks.
It takes a lot of work to pave the sidewalks, and the sidewalks are easy to be damaged.) Above is a picture of a sidewalk in the United States.
The surface is not covered; No secondary calendering; No watering for curing.
Among them, a small piece of ground in the basement was also completed, which was completed by workers who lifted the concrete to the basement in barrels.
When pouring, pour the left ground (6 × 7.8m）。 Pave the concrete first: then use the long handle wide trowel to smooth and compact the concrete: the long handle of the long handle wide trowel is spliced by several short handles and can be removed.
During construction, no water shall be added to the concrete.
Let’s see how they construct: the site is leveled and the sand cushion is paved.
The sidewalks in Xi’an are paved with floor tiles.
Use a long handle wide trowel, so that workers do not have to trowel and press in the unset concrete area; The width of one-time plastering is also wide.
In China, there have been accidents of electric leakage of frog rammer and electric death of workers.
There are several details to pay attention to when erecting the formwork: the diameter of the reinforcement rod for erecting the formwork is 20mm, and the length is 60cm or 70cm.
In addition, during the ground construction, the slump of their concrete was smaller by visual inspection, which was significantly smaller than the 180 ± 20 commonly used in Xi’an, and the concrete did not bleed.
There are 7 concrete workers in total without a foreman: from 8:00 a.m.
It may be that they have added some crack resistant admixture into the concrete.
Short handle wide trowel and ordinary trowel shall be used in narrow places: when troweling and compacting concrete, American workers tend to work on their knees: from the perspective of protecting lumbar spine, kneeling may be better than squatting.
The long handle trowel is made of aluminum alloy and is light in weight.
Including the retention of expansion joints and contraction joints; Formwork removal; Clean the road surface.
Other sidewalks we saw were basically free of cracks.
After concrete pouring, the sawdust board will remain in the concrete and will not be taken out.
At noon, the workers did not have a special lunch time, but took the time to eat their own food: bread; Banana; Beverages and yogurt, etc.
to 3:00 p.m., a total of 7 hours, and all the ground works have been completed.
But there was no crack in the concrete: This was the picture taken the next morning.
A hole is drilled in it.
After the concrete is roughened, the whole process of ground construction is completed.
It is a tool that can be reused: the nail is a double nail cap nail: it can control the depth of the nail, and it is convenient to pull out the nail.
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In fact, many construction sites failed to do so.
However, it took only 7 workers and 7 hours for the US construction to complete all the above processes.
Without a special loader driver, the concrete workers will drive this small loader; No carpentry is required.
These two are also important reasons for no cracks.
According to the safety regulations, the frog rammer shall be operated with insulated gloves and insulated shoes.
The pump truck also needs people to master the discharge pipe.
This is a concrete floor in front of the garage of condo (two houses connected together).
While the site is leveled and the sand cushion is paved, the formworks around the ground are supported: the elevation of the formworks is controlled by the workers themselves, and the foreman is not required: the formworks and the loader are all concrete workers.
The expansion joint is to first place the sawdust plate soaked with asphalt: the sawdust plate is 10mm thick.
The front two sections of the discharge chute are hung on the construction site: the rear section can be rolled up: such a tank car can replace the pump car on the flat ground, even more convenient than the pump car.
It can be seen that the concrete has no cracks and the surface flatness is very good.
Compared with the construction in the United States, we should be inspired.
Use a right angle trowel with an arc to close the edge: finally, use a brush to roughen the concrete surface: snap the line at the contraction joint first; then use a trowel with a convex edge to cut the groove: the height of the convex edge, that is, the depth of the contraction joint: 20mm.
