1. Check the mixing level
To obtain high-quality concrete, you must correctly select the mixer and establish a mixing system. Including mixing time, feeding sequence, feeding amount, etc. The control of stirring time is easily overlooked in practice.
If the mixing time is too short and the mixing is uneven, it will reduce the working performance of the concrete. If the mixing time is too long, it will not only affect the working efficiency of the mixer, but also reduce the cement quality. The gelling properties of the slurry will further reduce the working performance of the concrete. The concrete mixing time shall not be less than the minimum time.
There should be no agglomerated cement and mortar in the cement mortar, so that the cement mortar can completely wrap the stone, because the aggregate is dry and has no fluidity, and the cement acts as a lubricant. , which can make concrete fluid and plastic and reduce the relative resistance between aggregate particles.
2. Secure the loading switch
When the concrete is loaded into the trolley or hopper by the mixer , the discharge plate of the mixer should be placed in the middle of the loader as much as possible, and the inclination of the material plate can be adjusted to avoid the occurrence of “stone nests” and “sand nests”.
3. Check the transportation well
Transport by trolley, bucket, hopper or funnel For concrete, vibration should be avoided, the road surface should be smooth, the lifting should be smooth, the shortest route should be taken, and the transportation time should be the shortest. The aggregate particles in the cement slurry have viscosity and adhesion in addition to the effects of gravity. When vibration occurs, these effects will be reduced and delamination and segregation of concrete will be enhanced. After the concrete has been transported for a long time, it should generally be mixed twice before entering the membrane.
4. Secure the discharge switch
Pour concrete directly from the trolley or hopper When installing formwork, the free falling height should not exceed 2m. When the drop height of concrete exceeds 2m, it is advisable to use a barrel or chute, or leave a lateral mold opening on the vertical component formwork to shorten the drop height and avoid concrete segregation.
When using a string tube to pour concrete into the formwork, the lower opening of the string tube should be kept vertical to allow the concrete to fall vertically to avoid the “stone nest” phenomenon. (Figure 8-68) When using large formwork for construction, a hopper should be used to unload materials to avoid entering the formwork. The hopper should be moved horizontally to allow the concrete to enter the formwork in layers (Figure 8-69).
5. Set up baffles and drop pipes
When concrete follows a slope or chute When sliding down, the heavy part of the aggregate moves quickly, causing segregation. If a baffle is installed in front of the belt conveyor, it can also play the same role. At one end of the chute or conveyor belt, the concrete drop is relatively large. If a drop tube with a height greater than 60cm is installed, the occurrence of concrete segregation can also be reduced (Figure 8-70).
6. Measures to avoid “root rot” and bleeding of vertical components
In The bottom of the wall or column is first poured with 50~100mm thick cement mortar to prevent stones from directly contacting the bottom. The stones are heavy and fall onto the mortar cushion first, which can prevent “root rot”. If along the height of the vertical components, the slump of the concrete should be gradually reduced from bottom to top (Figure 8-71), which can effectively prevent the bleeding phenomenon of gravel settling and cement slurry floating.
<img src="/upfile/202304/2023041334528065.jpg"/
微信扫一扫打赏
