What are the precautions for castable construction?
1. Before castable construction, the following inspections should be strictly carried out:
1) Check the appearance and cleanliness of the equipment to be casted.
2) Check the integrity of the construction machinery and tools, and vibrating tools and other tools must have intact spare parts.
3) Check the type, size, layout and welding quality of the anchors, and the metal anchors must be well compensated for expansion.
4) Check the measures to prevent castable water loss in the surrounding refractory brick lining and insulation layer.
5) Check the packaging and factory date of the castable, and conduct a preliminary test to check whether it is invalid.
6) Check the construction water, and its water quality must reach the quality of drinking water.
If the above items are unqualified, they should be treated and qualified before construction. Expired and invalid materials shall not be used. During castable construction, ensure that there is no power outage and no interruption in construction.
2. The templates for castable construction can be made of steel plates or hardwood boards, and the surface must be smooth. The formwork should be strong enough, rigid, not deformed, not shifted, and not leaking. The formwork should be firmly fixed to avoid expansion due to vibration. The gap between the formwork and the joint should be small to avoid exposure of the slurry. Steel formwork should be coated with release agent, wooden formwork should be painted with waterproof paint, and reusable formwork should be cleaned and painted before use.
3. The amount of water added to the castable should be strictly controlled according to the instruction manual and should not exceed the limit. Under the premise of ensuring the construction performance, the amount of water added should be less rather than more.
4. The mixing time of the castable should be no less than 5 minutes. A forced mixer should be used during operation. When mixing, it is advisable to dry mix in advance, then add 80% of the water used to mix, and then slowly add the remaining water and continue mixing according to the dryness and wetness until a suitable working consistency is obtained. When mixing different castables, the mixer should be cleaned first.
5. The castable should be used in whole barrels and bags. The mixed castable is generally used up within 30 minutes. In a high temperature and dry working environment, this time should be shortened appropriately. Casting materials that have already set or even agglomerated should not be poured into the mold frame, nor should they be stirred with water for reuse.
6. Casting materials poured into the mold frame should be immediately compacted in layers with a vibrating rod, with each layer no higher than 300mm and a vibration interval of about 250mm. Try to avoid touching the anchors during vibration, and do not vibrate or re-vibrate at the same position for a long time. After seeing the slurry on the surface of the castable, the vibrating rod should be slowly withdrawn to avoid segregation and voids in the castable layer, and ensure that the gas in the castable is discharged. After the casting is completed, the castable body should not be subjected to pressure and vibration before solidification.
7. When casting a large area, construction should be carried out in blocks. The area of each casting area should be about 1.5m2. Generally, 3-5mm plywood is used as the expansion joint. The plywood should be placed on the working surface of the castable. The expansion should be reserved according to the design and should not be omitted. The depth of the expansion joint should be about half of the thickness of the castable. If the pouring height of the castable is low, an expansion joint should be left between 1.2-1.5m, and the expansion joint should be left at the position of the anchor interval.
8. After the surface of the castable is dry, the part exposed to the air should be immediately covered with plastic film or straw bags. After the initial setting, it should be regularly watered to keep the surface moist. The curing time is at least two days, and watering should be done frequently in the first day. After the final setting of the castable, the side formwork can be removed and watering can be continued, but the load-bearing formwork can only be removed after the strength reaches 70%.
9. After the formwork is removed, the cast body should be inspected in time. Quality problems such as honeycombs, peeling and voids should be dealt with and repaired in time. If the problem is serious, the defective part should be chiseled off to expose the anchor, and then filled with tamping material of the same quality and compacted, and continued to be cured. It is forbidden to use cement mortar to cover up the problem.