How to prevent curing castable cracking



A large crack appeared on the wall of a heating furnace after construction. The furnace wall uses low cement castable in accordance with 1.5×1.5m block pouring construction, pouring thickness of 230mm, after maintenance 12 hours after the construction of the mold, the material has hardened, but the strength is not high. The upper part of the furnace wall has a "cut" in the department. Crack size: 500mm high from top to bottom, 5mm to 1mm wide to narrow. The construction adopts chute feeding, chute width 100mm; The castable has good vibrational flow, poor artesian flow and large flow loss. After the crack occurs, the construction personnel take longer vibration time in order to discharge the air more fully; There are furnaces working around the construction site.

According to expert analysis: the existence of heat source will not affect the constructability of the material in a short time, but it will cause the water of the casting body of the furnace wall to migrate rapidly from bottom to top in a long time after construction, causing the lower part of the castable to lose the constructability and harden first; There is more water in the middle and upper part of the furnace wall, and the hardening is slow. The furnace wall part contacts air and loses water too quickly. The middle part of the furnace wall is prefered to harden. The ordinary castable can not form fast feeding in the narrow chute, the water added will be slightly more than normal and the vibration is too long, resulting in the reduction of sinking particles on the furnace wall, which intensifies the generation of cracks.

Based on the above situation, in order to avoid the occurrence of pouring material cracking, the corresponding measures were taken.

First of all, strict quantitative control of the pouring water, record the water per ton of material, form a written document, strict requirements for construction, for the construction of narrow chute, adopt a forced push way, later changed to plastic pipeline to improve the chute effect is not good.

Secondly, when the castable vibrates, 300mm~ 500mm pile is used for vibration exhaust, and each vibration is kept uniform in the wall of the castable furnace, to avoid too long time vibration at one point, through visual inspection with no porosity floating, the surface is still visible large particles shall prevail.

Thirdly, the method of removing heat source was adopted in the construction part during the curing period. During the curing period, the hot billet was placed in the part with a distance of more than 5m from the furnace to avoid the existence of abnormal heat source during the furnace curing. Finally, the surface of the castable was covered with plastic film. Through the above improvement measures, the castables were dismantled 12 hours after construction, the castables hardened normally, and the surface of castables was smooth and without cracks.

The amount of water added to castable has many key effects on the properties of castable. After subsequent material analysis, it was found that the castable used in this time was not sensitive to the amount of water added. This problem is difficult to find during the sampling inspection of pouring materials, the material in the laboratory speed of the mixer can achieve rapid construction within the scope of requirements; However, in the construction site of large volume mixing and slow speed mixer is difficult to stir evenly, usually resulting in a large amount of water added. In the field of castables, there have been large-scale and rapid mixing equipment. It should also be noted here that too fast speed will also cause some problems, material friction heating can not be ignored; In terms of materials, high efficiency water reducing agent can greatly reduce the amount of water added, but the reaction speed is too slow water reducing agent is not suitable for some projects, should be in the appropriate choice between water reduction and instant solubility. (Expert Group of Beijing United Rongda Engineering Materials Co., LTD.)