Notes for construction of refractory castables in winter

Recently, the temperature is getting lower and lower, so a lot of construction will be affected, mainly in the shape of refractory castables. Here, Topower offers some tips for winter refractory castables construction.
Such as aluminum acid salt mud, Portland cement and ordinary Portland cement in summer can be used for cementing agent of refractory castable, in winter, it emphasizes should first choose aluminate cement, because the aluminate cement with a rapid hardening, high strength, refractory and the characteristics of sulfate erosion resistance, winter construction cement refractory castable is good cementing agent. Its main varieties have CA-50 cement, CA-60 cement, CA-70 cement, CA-80 cement. Other slag Portland cement, volcanic limestone Portland cement, fly ash Portland cement can also be used, the label is not less than 42.5. Especially the winter construction use early its low strength cement, its label should not be less than 42.5.
In the mixing process of refractory castables, sewage, sea water and water containing harmful impurities should not be used.

On the one hand, the construction performance and hardening process of refractory castables will be affected, and on the other hand, the high temperature performance of refractory castables will be reduced and the index will not be reached. The depth of chloride ions in the water used should not be greater than 300mg/L.
In the process of pouring construction, people also tend to ignore the temperature of the surface in contact with the castable, because in winter construction, the temperature of the castable itself can be controlled, but if the temperature of the contact surface is too low, it will lead to a rapid drop in the temperature of the newly poured castable, affecting the growth of the strength of the castable. Because it is stipulated in the standard that the surface temperature in contact with refractory castable shall not be less than 5℃.
Taking the refractory castable combined with calcium aluminate cement as an example, low temperature or negative temperature is very unfavorable to the construction of castable. Low ambient temperature, slow hydration reaction of cement, hinder the growth of castable strength. When the temperature is lower than 0℃, the free water will begin to freeze, the temperature reaches -15℃, the free water almost all frozen into ice, resulting in the hydration and hardening of cement completely stopped. When water is transformed into solid ice, its volume increases by about 9%, which causes internal stress of castable material, relative displacement of aggregate and cement particles and internal moisture migration to the negative temperature surface. The formation of ice polymers in the castable can cause local structural failure. Water has the maximum density at 4℃. When the temperature drops below 4℃, the actual volume of water has begun to expand, which will cause damage to the newly formed cement hydrate structure of the castable.
Amorphous refractory castable for parts after frostbite cold material surface ice, spiral lines, color white, uneven phenomenon, such as material seems relatively wet, darker edge, Angle, it is easy to fracture, the edge of the pit with the naked eye can see aggregate nest and bottom surface of the ice crystals, fragile, with steel (anchor) almost no cohesive force, the material within has more large pores. Therefore, winter construction has a greater impact on amorphous refractories. From the condensation hardening, low temperature, condensation hardening speed is slow, shadow sound construction speed. When the temperature is negative, not only can not be normal hardening, but also will have a negative impact on the construction structure.
Unshaped refractories include mixing and transportation before construction. The heat gained by heating the material when it is stirred shall be minimized during transportation. Such as the selection of appropriate means of transport, reduce the number of operations, shorten the transport distance, etc.
After the construction of amorphous refractory castable in winter, the heat of the material itself and the hydration heat released after cement hydration should be made full use of for maintenance, and part of the heat should be added when necessary. The methods of adding heat are:
(1) heat storage method. The thermal insulation covering material used in maintenance should be of low thermal conductivity, good sealing, windproof, moisture-proof, light weight, low price and can be used for multiple turnover. There are thermal insulation felt made of ethylene foam, plastic as the surface layer, thermal insulation with foam core inside, and heat insulation plate with light steel as the frame. (2) greenhouse method. The site will be enclosed, and a heat source, so that the shed to maintain the required temperature. (3) heating curing method. There are furnace heating, steam heating, hot air heating, infrared heating and electric heating, etc.
In addition, antifreeze or coagulant can be added to the irregular refractory castables. For example, aluminate cement combined refractory castables commonly used lithium salt, sodium salt to speed up the hardening of castables; Sodium fluosilicate is often used as hardening agent for sodium silicate bonded castables. Magnesium powder and aluminate cement are commonly used as hardeners for phosphate bonded castable or ramming materials.

Post time: Feb-08-2021