Application of Castables
Castable which show a sign of having set (lumps or hardness throughout) prior to installation shall be rejected.
This type of castable refractory product has hydraulic bonding activated by the addition of water as do the standart castables. However. the high purity of the binder requires special care in the application, installation and initial firing of the material prio to actual sevice operation. On castables of this nature, the high purity binder has cristical setting charracteristics and as sucher requires carefully controlled water amounts, temperatures; atmospheric curing temperatures and conditions. The high purity nature results in some conditions not generally noticable in standard in standard castables some of which are:
False Set or Stiffening High heat release Rapid setting time High density surface sealing.
The castable with this type binder are very carefully premixed as manufactured and contamination by dirty water or dirty mixing equipment when installating can detrimentally affect the final strength and service life of this type product.
Water temperature below the recommended temperature will retard the setting character and water or atmospheric conditions over those recommended will accelerate the set Once the set has occured, this type of product should never be reworked or be subjected to surface finishing.
MIXING and APPLICATION OF CASTABLE
Poured refractories shall conform to the following minimum requirements in addition to other requirements of good practice not enumerated herein. The quantity of refractory material mixed at one time shall not be greater than can be poured prior to initial set. Precautions shall be taken to prevent the separation of aggregate and cement prior to placement. Dry mix contents of entire bag before adding water. Add the minimum amount of water to obtain the desired consistency suitable for the method of application. Use only clean, fresh, potoble water which must be at a temperature of between 20 °C and 27°C, but not lower than 20°C Use only clean mixers, tools and equipment as any foreign material will advversely affect the strength and settin gproperties of this castable.
Add proper amout of water per bag of castable. Any interior reinforcement should be coated or painted to allow for expansion of the metal. Castable shoud be placed within 20-30 minutes from the time of the first water addition. Poured refractory shall be placed in a manner which will minimize material segregation. It shall be deposited as nearly as practicable in its final position with the free fall limited to a maximum of 1 m. Work shall not be terminated until a panel or section is complete. When work is resumed the contact surface of the lining in place shall be thoroughly cleaned, roughened, and wetted. Any excess water shall be removed.
On projects where the application of the refractory is not a continuous operation, the days work shall not be terminated until or section is finished. In other words, work shall cease only at natural stopping points. If aplication stops for more than one hour, any refractory applied less than the full specified thickness shall be removed and discarded.
Refractory lining temperature shall be maintained between 20°C and 38°C during application and for a period of 24 hours thereafter.
Lining shall be finished reasonably smooth and true to contour. Surface irregularities shall be stuch off with asteel trowell before the refractory has set. Excessive trowelling shall be avoided any deficiencies in thickness shall be immediately corrected by the application of additonal material. Depressions, pockets or high spots on the surface are not acceptable.
Setting of castable takes place with the evolution of heat which results in a temperature rise of the castable massand evaporation of water from the mix. Curing of exposed castable surfaces should start when a finger rubbed across the surface comes away clean or when the surface feels warm to the touch.
All concrete linings shall be protected from damage during the early stages of setting.Refractory lined equipment shall not be trasported until at least 24 hours after the curing operation has been completed. The curing of this castable should be accomplished at atmospheric temperatures of no less than 20°C and no more than 38°C Curing consists of keeping the surface damp from the initial set or when it feels warm to the touch until heat can no longer be felt. Curing of castables can be accomplished by either keeping the surface wet or maintaining a humid atmosphere. Water sprays, for nozzles or wet burlap may be used to keep the surface cool and moist. The rate of water application of pools in low spots. Curing should continue 18-24 hours or until the heat of hydration has been dissipated. Vapour proof membranes applied over exposed castable surfaces, within 30 minutes after installation, also provide an effective means of curing castable refractories. This procedure is of particular advantage under conditions where extreme ambient temperatures are encountered or where facilities for water curing are not available or not practical. Its color shall controst with the color of the refractory. The film thickness shall be 10 to 15 mm. Application can be made with a hand garden sprayer,paint spray gun, or soft full paint brush. Safety precautions used to paint application shall be observed when curing temperature should not be allowed to fall below 20°C or exceeds 32 °C, corrective action is necessary to rectify the condition by either insulation covering to retain the heat or by cooling with water sprays,whichever is required.
On completion of the curing period, the castable can be air dried indefinitely without adverse effect. (Optimum results will be obtained with an air drying period of 24 to 48 hours. However, heating can commence immediately
after completion of the curing period if necessary. Development of strength ceases upon the first application of heat.) The castable should be allowed to air dry for 48 hours before any heat is applied.
If the cast section is to be stored at temperatures below 0°C, the section should be fired before storage.