Installation, Mixing, and Curing Practices
Mixing, placement, and curing
Installation quality depends on water control, mixing discipline, and curing. Use clean potable water at the manufacturer's specified range; never add water to improve flow after mixing. Excess water increases porosity, lowers CCS and MOR, and raises shrinkage and spalling risk. Measure water by volume or mass for each batch, not by eye. Mix in a clean mixer for the specified time; overmixing can entrain air and break down aggregates, while undermixing leaves dry pockets. Place castable promptly and consolidate with the correct vibration technique: enough to remove air, not so much that aggregate segregates. For gunning, control nozzle distance, water at the nozzle, and rebound; do not use rebound in the lining. Curing is not drying: hydraulic castables need moist curing at a controlled temperature to develop hydraulic bonds, while chemical-bonded systems may need air curing. Traps: adding water at the mixer or nozzle; using a dirty mixer; casting in direct sun or freezing conditions; and starting dryout before the specified cure is complete. Worked example: a 25 kg bag with a maximum water addition of 5.0 L (20%) is mixed; adding 5.5 L is 22%, a 10% excess over the maximum. That excess can reduce strength significantly and should be rejected, not accepted as easier to place. Rule of thumb: record batch weight, water added, mix time, ambient temperature, and curing start/end on the installation record.