Refractory castables in lining design: they are typically used to (i) produce monolithic linings, (ii) perform patchwork repairs, and (iii) minimize the number of joints in structures. Which statement best describes their use?

Introduction / Context:
Refractory castables are unshaped refractories installed by casting, gunning, or pumping after mixing with water or other binders. They have transformed furnace construction by enabling seamless monolithic linings, fast repairs, and geometrically complex sections without extensive brick cutting. This question asks you to recognize the full scope of their advantages and common uses.

Given Data / Assumptions:

• Castables include conventional, low cement, ultra-low cement, and no-cement sol–gel systems.
• Installation methods may be cast-in-place, self-flow, shotcrete, or gunning.
• Proper dry-out and curing are assumed.

Concept / Approach:
Because castables are placed as a fluid or thixotropic mass that sets and sinters into a dense ceramic, they naturally produce monolithic, joint-free linings (or greatly reduced joints). The same placement versatility allows patchwork for worn sections without full relining. Fewer joints reduce leak paths and stress concentrations, improving integrity and reducing maintenance downtime.

Step-by-Step Solution:
Identify capability (i): casting creates monolithic sections → true.Capability (ii): placement versatility supports patch repairs → true.Capability (iii): monoliths minimize joints compared with brick courses → true.Therefore, all listed statements apply.

Verification / Alternative check:
Industry case studies show castables replacing intricate brickwork in burner quarls, ladle back-up linings, and cyclone inlets, confirming their suitability for the three listed uses.

Why Other Options Are Wrong:
Selecting only one or two uses underestimates the versatility of modern castables.

Common Pitfalls:
Ignoring critical steps like mixing control, vibration/self-flow, and controlled dry-out that determine performance.Assuming castables always outperform bricks; application specifics still matter.

Final Answer:
All (a), (b) and (c)