Difficulty: Easy
Correct Answer: 150 cm
Explanation:
Introduction / Context:
Segregation occurs when coarse aggregate separates from mortar during handling or placing. Excessive free fall increases particle velocity and separation, leading to honeycombing, weak zones, and variable cover. Limiting drop height is a simple and effective control measure on site.
Given Data / Assumptions:
Concept / Approach:
Many practical guides recommend limiting free fall to about 1.5 m for ordinary concretes. For taller forms, use inclined chutes or drop chutes to reduce velocity and maintain a vertical drop within the recommended height, thereby preserving uniformity and finish quality.
Step-by-Step Solution:
Verification / Alternative check:
Quality checklists for sites emphasize “free fall ≤ 1.5 m” unless special measures are adopted; this aligns with standard good practice.
Why Other Options Are Wrong:
100–125 cm is overly restrictive for most ordinary placements; 200–250 cm exceed common recommendations and can promote segregation and paste splashing.
Common Pitfalls:
Pouring from great heights into congested reinforcement; not using trunking; vibrating excessively to “fix” segregation rather than preventing it.
Final Answer:
150 cm
Discussion & Comments