During concrete placement, what is the maximum recommended free fall height to prevent segregation?
Correct Answer
A) 5 feet
ACI standards recommend a maximum free fall of 5 feet for concrete to prevent segregation of aggregates. Falls greater than this can cause the heavier aggregates to separate from the cement paste.
Why This Is the Correct Answer
The ACI (American Concrete Institute) standards specifically recommend a maximum free fall height of 5 feet during concrete placement to prevent segregation. When concrete falls from greater heights, the kinetic energy causes the heavier coarse aggregates to separate from the lighter cement paste and fine aggregates. This segregation compromises the concrete's structural integrity and uniformity. The 5-foot limit ensures proper consolidation while maintaining the homogeneous mixture of all concrete components.
Why the Other Options Are Wrong
Option B: 3 feet
3 feet is overly conservative and unnecessarily restrictive for concrete placement operations, making construction less efficient without providing additional benefits over the established 5-foot standard.
Option C: 8 feet
10 feet is double the recommended limit and would definitely cause significant segregation, resulting in poor concrete quality with separated aggregates and compromised structural properties.
Memory Technique
Think 'FIVE ALIVE' - concrete stays alive (well-mixed) up to 5 feet of free fall, beyond that it 'dies' (segregates).
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter on Concrete Construction and Quality Control
More Project Mgmt Questions
What is the minimum R-value required for wall insulation in Florida Climate Zone 2?
A subcontractor brings a new chemical product to your jobsite. Under the Globally Harmonized System (GHS), what information must be immediately available to workers?
A construction site has a trench that is 8 feet deep in Type B soil. What is the maximum allowable slope ratio for the trench walls without protective systems?
What is the maximum recommended spacing between drywall screws when attaching to wood studs?
Your crew discovers suspected asbestos-containing materials during a renovation project. What is the first action you should take?
A scaffold platform is 12 feet long and 5 feet wide. If the maximum load capacity is 25 pounds per square foot, what is the total weight capacity of this platform?
Which CSI MasterFormat Division would contain specifications for fire-stopping and firesafing materials?
In tilt-up concrete construction, what is the primary advantage of this method over conventional cast-in-place construction?
Which OSHA standard specifically addresses construction industry safety and health regulations?
A structural drawing shows a beam labeled 'W12x26'. What does the '26' represent?
People Also Study
Business & Financial Management
120 questions · 70% to pass
Contract Administration
60 questions · 70% to pass