Segregation risk in fresh concrete: the likelihood of segregation increases most in which of the following situations?

Introduction / Context:
Segregation is the separation of coarse particles from mortar in fresh concrete. It results in non-uniform strength and honeycombing. Recognizing the conditions that exacerbate segregation helps in preventing defects during placement and compaction.

Given Data / Assumptions:

• Fresh concrete is being handled and placed without special admixtures.
• Aggregate shape and grading influence stability of the mix.
• Workability (slump) is increased primarily by water content.

Concept / Approach:
Higher water content (wetter mix) thins the paste and reduces its ability to keep heavier coarse particles suspended. Larger maximum aggregate size increases the tendency of heavy particles to settle. Coarser grading with insufficient fines reduces the cohesion (paste “mesh”) that would otherwise restrain separation.

Step-by-Step Solution:
Evaluate each factor's physical effect on particle stability.Wetter → lower viscosity → easier separation.Larger size → greater settling force for coarse particles.Coarser grading → weaker mortar matrix, less cohesion.All contribute to increased segregation; choose “All of the above.”

Verification / Alternative check:
Practical controls: maintain proper grading, use admixtures (VMA), avoid over-vibration, and optimize slump for placement method.

Why Other Options Are Wrong:
Each single factor is true, but picking only one ignores the combined mechanisms; “None” contradicts established behavior.

Common Pitfalls:
Chasing very high slump by adding water in the field; neglecting the role of fines and angularity in cohesion.

Final Answer:
All of the above