Concrete quality essentials: For producing good-quality concrete on site, which of the following requirements must be satisfied?

Introduction / Context:
Concrete performance depends on the quality of its constituents and how well they are proportioned and mixed. This item checks practical field knowledge about materials selection and batching/ mixing practices that directly influence compressive strength, durability, and finish.

Given Data / Assumptions:

• Ordinary Portland cement concrete used for structural work.
• Field production with conventional mixers and compaction.
• No special admixtures unless stated; focus on fundamentals.

Concept / Approach:
Durable, strong concrete requires sound aggregates (free from soft, porous, and reactive particles), sufficient cement paste to coat aggregates and fill voids, clean water without sugars, oils, or organic impurities, and uniform mixing so that every batch has consistent proportions. Any weakness in these areas leads to segregation, honeycombing, loss of strength, or durability problems.

Step-by-Step Solution:
Assess aggregates → must be hard and durable to resist crushing and weathering.Check cement content → must meet mix design to achieve target strength and cover absorptive fines.Evaluate water quality → potable-quality water is a safe rule to avoid setting delays and strength loss.Ensure mixing → uniform distribution of paste and fines prevents weak pockets.Since all statements are true and jointly necessary, select “All of the above.”

Verification / Alternative check:
Site quality control checklists always include aggregate quality tests, water acceptance criteria, cement receipt verification, and specified mixing time/speed to ensure uniformity.

Why Other Options Are Wrong:
Picking any single requirement ignores the interdependence of materials quality and mixing on concrete performance.

Common Pitfalls:
Using marginal aggregates without screening; adding water to “improve” workability instead of adjusting mix or using admixtures; under-mixing leading to segregation and variable strength.

Final Answer:
All of the above.