Concrete Technology – Achieving low permeability in hardened concrete: Choose the most comprehensive set of measures that reduce ingress of water and aggressive ions.
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AUse strong and dense aggregates only
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BUse a low water–cement ratio only
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CEnsure proper curing only
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DEnsure proper compaction only
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EAll the above (combined measures)
Answer
Correct Answer: All the above (combined measures)
Explanation
Introduction:Permeability governs durability. Lower permeability reduces penetration of chlorides, sulfates, and carbon dioxide, extending service life of reinforced concrete by slowing corrosion and chemical attack.
Given Data / Assumptions:
- Normal-weight concrete with ordinary Portland cement.
- Durability focus (water and ion ingress).
- Site practices influence pore structure.
Concept / Approach:
Permeability is controlled by capillary pore continuity and microcracking. Aggregates, w/c ratio, curing, and compaction each affect pore refinement and connectivity. Best performance comes from combining all good practices.
Step-by-Step Solution:
1) Dense aggregates reduce weak ITZ zones and microvoids.2) Low w/c ratio decreases capillary porosity: fewer continuous pores.3) Proper curing promotes continued hydration → pore refinement.4) Proper compaction expels entrapped air → reduces permeability pathways.Verification / Alternative check:
Rapid chloride permeability or sorptivity tests show pronounced improvement when all measures are adopted together rather than one measure alone.
Why Other Options Are Wrong:
Options A–D individually help but are incomplete. The most correct is the combined approach.
Common Pitfalls:
Relying solely on low w/c without curing, or over-vibrating and causing segregation.
Final Answer:
All the above (combined measures)