Which of the following properties of plastic (fresh) concrete is modified by air-entraining agents?

Detailed Explanation: Air-Entraining Agents Modify Workability, Segregation, AND Bleeding

Why D (All options) is correct: Air-entraining agents introduce a carefully controlled system of tiny, discrete, stable air bubbles into the concrete mix. These bubbles act simultaneously on multiple fresh concrete properties, improving all three listed characteristics. This makes air-entraining agents one of the most versatile admixture types for improving fresh concrete quality.

How Entrained Air Affects Each Property

Property	How Entrained Air Modifies It	Magnitude of Effect
A. Workability	Air bubbles act as micro-ball-bearings between aggregate particles; reduce inter-particle friction; paste flows more easily → workability increases without adding water	Can replace 3–4% mix water per 1% air entrained
B. Segregation	Entrained air increases mix cohesion (paste viscosity); bubbles help suspend aggregate particles; heavier aggregates less likely to settle or separate	Significant reduction in segregation tendency
C. Bleeding	Air bubbles interrupt capillary channels through which bleed water migrates upward; discrete bubbles block water migration paths; reduces bleeding significantly	Bleeding can be reduced by 30–50%

Air-Entraining Agents: Types and Dosages

Agent Type	Example	Dosage
Natural resins	Vinsol resin, abietic acid	0.005–0.02% by wt. cement
Animal fats / tallows	Sodium stearate, calcium oleate	0.005–0.05% by wt. cement
Soap / detergents	Sodium lauryl sulphate, alkyl sulphates	0.01–0.1% by wt. cement
Synthetic surfactants	Petroleum sulphonate	Up to 1% by wt. cement

Effects on Hardened Concrete

Property	Effect
Freeze-thaw resistance	Significantly improved; entrained air provides pressure relief for freezing water
Compressive strength	Slightly reduced; each 1% air entrained reduces strength by ≈4–5%
Permeability	Slightly increased (more air = more voids); offset by improved workability enabling better compaction

• Air-entraining agents modify all three: workability (improved), segregation (reduced), bleeding (reduced).
• Target air content for freeze-thaw resistance: 4–7% by volume of concrete.
• Common agents: natural resins, animal fats, soaps. Dosage: 0.005–1% by wt. cement.