Consider the following pairs.

Admixtures	Chemicals
a) Water reducing admixtures	Calcium chloride
b) Air-entraining agent	Neutralized vinsol resin
c) Super plasticizer	Sulphonated melanin
d) Accelerator	Lignosulphonate

Which of the pairs given above is/are correctly matched?

Explanation:

Water-Reducing Admixtures

• Purpose and Function:
  Water reducers decrease the required mixing water for a given workability, thus reducing the water-cement ratio and improving concrete strength and durability.

• Mechanism:
  These admixtures disperse the cement particles in the mix, reducing friction and allowing for better flow with less water.

• Common Compounds Used:
  Examples include lignosulphonates, hydroxylated carboxylic acids, and polycarboxylates (in modern applications).

• Applications:
  Used in residential and commercial concreting, precast elements, and for improving concrete finishes where water reduction is needed without sacrificing workability.

​Air-Entraining Admixtures

• Purpose and Function:
  These admixtures intentionally create microscopic air bubbles in concrete, which improve its resistance to freeze-thaw cycles, scaling, and deicing chemicals.

• Mechanism:
  The entrained air forms tiny voids that act as buffers when water in concrete freezes, preventing internal cracking.

• Common Compounds Used:
  Includes neutralized vinsol resin, wood resins, animal fats, and synthetic detergents.

• Applications:
  Essential for concrete used in cold climates, highways, airport pavements, and bridge decks, where freeze-thaw durability is critical.

Additional InformationSuperplasticizers (High-Range Water Reducers)

• Purpose and Function:
  Superplasticizers significantly increase workability and flowability without increasing water, or reduce water content drastically (up to 30%).

• Mechanism:
  They use advanced polymers (like sulphonated melamine, sulphonated naphthalene, and polycarboxylate ethers) to disperse cement particles efficiently.

• Common Compounds Used:
  Examples include sulphonated melamine formaldehyde (SMF), sulphonated naphthalene formaldehyde (SNF), and polycarboxylate ether (PCE).

• Applications:
  Used in self-compacting concrete (SCC), high-performance concrete (HPC), precast units, and mass concrete pours where flow and strength are both needed.

Accelerating Admixtures

• Purpose and Function:
  Accelerators are added to shorten the setting time and speed up early strength development, especially useful in cold weather.

• Mechanism:
  They promote faster hydration of C3S (tricalcium silicate) phase of cement, allowing earlier formwork removal or load application.

• Common Compounds Used:
  Includes calcium chloride (most common), triethanolamine, sodium thiocyanate, and calcium nitrate.

• Applications:
  Ideal for repair works, precast production, cold weather concreting, and early load-bearing structural elements.
  Note: Use of calcium chloride is restricted in reinforced concrete due to corrosion risk to steel.