Super plasticisers are also called
Correct Answer: B. high-range water reducers
🧱 Detailed Explanation: Super Plasticisers — High-Range Water Reducers
Super plasticisers (SPs) are fourth-generation chemical admixtures that dramatically improve fresh concrete workability without increasing water content, or — conversely — allow a significant reduction in mixing water while maintaining the same consistency. Because of this high-magnitude water reduction capability, they are officially classified as High-Range Water Reducers (HRWRs) under both IS 9103 (Indian standard for admixtures) and ASTM C494 (Type F and G).
Why B (High-Range Water Reducers) is correct:
Ordinary plasticisers (normal water reducers) achieve 5–15% water reduction. Super plasticisers achieve 20–30%+ water reduction — hence the designation “high-range.” SP molecules (typically long polymer chains) adsorb onto cement particles and create electrostatic repulsion or steric hindrance, causing particles to disperse and the mix to flow freely at a lower w/c ratio.
Ordinary plasticisers (normal water reducers) achieve 5–15% water reduction. Super plasticisers achieve 20–30%+ water reduction — hence the designation “high-range.” SP molecules (typically long polymer chains) adsorb onto cement particles and create electrostatic repulsion or steric hindrance, causing particles to disperse and the mix to flow freely at a lower w/c ratio.
Retardants (A) slow setting; accelerators (C) speed it up; low-range water reducers (D) describes normal plasticisers. None of these match super plasticisers.
Admixture Classification by Water-Reduction Range
| Admixture | Water Reduction | Classification |
|---|---|---|
| Normal plasticiser | 5–15% | Low / mid-range water reducer |
| Super plasticiser (SP) | 20–30%+ | High-Range Water Reducer (HRWR) |
| Retarder (Type B) | Minimal | Set-time extender |
| Accelerator (Type C) | Minimal | Set-time shortener |
Common SP Types Used in India
| Type | Chemical Basis | Water Reduction |
|---|---|---|
| SNF (Sulphonated Naphthalene Formaldehyde) | Electrostatic repulsion | 20–25% |
| SMF (Sulphonated Melamine Formaldehyde) | Electrostatic repulsion | 20–25% |
| PCE (Polycarboxylate Ether) — latest gen. | Steric hindrance | 25–30%+ |
Key Concepts for Students
- Super plasticisers = High-Range Water Reducers — the two terms are interchangeable in IS codes and international standards.
- They do NOT retard or accelerate setting when used at the correct dosage (unlike Type G admixtures, which combine SP + retarder).
- Key applications: Self-Compacting Concrete (SCC), high-strength concrete (M60+), and ready-mix concrete requiring long workability retention.
- Excess dosage causes segregation and bleeding — manufacturer-specified dosage limits must be followed precisely.
