- At a glance
- 1. Introduction
- 2. Role of Admixtures in Mix Design
- 3. Classification of Chemical Admixtures
- 4. Codes & Standards
- 5. Selection Matrix — Based on Mix Design Parameters
- 6. Typical Performance Benchmarks
- 7. Comparative Study — With vs Without Admixture
- 8. Admixture Systems
- Disclaimer
How to use this page
- Use the table of contents to jump to classifications, standards, selection matrix, and benchmarks.
- Start with the Selection Matrix for quick recommendations by grade and constraints.
- Validate against Codes & Standards and benchmarks before finalizing specs.
At a glance
- Core outcomes: controlled rheology, reliable retention, targeted early strength, durable low‑permeability concrete
- Common chemistries: SNF, PCE, lignosulphonate, retarders/accelerators, air entrainers, SRA, integral waterproofing
- Key standards referenced: IS 9103, IS 10262, IS 456, ASTM C494, EN 934‑2, IS 2645
- Typical ranges: water reduction 15–35%, slump retention ≥75% @ 3 h, strength ≥100% of control
1. Introduction
Concrete admixtures are chemical ingredients added during mixing to modify properties of fresh and hardened concrete. They allow precise control of workability, setting, strength, and durability, essential for modern high‑performance concretes such as M50+, SCC, or mixes with high fly ash or GGBS content.
“Right admixture = controlled rheology, consistent quality, longer life, lower cost.”
2. Role of Admixtures in Mix Design
Parameter | Without Admixture | With PCE-based Admixture (0.8%) | Improvement |
Target Strength (M35) | 43.7 MPa | 43.7 MPa | — |
Workability (Initial Slump) | 100 mm | 180 mm | +80% |
Water‑Cement Ratio | 0.50 | 0.42 | ↓ by 15% |
Strength @ 7 Days | 29.8 MPa | 33.9 MPa | +13% |
Strength @ 28 Days | 39.3 MPa | 43.7 MPa | +11% |
Durability | Moderate | High (Low permeability) | Improved |
Cost Impact | — | +INR 85/m³ | Marginal vs benefits |
3. Classification of Chemical Admixtures
Admixture Type | Function | Base Chemistry | Key Standards | Application Zone |
Water‑Reducing Admixture (Plasticizer) | Improves workability | Lignosulphonate | IS 9103:2019 (Type WR) | Site concrete, mass pours |
Superplasticizer (SNF / PCE) | High water reduction | Sulphonated Naphthalene / Polycarboxylate Ether | ASTM C494 Type F / G | RMC, SCC, precast |
Mid‑Range Water Reducer | Controlled flow | Modified PCE | EN 934‑2 | Pumped concrete |
Retarder | Delays set | Hydroxycarboxylic acids | ASTM C494 Type D | Hot climates, long hauls |
Accelerator | Speeds up set | Calcium nitrate / formate | ASTM C494 Type E | Cold weather, precast |
Air Entrainer | Introduces micro air | Surfactants | ASTM C260 | Pavements, freeze–thaw |
Shrinkage Reducer | Reduces drying shrinkage | Glycol ethers | ASTM C1579 | Large slabs |
Corrosion Inhibitor | Prevents rebar corrosion | Calcium nitrite | EN 934‑2 | Marine / coastal works |
Integral Waterproofing | Reduces permeability | Hydrophobic polymer / pore blocker | IS 2645 | Tanks, basements |
4. Codes & Standards
Code | Description |
IS 9103:2019 | Chemical admixtures – Classification, tests, and dosage ranges |
IS 10262:2019 | Concrete mix design – method for proportioning |
ASTM C494 | Specification for admixtures – Types A to G |
EN 934‑2 | Admixtures for concrete, mortar, and grout |
IS 2645 | Integral waterproofing compounds |
IS 456:2000 | General structural concrete practices |
5. Selection Matrix — Based on Mix Design Parameters
Parameter / Constraint | Typical Challenge | Recommended Admixture Type | Dosage (% by wt of cement) | Target Outcome |
M20–M30 (Normal strength) | Moderate workability | Plasticizer | 0.3–0.5% | 100–120 mm slump |
M35–M45 (RMC, fly ash mixes) | Retention for 2–3 hrs | SNF Superplasticizer | 0.6–0.9% | 150 mm slump |
M50+ / HPC / SCC | Self-compacting concrete | PCE Superplasticizer | 0.6–1.0% | 600–700 mm flow |
Precast | Early strength | Accelerator + PCE | 0.5–1.0% + 1–2% | 10 MPa @ 8 hrs |
Hot Weather Concreting | Rapid set, loss of slump | Retarder + PCE | 0.7–1.0% | 3–4 hr retention |
Marine / Coastal | Chloride attack | PCE + Corrosion inhibitor | 0.7% + 1.5% | <0.1% chloride diffusion |
Slab on Grade / Tanks | Shrinkage & cracking | SRA + Integral waterproofing | 0.8% + 1.0% | <400 microstrain |
6. Typical Performance Benchmarks
Property | Test | Acceptance Criteria |
Water reduction | ASTM C494 | ≥15% (WR) / ≥25% (SP) |
Slump retention (3 hr) | IS 9103 | ≥75% retention |
Setting time | IS 8142 | ±90 min (retard/accel) |
Compressive strength | IS 516 | ≥100% of control mix |
Chloride content | IS 9103 | ≤0.1% |
Compatibility (Cement) | IS 9103 Appx B | No segregation or bleeding |
7. Comparative Study — With vs Without Admixture
Parameter | Without Admixture | With PCE Admixture |
Workability (Slump, mm) | 100 | 180 |
Water‑Cement Ratio | 0.50 | 0.42 |
Compressive Strength (7d / 28d) | 29.8 / 39.3 MPa | 33.9 / 43.7 MPa |
Density (kg/m³) | 2489 | 2562 |
Durability Index | Moderate | High |
Cost (INR/m³) | Base | +85 |
Overall Quality | Standard | Premium |
8. Admixture Systems
Admixture Type | Chemistry | Primary Use | Mix Design Input Link | Performance Range | Standard Reference |
Plasticizer | Lignosulphonate | Water reduction | Normal concrete | 10–15% water reduction | IS 9103 |
Superplasticizer (SNF) | Naphthalene | High slump retention | RMC | 15–25% | ASTM C494 Type F |
Superplasticizer (PCE) | PCE | Self-compacting, HPC | SCC / M60 | 25–35% | EN 934-2 |
Retarder | Organic acid | Hot weather | RMC | Delay 3–5 hrs | ASTM C494 Type D |
Accelerator | Calcium nitrate | Cold weather / Precast | Precast | Early set | ASTM C494 Type E |
SRA | Glycol ether | Shrinkage control | Large slabs | <400 µstrain | ASTM C1579 |
Integral Waterproofing | Polymer | Permeability control | Basements | <1×10⁻¹² m/s | IS 2645 |
Disclaimer
SpecX is an industry initiative and a neutral resource, compiled from industry references and best practices. Always cross‑check with project requirements and local codes before finalizing specifications.