4.6 QUALITY CONTROL OF ADMIXTURES
Admixtures are materials (other than water, aggregates, and cement) added to concrete to modify its properties. Their quality control is essential to ensure compatibility with cement, stability of performance, and long-term durability of concrete.
4.6.1 Classification of Admixtures (as per IS 9103)
| Type of Admixture |
Purpose / Function |
Examples / Typical Use |
| Plasticizers (Water-reducing admixtures) |
Improve workability without increasing water content |
Lignosulfonates, Hydroxycarboxylic acids |
| Superplasticizers (High range water reducers) |
Large reduction in water for high strength and flowability |
Sulphonated naphthalene formaldehyde (SNF), Polycarboxylate ethers (PCE) |
| Retarders |
Delay setting time, useful in hot weather concreting |
Sugars, Phosphates, Gypsum-based |
| Accelerators |
Reduce setting time, useful in cold weather concreting |
Calcium nitrate, Triethanolamine |
| Air-entraining agents |
Introduce microscopic air bubbles for frost resistance |
Vinsol resin, Synthetic detergents |
| Waterproofing admixtures |
Reduce permeability |
Metallic stearates, Silicates |
| Mineral admixtures |
Improve strength, durability, and economy |
Fly ash, Silica fume, GGBS, Metakaolin |
4.6.2 Sampling and Storage
- Sampling of admixtures should be done as per IS 9103 (Annex B).
- Store admixtures in airtight, corrosion-resistant containers away from direct sunlight.
- Liquid admixtures must be stirred or shaken before sampling.
- Shelf life and batch number should always be checked before use.
4.6.3 Laboratory Quality Tests for Admixtures
| Test Name |
Description / Objective |
Typical Requirement / Acceptance Criteria |
Standard Reference |
| 1. Dry Material Content / Solid Content Test |
Determines the percentage of solids present in liquid admixture |
Within manufacturer’s declared range (±2%) |
IS 9103 |
| 2. pH Value Test |
Measures acidity or alkalinity to ensure compatibility with cement |
pH between 6 – 10 (generally acceptable range) |
IS 9103 |
| 3. Specific Gravity Test |
Ensures uniform concentration and helps in dosage control |
As per manufacturer’s declaration (commonly 1.05–1.20) |
IS 9103 |
| 4. Compatibility with Cement |
Checks for abnormal setting, flash set, or segregation when mixed with cement |
No abnormal setting or segregation observed |
IS 9103, Annex C |
| 5. Effect on Setting Time |
Measures change in initial and final setting time compared to control |
Change within ±1 hour for plasticizers; within limits of IS 9103 Table 1 |
IS 9103, IS 4031 (Part 5) |
| 6. Effect on Compressive Strength |
7 and 28-day compressive strength of concrete with admixture vs. control |
≥90% of control mix (unless otherwise specified) |
IS 9103, IS 516 |
| 7. Workability Test (Slump / Flow Table) |
Evaluates improvement in workability due to admixture |
Increase in slump / flow as per requirement |
IS 1199 |
| 8. Air Content Test (for air-entraining agents) |
Determines total air content in concrete |
3–6% air (depending on exposure conditions) |
IS 1199, IS 9103 |
| 9. Chloride Content Test |
Ensures chloride levels are within permissible limits to avoid corrosion |
≤0.1% by mass of cement (for reinforced concrete) |
IS 9103, IS 456 |
| 10. Sulphate Content Test |
Ensures sulphate levels are within safe limits |
≤0.5% by mass of cement |
IS 9103, IS 456 |
4.6.4 Field Quality Control Measures
- Use admixtures only from approved sources and batches.
- Maintain dosage records (ml/kg of cement or % by weight).
- Trial mixes must be conducted at site to confirm compatibility with available materials.
- Check uniform dispersion of liquid admixtures; avoid overdosing.
- Observe any abnormal setting, bleeding, or segregation in trial concrete.
4.6.5 Key Quality Considerations
| Aspect |
Quality Guideline |
| Storage Stability |
Inspect regularly for precipitation or phase separation |
| Compatibility with Cement |
Must be tested whenever there is a change in cement source or type |
| Dosage Control |
Use graduated dispensers for liquid admixtures |
| Record Keeping |
Maintain test certificates, batch details, and field performance logs |
| Environmental Conditions |
Avoid exposure to direct sunlight and temperature above 40°C |
4.6.6 Relevant BIS and ASTM Standards
| Standard No. |
Title / Description |
| IS 9103 |
Specification for Concrete Admixtures |
| IS 2645 |
Integral Waterproofing Compounds for Cement Mortar and Concrete |
| IS 456 |
Code of Practice for Plain and Reinforced Concrete (limits on admixture use) |
| IS 383 |
Specification for Coarse and Fine Aggregates (compatibility considerations) |
| ASTM C494 |
Standard Specification for Chemical Admixtures for Concrete |
| ASTM C260 |
Air-Entraining Admixtures for Concrete |