Stripping Value Test of Aggregate – Purpose, Importance, Applications & Apparatus
By Kishor Kumar | Highway Quality Test
Updated: February 2026 • Read Time: 8 Minutes
The Stripping Value Test of Aggregate evaluates the ability of bitumen to remain firmly adhered to the surface of coarse aggregates when exposed to water. From a contractor's perspective, this test is one of the most important quality control checks before approving aggregates for bituminous works because poor adhesion between bitumen and aggregate is a major cause of premature pavement failures.
As a Material Engineer on highway projects, I always recommend conducting the stripping value test before large-scale production of Dense Bituminous Macadam (DBM), Bituminous Concrete (BC), and other hot mix asphalt layers. The test helps identify whether the selected aggregate source is suitable or whether an anti-stripping additive will be required to achieve durable pavement performance.
1. What is the Stripping Value Test?
The Stripping Value Test determines the percentage of aggregate surface from which the bitumen film gets detached after immersion in hot water under specified laboratory conditions. The higher the stripping value, the poorer the bond between aggregate and bitumen, increasing the likelihood of moisture damage and pavement deterioration.
The test primarily evaluates:
- Adhesion between bitumen and aggregate.
- Resistance of coated aggregates to moisture attack.
- Suitability of aggregate for bituminous pavement construction.
- Need for anti-stripping agents or alternative aggregate sources.
2. Engineering Significance
Water is one of the biggest enemies of flexible pavements. Once moisture penetrates the pavement structure, it weakens the adhesive bond between bitumen and aggregate. This process, known as stripping, causes gradual separation of the binder from the aggregate surface.
From practical highway construction experience, aggregates exhibiting high stripping values often lead to:
- Ravelling of the pavement surface.
- Premature pothole formation.
- Loss of aggregate from the wearing course.
- Reduced fatigue life of asphalt layers.
- Higher maintenance costs during the concession period.
Selecting aggregates with good stripping resistance significantly improves the durability and service life of bituminous pavements.
3. Importance of the Stripping Value Test
The Stripping Value Test is an essential quality control test for highway construction because it verifies whether aggregates can maintain a durable bond with bitumen under wet service conditions.
- Evaluates moisture susceptibility of aggregates.
- Ensures proper adhesion between bitumen and aggregate.
- Helps comply with MoRTH and project specifications.
- Reduces the risk of early pavement failures.
- Assists in selecting suitable aggregate sources.
- Determines the requirement of anti-stripping additives.
- Improves long-term pavement durability.
Engineering Note:
Lower stripping values indicate better adhesion between bitumen and aggregate, resulting in improved resistance to moisture damage and longer pavement service life.
4. Applications in Highway Construction
The Stripping Value Test is routinely carried out during material approval and mix design stages of highway projects. Contractor laboratories perform this test before approving aggregates for bituminous works.
Typical applications include:
- Approval of aggregate quarries for asphalt works.
- Selection of coarse aggregates for Bituminous Concrete (BC).
- Quality control of Dense Bituminous Macadam (DBM).
- Evaluation of aggregates used in Bituminous Macadam (BM).
- Assessment of aggregate compatibility with different penetration grade bitumen.
- Verification of aggregate quality during source changes.
- Determining the necessity of anti-stripping additives.
The test is widely specified for National Highways, State Highways, Expressways, PMGSY roads, EPC projects, HAM projects, and other flexible pavement works where long-term moisture resistance is critical.
5. Applicable Standards
- IS 6241 – Method for Determination of Stripping Value of Road Aggregates.
- MoRTH Specifications – Requirements for Bituminous Layers.
- IRC:SP:62 – Guidelines for Design and Construction of Bituminous Pavements.
6. Apparatus Required
The following equipment is required to perform the Stripping Value Test:
- Clean coarse aggregate sample.
- Bitumen of the specified penetration grade.
- Water bath maintained at 60 ± 1°C.
- Glass beakers or suitable containers.
- Oven for drying aggregates.
- Electronic weighing balance.
- Sieves for sample preparation.
- Mixing tray and spatula.
- Thermometer.
- Tongs and laboratory accessories.
Contractor's Practical Tip:
Before approving any new aggregate source for DBM or BC production, always perform the Stripping Value Test. If excessive stripping is observed, use an approved anti-stripping agent or consider changing the aggregate source. Addressing adhesion issues during material selection is far more economical than repairing moisture-induced pavement failures after construction.
7. Test Procedure
The Stripping Value Test should be carried out carefully under controlled laboratory conditions to obtain reliable and repeatable results. From a contractor's QA/QC perspective, maintaining the correct temperature and ensuring uniform coating of aggregates are the most critical aspects of this test.
- Wash and oven-dry the aggregate sample to remove dust, moisture, and other contaminants.
- Heat the bitumen to the specified temperature until it becomes sufficiently fluid for proper coating.
- Coat the aggregate particles uniformly with bitumen so that every exposed surface is completely covered.
- Allow the coated aggregates to cool slightly before placing them in a clean glass container.
- Immerse the coated aggregates in a water bath maintained at 60 ± 1°C for 24 hours.
- After immersion, carefully remove the aggregates without disturbing the remaining bitumen coating.
- Dry the aggregates in an oven at approximately 105°C until a constant weight is achieved.
- Inspect the aggregate surface visually and record the amount of bitumen stripped from the aggregate surface.
- Measure the required weights and calculate the stripping value.
Practical Site Tip:
Always use clean, dust-free aggregates. Even a thin layer of dust can significantly reduce bitumen adhesion and produce misleading stripping results.
8. Stripping Value Calculation
The stripping value is expressed as the percentage loss of bitumen coating from the aggregate surface after immersion in water.
Stripping Value (%) = ((W1 − W2) / W1) × 100
Where:
- W1 = Initial weight of coated aggregate (g)
- W2 = Final weight after immersion and drying (g)
| Initial Weight (W₁) | Final Weight (W₂) | Stripping Value (%) |
|---|
| 500 g | 460 g | 8% |
| 500 g | 450 g | 10% |
A lower stripping value indicates stronger adhesion between bitumen and aggregate, resulting in better resistance against moisture-induced pavement damage.
9. Result Interpretation
The following table provides a general guideline for interpreting stripping value results during material approval.
| Stripping Value (%) | Aggregate Adhesion Quality | Recommendation |
|---|
| < 10% | Excellent | Highly Suitable |
| 10–20% | Good | Suitable |
| 20–30% | Fair | Use with Caution |
| > 30% | Poor | Not Recommended |
Material Engineer's Recommendation:
If stripping exceeds the project specification limits, evaluate the use of an approved anti-stripping agent or consider changing the aggregate source before commencing asphalt production.
10. Practical Notes for Field & Laboratory Engineers
- Use clean, dry, and dust-free aggregates.
- Ensure complete and uniform bitumen coating on every aggregate particle.
- Maintain the water bath temperature at 60 ± 1°C throughout the test.
- Use the aggregate size specified in IS 6241.
- Perform the test on multiple samples and report the average value.
- Calibrate weighing balances and thermometers periodically.
- Record all observations immediately to avoid transcription errors.
11. Common Mistakes to Avoid
The following mistakes frequently lead to inaccurate stripping values and should be avoided during testing.
- Overheating bitumen, causing oxidation and loss of adhesive properties.
- Improper or non-uniform coating of aggregates.
- Using dusty or damp aggregate samples.
- Failure to maintain the specified water bath temperature.
- Insufficient drying before final weighing.
- Using uncalibrated laboratory equipment.
- Recording incorrect weights or calculation errors.
Quality Control Advice:
Always verify equipment calibration, strictly follow IS 6241, and maintain complete laboratory records. Accurate testing during material approval helps prevent moisture-related pavement failures and costly repairs after construction.
12. Who Should Read This Guide?
This comprehensive guide has been prepared from the practical perspective of a contractor's Material Engineer and is beneficial for professionals involved in the design, construction, supervision, and quality control of flexible pavements.
- 👷 Highway Site Engineers responsible for bituminous works.
- 🧪 QA/QC Engineers involved in material approval and quality assurance.
- 🏗 Laboratory Technicians performing aggregate and bitumen testing.
- 🎓 Civil Engineering Students preparing for laboratory practicals and competitive examinations.
- 📋 EPC Contractors, Consultants, Independent Engineers (IE), and Authority Engineers supervising highway construction.
- 🏢 Material Engineers working in asphalt plants and highway laboratories.
Professional Insight:
Understanding the Stripping Value Test helps engineers select suitable aggregate sources, improve asphalt mix durability, minimize moisture damage, and reduce long-term maintenance costs of flexible pavements.
13. Conclusion
The Stripping Value Test is one of the most important quality control tests for aggregates used in bituminous pavements. It evaluates the adhesive bond between bitumen and aggregate under the influence of water, helping engineers assess the moisture susceptibility of asphalt mixtures before construction begins.
From a contractor's perspective, conducting this test during material approval significantly reduces the risk of stripping, ravelling, pothole formation, and premature pavement failures. Selecting aggregates with excellent adhesion characteristics improves pavement durability, extends service life, and minimizes future maintenance requirements.
By following IS:6241, maintaining proper laboratory procedures, and accurately interpreting the results, engineers can confidently approve aggregate sources for use in Dense Bituminous Macadam (DBM), Bituminous Concrete (BC), and other asphalt layers.
Key Takeaway:
A lower Stripping Value indicates stronger bitumen-aggregate adhesion and better resistance to moisture damage, ultimately resulting in safer, more durable, and longer-lasting highway pavements.
Frequently Asked Questions (FAQs)
1. What is an acceptable Stripping Value for road aggregates?
Generally, a stripping value of less than 10% indicates excellent adhesion, 10–20% is considered good, 20–30% indicates fair performance, while values greater than 30% suggest poor adhesion and the aggregate should normally not be used without appropriate anti-stripping treatment.
2. Why is the water bath maintained at 60 ± 1°C?
Maintaining the water bath at 60 ± 1°C simulates elevated pavement temperatures commonly experienced in tropical climates. It accelerates the moisture exposure process and provides a reliable assessment of the bond between bitumen and aggregate under adverse conditions.
3. Can the Stripping Value Test be performed on any aggregate size?
No. Only the aggregate size fraction specified in IS:6241 should be used. Standardizing the sample size ensures consistency, repeatability, and accurate comparison of test results.
4. Why do Stripping Value results sometimes vary?
Variations may occur due to several factors, including:
- Improper or non-uniform bitumen coating.
- Differences in aggregate mineral composition and surface texture.
- Incorrect water bath temperature.
- Inadequate drying before weighing.
- Uncalibrated laboratory equipment.
- Operator errors during testing or observation.
Following standard laboratory procedures, maintaining equipment calibration, and conducting multiple trials help achieve reliable and repeatable results.
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