IS 6241 : 1971Method of Test for Determination of Stripping Value of Road Aggregates

IS 6241:1971 specifies the method of test for determination of the stripping value of road aggregates — the laboratory test that measures how readily a bituminous binder film peels off an aggregate in the presence of water. It is a core acceptance test for any bituminous pavement layer (BC, DBM, premix carpet, surface dressing) where moisture-induced stripping is the dominant durability risk.

It is read with the road-materials and pavement stack:

• IRC 37 — flexible pavement design (the layers that depend on good aggregate–binder adhesion)
• IS 383 / IS 2386 (parts) — aggregate quality and the other aggregate tests
• IS 73 — paving bitumen · IS 8887 — cationic bitumen emulsion
• MoRTH Specifications Section 500 — the contractual acceptance limits

Aggregate is coated with hot bitumen, the coated aggregate is immersed in water at a controlled temperature (around 40 °C) for a fixed period (commonly 24 h), and the percentage of the aggregate surface from which the bitumen has stripped is estimated visually.

• Stripping value = % of stone surface that has lost its bitumen film
• A *low* stripping value is good (binder stays bonded); typical specifications require the retained coating to be high — i.e. stripping not more than about 5% for important bituminous work
• Hydrophilic (acidic, siliceous) aggregates such as quartzite and some granites strip readily; hydrophobic (basic) aggregates such as basalt/limestone hold bitumen better

When an otherwise good aggregate fails, the standard remedy is an anti-stripping agent or hydrated lime addition, then re-test — the decision is made on the IS 6241 number, not on appearance of the dry mix.

Scenario: quarry aggregate proposed for a DBM layer; IS 6241 test run before approving the source.

Step 1 — test: bitumen-coated aggregate immersed 24 h at 40 °C; visual estimate shows ~12% of the surface stripped → stripping value ≈ 12%.

Step 2 — compare: the specification (MoRTH/IRC for important bituminous work) effectively wants stripping ≤ ~5% (retained coating ≥ ~95%). 12% fails.

Step 3 — remedy: add a dosed anti-stripping agent (or ~1–2% hydrated lime as filler) to the mix and re-run IS 6241.

Step 4 — re-test: treated sample now strips ~3% → passes; approve the source *with* the mandated anti-stripping treatment written into the job mix formula. Without the re-test, the treated mix is unproven and the layer is a moisture-failure risk.

1. Skipping the test for a 'good-looking' aggregate. Adhesion is a chemistry issue, not an appearance one — a strong, clean, well-graded siliceous aggregate can still strip badly.

2. Not re-testing after adding anti-stripping agent/lime. The whole point is to *prove* the remedy worked at the chosen dosage — an untested treated mix is non-compliant.

3. Wrong immersion temperature/time. Adhesion is temperature-sensitive; deviating from the prescribed conditioning makes the result non-comparable.

4. Treating stripping value in isolation. Read it with the IS 2386 soundness/water-absorption and the mix's retained-stability/TSR — moisture durability is a system property.

5. **Approving the source, not the *treated* mix.** If the source needs an anti-stripping agent, the approval and the JMF must lock the agent and dosage, not just the stone.

• IRC 37 — flexible pavement design · IRC 111 — dense graded bituminous mixes
• IS 383 — coarse and fine aggregate · IS 2386 (parts) — methods of test for aggregates
• IS 73 — paving bitumen · IS 8887 — cationic bitumen emulsion · IS 15462 — modified bitumen
• MoRTH Specifications for Road and Bridge Works, Section 500
• IS 6241 / IS 14982 — anti-stripping / adhesion-related test references

IS 6241 is dated (1971) but reaffirmed and still the routine Indian stripping test; the static-immersion visual estimate is operator-subjective, so for important work many agencies supplement it with the tensile-strength-ratio (TSR / AASHTO T283) retained-strength test required by IRC 111, which is more quantitative. Treat IS 6241 as the quick screen and TSR as the confirmatory moisture-damage check.

The field consequence of getting this wrong is severe and visible — ravelling, potholing and stripping of bituminous layers within a monsoon or two — almost always traced to a siliceous aggregate used without (or with under-dosed) anti-stripping treatment. The discipline is simple: test the source, and if it strips, fix the *mix* with a dosed agent/lime and re-test to IS 6241 before the JMF is frozen.