IS 10050 : 1981Method for determination of slake durability index of rocks

IS 10050 specifies the method for determination of slake durability index (SDI) of rocks — a quick test to characterise rock weathering resistance under repeated wetting-drying cycles. SDI is widely used to classify rock quality for construction aggregates, embankment fill, road base, and rock-fill dam construction.

Use IS 10050 SDI when: - Source qualification of new aggregate quarry - Highway / dam embankment fill from rock cuttings - Road base course material assessment - Foundation rock characterisation (where weathering matters) - Rip-rap stone quality verification (river training, slope protection) - Forensic investigation of premature rock-fill degradation

SDI complements IS 2386 Part 5:1963 (sulphate soundness for aggregate) — different test methodology, both characterise durability: - IS 2386 Part 5: chemical attack via sulphate cycles (suitable for concrete aggregate) - IS 10050 (this code): physical wetting/drying (suitable for rock fill, stone in soil contact)

Typical SDI values for Indian rocks:

| Rock type | SDI (2-cycle) | Quality | |---|---|---| | Hard granite, basalt, quartzite | 95-100 | Excellent | | Limestone (sound) | 90-99 | Very good | | Sandstone (well-cemented) | 85-95 | Good | | Weathered granite, schist | 70-90 | Moderate | | Mudstone, siltstone | 30-70 | Poor (rapid degradation) | | Highly weathered / shale | < 30 | Very poor (avoid) |

Equipment: - Slake durability apparatus: 2 mm wire mesh drum (140 mm diameter × 100 mm wide) - Drum rotates inside water trough at 20 rpm for 10 minutes - Oven for drying - Balance

Sample preparation: - 10 oven-dry rock fragments, each 40-60 g (total ~500 g) - Approximately spherical / equidimensional shape - Free of dust - Initial mass M₁ recorded

Procedure (cycle): 1. Place 10 fragments in mesh drum. 2. Submerge drum in water bath at 20 ± 2 °C. 3. Rotate drum at 20 rpm for 10 minutes. 4. Remove drum; oven-dry retained fragments at 105-110 °C overnight. 5. Weigh dried mass M₂. 6. One cycle complete.

Repeat for 2 cycles (standard). For research / extended characterisation, more cycles.

SDI calculation (after 2 cycles):

`SDI₂ = (M₂ / M₁) × 100 %`

Where M₂ = mass after 2 cycles, M₁ = initial dry mass.

Interpretation: - High SDI = durable rock (resists weathering) - Low SDI = weak / weathered rock (degrades rapidly)

Reporting: - SDI₁ (after 1 cycle) — interim - SDI₂ (after 2 cycles) — standard reported value - Visual observation of fragment after each cycle (rounding, fissures, discoloration) - Lithology classification

Test cadence: - Source qualification: 3-5 samples per quarry - Periodic re-test: per quarry face change OR annually - Dispute resolution: as needed

SDI classes (proposed by Gamble — widely used internationally):

| SDI₂ | Classification | Use | |---|---|---| | 95-100 | Very high durability | All applications including PQC aggregate | | 85-95 | High durability | General concrete + most fills | | 70-85 | Medium durability | Embankment fill, road base (verify) | | 50-70 | Medium-low | Limited use; specific design | | 25-50 | Low | Only buried fill; not exposed | | < 25 | Very low | Avoid; unsuitable for construction |

Acceptance for typical applications:

| Application | SDI₂ minimum | |---|---| | PQC concrete aggregate | ≥ 95 | | General concrete aggregate | ≥ 90 | | Highway embankment fill | ≥ 80 | | Granular sub-base (GSB) | ≥ 75 | | Rip-rap (river / slope protection) | ≥ 90 | | Dam rock-fill | ≥ 85 | | Building foundation rock | ≥ 70 |

SDI vs other rock tests:

| Test | Method | Use | |---|---|---| | Slake durability (IS 10050) | Wet-dry cycles | Quick durability assessment; good for shales / mudstones | | Soundness (IS 2386 Part 5) | Sulphate cycles | Aggregate durability for concrete | | LA abrasion (IS 2386 Part 4) | Steel ball abrasion | Mechanical wear resistance | | Aggregate impact value (AIV) | Hammer impact | Toughness / impact strength | | Aggregate crushing value (ACV) | Crushing under load | Compressive strength | | Petrographic exam (IS 2386 Part 8) | Microscopic | Mineralogy + soundness assessment |

For comprehensive rock quality, combine multiple tests: SDI + AIV + LA abrasion + petrographic.

Cost: - SDI test: ₹2000-5000 per sample (NABL lab) - Quick + cheap; useful screening test - Full rock characterisation panel: ₹10000-25000

Sample size: - 10 fragments × 40-60 g = ~500 g per test - Multiple tests per source for reliable result

Calibration: - Slake durability apparatus calibrated against reference rock (Gamble's standard); verify monthly

• IS 2386 Part 5:1963 — soundness of aggregates (sulphate-cycle test).
• IS 2386 Part 1:1963 — particle size + shape.
• IS 2386 Part 4 — mechanical properties (LA abrasion, AIV, ACV).
• IS 2386 Part 8 — petrographic examination.
• IS 383:2016 — coarse + fine aggregates for concrete.
• IS 9143 — code of practice for design of foundations on rock.
• IS 1080:1985 — design of shallow foundations.
• IS 6403:1981 — bearing capacity (rock).
• IS 1893 Part 1:2016 — earthquake design.
• IRC:36:2010 — earth embankment construction.
• IRC:5:2015 — bridge design (foundation on rock).
• IS 7196 — pre-cast plain + reinforced concrete masonry units.
• ASTM D4644 — international counterpart for slake durability.
• ISRM Suggested Methods for Rock Characterisation.

1. SDI used as sole rock quality measure. SDI characterises one aspect; combine with LA abrasion, AIV, soundness for comprehensive view. 2. Sample fragments too small / too large. Standard 40-60 g; smaller breaks rapidly, larger doesn't fit drum properly. 3. Sample not representative. Hard fragments selected; weak ones rejected; result over-stated. Random sampling. 4. Single sample tested. Quarry heterogeneity ignored. Multiple samples per source. 5. Drum rotation rate wrong. 20 rpm standard; faster degrades more, slower less. Calibrate apparatus. 6. Drum mesh damaged / clogged. Affects water circulation + fragment retention. Inspect + clean periodically. 7. Oven temperature too high. > 110 °C may damage rock further. Stick to 105-110 °C. 8. No comparison with reference rock. Apparatus may drift; use reference rock periodically for calibration check. 9. Acceptance applied without context. SDI ≥ 80 may suffice for embankment but not PQC aggregate; match acceptance to application. 10. Visual observation skipped. Photograph + describe fragment after each cycle; reveals weathering pattern (laminated vs uniform). 11. Result not correlated with field performance. Database of SDI vs field weathering essential; refine acceptance over time. 12. Test on weathered surface fragments. Quarry face fragments may be weathered; test fresh interior rock for true characterisation.

Rock + aggregate source qualification:

1. Reconnaissance — geological map; identify source. 2. Field characterisation: - Rock type identification (lithology) - Visual weathering grade - Drilling / sampling for fresh rock 3. Lab tests on fresh rock: - SDI (this code, IS 10050) - Petrographic (IS 2386 Part 8) - Mechanical (LA abrasion, AIV, ACV per IS 2386 Part 4) - Specific gravity, water absorption (IS 2386 Part 3) - Soundness (IS 2386 Part 5) 4. Acceptance vs application: - Concrete aggregate: SDI ≥ 90 + LA ≤ 35 + soundness ≤ 12 % - Embankment fill: SDI ≥ 80 + lower bar on others - Rip-rap: SDI ≥ 90 + visible sound rock 5. Quarry approval — for project use. 6. Periodic re-test — quarry face changes over time; verify quality maintained. 7. Dispute resolution — if rock-fill degrades in service, re-test source rock.

SDI is one of the most cost-effective screening tests for rock durability — quick, cheap, indicative. Combined with mechanical + soundness tests, it provides comprehensive rock quality characterisation for construction use.