IS 2386 Part 5 : 1963Methods of Test for Aggregates for Concrete - Part 5: Soundness

IS 2386 (Part 5) specifies the methods of test for soundness of aggregates for concrete — the durability test that predicts how aggregate will behave under repeated wetting/drying or freeze/thaw cycles in service. Soundness is a critical aggregate quality parameter especially for projects in cold zones, marine exposure, and water-retaining structures.

Use IS 2386 Part 5 when: - Source qualification of new aggregate quarry - Verification of aggregate durability for marine / coastal projects - Aggregate for water-retaining structures - Aggregate for cold-zone concrete (Himalayan / hill stations) - Aggregate for high-durability bridge / infrastructure projects - Forensic investigation of premature concrete deterioration

The test simulates weathering by exposing aggregate to repeated cycles in concentrated sodium sulphate (or magnesium sulphate) solution. Salts crystallise in pores → expand → fracture aggregate. Mass loss is measured as soundness indicator.

Per IS 383:2016 acceptance: - General concrete: ≤ 12 % loss for sodium sulphate (5 cycles); ≤ 18 % for magnesium sulphate - Marine / aggressive: ≤ 10 % loss - Pavement quality concrete (PQC): ≤ 12 % (also subject to LA abrasion limits)

Why soundness matters: - Unsound aggregate degrades under environmental cycles → microcracks in concrete → reduced strength + durability + corrosion of reinforcement - Particularly relevant for: aggregate from weathered rock sources, lateritic gravels, certain limestones with pyritic / shale inclusions

Sample preparation: - Aggregate dried + sieved into size fractions - Each fraction: 100-300 g (standard mass per fraction) - Mass recorded

Test cycle (sodium sulphate): 1. Immerse aggregate in saturated sodium sulphate solution (32 g/100 mL water at 22 °C) for 16-18 hours. 2. Drain solution; oven-dry at 105-110 °C for 4-6 hours. 3. Cool to room temperature. 4. One cycle complete.

Repeat for 5 cycles (standard) OR 10 cycles (extended).

After cycles: 5. Wash sample with water until no chloride / sulphate residue. 6. Oven-dry to constant mass. 7. Sieve through next-smaller IS sieve. 8. Weigh material retained. 9. Mass loss = (initial mass − final mass retained) / initial mass × 100 %

Reporting: - Mass loss per fraction - Weighted average mass loss (per IS 383:2016 calculation) - Comparison to acceptance limits

Magnesium sulphate variant: - Same procedure but with magnesium sulphate - More aggressive than sodium sulphate (different acceptance limit) - Less commonly used in Indian practice

Cycle vs strength loss correlation: - 12 % mass loss after 5 cycles ≈ aggregate likely durable for normal exposure - 18-25 % loss = marginal; trial concrete needed before accepting - > 25 % loss = aggregate not suitable for durable concrete; rejection or alternative source

Aggregate acceptance criteria (per IS 383:2016):

| Application | Sodium sulphate, max % loss | Magnesium sulphate, max % loss | |---|---|---| | General concrete | 12 % | 18 % | | Pavement concrete (PQC) | 12 % | 18 % | | Severe / marine exposure | 10 % | 15 % | | Very severe / extreme exposure | 8 % | 12 % | | Reinforced water-retaining structure | 10 % | 15 % |

Aggregate types + soundness: - Hard granite / quartzite: typically 1-5 % loss (excellent) - Basalt: 5-10 % loss (good) - Limestone: 3-15 % loss (variable; pure limestone good, dolomitic limestone may fail) - Sandstone: 5-20 % loss (variable; quartzitic sandstone better) - Gravel from river bed: usually good, sometimes pollution / pyrite issues - Lateritic gravel: 15-30 % loss (often marginal; may not meet PQC requirement) - Recycled concrete aggregate (RCA): 10-25 % loss (variable)

Cost of test: - Single sample (5 cycles, sodium sulphate): ₹3000-6000 at NABL lab - Source qualification batch: ₹10000-25000

Test cadence: - Source qualification (one-time per quarry): mandatory - Periodic re-test (annual or per major source change) - Forensic investigation (when concrete fails due to suspected aggregate issue)

Test sample size: - Multiple sieve fractions tested separately - Each fraction: 100-300 g - Result computed on weighted basis (proportional to fraction mass in actual aggregate gradation)

Field-level sanity check (without lab): - Visual inspection: aggregate that breaks easily by hand pressure or chips with finger nail = suspect - Ring test: hard aggregate gives sharp ring when struck; weak gives dull thud - Slake durability test (IS 10050:1981) — alternative for rock characterisation

• IS 2386 Part 1:1963 — particle size and shape (gradation, flakiness, elongation).
• IS 2386 Part 2 — deleterious materials (clay lumps, soft particles, organic).
• IS 2386 Part 3 — specific gravity, density, voids, absorption, bulking.
• IS 2386 Part 4 — mechanical properties (LA abrasion, AIV, ACV).
• IS 2386 Part 6 — measuring mortar making properties of fine aggregate.
• IS 2386 Part 7 — alkali-aggregate reactivity.
• IS 2386 Part 8 — petrographic examination.
• IS 383:2016 — coarse and fine aggregates for concrete (acceptance specification).
• IS 456:2000 — RCC code (durability provisions).
• IS 10262:2019 — concrete mix design.
• IS 10050:1981 — slake durability of rocks (alternative durability test).
• IS 12330:1988 — sulphate-resisting cement (paired with sound aggregate for aggressive environments).
• IS 9013:1978 — water permeability of concrete (related durability test).
• ASTM C88 — international counterpart for soundness test.
• ASTM C535 — abrasion test (companion to soundness).

1. Test on insufficient sample size. Each fraction needs 100-300 g; less = imprecise. Use full sample. 2. Solution concentration drift. Sodium sulphate concentration must be saturated; weak solution = under-test. Use fresh saturated solution per cycle. 3. Drying temperature too high. > 110 °C may damage aggregate further; bias result. Stick to 105-110 °C. 4. Test in lab without proper ventilation. Sulphate fumes hazardous. Use fume hood. 5. Not running 5 cycles. Acceptance based on 5 cycles per IS 383; 3 cycles inadequate. 6. No fraction-wise weighing. Different fractions have different soundness; weighted average needed. 7. Test on single sample without repeats. Aggregate variability; need 2-3 samples for confidence. 8. Acceptance applied uniformly without environment context. Severe / marine exposure needs stricter limit (10 %); routine concrete 12 %. 9. Magnesium vs sodium sulphate acceptance values mixed up. Different limits; verify which test was run. 10. Substitute test (LA abrasion only) without soundness. LA abrasion measures abrasion; soundness measures durability under cycles — different aspects. Both needed for durability assessment. 11. No field-level sanity check before lab test. Obviously weak / weathered aggregate sent to lab; waste of time + money. Visual + ring test first. 12. Acceptance based on 'meets IS 383' alone. IS 383 acceptance varies by exposure; verify project-specific requirement.

Aggregate source qualification cascade:

1. Reconnaissance — identify quarry source; geological assessment. 2. Sample collection — representative samples from active production face. 3. Tests per IS 2386 series: - Part 1 — gradation, flakiness, elongation - Part 2 — deleterious materials - Part 3 — specific gravity, water absorption - Part 4 — LA abrasion, AIV (mechanical) - Part 5 (this code) — soundness - Part 7 — AAR screening 4. Acceptance against IS 383:2016 for aggregates for concrete. 5. Trial concrete — 28-day strength, durability tests. 6. Approval — source qualified for project.

Routine acceptance (per delivery): - Gradation, flakiness, elongation per delivery - Deleterious materials, AIV per source qualification + monthly - Soundness re-test — annually OR per major source change - Strength + durability indirect via concrete cube test + permeability

For demanding projects (marine, dam, bridge): - Stricter soundness limit (8-10 %) - AAR petrographic examination per Part 8 - Periodic re-qualification - Additional in-situ verification of concrete durability

Soundness is one of the cheapest insurance policies in concrete construction — testing early prevents premature deterioration that costs orders of magnitude more to fix.