IS 2386 Part 6 : 1963Methods of Test for Aggregates for Concrete - Part 6: Measuring Surface Moisture

IS 2386 (Part 6):1963 covers the method for measuring mortar-making properties of fine aggregate — i.e., how 'good' a sand is when used in cement-sand mortar. It is the specialist supplement to IS 2386 series for cases where simple sieve analysis (Part 1) and silt content (Part 2) don't tell the full quality story.

Use it when: - Comparing alternative sand sources — river sand vs M-sand vs manufactured fines - Auditing a sand source before contracting bulk supply for a large project - Investigating mortar/plaster failures where sand is suspected (low workability, low strength, excessive shrinkage) - Specifying sand for premium applications — exposed cement plaster, decorative pointing, restoration work on heritage structures

The test is rarely run for routine concrete sand (where Part 1 + Part 2 + IS 383 limits suffice). It is more common for plaster and masonry mortar applications governed by IS 1542:1992 (sand for plaster) and IS 2116:1980 (sand for masonry mortar).

Principle: A standard cement-sand mortar is mixed using the test sand at specified proportions and consistency, then tested for workability (flow) and 28-day compressive strength. Results are compared with a control sand of known quality (typically Ennore Standard Sand to IS 650, which is the calibration reference).

Procedure summary (Clause 3 of Part 6):

1. Sand prep: oven-dry the test sand at 105°C to constant mass. Cool to room temperature in a desiccator.

2. Mix proportion: 1 part cement (OPC 43 grade, freshly tested for normal consistency per IS 4031) to 3 parts test sand by mass. Water content set to give a 'standard flow' of 110 ± 5% on a 100 mm flow table.

3. Casting: 70.6 mm cubes (5 cm² face area, 50 cm² total — historic Indian standard cube size, distinct from the 150 mm cube used for concrete in IS 516). Three cubes per age × two ages (7 and 28 days) = 6 cubes per test.

4. Curing: standard wet curing — 24 h in mould, then submerged in saturated lime water at 27 ± 2°C until test age.

5. Test: compressive strength per IS 4031 Part 6 (using 70.6 mm mortar cubes). Loading rate 350 ± 50 kg/cm²/min.

6. Compute relative properties: - Water requirement ratio = water needed for standard flow with test sand ÷ water needed with Ennore standard sand. Values > 1.0 mean the sand is more water-demanding (poor shape, high surface area, or excess fines). - Strength ratio = 28-day compressive strength of test mortar ÷ Ennore reference mortar strength. Values < 0.85 suggest the sand makes weak mortar.

Acceptable thresholds (not in Part 6 itself, drawn from companion codes): - Water requirement ratio ≤ 1.10 (preferred), ≤ 1.20 (acceptable) - Strength ratio ≥ 0.85 (preferred), ≥ 0.75 (acceptable for masonry mortar; lower for plaster)

M-sand acceptance: with river-sand bans in many Indian states (Kerala, Tamil Nadu, Karnataka post-2018) and rising use of manufactured sand from crushed stone, IS 2386 Part 6 has become more relevant. M-sand often has higher fines content, more angular particles, and different gradation than river sand — even when it 'passes' Part 1 (sieve) and Part 2 (silt), it can require 10-15% more water for the same workability, and produce mortar 10-20% weaker than equivalent river sand.

Project reality: many large urban projects in India now demand both Part 1/2 conformance AND Part 6 strength ratio ≥ 0.85 before approving an M-sand source. Without Part 6, projects discover the issue too late — after 200-300 tonnes of plaster has bond-failure issues.

Mixed-source supply audit: if a project receives sand from multiple quarries/sources, Part 6 testing on each source helps decide which to blend and which to reject. The data informs the mix design and any cement-content adjustments (richer mixes can compensate for weaker sand, at higher cost).

1. Comparing absolute strength, not ratio — Part 6 strength varies with cement quality, water temperature, curing conditions. The MEANINGFUL number is the strength RATIO against the same-batch Ennore reference. A 'test mortar strength of 25 MPa' is meaningless without the reference value.

2. Skipping the Ennore reference — some labs report only the test-sand mortar strength. This is invalid per Part 6 — you must run the Ennore reference in parallel with the same cement batch, water source, curing tank, and operator. Otherwise the comparison is uncalibrated.

3. Using rapid-strength estimates — 7-day strengths are reported sometimes but Part 6 specifies 28-day. Sand effects (especially fines + clay) manifest more strongly at 28 days. Don't accept 7-day-only results.

4. Wrong cube size — Part 6 uses 70.6 mm cubes (cement-mortar standard). Some labs mistakenly cast 150 mm cubes (concrete standard). Same paste, different strength — not directly comparable.

5. Ignoring water-cement ratio — Part 6 requires standard flow (110 ± 5%), not standard W/C. The water content is whatever achieves the flow. Reporting only the W/C without the flow check defeats the test's purpose.

• IS 2386:1963 — the parent code; Parts 1, 2, 3, 4, 5, 7, 8
• IS 383:2016 — Coarse and Fine Aggregates for Concrete (acceptance limits, requirements)
• IS 1542:1992 — Sand for Plaster (specification + Part 6 reference)
• IS 2116:1980 — Sand for Masonry Mortar (specification + Part 6 reference)
• IS 650:1991 — Standard sand for testing of cement (Ennore sand specification — the reference for Part 6)
• IS 4031 Parts 1-15 — Methods of Physical Tests for Hydraulic Cement (includes mortar cube testing)
• IS 1727:2004 — Methods of Test for Pozzolanic Materials (parallel methodology)
• IS 10262:2019 — Concrete Mix Design (uses sand FM and absorption from IS 2386 Parts 1+3, not Part 6)
• MoRTH 5th Revision — Section 1000 (aggregates for various road-work components)

IS 2386 Part 6 is rarely run on routine projects. The mainstream Indian sand QC pipeline is: Part 1 (gradation) → Part 2 (silt/clay/organic) → density and bulking from Part 3 → accept/reject. Part 6 (mortar properties) is the deep-dive test reserved for problem sources, alternative sand procurement decisions, and forensic investigation of mortar failures.

With the M-sand transition post-2018 in many Indian states, Part 6 testing has become more commercially relevant — but most laboratories charge ₹3,000-6,000 per test (vs ₹500-800 for routine Parts 1+2), and turnaround is 30+ days because of the 28-day strength wait. For this reason, Part 6 is typically run once per source per project during pre-qualification, then routine Parts 1+2 monitor the source during execution.

Looking ahead: the IS 383:2016 revision (under BIS sectional committee CED 2 consultation) is expected to introduce stricter M-sand acceptance criteria that may make Part 6 testing mandatory for M-sand sources above a project-size threshold. Worth tracking — if you specify M-sand for projects > 10,000 m³ concrete, you may soon need Part 6 documentation as part of the procurement file.