IS 4031 Part 7 : 1988Methods of Physical Tests for Hydraulic Cement - Part 7: Determination of soundness by Le Chatelier method

IS 4031 (Part 7) specifies the method for determining compressive strength of masonry cement — the test for masonry-specific cement variants used in mortar for brickwork + plaster. Masonry cement (per IS 3466) is a special blend optimised for mortar workability + bond rather than concrete strength.

Use IS 4031 Part 7 when: - Source qualification of masonry cement supplier - Routine acceptance testing of delivered masonry cement - Forensic investigation of masonry mortar issues (poor bond, cracking) - Mix design verification for mortar

The IS 4031 series covers all physical tests on cement; Part 7 is specifically for masonry cement, which has different acceptance criteria than ordinary Portland cement (covered by IS 4031 Part 6).

Masonry cement vs OPC: - Masonry cement (IS 3466): pre-blended OPC + lime / fly ash + plasticizer; cheaper, easier to use; lower strength (5-7 N/mm² mortar) but better workability + bond - OPC + lime + sand: traditional cement-lime mortar; higher quality - OPC + sand only: high-strength but harsh, low workability

Masonry cement is popular for high-volume brick / block construction where workability matters more than mortar strength.

Specimens: - 50 × 50 × 50 mm mortar cubes (smaller than concrete cubes per IS 516) - Mix: 1 part masonry cement : 3 parts standard sand (per IS 650:1991) - Water: per consistency (typical w/c ≈ 0.40)

Procedure: 1. Mix per IS 4031 Part 4 consistency, then 1:3 mortar with standard sand. 2. Fill mortar in 50 mm cube moulds in 2 layers; tamp 25 strokes per layer. 3. Demould after 24 hours; cure in water at 27 ± 2 °C. 4. Test at 7 days + 28 days (3 cubes per age). 5. Apply load at 350 ± 35 N/sec rate. 6. Compute: strength (N/mm²) = peak load / 50 × 50 mm² area. 7. Report mean of 3 cubes.

Acceptance criteria (per IS 3466):

| Age | Min compressive strength (N/mm²) | |---|---| | 7 days | ≥ 2.5 | | 28 days | ≥ 5.0 |

Masonry cement is significantly lower strength than OPC (which would be ≥ 33 N/mm² at 28 days). The lower strength is by design — masonry mortar's main job is bond + flexibility, not load-bearing.

Cube dimension tolerance: - 50 mm ± 0.5 mm - Surface flatness: ≤ 0.05 mm under 50 mm straightedge - Surfaces in contact with platens: machined / ground if not flat

Masonry cement composition (per IS 3466): - OPC clinker: 50-70 % - Lime stone / fly ash: 20-40 % - Plasticiser / air-entrainer: 1-3 %

Mortar mixes using masonry cement:

| Application | Mix (masonry cement : sand) | Wall use | |---|---|---| | Brick / block masonry | 1:5 to 1:6 | Standard load-bearing | | Plaster (cement plaster) | 1:5 to 1:6 | Internal walls | | Pointing | 1:3 | Cement pointing on brick | | Backfill | 1:8 | Non-structural |

Masonry mortar's strength: 1-3 N/mm² typical (lower than concrete; matches the masonry strength so brick + mortar fail together rather than mortar being too strong + cracking the brick).

Comparison vs OPC + lime mortar:

| Mortar type | Workability | Bond | 28d strength (N/mm²) | Cost | |---|---|---|---|---| | OPC + sand 1:6 | Poor | Moderate | 3-4 | Low | | OPC + lime + sand 1:1:6 | Good | Good | 2-3 | Higher (lime added) | | Masonry cement 1:6 | Excellent | Excellent | 1.5-2.5 | Lowest (single bag) | | Pre-mixed dry mortar | Excellent | Excellent | per spec | Highest |

Project cost impact: - Masonry cement: ₹350-450 per 50 kg bag - OPC: ₹400-450 per 50 kg bag (similar) - Lime: ₹180-300 per 50 kg bag - Pre-mix mortar: ₹500-800 per 50 kg bag - Time savings with masonry cement / pre-mix: 10-20 % faster laying

Failure modes if cement strength deficient: - Mortar < 1 N/mm² at 28 days: masonry has poor cohesion; cracks under minor settlement / vibration - Mortar > 5 N/mm²: too rigid; brick cracks before mortar yields (counter-productive in seismic zones) - Goldilocks: 1.5-3 N/mm² for typical brick masonry — flexible enough to accommodate movement, strong enough to transfer load

• IS 4031 Part 1-15 — physical tests on cement (multi-part series).
• IS 4031 Part 6 — compressive strength on hydraulic cement other than masonry.
• IS 4031 Part 4:1988 — consistency of cement paste.
• IS 4032:1985 — chemical analysis of cement.
• IS 8112:1989 / IS 12269:2013 — OPC standards.
• IS 3466 — masonry cement specification.
• IS 650:1991 — standard sand for testing of cement.
• IS 1077:1992 — common burnt clay bricks.
• IS 1905:1987 — code of practice for structural use of unreinforced masonry.
• IS 4326:1993 — earthquake resistant design (masonry).
• IS 712:1984 — building limes (alternative for compound mortar).
• IS 1489 — Portland-Pozzolana Cement (alternative cement for mortar).
• IS 383:2016 — sand specification for mortar.

1. Test on too few specimens. 1-2 cubes; can't establish statistical mean. Use 3 minimum. 2. Wrong sand for test. Project sand vs standard sand (IS 650) — different result. Test with standard sand for IS 4031 acceptance. 3. Loading rate too fast. Stress-rate dependent; reads higher. Stick to 350 N/sec. 4. Specimens not water-cured. Air-cured cubes test 30 % low. Water cure at 27 ± 2 °C. 5. Substandard masonry cement supplier. Local 'masonry cement' may not meet IS 3466. Demand ISI marked + IS 4031 Part 7 certificate. 6. Old cement (> 6 months). Reactivity drops; mortar weak. FIFO; use within shelf life. 7. Damp storage. Cement absorbs moisture; lump formation; weak mortar. Dry storage. 8. No cube identification. Tracking lost; can't assign result to consignment. Mark each cube. 9. Mortar mix on site without trial. Site mortar may not match design; weak. Trial mix verification. 10. Excess water in mortar. Reduces strength; over-workable. Stick to design w/c. 11. Use of masonry cement in concrete. Insufficient strength; concrete fails. Use OPC (IS 8112 / IS 12269) for concrete. 12. Masonry cement in load-bearing structural mortar > 6 m height. Per IS 1905:1987, structural masonry > 6 m needs cement-sand mortar with adequate compressive strength; masonry cement may be inadequate.

Masonry construction cascade:

1. Design (IS 1905:1987) — wall load, mortar strength target. 2. Mortar specification: - Masonry cement (cheap, fast) for non-structural / low-rise - Cement-sand 1:6 for routine load-bearing - Cement-lime-sand 1:1:6 for breathable / heritage - High-strength cement-sand 1:4 for heavy load 3. Cement source qualification (IS 4031 Part 7 — this code for masonry cement; Part 6 for OPC). 4. Mix design — cement + sand + water proportions. 5. Trial mix — verify mortar strength + workability. 6. Procurement — ISI marked, batch-tested cement. 7. Mortar mixing on site: - Dry-mix cement + sand thoroughly - Add water gradually to achieve workability - Use within 30-60 minutes of mixing 8. Brick / block laying: - Pre-soak bricks - 10 mm joint thickness - English / Flemish bond - Plumb + level + line check daily 9. Curing: - 7-14 days water curing - Avoid drying winds, direct sun on fresh masonry 10. Quality acceptance: - Joint thickness uniformity - Plumb / level - Crack-free (≤ 0.3 mm cracks acceptable) - Mortar cube tests at 7 + 28 days

IS 4031 Part 7 ensures masonry cement quality — the foundational input to masonry mortar that determines wall durability + load capacity.