IS 4031:1988 Part 5 is the Indian Standard (BIS) for methods of physical tests for hydraulic cement - part 5: determination of compressive strength. This part of IS 4031 establishes the standard procedure for determining the compressive strength of hydraulic cement. It details the preparation of a 1:3 cement-standard sand mortar, casting into 70.6 mm cubes, compaction via a vibration machine, curing conditions, and testing under a compression testing machine.
Describes the procedure for determining the compressive strength of hydraulic cement mortar cubes at various ages.
Key parameters for preparing, curing, and testing cement mortar cubes for compressive strength, including mix ratios, timings, and tolerances.
| Reference | Value | Clause |
|---|---|---|
| Test Specimen Size— Provides a testing area of 5000 mm² (50 cm²). | 70.6 mm cube | Cl. 5.1.2 |
| Test Room Temperature | 27 ± 2 °C | Cl. 4.1 |
| Test Room Humidity | ≥ 65% RH | Cl. 4.1 |
| Moist Curing Temperature | 27 ± 2 °C | Cl. 4.2 |
| Moist Curing Humidity— For initial curing in a moist closet or room. | ≥ 90% RH | Cl. 4.2 |
| Water Curing Temperature | 27 ± 2 °C | Cl. 8.4 |
| Cement : Standard Sand Ratio | 1 : 3 (by mass) | Cl. 7.1 |
| Mass of Cement (for 3 cubes) | 200 g | Cl. 7.1 |
| Mass of Standard Sand (for 3 cubes)— Standard sand must conform to IS 650. | 600 g | Cl. 7.1 |
| Water Quantity for Mortar— Of combined cement & sand mass. P = % water for standard consistency. | (P/4 + 3.0) % | Cl. 7.2 |
| Vibrating Machine Frequency | 12000 ± 400 vibrations/min | Cl. 5.1.1 |
| Vibration Time for Compaction | 2 min ± 2 s | Cl. 8.2 |
| Initial Curing Period (Moist Air) | 24 ± 1 h | Cl. 8.4 |
| Standard Testing Ages— Other ages like 1 day may be tested if required. | 3, 7, and 28 days | Cl. 8.5 |
| Number of Cubes per Age | 3 cubes | Cl. 8.5 |
| Rate of Loading | 35 N/mm²/min | Cl. 9.1 |
| Test Result Variation Limit— If exceeded, the test for that period must be repeated. | ±15% of the average | Cl. 9.3 |
| Cube Mould Internal Face Flatness | Tolerance of 0.01 mm | Cl. 5.1.2 |
| Cube Mould Internal Angle | 90 ± 0.5° | Cl. 5.1.2 |
| Poking Rod Diameter— Used for the alternative hand-compaction method. | 12.5 mm | Cl. 5.1.3 |
IS 4031 Part 5:1988 covers the determination of the compressive strength of cement mortar cubes — the test that assigns a cement its grade (OPC 33/43/53 etc.) from the strength of standard mortar cubes at 3, 7 and 28 days. It is the single most consequential cement physical test: the number that decides whether a consignment meets IS 269/IS 8112/IS 12269.
It sits at the centre of cement testing:
Cement strength is only comparable if everything except the cement is held constant — which is why this test chains a series of standards:
The engineering point: the strength figure is the verdict, but its validity depends on every link — IS 650 sand, the right P-derived water, standard compaction, calibrated CTM, correct loading rate. A 'failing' consignment is, very often, a fault somewhere in that chain rather than in the clinker.
Scenario: verify an OPC 43 consignment to IS 8112 by 28-day strength.
Step 1 — establish P: normal consistency via IS 4031 Part 3 → mortar water = (P/4 + 3.0)%.
Step 2 — standard mortar: 1:3 cement : IS 650 sand at that water.
Step 3 — mould & compact: 70.6 mm cubes, standard compaction on IS 10080/IS 10078 for the fixed time.
Step 4 — cure & crush: controlled curing; crush at 3/7/28 d in a calibrated IS 14858 CTM at the specified rate.
Step 5 — judge vs spec: 28-day ≥ 43 MPa (with 3/7-day) → accept; below → before blaming the cement, audit the chain (P/water, IS 650 sand, compaction, CTM calibration, loading rate).
The number grades the cement only if the whole standardised chain held — which is the practical heart of every cement-strength dispute.
1. Non-standard sand or wrong water. Site sand instead of IS 650, or water not derived from P (IS 4031 Part 3) — invalidates the comparison entirely.
2. Compaction not standardised. Off-frequency IS 10080 machine, loose mould or wrong vibration time → false strength.
3. Un-calibrated CTM / wrong loading rate. IS 14858 calibration and the specified rate decide the reading as much as the cement.
4. Confusing cement-mortar strength with concrete strength. This grades the *cement*; concrete strength is the separate IS 516 Part 1 test.
5. Blaming the clinker first. Most disputed low results trace to a broken link in the test chain, not the cement — audit the chain before the consignment.
IS 4031 Part 5 produces the number that defines cement grade and therefore sits under most cement-acceptance disputes and a great deal of money. The single most useful practitioner habit it teaches: a cement-strength result is the output of a standardised chain — IS 650 sand, P-derived water (IS 4031 Part 3), standardised compaction (IS 10080/IS 10078), calibrated CTM (IS 14858), correct loading rate — and a 'failing consignment' is far more often a broken link in that chain than bad clinker. When a result is contested, audit the chain before condemning the cement, and never conflate this cement-mortar grading test with the IS 516 Part 1 concrete-strength test. Standardisation is the whole point; defend it and the test is a fair referee, neglect it and you litigate an instrument/method error as a material defect.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Test Temperature | 27 ± 2 °C | 23.0 ± 2.0 °C | ASTM C191-21 |
| Test Humidity (for specimens) | ≥ 90% RH | ≥ 95% RH | ASTM C191-21 |
| Initial Set Needle Cross-Section | 1 mm square | 1 mm diameter (circular) | ASTM C191-21 |
| Criterion for Initial Setting Time | Penetration to 5.0 ± 0.5 mm from mould bottom | Penetration to 25 ± 0.5 mm from surface | ASTM C191-21 |
| Criterion for Final Setting Time | Needle makes an impression, but annular attachment does not | Needle does not sink visibly into the paste | ASTM C191-21 |
| Mass of Cement for Test Paste | 400 g | 650 g | ASTM C191-21 |
| Mould Height | 40 ± 0.2 mm | 40 ± 1 mm | ASTM C191-21 |