IS 4926:2003 is the Indian Standard (BIS) for ready-mixed concrete - specification. This standard lays down the requirements for the production, transport, and supply of ready-mixed concrete (RMC). It outlines batching tolerances, delivery conditions, and quality control procedures to ensure the concrete meets structural design specifications.
Specifies requirements for ready-mixed concrete, including production, delivery, and quality control.
Key tolerances, delivery limits, sampling rates, and acceptance criteria for ready-mixed concrete production and supply.
| Reference | Value | Clause |
|---|---|---|
| Max Time from Batching to Discharge— Can be modified with retarders or in cool/humid weather as agreed. | 2 hours | Cl. 11.3 |
| Max Concrete Temperature at Delivery— Purchaser may specify a lower temperature for special applications. | 40 °C | Cl. 7.1.3 |
| Batching Tolerance - Cementitious Material | ± 2% | Cl. 7.1.1 (Table 1) |
| Batching Tolerance - Aggregates | ± 3% | Cl. 7.1.1 (Table 1) |
| Batching Tolerance - Water | ± 3% | Cl. 7.1.1 (Table 1) |
| Batching Tolerance - Admixtures | ± 5% | Cl. 7.1.1 (Table 1) |
| Slump Tolerance (Specified Slump ≤ 50 mm) | ± 25 mm | Cl. 10.2 |
| Slump Tolerance (Specified Slump > 50 mm) | ± 1/3 of specified slump | Cl. 10.2 |
| Sampling Frequency (1-5 m³) | 1 sample | Cl. 10.1 (Table 2) |
| Sampling Frequency (6-15 m³) | 2 samples | Cl. 10.1 (Table 2) |
| Sampling Frequency (16-30 m³) | 3 samples | Cl. 10.1 (Table 2) |
| Sampling Frequency (>50 m³) | 4 + 1 per addl. 50 m³ | Cl. 10.1 (Table 2) |
| Strength Acceptance - Mean of 4 Samples— For M20 & above. σ is established standard deviation. | ≥ max(fck + 0.825σ, fck + 4 MPa) | Cl. 12.2 (Ref. IS 456) |
| Strength Acceptance - Individual Sample— For M20 & above. No single result should fall below this limit. | ≥ fck - 4 MPa | Cl. 12.2 (Ref. IS 456) |
| Max Total Chloride Content (RCC/PSC)— For concrete containing embedded metal. | 0.6 kg/m³ of concrete | Cl. 5.1 (Ref. IS 456, Table 7) |
| Max Total Chloride Content (PCC)— For plain concrete with no embedded metal. | 3.0 kg/m³ of concrete | Cl. 5.1 (Ref. IS 456, Table 7) |
| Min Cement Content - Severe Exposure (RCC)— Durability requirement for ordering RMC. | 320 kg/m³ | Cl. 5.1 (Ref. IS 456, Table 5) |
| Max W/C Ratio - Severe Exposure (RCC)— Durability requirement for ordering RMC. | 0.45 | Cl. 5.1 (Ref. IS 456, Table 5) |
| Uniformity Test - Density Variation— Max difference between two samples from the same batch. | ≤ 16 kg/m³ | Annex B (Table B-1) |
| Uniformity Test - Slump Variation— For average slump < 100 mm. Max difference is 40 mm if average slump ≥ 100 mm. | ≤ 25 mm | Annex B (Table B-1) |
| Agitator Speed (in transit) | 2 to 6 rpm | Cl. 6.2.2 |
IS 4926 is the specification for Ready-Mixed Concrete (RMC) — concrete batched at a central plant and delivered fresh to site by transit mixer. It governs the supply contract: how the producer must batch, mix, transport, deliver, and certify, and how the buyer must receive, sample, and accept.
Use IS 4926 when: - Project pour size or schedule makes site-batching impractical (urban high-rise, infrastructure spans, water-tank rafts) - Quality control needs are higher than a small site-mixer can deliver consistently (M40+ / pumped / SCC) - Contracts are split: structural designer + RMC supplier + executing contractor
IS 4926 covers two purchase modes: - Designed mix — buyer specifies grade, slump, exposure; producer designs the mix and is responsible for strength. - Designated mix — buyer specifies grade and exposure only (per IS 456 Table 5); producer uses a standard catalogue mix; producer responsible for strength. - Standard mix (rarely used now) — fixed cement content per concrete grade, no statistical strength guarantee.
Designed mix is overwhelmingly the default for any structural pour above M20 today.
Tolerance on delivery (to site, before discharge): - Slump: ±25 mm of specified, or ±1/3 of specified — whichever is greater - Maximum time from batching to discharge: 90 minutes (or until initial set, whichever is earlier). Hot weather: lock at 60 minutes unless retarder + ice/chilled water is used. - Concrete temperature at delivery: ≤ 30 °C (general); ≤ 25 °C (mass concrete or hot-weather pour)
Sampling at delivery (per IS 4926 Clause 12): - One sample per 50 m³ for the first 50 m³, then per 100 m³, OR per truck (whichever is more frequent) - One sample = 6 cubes (3 for 7-day, 3 for 28-day) plus slump test - Acceptance per IS 456 Clause 16 — 3-result rolling mean ≥ specified, no individual < specified − 3 N/mm² (M20+)
Permitted variation in batch quantities (Clause 8.6): - Cement: ±2 % - Aggregates (fine + coarse): ±3 % - Water (including admixture): ±3 % - Admixture: ±5 %
Plant production calibration: - Weighing-system accuracy: ±0.5 % FSD (verified at least monthly) - Moisture probes on aggregates: calibrated weekly
1. Discharge after 90 minutes. The concrete may look fine but the workability has been chasing-the-curve with extra slump retention. Hardened strength is unaffected only if the SP dose was correct; otherwise expect a 5-15 % strength loss. Reject loads exceeding 90 min from batching. 2. Site water added by the contractor at delivery. This destroys the supplier's mix design — w/c jumps, strength drops, and the warranty voids. Site water addition is permitted only with the producer's representative present and only if recorded on the delivery challan. 3. Sampling from the first 50 L of discharge. Wash-down water dilutes the first slug. Take samples after the first 0.3 m³ has been discharged. 4. Confusing 'pumpable' with 'high strength'. Pumpability is about cohesion + sand grading + paste volume; strength is about w/c. A mix can be highly pumpable with low strength or vice versa — specify both in the BOQ. 5. Not booking the concrete truck for the right size. Mixers are typically 4-8 m³. Ordering 0.5 m³ stranded loads is wasteful; ordering loads bigger than your placement crew can handle in 90 minutes risks rejection. 6. Accepting plant certificates blindly. Many small plants don't run regular calibration on weigh-batchers or moisture probes. Audit during source qualification — the certificate must be auditable. 7. Hot-weather discharge target temperature. RMC delivered at 35 °C in summer afternoons + Sun-exposed pour = thermal cracking + accelerated set. Specify chilled water / ice as part of the contract for May-June pours in north India.
Before placing the first order, demand: 1. Plant compliance: IS 4925:2004 type certificate (capacity, batching system, mixing system). 2. Materials qualification: cement IS 8112/12269/1489 reports; aggregates IS 383 reports; admixture IS 9103 datasheet. 3. Mix designs (per grade and exposure) ready for the project — at minimum your specified M-grade and any standby grades. Each mix design must show: trial mix records, target mean strength, w/c, cement content, water content, aggregate gradation, admixture dose, and 28-day cube results. 4. QC system documentation — laboratory accreditation (NABL preferred), instrument calibration log, raw-material test records. 5. Trial cubes at project: producer should pour a small trial pour at site and produce cubes — verify acceptance under your project conditions before opening the regular supply.
A reputable RMC supplier produces this dossier in a day. If they push back, that's a signal.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Discharge Time Limit (General) | 2 hours from loading (Clause 7.1) | 90 minutes or 300 drum revolutions (Clause 12.7) | ASTM C94 |
| Batching Tolerance (Cement) | ± 2% of mass (Table 2) | ± 1% of required mass (Table 1) | ASTM C94 |
| Batching Tolerance (Aggregates) | ± 3% of mass (Table 2) | ± 2% of required mass (Table 1) | ASTM C94 |
| Slump Tolerance (for slump 51-100 mm) | ± 25 mm (Table 4) | ± 38 mm (Table A1.1) | ASTM C94 |
| Minimum Sampling Frequency | 1 per 50 m³ (after first 5 m³) (Clause 9.3.1) | Varies by production control, e.g., 1 per 200 m³ for certified continuous production (Table 19) | EN 206 |
| Maximum Recommended Concrete Temperature | 40°C (Clause 6.3) | Typically 32-35°C (Guidance from ACI 305R) | ASTM C94 (via ACI guidance) |
| Records Retention Period | 1 year (Clause 10.1) | 2 years (Clause 20.1) | ASTM C94 |