Complete acceptance criteria for ready-mixed concrete at site. Covers delivery ticket verification, slump testing, transit time limits, cube casting frequency, and strength acceptance rules per IS 4926 and IS 456.
Delivery Checks
Verify before unloading each transit mixer at site
| Check | Requirement | Tolerance | If Failed |
|---|
| Delivery ticket / challan | Must accompany every transit mixer and state: batch time, grade, mix design reference, slump ordered, volume, batch plant address | No tolerance — mandatory document | Do not accept concrete without a valid delivery ticket |
| Grade ordered vs delivered | Grade on ticket must match site order (e.g., M30, M40) | No tolerance — exact match required | Reject the load; do not use higher or lower grade as substitute without engineer's approval |
| Volume delivered | Actual volume must match ordered quantity within tolerance | ±3% by volume | Record shortage; raise claim with RMC supplier |
| Batch time vs arrival time | Note exact time of batching (from ticket) and arrival at site | Transit time ≤ 2 hours from batching | Reject if transit time exceeds 2 hours; concrete may have started initial set |
| Drum revolution counter | Total drum revolutions from batching to discharge must not exceed 300 | Max 300 revolutions total | Reject concrete — over-mixing causes segregation and loss of workability |
| Seal / lock on water tank | Water tank on transit mixer must be sealed to prevent unauthorised water addition | Seal must be intact | If seal is broken, reject the load — water may have been added in transit (retempering) |
Slump & Workability Tests
Slump test per IS 1199 — at point of discharge before placing
| Check | Requirement | Tolerance | If Failed |
|---|
| Slump test for ordered slump ≤ 75 mm | Measured slump must be within ±25 mm of ordered value | ±25 mm | Reject if outside tolerance; record and report to supplier |
| Slump test for ordered slump 75–100 mm | Measured slump must be within ±25 mm of ordered value | ±25 mm | Reject if outside tolerance |
| Slump test for ordered slump > 100 mm | Measured slump must be within ±25 mm of ordered value | ±25 mm | Reject if outside tolerance |
| Slump testing frequency | Test every transit mixer load at site | — | No test = no acceptance — insist on testing every load |
| Visual check for segregation | Concrete must appear uniform with no separation of paste and aggregate | No visible segregation or bleeding | Reject load; segregated concrete cannot be re-mixed |
| Shear slump or collapse slump | Slump cone must give a true slump (not shear or collapse) | If shear slump occurs, re-test with fresh sample | Repeated shear slump indicates poor mix design — reject and report |
Strength Acceptance (IS 456 Cl. 16.1)
Cube strength acceptance based on 28-day compressive strength results
| Check | Requirement | Tolerance | If Failed |
|---|
| Cube casting frequency | Minimum 1 sample per 25 m³ or part thereof | 1 sample = 3 cubes (150 mm) | If frequency not maintained, quality records are considered incomplete |
| Individual test result (3-cube average) | ≥ fck − 3 MPa | No individual result shall fall below this | Investigate — may require core testing of structure (IS 456 Cl. 17.4) |
| Mean of 3 consecutive results (M20 and above) | ≥ fck + 0.825σ or ≥ fck + 4 MPa, whichever is higher | σ = standard deviation from 30+ results; use assumed σ if < 30 results | Non-compliant — review mix design, increase cement content, or change supplier |
| Mean of 3 consecutive results (below M20) | ≥ fck + 4 MPa | — | Mix design to be revised by supplier |
| Core test (if cubes fail) | Core strength ≥ 0.85 × fck | Average of 3 cores ≥ 0.85 × fck; no individual core < 0.75 × fck | If cores also fail, structural assessment required — may need strengthening or demolition |
Temperature & Time Limits
Transport and placing temperature requirements for RMC
| Check | Requirement | Tolerance | If Failed |
|---|
| Concrete temperature at discharge | Measure with stem thermometer at point of discharge | 5°C to 40°C (normal range); preferred ≤ 30°C in hot weather | Reject if outside 5–40°C range |
| Transit time — normal weather | ≤ 2 hours from time of adding water to cement | No extension without retarder | Reject concrete exceeding 2 hours transit |
| Transit time — hot weather (> 35°C) | ≤ 1 hour recommended; max 1.5 hours with retarder | Use retarding admixture per IS 9103 | Reject if workability is lost even within time limit |
| Placing time after discharge | Place within 30 minutes of discharge from transit mixer | No holding in chutes or pumps beyond 30 min | Discard concrete that has been standing for > 30 min after discharge |
| Retempering with water | Not permitted under any circumstances | Zero tolerance | Reject immediately — water addition alters w/c ratio and destroys mix design |
Notes
• Retempering (adding water at site to increase slump) is strictly prohibited by IS 4926. Only addition of superplasticiser by trained RMC technician is permitted for slump recovery.
• Pump line losses: expect 25–50 mm slump loss through the pipeline. Order slump 25 mm higher than required at point of placing when using a boom pump.
• Rejection protocol: rejected loads must be documented with ticket number, reason, time, and photographed. Notify RMC supplier immediately and confirm in writing.
• For structural concrete, insist on RMC plants certified under IS 4926 with current BIS licence. Uncertified plants may not follow proper batching and QC procedures.
• Cube moulds must be oiled and kept on a level vibration-free surface. Cubes should be covered with wet cloth within 30 minutes of casting.
• Maintain a concrete register at site recording: date, structural element, grade, ticket number, supplier, transit mixer number, slump, temperature, cube IDs, and acceptance/rejection status.
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