Know exactly when to accept or reject a concrete delivery — before it's too late
A complete Australian guide to concrete rejection criteria on site for 2026. Covers slump, temperature, time limits, drum revolutions, air content, visual inspection, compressive strength, and delivery docket checks per AS 1379 and AS 3600.
Understanding when and why to reject a concrete load protects structural integrity, ensures compliance with Australian Standards, and prevents costly remedial work on site.
Placing non-conforming concrete can lead to structural failure, cracking, reduced durability, and costly demolition. Australian Standard AS 1379:2007 sets out the specification and supply requirements for concrete. Knowing the on-site rejection criteria before the truck arrives is the first line of defence for any site supervisor, engineer, or concretor in Australia.
Rejection of a concrete batch must occur before placement. Once concrete is poured into formwork, removal becomes extremely difficult and expensive. Every site team member — from the site engineer to the labourer — should understand the key triggers: excessive slump, high temperature, overtime in the drum, incorrect mix, and visual defects that indicate compromised quality.
On Australian construction sites, the site engineer, inspector, or authorised supervisor holds the authority to reject a concrete load. The decision should be documented immediately on the delivery docket, and the supplier must be notified. Rejection is not a dispute — it is a contractual and standards-based right under AS 1379 and the project specification.
If any single rejection criterion is triggered, the entire load must be refused — even if all other parameters are within limits.
The slump test is the most common on-site quality check and one of the primary concrete rejection criteria used across Australian projects. It measures workability and indirectly reflects water content and consistency. Testing is conducted per AS 1012.3.1 using a standard slump cone.
If the measured slump falls outside these tolerance bands, the load must be rejected.
Adding water to concrete on site to restore slump is a direct violation of AS 1379 and project specifications. It increases the water-to-cement (w/c) ratio, reduces compressive strength, increases shrinkage, and compromises durability. Any load that has had water added on site without authorisation from a qualified engineer must be rejected immediately.
Slump exceeding the specified value plus tolerance indicates excess water content, potential mix error, or excessive admixture dosing. High slump leads to segregation, bleeding, reduced strength, and surface defects. The load must be rejected — not adjusted on site.
Slump below the specified value minus tolerance indicates the mix is too stiff — possibly due to excessive mix time, hot weather absorption, or batching error. Stiff concrete is difficult to compact, particularly in congested reinforcement zones. It must be rejected — water must not be added.
If a single slump result appears borderline, AS 1379 allows a single retest from a fresh sample taken from the same truck. If the retest also fails, rejection is mandatory. Always document both results on the delivery docket before the truck leaves site.
In Australia's climate, temperature is a critical concrete rejection criterion on site — particularly during summer in states like Queensland, Western Australia, and the Northern Territory. High concrete temperature accelerates hydration, reduces workability rapidly, increases cracking risk, and can lower final compressive strength.
| Temperature at Discharge | Action Required | Basis |
|---|---|---|
| ≤ 32°C | ✅ Generally acceptable — proceed with testing | AS 1379 / Project Spec |
| 33°C – 35°C | ⚠️ Caution zone — monitor closely, expedite placement | Site Engineer Discretion |
| > 35°C | 🚫 Reject — exceeds AS 1379 maximum discharge temperature | AS 1379:2007 Clause 4.5 |
| < 5°C | 🚫 Reject — concrete too cold, hydration compromised | AS 1379 / Cold Weather Concreting |
Concrete temperature must be measured at the point of discharge using a calibrated thermometer inserted directly into the concrete sample. Readings taken from the drum exterior or the delivery docket alone are not acceptable for rejection decisions. Always measure fresh from the chute.
Time is one of the most straightforward concrete rejection criteria on site. AS 1379 specifies that concrete must be discharged within a defined time window from the point of first water contact. Once this window closes, the load must be rejected regardless of its apparent workability.
The delivery docket records the batch time and first water addition time. Site personnel must check these times upon arrival. If the truck arrives late due to traffic or delays and the 90-minute window has closed — or will close before discharge is complete — the load must be rejected. Assessing concrete structures after placement of out-of-time concrete often reveals significant quality defects.
The agitator drum of a ready-mix truck must not exceed 300 revolutions at mixing speed before discharge. Beyond this limit, the concrete experiences over-mixing, which can break down aggregates, alter air content, and reduce strength. The revolution counter on the truck's delivery docket must be checked. If it reads above 300, the load is rejected.
Every concrete delivery in Australia must be accompanied by a delivery docket that complies with AS 1379 Clause 6. The docket is a legal document and the first thing a site inspector should check before any physical testing. Discrepancies between the docket information and the project specification are grounds for immediate rejection.
Confirm the specified compressive strength grade (e.g., N32, N40, N50) matches the project specification exactly. A common error is delivery of a lower-grade mix, particularly when the plant is producing multiple mixes simultaneously. Never accept a lower-grade substitution without written engineer approval.
The exposure classification (A1, A2, B1, B2, C1, C2 per AS 3600) affects minimum cement content, maximum water-to-cement ratio, and minimum cover. If the docket lists a different exposure class than specified, the mix may not meet durability requirements — reject the load.
Verify that admixtures (water reducers, retarders, accelerators) and cement type (GP, GB, HE, SR, SL) match the mix design. Incorrect cement type, particularly in aggressive environments like sulphate soils or marine exposure zones common in coastal Australia, can cause long-term deterioration.
Confirm the batch plant time, water addition time, and total volume. Volume discrepancies can indicate partial loads that may have had additional water added to restore yield. Cross-check the load volume against the pour schedule to ensure the correct quantity has been ordered and dispatched.
Experienced site personnel can identify several visual defects that justify rejection of a concrete batch before any formal testing. Visual inspection is the first and fastest rejection tool available on site and should always be performed at the point of discharge from the chute.
Even when a load is accepted after visual inspection, record observations on the site diary and delivery docket. Photographs taken at the chute provide valuable evidence if strength test failures arise later. Good documentation protects the site team, the engineer of record, and the principal contractor.
Compressive strength is tested retrospectively via cylinder samples taken at the time of pour and cured to 28 days per AS 1012.9. While this cannot stop a non-conforming load from being placed, strength results below the specified characteristic value (f'c) trigger a formal non-conformance and may require assessment of the existing concrete structure and possible remediation or demolition.
| Strength Test Result | Criteria (AS 1379 / AS 3600) | Required Action |
|---|---|---|
| ≥ f'c at 28 days | ✅ Conforming result | Accept — file results |
| f'c − 3.5 MPa to f'c | ⚠️ Marginal — review required | Engineer assessment, possible core testing |
| < f'c − 3.5 MPa | 🚫 Non-conforming batch | Formal NCR, structural assessment, possible demolition |
| < 0.85 × f'c | 🚫 Serious non-conformance | Engineer of record notified — remediation or removal required |
Air-entrained concrete is commonly specified for exposure to freeze-thaw cycles, sulphate attack, and certain aggressive environments across Australia. The air content is measured on site per AS 1012.4 using a pressure metre. Deviations from the specified air content percentage are a valid concrete rejection criterion.
For more information on how air content affects concrete performance in Australian conditions, refer to our detailed guide on air-entrained concrete uses and benefits.
Following a consistent, documented process when rejecting concrete protects all parties involved and ensures compliance with AS 1379 and project contractual requirements. The following steps should be applied every time a rejection trigger is identified.
The following table provides a consolidated reference for all primary concrete rejection criteria applicable on Australian construction sites in 2026. All criteria are based on AS 1379:2007, AS 3600:2018, and standard industry practice.
| Criterion | Rejection Limit | Test Method | Standard |
|---|---|---|---|
| Slump (≤ 40 mm specified) | Outside ± 10 mm tolerance | AS 1012.3.1 | AS 1379 |
| Slump (50–100 mm specified) | Outside ± 20 mm tolerance | AS 1012.3.1 | AS 1379 |
| Slump (≥ 120 mm specified) | Outside ± 30 mm tolerance | AS 1012.3.1 | AS 1379 |
| Concrete Temperature (Max) | > 35°C at discharge | Calibrated thermometer | AS 1379 Cl. 4.5 |
| Concrete Temperature (Min) | < 5°C at discharge | Calibrated thermometer | AS 1379 |
| Time from First Water | > 90 minutes | Delivery docket check | AS 1379 |
| Drum Revolutions | > 300 at mixing speed | Drum counter / docket | AS 1379 |
| Air Content | Outside specified ± 1.5% | AS 1012.4 | AS 1379 / Mix Design |
| Compressive Strength (28d) | < f'c − 3.5 MPa | AS 1012.9 | AS 1379 / AS 3600 |
| Water Added on Site | Any addition without engineer approval | Visual / docket | AS 1379 |
| Incorrect Grade / Class | Docket does not match specification | Docket review | AS 1379 Cl. 6 |
| Segregation / Contamination | Visible at discharge | Visual inspection | AS 1379 / AS 3600 |
The maximum allowable slump deviation depends on the specified slump value. For specified slumps up to 40 mm, the tolerance is ± 10 mm. For slumps between 50–100 mm, the tolerance is ± 20 mm. For slumps of 120 mm or above, the tolerance is ± 30 mm. These tolerances are defined in AS 1379:2007. Any measured slump falling outside these bands is grounds for rejection of the entire load.
No. Adding water to concrete on site is prohibited under AS 1379 unless specifically authorised in writing by the mix designer or engineer of record, and only within defined limits that do not exceed the maximum water-to-cement ratio of the mix. In practice, adding water on site almost never receives approval, because it directly reduces 28-day compressive strength and increases shrinkage and cracking risk. If slump is too low, the load should be rejected and a replacement ordered.
AS 1379:2007 specifies a maximum concrete temperature of 35°C at the point of discharge. Many project specifications in hot climates such as Queensland and Western Australia set a lower limit of 32°C. Concrete delivered above 35°C must be rejected. Temperature is measured with a calibrated thermometer inserted directly into the fresh concrete at the discharge chute — not from the docket or the truck body.
AS 1379 sets a maximum time of 90 minutes from the first addition of water to the mix until discharge is complete. Additionally, the drum must not exceed 300 revolutions at mixing speed before discharge. In hot weather or when retarding admixtures are not used, this window may be further reduced by the project specification. The batch time on the delivery docket must be checked on arrival — if 90 minutes have elapsed or will elapse before discharge is complete, reject the load.
The site engineer, inspector, or authorised site supervisor holds the authority to reject a concrete load. This authority is typically established in the project quality plan and the concrete supply contract. The decision to reject must be documented on the delivery docket, signed, and recorded in the site diary. The supplier must be notified, and where applicable, a Non-Conformance Report (NCR) must be raised. Junior site staff should escalate to the engineer of record if uncertain about whether to reject.
If a concrete batch is placed and later found to be non-conforming — for example, due to failed 28-day strength cylinders — the site must issue a formal Non-Conformance Report (NCR). The engineer of record must assess the structural impact, which may involve in-situ core testing per AS 1012.14, load testing, or review against AS 3600 reduced strength provisions. In serious cases, demolition and reconstruction may be required. This makes on-site rejection — before placement — far more cost-effective than retrospective action. See our guide on assessing existing concrete structures for post-placement assessment methods.
Yes. Visible segregation, contamination, partial setting, or obvious mix defects are valid grounds for rejection under AS 1379 even without formal test results. The site engineer or inspector must document the visual observations with photographs and written notes on the delivery docket. A visual rejection is particularly important when the defect makes testing impractical — for example, concrete that has partially set cannot produce a valid slump cone result anyway.
The primary Australian Standard governing the specification and supply of concrete. Covers mix design, delivery docket requirements, slump tolerances, temperature limits, time limits, and testing procedures for ready-mixed concrete supplied to Australian construction sites.
Standards Australia →Australia's concrete structures standard. Sets minimum strength grades, durability requirements, exposure classifications, and acceptance criteria for concrete used in structural applications. Essential reading for engineers managing concrete quality on site.
View Standard →The CIA publishes recommended practice guides, technical notes, and training resources for concrete professionals in Australia. Their guidance on concrete placement, testing, and quality control complements the requirements of AS 1379 and AS 3600.
CIA Website →