Ready mix concrete typically stays workable in a concrete truck for about 90 minutes after water is added at the plant. However, this time window varies based on temperature, mix design, admixtures, and site readiness. Understanding these limits helps contractors avoid rejected loads and compromised structural integrity.
Typical Time Limits in 2026
The common industry guidance states that ready mix concrete remains workable for approximately 1 to 2 hours after batching, with 90 minutes serving as the traditional benchmark most suppliers and specifiers reference.
Crucially, this clock starts when water is added at the batching plant, not when the truck arrives on site. If a truck spends 45 minutes in traffic, you have already lost half your working time before the first drop hits the forms.
Exceeding this window risks several problems:
- Loss of slump, making the concrete difficult to place and finish
- Reduced compressive strength in the hardened product
- Compromised durability and long-term performance
- Potential load rejection by quality control inspectors
What Industry Standards and Codes Say?
Historic standards like ASTM C94 established the 90-minute discharge limit that became embedded in construction practice worldwide. This specification also capped drum revolutions at 300 to prevent overmixing and aggregate degradation.
However, more recent evaluations have shown that concrete can maintain acceptable performance for 120 to 150 minutes under favourable conditions. Updated guidance from BS 8500 and ASTM revisions has softened rigid time caps in favour of performance-based criteria.
Modern approaches focus on:
- Concrete temperature at discharge rather than arbitrary time limits
- Fresh property tests, including slump and air content
- Documentation that the mix still meets specification requirements
This shift gives contractors more flexibility while maintaining quality standards. Suppliers like Pro-Mix Concrete work within these updated frameworks to deliver reliable results even on complex pours.
5 Key Factors That Change How Long Concrete Can Stay in the Truck
The 90-minute rule is a starting point, not an absolute. Several variables can extend or shorten the actual working time available.
1. Ready Mix Plant and Batch Timing
Everything begins at the batching plant. The moment water contacts cement, hydration starts, and the workability clock begins ticking. Dispatch scheduling, loading efficiency, and communication between the plant and the site all affect how much of that window remains when the truck arrives.
2. Mixing Truck and Drum Revolutions
The concrete truck drum plays a critical role in maintaining mix quality during transit. Drum speed and total revolutions matter significantly:
- Most specifications cap total revolutions at around 300
- Continuous mixing generates more heat and accelerates hydration
- Intermittent or agitation speed mixing preserves workability longer
Proper drum speed management during transit helps maintain workability and mix quality.
3. Temperature and Weather Conditions
Ambient and concrete temperature dramatically affect hydration rate. Hot summer days accelerate the chemical reaction, potentially cutting workable time to 60 minutes or less. Cool conditions slow hydration, sometimes extending the window beyond 120 minutes.
On extremely hot days, suppliers may add ice to the mix or use chilled water to buy additional time. Conversely, cold weather presents its own challenges with delayed setting.
4. Admixtures and Mix Design
Chemical admixtures give contractors powerful tools to manage workability:
- Retarders slow hydration and extend working time significantly
- Water reducers maintain the slump without adding excess water
- High-performance mix designs may have tighter or looser time tolerances
Discussing admixture options with your supplier before ordering can solve many timing challenges, especially for large pours requiring concrete pump hire and extended placement periods.
5. Site Crew and Pour Readiness
The best concrete in the world becomes useless if the site is not ready to receive it. Factors that determine whether you discharge within the safe time limit include:
- Site access for trucks and any concrete pump hire equipment
- Formwork preparation and inspection completion
- Pump setup and priming if using pumped placement
- Crew availability and task assignments
A well-coordinated site team can discharge a full load in minutes. A disorganised site might waste 30 minutes just positioning equipment.
What Happens If Concrete Stays Too Long in the Truck?
Exceeding the workable time window leads to practical problems that affect both placement and final quality:
- Reduced slump makes concrete stiff and difficult to move through forms
- Harder discharge increases placement time and labour costs
- Cold joints form when fresh concrete meets partially set material
- Segregation occurs as the mix loses its homogeneity
- Weaker, less durable concrete results if over-aged material is placed
Adding water on site to re-loosen stiff concrete, called retempering, alters the water-cement ratio and can reduce strength. Specifications typically prohibit or strictly limit this practice.
How Contractors Can Plan Around the Time Window?
Successful concrete pours require tight coordination between batching, delivery, and placement. These strategies help contractors stay within workable limits:
- Coordinate batching and delivery times closely with pour start times
- Stagger truck arrivals so each load discharges within its window
- Account for traffic conditions, especially on hot days or congested routes
- Discuss the expected transport time with the ready mix supplier before ordering
- Request retarders or extended time provisions for large or complex pours
- Arrange concrete pump hire early to ensure the equipment is set up and ready
Clear communication with your supplier about site conditions, pour volume, and timing expectations prevents surprises. Everyone should understand the limits and any testing requirements before the first truck leaves the plant.
Bottom Line
Concrete typically remains workable for 90 minutes after batching, though modern standards allow flexibility based on temperature and performance testing. Temperature, admixtures, drum revolutions, and site readiness all influence the actual time available. Planning deliveries carefully, coordinating with suppliers, and ensuring site readiness help contractors maximise every minute of that workability window and deliver quality results.
If you need a professional concrete supplier, Pro-Mix Concrete has earned a reputation for reliable ready mix delivery and expert guidance on timing, mix design, and admixture selection. Their experienced team works closely with contractors to coordinate batching schedules, manage challenging site conditions, and ensure every load arrives within its optimal working window. They deliver consistent quality backed by clear communication and technical support that helps projects stay on schedule and on budget.
