Concrete is one of the most widely used construction materials on the planet, known for its strength, durability, and versatility. But even though it’s incredibly tough once set, it’s surprisingly time-sensitive before it hardens. That ticking clock starts the moment it’s mixed. Once concrete is loaded into a mixing truck, the countdown begins, and getting the timing wrong can cause major issues on-site. Contractors, builders, and site managers all need to understand how long they have before the concrete becomes unusable.
This is not only about quality; it can affect safety, budget, and the entire project timeline. It’s a common but critical question in the industry: How long can concrete stay in a truck? The answer depends on several factors, from weather conditions to mixing speed, but there’s a clear industry standard, and some very real consequences for pushing those limits.
The Time Window for Truck-Mixed Concrete
When concrete is mixed at a batching plant and loaded into a ready-mix truck, it begins to hydrate. This is the chemical process where cement reacts with water, leading to hardening. The industry-standard rule of thumb is:
Concrete can typically stay in a truck for up to 90 minutes or 300 revolutions of the drum, whichever comes first.
Beyond this, the material may begin to set, making it difficult or impossible to place and finish properly.
Why the 90-Minute Rule Matters
The 90-minute guideline isn’t arbitrary. It’s based on the time required for the chemical reactions in concrete to begin significantly affecting its consistency and workability. After this point, even if the concrete hasn’t hardened completely, it may:
- Lose its slump (fluidity), making it harder to pour and shape.
- Start forming lumps or setting in the drum.
- Develop issues in strength and durability once cured.
- Be rejected at the job site for not meeting specifications.
Exceeding the 90-minute window could mean either costly delays due to rejected loads or compromised quality if the concrete is used anyway.
What Happens if Concrete Stays Too Long in the Truck?
Keeping concrete in a truck too long can trigger a series of challenges that snowball quickly.
Set Concrete in the Drum
If concrete begins setting inside the drum, it can lead to:
- Mechanical strain on the mixer truck
- Expensive cleaning or even replacement of parts
- Potential safety hazards for drivers and operators
Poor Structural Performance
Once hydration is underway, delaying placement can mean:
- Weakened structural integrity of the final product
- Uneven surfaces or finishes
- Lower resistance to weather or heavy loads
Project Delays and Cost Overruns
Time-sensitive projects depend on accurate scheduling. A delayed truckload can halt work entirely while a new batch is prepared, which wastes time and labour.
Key Factors That Influence How Long Concrete Can Stay in the Truck
While 90 minutes is a standard rule, certain elements can shorten or extend that window slightly.
Temperature and Weather Conditions
- High Temperatures: Speed up hydration, reducing usable time.
- Cold Weather: Slows down setting, potentially giving more flexibility.
Type of Mix
- Retarders: Admixtures that slow hydration can add 30–60 minutes of working time.
- Accelerators: Speed up setting and reduce allowable truck time.
Traffic and Site Access
- Delays due to road congestion or tight job sites may eat into the mixing time, reducing the buffer to pour effectively.
How to Maximise Concrete Viability in the Truck
There are several ways contractors can work within the 90-minute window and keep their projects on track.
Plan Efficient Delivery Routes
Choosing the fastest and most predictable route to the job site reduces the risk of delays that cut into the concrete’s usable time.
Use Admixtures Strategically
- Retarding Admixtures: Help slow the setting process without compromising final strength.
- Water Reducers: Improve flow without needing additional water, which can weaken the mix.
Keep the Drum Turning
Continuous rotation helps prevent the concrete from segregating or setting prematurely. Slowing the revolutions near the job site can preserve workability just a bit longer.
Stage Work Crews Ahead of Arrival
Ensure that workers and equipment are ready to receive the mix as soon as it arrives. Delays on-site can be just as damaging as delays on the road.
When Is Concrete Considered Too Old to Use?
There’s a difference between concrete that’s merely older and concrete that’s no longer viable. Some signs that concrete in a truck is no longer suitable for use include:
- Visible lumps or hardened clots forming inside the drum
- A significant drop in slump (too stiff to pour)
- Loss of air content, which affects freeze-thaw durability
- Failed slump or temperature test on arrival
If any of these are detected during inspection, the concrete load may be rejected and sent back.
Concrete Truck Time Guidelines and Risk Levels
| Time in Truck | Status | Risk Level |
| 0–60 minutes | Optimal delivery window | Low |
| 60–90 minutes | Acceptable, but monitor closely | Moderate |
| 90–120 minutes | The risk of setting begins | High |
| 120+ minutes | Likely unusable, often rejected | Very High |
Can Water Be Added to Extend Time?
Sometimes, workers ask if adding water on-site can extend the concrete’s usable time. The answer: Not really! Adding too much water can:
- Lower compressive strength
- Causes cracking and shrinkage
- Affect long-term durability
If necessary, small adjustments can be made under supervision, but this should follow strict quality control procedures and never be used as a fix for poor timing.
Safety Considerations
Old or partially set concrete can pose serious risks:
- Clogs in pumps or chutes
- Drastic changes in mix consistency, leading to splatter or unexpected flow
- Added strain on workers who have to manipulate stiffer, less workable mix
Proper timing helps avoid these risks and protects both people and equipment.
How Concrete Companies Monitor Truck Timing
Modern ready-mix providers often use GPS and digital dispatch systems to track:
- Departure and arrival times
- Revolutions of the drum
- Temperature and humidity during transit
These tools allow for better decision-making and reduce waste by ensuring that loads are still within the allowable time window before being poured.
Tips for Contractors and Site Managers
- Confirm ETA with the plant and avoid idle time.
- Prepare all equipment before the truck arrives.
- Reject any load older than 90 minutes unless verified safe with testing.
These steps go a long way toward keeping the concrete and the project within specifications.
Takeaway
Concrete is a time-sensitive material, and understanding how long it can stay in a truck is critical for maintaining quality and safety on the job site. The 90-minute window is a widely accepted benchmark, but real-world factors like temperature, mix type, and traffic conditions can impact that timing. Monitoring every phase from batching to pouring ensures that the concrete delivered is as strong and reliable as the structure it will support.
Pro-Mix Concrete is a trusted name in ready-mix delivery, offering high-quality, on-time service tailored for commercial, residential, and industrial projects. With reliable batching, experienced operators, and efficient logistics, we ensure that your concrete arrives fresh and ready to perform.
When precision matters, build with Pro-Mix Concrete.
