How many concrete trucks do you need for a pour?
A continuous pour needs a truck mixer arriving every time the previous one finishes discharging. The truck interval is set by how fast the pump or crane can place a load. Each truck then takes a round trip: loading at the plant, the haul to site, waiting and testing, discharge, washout and the return. Trucks needed = round trip ÷ interval, rounded up. Caltrans' Deck Construction Manual works the same example: a 75-minute round trip and a 14-minute interval give 5.4, so six trucks.
The planner also checks each load against a time limit from batching to the end of discharge, and builds a load-by-load dispatch schedule that shows what a stoppage on site does to the trucks already on the road.
Why does truck planning matter for a pour?
- Too few trucks: the pump and the crew wait between loads, and cold joints become a risk on a long pour.
- Too many trucks: trucks queue on site and the concrete in them gets older while it waits.
- Distance and traffic: a longer haul needs more trucks for the same pour, and traffic at the pour time changes the answer.
- Time limits: The current ASTM C94 (C94/C94M-24d) no longer sets a fixed time: the purchaser states the limit, or the producer sets one and tells the purchaser before delivery. Many specifications still use 1½ hours and 300 drum revolutions, for example HCAI PIN 82 in California. Late loads may be rejected.
What inputs do you need?
| Input | Where to find it | Tip |
|---|---|---|
| Volume to pour | Drawings and the pour plan | Add the waste margin you use. |
| Placement rate | Pump or crane and crew on similar pours | Use the rate achieved, not the pump's maximum. |
| Load per truck | Plant dispatch, delivery tickets | The load sent, often below the drum capacity. |
| Loading time, washout | Plant records, delivery tickets | Time several trucks. |
| Distance and speeds | Route at the pour time, tracking data of the mixers | Night and morning traffic differ. |
| Time limit | Project specification | 1½ hours is the example; enter the limit in your specification. Hot weather may shorten it. |
How are trucks and the schedule calculated?
Interval and round trip
Trucks needed and delivery time
The trucks-needed rule is the worked example in section 5-1.2 of Caltrans' Deck Construction Manual: trucks per hour = pour rate ÷ truck load, and trucks needed = round-trip time ÷ the interval between trucks. Section 5-1.4 lists the 90-minute rule and notes it can be shorter on a hot day.
Dispatch schedule
Sources
- California Department of Transportation (Caltrans), Deck Construction Manual, Chapter 5, Concrete Placement and Consolidation, October 2015, sections 5-1.2 (delivery rate) and 5-1.4 (90-minute rule). Source: Caltrans.
- California Department of Health Care Access and Information (HCAI), PIN 82: Ready Mix Concrete Placement Times, effective 9 October 2025 (discharge within 1½ hours and 300 drum revolutions; it notes that ASTM C94/C94M-24d no longer gives a specific time limit). Source: HCAI. Last reviewed 21 October 2026.
Worked example: a 120 m³ pumped pour
The defaults are examples; replace them with your project's figures.
- A 9 m³ load at 30 m³/h discharges in 18 minutes, so a truck is needed every 18 minutes.
- Round trip: 8 min loading + 25.7 min haul (15 km at 35 km/h) + 10 min on site + 18 min discharge + 10 min washout + 20 min return = 91.7 minutes.
- Trucks needed: 91.7 ÷ 18 = 5.1, so 6 truck mixers. The pour takes 14 loads (the last one 3 m³) and about 4 hours.
- Delivery time: 8 + 25.7 + 10 + 18 = 61.7 minutes, 28 minutes inside a 90-minute limit. Sites up to 31.5 km away stay within it at these speeds.
- Starting at 05:00, the first truck is batched at 04:16 and the pour ends at 09:00. With only 4 trucks the pump waits about an hour in total and the pour ends at 09:59.
- If the pump stops for 45 minutes after load 4, loads 5 to 10 are already on the road and reach about 107 minutes from batching: 6 loads over the limit.
How to read your results
- Interval set by the site: the usual case. More trucks than needed only queue.
- Interval set by the plant: the plant cannot feed the placement rate. Plan the pour at the plant's rate or use a second plant.
- Delivery time close to the limit: a little traffic or a short wait on site pushes loads over it. Shorten the haul or the waiting.
- Loads over the limit after a stop: the dispatcher needs to hold loads at the plant as soon as the site stops.
How to keep a pour on time
- Agree the interval with the plant before the pour, and confirm it with the first two loads.
- Tell the plant at once about any stop, so loads are held before batching.
- Check real haul times: time the route at the pour hour, or use the trip times of the mixers.
- Plan hot-weather pours early: follow the project specification for concrete temperature and time limits. For outdoor work in summer, see the Midday Work Ban Shift Checker.
Assumptions and limits
The planner uses average times: every truck carries the same load (except the last), drives at the same speeds and spends the same time on site, and one truck discharges at a time. The plant is treated as one loading point. The time limit is checked from batching to the end of discharge; drum revolutions, concrete temperature and slump are not checked. In the stoppage scenario the plant keeps sending loads on the planned times. All defaults are examples, not project or plant data. Use the result to plan, then follow your project specification and the plant's instructions.