Most concrete problems that surface on placement day were created at the order. A supplier can only batch what it was asked for, and an order that leaves out the exposure condition, the placement method or the real rate of placement produces concrete that meets its strength requirement and disappoints everyone anyway. This page sets out what a producer actually needs to know.
The technical half of the order
Specified compressive strength and the age at which it applies. Usually twenty-eight days, but not always — mass concrete and high-slag mixes are frequently specified at fifty-six days, and post-tensioning or early stripping introduces an earlier milestone that the mix has to be designed around. Give both if both apply.
Exposure conditions, not just strength. Freeze-thaw exposure, deicing chemicals, sulfate concentration in the soil or groundwater, chloride exposure, and any requirement for low permeability. These drive maximum water-cement ratio and cement type independently of strength, and a mix that satisfies the strength number may be entirely wrong for the exposure. The exposure class framework is published by the American Concrete Institute.
Nominal maximum aggregate size. Limited by section thickness, clear bar spacing, cover and, where relevant, pump line diameter. Larger is generally better for shrinkage and economy, so do not specify small aggregate without a reason.
Slump or slump flow at the point of placement, together with the tolerance. State where it is to be measured — at the truck or at the discharge end of a pump line — because the two differ.
Air content, with a range rather than a single value. Required for freeze-thaw exposure; usually undesirable otherwise, since air costs strength.
Any special requirements — fibre reinforcement type and dosage, shrinkage limit verified by length-change testing, permeability or resistivity limit, colour, unit weight for lightweight concrete, a maximum concrete temperature, or a hydration-stabilising admixture for a long haul.
The logistical half, which matters just as much
Quantity, with a waste allowance. Compute from dimensions and add for subgrade tolerance, form deflection, over-excavation and spillage. Under-ordering the last load of a slab is far more expensive than over-ordering it, because a cold joint in the middle of a placement is a defect and a leftover half-yard is not.
Rate of placement, honestly stated. Cubic yards per hour that the crew and equipment can genuinely achieve. This is the number dispatch uses to space the trucks, and an optimistic figure produces a queue of loads ageing in the sun. If a pump is being used, its practical throughput usually governs rather than the crew size.
Start time and site address, with access notes. Route in and out, ground conditions and any weight or height restriction, turning space, overhead lines, and the location designated for washout. A truck that cannot turn adds minutes to every cycle for the whole pour.
Placement method. Chute, pump, conveyor, crane and bucket, or buggy. Each has consequences for the mix — a pumped mix needs adequate fines and pumpability, and pumping changes air content — so the method belongs in the order, not in a conversation on the day.
Contact for the day and who may authorise changes. One named role on site who can accept a load, approve added water within the permitted limit, or stop the pour.
Lead time
Two different clocks run here. A standard mix in a normal market can often be scheduled within a day or two, subject to truck availability. A mix that has to be designed, trial-batched and submitted for approval needs weeks, and if it uses a material the plant does not normally stock, longer still. Bring unusual requirements forward early; they are cheap to solve in a submittal and expensive to solve at the chute.
In busy markets the binding constraint is drivers and trucks rather than batching capacity, so large placements are booked well ahead and confirmed close to the date. Weather contingency should be agreed in advance too — what happens if rain arrives mid-pour, and who bears the cost of a cancelled or diverted load. The commercial treatment is set out under procurement and terms.
The pre-construction meeting
For anything larger or more demanding than routine work, a pre-construction meeting with the producer, the concrete contractor, the testing laboratory and the specifier is the highest-value hour on the project. The agenda that repays itself:
- Where samples will be taken — truck or point of placement — and by whom.
- Acceptance criteria and what happens if a test is low.
- Curing method, duration and how its completion will be verified.
- Hot- or cold-weather protection plans and the trigger conditions for them.
- Water addition policy at the site and who authorises it.
- Joint layout, placement sequence and finishing requirements.
- Who to call, on both sides, when something is wrong.
On the day
Check each delivery ticket against the order: mix identification, quantity, batch time, and the water withheld. Perform the acceptance tests promptly on a properly taken composite sample, as described under testing. Reject a load at the chute if it does not conform, rather than placing it and arguing later — once it is in the forms, everyone's options narrow considerably.
And begin curing when finishing ends, not when the shift does. Guidance is under curing and protection.
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