Mix Design, Ordering Concrete & the Pour Plan

Welcome

Hello, and welcome. This is Super Structures General Contractors — a national general contractor headquartered in Powhatan, Virginia — here to help you and your clients build something that lasts. We're glad you're with us, and we look forward to connecting with you.

Alright, Mix Design, Ordering Concrete & the Pour Plan. Don't let the plain title fool you. Here's the part that actually matters on the job: The mix is engineered and approved before the first truck leaves the plant, and the pour plan decides whether it arrives at the right rate, in the right place, with everything ready to receive it. Learn it well and you'll stop losing pours to the two things the finishers can't fix: the wrong concrete and a truck line that stalls.

The intro course covered what is in concrete. This lesson is about the paperwork and planning that turn a specification into a pour that goes right: the mix design submittal, the order, the batch ticket, and the pour plan.

The mix design submittal

On most commercial work, ACI 301 requires the contractor to submit a mix design for every class of concrete before it is placed, usually weeks ahead so the engineer can review it. The ready-mix producer prepares it. A complete submittal shows:

• Specified strength (f'c) and the age it is measured at, normally 28 days, sometimes 56 days for mixes heavy in slag or fly ash.
• The exposure class from ACI 318: freezing and thawing (F), sulfate (S), contact with water (W), and corrosion of the reinforcing (C). The exposure class, not the strength, sets the maximum w/cm and the air content.
• Proportions per cubic yard: cementitious materials by weight, fine and coarse aggregate, water, and the resulting w/cm.
• Nominal maximum aggregate size, limited by ACI 318 to roughly one-fifth of the narrowest form dimension, one-third of the slab depth, and three-quarters of the clear spacing between bars.
• Slump or, for high-range water reducer mixes, slump flow; air content, commonly in the 5 to 7 percent range for freeze-thaw exposure depending on aggregate size; every admixture by type; and the test records or trial batches that back it up.

Read the submittal against the general notes on the S-sheets. A 4,000 psi mix is not right for a 4,000 psi garage slab if the notes also call for an F3 exposure and a 0.45 cap on w/cm.

Ordering by the numbers

Concrete is ordered in cubic yards and the arithmetic is unforgiving. Length times width times thickness in feet, divided by 27, gives neat yardage. Then add waste: 5 percent for formed work, 7 to 10 percent for slabs on a rough subgrade, more for footings dug by machine. A 12,000 square foot slab at 6 inches is 12,000 times 0.5 divided by 27, about 222 yards neat; order 235 to 240 and plan the last truck as a short load called in from the field when you can see the end.

Ready-mixed concrete is sold under ASTM C94. Tell the dispatcher the mix number from the approved submittal, the yardage, the spacing between trucks, the start time, the slump and air at the point of placement, the pump or chute requirements, and any admixture to be added at the site. Confirm the order the afternoon before.

The batch ticket and water at the site

Every truck arrives with a batch ticket showing the plant, the truck, the mix identification, the batched weights, the time batched, the admixtures, and the water the plant allows to be added. The foreman or the testing technician checks it against the approved mix before discharge. A wrong mix number is a rejected truck, not a judgment call.

ASTM C94 allows water to be added once at the site, only if the slump is below the specified value, only up to the maximum water in the mix design, and only before any concrete has been discharged, followed by about 30 drum revolutions at mixing speed. Write the gallons on the ticket. The traditional C94 limit is discharge within 90 minutes of batching; newer editions let the specifier set the limit, and hot weather shortens it.

Trucks hold about 8 to 11 yards, and the placement rate drives the spacing: a crew placing 40 yards an hour needs a 10-yard truck every 15 minutes. Too close puts trucks in line going stiff; too far apart starves the screed and builds cold joints.

The pour plan

The pour plan is the foreman's written answer to how tomorrow goes:

• Pour boundaries and the construction joints between them, drawn on the plan and matched to the joint layout.
• Placement method and access: pump location and boom reach, chute access, truck staging and washout.
• Crew and equipment: who runs the hose, vibrates, screeds, and finishes, plus the backup vibrator, generator, and screed.
• The testing agency notified with time, location, and yardage so the technician is there for the first truck.
• Weather: the forecast, and the hot or cold weather measures from the specifications.
• Finishing and curing materials on site before the first truck: evaporation retarder, curing compound or blankets, saw blades, and lighting if finishing runs past dark.

Going Deeper (Intermediate)

Pour size is a business decision. A larger pour spreads the fixed cost of the pump, the testing agency, and the crew over more yards, but it extends the finishing window, tires the crew, and raises the stakes if a truck breaks down. Experienced foremen size pours to what the finishers can close out in daylight with margin, and keep a planned stopping point where a bulkhead can go in without ruining the joint pattern. Order the slump the mix was designed around and let the water reducer do the work; loosening a stiff mix with a hose is the oldest mistake in the trade, and the cylinders tell on it at 28 days.

Advanced / Pro-Level

Pros use performance-based mixes where the specification allows it, giving the producer strength, durability, shrinkage, and finishability targets and letting the plant optimize cement content and SCM replacement. Lower cement content means less heat and shrinkage but slower early strength, which affects stripping and sawing. Pros also keep a pour log for every placement: mix, yardage, trucks, times, temperatures, slump, air, cylinders cast, and any field water. That log settles a low-break argument months later.

Practice Challenge

You are pouring a 4-inch sidewalk and a 5,000 psi column line on the same morning, and dispatch sends both mixes in identical trucks. The first ticket says mix 5035, which the pump operator thinks is the sidewalk mix. What do you do? (Answer: check the ticket against the approved submittal before discharging anything; the mix number identifies the design, not the use, so confirm with the plant which design 5035 is, route the truck to the element it was ordered for, and if it cannot physically go there, reject it rather than guess.)

In Practice

A foreman who builds the pour plan the day before has the pump set, the technician on site, and the curing compound stacked when the first truck turns in. A foreman who orders by feel runs 30 yards short, places the last truck at dusk, and finds a cold joint in the middle of the panel.

Common Mistakes to Avoid

• Ordering by strength alone and ignoring the exposure class and the w/cm cap
• Forgetting waste, then calling for a short load the plant can't deliver before the pour goes off
• Adding water after discharge has started, or without writing it on the ticket
• Spacing trucks for the pump's capacity instead of the crew's real placement rate

Takeaway: The mix is engineered and approved before the first truck leaves the plant, and the pour plan decides whether it arrives at the right rate, in the right place, with everything ready to receive it.

Educational content only — not structural design, engineering, or safety advice, and not a substitute for hands-on training or a licensed engineer. Follow ACI 318, ACI 301, ACI 117, and the building code as adopted in your jurisdiction, the project drawings and specifications, the formwork and shoring drawings for your project, and the manufacturer's instructions for every product you use.