How to Read a Concrete Mix Design Sheet
You’ve seen them a hundred times — those batch tickets and mix design sheets that come with every ready-mix delivery. Most guys on site glance at the MPa number and toss the sheet in the truck. But that piece of paper tells you exactly what’s being poured into your forms, and if you don’t know how to read it, you won’t catch problems until it’s too late.
Here’s how to read a concrete mix design sheet without an engineering degree.
What a Mix Design Sheet Is
A mix design sheet (also called a batch ticket or delivery ticket) is the recipe for your concrete. It lists every ingredient, every proportion, and every performance target. It’s issued by the batch plant or the ready-mix supplier for every load.
In Ontario, these sheets follow CSA A23.1 standards. If you’re on a spec job — municipal work, commercial, anything with an engineer’s stamp — the mix design has to match the project specification exactly. If it doesn’t, the concrete can be rejected on site.
The Key Numbers
Compressive Strength (MPa)
This is the big number everyone looks for. It tells you how much load the concrete can handle after 28 days of curing, measured in megapascals (MPa).
Common residential and commercial strengths in the GTA:
| MPa | Typical Use |
|---|---|
| 20 MPa | Non-structural — walkways, landscape curbs, base slabs |
| 25 MPa | Standard residential — footings, foundation walls, garage slabs |
| 30 MPa | High-strength residential — basement slabs, driveway aprons subject to heavy loads |
| 32 MPa | Commercial foundations, parking structures, exposed structural concrete |
| 35+ MPa | Engineered structural — high-rise cores, bridge components, industrial floors |
The spec on your drawing will state the required MPa. If the batch ticket shows a different number, do not pour. Call the plant or your supplier and get it corrected.
Slump
Slump measures how fluid the concrete is when it arrives. It’s tested by filling a cone-shaped mould, lifting the mould, and measuring how much the concrete drops (slumps). Measured in millimetres.
| Slump | What It Means |
|---|---|
| 50–75 mm | Stiff mix — good for slabs that need to hold grade, slope work |
| 80–100 mm | Standard — most residential and commercial pours |
| 120–150 mm | Wet mix — pump-friendly, good for walls and hard-to-reach forms |
| 180+ mm | Very wet or superplasticized — specialized applications only |
Why it matters on site: If your slump is too low, the concrete won’t flow into your forms properly and you’ll get honeycombing (voids in the surface). If it’s too high, the mix is too wet — it’ll bleed water on the surface, take forever to finish, and the final strength will be lower than specified.
Never add water to a drum truck to increase slump. You’re diluting the mix and reducing strength. If you need more workability, the plant should add a plasticizer (superplasticizer or water-reducing admixture) — not water.
Water-to-Cement Ratio (w/c)
This is the ratio of water to cement by weight. Lower is stronger but harder to work. Higher is easier to work but weaker.
Typical targets:
- 0.40–0.45: High-strength, durable concrete. Used for exposed structural work.
- 0.45–0.50: Standard residential and commercial.
- 0.50–0.55: General purpose, non-structural.
CSA A23.1 sets maximum w/c ratios based on exposure class. In Ontario, any concrete exposed to freeze-thaw cycles (which is almost everything exterior) has a maximum w/c of 0.45.
If the batch ticket shows a w/c ratio higher than the spec allows, reject the load. High w/c concrete in Ontario winters will scale, spall, and fail.
Air Content
Entrained air is tiny, deliberately introduced air bubbles that give concrete freeze-thaw resistance. In Ontario, air-entrained concrete is standard for any exterior or exposed application.
Target air content:
- 5–8% for most GTA exterior applications
- 4–7% for structural concrete with moderate exposure
- Non-air-entrained is acceptable only for interior, protected concrete
The air content is measured on site with a pressure meter (Type B test). If it’s below spec, the concrete lacks freeze-thaw protection. If it’s significantly above spec (over 9%), compressive strength drops noticeably.
Cement Content
Listed in kg/m³. Higher cement content generally means higher strength, but also more heat of hydration (which matters for mass pours) and more shrinkage.
Typical ranges:
- 280–320 kg/m³: Standard residential
- 320–380 kg/m³: High-strength commercial
- 380+ kg/m³: Specialized high-performance mixes
Aggregate Size
Maximum aggregate size affects workability and finish quality.
- 20 mm (3/4”): Standard for most residential and commercial work
- 14 mm (1/2”): Used for thin sections, pump mixes, and architectural finishes
- 10 mm (3/8”): Specialty applications — shotcrete, thin overlays
If you’re pumping concrete, check that the aggregate size is compatible with your pump line diameter. Trying to pump 20 mm aggregate through a 2” line will clog.
Admixtures
The batch ticket will list any chemical admixtures added to the mix. Common ones:
- Water reducer (WR): Reduces water needed for workability. Improves strength without changing slump.
- Superplasticizer (SP): High-range water reducer. Makes concrete very fluid without adding water. Essential for pump mixes and high-slump applications.
- Air-entraining agent (AEA): Creates the freeze-thaw-resistant air bubbles discussed above.
- Accelerator: Speeds up set time. Used in cold weather or when you need to strip forms faster.
- Retarder: Slows set time. Used in hot weather or for long hauls to keep the concrete workable.
- Fibre (polypropylene or steel): Added for crack control or structural reinforcement. Usually listed separately on the ticket.
What to Check When the Truck Arrives
When the ready-mix truck pulls up to your job site in Mississauga, Brampton, Pickering, or anywhere in the GTA, do this before the chute opens:
- Check the ticket against your order. Correct MPa? Correct slump? Correct volume?
- Check the timestamp. How long has the concrete been in the drum? If it’s been over 60 minutes and hasn’t been retarded, the workability window is shrinking fast.
- Visual check the first discharge. Does it look right? Proper consistency? Any segregation (aggregate separating from paste)?
- Run a slump test if required by spec. Takes two minutes and tells you exactly where the concrete stands.
- Take test cylinders if required. Standard is a set of three cylinders per 50 m³ or per day of pour, whichever is less. The testing lab picks them up and breaks them at 7 and 28 days.
Common Problems and What They Mean
- Truck arrives with slump too low: Plant may have under-dosed the water reducer. Ask the driver if they can add plasticizer (not water). If not, call the plant.
- Concrete sets too fast: Hot weather accelerates hydration. Request a retarder in the mix during summer months (July–August in the GTA can push 35°C).
- Surface bleeding: Mix may be too wet (high w/c) or have too much fine aggregate. Don’t finish until the bleed water evaporates.
- Batch ticket doesn’t match spec: Don’t pour. Call the plant and get it corrected. It’s cheaper to wait for the right truck than to remove and replace the wrong concrete.
Keep the Batch Tickets
Every batch ticket is a quality record. On spec jobs, the engineer or inspector will ask for them. On any job, they’re your proof of what was actually delivered if there’s a dispute down the road. Keep them for a minimum of 2 years — ideally 5.
Need concrete delivered to a GTA job site? Our ready-mix division dispatches volumetric mixers across Mississauga, Brampton, Pickering, and the surrounding regions. Get a quote or call 647-926-2597.