A prescriptive specification tells the plant what to put in the mixer. A performance specification tells the plant what the concrete has to do and leaves the recipe alone. The difference looks like a drafting preference until something comes back below spec, and then it is the only thing that matters, because the two alternatives put the liability for the mix in different hands.
That hand-off is set out in one table in CSA A23.1, and most disputes we see on Alberta projects start with a specification that quietly asks for both alternatives at once.
What Table 5 actually does
CSA A23.1 does not rank the two approaches. It presents them as alternatives and assigns the duties of each. Annex J is written as a guide for choosing between them, and Concrete BC’s bulletin on the submittal process points specifiers at exactly that pair — “CSA A23.1 Annex J and Table 5” — as the place to settle the question before a submittal is prepared.
The two alternatives are usually cited by number:
| Alternative 1 — performance | Alternative 2 — prescription | |
|---|---|---|
| What the owner states | Exposure class, the tests and acceptance criteria, required service life where applicable | Exposure class, and the tabulated or stated mix requirements |
| Who proportions the mix | The supplier, against the performance criteria | The supplier, against the owner’s stated criteria |
| Who carries the mix risk | The supplier, for the concrete as delivered | The owner, who has specified the recipe |
| Status of tabulated values | Guidance the supplier may use | Binding requirements the mix must meet |
Concrete International’s treatment of the Canadian model puts the prescriptive case in one line: under prescription the owner “specifies only the exposure class, such as C-1 concrete,” and the supplier proportions a mixture meeting all the tabulated criteria for that class. Concrete BC states the consequence directly — under the prescription alternative “the owner assumes responsibility for the concrete.”
The performance case inverts that. It applies “when the owner requires the concrete supplier to assume responsibility for the performance of the concrete as delivered,” and the owner’s specification then carries the tests and acceptance criteria instead of the proportions. If you take one thing from this page, take the phrase as delivered.
Where responsibility stops, exactly
Under the performance alternative the supplier’s responsibility ends when the mixture is discharged from the mixer or delivery unit. The contractor is responsible for the concrete in place — placing, consolidating and curing it so that it develops the strength and durability the specification asks for.
Annex J is blunt: custody passes from supplier to contractor while the material is still plastic, so “a high degree of coordination is required between supplier and contractor,” and the two quality control processes have to be compatible enough to “demonstrate compliance” together.
Read as deliverables, Table 5 under a performance specification allocates work like this:
The owner provides: required structural criteria including strength at age; required durability criteria including the class of exposure; additional criteria for volume stability, architecture and sustainability, plus any pre-qualification or verification criteria; quality management requirements, and whether the supplier must hold industry certification.
The contractor provides: joint work with the supplier to establish plastic and hardened properties that meet the criteria and still suit the placement method; documentation that pre-qualification requirements were met; and a quality control plan, implemented, with documentation of compliance.
The supplier provides: certification that the plant, equipment and materials comply with the standard; that the mixture design complies; that production and delivery will comply; and that the concrete complies with the specified performance criteria — plus a quality control plan where required.
Notice what is missing from the supplier’s list: a mix proportion sheet. Under a performance specification the proportions are the supplier’s to hold, and a spec that demands them has reverted to Alternative 2 without saying so.
What an Alberta prescriptive specification looks like
Alberta Transportation’s bridge specification is a clean example of prescription done thoroughly, and a useful benchmark whether or not you are building a bridge. Section 4 tabulates each class with the numbers the mix has to hit:
| Class | Min. 28-day strength | Nominal max. aggregate | Slump | Total air | Max. water-cementing ratio |
|---|---|---|---|---|---|
| S | 20 MPa | 28 to 5 mm | 50–70 mm | 4–7% | 0.50 |
| B | 25 MPa | 28 to 5 mm | 50–70 mm | 4–7% | 0.45 |
| Pile | 25 MPa | 28 to 5 mm | 100–140 mm | 4–7% | 0.45 |
| D | 30 MPa | 14 to 5 mm | 50–70 mm | 5–8% | 0.42 |
| C | 35 MPa | 20 to 5 mm | 60–80 mm | 5–8% | 0.40 |
| HPC | 45 MPa | 20 to 5 mm | 90–150 mm | 5–8% | 0.38 |
Class C goes to a 28 to 5 mm aggregate in mass pours, and HPC drops to a 14 mm top size for overlays 50 mm or thinner.
The prescription continues past the table. For Class HPC the specification requires a minimum of 335 kg/m³ of cement excluding supplementary cementing materials, caps fly ash at 30 per cent by mass of cementing materials for the general classes, and for HPC fixes silica fume at 6 to 8 per cent, fly ash at 11 to 15 per cent, and their sum at 17 to 20 per cent.
That is a recipe with very little room in it, and the responsibility clauses match. Section 4.4.4 requires that “the Contractor shall submit the mix design he proposes for each proposed class of concrete,” allows it to be “completed by the concrete supplier” with documentation stamped by an Alberta-registered Professional Engineer, and still requires an independent certified laboratory to review and stamp it. Section 4.4.5 closes the loop: “it remains the Contractor’s responsibility that the concrete meets all the requirements of this Specification.”
Three stamps, one owner of the outcome. Prescription is not the lighter option; it is a different distribution of the same work.
What a performance specification asks for instead
A real performance specification replaces the recipe with a test schedule longer than most specifiers expect. A major Canadian transit project documented by the University of Toronto’s Doug Hooton specified, among other criteria:
- Compressive strength of 29.8 MPa in place at 91 days — 0.85 of a 35 MPa specified strength, measured in the structure rather than in a standard cylinder.
- Chloride permeability of a maximum 1,500 coulombs at 56 days, with a target near 1,250 and no single value above 1,750.
- Chloride diffusion of a maximum 3.0 × 10⁻¹² m²/s at 28 days.
- Hardened air content of a minimum 3 per cent in place.
- Drying shrinkage of a maximum 0.040 per cent after seven days of moist curing plus 28 days of drying.
- Crack width not exceeding 0.3 mm.
- A maximum in-place temperature of 55 °C, with a maximum gradient of 20 °C in any element.
The qualification process behind those numbers is what changes a tender schedule. Suppliers had to pre-qualify proposed mixes on 1 m³ trial monoliths with cores taken from the block, submit the quality control plan at least eight weeks before that testing, run preconstruction identity tests confirming the delivered mix matched the proven mix, and place no concrete before written approval of the quality programme.
The resulting mix ran a 125 to 160 mm slump, 5 to 7 per cent air and a water-cementing ratio below 0.40 — numbers a prescriptive specification could have written in one line. The difference is that under the performance alternative the supplier chose them and stands behind them, and the eight-week clock buys the right to do so.
That is the honest trade: a performance specification transfers the mix risk to the plant and asks the schedule to pay for it.
The submittal is where the alternative becomes paperwork
Concrete BC’s bulletin separates two submittal types that get confused:
- A performance submittal lists each specification requirement with a compliance statement against it, and contains no mix proportions in kg/m³.
- A design, or proportioned, submittal gives the reviewing engineer all design quantities and constituent test reports. It can sit under either alternative.
The supporting documents the standard’s companion test-methods volume contemplates include cementitious mill certificates, an additional cementitious compliance report where alkali-aggregate reaction or sulphate resistance is in play, aggregate reports, admixture and fibre data sheets, water quality data where non-potable water is used, and environmental product declarations. The alternative decides which document closes the package: under Alternative 1, “documentation demonstrating that the proposed mix design will achieve the required plastic properties”; under Alternative 2, documentation showing compliance with the owner’s prescriptive criteria.
The bulletin also flags the ways a submittal stalls, all avoidable:
- Undisclosed discrepancies. Any departure from the specification has to be identified in the submittal, not discovered in review.
- A change of cement or supplementary cementing material type or source, which “may warrant a new mix submission with all related documents to qualify the product.”
- A change of aggregate source, where “full testing to confirm compliance with standards will need to be completed.”
- Products the region does not stock. A specified manufacturer not available locally is a schedule item.
- Conflict of interest. The producer cannot act as the reviewing and inspecting engineer.
The practical reading for Calgary work: material availability is a specification input. A mix that is routine in one region can be a qualification exercise here, and the difference shows up as weeks rather than dollars per cubic metre.
One mix-design trap worth knowing before you choose
Performance specifications are often chosen to open the door to high supplementary cementing material contents, and that door has a threshold on it. Concretes with more than 50 per cent slag, in severe exposure, must be designed with a water-cementing ratio 0.05 lower than the otherwise applicable limit — a provision aimed at thin elements where curing is limited.
If the whole reason for going performance is a high-slag mix in a freeze-thaw and de-icing environment, that compensating ratio has to be in the mix design and in the price before the alternative is selected, not discovered in review. The class that triggers it comes from the exposure classification, which we work through in our guide to the CSA A23.1 exposure classes.
Choosing between them
| If this is true of the project | The alternative that fits |
|---|---|
| Service life is the governing requirement and the owner has testing capacity | Alternative 1, performance |
| The owner has a proven standard mix portfolio and wants repeatability across contracts | Alternative 2, prescription |
| Tender-to-pour is under eight weeks | Alternative 2 — performance pre-qualification will not fit |
| The mix depends on a high supplementary cementing material content | Alternative 1, with the compensating water-cementing ratio priced in |
| The structure is routine and the exposure is mild | Alternative 2, specified by exposure class |
| Innovation or a lower-carbon mix is an objective | Alternative 1, where the criteria are properties rather than ingredients |
And the pattern to avoid, the most common one in the field: an exposure class, a full prescriptive table, a required cementitious content, and a clause making the supplier responsible for performance. That specification hands the supplier the liability and the owner the recipe, and nobody can meet it without a variance. The fix is one paragraph, cheaper to write before the tender closes than after the first break.
Where this page stops
This page is about who owns the mix, not what goes in it. Choosing the specified strength is covered in our guide to 3,000, 4,000 and 5,000 PSI concrete, and reading what was delivered against what was specified belongs to the numbers on your concrete batch ticket.
Send us your project details — pour date, mix type, PSI, volume — and our team will get back to you within 1 business hour with a quote and delivery slot. If the specification is still being written, send the draft instead: name the alternative you intend and we will tell you whether the mix you are describing is orderable in this market. Where the mix is proportioned on site rather than in transit, see how our volumetric mixers work, or start from custom mixed concrete.
FAQ
What is the difference between a performance and a prescriptive concrete specification? A prescriptive specification states the mix requirements — class, strength, aggregate size, slump, air content and water-cementing ratio — and the supplier proportions to them. A performance specification states the properties the concrete must achieve and the tests that will prove it, and leaves the proportions to the supplier.
Where does CSA A23.1 set this out? Table 5 presents the alternatives and assigns the duties of owner, contractor and supplier. Annex J is written as a guide to choosing between them.
Under a performance specification, when does the supplier’s responsibility end? When the mixture is discharged from the mixer or delivery unit. The concrete as delivered is the supplier’s; the concrete in place, including placing, consolidating and curing, is the contractor’s.
Who is responsible for the mix under a prescriptive specification? The owner, who has specified it. On Alberta Transportation work the contractor still submits the mix design, it may be prepared by the supplier and stamped by a professional engineer, an independent laboratory reviews it, and the contractor remains responsible that the concrete meets the specification.
Does a performance submittal include mix proportions? No. It lists each requirement with a compliance statement and no quantities in kg/m³. A design submittal gives the proportions, under either alternative.
Can a specification use both alternatives at once? Not coherently. A specification that prescribes the recipe and also makes the supplier responsible for performance cannot be met as written, because the party carrying the risk has no control over the variable.
Sources
- J. A. Bickley, Performance Specifications for Durable Concrete, Concrete International (hosted by the National Ready Mixed Concrete Association): https://www.nrmca.org/wp-content/uploads/2020/09/ci2809bickley.pdf
- R. D. Hooton, Development and Execution of a Performance Specification, American Concrete Institute webinar notes: https://www.concrete.org/portals/0/files/pdf/webinars/ws_2018_0827_Hooton_DevExecPerfSpecMCTS.pdf
- Concrete BC, Technical Bulletin — Concrete Mix Submittal Process: https://concretebc.ca/wp-content/uploads/2024/11/Technical-Bulletin-Concrete-Mix-Submittal-Process.pdf
- Alberta Transportation, Specifications for Bridge Construction, Section 4 — Cast-In-Place Concrete: https://www.transportation.alberta.ca/content/doctype246/production/10bcs04.pdf
