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Every drawing set has a written partner. On a building it is usually called the specification; on a highway job it may be the project's special provisions sitting on top of an agency's standard specifications. It is long, dense and essential: most of what decides quality and cost is written there, not drawn.
| System | Where used | How it's organised |
|---|---|---|
| MasterFormat (CSI) | US and Canada | Numbered divisions and sections (03 30 00 Cast-in-place concrete); each section in three parts: General, Products, Execution |
| NBS / Uniclass-based | UK | Sections by system or work type, with clauses for products and execution |
| Agency standard specifications | Highways (for example FHWA's FP series in the US) | Sections by work type, each ending with measurement and payment |
The shape of a section
Whatever the system, a section answers the same questions:
- What is the work? Scope, related sections, references to standards.
- What must the materials be? Grades, classes, sources, certificates, submittals.
- How is it done? Placing, tolerances, sequence, protection, curing.
- How is it checked? Tests, frequency, acceptance criteria.
- How is it measured and paid? Units, what is included, pay items (common on civil work).
The US Federal Highway Administration's Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (the FP series, a public-domain federal document) is a good example to read: each section describes the work, the materials, the construction requirements, and then how it is measured and paid.
Concrete strength in two languages
| United States | Europe (EN 206) | |
|---|---|---|
| How written | f'c = 4,000 psi | C30/37 |
| Meaning | Specified compressive strength at 28 days, on cylinders | Characteristic strength: 30 MPa on cylinders / 37 MPa on cubes |
| Durability | Exposure categories and maximum water-cement ratio | Exposure classes: XC (carbonation), XD (chlorides), XS (sea water), XF (freeze-thaw), XA (chemical) |
1 psi is about 0.0069 MPa, so 4,000 psi is about 27.6 MPa, and 5,000 psi about 34.5 MPa.
The model's slabs all carry "Concrete" as their material. The specification calls for C32/40 in the car park slabs (de-icing salts, exposure XD3) and C28/35 elsewhere. The quantity take-off lumps all concrete together, the tender prices one mix, and the change to the stronger, more durable mix for the car park becomes a claim.
The coordinator reads the concrete section, lists the classes and exposure classes by element, and asks the structural team to put them on the elements as properties. The take-off reports volumes by class, and the tender prices each mix separately.
A US specification asks for bridge deck concrete with f'c = 4,500 psi at 28 days. A European contractor will supply it.
- Convert the strength to MPa.
- Which EN 206 strength class is the nearest one that meets it?
- What else must you check in the specification before the supplier can price it?
Key takeaways
- Drawings show where and how big; the specification says what, how well, and how it is measured and paid.
- Specifications are organised in numbered sections: MasterFormat in North America, NBS or Uniclass-based in the UK, agency standards for highways.
- A typical section covers general requirements, materials (products), execution, and often measurement and payment.
- Concrete strength is written as f'c in psi (US) or as a strength class such as C30/37 (Europe); exposure classes add durability rules.