Your structural drawings specify a concrete strength and a steel grade. Cube and steel tests are how you check that what went into your building matches. Without them you are trusting the contractor and the supplier on their word.
What is included
| Test | What the lab does | What you learn |
|---|---|---|
| Concrete cube test | Cubes cast from concrete on site are cured, then crushed in a compression machine at the ages your engineer specifies | Whether the concrete reached the design strength |
| Steel bar tensile test | A bar sample is pulled until it yields and breaks | Yield strength, tensile strength and stretch (elongation), compared with the grade ordered, such as Grade 40 or Grade 60 |
| Steel bend test | A bar is bent around a set diameter | Whether the bar cracks when bent, as it will be on site |
| Bar weight and dimension check | Sample bars are weighed and measured | Whether bars are underweight for their stated diameter |
| Blocks and bricks (optional) | Crushing and water absorption tests on samples | Whether masonry units meet the spec |
When you need it
- Every major pour. Footings, columns, beams and slabs. Your engineer will say how many samples per pour.
- Each new steel consignment, especially if the supplier, diameter or source changes.
- When something looks wrong. Concrete that seems too wet, segregated or poorly compacted, or steel with unclear markings.
- Larger buildings. Under the LDA Building and Zoning Regulations, structure stability certificates, drawings and calculations are required above 38 feet (4 storeys) and must be vetted by an LDA-panel structural engineer (LDA regulations). Test records support that engineer's sign-off.
Step-by-step process
Concrete cubes
- Agree with your engineer how many cubes per pour and at what ages they are tested.
- On pour day, cubes are filled from the actual concrete going into the structure, not from a separate "good" batch.
- Label each cube with date, location (for example "first floor slab") and cube number. Photograph them.
- Leave cubes undisturbed, then de-mould and cure them in water as the lab instructs.
- Deliver cubes to the lab, or have the lab collect them, with a sample record sheet.
- The lab crushes them at the agreed ages and issues a report.
- Send results to your structural engineer.
Steel bars
- When steel arrives, check the delivery note and bar markings.
- Cut samples of each diameter in the presence of your representative.
- Label samples with diameter, delivery date and supplier invoice number.
- The lab tests and reports results against the grade ordered.
- Do not use the consignment in critical members until results are in, if your programme allows.
Approvals and documents
Keep a testing file with: sample record sheets, photos, lab reports, steel delivery notes and invoices. If your building needs a structure stability certificate, the engineer signing it may ask for these. For smaller houses there is usually no authority filing of cube results, but a dispute with your contractor is much easier to settle with test reports.
What affects the cost
Labs usually charge per cube or set of cubes and per steel sample or test. We do not list figures; get written quotes. Cost depends on:
- Number of cubes and test ages
- Number of bar diameters and tests per sample
- Whether the lab collects from site
- Urgent results
- Extra tests if early results are poor
Questions to ask the lab
- Which test methods do you follow, and is that stated on the report?
- When was your compression machine last calibrated?
- Do you collect cubes from site, and what do you charge for it?
- How do you record sample identity so cubes cannot be swapped?
- Will reports come directly to me as well as to the contractor?
Red flags
- The contractor makes, cures and delivers cubes with no one from your side present.
- Cubes cast from a separate, richer mix "for testing".
- Results that are always exactly on target.
- Steel samples cut from bars that were not part of the delivery.
- Bars with missing or unclear markings, or a delivery note that does not match the grade ordered.
- A lab report with no test method, date or signature.
FAQs
Who should pay for testing? Settle this in your contract. Many owners pay the lab directly so the lab reports to them.
What if a cube result is low? Tell your structural engineer at once. They may ask for more results, tests on the concrete in place, or a design check before work continues.
Do I need to test steel if the supplier gives a mill certificate? A certificate describes the steel as produced. Testing samples from your own delivery checks what actually reached your site. Ask your engineer.
Can cubes be tested on site? Crushing needs a calibrated compression machine, which is normally at the lab.
Is a slump test the same as a cube test? No. A slump test checks workability of fresh concrete on site; a cube test measures strength after curing. Your engineer may ask for both.
Sources
- LDA Building & Zoning Regulations 2019 (amended), copy hosted by khalidzafar.com
- Houseplot construction rate data (2026-10-18) for steel grades sold in Pakistan (Grade 40 and Grade 60)