Concrete testing
Checking the concrete, fresh and hardened
Testing shows whether fresh concrete has the workability the job needs, and whether hardened concrete has reached its required strength. Here’s what each test does.
Enquire about testingFive tests
Choose a test to see what it tells you
Slump, cube and beam tests use samples. Core and pull-out tests are carried out on the concrete in place and leave local damage that needs making good.
Slump
Tested on Fresh concrete
- What it measures
- Workability: how far a cone of fresh concrete slumps once the mould is lifted.
- Why it matters
- Shows the concrete can be placed and compacted the way the job needs, and that it matches the slump class ordered.
- When it may be needed
- At delivery, before or during the pour.
- Limitations
- It doesn’t indicate strength, and it isn’t suitable for very stiff or very fluid mixes.
How it’s done
The cone is filled in layers and rodded, then lifted straight up. The drop in height is the slump, and classes run from S1 to S5. Slump classes explained
Compressive strength
Tested on Cubes or cylinders
- What it measures
- Load-bearing strength, by crushing cubes or cylinders made from the concrete at the pour.
- Why it matters
- Confirms the concrete reaches the strength grade in the specification.
- When it may be needed
- When the specification or building control asks for strength results. Samples are taken at the pour.
- Limitations
- Results come after the samples have cured, not on the day, and they’re only meaningful if the samples are made and cured correctly.
How it’s done
C grades are defined by strength after 28 days, which is why samples are cured before they’re crushed. Strength guide
Flexural strength
Tested on Beams
- What it measures
- Resistance to bending, by loading a concrete beam until it breaks.
- Why it matters
- Pavements and slabs bend under load, so some designs specify bending strength rather than crushing strength.
- When it may be needed
- Where the design gives a flexural strength, typically for pavements and slabs.
- Limitations
- Beam samples are large and heavy, and need careful handling and curing.
How it’s done
The beam is supported near each end and loaded until it cracks. The load at failure gives the flexural strength.
Core
Tested on The structure, in place
- What it measures
- Strength and density, from a cylinder drilled out of the hardened concrete.
- Why it matters
- Checks concrete that’s already in place, rather than samples taken at the pour.
- When it may be needed
- When the strength of the finished structure needs confirming, for example if sample results are missing or in question.
- Limitations
- Partly destructive: it leaves a hole that needs repairing, and core positions have to avoid reinforcement.
How it’s done
The core is cut with a diamond drill, trimmed and crushed in a laboratory.
Pull-out
Tested on The structure, in place
- What it measures
- The force needed to pull an embedded insert out of the concrete, as an indirect estimate of compressive strength.
- Why it matters
- Gives an in-place strength estimate without drilling a full core.
- When it may be needed
- For example, to judge strength in place before formwork comes off or a structure is loaded.
- Limitations
- It’s indirect, so it needs relating to compressive strength for that mix. Partly destructive: it leaves local damage at the insert.
How it’s done
Inserts are usually cast into the concrete when it’s poured, then pulled out later with a jack.
Why test
- Meets the specification
- Shows the concrete matches what the drawings and building control ask for.
- Strength confirmed
- Confirms the concrete has reached the strength needed for load-bearing and durability.
- Problems found early
- Identifies issues with the mix or curing before they become costly.
- Less risk
- Lowers the chance of structural problems and the repairs that follow.
Enquire about testing
Tell us which tests your specification requires and when the pour is scheduled, and we’ll confirm what we can arrange.