Step 01
Fresh concrete
Slump by cone and temperature are measured on delivery, with sampling to ASTM C172 from the discharge stream rather than the first or last of the load.
Concrete Testing
Concrete is specified by a strength it will not reach for 28 days, on a site where it is placed in minutes. Testing is what connects the two.
Concrete Testing: what it actually tells you
Fresh concrete is checked before it goes in. Slump measures workability and, more usefully, consistency between loads: a slump that jumps between trucks means the mix or the water is not under control. Temperature is recorded because hot concrete, common on a Karachi summer site, stiffens fast, loses workability and can lose long term strength.
Compressive strength is determined on specimens cast from the same concrete that went into the structure, cured under controlled conditions and crushed at 7 and 28 days. The 7 day result is an early warning, typically around two thirds of the 28 day figure, and lets you react while the pour is still recent. The 28 day result is the one the specification is written against.
When the specimen results are in doubt, or the concrete is already in place and its history is unknown, the assessment moves to the structure itself. Cores are cut, prepared and tested, with corrections applied for length to diameter ratio and reinforcement. That result, read alongside Schmidt hammer and cover survey data, is what supports a decision about acceptance or strengthening.
At a glance
- Specimen150 mm cube or 150 by 300 mm cylinder
- Test ages7 and 28 days, others on request
- Core diameter100 mm typical, 150 mm preferred
- Sampling ratePer specification, commonly one set per 50 cubic metres
How we run it
The sequence we follow on site and in the laboratory, and the point of each stage.
Step 02
Cast specimens
Cubes of 150 mm or cylinders of 150 by 300 mm are cast in three layers with the specified compaction, marked and left undisturbed for the first 24 hours.
Step 03
Cure
Specimens are demoulded and cured in a water tank at controlled temperature until the test age, because curing conditions change the result more than most people expect.
Step 04
Compression test
Specimens are capped or ground flat and loaded to failure in a calibrated compression machine, with the failure mode recorded as well as the load.
Step 05
Cores
Where the structure must be assessed directly, cores are cut clear of reinforcement, prepared to a proper length to diameter ratio, and tested with the appropriate strength corrections.
What you receive
- Slump and fresh concrete temperature per load
- Compressive strength at 7 and 28 days with the failure mode noted
- Core compressive strength with length to diameter correction
- Density of hardened concrete
- Batch traceability against pour location and delivery ticket
When this test is the right one
- Routine quality control on every structural pour
- Acceptance of ready mix supplied to site
- Investigating a suspected low strength pour
- Assessing an existing structure before a change of use or added load
- Supporting a claim or dispute over concrete supplied
Methods and standards
Every result is reported with its method reference and the calibration status of the instrument used.
ASTM C39 compressive strength of cylindrical concrete specimensBS EN 12390 3 compressive strength of test specimensASTM C31 making and curing test specimens in the fieldASTM C143 slump of hydraulic cement concreteASTM C42 obtaining and testing drilled coresASTM C805 rebound number of hardened concrete
Common questions
What engineers most often ask us about concrete testing.
Not necessarily. A 7 day cube typically reaches about 65 to 70 percent of its 28 day strength, so judge it against that fraction of the specified strength rather than against the full figure. If it is well below that proportion, investigate the mix and the curing straight away rather than waiting three more weeks.
That is normal. Cores reflect concrete as compacted and cured in the structure, while cubes reflect concrete compacted in a mould and cured in a tank. Codes expect the in situ strength to be roughly 70 to 85 percent of the cube strength, and the acceptance criteria for cores are set accordingly.
Partly. Schmidt hammer and ultrasonic pulse velocity give a strength estimate and are excellent for mapping variation across a member, but they are indirect and need calibrating against cores to be relied upon for a number. For an acceptance decision, cores remain the reference.
Often ordered alongside
Most investigations combine several of these. We scope them together so you are not paying to mobilise twice.
Concrete Mix Design
A mix designed for your materials, your exposure and your placing conditions, then proven by trial batch before it goes...
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Schmidt Hammer Test
The fastest way to compare concrete across a structure.
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Reinforcement Bar Scanning
Find the steel before you cut, drill or core, and check that the cover protecting it is what the drawing said it would...
Read moreNeed concrete testing on your project?
Send us the location, the structure and your programme. You get a scoped quotation with the standard, the number of tests and the turnaround written into it.