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ASTM C42/C42M is the standard test method for obtaining, preparing and testing cores drilled from hardened concrete, with recommendations for sawed beams in an appendix. Labs use it when the strength of in-place concrete is in doubt, for example after low test results or signs of distress, or when strength data are needed on an older structure. The current edition on the ASTM store is C42/C42M-20.
Short answer
ASTM C42 tells a testing laboratory how to take a core out of a concrete element, prepare it and test it for length, compressive strength or splitting tensile strength. It does not decide whether the concrete passes. That decision belongs to the “specifier of the tests”, defined in the standard as the individual responsible for reviewing and accepting core results.
Definition and scope
The full title is “Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete”. The designation C42/C42M indicates that one document carries both inch-pound (C42) and SI (C42M) units. The method sits with ASTM Committee C09 on Concrete and Concrete Aggregates (subcommittee C09.61) and is published in the Book of Standards volume 04.02.
The scope covers three things:
- Obtaining, preparing and testing drilled cores from concrete, for length, compressive strength or splitting tensile strength.
- Exclusions: the method is not applicable to cores from shotcrete. ASTM C1604/C1604M covers obtaining, preparing and testing cores from shotcrete.
- Sawed beams: an appendix (Appendix X1) gives recommendations for obtaining and testing sawed beams for flexural performance.
How it is used in practice
According to the standard’s significance statement, test specimens are generally obtained when doubt exists about the quality of the in-place concrete, either because of low strength test results during construction or because of signs of distress in the structure. Another use is to provide strength information on older structures.
The standard names several factors that a lab and the person reviewing results should plan around before any core is cut:
- Location in the element. Concrete at the bottom of a structural element tends to be stronger than concrete at the top.
- Core orientation. Strength tends to be lower when measured parallel to the horizontal plane of the concrete as placed.
- Moisture. Core strength is affected by the amount and distribution of moisture at the time of test. No standard procedure guarantees a specimen matches the moisture condition of the concrete in the structure, so the method’s moisture conditioning procedures aim to give reproducible conditions and reduce within-laboratory and between-laboratory variation.
- Length-diameter ratio (L/D). The apparent compressive strength measured on a core is affected by its L/D ratio as tested, so this has to be handled when preparing cores and evaluating results.
How C42 hands off to other standards
C42 is a sampling-and-preparation method with an appendix, so it points elsewhere for neighbouring jobs. The table below shows where each job sits, based on the ASTM store text for C42/C42M-20 and a testing laboratory’s service description.
| Situation | What applies | Source |
|---|---|---|
| Cores drilled from hardened concrete | ASTM C42/C42M | ASTM store, scope 1.1 |
| Cores from shotcrete | ASTM C1604/C1604M, not C42 | ASTM store, Note 1 |
| Sawed beams for flexural performance | Recommendations in C42 Appendix X1 | ASTM store, Note 2 |
| Compressive strength of the prepared core | Geocomp describes core compressive strength as determined by ASTM C39 | Geocomp service page |
Edition status
| Edition | Status on the ASTM store (checked 2026-10-29) |
|---|---|
| C42/C42M-20 | Active; last updated May 5, 2020 |
| C42/C42M-18a | Labelled “Standard Historical” |
When a specification or lab report cites a C42 edition, check it against this status. A report that cites a historical edition is citing a method that ASTM no longer lists as current.
Where it matters for testing laboratories
Concrete coring is a materials-testing job rather than a clinical one, but the same discipline applies as in any lab: the written method, the sample, the conditioning and the acceptance rule must all be settled before testing begins. C42 puts the acceptance rule outside the test method itself. In the absence of core strength requirements in an applicable building code or contractual or legal documents, the specifier of tests should establish acceptance criteria in the project specifications.
As an example, the standard cites ACI 318 criteria for investigating low strength results from standard-cured cylinders: the concrete represented by the cores is considered structurally adequate if the average strength of three cores is at least 85% of the specified strength and no single core is below 75%. Under ACI 318-14 the specifier of the tests for such an investigation is the licensed design professional or building official. Treat these as an illustration the standard gives, not as a universal pass mark.
A pre-coring checklist built from the standard’s own statements
- Is there a documented reason for coring, such as low strength results, signs of distress or an older structure?
- Is the property needed length, compressive strength, splitting tensile strength or, for beams, flexural performance?
- Have core locations and orientation been chosen with the position and horizontal-plane effects in mind?
- Has a moisture conditioning approach been set, and is it the one the method specifies?
- Who is the specifier of the tests, and where are the acceptance criteria written down?
- Is the material hardened concrete rather than shotcrete?
- Which edition is cited, and is it the active one?
Laboratories that run standard test methods usually operate under written procedures and calibrated equipment. For background see standard operating procedure (SOP), what calibration is and how to read an ISO 17025 calibration certificate.
Common misunderstandings
“A core result is the same as the cylinder result”
The standard says the measured compressive strength of a core will generally be less than that of a corresponding properly molded and cured standard cylinder tested at the same age. For a given concrete there is no unique relationship between the two. Factors include the strength level of the concrete, in-place temperature and moisture histories, degree of consolidation, batch-to-batch variability, strength-gain characteristics, the condition of the coring apparatus and the care used in removing cores.
“C42 sets the pass/fail threshold”
It does not. Acceptance criteria come from the building code, contract documents or project specifications, and ACI 318 appears in C42 only as an example.
“C42 covers shotcrete cores”
It does not. Shotcrete cores fall under C1604/C1604M.
FAQ
What is ASTM C42 used for?
Obtaining, preparing and testing drilled concrete cores for length, compressive strength or splitting tensile strength, with appendix recommendations for sawed beams tested for flexural performance.
What is the current edition of ASTM C42?
C42/C42M-20 is listed as Active on the ASTM store as of 2026-10-29. C42/C42M-18a is listed as Historical.
Does ASTM C42 apply to shotcrete?
No. ASTM C1604/C1604M covers cores from shotcrete.
Who decides whether core results are acceptable?
The specifier of the tests, working from the building code, contract documents or project specifications.
Sources
- ASTM International, C42/C42M-20, Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete, store page with scope and significance text, checked 2026-10-29.
- ASTM International, C42/C42M-18a, store page showing Historical status, checked 2026-10-29.
- Geocomp, testing service description for drilled cores and sawed beams, checked 2026-10-29.
