Written and maintained by CASRAI Editorial Board
Last updated
Short answer
ASTM C31/C31M is the standard practice for making and curing concrete test specimens in the field: it covers how cylinder and beam specimens are made from representative samples of fresh concrete on a construction project and how they are cured before testing. It is a sampling-and-curing practice, not the strength test itself. “ASTM C31”, “ASTM C 31” and “ASTM C-31” all point to the same document.
What ASTM C31 covers (definition and scope)
ASTM International publishes the practice as “Standard Practice for Making and Curing Concrete Test Specimens in the Field” under Committee C09 on Concrete and Concrete Aggregates (subcommittee C09.61). Its scope clause says it covers procedures for making and curing cylinder and beam specimens from representative samples of fresh concrete for a construction project.
Three scope conditions matter to anyone receiving specimens:
- Sampling point. The concrete is sampled after all on-site adjustments to the mixture proportions, including added mix water and admixtures.
- Measurable slump. The practice is not satisfactory for concrete that has no measurable slump.
- Specimen shapes. It is not satisfactory where other sizes or shapes of specimen are required. It addresses cylinders and beams.
ASTM C 31 vs C-31 vs C31M
The spellings are the same standard written three ways. The “M” in C31/C31M marks the metric (SI) form: the document states that values in SI units or inch-pound units are each regarded separately as standard, that the two systems may not be exact equivalents, and that combining values from the two systems may result in non-conformance with the standard. In practice a lab should report one system consistently and not mix them within a record.
Standard-cured vs field-cured specimens
The practice distinguishes two curing routes, and the standard itself states what the resulting strength data can be used for. This is the decision logic that most summaries skip.
| Curing route | Uses of the test data named in ASTM C31/C31M (section 4) |
|---|---|
| Standard-cured | Acceptance testing for specified strength; checking the adequacy of mixture proportions for strength; quality control |
| Field-cured | Determining whether a structure is capable of being put in service; comparison with standard-cured results or in-place test methods; judging the adequacy of curing and protection of the concrete in the structure; form or shoring removal time requirements |
The practical reading: standard-cured specimens answer “does the delivered mixture meet the specified strength?”, while field-cured specimens answer questions about the concrete as it sits in the structure. A set labelled with the wrong curing route cannot answer the question it was cast to answer.
What a lab should receive with specimens
The full standard is a purchased document, so a lab should work from its own licensed copy for procedure details. A published training summary of the practice (SICerts) lists the report items as specimen identification, location, date and time, who molded the specimens, slump, air content, concrete temperature and curing method. The list below is an intake checklist based on that summary and a lab’s own SOP, not the standard’s wording:
- Unique specimen and set identification that matches the field paperwork (see specimen labeling error prevention).
- Curing route recorded: standard-cured or field-cured.
- Fresh-concrete data recorded by the person who molded the specimens (slump, air content, temperature).
- A single unit system on every record, consistent with the SI/inch-pound rule above.
Written procedures for these checks belong in a controlled document; see standard operating procedure (SOP).
What ASTM C31 does not cover
Use this as a scope-boundary check before accepting work under C31. Items one to three come from the ASTM scope clause; items four and five come from the DIN Media listing of the 2026 edition.
- Concrete without measurable slump.
- Specimens of other sizes or shapes than cylinders and beams.
- Concrete sampled before on-site mixture adjustments.
- Lightweight insulating concrete and controlled low-strength material (CLSM), to which the practice is stated not to apply.
- Ultra-high-performance concrete (UHPC) without modification: the practice requires modifications for UHPC, and the listing refers to ASTM C1856/C1856M for making and curing UHPC specimens.
Where it matters for labs and quality systems
Because the results of strength testing depend on how specimens were made and cured, a testing laboratory’s records have to show which curing route applied and who handled the specimens. Laboratories that hold accreditation will also need their measuring equipment under a calibration programme; see what is calibration and reading ISO 17025 calibration certificates. Accreditation bodies such as A2LA assess laboratories against such requirements.
Common misunderstandings
- “C31 is the compressive strength test.” It is not. C31 governs making and curing the specimens; the strength test is a separate practice.
- “C31 and C31M are two standards.” They are one document with SI and inch-pound values, each regarded as standard independently.
- “Any cylinder cast on site counts.” The scope ties the practice to representative samples taken after on-site adjustments, for concrete with measurable slump.
- “Field-cured and standard-cured results are interchangeable.” The standard assigns them different purposes, as the table shows.
FAQ
What is ASTM C31?
It is ASTM’s practice for making and curing concrete test specimens (cylinders and beams) in the field from representative samples of fresh concrete.
Is ASTM C 31 the same as ASTM C-31?
Yes. Both are alternative spellings of ASTM C31/C31M.
Which edition applies?
The practice is revised periodically. The scope and section 4 wording summarised here follows the C31/C31M-15 edition published by ASTM. Check ASTM for the edition your contract or specification cites.
Sources
- ASTM International, C31/C31M-15 abstract (scope, sections 1.1 to 1.3, 4.2 and 4.3): https://store.astm.org/c0031_c0031m-15.html, checked 2026-10-29.
- DIN Media listing of ASTM C 31/C 31M:2026 (exclusions): https://www.dinmedia.de/en/standard/astm-c-31-c-31m/399203887, checked 2026-10-29.
- SI Certs training summary (report items): https://www.sicerts.com/aci/making-curing-concrete-test-specimens, checked 2026-10-29.
