ASTM C31/C31M
Standard Practice for Making and Curing Concrete Test Specimens in the Field
How test cylinders and beams are sampled, molded, protected, and cured on the jobsite before they ever reach the lab.
Who needs it
Field technicians, testing labs, general contractors, and owners who want strength results that will hold up in a dispute.
What the test involves
It covers where in the load the sample is taken, how the concrete is placed and consolidated in the mold, and how the fresh specimens are shielded from sun, wind, freezing, and vibration during the first period after casting. It then separates two purposes: standard-cured specimens, which are used to judge whether the mix met the specification, and field-cured specimens, which are used to estimate the strength of the actual structure under actual site conditions.
Common misconceptions
- Cylinders left on the slab overnight are not standard-cured specimens. Once they experience site temperature and drying, they only represent the structure, not the mix.
- The two cure types are not interchangeable. Using field-cured cylinders to reject a supplier's concrete is a common and costly error.
- Sampling from the very first or very last concrete out of the truck is not representative, which is why the practice specifies where in the discharge to sample.
Official source
We summarize scope and purpose only. The full text belongs to the issuing body — read it at the official source. ASTM International