Technical Questions

Curing Cylinders for Acceptance Testing

Q. Are standard-cured cylinders allowed for acceptance testing of a concrete slab before it can be put into service (equipment can be installed on it) or should only field-cured specimens be used for that purpose?

A. Compliance requirements for concrete cylinders for strength testing in ACI 318-19 depend on the purpose of the testing. When it comes to strength acceptance testing of concrete (for example, determining the strength at designated ages), per Section 26.12.1.1, test cylinders should be made from the same sample of concrete taken in accordance with ASTM C172 at the point of delivery, handled and standard-cured in accordance with ASTM C31, and tested in accordance with ASTM C39 at 28 days or at test age designated for the specified compressive strength. However, in case of removal of formwork and putting the slab into service based on estimated in-place concrete strength, field-cured cylinders or other procedures should be used for strength testing (Section 26.11.2.1(e)). According to Commentary Section R26.11.2.1(e) of the Code, these testing methods include:

1. Testing of cast-in-place cylinders per ASTM C873 (for slabs with concrete depth between 5 and 12 in. [127 and 305 mm]);
2. Penetration resistance per ASTM C803;
3. Pullout strength per ASTM C900; and
4. Maturity index measurements and correlation per ASTM C1074.

These methods have to be approved by the licensed design professional and, when requested, by the building official. The Code also states that if using procedures (b), (c), and (d), sufficient data is required to demonstrate correlation of measurements on the structure with the compressive strength of molded cylinders or drilled cores. More detailed information on the use of these test methods to evaluate the in-place concrete strength are provided in ACI 228.1R.

Note that ACI 318-19 does not cover slabs-on-ground unless the slab transfers load from other portions of the structure to the soil. The previously listed provisions thus generally apply only to elevated slabs.

Finally, to determine the type of curing required for test cylinders on your project, check the specifications. If requested by the design professional or owner, project specifications may contain more stringent testing requirements than the Code. Also, discuss your concerns with the licensed design professional to come to an agreement on requirements relevant to concrete strength testing before equipment installation.

References: ACI 318-19; ACI 228.1R-19; ASTM C31; ASTM C39; ASTM C172; ASTM C873; ASTM C803; ASTM C900; ASTM C1074

Topics in Concrete: Testing of Concrete; Curing; 318 Building Code