Size of test cylinder

Q. We want to specify the use of 4 x 8 in. (100 x 200 mm) instead of 6 x 12 in (150 x 300 mm) cylinders for evaluation and acceptance of structural concrete. Do the ACI Building Code requirements permit this?

A. Section 26.12.3.1 of ACI 318-19 allows the use of 4 x 8 in. (100 x 200 mm) or 6 x 12 in. (150 x 300 mm) cylinders for strength tests provided that the requirements of ASTM C31 are met. ASTM C31 requires the cylinder diameter to be 3 times the nominal maximum size of the coarse aggregate. The nominal maximum size of an aggregate is the smallest sieve opening through which the entire amount of aggregate is permitted to pass. Hence, a 4 x 8 in. (100 x 200 mm) can be specified if no aggregate used for making the concrete cylinder is retained on a 1¼ in. (31.5 mm) sieve.

Note that sections 26.5.3.2 and 26.12.1.1 of ACI 318-19, ACI 301-20 “Specifications for Concrete Construction”, and ACI 311.6-18 “Specification for Testing Ready Mixed Concrete” require concrete strength tests for acceptance to be the average of at least three 4 x 8 in. (100 x 200 mm) cylinders as opposed to at least two 6 x 12 in. (150 x 300 mm) cylinders.

For high-strength concrete, ACI Committee 363 recommends using 4 x 8 in. (100 x 200 mm) cylinders for testing strength and 6 x 12 in. (150 x 300 mm) cylinders for testing modulus of elasticity. Using 4 x 8 in. (100 x 200 mm) cylinders is acceptable for testing modulus of elasticity per ASTM C469, but is not acceptable for testing the dynamic modulus of elasticity per ASTM C215. ACI Committee 363 also recommends that at least three cylinders be used for testing high strength concrete regardless of the size of cylinders.

References: ACI 301-20; ACI 311.6-18; ACI 318-19; ACI 363R-10; ACI 363.2R-11; ASTM C31; ASTM C39; ASTM C215; ASTM C469

Topics in Concrete: 318 Building Code; High Performance Concrete; Quality Assurance; Testing of Concrete