26.5.3 Curing Concrete
(a) If supplementary tests of field-cured specimens are required to verify adequacy of curing and protection, the number and size of test specimens and the frequency of these supplementary tests.
(a) Concrete, other than high-early-strength, shall be maintained at a temperature of at least 50°F and in a moist condition for at least the first 7 days after placement, except if accelerated curing is used.
(b) High-early-strength concrete shall be maintained at a temperature of at least 50°F and in a moist condition for at least the first 3 days after placement, except if accelerated curing is used.
(c) Accelerated curing to accelerate strength gain and reduce time of curing is permitted using high-pressure steam, steam at atmospheric pressure, heat and moisture, or other process acceptable to the licensed design professional. If accelerated curing is used, (1) and (2) shall apply:
(d) If required by the building official or licensed design professional, results of tests of cylinders made and cured in accordance with (1) and (2) shall be provided in addition to results of standard-cured cylinder strength tests.
(1) At least two 6 × 12 in. or at least three 4 × 8 in. field-cured cylinders shall be molded at the same time and from the same samples as standard-cured cylinders;
(2) Field-cured cylinders shall be cured in accordance with the field curing procedure of ASTM C31 and tested in accordance with ASTM C39.
(e) Procedures for protecting and curing concrete shall be considered adequate if (1) or (2) are satisfied:
(1) Average strength of field-cured cylinders at test age designated for determination of fc' is equal to or at least 85 percent of that of companion standard-cured cylinders.
(2) Average strength of field-cured cylinders at test age exceeds fc' by more than 500 psi.