AASHTO R 72:16(2020) Standard Practice for Match Curing of Concrete Test Specimens.
This recommended practice covers procedures for making and curing cylindrical concrete specimens at the same temperature as that measured in a concrete member.
The concrete sample used to make the specimens shall be taken from the concrete being placed in the same member where the temperature is to be measured.
This procedure can be deployed with confidence for both air chamber and insulated jacket (Surecure) systems and for both molded cylinders with nominal diameter to height dimensions of 100 by 200 mm (4 by 8 in.) or 150 by 300 mm (6 by 12 in.). However, users should be watchful of Type I error for air chamber systems and Type II error with insulated jacket mold systems. A Type I error represents the situation where loss of temperature control occurs over only a portion of the entire match-cure duration where control is later regained. A Type II error represents the situation where a constant level of temperature control error occurs during the entire match-cure duration.
The values sated in SI units are to be regarded as the standard.
3.1. For definitions of terms used in this practice. refer to ASTM Cl 25.
4. SIGNIFICANCE AND USE
4.1. This method provides a procedure for curing concrete cylinders at the same temperature as that monitored at a specific location in a concrete member. Consequently, the compressive strength of the cylinder more accurately represents the in-place concrete strength of the member. The method is particularly useful for determining the concrete compressive strength at early ages in the fabrication of precast concrete members or for determining the compressive strength of concrete at a critical location in a structural member.
5. APPARATUS —
5.1. The apparatus shall consist of a monitoring and heating system capable of maintaining concrete cylinders at a temperature within ±2°C (±4°F) of the temperature of the concrete at a specific location in the member. A satisfactory system may include a temperature sensor in the member, a controller, special insulated cylinder molds with built-in heating systems, and a temperature sensor in the molds.
5.2. Temperature Sensor in the Member—Temperature sensors shall he placed at the most critical locations for strength development. The purchaser shall determine the critical locations for temperature sensors in each type of member and show the locations on the project drawings or the contractor shall submit drawings showing proposed locations to the purchaser for approval.
5.2.1. Temperature sensor wire shall be durable enough to withstand the wear associated with construction operations and shall have a size of 20 awg or larger in diameter (Note 1). Note 1—In locations where electrical interference may affect the measured data, shielded wire should be used.
5.3. controller—The controller shall be capable of monitoring the temperatures of the member and cylinders and controlling the heating system to maintain the cylinder temperature within +2°C (+4°F) of the temperature measured in the member. Proper operaton of the system shall be verified on a regular basis in accordance with the manufacturer’s recommendations.AASHTO R 72 pdf download.