ASTM C31/C31M: Concrete Test Specimens in the Field

Standard Practice Overview

• Developed in accordance with international standardization principles by the World Trade Organization's TBT Committee.
• Designation C31/C31M - 19 indicates original adoption year or last revision year.
• Covers procedures for making and curing cylinder and beam specimens from fresh concrete samples.

Sample Collection Protocol

• Concrete must be sampled after all on-site adjustments including mix water and admixtures.
• Inadequate for samples of concrete without measurable slump or requiring different dimensions.

Measurement Units

• Standard values are provided in both SI units and inch-pound units.

Mold Specifications

• Molds should have smooth interior surfaces, and dimensions must maintain right angles and straight lines.
• Maximum variation from nominal cross-section is capped at 3 mm for molds 150 mm in depth.

Terminology Definitions

• Initial curing temperature refers to environmental temperature during the early curing stage, which may differ from concrete temperature.

Equipment Requirements

• Tamping rods should have a diameter as per specifications and extend beyond mold depth by at least 100 mm.
• Internal vibrators must operate at a frequency of at least 150 Hz and have dimensions that meet specific guidelines for mold compatibility.

Significance of Standard Practice

• Establishes standardized methods for making, curing, protecting, and transporting concrete test specimens in the field.
• Provides reliable data for strength testing, mixture adequacy checks, and quality control.

Molds Integrity and Maintenance

• Molds must maintain shape and dimensions; they should be watertight to prevent water leakage.
• Reusable molds should be treated with a non-reactive form release material prior to use.

Finishing and Sampling Equipment

• Recommended finishing tools include handheld floats or trowels for smooth finishing.
• Slump measurement requires specific apparatus to conform to industry standards.

Quality Assurance Measures

• Acceptance testing for concrete strength, mixture adequacy assessment, and ongoing quality control can be performed if specimens are correctly prepared and cured.