ASTM C31 Standard Practice for Making and Curing Concrete Test Specimens in the Field
What is ASTM C31?
ASTM C31 is a standard practice for making and curing concrete test specimens in the field. It covers preparing cylinder and beam specimens from representative samples of freshly mixed concrete used on a construction project. The practice sets requirements for specimen preparation and consolidation, initial curing, transportation, and subsequent curing under standard or field conditions. ASTM C31 (Standard Practice for Making and Curing Concrete Test Specimens in the Field) helps technicians produce consistent concrete specimens for subsequent strength testing. Applications of standard-cured specimens include acceptance testing, mixture-proportion evaluation, and quality control, while applications of field-cured specimens include estimating the strength of in-place concrete and evaluating curing and protection conditions.
Get Certified ASTM C31 for Reliable Concrete Specimen Evaluation
ASTM C31 is a method for field preparation and curing representative concrete cylinders and concrete beams in a controlled manner. Technicians take representative fresh concrete, make appropriate molds, pour and compact the concrete, smooth the ends and edges, and cover and initially cure the specimens. Specimens are then cured in the standard way or field cured before strength testing as appropriate for the application. Reliable results require accurate sampling, correct specimen preparation, appropriate consolidation, proper curing, proper identification, and careful transportation. Laboratories should also use the applicable ASTM test method when determining compressive or flexural strength.
What is the scope of ASTM C31?
ASTM C31 establishes procedures for making and curing cylinder and beam specimens from representative samples of fresh concrete for construction projects. The practice addresses both standard-cured and field-cured specimens and also includes requirements for transporting specimens to the laboratory.
Limitations: The practice does not apply to concrete with measurable slump or to concrete of other sizes or shapes.
Excluded materials: Lightweight insulating concrete or controlled low-strength material (CLSM).
What are the uses of ASTM C31?
ASTM C31 test methods enable laboratories and construction parties to make consistent, standardized concrete samples for subsequent strength testing. Standard-cured specimens can support acceptance testing for specified concrete strength, evaluation of mixture proportions, and quality control. This standard-
Supports concrete strength acceptance testing.
Helps evaluate the adequacy of concrete mixture proportions.
Supports construction quality-control programs.
Provides specimens for compressive-strength testing.
Supplies beam specimens for relevant flexural-strength testing.
Helps estimate in-place concrete strength using field-cured specimens.
Provides evaluation of curing and protection conditions.
Supports comparison of the results of field-cured and standard-cured specimens.
Supports decisions related to form or shoring removal.
Provides information useful for post-tensioning applications.
Which Materials Can Be Used Under ASTM C31?
ASTM C31 is used for freshly mixed concrete in construction work when the slump of the concrete is measurable and formed into cylinders or beams that are described in the practice. The procedure is specified for conventional concrete mixtures, including representative samples from the field, and for preparing the specimens. The practice does not apply to lightweight insulating concrete or controlled low-strength material.
Why is ASTM C31 important?
Concrete strength depends on the type of concrete mix and the method of sampling, molding, consolidation, curing, transporting, and testing. ASTM C31 includes common procedures for obtaining samples in the field to ensure that test specimens more closely reflect the concrete placed on the project. Standard-cured specimens provide a controlled basis for specified-strength acceptance and quality control.
ASTM C31 Equipment and Sample Preparation Guide
ASTM C31 provides molds, consolidation equipment, finishing equipment, and curing and transportation equipment suitable for the specimen type and curing conditions. Technical staff should verify that molds are clean, stable, and suitable to produce the required specimens.
Representative samples of freshly mixed concrete collected for a construction project. The practice covers molded cylinder and beam specimens prepared from representative fresh-concrete samples.
Sample Preparation
Technicians obtain representative concrete samples using the applicable sampling procedure and prepare the specimens promptly. The concrete should represent the mixture being placed, including applicable on-site adjustments made before sampling.
Specimen Dimension
Cylindrical specimens typically measure 150 × 300 mm (6 × 12 in.) or 100 × 200 mm (4 × 8 in.), maintaining a 1:2 diameter-to-length ratio. Beam specimens typically have a 150 × 150 mm (6 × 6 in.) cross-section, with length based on the required testing configuration and aggregate size.
Instrumentation
Suitable molds, tamping rods or internal vibrators, mallets, placing and finishing tools, stable molding surfaces, curing equipment, temperature-monitoring equipment, and suitable transportation/protection equipment are used as applicable.
Testing Procedures and Requirements for ASTM C31
ASTM C31 begins with representative sampling of freshly mixed concrete. Technicians then prepare the molds, pour and compact the concrete, smooth and cure the specimens, and protect them during early curing. After demolding, the specimens are either standard or field-cured depending on their purpose. Other reference ASTM documents include C125, C143, C172, C173, C231, C330, C403, C470, C511, C617, C1077, and C1758. The complete procedure for ASTM C31 is summarized below:
Technicians record project, batch, placement, specimen, and other identification information required for traceability and obtain a representative sample of freshly mixed concrete using the applicable sampling procedure.
Fresh Concrete Checks
They perform applicable fresh-concrete measurements, such as slump, temperature, and air content, and prepare clean, rigid molds that comply with the applicable requirements. Place them on a stable and suitable surface.
Concrete Placement
Analysts place the concrete into the molds according to the required procedure for the specimen type and concrete consistency and consolidate the concrete by rodding or internal vibration, as applicable, to produce a properly formed specimen without excessive segregation.
Surface Finishing
They then strike off and finish the specimen surface to obtain the required shape and a suitable testing surface.
Initial Protection and Initial Curing
Skilled personnel protect freshly molded specimens from moisture loss, temperature extremes, vibration, and physical disturbance, maintain specimens under the specified initial-curing conditions, and document relevant environmental or temperature information.
Demolding and Standard Curing
Remove specimens from the molds according to the applicable requirements while avoiding damage, and maintain standard-cured specimens under the specified moisture and temperature conditions until the required testing age.
Field Curing and Transportation
Technicians maintain field-cured specimens under conditions intended to represent the curing and protection of the concrete in the structure and transport specimens carefully to prevent damage, moisture loss, and significant temperature changes.
Specimen Inspection and Strength Testing
They inspect specimens for damage, defects, identification problems, or other conditions that could influence subsequent testing and test the cured cylinders or beams using the applicable ASTM strength-test method.
Data Recording
Technicians record specimen identification, curing condition, test age, relevant concrete information, and strength results.
ASTM C31 Process and Data Collection
The testing process begins with taking representative fresh concrete samples from the construction site. Technicians record, mold, and consolidate the proper cylinders or beams following the specified method. Technicians provide initial protection and curing treatment to the correct specimens. Once cured, specimens are treated according to the desired treatment. Standard-cured specimens are stored under controlled curing conditions, and field-cured specimens are kept in conditions specified to simulate the concrete structure. Analysts then record specimen history and use the applicable strength-test method to obtain the final test result. Important records include project and concrete identification, sampling information, specimen type and identification, fresh-concrete observations and applicable measurements, molding and consolidation information, initial curing conditions, standard- or field-curing condition, transportation information, testing age, strength-test results, deviations, and unusual observations.
ASTM C13 Procedure Using Concrete Pipe
Common Challenges and Troubleshooting
Several factors can affect the reliability of concrete specimen results, including sample representativeness, time between sampling and molding, sample size, consolidation, surface finishing, initial curing, transportation, final curing, sample identification, and further strength testing. Common challenges include non-representative sampling, delayed specimen preparation, improper consolidation, incorrect finishing, inadequate initial protection, incorrect curing, damage during shipping, identification errors, inconsistent procedures, and incorrect interpretation. Technicians should follow the applicable procedure to reduce errors in ASTM testing.
ASTM C31 Analysis Results and Interpretation
ASTM C31 is a standard specification that provides procedures for producing and curing specimens. Specimens are then tested using the appropriate ASTM procedures. The interpretation depends on the specimen type, curing condition, age at testing, and strength-test method.
Laboratories report the specimen type and curing condition, identifying whether the concrete specimen is a cylinder or beam and standard-cured or field-cured.
Technicians record the specimen age and identification, including the project, concrete batch, specimen type, curing condition, and relevant testing information.
Analysts document the specimen preparation and curing conditions, including any significant deviations from the prescribed field procedure that can influence the interpretation of the results.
Engineers and analysts use standard-cured specimens for acceptance testing and quality control, while field-cured specimens provide information for evaluating in-place strength and the effects of field curing and protection conditions.
Laboratories compare applicable strength results and maintain traceability between the reported results, concrete batch, specimen, curing condition, and project requirements.
It covers making and curing concrete cylinder and beam specimens from representative samples of fresh concrete in the field.
What is the difference between standard-cured and field-cured specimens?
Standard-cured specimens are stored under a set of controlled conditions and used for applications such as acceptance testing and quality control. Field-cured specimens are kept under conditions designed to simulate the concrete in the structure and can be used to assess in-place strength and curing conditions.
Can ASTM C31 be used for lightweight insulating concrete?
No, ASTM C31 specifically excludes lightweight insulating concrete. ASTM C495 covers preparation and compressive-strength testing of lightweight insulating concrete.
Does ASTM C31 determine concrete compressive strength?
No, C31 covers making and curing the specimens. The cured specimens are subsequently tested using the applicable strength-test method, such as ASTM C39, for compressive strength of cylindrical concrete specimens.
Why is specimen curing important?
Curing affects concrete strength development and specimen performance. Consistent curing helps ensure that results are interpreted according to the intended purpose of the specimen.
Pawan Kumar Mali is a Material Testing Associate at Matestlab Inc. and holds an Integrated Dual Degree (B. Tech + M. Tech) in Metallurgical Engineering from IIT (BHU), Varanasi. His academic background and research experience are centered on Physical Metallurgy, Materials Research, and Data Analytics, strengthened through academic research and industry experience. Know More
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