ASTM C157/C157M Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete

Get Certified ASTM C157 Testing for Reliable Concrete Length Change Data 

Concrete and mortar mixtures may shrink and expand due to drying, internal reactions, and curing, compromising a structure’s integrity long after construction. ASTM C157 provides engineers with direct insight into the behavior of a mixture design, rather than making assumptions, and supplements standard concrete material testing necessary for construction material evaluation. Engineers use ASTM C157 data to compare different mixture designs, examine new materials, and develop products with modified mixing or curing specifications.

• Material type: Hardened hydraulic-cement mortar and concrete fabricated as laboratory specimens.
• Purpose: Determination of length changes in mortar and concrete under specified curing and storage conditions.
• Properties evaluated: Expansion and contraction, including length changes associated with drying and internal reactions.
• Testing method: Measures the length of prismatic specimens at specified intervals using a length comparator and reference bar.
• Results: Results include the percentage change in specimen length relative to the original gauge length at the specified measurement ages.
• Test limitations: ASTM C157 does not measure length changes caused by externally applied forces or temperature changes.
• Use conditions: Technicians expose specimens to the specified moist-curing and air-storage conditions and record measurements at the required intervals.
• Applications: Concrete mixture comparison, dimensional-stability evaluation, quality control, research, and development of mortar and concrete mixtures.

What are the Uses of ASTM C157 Testing? 

ASTM C157 testing helps engineers assess dimensional changes in hardened hydraulic-cement mortar and concrete. Analysts compare measurements collected at different stages to determine how a mixture expands or contracts under the selected curing and storage conditions. This standard-

• Assesses length changes in hardened mortar and concrete.
• Evaluates expansion and contraction behavior.
• Assists in comparing different concrete mixtures.
• Supports cementitious-material research and development.
• Helps engineers evaluate dimensional stability.
• Assists quality-control and material-comparison programs.
• Supports evaluation of selected curing and storage conditions.

Which Materials Can Be Tested Under ASTM C157? 

ASTM C157 applies to hardened hydraulic-cement mortar and concrete specimens fabricated and cured in laboratory conditions. The test method suits cementitious mixtures where dimensional stability, rather than strength or response to applied loads, is the focus. Before testing, a technician casts prism specimens with a gauge stud embedded at each end and demolds them within the timeframe specified for the initial length reading.

Why is ASTM C157 Important? 

ASTM C157 provides a means for engineers to identify dimensional instability of a mortar or concrete mixture prior to construction. Shrinkage or expansion of a mixture that goes unnoticed can cause cracks or distortion to a structure long after it has been constructed and placed into service. ASTM C157 follows a long-term assessment of a specimen’s length change over the curing and drying period, capturing more information than a short-term evaluation and giving engineers a fuller picture than a single early-age measurement would provide.

ASTM C157 Testing Process and Data Collection 

A technician prepares a mortar or concrete prism specimen with a gauge stud at each end and demolds it within the timeframe specified by ASTM C157. The technician measures the length of the specimen with a comparator zeroed to an invar reference bar and stores the specimen under controlled moist-curing conditions before moving to air-curing conditions. The technician remeasures the specimen’s length at defined intervals throughout the curing and drying period. The analyst calculates the length change as a percentage of the original gauge length and records the results alongside the specimen’s mixture and curing details.

Common Challenges and Troubleshooting 

Accurate ASTM C157 results depend on properly embedded gauge studs, a correctly zeroed length comparator, and consistent curing conditions throughout testing. Damaged gauge studs or inconsistent curing temperature and humidity can introduce errors into the length-change readings. Technicians inspect gauge studs before each reading and maintain steady curing conditions to keep the recorded length changes reliable across the full testing period.

• The analyst calculates the percentage change in length of the specimen in comparison to the original gauge length and reports the results in the unit system designated by the standard.
• The report includes the length change values for the different measurement ages, since the shrinkage or expansion of the specimen can vary at different stages of curing.
• The analyst compares length-change results across different mixture designs rather than judging a single mixture against an absolute pass/fail value.
• The report notes the specimen’s curing history alongside the results, since curing conditions directly affect the measured length change.

Link to ASTM C157