AASHTO R 70M/R 70-2023
Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete

Standard No.

AASHTO R 70M/R 70-2023

Release Date

2023

Published By

American Association of State Highway and Transportation Officials  US  /  AASHTO

Latest

AASHTO R 70M/R 70-2023

Introduction

In-Depth Technical Analysis of Standard Practices

Standard Practice R 70M/R 70-231, published by the American Association of State Highway and Transportation Officials (AASHTO), provides comprehensive equipment specifications for determining the length change of hardened cementitious materials. This standard maintains technical consistency with ASTM C490/C490M-21 and reflects internationally recognized test method requirements.

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Analysis of Equipment Technical Requirements

Mold System Specifications

The standard specifies mold design requirements for two unit systems: the SI unit mold provides a 25×25×285mm prism with a 250mm gauge length; the imperial unit mold provides a 1×1×11¼-inch prism with a 10-inch gauge length. In the event of dispute, the test results for the 250mm (10-inch) gauge length will prevail.

Parameter type	SI unit requirements	English unit requirements	Tolerance range
Gage length	250.0 mm	10.00 in	±2.5 mm / ±0.10 in
Measuring rod embedment depth	17.5 mm	0.625 in	±0.5 mm / ±0.025 in
Mold size A	User specified	User specified	±0.7 mm / ±0.03 As a core measuring instrument, the length comparator has extremely stringent accuracy requirements: SI units must have a reading accuracy of 0.002mm, with an accuracy of ±0.002mm within a range of 0.020mm; Imperial units must have a reading accuracy of 0.0001inch, with an accuracy of ±0.0001inch within a range of 0.0010inch. Material and Process Specifications: Measuring Rod Material Selection. The standard recommends using AISI 316 stainless steel or a corrosion-resistant metal of similar hardness for the measuring rod. When testing with large temperature fluctuations, use Invar or a similar metal with a low thermal expansion coefficient to avoid measurement errors caused by temperature effects. Reference Rod Technical Requirements The reference rod must be made of alloy steel with a coefficient of thermal expansion not exceeding 2×10⁻⁶/°C. Both ends of the reference rod must be equipped with heat-treated, hardened, and polished contact tips with a diameter of 6±0.25mm. The central 100mm length must be covered with rubber tubing at least 3mm thick to reduce the effects of temperature fluctuations. Standardized Test Procedures Mold Preparation Process Before testing, seal the mold's external seams and the base contact line to prevent moisture loss from the newly molded specimen. After lightly coating the inner surface with mineral oil, install the measuring rod and ensure that it is clean and free of oil, grease, and foreign matter. Reference Rod Usage Specifications For each reading, the reference rod must be placed in the comparator in the same orientation and rotated slowly at least one full revolution while taking the measurement. When the ambient temperature differs by more than ±1.0°C from the last time the comparator was used, calibration must be performed using a reference rod. Test conditions Reference rod usage requirements Reading and recording specifications Temperature control Routine test Use at the beginning and end of half a day Record minimum reading ±1.0℃ temperature difference requirement Dispute test Use before and after each reading Record reference rod readings twice Strict temperature monitoring High precision test Calibrate before each sample reading Average value when the difference is greater than 0.010mm Constant temperature environment Length change calculation method Calculation formula standardization The length change calculation formula specified in the standard is: L = (Lx - Li)/G × 100, where Lx is the difference between the specimen reading and the reference rod reading during testing, Li is the difference between the initial reading and the reference rod reading, and G is the gauge length (250 mm or 10 inches). Calculated results are accurate to 0.001%, and reported averages are accurate to 0.01%. Measurement Accuracy Control To ensure measurement accuracy, the standard requires that mold dimensions, projected lengths of measuring rods, length comparators, and measuring equipment be inspected and documented every 2.5 years to ensure continued compliance with the standard. Environmental Condition Control Requirements Under laboratory testing conditions, the temperature of all mixing rooms, curing rooms, water tanks, equipment, and raw materials, as well as the humidity in the mixing or curing rooms, must be maintained in accordance with M 201 and monitored using thermometers that comply with the requirements of M 339M/M 339. The control accuracy of the time interval and test age must be within ±2%. Technological Evolution and Standard Value Standard Development History This standard practice was first published in 2016 as M 210M/M 210, with technical revisions completed in 2023. Its technical coordination with ASTM C490/C490M-21 reflects the collaborative efforts of international standardization organizations and promotes global harmonization of test methods. Engineering Application Value Through standardized equipment specifications and usage procedures, the comparability of test results from different laboratories and at different time points is ensured, providing a reliable technical foundation for shrinkage performance research, durability assessment, and engineering quality control of cementitious materials. Accurate shrinkage deformation data is particularly important for structural design and long-term performance prediction in large-scale infrastructure projects. Implementation Recommendations and Precautions Equipment Selection Recommendations When selecting a length comparator, a horizontal design should be preferred, especially when the cross-sectional area of the prism is greater than 58 cm² (9 square inches). The equipment should have a measuring range of at least 8.0 mm (0.3 inches) to accommodate the actual length variations of different specimens. Operational Quality Control During testing, special attention should be paid to the cleanliness and maintenance of the measuring rod to avoid wear on the tip of the reference rod caused by frequent use. When the readings of the reference rod differ by more than 0.010 mm, the average of the starting and ending readings should be used for calculation to ensure measurement accuracy. Temperature Effect Control Because temperature changes can significantly affect measurement results, it is recommended that the test be performed in a constant temperature laboratory environment and that ambient temperature changes be strictly monitored. The rubber protective cover on the middle of the reference rod should remain intact to minimize temperature effects during operation. AASHTO R 70M/R 70-2023 history 2023 AASHTO R 70M/R 70-2023 Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete Standard and Specification AASHTO R 70M/R 70-2018 Paste, Mortar, and Concrete R 70-2016 Paste@ Mortar@ and Concrete R 70M/R 70-2018 Paste@ Mortar@ and Concrete ASTM C490-04 Paste, Mortar, and Concrete ASTM C490-00a Paste, Mortar, and Concrete ASTM C490-07 Paste, Mortar, and Concrete M 210-2011 Cement Paste@ Mortar@ and Concrete M 210-2012 Cement Paste@ Mortar@ and Concrete M 210-2009 Cement Paste@ Mortar@ and Concrete Copyright ©2026 All Rights Reserved Update: Mon, 09 Mar 2026 09:11:46 +0000