AUTHOR: Marc Robert
Technical Services Director
G3 Quality, Inc.
The Industry and State of California Department of Transportation (Caltrans) is excited to roll out a new version of California Test Method (CTM) 523, the “Method of Test for Flexural Strength of Concrete.”
Effective April of 2020, the new Revised Standard Specifications (RSS) will refer the CTM 523 to now use ASTM C31, Standard Practice for Making and Curing Concrete Test Specimens in the Field and ASTM C78, Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading).
It was decided by the State of California to slowly convert from California test methods to nationally accepted standard test methods, either ASTM or AASHTO, after many years of working with State and Industry partners. In 2019, G3 participated in a formal study through an on-call R&D contract with Caltrans to determine the precision variations between the CTM and ASTM methods. This study provided extensive data and analysis which provided conclusions for consideration and the decision to move forward with the two ASTM methods to replace CTM 523. Below are some of the differences between the methods:
Fabrication of Beams
CTM 523: Must rod, no vibration allowed.
ASTM C31/ASTM C78: Vibration must be used at 0 to 0.5 penetration; greater than 0.5 vibration or rodding is allowed.
CTM 523: Beams must be surrounded by moist sand on all sides. The Top of the beam is covered with curing compound that is used on the project.
ASTM C31/ASTM C78: Beams must be protected from direct heat, cold, or winds. Must be cured in the field at 60 to 80 Degrees Fahrenheit while in the field.
CTM 523: The specimen is “de-molded” but remains on the base plate and is protected from drying out during transportation to the testing lab.
ASTM C31/ASTM C78: The specimen remains in the mold and is protected from drying out during transportation to the testing lab.
CTM 523: Beams are placed in a moist sandpit immediately. The beam is removed from the pit and placed in a water tank 24 hours prior to testing.
ASTM C31/ASTM C78: Beams are placed in a water tank or a moist cure room immediately. Beams that are curing in a moist cure room must be put in a water tank 24 hours prior to testing.
Testing of Beams
CTM 523: Beams are tested on a center point machine; apply a 1.05 correction factor to strength.
ASTM C31/ASTM C78: Beams are tested on a third point loading machine and with no correction factors necessary.
It is estimated this change from the CTM 523 method to ASTM C31/C78 methods will reduce the amount of highly variable results the State has been receiving due to fabricating, initial curing, and final curing of the beams. It is exciting to have the same flexural beam test method as other State and Federal agencies, for it reduces the possible variations of the old method.
If a Resident Engineer or contractor would like to use the new CTM 523 that now references the ASTM methods, they can do so on their current projects through a no-cost change order. Please call your G3 Project Manager or Technical Services Director for further information. We will gladly partner with you on this transition.
To learn more about how we can add value and expertise to your project, contact us.