There is a new section in Section 40 of the 2018 (RSS) October 2021, that will free the contractor from the variability of modulus of rupture (MOR) flexural beams and reduce disputes for early opening to traffic. Section 40-1.03L now gives the contractor an alternative to MOR testing, by following ASTM C1074 concrete maturity method to determine the equivalent compressive strength for opening age.
So, what is involved in the test method for maturity of concrete? Based on Section 40-1.03J, paragraph four, “Do not allow traffic or use equipment on concrete pavement before the concrete has attained a modulus of rupture of 550 psi, or equivalent compressive strength if using maturity per section 40-1.03L, based on your testing unless:” Per this paragraph, if the contractor has the option to use flexural testing, they can now use Section 40-1.03L which references ASTM C1074, “Estimating Concrete Strength by the Concrete Maturity Method.”
From Section 40-1.03L Use Maturity Method
As an alternative to modulus of rupture testing, you can use the maturity method under ASTM C1074 to estimate the equivalent compressive strength for opening to traffic, use of equipment, and for early use of concrete pavement under section 40-1.03K.
Provide, install, and maintain all the concrete maturity testing equipment.
Develop the strength-maturity relationship using:
- Specimens prepared under ASTM C1074
- Datum temperature of 14 degrees F
- Nurse-Saul Method
- Logarithmic best-fit curve with a R2 value of at least 0.90
Develop the strength-maturity relationship in the laboratory when you are designing your mix or in the field during the test strip or first day of production and submit the results to the Engineer. During test strip and production:
- Place a sensor at mid-depth and at 1.5 ft from the edge of pavement at the beginning and at the end of the placement.
- Estimate in-place strength of concrete based on your strength-maturity relationship per ASTM C1074.
- Validate once for test strip and every 15,000 cubic yards or 30 days of concrete production, whichever comes first.
The maturity method is not used to estimate compressive strength for acceptance of concrete pavements.
What Steps does a Contractor have to do to use 40-1.03L
This new section can be accomplished during the mix study phase, 40-1.01C(4), with the designated ages 3, 7, 14, 21, 28 and 42 day MOR flexural beams correlating to the compressive strengths when tested. Two extra beams and two extra cylinders would be fabricated and sensors placed to measure the temperatures of each specimen during the course of the MOR and compressive testing. The temperature is then applied to the Nurse-Saul method of calculating temperature, density to strength during the 42 days period. Once the testing is completed in the concrete laboratory, a curve is developed to be applied when the concrete is placed, and the maturity of the concrete can be measured.
During the test strip or first day of production, sensors are placed in the concrete to measure in 14° increments and will measure the temperature (hydration) progress of the concrete in-place. When it comes to the maturity measurement of a minimum of 3 days or more, readings will be taken from these sensors and applied to the established concrete laboratory curve. If the maturity meets or exceeds the expected correlated strength of compressive strength (compressive strength equivalent to 550 psi), the concrete may be opened to traffic.
If during the mix study phase in the laboratory, the option to use the maturity method was not tested, the contractor can still run the concrete strength-maturity in the field at the time of the test strip or first days production, with the approval of the resident engineer of the project.
This Option Should be Considered by the Contractor
The concrete maturity method now eliminates the need for MOR flexural beams which can be heavily influenced by ambient conditions, drying out the specimen due to lack of protective curing, and improper transportation to the concrete testing lab. This also gives both the contractor and Caltrans more confidence during extremely cold weather, on whether the concrete has truly achieved its strength compared to a 6”x6”x21” specimen.
G3 Quality, Inc. is excited to be a part of this new section, 40-1.03L process on two different projects in the Central and Southern California areas. We will continue to monitor its progress and share lessons learned. We are available to assist on any of your upcoming projects to adapt this new procedure.
Our team is here to provide any further information you may need and how to implement these revisions on your current or upcoming projects. For more information, reach out to our Technical Services Director, Marc Robert by email at firstname.lastname@example.org or by phone at 562.321.5561.
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