On April 17, 2020, the State of California Department of Transportation released their revised standard specifications (RSS) to the 2018 Standard Specifications. In this blog, we will talk about additions to Section 40 that now require an earlier age testing in the laboratory mix design study and compressive cylinders to be prepared during this study.
In the previous 2018 Standard Specification Section 40-1.01C(4) Mix Design 2nd paragraph, it states:
At least 15 days before starting field qualification, submit the proposed concrete mix proportions, the corresponding mix identifications, and laboratory test reports, including measurements of the modulus of rupture, for each trial mixture at 10, 21, 28, and 42 days.
The purpose of the mix design study was to allow the contractor, not the State, to find the most efficient cementitious content for the needs of the project. The study is a laboratory three-point water/cementitious ratio (w/c ratio) curve, with the high point (0.50) at 505 pounds, a middle point (0.45) at 590 pounds and the low point (0.38) at 675 pounds. If an aggregate source has not been used previously and has no flexural strength history, the mix design study provides assurance to the State that the cementitious content chosen by the contractor will comply to the project requirements.
The new 2018 RSS Section 40-1.01C(4) 2nd paragraph now specifies:
At least 15 days before starting field qualification, submit the proposed concrete mix proportions, the corresponding mix identifications, and laboratory test reports, including measurements of the modulus of rupture and compressive strength, for each trial mixture at 3, 7, 10, 21, 28, and 42 days.
Caltrans has now updated this section to provide early opening age after removing from the specification the 10-day minimum requirement. It now only specifies a minimum of 550 psi in order to open to traffic. This now can be achieved without using Section 40-5 Rapid Setting paving specification by using the new 2nd paragraph in section 40-1.01C(4). It now has the addition to the w/c ratio curve, a 3-day and 7-day flexural test to provide early age data for opening traffic as per the contractor schedule.
In addition to the 3 and 7-day testing, the new 2018 RSS also specifies to have compressive strength data at the same age. These cylinders are part of a research process Caltrans is reviewing to possibly correlate the beams to cylinders, like a K factor similar to what is required on Harbor/Port projects. This is where they test beams and cylinders concurrently and create a K factor correlation to represent the flexural to compressive. With this K factor established, they proceed with a minimum compressive strength requirement to represent the in-place flexural strength. This research will take some time but is a very positive step towards what is being specified nationwide.
The changes to 2018 RSS Section 40-1.01C(4) 2nd paragraph are to help the contractor to open traffic earlier than 10 days and provide the engineer data without going to the rapid setting specification. It also provides for the future use of compressive strength for acceptance instead of flexural beams.
G3 Quality, Inc. is here to provide any further information you may need and how to implement on your current or upcoming projects. The next blog will talk about Section 40-1.01C(4) for acceptance testing by Quality Assurance. For more information, reach out to our Technical Services Director, Marc Robert by email at mrobert@g3quality.com or by phone at 562.321.5561.
At G3 Quality, we are industry leaders who are always embracing change and excellence. Research and strategy are at the forefront of our operation. Our services include quality management, materials testing and inspection, geotechnical engineering, pavement design, and materials designs on infrastructure projects in California. To learn more about how G3 Quality can contribute knowledge, expertise, consulting, and professional services to your project, contact us.