In the past 2 years, we have seen more changes to Section 40 than ever before at Caltrans. It has been leading to this most recent 2018 Revised Standard Specifications (RSS) (10/2021) version that will be very beneficial to the construction of high-performance concrete pavements in California. In this blog, we will look at the change in Section 40-1.01C(4) Mix Design.
When the 2018 Standard Specifications came out, Section 40-1.01C(4) required a 3-point water/cementitious (w/c) ratio curve using modulus of rupture (MOR) flexural breaks at 10, 21, 28, and 42 days. Then based on the 3-point flexural strength results, the contractor was able to choose the cementitious content that was most cost-effective, or that would meet the 550 psi at 10 days to open to traffic.
In April of 2020, the 2018 RSS changed the second paragraph to now read “… including measurements of the modulus of rupture and compressive strength, for each trial mixture at 3, 7, 10, 21, 28, and 42 days.” As we blogged in May of 2020, “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.”
Well, it only took 2 years and a great deal of collaboration between CalTrans and industry to move to the next step of specifying concrete cylinders for acceptance of the pavement. The strength correlation needs to be performed in a laboratory to establish the value of flexural to compressive as per Section 40-1.01C(4) with a minor change to one break day, 14 days instead of 10 days.
The next section to follow 3 point w/c ratio curve is 40-1.01D(5) the 3rd paragraph is now replaced with “To determine the minimum content of cementitious materials or the maximum ratio of water to cementitious materials, use the compressive strength equivalent to modulus of rupture values of at least 570 psi for 28 days age and at least 650 psi for 42 days age. Compressive strength must be tested under CT 521.” This now establishes compressive strength concrete for acceptance with the change “modulus of rupture at 28 days” in the table 40-1.01D(8)(a) with:
Compressive strength at 42 days California Test 521 1,000 cu yd
This is the direction both CalTrans and paving contractors have been hoping to achieve to align with other agencies nationwide.
G3 Quality, Inc. 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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