AUTHOR: Marc Robert
Technical Services Director
G3 Quality, Inc.
After many years of the concrete industry and the State of California Department of Transportation (Caltrans) working together, Caltrans has released a solution for Resident Engineers (R.E.) regarding low beams acceptance testing. 
In the past, Section 40 for concrete paving only stated that if the acceptance flexural beams were below 570 psi at 28 days, the concrete would be removed at the expense of the contractor. This would leave the contractor no means to dispute low beam breaks, ultimately leading them to a multitude of attempts to prove the in-place pavement did meet the required strength.
Both the Industry and Caltrans agreed to take on the task of specifying a way to investigate a low acceptance flexural beam result. After much insightful discussion, they have released a new item in Section 40-1.01D(8)(c)(v), Determining Modulus of Rupture from Pavement Cores. This resolution gives the opportunity for a project R.E. to evaluate the in-place strength of the concrete pavement.
The procedure for this investigation is designated to be done during the test strip. If no test strip is performed, then a section of pavement is chosen with the R.E. At this mutually agreed location, the concrete is sampled, and 3 beams are required to be fabricated and tested for flexural psi at 28 days. At 23 days, cores are taken, as per ASTM C42, to be tested at 28 days from the test strip or section of designated pavement corresponding to the material represented by the flexural strength beams.
The beams and core results are then used to develop a K factor to convert the compressive strength to flexural strength. The coring is repeated 5 days prior to the following designated days: 42, 56, 70, and 91. When all dates are converted from the compressive strength of the cores to flexural psi, the contractor can then use this formula during the entirety of the project to estimate the approximate flexural value at 28 days.
When a low beam acceptance test occurs, the contractor can request to have the cores taken in the area in question 5 days prior to 42, 56, 70, or 91 days. The core psi results are then applied to the K factor formula, resulting in an estimate of the 28-day in-place concrete pavement.
G3 Quality, Inc is the first in the State to apply this new method from a designated slab section of OHL Partners design/build project for the OCTA (Orange County Transit Authority) on the 405 Freeway widening. We are excited to partner with OHL partners and Caltrans on this new method and will update its success in the future of its use.
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.