2020, Asphalt Pavements, California

Caltrans issues formal guidance to address HWTT variability for HMA-A mixes

Caltrans on Friday published long-sought technical guidance to address industry concerns with regard to the Hamburg Wheel Track Test (HWTT) for Hot Mix Asphalt mixes. The Construction Policy Directive (CPD) replaces the AASHTO T324 test reference and HWTT requirements on existing projects with the recently completed CT389 test method and revised acceptance requirements. The CPD can be viewed in its entirety HERE.

The changes address test variability issues that were identified in a 2016 National Cooperative Highway Research Program (NCHRP) study (which can be downloaded HERE), as well as a separate Caltrans study. The Caltrans-industry Pavement & Materials Partnering Committee (PMPC) worked together to identify changes to the sample-preparation procedure in CT125, the AASHTO T324 test method and the Standard Specifications. At the end of 2019, the changes were vetted and implemented.

The changes resulted in the revision of CT125, the creation of a new test method, CT306 for RHMA, and the revision of Section 39 of the Caltrans Standard Specification. The changes are incorporated in the April 2020 Revised Standard Specifications. A previous policy directive, CPD 19-8, addressed the changes on existing projects with Rubberized Hot Mix Asphalt (RHMA). The CPD issued Friday applies to existing projects with conventional HMA.

Discussions on the concerns of variability issues between Caltrans and industry were part of the Pavement and Materials Partnering Committee’s (PMPC) predecessor, the Rock Products Committee (RPC), as far back as 2015. The need for a revision was formalized and a recommendation proposed in a Joint Caltrans-industry report produced by the PMPC’s Asphalt Subtask Group. Caltrans ultimately implemented the recommendations through a CPD for RHMA-G, and the revisions for both RHMA-G and HMA-A were included in the April 2020 Revised Standard Specifications. A CPD for the changes for HMA-A mixes on existing projects was not included, however, and contractors continued to face rejection and large penalties for failed test results for HMA-A mixes into 2020.

As reports of penalties and conflict continued to pile up, CalAPA continued to press Caltrans that the additional formal guidance from the department was necessary.

“I applaud Caltrans for finally doing the correct thing with regard to the HWT test’s high variability SIP (Stripping Inflection Point),” said Pat Imhoff with CalPortland, a PMPC Asphalt Task Group industry represenative. “The HMA Industry has been asking for this CPD to address the SIP for a very long time, so this CPD will provide the relief that should have been available when the SIP became report-only for RHMA.”

“The publishing of this CPD is a good thing for the industry and Caltrans,” added Phil Reader with George Reed Construction, Inc., a PMPC Asphalt Task Group industry representative. “It was good to see Caltrans and industry working together to resolve an issue with a focus on statewide consistency.”

CalAPA Technical Director Brandon Milar, PE., said the input and participation of numerous CalAPA members over several years was essential to bringing the issue to resolution. For more information, contact Milar at (916) 791-5044. More information on the Caltrans-industry Pavement & Materials Partnering Committee can be found HERE.

Article from CalAPA Asphalt Insider.