University of California Berkeley Pavement Research Center

Research

Research at the Pavement Research Center is constantly evolving.

History of the Pavement Research Center

In 1948, the Institute for Transportation Traffic Engineering (the precursor to today's Institute of Transportation Studies) was formed at the University of California Berkeley. Professor Harmer Davis early on recognized the importance of a viable pavement system to California. One of his first activities was to establish a program of instruction and research in pavement-related areas, bringing in several well-known people in the field including Professor Ralph Maoyer, Bernard A. Vallerga, Robert Horonjeff, H. B. Seed, C. L. Monismith.

1954 marked the construction of the Soils and Bituminous Materials Laboratory at the University of California Berkeley Richmond Field Station. C. K. Chan was hired as a Research Engineer to provide continuous professional support to the Soils and Bituminous Materials Laboratory. The faculty, staff, and state-of-the-art laboratory contributed to the growing reputation of the pavement engineering program at the Institute for Transportation Traffic Engineering and Civil Engineering at the University of California Berkeley.

In the late 1980s and early 1990s, the Soils and Bituminous Materials Laboratory provided a research center for the Strategic Highway Research Program (SHRP). SHRP research conducted at the facility led to the development of the repeated simple shear test at constant height (RSST-CH) and associated equipment, as well as the SHRP fatigue testing protocol and associated equipment.

The facility, later renamed the Pavement Research Center to better include the widening scope of research conducted therein, was also a participant in the WesTrack project and conducted laboratory testing of samples from WesTrack for fatigue and rutting properties.

The current primary project at the Pavement Research Center is the CAL/APT program. CAL/APT was begun in 1993 and is now in its seventh year with two Heavy Vehicle Simulators (HVS) operating at the Richmond Field Station and mainline pavement test sections around California. Funding is provided largely by the California Department of Transportation (Caltrans), the Washington State DOT, and other contributing private and public organizations.

(top)

History of the CAL/APT Program

Pavement construction, including maintenance and rehabilitation, requires a significant portion of the California Department of Transportation (Caltrans) budget each year. Caltrans must ensure that the extensive highway system will continue to serve the needs of the state for both passenger and goods transport to maintain the state's economic viability.

Recognizing the potential benefits that could result from an accelerated pavement testing (APT) capability to ensure the viability of these systems through improved design, construction, and maintenance methodologies, Caltrans began serious investigation of full-scale APT in 1989. By 1992, Caltrans engineers had decided to further investigate the Heavy Vehicle Simulator (HVS) developed and used by the Council for Scientific and Industrial Research (CSIR) of South Africa. This decision was supported by the long and productive operation by CSIR of the HVS equipment leading to improved pavement technologies in South Africa. Further, a database had been developed by CSIR with data from more than 400 pavement test sections and validation of HVS predictions by results from in-service pavements.

Before purchasing the equipment and services from CSIR needed to implement an APT program in California, a pilot project termed Phase I was initiated and completed in 1993 which involved Caltrans, the University of California, Berkeley (UCB), Dynatest Consulting, Inc. of Ojai, California, and CSIR, known collectively as the UCB Contract Team. Successful completion of the pilot project provided ample justification for Caltrans to proceed. The current program was approved in February 1994 and began with the purchase of two HVS units from CSIR and the Phase II contract with UCB in June 1994. By June 1995, both HVS units were accepted by Caltrans and the first HVS testing began.

Since June 1994, a fully functional accelerated pavement testing capability has been established at the Pavement Research Center (PRC) of UCB resulting from the successful partnership between Caltrans, UCB, Dynatest, and the CSIR of South Africa. In January 1996, after Phase II of the CAL/APT program had been underway for about 18 months, an assessment was made of the progress and future directions established. These directions, in conjunction with the CAL/APT Strategic Plan (July 1995-July 1997) have served as the basis for the program followed by the PRC to date.

In January 1998, the contract with UCB was modified and the program broadened to include investigations related to concrete pavements; also, responsibility for operation of HVS2 was shifted from Caltrans to the CAL/APT Contract Team. The rapid assimilation and initiation of the concrete pavement research program has demonstrated the ability of the CAL/APT program to respond to the changing needs of Caltrans in a timely manner. The CAL/APT program officially ended on June 30, 2000.

The current research being conducted by the University of California Berkeley Pavement Research Center and its partner agencies falls under the Partnered Pavement Research Center (PPRC) project, as described below.

(top)

Results of the CAL/APT Program

CAL/APT (California Accelerated Pavement Testing) functioned as a client- and product-oriented program, the client being the California Department of Transportation (Caltrans) and ultimately, the traveling public. The critical concerns facing Caltrans are: Quality Control/Quality Assurance (QC/QA) Design structures and methodology Construction practices and specifications Overlay practice and design Long-life pavement rehabilitation In order to address these concerns, the initial phase of the CAL/APT program has included the following investigations:

Fatigue performance of asphalt concrete and its relationship to pavement performance in California

Rutting studies of various mixes under elevated temperatures using the HVS equipped with a super single tire, conventional bias ply and radial tires, and an aircraft tire (a total of 10 tests)

Accelerated loading on overlaid pavements to compare conventional dense-graded asphalt concrete (DGAC) and gap-graded asphalt-rubber hot mix (ARHM-GG) overlay strategies

Comparison of the Caltrans and AASHTO structural pavement design methods and the methodology to mitigate fatigue listed in Item 1

Development of pay factors for asphalt concrete for QC/QA specifications based on the fatigue design and analysis system listed in Item 1

The establishment of the CAL/APT program provided Caltrans with the capability to rapidly test and evaluate new pavement technology and design methodologies and enabled these studies to be completed in a relatively short time. Major findings from the studies, when viewed collectively, have resulted in well-documented recommendations to Caltrans. The results of the CAL/APT program are summarized in Caltrans Accelerated Pavement Test (CAL/APT) Program Summary Report Six Year Period: 1994-2000.(PDF 1.0Mb)

(top)

CAL/APT Work Continued in Partnered Pavement Research Center (PPRC) Plan

The current contract between the University of California Berkeley Pavement Research Center and Caltrans is called the Partnered Pavement Research Center, or PPRC. The new name for the research effort reflects the partnership between Caltrans, The University of California Berkeley Pavement Research Center, Dynatest, the CSIR of South Africa, Washington State DOT, and other state departments of transportation to seek new and innovative pavement technology solutions to address the problems affecting today's pavements. The PPRC project continues the ongoing research from the CAL/APT Program as beginning several new areas of investigation.

(top)

LLPRS-Rigid

CAL/APT began its first field-testing operation near Palmdale, California in summer of 1998. The testing in Palmdale was part of the California Department of Transportation Long Life Pavement Rehabilitation Strategies for rigid pavements (LLPRS-Rigid). The objectives of the LLPRS-Rigid strategies are to provide 30 or more years of service life, to require minimal maintenance, and to have a construction production capability of about 6 lane-kilometers in a weekend construction window. The original proposed strategy for LLPRS is to use high early strength concretes primarily based on calcium sulfoaluminate technology instead of Portland cement, retain current base structures below the existing concrete slabs, remove and replace current 200- to 225-mm thick slabs with new slabs of same thickness, and potentially include design features such as dowels, tied concrete shoulders and wide truck lanes.

The objectives of the research were to evaluate potential LLPRS strategies with respect to structural adequacy of the designs, materials selection, and construction issues. To meet these objectives, the UCB Contract Team, which includes Caltrans, the UCB Pavement Research Center, Dynatest Consulting, Inc., and CSIR, performed mechanistic analyses of the proposed structures, investigation of design parameters, laboratory testing of paving materials, and verification of failure mechanisms and expected performance through Heavy Vehicle Simulator testing in the field. Initial results have been published and can be found on the Publications page. The entire study will be completed in 2001.

One of the focuses of the PPRC project is to investigate new uses for the Paldmale test site, including a dowel bar retrofit project. Installing dowel bars on the failed Palmdale test sections presents an invaluable opportunity to test a pavement rehabilitation effort on a pavement for which the entire history is documented.

(top)

Design and Use of ATPB Under Wet Conditions (HVS Goal 5)

This study extends the results of the Design and Use of ATPB Study. This study includes HVS testing with insertion of surface water into the pavement, laboratory testing, and analysis. The study is also examining the impact of granular base compaction on the performance of pavements under wet conditions. The CSIR database is being examined with the California data to further validate the CAL/APT results. The results of this study should be available in 2001.

(top)

Development of a Pavement Research Database

The production of reports and other research products at the completion of a research goal captures the immediate results of the research. However, data produced from later research goals can be combined with those results to produce better results, or entirely new insights. Ideas may be developed that can be tested against the data and models can be developed from the data that were not included in the original research.

As part of the CAL/APT program, a database of all CAL/APT test data is being created. Partners in the CAL/APT research will be supported in their use of the database.

(top)

Calibration of Mechanistic-Empirical Design Procedures

The mechanistic-empirical design procedures being developed for Caltrans need calibration with field data as well as HVS and laboratory testing and analysis. Laboratory data, field performance data, and data from state Pavement Management System databases will be used to calibrate mechanistic models for key pavement distresses. Laboratory testing will be performed on field specimens using the flexural beam and simple shear equipment for asphalt concrete and asphalt-rubber hot mix, using the concrete compressive strength equipment for concrete and cemented materials, and using the triaxial equipment and other tests for unbound granular and subgrade materials. Deflection data and back-calculated moduli and load transfer efficiencies will be obtained from field sites.

Distresses to be modeled include reflection cracking, fatigue cracking, thermal cracking and rutting of flexible and composite pavements, and cracking (transverse, corner, and longitudinal), faulting, and pumping of rigid pavements.

The modeling approach will use techniques recently developed by the UCB Contract Team for joint estimation using different kinds of performance data such as field, HVS, and laboratory data.

(top)

Rehabilitation Construction Productivity Analysis

One of the primary objectives of the Caltrans Long-Life Pavement Rehabilitation Strategies (LLPRS) is minimization of traffic delays during rehabilitation or reconstruction work. During the CAL/APT project, it was found that quantitative methods for estimating construction duration and the impacts of material types, structural cross-sections, the number of lanes closed to traffic, and contractor resource constraints were not available. Similarly, no method was available to Caltrans traffic planners regarding the estimated duration of reconstruction and rehabilitation projects until the plans were completed and the contractor selected.

With the assistance of concrete and asphalt concrete paving contractors in California, the Pavement Research Center has performed constructability analyses to explore the effects of the following varaiables: rehabilitation materials, design profiles, curing/cooling time, number and capacity of construction resources, type of construction scheduling, and alternative lane closure strategies. Prototype constructability analysis programs have been developed to interactively link all factors. The analysis programs are designed to help road agencies and paving contractors determine which rehabilitation strategies were the most feasible in an urban environment to balance the maximization of production capability and minimization of traffic delay. In addition, sensitivity analyses have been conducted to find which parameters constrain the production capability of the rehabilitation. One case study for each rehabilitation material is included as part of the research for the validation and calibration of the constructability analysis models. The results of the deterministic and stochastic constructability analyses were shown to be consistent with the actual performance of the case study projects.

With research funding from four state departments of transportation (California, Washington, Texas, and Minnesota) the Pavement Research Center has begun to develop a constructability analysis simulation system for pavement rehabilitation due to be completed March 2002.

(top)

New Goals Outlined in the PPRC Plan

Verification of Asphalt Concrete Long-Life Pavement Strategies (HVS Goal 6)

The objective of this study is to evaluate and verify the effectiveness of long-life pavement rehabilitation strategies for damaged pavements that involve asphalt concrete (AC Long Life Strategies). These strategies include Crack, Seat, and Overlay strategies; and full-depth asphalt concrete pavements. Methods to improve these strategies have been developed based on the results from previous CAL/APT research, through and partnership of the AC paving industry, Caltrans, and the UCB Contract Team. The research includes laboratory testing at the Pavement Research Center, HVS tests on sections constructed at the Pavement Research Center, laboratory testing of alternative materials and the impacts of construction quality, structural modeling, analysis, and technology transfer.

(top)

Dowel Bar Retrofitting of Concrete Pavements (HVS Goal 7)

Since the early 1950s, Caltrans rigid pavement practices have relied on non-erodable bases and aggregate interlock at the transverse joints to control transverse joint faulting. At that time, Caltrans stopped using dowels because of problems encountered with dowel alignment during construction, the relatively small benefit obtained from the small dowels used at the time, and the level of traffic at the time.

Currently, Caltrans faulting typically occurs on rigid pavements within several years after construction or reconstruction. Faulting results in a rough ride and can increase noise. Caltrans is moving towards the use of dowels in all new construction and reconstruction. Improved techniques for retrofitting existing concrete pavements have been developed over the past sever years by the Washington State DOT, among others. Dowel bar retrofitting consists of sawing grooves, insertion of dowels across the transverse joints and grouting, followed by grinding to remove the faulting and smooth the grout surface. The joint load transfer provided by the retrofitted dowels significantly slows the development of new faulting under truck loads. The life of dowel bar retrofitting of slabs with longitudinal cracks, and retrofitting of transverse cracks is of interest since many older Caltrans pavements have some form of cracking, but the cracks have not led to widespread failure.

Heavy Vehicle Simulator testing has included sections of old existing concrete pavement that are faulted in order to determine the load transfer restoration of dowel bar retrofit and evaluate the loss of load transfer efficiency under traffic of retrofitted pavements, new doweled and undoweled pavements, and old pavements that have not been retrofitted. It is anticipated that several locations will be used for HVS testing of dowels around the state. The first location has been identified in Ukiah, and testing was conducted at that location between January and May 2001.

(top)

Institute of Transportation Studies Technology Transfer Program

Training of pavement engineering personnel is considered an essential task of the Pavement Research Center. An objective of the Center is to expedite the implementation of research results by providing a link between innovative technology developments and practical engineering applications. The ITS Technology Transfer Program includes among its courses a few programs intended to familiarize paving industry professionals with the latest test methods and test equipment.

(top)