University of California Pavement Research Center

Warm mix asphalt (WMA) is a relatively new technology. It was developed in response to needs for reduced energy consumption and stack emissions during the production of asphalt concrete, improved workability and compaction after long hauls and when using lower placement temperatures, and better working conditions for plant and paving crews. Studies in the United States and Europe indicate that significant reductions in production and placement temperatures, and, potentially, in related emissions are possible. However, concerns exist about how these lower production and placement temperatures could influence asphalt binder aging and, consequently, short- and longterm performance, specifically rutting. The overall objective of this warm mix asphalt study was to determine whether the use of technologies that reduce the production and construction temperatures of asphalt concrete mixes influences performance of the mix. The testing completed in this warm mix asphalt study provided no results to suggest that warm mix technologies should not be used in conventional, gap-graded asphalt rubber, and open-graded friction course mixes in California, provided that standard specified mix design, construction, and performance limits for hot mix asphalt are met. The use of warm mix asphalt has clear benefits when compared to hot mixes. These include significant reductions in, or even elimination of, smoke and odors, lower emissions, improved workability, better working conditions, and better performance on projects with long hauls or where mixes are placed under cool conditions. The slightly higher costs of using warm mix technologies are outweighed by these benefits. Based on the findings of this study, the use of warm mix asphalt technologies in asphalt mixes is encouraged, especially on asphalt rubber projects, projects in urban areas, and on projects with long hauls and/or where mixes are placed under cool conditions. Given that warm mix asphalt may be produced at significantly lower temperatures than hot mix asphalt (with associated lower aggregate heating temperatures), moisture sensitivity, especially on water-based warm mix asphalt technologies, should be closely monitored in mix design and quality control/quality assurance testing.

This document is a compilation of the executive summaries of the four reports developed for this research project. Each of the four individual reports covers a specific aspect of the project, and this report provides an overview of the entire project. For details on each of the tasks in the overall project, readers should access the individual reports.

Warm-mix asphalt (WMA) is a relatively new technology. It was developed in response to needs for reduced energy consumption and stack emissions during the production of asphalt concrete, long hauls, lower placement temperatures, improved workability, and better working conditions for plant and paving crews. Studies in the United States and Europe indicate that significant reductions in production and placement temperatures, and, potentially, in related emissions are possible. However, concerns exist about how these lower production and placement temperatures could influence asphalt binder aging and, consequently, short- and long-term performance, specifically rutting. The overall objective of the warm-mix asphalt study was to determine whether the use of technologies that reduce the production and construction temperatures of asphalt concrete mixes influences performance of the mix. The objective of this part of the study was to identify limitations and benefits of using warm-mix asphalt technologies in rubberized asphalt mixes. The testing completed in this phase of the warm-mix asphalt study provided no results to suggest that warm-mix technologies should not be used in rubberized mixes in California, provided that standard specified mix design, construction, and performance limits for hot-mix asphalt are met. The use of warm-mix asphalt technologies in rubberized asphalt mixes has clear benefits when compared to hot mixes. These include significant reductions in, or even elimination of, smoke and odors, lower emissions, improved workability, better working conditions, and better performance on projects with long hauls or where mixes are placed under cool conditions. The slightly higher costs of using warm-mix technologies are outweighed by these benefits. Based on the findings of this study, the use of warm-mix asphalt technologies in rubberized asphalt mixes is encouraged, especially on projects in urban areas and on those with long hauls and/or where mixes are placed under cool conditions. Given that warm-mix asphalt may be produced at significantly lower temperatures than hot-mix asphalt (with associated lower aggregate heating temperatures), moisture sensitivity, especially on water-based warm-mix asphalt technologies, should be closely monitored in mix-design and quality control/quality assurance testing.

This study evaluates the open-graded friction course (OGFC) mix design proposed by the National Center for Asphalt Technology (NCAT) in order to suggest revisions to California Test 368, Standard Method for Determining Optimum Binder Content (OBC) for Open-Graded Asphalt Concrete. Three asphalt types (PG 64-10, PG 64-28 PM, and asphalt rubber [AR]), three aggregate types (Sacramento, Watsonville, and San Gabriel) and three gradations (coarse, fine, and middle) that comply with Caltrans specifications of binder and the 1/2 in. OGFC gradation and aggregate quality were used in this study. The NCAT approach includes selection of optimum gradation, selection of optimum asphalt binder content, and evaluation of moisture susceptibility using a modified Lottman method in accordance with AASHTO T 283 with one freeze-thaw cycle. It was found that, regardless of binder and aggregate types, the optimum gradation selected per the NCAT approach—usually a coarse gradation with fewer fines—did not guarantee the success of an OGFC mix design. None of the mixes with coarse gradation, fabricated using the optimum asphalt binder content, simultaneously met the criteria for percent air-void content, draindown, and Cantabro loss. The resulting test data also show that binder type is the most significant factor affecting both draindown performance and Cantabro performance. This study proposes a volumetric-based OGFC mix design (1) to provide a better way to determine the initial binder content rather than basing it on the bulk specific gravity of the aggregate blend as suggested by NCAT; (2) to account for asphalt absorption; and (3) to allow direct selection of trial binder contents to prepare specimens for performance testing. Accordingly, an OGFC mix design procedure integrated with volumetric design and performance testing is proposed. A moisture susceptibility test in accordance with AASHTO T 283 is known to have considerable within- and between-variations of test results. Thus, the Hamburg Wheel-Track Device test seems to be a better candidate to evaluate moisture susceptibility. However, further study is required to establish how Hamburg performance results relate to field performance.

This report summarizes a detailed report presenting the first and second year of field and laboratory measurements and statistical analyses and performance estimates for tire/pavement noise, permeability, ride quality, distress development, and friction properties of four types of asphalt pavement surface types used by the California Department of Transportation: open-graded asphalt concrete (OGAC), rubberized open-graded asphalt concrete (RAC-O), rubberized gap-graded asphalt concrete (RAC-G) and dense-graded asphalt concrete (DGAC). Tire/pavement noise was measured using the on-board sound intensity method (OBSI). A factorial experiment was developed and executed that considered these surface types, rainfall, traffic and age, with sections selected in the following age groups: less than one year old, one to four years old, and four to eight years old. A partial factorial was included for another type of open-graded mix, called F-mix. In addition, special sections placed by various Caltrans pilot and research projects were also included in the plan for field monitoring and laboratory testing. The report summarizes the measured performance and presents summary statistics for the results. Statistical analyses were performed, including single-variate regression to identify significant variables, multivariate regression, survival analysis, and principal components regression, depending on the type of data, in order to estimate performance. The performance models were used to estimate the life of the various surface types for the conditions in the experiment. The median noise reduction across the population included in the experiment is approximately 2 dB(A) for OGAC and approximately 3 dB(A) for RAC-O mixes compared to the DGAC mixes for the Standard Reference Test Tire (SRTT), with values converted from the Aquatred tire measurements used in the project. The Aquatred results are slightly different prior to conversion to the SRTT values, indicating slightly less noise benefit from open-graded mixes and less difference between OGAC and RAC-O.

This report summarizes the investigations undertaken by the University of California Pavement Research center between 1998 and 2005 to assess Caltrans strategies for the construction of rigid pavements, specifically jointed plain concrete pavement. The overall objectives of the study are reviewed and the studies undertaken to meet these objectives, namely desktop studies and laboratory and full-scale experiment are discussed. The reports and recommendations from each study are listed, as well as some details on how the recommendations have been implemented.

UCPRC staff attended the 2006 RPA conference in Palm Springs, CA. This document contains brief summaries of the technical papers/presentations given in both the technical and practical portions of the event. Items within specific papers that may be implementable by Caltrans are noted. Suggestions for future research, development, and information dissemination are given.

Moisture damage in asphalt pavements is a complex phenomenon affected by a variety of factors, and has not been fully understood, with major knowledge gaps in three areas: major factors contributing to moisture damage in the field, appropriate laboratory test procedures, and the effectiveness of treatments. Both field and laboratory investigations were performed in this study to provide additional information in these three areas. Statewide condition survey and field sampling were conducted to identify factors contributing to moisture damage, other than aggregate source. Statistical analysis revealed that air-void content, pavement structure, cumulative rainfall, mix type (DGAC versus RAC-G), use of anti-strip additive (lime or liquid), and pavement age significantly affect the extent of moisture damage. Laboratory experiments revealed that high air-void contents not only allow more moisture to enter mixes, but also significantly reduce the fatigue resistance of mixes in wet conditions. Less than optimum binder contents also reduce the moisture resistance of asphalt mixes under repeated loading. The effectiveness of the Hamburg Wheel Tracking Device (HWTD) test to determine moisture sensitivity of asphalt mixes was evaluated by testing both laboratory-fabricated specimens and field cores. It was found that the test can correctly identify the effect of anti-strip additives; its results generally correlate with field performance except that the test may sometimes fail mixes that perform well in the field and, in a very few cases, provide false positive results. A fatigue-based test procedure for evaluating moisture sensitivity was explored in this study based on AASHTO T 321. A test procedure was developed for comparative evaluation of different mixes. Application of the test procedure for use in pavement analysis/design is suggested for expensive projects. The long-term effectiveness of both hydrated lime and liquid anti-strip agents was evaluated by both the tensile strength ratio (TSR) test and the fatigue beam test. Results showed that both types of treatment are effective in preventing moisture damage for up to one year’s continuous moisture conditioning. A database with all field and laboratory results has been prepared for Caltrans.

This report provides a summary of the results of the various studies completed in the Partnered Pavement Research Program (PPRC) during the period 2000–2004. In addition, preliminary findings of investigations, initiated but not yet implemented during this period, are included. The results are based on the combined results of analytical developments, laboratory testing of pavement materials, and HVS tests of full-scale pavement test sections. Summaries of developments in the following areas are included: 1. Asphalt Mixes — Materials and Flexible Pavement Studies. These include studies of mix fatigue, moisture sensitivity, reflection cracking, performance of drained and undrained pavements, and those associated with I-710 freeway rehabilitation. 2. Concrete — Materials and Rigid Pavement Studies. These include: evaluation of long-life rehabilitation strategies, results of the SR-14 (Palmdale), HVS rigid pavement studies, dowel retrofit investigations on US-101 and the SR-14 test pavements, studies of the physical properties of fast-setting hydraulic cement concrete (FSHCC),alkali-silica reaction (ASR) accelerated pavement testing, evaluation of maturity method for concrete flexural strength, and HIPERPAV for early age cracking in plain jointed concrete pavements. Also included are: construction-related activities including pay factors for asphalt mixes and use of CA4PRS; M-E pavement design and rehabilitation; a summary of databases containing the results of the various investigations; deep in-situ recycling (DISR); pavement management-related activities; permanent deformation response of asphalt mixes; and implementation and technology transfer activities during the 2000–2004 period.