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Open Access Publications from the University of California
Cover page of Effects of Increased Weights of Alternative Fuel Trucks on Pavement and Bridges

Effects of Increased Weights of Alternative Fuel Trucks on Pavement and Bridges


California’s truck fleet composition is shifting to include more natural gas vehicles (NGVs), electric vehicles (EVs), and fuel cell vehicles (FCVs), and it will shift more quickly to meet state greenhouse gas (GHG) emission goals. These alternative fuel trucks (AFTs) may introduce heavier axle loads, which may increase pavement damage and GHG emissions from work to maintain pavements. This project aimed to provide conceptual-level estimates of the effects of vehicle fleet changes on road and bridge infrastructure. Three AFT implementation scenarios were analyzed using typical Calif. state and local pavement structures, and a federal study’s results were used to assess the effects on bridges. This study found that more NGV, EV, and FC trucks are expected among short-haul and medium-duty vehicles than among long-haul vehicles, for which range issues arise with EVs and FCs. But the estimates predicted that by 2050, alternative fuels would power 25–70% of long-haul and 40–95% of short-haul and medium-duty trucks. AFT implementation is expected to be focused in the 11 counties with the greatest freight traffic—primarily urban counties along major freight corridors. Results from the implementation scenarios suggest that introducing heavier AFTs will only result in minimal additional pavement damage, with its extent dependent on the pavement structure and AFT implementation scenario. Although allowing weight increases of up to 2,000 lbs. is unlikely to cause major issues on more modern bridges, the effects of truck concentrations at those new limits on inadequate bridges needs more careful evaluation. The study’s most aggressive market penetration scenario yielded an approximate net reduction in annual well-to-wheel truck propulsion emissions of 1,200–2,700 kT per year of CO2 -e by 2030, and 6,300–34,000 kT by 2050 versus current truck technologies. Negligible effects on GHG emissions from pavement maintenance and rehabilitation resulted from AFT implementation.

Cover page of Development of Performance-Based Specifications for Asphalt Rubber Binder: Interim Report on Phase 1 and Phase 2 Testing

Development of Performance-Based Specifications for Asphalt Rubber Binder: Interim Report on Phase 1 and Phase 2 Testing


In the United States, the Superpave Asphalt Binder Performance Grading (PG) system proposed by the Strategic Highway Research Program (SHRP) is the most common method used to characterize the performance-related properties of unmodified and polymer-modified asphalt binders. Dynamic shear modulus (G*) and phase angle (δ) are the two main binder properties and they are measured using a dynamic shear rheometer (DSR) with parallel plate geometry and either a 1-mm or 2-mm gap between the plates. Since these Superpave parameters were developed for binders that do not contain additives or particulates, the California Department of Transportation (Caltrans) does not use them for asphalt rubber binder specifications. Instead, penetration and viscosity are used as acceptance of quality control; however, these parameters do not necessarily provide a satisfactory link between the measured binder properties and potential performance in the field over a range of operating temperatures. In California, current specifications require that crumb rubber particles used to produce asphalt rubber binder in the “wet process” must be smaller than 2.36 mm (i.e., 100 percent passing the #8 sieve), and typically these particles vary in size between 1 mm and 2 mm. Consequently, when the parallel plate geometry is used to test this type of binder, the larger incompletely digested rubber particles can contact the plates. If this occurs, the rubber particle rheology can potentially dominate the results, which in turn may not be representative of the modified binder as a whole. To address this problem, a potentially more appropriate DSR testing protocol using concentric cylinder geometry was investigated in Phase 1 of this study to explore an alternative means of determining the performance properties of asphalt rubber binders. Phase 2 of the study, documented in this report, continued the investigation into the use of the concentric cylinder geometry and alternate parallel plate geometry with a 3-mm gap. The use of these geometries for intermediate-temperature testing and multiple stress creep recovery testing was also investigated, along with modified procedures for short- and long-term aging in the rolling thin-film oven and pressurized aging vessel, respectively, and specimen preparation procedures for bending beam rheometer (BBR) testing. Limited mix testing was also conducted to relate high- and low-temperature mix performance to the performance grades determined for the binders used in the mixes. The concentric cylinder testing approach to measuring the rheological properties of asphalt rubber binders is considered feasible, and that with its use, the edge effects and trimming issues associated with parallel plate testing can be eliminated. However, the concentric cylinder method requires a longer testing time and a larger binder sample than the parallel plate test method. Initial findings from performance grading and related mix testing indicate that the incompletely digested rubber particles, which have different sensitivities to temperature and applied stress and strain than the asphalt binder, appear to dominate the test results. This will need to be factored into analyses and interpretation of rheology and mix performance test results. The proposed modifications to the short- and long-term aging procedures and to the BBR specimen preparation procedures are considered to be more aligned with the original intent of the tests and will likely reduce the variability between replicate specimens during testing. The results from Phase 2 support the continuation of testing, which should be in line with the original workplan and objectives of this research effort. The research should continue to refine the testing procedures on additional field binder sources, assess the repeatability and reproducibility of any proposed test methods, and evaluate the applicability of the results to the actual performance properties of mixes produced with asphalt rubber binders.

Cover page of Life Cycle Assessment and Life Cycle Cost Analysis for Six Strategies for GHG Reduction in Caltrans Operations

Life Cycle Assessment and Life Cycle Cost Analysis for Six Strategies for GHG Reduction in Caltrans Operations


California state government has established a series of mandated targets for reducing the greenhouse gas (GHG) emissions that contribute to climate change. With a multiplicity of emissions sources and economic sectors, it is clear that no single change the state can make will enable it to achieve the ambitious goals set by executive orders and legislation. Instead, many actors within the state’s economy—including state agencies such as the California Department of Transportation (Caltrans)—must make multiple changes to their own internal operations. The focus of this study and technical memorandum is to examine several strategic options that Caltrans could adopt to lower its GHG emissions in operating the California (CA) state highway network and other transportation assets so it can help meet the state’s GHG reduction goals. Although many GHG reduction strategies appear to be attractive, simple, and effective, most also have limitations, trade-offs, and unintended consequences that cannot be identified without a preliminary identification and examination of the full system they operate in and their full life cycle. To achieve the most rapid and cost-effective changes possible, the costs, times to implement, and difficulty of implementation should also be considered when the alternative strategies are being prioritized. This project first developed an emissions reduction “supply curve” framework by using life cycle assessment (LCA) to evaluate full-system life cycle environmental impacts and life cycle cost analysis (LCCA) to prioritize the alternative GHG-reduction strategies based on benefit and cost. This framework was then applied to an example set of strategies and cases for Caltrans operations. This technical memorandum presents the results of the supply curve framework’s development and its application to six strategies for changing several Caltrans operations identified by the research team. The six strategies were: (1) pavement roughness and maintenance prioritization, (2) energy harvesting using piezoelectric technology, (3) automation of bridge tolling systems, (4) increased use of reclaimed asphalt pavement, (5) alternative fuel technologies for the Caltrans vehicle fleet, and (6) solar and wind energy production on state right-of-ways. A summary of the methodology and the resulting supply curve that includes all the strategies considered and ranked is published in a separate white paper. This technical memorandum provides the details, assumptions, calculation methods, and results of the development of the GHG reduction supply curve for each strategy. Although this current study’s scope is limited to development of a supply curve for GHG emissions only, there are plans to expand the study’s scope to include other environmental impacts and to develop supply curves for them as well.

Cover page of Optimizing Rubberized Open-graded Friction Course (RHMA-O) Mix Designs for Water Quality Benefits: Phase I: Literature Review

Optimizing Rubberized Open-graded Friction Course (RHMA-O) Mix Designs for Water Quality Benefits: Phase I: Literature Review


Historically, rubberized and non-rubberized open-graded friction courses (OGFCs) have been placed to provide three benefits: to increase traffic safety, to reduce urban highway noise, and to preserve the surface of the main pavement structural section. However, stringent environmental regulations on stormwater runoff management enacted recently have forced transportation agencies with limited right of ways in urban areas to search for creative methods to treat runoff and receive credits for preventing pollution from highways. This literature review was undertaken to explore ways to optimize current RHMA-O mix designs to provide multifunctional benefits, including water quality treatment. The literature review showed that permeability measurement is an essential parameter that influences a wide range of OG (both rubberized and non-rubberized) pavements’ performance. Further, current Caltrans aggregate gradations contain a larger fraction of fine aggregate sizes and this may also influence the permeability and functional performance of RHMA-O pavements. Part of this literature review includes an action plan recommending that the next phase of this work include optimizing current Caltrans mix designs and the mix design procedure in the laboratory and undertaking subsequent field investigations.

Cover page of Laboratory Evaluation of the Mechanical Properties of Asphalt Concrete Reinforced with Aramid Synthetic Fibers

Laboratory Evaluation of the Mechanical Properties of Asphalt Concrete Reinforced with Aramid Synthetic Fibers


The research project presented in this report evaluates the effects that the addition of aramid fibers has on the mechanical properties of a dense-graded mix frequently used in California, a Superpave mix with 19 mm (3/4 in.) nominal maximum aggregate size, 15 percent reclaimed asphalt pavement (RAP) content, and PG 64-10 binder. A fiber-reinforced asphalt concrete (FRAC) was prepared by adding aramid fibers at a rate of 0.013 percent of total mix weight. The mechanical properties of the two mixes, original and FRAC, were determined in the laboratory. Based on laboratory testing, adding the fibers improved fatigue resistance of the original mix at high strain levels considerably. It also improved rutting resistance while only changing the stiffness a little. The added fibers did not negatively impact the compactability of the mix nor did it seem to change the mix volumetrics. The laboratory testing results indicate that adding aramid fibers would be of greatest value where asphalt is subjected to high strain levels, such as in overlays of jointed concrete pavements or in pavements with considerable cracking. This study did not consider any occupational health risks, environmental risks or cost considerations, effects on constructability (particularly compaction) in the field, or what effects added fibers might have on the ability to recycle fiber-reinforced asphalt pavement.

Cover page of Mechanistic-Empirical (ME) Design: Mix Design Guidance for Use with Asphalt Concrete Performance-Related Specifications

Mechanistic-Empirical (ME) Design: Mix Design Guidance for Use with Asphalt Concrete Performance-Related Specifications


Caltrans has adopted mechanistic-empirical (ME) methods for flexible pavement design, and is using performance-related construction specifications on some projects for hot mix asphalt. Performance-related specifications are used to help ensure that as-built materials meet the performance requirements assumed in ME pavement structural designs. PRS pose new challenges for materials producers and contractors who have never had to relate volumetric mix design parameters to achievement of mechanistic parameters for fatigue life and rutting resistance based on results from performance-related laboratory tests. The objective of this project is to provide guidance to mix designers and contractors to support their decision making regarding changes to mix designs to achieve PRS requirements. The guidance presented in this report was initially developed based on past experience. To validate the guidance and demonstrate its usage, a production mix approved by the California Department of Transportation was selected as the starting point for a set of adjustments applied to the mix and measurement of the effects of each adjustment on mechanistic performance indicators. A total of three sets of adjustments were evaluated, which resulted in a total of four mixes including the baseline. The mechanistic performance parameters evaluated in this study include stiffness, fatigue resistance, and rutting resistance. In addition to direct comparison of laboratory test results, mechanistic-empirical simulations were conducted to evaluate the laboratory mix performance results on predicted pavement performance when the mix was used as a pavement surface layer. The initial mix design guidance was found to be generally consistent with the laboratory test results for the example mix albeit with some minor exceptions. The mix design guidance was then revised based on findings from this study. It is recommended that the revised guidance be used and more data collected to make further improvements.

Cover page of Effects of Milling and Other Repairs on Smoothness of Overlays: Additional Testing on Construction Under Profiler-Based Smoothness Specifications

Effects of Milling and Other Repairs on Smoothness of Overlays: Additional Testing on Construction Under Profiler-Based Smoothness Specifications


This technical memorandum provides additional information regarding smoothness on several thin asphalt overlay projects constructed soon after changes in Caltrans specifications for constructed pavement surfaces using the International Roughness Index (IRI) as the quality metric. The IRI data were collecting using inertial profilers, before and after construction, on overlaid surfaces employing one of three repairs—digouts, cold in-place recycling (CIR), mill and filling—or none. Because the data were collected after the close of the construction contract, they include the effects of any grinding that Caltrans required the contractor to perform prior to that close. However, the data provide a preliminary look at whether changes in the construction smoothness specification necessitate changes to any of the recommendations in a previous report regarding repairs before overlay. The results indicate that the recommendations in the previous report are generally being followed. The results also indicate that the previous recommendation to not include milling before overlay when IRI is less than 120 inches/mile or below 95 inches/mile may need to be revised under the new specification. However, additional data are needed, since only two projects with milling were included in this data set. A survey of district practices conducted in September 2017 indicated that decisions regarding the inclusion of digouts, milling, and CIR prior to overlay were based on addressing load-related cracking, not roughness. It was observed that decisions regarding pre-overlay repairs for the small set of projects reviewed have generally resulted in smoother existing pavements not being subjected to pre-overlay repairs, and digouts, milling, and CIR being used on successively rougher existing pavements.

Cover page of Development of Improved Guidelines and Designs for Thin Whitetopping: Construction and Initial Environmental Response of Full-Scale BCOA Sections

Development of Improved Guidelines and Designs for Thin Whitetopping: Construction and Initial Environmental Response of Full-Scale BCOA Sections


Thin bonded concrete overlay of asphalt (BCOA) is a rehabilitation alternative consisting of a 100 to 175 mm (0.33 to 0.58 ft) thick portland cement concrete (PCC) overlay of an existing flexible or composite pavement. Fifteen BCOA sections were built at the Davis facilities of the University of California Pavement Research Center in February 2016. Eleven of these full-scale sections were tested under accelerated loading, while four of them were used for monitoring the response of BCOA to the ambient environment and cement hydration. This full-scale experiment is part of a research project whose primary goal is to develop recommendations and guidance on the use of thin BCOA as a rehabilitation alternative in California. The design and construction of these sections is presented in this report, together with results from the quality control/quality assurance testing that was conducted. This testing was focused on the four early high-strength mixes that were used in the construction. The concrete mixes included Type II/V and Type III portland cements and calcium sulfoaluminate cement, and they were designed to provide 2.8 MPa (400 psi) flexural strength after either 4 or 10 hours. Concrete overlays were built either on top of old asphalt pavements that had been tested for another research project or on top of a new gap-graded rubberized hot mix asphalt (RHMA-G) layer. Three slab sizes were built: 1.8x1.8 m (6x6 ft), 2.4x2.4 m (8x8 ft), and 3.6x3.6 m (12x12 ft). This report also describes the instrumentation of the sections and evaluates the engineering reasonableness of the initial data collected by the sensors up to August 2016. There are no recommendations presented in this report. Recommendations regarding implementation of BCOA will be included in the final report of this project.

Cover page of Development of the CalME Standard Materials Library

Development of the CalME Standard Materials Library


The main purpose of the project is to improve the ability of Caltrans pavement designers to use mechanistic-empirical (ME) pavement design procedures that were developed and calibrated for California conditions as part of Partnered Pavement Research Center Strategic Plan Element (PPRC SPE) 4.1 and refined in SPE 3.4. Specifically this project is part of a long-term series of tasks to collect regional materials data for use by Caltrans in ME flexible pavement designs and rehabilitations. This technical memorandum documents the current state of the Standard Materials Library (SML) for CalME, the ME analysis and design computer program for flexible pavements developed by the UCPRC for Caltrans. This technical memorandum summarizes the role of the SML in the ME design process, the classifications of different pavement materials, the relevant models applicable to each material group, and the processes for identifying various model parameters. The technical memorandum also describes how construction variabilities are accounted for in the SML. A full list of materials included in the SML at the completion of this task in 2014 is presented, including the research conducted up to that time on the materials and how their model parameters were determined.

Cover page of Permeability Testing on Dense-Graded Hot Mix Asphalt (HMA) and Gap-Graded Rubberized Hot Mix Asphalt (RHMA-G) Surfaces

Permeability Testing on Dense-Graded Hot Mix Asphalt (HMA) and Gap-Graded Rubberized Hot Mix Asphalt (RHMA-G) Surfaces


Falling head permeability tests were conducted on seven projects, four with dense-graded hot mix asphalt surfaces and three with gap-graded rubberized hot mix asphalt surfaces. Tests were conducted between the two wheelpaths and in the right wheelpath, and in both directions of traffic. Averaging all the test results shows that the permeability of RHMA-G is much greater than that of HMA: 2.9E-3 cm/sec versus 6.1E-4 cm/sec, respectively. However, one of the three projects with a gap-graded rubberized hot mix asphalt surface had permeabilities not consistent with the other two. When data from that gap-graded rubberized hot mix asphalt surface was removed, the average value for the surface permeability dropped over 80 percent, to 4.2E-4 cm/sec. This average is lower than the average permeability for dense-graded hot mix asphalt, and the data remaining from the six projects—four dense-graded and two gap-graded—showed no statistical difference in the average surface permeability of HMA and RHMA-G when tested at the 95% confidence level. On four of the seven projects, including all three of the RHMA-G sections, testing in both directions and in both wheelpaths locations showed no statistical difference in surface permeability. But, one HMA project showed dissimilarity in both directions and in the wheelpaths. Five pairs of cores from this project were then tested for permeability and specific gravity in the laboratory. Unfortunately, no conclusions could be drawn due to a lack of spatial information; however one of the five locations had very little variability between core pairs in either specific gravity or permeability, while another location had significant differences between the specific gravity and permeability measurements. When data from this dense-graded hot mix asphalt surface were removed along with the data from the one gap-graded rubberized hot mix asphalt surface with very high permeability, the remaining five projects—three dense-graded and two gap-graded—again showed no statistical difference in the average surface permeability of HMA (3.3E-4 cm/sec) and RHMA-G (4.2E-4 cm/sec) when tested at the 95% confidence level. It is recommended that testing of more RHMA-G mixes may be warranted to see if the high permeability on one mix in this study is unique. Construction QC/QA should also be examined to see if that mix met compaction specifications.