University of California Pavement Research Center

Unacceptable levels of dust, poor riding quality, impassability in wet weather, and unsustainable maintenance and gravel replacement practices are experienced on most unpaved road networks, and although it is acknowledged that unpaved roads are fundamental to local, regional, and national economies, many current management practices used on these roads leave much to be desired. Over the past 100 years a range of chemical treatments has been developed to fill the need for reducing the environmental and social impacts of road dust, improving the performance and safety of unpaved roads, and/or improving the properties of marginal materials to the extent that a road can be given all-weather status or upgraded to a paved standard. Most of these chemical treatments are proprietary and there is often little documented information regarding the chemistry of the treatment, the results of experimental trials to determine under what conditions the chemical treatment will work best, or guidelines on where and how to use the treatment. Most unpaved road chemical treatments carry no formal specification nor do they adhere to formal environmental testing requirements. Consequently, there has been no large-scale effort to establish and/or implement formal unpaved road chemical treatment programs anywhere in the world, other than those used in site-specific industrial applications such as mining operations. This guide introduces a new process for selecting an appropriate chemical treatment category for a specific set of unpaved road conditions using ranked potential performance. The process is based on the practitioner setting an objective for initiating a chemical treatment program and understanding the road in terms of materials, traffic, climate, and geometry. Using the information collected, the most appropriate chemical treatment subcategories for a given situation can be selected from a series of charts and ranked using a simple equation. This process can be completed manually using a paper form, or by using a web-based (www.ucprc.ucdavis.edu) or spreadsheet tool. Matrices for each of the objectives were developed based on documented field experiments and the experience of a panel of practitioners. Guidance on specification language for procuring and applying unpaved road chemical treatments is also provided, along with comprehensive guidance on understanding unpaved road wearing course material performance.

This document provides guidelines for the establishment, monitoring and reporting of pavement preservation experiments in California. Information is provided in chapters covering: Management and responsibilities, Project fundamentals, Experiment work plan, Site selection, Experiment construction, Experiment monitoring, Forensic investigations, Laboratory testing, Data analysis, reports and implementation, Data management and documentation, Example experiment work plans, checklists and form. The document aims to assist with achieving successful completion of experiments and implementation of the findings.

This document provides guidelines for the establishment, monitoring and reporting of pavement preservation experiments in California. Information is provided in chapters covering: Management and responsibilities, Project fundamentals, Experiment work plan, Site selection, Experiment construction, Experiment monitoring, Forensic investigations, Laboratory testing, Data analysis, reports and implementation, Data management and documentation, Example experiment work plans, checklists and forms The document aims to assist with achieving successful completion of experiments and implementation of the findings.

Many rural county road networks were created at a time when funding was greater and rural populations were often larger than they are today. Eventually, surface treatments such as chip seals or thin asphalt were applied to many of these gravel roads to provide them with an all‐weather surface. These treated surfaces were also desirable because conventional gravel roads are dusty, often develop wash boarding quickly, and have high rates of gravel loss—which result in unsafe and uncomfortable conditions and greater damage to vehicles and crops. A solution to this problem is called ‘unpaving using engineered gravel roads’.

This document constitutes the user manual for tBeam, standalone software for the analysis of energy dissipation in pavements under moving vehicles. tBeam was developed as part of the improvement of modeling capabilities for environmental life cycle assessment of pavements being conducted by the University of California Pavement Research Center for the California Department of Transportation. tBeam is finite element based, employing multi-layered three-node Timoshenko beam elements resting on a viscoelastic Winkler foundation. It provides an approximation of the deflection bowl of pavements and the energy dissipated in pavement structures when subjected to loads moving at constant velocities. tBeam supports two loading options: a uniform pressure (per unit length) applied to a segment at the center of the beam, and a rolling rigid wheel. To achieve numerical efficiency the load-beam-foundation system is represented relative to a moving coordinate system attached to the moving load. The higher efficiency is made possible because, in this framework, an observer attached to the moving coordinate system perceives a “static” state (i.e., independent of time). The standalone tBeam software serves two purposes. First, to provide developers of pavement LCA tools a “guide” as to how to integrate tBeam technology into their program. To this end, the “main” of tBeam can be used as “guide” for integrating tBeam capabilities within the LCA tool. Second, tBeam capabilities are relevant to pavement research in general. Thus, it could represent a useful addition to the toolset for pavement viscoelastic mechanics.

The work described in this report is adjunct to a five-year study of tire/pavement noise undertaken by the University of California Pavement Research Center for the California Department of Transportation under the Partnered Pavement Research Center program (PPRC). This part of the study was performed in cooperation with the Danish Road Institute/Road Directorate, and it examined the influence of air temperature on tire/pavement noise measurements performed on two types of tires (Aquatred and Standard Reference Test Tire [SRTT]) on different asphalt pavement surfaces using the On-board Sound Intensity (OBSI) method. Field noise measurement testing was carried out in two series: one in the Southern California desert on State Route 138 using the SRTT, and the other with data collected on a statewide selection of pavements tested with the Goodyear Aquatred tire in an earlier part of the PPRC noise study. The field measurements yielded data for deriving air temperature coefficients for the two types of tires, and a comparison of them is made. A worldwide survey of the available literature accompanies the field work and analysis, and a summary of it is used to compare the air temperature coefficients of the SRTT with a combination of tire types used in European testing. In addition, findings in the literature serve as the basis for a series of predicted temperature coefficients for passenger cars on various cement concrete and asphalt pavements. Finally, the report presents ten general conclusions drawn regarding the relationship between air temperature correction and tire/road noise on asphalt and concrete pavements.

One of the most important contributors to the environmental impacts from use of highways is the energy exerted by vehicles, particularly routes that carry higher volumes of traffic. Part of this energy is consumed by response of the vehicle’s tires and suspension to pavement surface roughness and macrotexture. Another part of the energy consumed is by energy dissipation due to the structural response of the pavement itself under the moving load. This document is the theoretical and validation manual tor tBeam, standalone software for the analysis of energy dissipation in pavements under moving vehicles. tBeam was developed as part of the improvement of modeling capabilities for environmental life cycle assessment of pavements being conducted the University of California Pavement Research Center for the California Department of Transportation. The energy consumed due to structural response are controlled by the structural properties of the pavement which are dependent on the time of day, the season, and the condition (damage) of the pavement. The energy dissipation also depends on the speed and weight of each moving wheel load. As a result, estimating the lifetime energy dissipated in a pavement structure requires multiple analyses considering the thousands of permutations of these variables for a given segment of the highway network. Therefore, models for pavement-vehicle energy dissipation must balance two opposing needs: obtaining a reasonably accurate estimate of the dissipated energy, and high numerical efficiency. For numerical efficiency, the tBeam software employs a one-dimensional finite-element based solution of a wheel traveling at a constant velocity on a viscoelastic beam-foundation system, and a further reduction of numerical effort is obtained by formulating the model relative to a moving coordinate system attached to the wheel. The one-dimensional solution is, by nature, an approximation to the three-dimensional world. This approximation can be improved by incorporating a “correction factor,” which is based on comparisons with pavement simulations accounting for the double curvature observed in loaded pavements. In this report prediction disparity for a single structure is studied. The results show a clear trend where the correction factor decreases with rising temperature, and increases with higher velocity. The present study was insufficient to establish a law for the correction factor even for the single case studied. The correction factor ranged from about 1.25 at low temperature and high velocity to about 0.6 for high temperature and low velocity. The first part of this report presents the underlying theory for tBeam and implementation details. The second part presents closed form solutions for specialized pavement-foundation systems. The third component of the report presents some of the validation simulations undertaken to demonstrate the performance of tBeam, including comparisons with closed form solutions provided in this report, and recommendations for further development of tBeam.

This pilot study applies the principles of Vehicle-Pavement Interaction (V-PI) and state-of-the practice tools to simulate and measure peak loads and vertical acceleration of trucks and their freight on a selected range of typical pavement surface profiles on the State Highway System. Outputs from the pilot study are expected to provide input for planning and economic models to enable an improved evaluation of the freight flows and costs in selected regions. The San Joaquin Valley corridor, a major production and transportation corridor in California, is identified as well-suited to be the pilot area for the remainder of this project.

The Mechanistic-Empirical Pavement Design Guide (MEPDG) is a comprehensive method, including models and guidance, developed in 2002 by the American Association of State Highway and Transportation Officials (AASHTO) to analyze and design both flexible and rigid pavements. The MEPDG is implemented in a software called Pavement ME. The MEPDG models were calibrated using data from the Long-Term Pavement Performance (LTPP) sections from throughout the United States, including some from California. The MEPDG recommends that nationally calibrated models be validated using local data and, if necessary, recalibrated. This recommendation is particularly applicable to the Caltrans road network, considering the climate and materials differences between California and the rest of the nation. The first step in recalibrating Pavement ME is to perform a sensitivity analysis to identify which variables are most important and to look for results that do not match expected performance. This was the subject of a previous report titled Pavement ME Sensitivity Analysis. Based on the sensitivity analysis, the decision was made to perform a new calibration of the MEPDG models as implemented in Pavement ME software. A new approach was developed for the calibration. This new approach uses network-level performance data from the pavement management system (PMS) with orders of magnitude more observations and length of pavement than are used in the traditional approach and in the national calibration of the MEPDG models. The framework does not require sampling of materials from specific sections in the network. Rather, it uses the statewide median values from mechanistic testing from a representative sample of materials across the network. Variability of performance and reliability of design (probability that the design will meet or exceed the design life) is accounted for through separate consideration of within-project and between-project variability. The calibration reduced significant bias in the application of the nationally calibrated models to California. This report presents the results of the application of the new procedure to calibrate the Pavement ME transverse cracking model for jointed plain concrete pavements (JPCP). The California pavement management system (PaveM) database—with about 4600 lane-miles of JPCP built on 446 lane replacement projects completed between 1947 and 2017—was used to calibrate the transverse cracking model in Pavement ME. The nationally calibrated Pavement ME transverse cracking model prediction on the PaveM performance database has bias and standard error of 13.3% and 23.03%, respectively. After calibration, the bias and standard error of the locally calibrated model decreased to 0.039% and 5.69%, respectively.

This is the second of two reports that present fatigue cracking performance models for asphalt concrete overlays placed on existing asphalt concrete pavement. The models were developed from the pavement management system (PMS) database of the Washington State Department of Transportation (WSDOT). The database included existing pavement structure, overlay thickness and type, truck traffic, and observed percent of the wheelpath cracked from annual condition surveys. Climate data was developed by the UCPRC to augment the WSDOT data. This report presents a model for crack propagation, starting from crack initiation, which was defined as 5 percent of the wheelpath with longitudinal cracking. The combined initiation and propagation models were included in a spreadsheet calculator which was used to perform an analysis of the sensitivity of crack initiation and propagation to the input variables. The models are extremely useful for predicting pavement performance. For use in California they will need recalibration of the coefficients to reflect differences in WSDOT and California practice, primarily the use of thicker overlays in California, placement of overlays at much more advanced states of cracking in the existing pavement, and possible differences in routine maintenance activities.

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.

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.

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.

The objective of this study was to develop a framework for determining the fuel use and environmental impacts caused by construction work zones (CWZs) on a range of vehicles and to produce initial calculations of these impacts by modeling traffic closure conditions for highway maintenance and rehabilitation (M&R) activities. The framework was developed and demonstrated in several scenarios. The study included three common highway categories—freeways, multi-lane highways, and two-lane highways—and common California vehicle types. The framework uses realistic drive cycle values and CWZ operation scenarios as inputs to the simulation software MOtor Vehicle Emission Simulator (MOVES) to estimate total fuel consumption and air pollutant emissions. In this study, the framework was demonstrated using three CWZ operations under different traffic congestion levels: light, medium, and heavy.

Fuel consumption and pollutant emissions results obtained for the CWZ operation scenario with and without congestion were compared with those for a no-CWZ, no-congestion scenario. In the simulation results for a freeway with a CWZ and heavy congestion, fuel consumption increased by 85% and the CO2 equivalent (CO2-e) emissions increased by 86%, NOx by 62%, SOx by 85%, and PM2.5 by 128%. In the multi-lane highway scenarios, fuel consumption increased by 85%, and CO2-e emissions increased by 88%, NOx by 75%, SOx by 87%, and PM2.5 emissions by 129% for a CWZ with heavy congestion. Lessening traffic congestion in a CWZ from heavy (average speed 5 mph) to medium (average speed 25 mph for a freeway section and 15 mph for a multi-lane road section) reduced fuel consumption by 40% on a freeway and 33% on multi-lane highway.

This study also included use of a pilot car in a CWZ on a two-lane road. This approach was undertaken to estimate the possible benefits of different CWZ lane closure strategies and traffic management plans. The pilot-car operation scenario results indicate that a one-lane closure with pilot-car operation on a two-lane road might consume 13% more fuel because of idling time and the slow movement of vehicles following the pilot car. This scenario generated emissions increases of 10% for CO2-e, 14% for NOx, 13% for SOx, and 65% for PM2.5.

The results of these scenarios indicate that the impacts from heavy vehicles far exceed those from smaller vehicles in CWZs. Phase 2 of the study will develop methods for pavement management, conceptual evaluation, and project design that consider construction closures by implementing this life cycle assessment framework. These methods will also be used in studies to evaluate pavement design lives (20 years versus 40 years) and pavement selection for truck lanes and in-place recycling and to evaluate lane closure schedules and tactics to minimize CWZ impacts on highways by using project-specific traffic congestion levels.

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.

This technical memorandum presents the results of pavement evaluation and rehabilitation design of 02-PLU-36, PM 6.3/13.9. The pavement evaluation consists of deflection testing, coring, material sampling, backcalculation of stiffnesses, and condition assessment. Rehabilitation designs were developed using standard Caltrans methods. Alternative rehabilitation designs were developed using mechanistic-empirical software and models (CalME). Performance of all designs was assessed using mechanistic-empirical models. Suitable designs are recommended.

The purpose of this white paper is to provide Caltrans with a methodology that uses LCA and LCCA analyses to create a “supply curve” that ranks the different strategies/actions that can be taken to reduce GHG emissions and lessen any other environmental impacts that affect ecosystems and human health. For Caltrans to implement the proposed methodology, the process must be validated and assessed using currently available actions. This white paper presents the methodology and demonstrates its initial use in quantifying and ranking several potential strategies.

More than 90 percent of the road and highway network in the United States is paved with asphalt concrete. Maintenance and periodic rehabilitation require a continuous supply of aggregates and asphalt binder, both of which are becoming increasingly scarce and expensive. Recycling and reusing these resources can reduce costs and improve sustainability. The most common recyclable material used in road construction is reclaimed asphalt pavement (RAP), which is milled asphalt surface layers that have been removed from existing pavements before new asphalt overlay is placed. Reclaimed asphalt roofing shingles (RAS) are another potential source of asphalt binder.

There is growing interest in allowing significantly higher percentages of RAP and RAS in asphalt mixes used on state and local roadways. However, making this change has raised concerns regarding how these composite binders may influence the performance and durability of asphalt mixes, depending on the blends of different virgin and reused binders. Researchers at the UC Pavement Research Center investigated the use of higher percentages of RAP and RAS as a partial replacement for the virgin binder in new asphalt mixes and their effect on pavement performance in California. This research brief summarizes findings from that study.

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The processes in the pavement life cycle can be defined as: material extraction and production; construction; transport of materials and demolition; the use stage, where the pavement interacts with other systems; the materials, construction, and transport associated with maintenance and rehabilitation; and end-of-life. Local governments are increasingly being asked to quantify greenhouse gas emissions from their operations and identify changes to reduce emissions. There are many possible strategies that local governments can choose to reduce their emissions, however, prioritization and selection of which to implement can be difficult if emissions cannot be quantified. Pavement life cycle assessment (LCA) can be used by local governments to achieve the same goals as state government. The web-based software environmental Life Cycle Assessment for Pavements, also known as eLCAP has been developed a project-level LCA tool. The goal of eLCAP is to permit local governments to perform project-level pavement LCA using California specific data, including consideration of their own designs, materials, and traffic. eLCAP allows modeling of materials, transport, construction, maintenance, rehabilitation, and end-of-life recycling for all impacts; and in the use stage it considers the effects of combustion of fuel in vehicles as well as the additional fuel consumed due to pavement-vehicle interaction (global warming potential only). This report documents eLCAP and a project that created an interface for eLCAP that is usable by local governments.

In early 2017, the University of California Pavement Research Center (UCPRC) and the National Center for Sustainable Transportation (NCST), working with the Interlocking Concrete Pavement Institute (ICPI), identified gaps in knowledge and other barriers to wider implementation that were perceived to be holding back the full potential for deployment of pavements that can simultaneously solve transportation, stormwater quality, and flood control problems. Further discussions were held with the National Ready Mixed Concrete Association (NRMCA), the National Asphalt Pavement Association (NAPA), and the Tongji University Sponge City Project (Shanghai, China). A workshop was organized in November 2017 based on those discussions with the goal of identifying knowledge, information, and communication barriers to adoption of permeable pavement of all types, and creation of a road map to address and overcome them. The workshop brought together a diverse group of stakeholders from the planning, stormwater quality, flood control, and pavement communities to hear listen to presentations, exchange and discuss unanswered questions identified by the group, and then to discuss a proposed road map to fill the gaps in knowledge, processes, and guidance. This document is the result of that workshop and additional development of the road map. It presents the organization of the workshop, summaries of the presentations and the breakout and plenary discussions, and the final road map developed from the results of the workshop.

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