Maria Carolina Rodezno

Porous Asphalt Pavement Temperature Effects for Urban Heat Island Analysis

Increased nighttime temperatures caused by retained heat in urban areas is a phenomenon known as the urban heat island (UHI) effect. Urbanization requires an increase in pavement surface area, which contributes to UHI as a result of unfavorable heat retention properties. In recent years, alternative pavement designs have become more common in an attempt to mitigate the environmental impacts of urbanization. Specifically, porous pavements are gaining popularity in the paving industry because of their attractive storm water mitigation and friction properties. However, little information regarding the thermal behavior of these materials is available. This paper explores the extent to which porous asphalt pavement influences pavement temperatures and investigates the impact on UHI by considering the diurnal temperature cycle. A one-dimensional pavement temperature model developed at Arizona State University was used to model surface temperatures of porous asphalt, traditional dense-graded asphalt, and portland cement concrete pavements. Scenarios included variations in pavement thickness, structure, and albedo. Thermal conductivity testing was performed on porous asphalt mixtures to obtain values for current and future analysis. In general, porous asphalt exhibited higher daytime surface temperatures than the other pavements because of the reduced thermal energy transfer from the surface to subsurface layers. However, porous asphalt showed the lowest nighttime temperatures compared with other materials with a similar or higher albedo. This trend can be attributed to the unique insulating properties of this material, which result from a high air void content. As anticipated, the outcome of this study indicated that pavement impact on UHI is a complex problem and that important interactions between influencing factors such as pavement thickness, structure, material type, and albedo must be considered.

Evaluation of Fiber-Reinforced Asphalt Mixtures Using Advanced Material Characterization Tests

The objective of this study was to evaluate the material properties of a conventional (control) and fiber-reinforced asphalt mixtures using advanced material characterization tests. The laboratory experimental program included triaxial shear strength, dynamic (complex) modulus, repeated load permanent deformation, fatigue, crack propagation, and indirect tensile strength tests. The data was used to compare the performance of the fiber-modified mixture to the control. The results showed that the fibers improved the mixture’s performance in several unique ways against the anticipated major pavement distresses: Permanent deformation, fatigue cracking, and thermal cracking.

Development of a Flow Number Predictive Model

The NCHRP 9-19 panel recommended the repeated load permanent deformation test as a laboratory procedure that could be used to evaluate the resistance of a hot-mix asphalt (HMA) to tertiary flow. No standard test protocol addresses the required laboratory stress to be applied. The test can take several hours until tertiary flow is reached and in many cases the sample may never fail. A model capable of predicting or providing general guidance on the flow number characteristics of a mix can be of great value. The model can be ideally used as a guideline to determine the stress–temperature combination that will yield tertiary flow within a reasonable testing time. In this study, an effort was undertaken to develop a flow number predictive model. The model uses HMA mixture volumetric properties and stress–temperature testing conditions as predictor variables. The laboratory test data used are a combination of two valuable databases. The first one included tests conducted at Arizona State University; the second one included tests conducted by the FHWA Mobile Asphalt Material Testing Laboratory. Ninety-four mixtures were evaluated, and 1,759 flow number test results were available. Various regression models were evaluated by combining several independent variables. The final model selected had fair statistical measures of accuracy, and it covered a wide range of mixtures, gradations, and binder properties, as well as laboratory-applied stress. As more testing data become available, the model could be refined and recalibrated for better accuracy.

Assessment of Distress in Conventional Hot-Mix Asphalt and Asphalt–Rubber Overlays on Portland Cement Concrete Pavements: Using the New Guide to Mechanistic–Empirical Design of Pavement Structures

The purpose of this study is to assess the way distresses are predicted by using the new Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures (design guide), developed under NCHRP Project 1-37A. Two pavement sections were used: a conventional hot-mix asphalt reconstruction and an asphalt-rubber overlay on a portland cement concrete (PCC) pavement. The design guide does not include rehabilitation design for asphalt-rubber overlays. However, many large-scale asphalt-rubber overlays on interstate highways in Arizona have been built and monitored for performance, providing an opportunity to determine to what degree the design guide can predict their performance. The input data for both types of pavements were derived from two different projects on the same highway, Interstate 40. The actual data measurements that summarize the pavement performance were compared with calculated values obtained by using the design guide. Three pavement performance parameters were evaluated on the basis of t...

Flow Number Test and Assessment of AASHTO TP 79-13 Rutting Criteria: Comparison of Rutting Performance of Hot-Mix and Warm-Mix Asphalt Mixtures

The flow number (FN) test was recommended in NCHRP Project 9-19 as a simple performance test for rutting evaluation of asphalt mixtures. The test showed good correlation with rutting performance of mixtures from WesTrack, MnROAD, and FHWAs accelerated loading facility. Despite this fact, no standard protocol was recommended for temperature and required stress level. Subsequent NCHRP studies allowed the development of a provisional standard. AASHTO TP 79-13 includes test parameters for stress and temperature, specimen conditioning, and minimum FN criteria that were established for hot-mix asphalt (HMA) and for warm-mix asphalt (WMA) on the basis of traffic level. In NCHRP Project 9-47A, the rutting potential of WMA mixtures was compared with that of HMA mixtures by using the FN test and the rutting criteria included in the AASHTO TP 79-13 were also evaluated. The analysis included results of samples produced by using field and lab mixtures. Thirteen mixes using 10 WMA technologies and eight corresponding HMA mixes were included. The FN test results for plant-produced WMA mixes were found to be statistically lower than those for corresponding HMA mixes in more than two-thirds of the comparisons. The study also found that the FN criteria recommended for both HMA and WMA seemed appropriate for evaluating plant-produced mixes. Another finding from the study was that FN results from lab-produced WMA mixtures were consistently lower than FN values from field mixtures; this result suggests that adjustments to the specimen conditioning requirements should be considered.

Implementation of Asphalt-Rubber Mixes into the Mechanistic Empirical Pavement Design Guide

ABSTRACT The Mechanistic-Empirical Pavement Design Guide (MEPDG) developed by the National Cooperative Highway Research Program (NCHRP) utilizes material properties to predict distresses in pavement structures. This new MEPDG is in the process of replacing the traditional pavement design based on the AASHTO 1993 Design Guide. The Arizona Department of Transportation (ADOT) uses Asphalt- Rubber (AR) mixes state-wide. These mixes include both gap and open gradation designs. However, the national calibration process that was undertaken for the MEPDG did not include asphalt-rubber mixes. Because of their unique characteristics, this paper addresses steps and efforts undertaken in a recent study to implement these AR mixes into the MEPDG. There were several issues and limitations identified pertaining to the implementation of AR mixes in the MEPDG. Short and long term recommendations were provided. An important outcome includes a modified Dynamic Modulus predictive equation for AR mixes that is expected to be used in a future implementation of AR mixes in MEPDG.

Temperature Gradient and Curling Stresses in Concrete Pavement with and without Open-Graded Friction Course

Curling stresses of concrete pavement can be very damaging, and reducing the temperature swings would be very beneficial. This study includes a field instrumentation effort with pavement temperature sensors to quantify the thermal behavior of concrete pavement with and without an open-graded asphalt rubber friction course. The study shows a nonlinear temperature profile across slab thickness, with a large change in temperature between day and night at the top of the concrete slab, and little change at the bottom of the slab. Adding an open-graded friction course over the concrete pavement reduces the temperature fluctuation between day and night as a result of the aeration effect, which is increased by traffic. A three-dimensional (3D) finite-element analysis with a nonlinear temperature gradient shows that adding the friction course reduces the curling stresses in the summer. Furthermore, since traffic increases the aeration effect, sections without traffic show lower effect of friction course on reducin...

Comparison of Asphalt Rubber and Conventional Mixture Properties: Considerations for Mechanistic–Empirical Pavement Design Guide Implementation

In 1999 the Arizona Department of Transportation (ADOT) started outlining and developing a long-range pavement research program. This research program was established in cooperation with Arizona State University (ASU) and had the ultimate goal of implementing the Mechanistic–Empirical Pavement Design Guide (MEPDG) for Arizona. Since ADOT uses asphalt rubber (AR) mixes for new and rehabilitation pavement designs, an integral part of the MEPDG calibration effort must include AR mixtures, which were not included in the MEPDGs development. The objective of this study was to perform a comparison between AR properties and those of the conventional dense graded asphalt mixtures typically used for MEPDG development, calibration, and validation. Another important task was to evaluate how these mixes could be implemented into the MEPDG in the short term and to make recommendations on how to use them in future designs. A total of 23 AR mixtures were available for analysis from a joint ADOT-ASU database. The database contains several engineering properties of AR mixes and binders. These data were used to compare properties, select MEPDG input parameters, generate design analysis for permanent deformation and fatigue cracking, run case studies to predict performance, and compare results with field performance data. Several issues were identified pertaining to the implementation of AR mixes in the MEPDG, and recommendations were provided.

Effect of different dosages of polypropylene fibers in thin whitetopping concrete pavements

This article describes how an experimental laboratory study was undertaken to evaluate the engineering properties for four different concrete mixtures: a control mixture with no fibers and mixtures with polypropylene fibers using the following dosages: 3, 5, and 8 lb/yd³ (1.78, 2.97, and 4.75 kg/m³). Various samples were collected during construction and tested for compressive strength, flexural strength, and toughness using cylindrical, prismatic, and round panel specimens. Because the toughness results cannot be taken into account using common concrete pavement design methodologies, which is especially true for the round panel test, an analysis was performed that took into account the additional benefit of the polypropylene fibers using a residual strength approach. It was concluded that the effect of the addition of fibers was best captured using the round panel test. It was also concluded that the use of 5 lb/yd³ (2.97 kg/m³) fiber dosage had the best value-added benefit to the mixture.

Guide on the selection of appropriate laboratory stress levels for the flow number test

This study examines the use of the triaxial shear strength parameters (c and φ) in providing guidelines for selecting the appropriate laboratory stress level for the flow number test of asphalt mixtures. The approach is based on the concept that the flow number (tertiary flow) is inversely related to the applied stress-to-strength ratio of the material. The correlation of the flow number with the stress-to-strength ratio can provide a good estimate of the stress level that will yield tertiary flow within a reasonable testing time. It was also realized that the triaxial shear strength test is not routinely conducted by Department of Transportation agencies and testing laboratories. Therefore, a database of triaxial shear strength test data was used to develop predictive models of the shear strength parameters for a particular asphalt mixture. The models’ predictor variables were based on the volumetric properties of 46 different asphalt mixtures and a total of 276 test results. Regression models to estimate the c and friction (φ) parameters had good statistical measures of model accuracy. The models were used to develop guidelines for laboratory stress-to-strength ratios to achieve tertiary flow within a reasonable testing period.