Innovative Modification and Testing of Asphalt Crack Sealants

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Description
Asphalt crack sealants are essential for preserving the integrity of asphalt pavements. They act as a barrier against water infiltration, a primary cause of base erosion and structural failure. However, these sealants are susceptible to degradation from traffic wear, weathering,…

Asphalt crack sealants are essential for preserving the integrity of asphalt pavements. They act as a barrier against water infiltration, a primary cause of base erosion and structural failure. However, these sealants are susceptible to degradation from traffic wear, weathering, and thermal stresses. This degradation manifests in multiple failure modes, including loss of cohesion, adhesion, and settlement. Being one of the most cost-effective pavement maintenance techniques, its market size is expected to be worth about $1.1 billion by 2028, with a 56% market share in North America alone. With extreme climatic events, sealants will have a tendency to fail more often. Therefore, this research effort investigated the incorporation of various modifiers into asphalt crack sealants and fillers to enhance their performance and durability, to perform beyond their designed life. Four different modifiers were selected and tested using a specific laboratory testing protocol targeting the failure modes observed in the field and ultimately leading to extended pavement lifespans and reduced maintenance expenditures. Furthermore, a novel test procedure to measure the coefficient of expansion and contraction of control and modified sealants was developed and calibrated as part of this study. These modifiers included an aerogel modified bituminous material, a pre-activated crumb rubber material, a recycled aerogel composite, and synthetic fibers.The testing program included durability and strength testing such as bonding strength, shear thinning, toughness, and tenacity; and thermal behavior testing such as expansion and contraction, thermal conductivity, and specific heat capacity. The coated aerogel modifier provided better toughness, tenacity, and bonding properties with improved thermal properties. The pre-activated crumb rubber reduced the effect of aging, whereas fibers showed promising results across most parameters. As for the recycled aerogel composite, thermal susceptibility was slightly improved, in addition to low temperature behavior for the filling material. Finally, a multiple decision-making criteria method was adopted to rank the best modifier for each material for parking lots and roadways followed by a life cycle cost analysis. A survey was conducted to rate the importance of each factor affecting performance, based on the integration of both quantitative and qualitative criteria, thereby accommodating diverse decision contexts and preferences.
Date Created
2024
Agent

Impact of Three-Dimensional Stress Pulse Configurations and Rest Period on Permanent Deformation Characteristics of Asphalt Concrete Mixtures

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Description
Asphalt concrete (AC) layers in airfield and highway pavements are subjected to complex 3-D stress states due to moving load and maneuvering effects of heavy trucks and aircrafts in highway and airfield pavements. The conditions AC layers are subjected to…

Asphalt concrete (AC) layers in airfield and highway pavements are subjected to complex 3-D stress states due to moving load and maneuvering effects of heavy trucks and aircrafts in highway and airfield pavements. The conditions AC layers are subjected to in pavements evolved significantly with increasing truck loads and repetitions. In addition, truck platooning was recently introduced with the development in automation and connected technologies in the transportation industry. Reliability of pavement designs against permanent deformations can be compromised under such traffic loading conditions.The main goal of this dissertation is to characterize permanent deformation resistance of asphalt mixtures under various stress pulse configuration with varying stress states and rest periods. While the effects of loading duration and stress states were commonly studied in the literature, rest period effect was relatively less understood. Therefore, the focus of this thesis is to assess the effect of rest period using advanced triaxial permanent deformation experiments simulating stress states of truck platoons and maneuvering aircrafts. An experimental program was developed to assess the influence of rest periods under varying stress pulse configurations and paths on the permanent deformation of AC layers. Result showed that increasing rest periods led to increase in permanent deformations consistently about 2-3 times in high temperatures due to the hardening-relaxation or hardening–softening mechanisms. Rest period impact was found to be as important as temperature and stress magnitude for asphalt mixture’s permanent deformation resistance. ii Furthermore, the results showed that the changing stress paths had a significant effect on permanent deformation resistance when compared to conventional repeated-load experiments. A novel repeated load permanent deformation experiment was developed as part of the thesis research. The main idea of the experiment was to induce dynamic and independent stress pulses in the axial as well as the horizontal direction as confinement. With the individual pulsing in axial and horizontal direction, stress states simulating platoon moving loads or aircraft shear loading can be simulated and compared to conventional flow number experiment with dynamic axial pulsing with constant confinement pressure.
Date Created
2024
Agent

Development of a Novel Aerogel-Based Modified Bituminous Materials

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Description
Thermal susceptibility is one of the biggest challenges that asphalt pavements must overcome. Asphalt mixture’s thermal susceptibility can increase problems related to permanent deformation, and the expansion-contraction phenomenon triggers thermal cracking. Furthermore, there is a common worldwide interest in environmental…

Thermal susceptibility is one of the biggest challenges that asphalt pavements must overcome. Asphalt mixture’s thermal susceptibility can increase problems related to permanent deformation, and the expansion-contraction phenomenon triggers thermal cracking. Furthermore, there is a common worldwide interest in environmental impacts and pavements. Saving energy and mitigating the urban heat island (UHI) effect have been drawing the attention of researchers, governments, and industrial organizations. Pavements have been shown to play an important role in the UHI effect. Globally, about 90% of roadways are made of asphalt mixtures. The main objective of this research study involves the development and testing of an innovative aerogel-based product in the modification of asphalt mixtures to function as a material with unique thermal resistance properties, and potentially providing an urban cooling mechanism for the UHI. Other accomplishments included the development of test procedures to estimate the thermal conductivity of asphalt binders, the expansion-contraction of asphalt mixtures, and a computational tool to better understand the pavement’s thermal profile and stresses. Barriers related to the manufacturing and field implementation of the aerogel-based product were overcome. Unmodified and modified asphalt mixtures were manufactured at an asphalt plant to build pavement slabs. Thermocouples installed at top and bottom collected data daily. This data was valuable in understanding the temperature fluctuation of the pavement. Also, the mechanical properties of asphalt binders and mixtures with and without the novel product were evaluated in the laboratory. Fourier transform infrared (FTIR) and scanning electron microscope (SEM) analyses were also used to understand the interaction of the developed product with bituminous materials. The modified pavements showed desirable results in reducing overall pavement temperatures and suppressing the temperature gradient, a key to minimize thermal cracking. The comprehensive laboratory tests showed favorable outcomes for pavement performance. The use of a pavement design software, and life cycle/cost assessment studies supported the use of this newly developed technology. Modified pavements would perform better than control in distresses related to permanent deformation and thermal cracking; they reduce tire/pavement noise, require less raw material usage during their life cycle, and have lower life cycle cost compared to conventional pavements.
Date Created
2022
Agent

Evaluating the Effectiveness of a Pavement Preservation Program: A Case Study

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Description
A successful implementation of a Pavement Management System (PMS) allows agencies to make objective and informed decisions in maintaining their pavement assets effectively. Since 2008, the City of Phoenix, Arizona, has implemented PMS to maintain approximately 7,725 km (4,800 mi)…

A successful implementation of a Pavement Management System (PMS) allows agencies to make objective and informed decisions in maintaining their pavement assets effectively. Since 2008, the City of Phoenix, Arizona, has implemented PMS to maintain approximately 7,725 km (4,800 mi) of pavements. PMS is not a static system but a dynamic system requiring regular updates to reflect pavement performance and meet the agency's goals and budget. After upgrading to the Automated Road Analyzer (ARAN) 9000 in 2017, there is a need for Phoenix to evaluate its PMS. A low pavement condition index (PCI) for newly paved roads and the requirements for more than 35% of scheduled fog seal projects to be upgraded to heavier treatments observed, also motivated this research effort. The scope of this research was limited to the flexible pavement preservation program and the objectives are: (1) to evaluate the effectiveness of the existing City of Phoenix PMS and (2) to recommend improvements to the existing PMS. This study evaluated technical and non-technical aspects of Phoenix’s preservation program. Since pavements in a structurally sound condition are good candidates for preservation treatment, a single pavement performance indicator, which allows agencies to be more flexible with their preservation treatments and minimize the pavement performance data collection and modeling efforts, was explored. A simple yet measurable and trackable pavement performance indicator, Surface Cracking Index (SCI), representing the overall pavement condition to perform PMS analysis for a preservation program, was proposed. In addition, using a performance indicator, the International Roughness Index (IRI) to represent the ride quality or roughness, is a challenge for many local governments due to the nature of urban roadway related conditions such as stop and go driving conditions, abrupt lane change maneuvering, and lower prevailing speed. Therefore, a surface roughness indicator, Mean Profile Depth (MPD) measuring pavement surface macrotexture, was explored, and is proposed to be integrated in the PMS to optimize preservation treatments and recommendation strategies. While Phoenix will directly benefit from this research study outcomes, any agency who uses PMS, or plans to use PMS for their preservation program, will also benefit from this research effort.
Date Created
2022
Agent

Implementation of AASHTOWare Pavement ME Design in Saudi Arabia

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Description
Ministry of Transport (MOT) in the Kingdom of Saudi Arabia (KSA) is considering adopting the Mechanistic-Empirical Pavement Design method with its associated software the AASHTOWare Pavement ME Design (PMED) for its flexible pavements in the near future. The AASHTOWare PMED…

Ministry of Transport (MOT) in the Kingdom of Saudi Arabia (KSA) is considering adopting the Mechanistic-Empirical Pavement Design method with its associated software the AASHTOWare Pavement ME Design (PMED) for its flexible pavements in the near future. The AASHTOWare PMED consists of distresses and international roughness index (IRI) prediction models that are nationally calibrated mainly using Long-Term Pavement Performance (LTPP) database in the United States. Implementing the AASHTOWare PMED in KSA requires two main tasks: 1. convert KSA data format to AASHTOWare PMED format, and 2. calibrate the distress and IRI models to KSA conditions. This study first prepared the KSA data to be accepted by AASHTOWare PMED and then calibrated the models to improve the pavement performance models predictions. After calibration, validation of these models was conducted to ensure accurate results with independent pavement sections. Goodness-of-fit statistics and null hypothesis test were used to assess each models’ prediction. Three flexible pavement models were successfully calibrated: asphalt concrete (AC) permanent deformation, top-down cracking, and IRI models. The results showed that the distress and IRI models with national (default) calibration are biased in predicating KSA pavements performance which required recalibration. Calibrating AC rutting, top-down cracking, and IRI models improved the prediction of KSA pavement performance. Most of the data used in this study were obtained from MOT. The AASHTOWare Pavement ME software (version 2.6.0) was used to complete the study.
Date Created
2021
Agent

Advancing Knowledge of Mechanically-Fiber Reinforced Asphalt Concrete

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Description

The use of reinforcing fibers in asphalt concrete (AC) has been documented in many studies. Published studies generally demonstrate positive benefits from using mechanically fiber reinforced asphalt concrete (M-FRAC); however, improvements generally vary with respect to the particular study. The…

The use of reinforcing fibers in asphalt concrete (AC) has been documented in many studies. Published studies generally demonstrate positive benefits from using mechanically fiber reinforced asphalt concrete (M-FRAC); however, improvements generally vary with respect to the particular study. The widespread acceptance of fibers use in the asphalt industry is hindered by these inconsistencies. This study seeks to fulfill a critical knowledge gap by advancing knowledge of M-FRAC in order to better understand, interpret, and predict the behavior of these materials. The specific objectives of this dissertation are to; (a) evaluate the state of aramid fiber in AC and examine their impacts on the mechanical performance of asphalt mixtures; (b) evaluate the interaction of the reinforcement efficiency of fibers with compositions of asphalt mixtures; (c) evaluate tensile and fracture properties of M-FRAC; (d) evaluate the interfacial shear bond strength and critical fiber length in M-FRAC; and (e) propose micromechanical models for prediction of the tensile strength of M-FRAC. The research approach to achieve these objectives included experimental measurements and theoretical considerations. Throughout the study, the mechanical response of specimens with and without fibers are scrutinized using standard test methods including flow number (AASHTO T 378) and uniaxial fatigue (AASHTO TP 107), and non-standard test methods for fiber extraction, direct tension, semi-circular bending, and single fiber pull-out tests. Then, the fiber reinforcement mechanism is further examined by using the basic theories of viscoelasticity as well as micromechanical models.

The findings of this study suggest that fibers do serve as a reinforcement element in AC; however, their reinforcing effectiveness depends on the state of fibers in the mix, temperature/ loading rate, properties of fiber (i.e. dosage, length), properties of mix type (gradation and binder content), and mechanical test type to characterize M-FRAC. The outcome of every single aforementioned elements identifies key reasons attributed to the fiber reinforcement efficiency in AC, which provides insights to justify the discrepancies in the literature and further recommends solutions to overcome the knowledge gaps. This improved insight will translate into the better deployment of existing fiber-based technologies; the development of new, and more effective fiber-based technologies in asphalt mixtures.

Date Created
2020
Agent

Structure-Property Relationships to Understand Comprehensive Rejuvenation Mechanisms of Aged Asphalt Binder

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Description
This research focused on the structure-property relationships of a rejuvenator to understand the comprehensive rejuvenation mechanism of aged asphalt binder. Aged asphalt such as recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) contain various amounts of asphalt binder. However,…

This research focused on the structure-property relationships of a rejuvenator to understand the comprehensive rejuvenation mechanism of aged asphalt binder. Aged asphalt such as recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) contain various amounts of asphalt binder. However, the asphalt binder in RAS and RAP is severely aged and inferior in properties compared to a virgin binder. To address this issue, liquid additives have been used under the general title of rejuvenators. That poses an additional challenge associated with the lack of clear metrics to differentiate between softeners and rejuvenators. Therefore, there is a need for a thorough study of rejuvenators. In this study, diverse-sourced rejuvenators have been used in RAS and RAP-modified binders as well as laboratory-prepared aged binders. The properties of the rejuvenated aged binder were characterized at a macro-level and molecular level. The study showed that the performance of the RAS-modified binder was significantly improved after bio-modification by a bio-rejuvenator.

This study further evaluated laboratory-prepared aged asphalt rejuvenated with different rejuvenators. The results found that oxidized bitumen became soft after adding rejuvenators, regardless of their source. Molecular dynamics simulation showed that the effective rejuvenator restored the molecular conformation and reduced the size of asphaltene nanoaggregates.

The study results showed that due to the specific chemical composition of certain rejuvenators, they may negatively impact the durability of the mixture, especially about its resistance to moisture damage and aging. Computational analysis showed that while the restoration capacity of rejuvenators is related to their penetration into and peptizing of asphaltene nanoaggregates, the durability of the restored aged asphalt is mainly related to the polarizability values of the rejuvenator. Rejuvenators with lower polarizability showed better resistance to aging and moisture damage.

In summary, this study develops the rheology-based indicators which relate to the molecular level phenomenon in the rejuvenation mechanism. The rheology-based indicators, for instance, crossover modulus and crossover frequency differentiated the rejuvenators from recycling agents. Moreover, the study found that rejuvenation efficiency and durability are depended on the chemistry of rejuvenators. Finally, based on the learning of chemistry, a chemically balanced rejuvenator is synthesized with superior rejuvenation properties.
Date Created
2020
Agent

Using Mixture Design Data and Existing Prediction Models to Evaluate the Potential Performance of Asphalt Pavements

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Description
Several ways exist to improve pavement performance over time. One suggestion is to tailor the asphalt pavement mix design according to certain specified specifications, set up by each state agency. Another option suggests the addition of modifiers that are known…

Several ways exist to improve pavement performance over time. One suggestion is to tailor the asphalt pavement mix design according to certain specified specifications, set up by each state agency. Another option suggests the addition of modifiers that are known to improve pavement performance, such as crumb rubber and fibers. Nowadays, improving asphalt pavement structures to meet specific climate conditions is a must. In addition, time and cost are two crucial settings and are very important to consider; these factors sometimes play a huge role in modifying the asphalt mix design needed to be set into place, and therefore alter the desired pavement performance over the expected life span of the structure. In recent studies, some methods refer to predicting pavement performance based on the asphalt mixtures volumetric properties.

In this research, an effort was undertaken to gather and collect most recent asphalt mixtures’ design data and compare it to historical data such as those available in the Long-Term Pavement Performance (LTPP), maintained by the Federal Highway Administration (FHWA). The new asphalt mixture design data was collected from 25 states within the United States and separated according to the four suggested climatic regions. The previously designed asphalt mixture designs in the 1960’s present in the LTPP Database implemented for the test sections were compared with the recently designed pavement mixtures gathered, and pavement performance was assessed using predictive models.

Three predictive models were studied in this research. The models were related to three major asphalt pavement distresses: Rutting, Fatigue Cracking and Thermal Cracking. Once the performance of the asphalt mixtures was assessed, four ranking criteria were developed to support the assessment of the mix designs quality at hand; namely, Low, Satisfactory, Good or Excellent. The evaluation results were reasonable and deemed acceptable. Out of the 48 asphalt mixtures design evaluated, the majority were between Satisfactory and Good.

The evaluation methodology and criteria developed are helpful tools in determining the quality of asphalt mixtures produced by the different agencies. They provide a quick insight on the needed improvement/modification against the potential development of distress during the lifespan of the pavement structure.
Date Created
2020
Agent

Laboratory and Field Evaluation of Plant Produced Asphalt Mixtures Containing RAP in Hot Climate Areas

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Description
The use of Reclaimed Asphalt Pavements (RAP) in newly produced asphalt mixtures has been gaining a wide attention from state Departments of Transportations (DOTs) during the past four decades. However, the performance of these mixtures in harsh and hot climate…

The use of Reclaimed Asphalt Pavements (RAP) in newly produced asphalt mixtures has been gaining a wide attention from state Departments of Transportations (DOTs) during the past four decades. However, the performance of these mixtures in harsh and hot climate areas such as Phoenix, Arizona has not been carefully addressed. This research focuses on evaluating the laboratory and field performance of Hot Mix Asphalt Mixtures (HMA) produced with two different RAP contents 15%, and 25%. A road section was identified by the City of Phoenix where three test sections were constructed; the first being a control (0% RAP), the second and the third sections with 15% and 25% RAP contents, respectively. The 25% RAP mixture used a lower Performance Grade (PG) asphalt per local practices. During construction, loose HMA mixtures were sampled and transported to the laboratory for advanced material characterization.

The testing included Dynamic Modulus (DM) test to characterize the stiffness of the material, Flow Number (FN) test to characterize the rutting resistance of the mixtures, IDEAL CT test to characterize the crack initiation properties, C* Fracture test to investigate the crack propagation properties, Uniaxial Fatigue to evaluate fatigue cracking potential, and Tensile Strength Ratio test (TSR) to evaluate the moisture susceptibility. Field cores were obtained from each test section and were tested for indirect tensile strength characteristics. In addition, asphalt binder testing was done on the extracted and recovered binders.

The laboratory results, compared to the control mixture, indicated that adding 15% and 25% RAP to the mix did not have significant effect on the stiffness, improved the rutting potential, had comparable cracking potential, and gave an acceptable passing performance against potential moisture damage. The binder testing that was done on the extracted and recovered binders indicated that the blended RAP binder yields a high stiffness. Based on results obtained from this study, it is recommended that the City of Phoenix should consider incorporating RAP in their asphalt mixtures using these low to moderate RAP contents. In the future implementation process, it is also recommended to include specifications where proper mixture designs are followed and supported with some of the laboratory tests outlined in this research.
Date Created
2019
Agent

Superpave Mix Design and Laboratory Testing of Reacted and Activated Rubber Modified Asphalt Mixtures

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Description

Crumb rubber use in asphalt mixtures using wet process technology has been in practice for years in the United States with good performance history; however, it has some drawbacks that include the need for special blending equipment, high rubber-binder temperatures,…

Crumb rubber use in asphalt mixtures using wet process technology has been in practice for years in the United States with good performance history; however, it has some drawbacks that include the need for special blending equipment, high rubber-binder temperatures, and longer waiting time at mixing plants. Pre-treated crumb rubber technologies are emerging as a new method to produce asphalt rubber mixtures in the field. A new crumb rubber modifier known as Reacted and Activated Rubber (RAR) is one such technology. RAR (industrially known as “RARX”) acts like an Enhanced Elastomeric Asphalt Extender to improve the engineering properties of the binder and mixtures. It is intended to be used in a dry mixing process with the purpose of simplifying mixing at the asphalt plant. The objective of this research study was first to perform a Superpave mix design for determination of optimum asphalt content with 35% RAR by weight of binder; and secondly, analyse the performance of RAR modified mixtures prepared using the dry process against Crumb Rubber Modified (CRM) mixtures prepared using the wet process by conducting various laboratory tests. Performance Grade (PG) 64-22 binder was used to fabricate RAR and CRM mixtures and Performance Grade (PG) 70-10 was used to fabricate Control mixtures for this study. Laboratory tests included: Dynamic Modulus Test, Flow Number Test, Tensile Strength Ratio, Axial Cyclic Fatigue Test and C* Fracture Test. Observations from test results indicated that RAR mixes prepared through the dry process had excellent fatigue life, moisture resistance and cracking resistance compared to the other mixtures.

Date Created
2018
Agent
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