Civil and Environmental Engineering

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This is the collection for the University of Waterloo's Department of Civil and Environmental Engineering.

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Characterization of Fresh and Hardened Properties of 3D Printable Cementitious Materials Produced with Ground-Granulated Blast-Furnace Slag
(University of Waterloo, 2021-09-24) Shoueb, Mohamad Basel; Baaj, Hassan; Polak, Maria Anna
Application of additive manufacturing technology to promote the digital construction practice in civil engineering has been gaining momentum, especially during the past 5 years. To this end, three dimensionalconcrete printing (3DCP) for structural elements has been the focus of several research groups around the globe.A comprehensive review of the existing literature was conducted as the first stage of this study with a focus on the fresh concrete properties, and deposition platform. Review of the literature indicates that in almost all of the published research, fly ash has been dominantly used as the supplementary cementitious material (SCM) in additive manufacturing of concrete mixes. However, fly ash is not domestically available in the majority of Canadian provinces, except for specific west coast areas, and hence is typicallyan imported material from the U.S. Since the fly ash is not a domestic material, its use leads to significant increase in the cost of 3D-Printed concrete mixes in Canada. On the other hand, proper use of concrete admixtures is a key when designing a printable concrete mix. Among the several admixtures that can be used such as accelerators, retarders, water reducers, and air-entraining agents;high range water reducers (a.k.a. superplasticizers) are considered essential. The existing literaturesin this area of technology have not addressed the effect of powder formed high range water reducers on the hardened properties for both castand printed concrete or on the printability. Furthermore, the literature review reports contradictory findings in terms of thecompressive and flexural strengths of castspecimens as compared to those of the printed specimens. In addition to these contradictory reports, the specimen dimensions used for such testing were not large enough to represent the effect of bond strength between the printed layers on the hardened concrete properties. It should also be noted that the stress-strain curves are not provided in almost all the materials published at the time of writing this paper. The lack of such information is considered a hindrance for successful modeling of 3D printed concrete objects using numerical methods such as finite element method (FEM). Developing a high performance 3D printable concrete mixes through the use of the domestically raw materials in Ontario and Canada was set as the primary goal, therefore, Ground Granulated Blast Furnace Slag (GGBFS) had been chosen as a cement replacement along with the use of powder superplasticizers. The experimental results had shown the mixes with GGBFS up to 39% along with a specific range of superplasticizer dosages have resulted in high-performance 3D printable mixes. However, the printed specimens exhibited sever anisotropic material behavior and reductions in compressive and flexural strengths comparing with the castspecimens.In robotic side, the developed platform at the University of Waterloo includes a six-degree of freedom robotic arm, a combined mixer and pump system, a replaceable nozzle connection, and safety cages. The system could be programmed to execute complicated shapes and printing patterns and is synchronized with aduo system to maintain a steady supply of materials proportional to the printing pace and interruptions. The selected system has the capability of being used in both laboratory and actual job site environments. To minimize the materials usage, the system was selected to run on dry ingredients (including sand, cementitious materials, and powder-form admixtures) with the water being added separately. Therefore, the production could be stopped at any point without the need to discard a considerable amount of mixed materials asitcommonly happens in conventional construction practices.
Chemo-rheological Characterization of Asphalt Binders Using Different Aging Processes
(University of Waterloo, 2025-03-17) Sharma, Aditi; Baaj, Hassan; Tavassoti, Pejoohan
The performance and longevity of asphalt pavements depend heavily on the properties of asphalt binders, which are affected by aging, binder modifications, and the incorporation of reclaimed asphalt pavement (RAP) materials. However, significant gaps exist in understanding the long-term chemical and rheological changes induced by aging processes (particularly with respect to differences between thermo-oxidative aging and UV exposure), and in the use/standardization of chemical analytical techniques such as Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy for binder characterization. Furthermore, the behaviour in RAP-virgin binder blends, along with the influence of bio-based rejuvenators and anti-aging additives under different aging conditions, remains underexplored. Addressing these gaps are crucial to developing more durable, sustainable pavements. This thesis bridges these research gaps through comprehensive investigation of chemo-rheological binder characterization, combining experimental testing with advanced analytical tools and varying aging methods. The findings offer essential insights into binder aging, rejuvenation strategies, and modification techniques, with significant implications for pavement durability and environmental sustainability. The first chapter presents an evaluation of Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) spectroscopy combined with functional group and multivariate analysis techniques to characterize asphalt binders. The research identifies challenges in repeatability across binder sources and aging states demonstrating the importance of standardized protocols for improving reliability. Repeatability as described by AASHTO standards is listed in the precision and bias statement as single operator precision. This is the allowable difference in two test results measured under the repeatability conditions (same asphalt binder, measured by the same operator, on the same piece of equipment in the same lab). Principal Component Analysis (PCA) and k-means clustering successfully classified binder types and aging states, with large quantity (LQ) sample preparation yielding more consistent results than small quantity (SQ) preparation. These findings underscore the need for uniform procedures in binder analysis, addressing inconsistencies prevalent in the current literature. The second part of the thesis investigates the impact of Styrene-Butadiene-Styrene (SBS) polymer modification on binder performance and oxidative resistance. Using Nuclear Magnetic Resonance (NMR) and ATR-FTIR spectroscopy, along with PCA and Partial Least Squares Regression (PLSR), the research highlights the ability of SBS to enhance high-temperature performance and slow thermo-oxidative aging. This work not only confirms previous findings on SBS but also provides new insights into the molecular interactions contributing to aging resistance. The study fills a gap in understanding how SBS-modified binders behave under various aging scenarios, offering a deeper perspective on polymer-modified asphalt technologies. The thesis also addresses a critical gap related to UV-induced aging, which has been underexplored in comparison to thermo-oxidative aging. A novel UV aging chamber was developed to simulate real-world environmental conditions, incorporating UV exposure, water spray cycles, and controlled heating at 70°C. Comparative analysis revealed that different additives exhibit varying effectiveness under UV and thermo-oxidative conditions. Zinc diethyldithiocarbamate (ZDC) showed strong resistance to thermo-oxidative aging but limited efficacy under UV aging, while ascorbic acid (Vit. C) accelerated aging under UV exposure, contrary to expectations. These findings emphasize the challenges involved in designing effective anti-aging strategies for asphalt binders, demonstrating the value of combining conventional rheological tests with spectroscopic techniques and further highlighting the need for more targeted approaches to additive selection and development. This thesis advances the understanding of asphalt binder behaviour and aging processes by integrating chemical, rheological, and multivariate analysis techniques. It offers critical contributions to the standardization of binder characterization protocols, the optimization of polymer-modified asphalt technologies, and the development of more effective anti-aging strategies. The research also demonstrates the potential of machine learning and artificial intelligence (AI) in predicting binder performance from spectroscopic data using multivariate analysis, paving the way for future innovations in asphalt binder characterization. In conclusion, the work in this thesis addresses significant gaps in the literature, providing new insights into aging mechanisms, additive/rejuvenation strategies, and RAP binder interactions. By combining chemical analysis, rheological testing, and multivariate techniques, this research contributes both to academic knowledge and practical pavement engineering, promoting the development of more sustainable, long-lasting asphalt pavements.
Development and Evaluation of Testing Protocols for Fatigue Damage and Crack-Healing of Bituminous Mixtures
(University of Waterloo, 2023-04-26) Zhao, Dandi; Baaj, Hassan; Tavassoti, Pejoohan
Fatigue testing is a very important performance test for asphalt concrete mixtures and has been studied for many years with varying levels of success. However, there are several imperfections in the commonly used fatigue tests. Furthermore, there is currently no universal standard to define fatigue failure in these tests, as fatigue damage cannot be effectively quantified due to the presence of bias effects. Researchers have used modified fatigue tests to study the self-healing capability of bituminous material. The healing capability of the material is typically quantified by comparing the modulus change with and without rest periods. However, the presence of reversible phenomena makes it even harder to quantify the healing effects. This research aims to improve the laboratory asphalt concrete fatigue damage and crack-healing tests by combining Non-destructive testing (NDT) methods. This study was conducted on polymer-modified asphalt concretes. The properties of the material used has been well studied in previous research and were used to compare with the results from this research. An ultrasonic pulse propagation test (UPPT) was conducted on undamaged specimens, specimens under monotonic loading and cyclic loading conditions, and during the healing processes. Two experimental protocols that combine traditional asphalt fatigue or cracking tests with UPPT to quantify and evaluate the damage and self-healing property of asphalt concrete were proposed. Several signal processing techniques were applied to study the performance of the test material. The results indicate that the UPPT method is sensitive to the microstructure, viscosity, elasticity, damage level and healing properties of asphalt concrete. The proposed Dynamic High-frequency Healing with Rest Period (D2HRP) test protocol successfully distinguishes changes in healing between stiffer and more aged binders. The combination of ultrasonic pulse propagation tests and tension-compression tests provides an indirect observation of changes of material property during the test, and the proportion of the bias effects were successfully quantified. The improved laboratory cracking and fatigue tests can promote sustainability in pavement materials and designs. Furthermore, this project will also contribute to a better understanding of crack initiation and propagation processes in pavement materials, which can improve the existing state of pavement rehabilitation and maintenance techniques as well as pavement condition prediction models.
DEVELOPMENT OF HIGH MODULUS ASPHALT CONCRETE MIX DESIGN TECHNOLOGY FOR USE ON ONTARIO’S HIGHWAYS
(University of Waterloo, 2019-01-07) Baghaee Moghaddam, Taher; Baaj, Hassan
Asphalt pavement is subjected to external loads including mechanical loading induced by traffic and thermal loading induced by thermal variations. The last decades have witnessed a significant rise in number of heavy vehicles especially commercial trucks with higher axle loads on rural and arterial roads in Ontario. Consequently, by increasing the number and amplitude of traffic loading and severe environmental condition, servile life of asphalt pavements has been adversely affected. In many cases, premature distresses were occurred before expected service life of asphalt pavements reaches to its end. On the other hand, new pavement materials, design procedures and construction technologies have been developed worldwide. One of these technologies is “Enrobé à Module Élevé- (EME)” or “High-Modulus Asphalt Mix”. EME is a type of asphalt concrete that represents high modulus/stiffness, high durability, superior rutting performance and good fatigue resistance. This type of mix was developed in France in the 1980’s. EME is a very good option to be used in lower and upper binder courses in the pavement structure which are subject to the highest levels of tensile and compressive stresses. EME offers several advantages over conventional binder course materials including reducing the thickness of the pavement structure with improved service life and reduction in raw materials consumption. Despite the excellent performance at higher and intermediate temperatures, traditional EME mixes would be very susceptible to low-temperature cracking which is associated to using very hard grade asphalt binder. In addition to the cold climate condition, some other aspects such as traffic volume, vehicle attributes, properties of raw materials, construction methods, and testing standards are specific to Ontario. Based on the aforementioned reasons, adopting EME technology will be beneficial to Ontario’s highways. However, development of a suitable EME mix design procedure in Ontario cannot be a duplicate copy of the French method, or any other methods used in other countries or jurisdictions. This study, funded by the Highway Infrastructure Innovation Funding Program (HIIFP-2015), aims to introduce a new approach to EME mix design that contributes to good performance at high, medium and low temperatures. This could be achieved by using premium aggregate particles with dense structure (high packing density), along with utilizing high quality asphalt binder with precise content in the mix. A performance-based mix design approach is developed for EME mix design in Ontario which is a modified version of Superpave mix design procedure. Compressible Packing Model (CPM) was used for the first time to optimize the packing density of aggregate particles for two categories of mixes (12.5 mm and 19 mm Nominal Maximum Aggregate Size (NMAS)). Three types of modified asphalt binders were also considered: PG 88-28, PG 82-28 and PG 58-28 + modifiers (Elastomer additives). In addition to measuring compaction ability (compactibility) of the developed mixes, several thermo-mechanical testing methods were designated to be used in this study to evaluate the performance of asphalt mixes at different levels. Results of this study showed that the CPM-obtained gradation limits were within the grading control points of EME mixes recommended by French specification. The asphalt mixes had higher compactibility than the conventional mix, and, EME 19 was more compactible than EME 12.5 although it had less binder content than EME 12.5. Complex modulus test results illustrated that the mixes had high modulus values, and that the values of EME 19 were generally higher than those of EME 12.5. Hamburg wheel track rutting test results showed both mix types had superior rutting performance. Fatigue performance of developed mixes was assessed using four-point bending beam fatigue test at different strain levels to develop fatigue curves. The test results showed that the minimum strain level to meet 1,000,000 cycles of fatigue life (ε6) was more than 300 μm/m for all the mixes. Additionally, Thermal Stress Restrained Specimen Test (TSRST) results showed that the cracking temperatures of the developed mixes were less than -25˚C; and that EME 12.5 performed slightly better than EME 19. Binder microstructure and rheological properties were assessed using environmental scanning electron microscope (ESEM) and dynamic shear rheometer (DSR) equipment respectively. Two springs, two parabolic elements and one dashpot (2S2P1D) rheological model is used to model and compare the viscoelastic behavior of the binders as well as the mixes. ESEM test results showed that microstructure of PG 88-28 binder was the densest and connected with thicker fibril size. PG 58-28 + Elastomer additives had highly intertwined structural network with the thinnest fibril size among the binder types. 2S2P1D results showed it is a powerful tool for modeling highly polymer modified asphalt binders as well as EME mixes. According to developed master curves the mixes’ moduli have followed the same pattern as for the binders’ although phase angles’ patterns were different. Correlations were found between the binders’ microstructures and their rheological properties. Binders with denser structure and stronger bonds showed to have lower phase angles. Although binders with more intertwined structural network had higher modulus particularly at higher frequencies. The EME mix design approach was validated by using the second source of aggregate materials and PG 82-28 asphalt binder. The SGC compactibility test results showed that the mixes were more compactible than the conventional Superpave mix. According to the rutting test results, the mixes had almost not rut after 20,000 wheel passes on the submerged specimens at 50°C (rut-depth < 1 mm). In addition, the developed mixes with the second source of aggregates had relatively higher fatigue resistance where ε6 values were greater than 550 μm/m for both EME 12.5 and EME 19. TSRST results also depicted that the cracking temperatures of both mixes were below -30°C.
Development of Sustainable Asphalt Mix Solution for use in Approach Intersection Pavements in Southern Ontario
(University of Waterloo, 2023-04-24) Kafi Farashah, Mehran; Tighe, Susan; Baaj, Hassan
Due to the continuous rise in heavy truck traffic and the impacts of climate change, York Region is facing premature pavement failure at many of its heavy truck traffic intersections, primarily in the form of deformation or rutting. This implies that the pavement materials commonly used in the York Region for heavy truck traffic volume intersections may not meet desired resilience. As a result, the York Region selected six approach intersections for examination to assess their in-service performance and determine any need for material improvement. The findings from the field investigation revealed that rutting damage was only present in the asphalt surface layer, suggesting that the pavement structures were structurally sound, and the rutting was possibly caused by inadequate asphalt mix stability. In addition, three (3) currently specified plant-produced asphalt surface mixes by York Region were investigated to evaluate their rutting resistance: HMA-SP12.5 FC1 PG64-28, HMA-SP12.5 FC1 PG70-28, and WMA-SP12.5 FC2 PG70-28. The research used HWTT, Flow Number, IDEAL-RT, and a modified Uniaxial Shear Tester. Although the WMA-SP12.5 FC2 provided the best results, the conclusion was that the current asphalt mixes are not suitable for intersections with high traffic volume due to inadequate rutting resistance. The results from both field investigation and laboratory tests on plant-produced asphalt surface mixes indicated that relying solely on volumetric design may not fully reflect the mix's performance under heavy traffic. It is advised to incorporate performance testing in the design stage for a more comprehensive understanding of the mix's rutting resistance and desired reliability. The intend of this research was to propose a sustainable asphalt surface mix for the heavy truck traffic approach intersections in Southern Ontario, aimed at improving its resilience to rutting and cracking through performance testing. Therefore, a total of seven lab-produced asphalt surface mixes including six SMA and one EME asphalt mixes were investigated. The SMA mixes were produced by using two Nominal Maximum Aggregate Sizes (NMAS), 9.5mm and 12.5mm, and three polymer-modified asphalt binders, namely PG70-28, PG76-28, and PG82-28. The EME mix was produced with a 12.5mm NMAS and PG82-28 asphalt binder. In addition, HWTT, IDEAL-RT, Flow Number, and Dynamic Modulus tests were conducted to evaluate the shear resistance of asphalt mixes. Moreover, I-FIT and IDEAL-CT tests were applied to determine the intermediate temperature cracking resistance. While the DC(T) test was employed to evaluate the low-temperature cracking resistance. Furthermore, BPT and TSR tests were conducted to investigate the friction and moisture susceptibility of asphalt mixes, respectively. To establish performance specifications for evaluating the resistance of asphalt surface mixes to rutting and cracking at approach intersections with high truck volume in Southern Ontario, the results of the HWTT, IDEAL-CT, I-FIT, and DC(T) tests on seven proposed heavy-duty asphalt mixes were analyzed. The proposed preliminary specifications stated that the HWTT test should be performed at a temperature of 58°C and with 40,000 wheel-track passes. Furthermore, it was suggested that the rut depth acceptance threshold be reduced from 12.5mm to 6mm to address safety concerns at approach intersections. Based on the study data, a pre-determined threshold DC(T) fracture energy value of 900 J/m2 can be used. Additionally, it was recommended that the Flexibility Index (FI) value be set at 20 and the CT Index value at 500 for the heavy-duty asphalt mixes. The overall ranking based on the results of the HWTT, I-FIT, DC(T), and IDEAL-CT tests indicated that the best performing lab-produced asphalt mix was SMA12.5-PG76-28. The results of the life cycle analysis demonstrated a substantial increase in the service life of the pavement, leading to both material and cost savings when using the SMA12.5-PG76-28 asphalt mix in comparison to a currently specified asphalt mix in the York Region.
Engineering and Environmental Assessment of Foam Glass Lightweight Aggregate for Pavement Application
(University of Waterloo, 2019-04-02) YOUSEFI, YASSAMAN; Baaj, Hassan; Tighe, Susan
Foam-Glass Lightweight Aggregate (FG-LWA) is an innovative lightweight material based 95% on waste and recycled glass. Several European countries use this type of material in the pavement structure and mainly as lightweight fill material. The major advantage of the FG-LWA is being more than 10 times lighter than traditional mineral aggregates, which makes it an ideal solution in cases where the dead load of the aggregates is an issue. The objective of this thesis is to evaluate and assess the potential of using FG-LWA, as an alternative to other lightweight fill materials such as Expanded Polystyrene (EPS) Blocks, in flexible pavements structures. Physical and mechanical properties of two commercially provided types of FG-LWA were previously studied at the CPATT laboratories of the University of Waterloo. To this end, particle size distribution, particle density, water absorption, minimum and maximum dry densities, California Bearing Ratio (CBR), Los Angles (LA) abrasion, resilient modulus, Mico-Deval and freez-thaw resistance of the material were evaluated by Schneider (2016). The results from this previously conducted study are summarized in this thesis and are used to determine whether the FG-LWA material is suitable to be employed as an alternative granular material in pavement construction, and whether it conforms to the requirements of the Ontario Provincial Standard Specification (OPSS) 1010 for granular A, M, O, S and B. In this thesis, it was deemed necessary to further investigate the effect of changes in the manufacturing processes on the formulation and microstructure of the FG-LWA with the aim of enhancing its mechanical properties for pavement construction applications. Therefore, the manufacturing processes were modified to adjust the microstructure (e.g. shapes and sizes of the pores) and phase compositions. Furthermore, in order to produce an enhanced FG-LWA, the application of ceramic colors, other glassy raw materials and glass-ceramics with a controlled microstructure was also investigated in this thesis. Examining the microstructure of the products indicated improvements in the physical characteristics of the enhanced FG-LWA as compared to the original product containing waste glass. Incorporation of coloring oxides in the foam formulation was also examined as an innovative method to increase the mechanical strength of a colorful product. In addition, chemical evaluation was conducted based on the results of leachate test. The results were evaluated thoroughly, and further tests were conducted at the Golder & Associates laboratories, accordingly. Given the considerable economic, environmental and societal impacts related to pavement construction and maintenance activities, it is crucial to evaluate the sustainability of the proposed pavement structure with FG-LWA. Several techniques are available to measure sustainability of a pavement structure. In this thesis, the mechanistic pavement design approach, along with a conceptual Life Cycle Assessment (LCA) model are used to evaluate the effectiveness of using FG-LWA as an alternative lightweight fill material as compared to the commonly used Expanded Polystyrene (EPS). For the purpose of mechanistic evaluation of FG-LWA application in the pavement structure, an existing Ministry of Transportation (MTO) project was re-evaluated and the results were used as the baseline of this study. The re-evaluation consisted of two phases of pavement design. Under phase one, the same pavement structure proposed by the MTO was adopted identically, except that the EPS in the original design was replaced with the same thickness of the FG-LWA material. In the second phase, four scenarios with different structural layer types and thicknesses were studied. The objective of the second phase was to find different, but equivalent, pavement structures with the use of FG-LWA, while achieving equal or smaller values than the original MTO design for the critical strains at the bottom of the asphalt layer and on top of the subgrade layer. To this end, KenPave program was used to determine the stresses and strains in the pavement layers using a multilayer elastic approach. Finally, LCA approach was used to quantify the relative environmental impacts of using FG-LWA and EPS in the pavement structure. The SimaPro software program was used to analyze the performance of the products with respect to sustainability measures. Two flexible pavement structures, previously designed at the University of Waterloo for a specific set of traffic and climatic conditions (Schneider, 2016), were used in the LCA study. The first pavement structure, considered as the reference scenario, used Expanded Polystyrene (EPS) as lightweight fill material. In the second scenario, the EPS was replaced by FG-LWA, and thicknesses of all other layers (i.e. asphalt concrete and granular layers) were determined using the AASHTO 93 Pavement Design Approach, hence the two pavement structures could be assumed equivalent and structurally comparable. The environmental impact categories considered in the LCA studies included: Ozone depletion potential, global warming potential, acidification potential, eutrophication potential, carcinogens, noncarcinogens, smog potential, respiratory effects, ecotoxicity, and fossil fuel depletion. The impacts are calculated using the characterization factors from the TRACI 2.1 LCA model. Two methods of manufacturing foam glass are evaluated, namely using electricity versus natural gas in Ontario. Based on this comparison, it was determined that it is feasible to transfer the new foam glass technologies to Canada’s road network instead of using other non-environmentally friendly materials. The results indicate that FG-LWA can be used as a light fill material in the flexible pavement structure to achieve better or equivalent structural capacity as compared to the traditional EPS. The environmental impacts assessments also indicate lower emission level and environmental impacts when using FG-LWA instead of EPS for pavement construction.
Enhancing Real-Time Data Acquisition from Embedded Road Structural Health Monitoring Systems
(University of Waterloo, 2024-04-23) Ceric, Matea; Baaj, Hassan; Tavassoti-Kheiry, Pezhouhan
Canada's economy heavily relies on its roadways, yet managing pavement assets faces challenges due to past infrastructure spending cuts. Addressing this, a pavement management system (PMS) is essential for efficient resource allocation. Traditional surface condition monitoring within PMS is time-consuming and costly. In response, in situ condition monitoring, integrating AI and ML, emerges as a viable alternative, aligning with the development of "smart" pavements. This thesis, part of the Smart Pavements project at the University of Waterloo, assesses an instrumented pavement section on Courtland Avenue, Kitchener. It provides a comprehensive assessment of the implementation, data collection, data analysis and database concept development processes of an instrumented test section. It integrates advanced monitoring technologies and predictive modeling, yielding promising results. Identified gaps in the literature are addressed, with scalability and cost-benefit analysis highlighted for future research. Challenges in instrumentation and testing, including weather delays, are discussed, with recommendations provided. Material testing procedures and truck testing results are outlined, emphasizing seasonal variations and the impact of vehicle wander on pavement behavior. Software comparisons and detailed trend analysis reveal insights into pavement performance. Additionally, a basic database framework is proposed for efficient data management. This study contributes to understanding pavement instrumentation, long-term behavior, and the efficacy of simulation methods. Recommendations for future work include AI/ML integration, long-term data collection, database development, and standardized guidelines for sensor implementation, aiming to enhance pavement management practices nationwide.
Evaluating the Effect of a Self-Healing Elastomer on the Self-Healing Properties of Asphalt Cement
(University of Waterloo, 2020-09-25) Aurilio, Mike; Baaj, Hassan
Asphalt pavements exhibit an interesting behaviour when the traffic loading is removed. The chemical structure of asphalt cement lends itself to the ability to heal damage and improve the longevity of the pavement. This phenomenon was first discovered in the 1960s and makes up an interesting area of research. The area of self-healing materials has been a growing area of research for materials in general, but recently attempts have been made to improve the natural healing capabilities of asphalt cement. Other branches of science have begun using microcapsules dispersed through the matrix to distribute healing agent upon damage. Styrene Butadiene Styrene (SBS) modification of asphalt cement is already a common technology in the pavement industry, and this has inspired the idea to introduce a polymer that has self-healing properties into asphalt cement. This thesis looks at the effect of traditional elastomeric modification on the healing efficiency of asphalt cement and explore the use of a novel self-healing elastomer (SHE) to modify the asphalt cement healing properties. Data in this thesis indicates that the self-healing elastomer used here was unable to improve the healing efficiency of asphalt cement, while SBS has shown some ability to improve crack healing. SBS has also shown a great ability to improve adhesion, which may influence the cohesive healing ability of asphalt cement.
Experimental Investigation and ANN Modelling of the Behavior of Asphalt Binders Modified with Novel Geopolymers
(University of Waterloo, 2022-08-24) Hamid, abdulrahman; Baaj, Hassan; El Hakim, Mohab
The design of asphalt pavement has an impact on a country’s economic and environmental development. The main factors limiting the service life of flexible pavements are severe weather and increasing traffic volumes. Rutting and cracking of flexible pavement are two common types of distress that affect the serviceability and quality of the world’s transportation network. This subject has been studied extensively for decades, and it has evolved into a serious challenge that has yet to be fully resolved. Multiple research efforts have been undertaken around the world to increase pavement service life to fulfil future demand for economic expansion and community development. Multiple options for developing sustainable and cost-effective asphalt mixes with extended service life are being investigated. Although improving the characteristics of the asphalt binder has been shown to be a promising strategy. Geopolymer research is gaining a lot of attention these years because it can be employed in a variety of applications, such as geopolymer concrete and mortar, soil stabilization, and pavement construction. The geopolymer is formed when the aluminosilicate source, such as fly ash, reacts with the alkaline solution. Geopolymers are environmentally friendly materials that emit minimal CO2 during manufacture and can be used to eliminate waste and by-product materials like fly ash. It has also demonstrated its potential to rapidly acquire mechanical properties, improve fire resistance, and reduce energy use and greenhouse emissions. Despite, the use of geopolymer materials as a modifier for asphalt binder and mixture has gotten minimal attention, which could be due to the lack of research linking the effect of temperature and curing time on geopolymer performance and asphalt binder rheological behavior. Thus, considering these effects could motivate scientists to employ various types of geopolymers using by-products and waste materials, which would have significant financial and environmental benefits. This research aimed to evaluate the effects of geopolymers on the rheological and performance of asphalt binder, considering the impact of temperatures, frequencies, and stresses. The rheological and performance properties of neat and modified asphalt binder were investigated using Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR), and Environmental Scanning Electron Microscopy (ESEM) imaging devices. Also, the Viscoelastic Continuum Damage (VECD) model with the Linear Amplitude Sweep (LAS) was utilized to evaluate the fatigue behavior of the asphalt binder. Moreover, the Multiple Stress Creep Recovery (MSCR) test was conducted at various temperatures and stresses to calculate the non-recoverable creep compliance (Jnr) and the percent strain recovery (R). Furthermore, the Hamburg Wheel Rut Test (HWRT), dynamic/complex modulus, and moisture damage evaluation tests were conducted to evaluate the effect of additives on the performance of asphalt mixes. On the other hand, the interactive effects of geopolymer content and temperature on non-recoverable creep compliance (Jnr) and creep recovery percentage (R) of geopolymer-modified asphalt binders were investigated and predictive mathematical models were developed using the Response Surface Method (RSM) and regression method. Also, the Artificial Neural Networks (ANNs) model was developed to predict the recovery and non-recovery performance of asphalt binders using five input parameters (temperature, frequency, storage modulus, loss modulus, and viscosity) and one hidden layer with five neurons. To implement a backpropagation learning process in a feed-forward neural network, Scaled Conjugate Gradient (SCG), Levenberg-Marquardt (LM), and Bayesian Regularization (BR) training algorithms were performed. The results showed that fly ash and glass powder could be used as an aluminosilicate source during the preparation of geopolymer as an asphalt modifier, which has an essential influence on the rheological and performance of asphalt binder. While increasing the percentage of the geopolymer does not seem to affect the microstructure of the asphalt binder. The geopolymer has a significant impact on the binder’s sensitivity to temperature, whereby the temperature sensitivity for both unaged and RTFO-modified asphalt binders decreases. While adding the geopolymer to SBS enhances the binder’s ability to withstand extremely heavy traffic under high stress and temperature, the permanent deformation of the asphalt mix decreases by 82% compared with using the neat asphalt binder. Therefore, the combination of geopolymer and SBS could be used to improve the rutting resistance capability of asphalt concrete in hot climate countries. Furthermore, it was noted that the ANNs model is appropriate to predict the percent recovery and non-recovery compliance of modified asphalt binder using unaged or aged binders at different temperatures.
Fatigue Characterization of Asphalt Mixes with Polymer Modified Asphalt Cement
(University of Waterloo, 2018-11-14) Qabur, Ali; Baaj, Hassan
Asphalt pavement cracking is the most prevalent distress in pavements. In flexible pavements, fatigue cracking is a major cause of deterioration and can significantly reduce the service life of pavements [1]. Fatigue cracking is caused by traffic loading and can be accelerated by aging of the asphalt, freeze-thaw cycles, and poorly designed asphalt concrete mixture. Fatigue resistance of asphalt mixes could be improved by adding Polymer Modified Asphalt Cement (PMAC) [2]. In particular, the use of Styrene-Butadiene-Styrene (SBS) was found to be an efficient way to increase the fatigue life of mixes [3]. However, the primary issue is the lack of consistent performance testing methods to determine fatigue performance. In addition, the relationship between the PMAC properties and mixture performance is not fully understood. This thesis will focus on the evaluation of asphalt mixes with PMAC using the 4 point-bending beam (4PB) test to determine the fatigue performance of asphalt mixtures. The classical fatigue “WÖHLER’’ curve and “DGCB” damage rate method, which was developed at Département Génie Civil et Bâtiment in Lyon, have been used to evaluate and characterize the fatigue of the asphalt mixes in this study. In general, it was found that the fatigue life (Nf50%) was improved when Polymer Modified Asphalt Cement was used, and the polymer content increased. Both fatigue analysis methods, by WÖHLER curve and the DGCB method, showed that the addition of SBS polymer improved the fatigue life and reduced the damage from fatigue loading. Finally, some recommendations were made with regards to fatigue testing.
Full-Depth Reclamation with Hydraulic Road Binders
(University of Waterloo, 2020-01-20) Melese, Eskedil Abebaw; Tighe, Susan; Baaj, Hassan
According to a recent report, 16.4% of Canadian roads are in a poor or very poor condition. This means 146,255 km of the Canadian roads are either unfit for service or are approaching the end of their service life. The roads in these conditions require immediate action to restore their serviceability. One of the plausible techniques that could be applied to restore the serviceability of roads in poor or very poor conditions is full-depth reclamation (FDR). Full depth reclamation is a type of pavement cold in-place recycling in which the existing old and deteriorated pavement is pulverised, treated with appropriate stabilizer and compacted to form a strong base layer. In Canada, the stabilizers commonly used in the FDR process are asphalt emulsions, foamed asphalt, and Portland cement. Hydraulic road binders (HRB), however, are alternative cementitious stabilizers that can be used in full-depth reclamation process with some better attributes than Portland cement. The main objectives of this research are characterisation and impact assessment of fully reclaimed pavement materials treated with HRB. The study was conducted in the form of comparative assessment by using reclaimed materials treated with General Use (GU) cement as control mixes. Four types of reclaimed materials and four types of cementitious binders, including GU cement, were used to make sixteen different mixes. Characterisation and performance tests were conducted to understand the behaviour of the mixtures under static and dynamic loadings. Besides, life-cycle assessment was conducted to investigate the environmental impacts of the different cementitious binders. The findings of the study indicate that HRB, of the type used in the study, can be used in full-depth reclamation process without compromising the strength and durability of the mixtures. However, not all HRB substantially reduce the environmental impacts and energy requirements. Among the binders used in the study, the HRB with the lowest C/S ratio can significantly reduce the global warming potential.
Hydraulic Road Binder (HRB) and Its Use for Subgrade Stabilization in Ontario, Canada
(University of Waterloo, 2019-12-18) Wang, Shenglin; Baaj, Hassan
The term “subgrade” refers to the in-situ material composed of natural soil located underneath the pavement structural layers. The quality of natural subgrade is highly influenced by soil type, moisture content, and organic content. Furthermore, the failure of subgrade soils may lead to severe pavement distresses including rutting, potholes, and cracking. In order to enhance the subgrade engineering properties, a variety of stabilization methods have been developed. One of the most popular and cost-effective methods is in-situ subgrade soil stabilization using hydraulic binders. In-field soil modification and stabilization frequently use Portland cement as the chemical additive. Such method significantly enhances the engineering characteristics of soils in terms of plasticity, strength, stiffness, and durability. Despite the advantages, the chemical mixing also brings some disadvantages including rapid setting, drying shrinkage cracking, and higher cost. Recently, Supplementary Cementitious Materials (SCMs) made of by-products and industrial secondary materials (e.g. granulated blast furnace slag, cement kiln dust and fly ash) have been studied extensively to reduce the use of cement. Hydraulic Road Binder (HRB) is a European specified material designed for treatment of road bases, subbases as well as earthworks. HRB contains both cement clinker and a substantial amount of SCMs. Therefore, the use of HRBs has the potential to be more cost-effective and environmentally friendly than Portland cement. However, the research and application of HRB is new in Canada. The study started with an investigation of cement and different formulated HRBs in the form of paste and mix (mortar). Then, selected HRBs were used to evaluate their impacts on the chemical and physical properties of three local subgrade soils. In addition, a field application of weak subgrade stabilization using cement was introduced. Lastly, a study aiming to predict the long-term pavement performance was conducted in order to simulate the impact of stabilized subgrade in pavement design. The research findings are summarized as follows: • HRBs were found to reduce the setting time, reduce the speed of hydration, and the hydration temperature compared to Portland cement. The hydration products in hydrated HRBs and Portland cements were generally the same, but their contents were different. In addition, a reduction of drying shrinkage was observed in HRB mortars especially in those containing substantial SCMs. Regarding the strength, several HRB mortars had equivalent strength as cement mortars after 28 days of curing. Furthermore, a linear correlation was found between the compressive strength and flexible strength. Statistical analysis further revealed that the strength of HRB mix highly correlated to the content of GU, GUL, and GGBFS. • All the three subgrade soils (named Dresden, Blenheim, and Niagara) were fine-grained soils with substantial silt- and clay- sized particles. Ignition test indicated that all the three soils include high content of organic matters. In particular, Niagara soil with high plasticity, high organic material content had lower strength and modulus compared to the other two soils. Using the stabilizers, the soil’s pH values increased to around 12 and above. In addition, significant improvement had been observed in stabilized soils in terms of strength, durability, and resilient modulus. Nevertheless, the clay particles and organic matters inhibited the treatment. Increase of stabilizer content further promoted improvement. In particular, HRB-4LS had the best stabilization effect followed by GU, HRB-4LF, and HRB-3S. On the other hand, HRB-2S and HRB-3C treated soils had lower strength and modulus values. Finally, statistical analysis indicated that soil’s UCS values correlated with binder strength, binder content, curing, and untreated soil’s strength. • Field testing indicated that the workability and conditions of subgrade were significantly improved by hydraulic binder. Moreover, the modulus of subgrade surface further increased with curing time. After one year of service, the conditions of roads were good in most test sections. Furthermore, long-term pavement performance prediction (LTPP) revealed the feasibility of using cement and HRB stabilized subgrade to reduce the thickness of subbase layer. In terms of international roughness index and subgrade deformation, pavements constructed with HRB stabilized subgrade materials had equivalent performance as cement treated one over their design life. To summarize, this study focused on evaluating the used of Hydraulic Road Binders formulated in Canada for pavement subgrade stabilization. The research showed that HRB mortars have similar or slightly better strength compared to Portland cement alone with sufficient curing time. Moreover, The HRB improved subgrade soils were shown to perform adequately using several HRB types. In addition, the use of HRB-stabilized subgrade in pavement structure would improve the LTPP of pavement. Therefore, the use of HRB in the subgrade stabilization could be a promising solution in pavement construction due to its equivalent performance and with the potential environmental and cost advantages.
Improving Durability of Asphalt Mixes Produced With Reclaimed Asphalt Pavement (RAP) by Enhancing Binder Blending
(University of Waterloo, 2019-04-30) Kadhim, Hawraa; Baaj, Hassan
Reclaimed Asphalt Pavement (RAP) has been favoured over virgin materials in the light of the unstable cost of virgin asphalt binders, shortage of quality aggregates, and compelling need to preserve the environment and natural resources. Mixes containing up to 20% RAP are commonly considered to have similar behaviour to virgin mixes. However, during the production process of HMA with RAP, the blending between aged and virgin binders would be partial, which would create heterogeneity in distribution of the aged recycled binder and the soft virgin binder in the HMA-RAP mixes. Hence, it is important to control the blending process between old and new binders to obtain more homogenous mix. Therefore, the main objectives of this research are to examine the kinematics of blending of aged and virgin binders by considering the time-temperature effect during mixing and silo-storage, and assess the thermo-mechanical behaviour of Hot Mix Asphalt (HMA) containing RAP at different blending states. The asphalt mixes used in this research were produced and collected at two plants (Plant 1) and (Plant 2) located in Ontario, Canada. Two Marshall mixes were produced and collected from Plant 1 including a surface course HL-3 containing 15 percent RAP and a base course HL-8 containing 30 percent RAP. These mixes were labelled as 1HL-3 and 1HL-8 respectively. In addition, two Marshall mixes were produced and collected from Plant 2 including a surface course HL-3 containing 20 percent RAP and a base course HL-8 containing 40 percent RAP. These mixes were labelled as 2HL-3 and 2HL-8 respectively. To investigate the impact of storage time on the blending progress and achieving a cohesive final binder, the mix samples were collected as a function of storage time in the silo. The first sampling was done immediately after production (t = 0-hour), and then at several time intervals of silo-storage; i.e., at 1, 4, 8, and 12 hours. In case of Plant 2, the samples were additionally collected after 24-hour of storage time. All samples were then kept in a storage room at 7˚C until the day of compaction to minimize any further blending between aged and virgin binder. To understand the blending phenomena and its effect on the performance of the pavement, a multi-scale investigation is carried out. The blending was examined in terms of micro-mechanical and rheological properties. The microstructure of the blending zones were examined under The Environmental Scanning Electron Microscope (ESEM). In addition the effect of the silo-storage time on the rheology of the binders was investigated. The results indicate that increasing the interaction time and temperature between the aged and virgin binder significantly results in a better blending. The performance of RAP-HMA with respect to the silo-storage time was examined using Dynamic Modules Test, Thermal Stress Restrained Specimen Test (TSRST), Rutting Test, and Flexural Beam Fatigue Test. The experimental data indicates that samples collected after 12-hour of silo storage exhibited a reduction in the stiffness due to better blending of aged and virgin binder. In addition, the 12-hour samples showed enhancement in their fracture temperature, rutting depth, and fatigue life, accompanied with a better blending between their aged and virgin binder. On the other hand, the samples that collected after 24-hour silo-storage had a higher stiffness in comparison with the 8 and 12-hour samples. Moreover, the AASHTOWare Pavement Mechanistic-Empirical Design was utilized to examine the effect of the 12-hour silo-storage time on the long term performance of the pavements. Four pavement structures have been designed for this purpose. These pavements have the same structure of their granular A, granular B, and the subgrade. Yet, the first layer (surface course and base course) is a silo-storage time-dependent. The long-term field performance prediction indicates a slight improvement with the 12-hour pavements (Plant1 12hrs and Plant2 12hrs). However, it should be noted that AASHTOWare Pavement Mechanistic-Empirical Design does not appear to properly capture the effect of blending in the pavement performance. The collected experimental evidences unveils correlations between time-temperature effects and mixture performance. Based on these findings, the research provides practical recommendations to the professionals of the Canadian asphalt industry for a better use of RAP. Ultimately, this research recommends a 12-hour silo-storage time for the RAP-HMA for better performance and durability of the mixes
Investigating and Developing Fatigue-Healing Characterization of Asphalt Materials
(University of Waterloo, 2023-04-25) Aurilio, Roberto; Baaj, Hassan
Canada’s aging highway network, consisting of over 1.1 million kilometres of roads, is a vital component in ensuring the safe and reliable day-to-day movement of people and goods. Flexible asphalt pavements experience deterioration due to repeated traffic and environmental loading, and as a consequence, may require costly maintenance and rehabilitation treatments to remain functional over their service life. An alternative strategy to these reactive treatments can be found in the form of self-healing asphalt pavements. The innovative strategies employed in self-healing materials are rooted in natural and biological processes. In the simplest sense, as these materials become damaged, a natural healing response allows them to restore their integrity or functional properties. Bitumen and asphalt materials have a very similar intrinsic healing ability which has been recognized since it was first observed in the 1960s. Asphalt material self-healing arises from the asphalt cement and its ability to fill microcracks caused by repeated small strain amplitude loading (i.e., fatigue). Intrinsic healing is influenced by internal factors (e.g., asphalt cement chemistry, aging level, and modification type) and external factors (e.g., moisture, UV exposure, rest period duration and temperature, etc.). To overcome the limitations of intrinsic healing, several extrinsic healing technologies have been used in literature including molecular interdiffusion techniques, structures containing healing agents and secondary self-healing polymer phases. In recent studies, healing is primarily characterized using destructive accelerated fatigue and fracture-based tests with rest periods, but the lack of industry-standard tests and terminology for both asphalt cement and mixtures leads to an often-ambiguous understanding of healing itself. This lack of standardization limits the capability of researchers to effectively characterize the intrinsic healing ability, but also develop new extrinsic healing technologies. The principal goal of this thesis is then to investigate current self-healing characterization techniques and develop new testing protocols for asphalt materials. The work presented in this thesis uses a multiscale approach to the healing characterization of asphalt materials in collaboration with RILEM Technical Committee CHA-278 (Crack Healing of Asphalt Materials). Based on the initial healing study of unaged and aged asphalt cement containing a chemical warm mix additive using the linear amplitude sweep healing (LASH) test, it was evident that current generation DSR-based fatigue and healing characterization techniques experience measurement artifacts caused by geometry changes/ specimen flow under loading. As a result, a comprehensive evaluation of the linear amplitude (LAS) test and different failure criteria found in literature was conducted. These failure criteria were then supplemented with the complementary parameters: the electric torque inflection point, the peak normal force, and the flow strain amplitude (FSA) as determined from the novel DSR Visual Analysis workflow. From the analysis of the LAS test, it was shown that failure criteria strain amplitudes could be categorized as either peak or post-peak behaviour; the traditional peak shear strain amplitude was concluded to be the most conservative failure criteria for all aging levels. From the FSA analysis, it was demonstrated that the shear stress-strain peak correlated with the onset of specimen flow, thus, the peak value was selected as the maximum strain amplitude for the first phase end condition for subsequent healing tests. In cooperation with the RILEM CHA-278 Task Group (TG) 2a, a second version of the LASH test protocol was proposed and evaluated based on the recommendations of the LAS visual analysis. From various works in literature, the Pure-LASH or P-LASH peak-based analysis method was derived using fracture mechanics to model the restoration ability of several binders at different aging levels using the LASH V2 protocol. Test parameters such as rest period duration and aging level were found to not be statistically significant factors, but further analysis determined that “damage” was only observed when the first loading phase end condition was the peak shear stress strain amplitude (γpeak) as flow had already irreparably change the geometry of the DSR specimen. The general conclusion of these works was that geometric changes of the DSR sample during loading produce increasingly inaccurate measurements of post-peak data in amplitude sweep tests, thus, future work should take a greater emphasis on the characterization of pre-peak behaviour. As a contribution to RILEM CHA-278 TG 2b, intermediate temperature fatigue tests with rest periods were conducted on a single asphalt mix at two strain levels. From the fatigue tests, a new fatigue model called the Intrinsic-VECD or iVECD linearization model was derived from the DGCB intrinsic damage model and simplified viscoelastic continuum damage model (VECD). The iVECD model was then extended to healing tests to separate “true” fatigue damage from common bias prevalent in accelerated fatigue testing of asphalt materials. From the iVECD model, several restoration/healing and damage indices were proposed: %Heal, %Recovery, %Restoration and Permanent Damage (%PD). Results of the iVECD healing indices indicated that the majority of recovery and healing occurs within the first 4 to 6 hours of the rest period. However, it was observed that increasing the strain level produces more permanent damage for the same loading duration. Finally, non-invasive ultrasonic measurements were coupled to these destructive fatigue tests and coda wave interferometry (CWI) was used to analyze the effects of multiple scattering due to damage and healing. Two windowing selection methods were proposed (i.e., a simplistic statistical method and an adaptive analytical method). Using both window selection techniques, it was demonstrated that CWI could capture the effect of both loading/unloading and was sensitive enough to clearly distinguish between different strain levels.
Investigating Solutions for Self-Healing and Crack Mitigation of Flexible Pavement Materials
(University of Waterloo, 2023-01-23) Almutairi, Haya; Baaj, Hassan
In Canada, cracking is the most common deterioration mode of flexible pavements that occurs for different reasons such as traffic loading, and low temperature. Moreover, the propagation of cracks can be accelerated by the oxidation of the asphalt. In this study, innovative new solutions to improve the self-healing of asphalt materials and extend the service life of pavements were investigated. This research involves investigating the self-healing behavior of both Hot Mix Asphalt (HMA) modified with aramid fibres and asphalt cement modified with Polymers, Glass Powder (GP), Phase-Change Materials (PCM). For the HMA modified mixtures with aramid fibres with different dosages and lengths of 110 g/tonne, 138 g/tonne and 164 g/tonne; and 13, 20, 25mm, respectively, rutting, fatigue, and low-temperature cracking tests were used to assess the feasibility of these fibres to improve the healing capacity. It was found that there was no positive impact of using these fibres as a reinforcement of the asphalt mixture; therefore, the self-healing behavior of these mixtures could not be evaluated. As for the asphalt binder evaluation, a laboratory study on the rheological, spectroscopic, and chemical characterization of asphalt binders modified with Polymers, GP and PCM was conducted. Different binders, which are Control, PG 70-28, 5%PCM, 5%GPCM, 7%GPCM, 5% GPCM-SBS and 7% GPCM-SBS binders were assessed using Differential Scanning Calorimetry (DSC), Thermogravimetric Analyzer (TGA) Fourier Transforms Infrared Spectroscopy (FTIR), Viscometer, Dynamic Shear Rheometer (DSR) and Environmental Scanning Electron Microscopy (ESEM). The results showed that the degradation temperature for the PCM was low; therefore, the PCM cannot be used in HMA. In addition, modified binders with PCM and GPCM showed a low viscos behavior compared to the control binder. The DSR rheological analysis showed that the Control binder and 5%PCM, 5%GPCM, 7%GPCM, 5%GPCM-SBS and 7%GPCM-SBS binders had a similar overall property. However, the addition of GPCM significantly decreases the stiffness at intermediate temperatures. Moreover, the DSR was used to investigate the self-healing and fatigue resistance properties of asphalt binders. Two different types of binders, PG 58-28 and PG 70-28, were modified with GP and GPCM and evaluated. Three different percentages of GP and GPCM of 3.5%, 5% and 7% by weight of the binder were considered. The LAS test was conducted with/without rest period (5-min or 30-min) to measure the healing index and fatigue behavior of the asphalt binders. The binders were evaluated based on its fatigue resistance and healing capacity. The Linear Amplitude Sweep (LAS) and Pure Linear Amplitude Sweep (PLAS) were used to evaluate the fatigue resistance; whereas the self-healing capacity was assessed using Pure Linear Amplitude Sweep Healing (PLASH). The evaluation using LAS and PLAS methods demonstrated that the addition of GP does not improve the fatigue resistance of the binders in both; however, the highest fatigue resistance was reported with the addition of 7%GPCM. It was noticed that a small improvement in the self-healing ability when a 5-min rest period is introduced. Finally, the healing capacity of asphalt binders was significantly improved when a longer rest period was introduced.
Investigation of Different Factors Affecting Asphalt Cement Ageing and Durability
(University of Waterloo, 2019-08-21) Azimi Alamdary, Yashar; Baaj, Hassan
Asphalt cement is an organic material and, like any other organic material tends to react with atmospheric oxygen, thus changing its physical properties (more accurately rheological properties) gradually over time. Although there is no doubt that chemical changes happen in asphalt cement due to gradual oxidation, it is not the only factor resulting in changes in asphalt cement properties over time. Other factors such as loss of volatiles, the selective absorbance of lighter oily molecules by the aggregates’ surface, molecular reorientation, and so forth, could lead to changes in asphalt cement properties, most of which result in hardening. The alteration in physical properties of asphalt cement during construction and its performance period is called ageing. The severity of the age-hardening significantly depends on environmental factors such as temperature, latitude (which affects the angle of sunshine radiation), humidity, ultraviolet, etcetera, as well as mixture properties (such as aggregate gradation, aggregate type, air-void distribution, filler composition, and additive’s properties). There are several conditioning procedures to simulate short- and long-term ageing for both asphalt cement and mixes. Unfortunately, most of the existing methods are using excessively high conditioning temperatures and not realistic conditioning parameters. This project aims to identify the importance of less considered factors, such as the possible catalytic effect of minerals, solar radiation, and humidity conditioning and to define a laboratory long-term age conditioning procedure for asphalt mixes by considering different affecting factors to enable designers to include an ageing mechanism in their predictions. To reach to the goals of this project, compacted asphalt mix samples prepared using aggregates with different petrology and conditioned using standard (AASHTO R30) procedure and bespoke methods to include as much as environmental factors as possible. Complex (Dynamic) Modulus test will be used to evaluate the changes in the rheological behaviour of mixes. The 2S2P1D model fitted on laboratory results and used to investigate the rheological behaviour. Asphalt cement of the conditioned mixes extracted for further investigation on the rheological and chemical changes in asphalt cement. Frequency sweep test performed on extracted asphalt cement and results were processed using the 2S2P1D model. FT-IR spectroscopy was also used to investigate the change in the chemistry of asphalt cement by following the changes in carbonyl and sulfoxide indices and the ratio between them. Thermal sensitivity of rheological properties of both asphalt mix and asphalt cement was also investigated using time-temperature superposition shift-factors and utilizing Arrhenius and William-Landel- Ferry (WLF) theorems to further investigate the effect of different age conditioning and aggregates. Results of this research confirmed the effect of iron sulphide oxidation products in altering the chemistry of changes during ageing, while it didn’t capture significant acceleration in the process. Moreover, it was found that the coupling water treatment with solar radiation can effectively age asphalt mix samples and the product of ageing using these parameters are considerably different from extended heating procedures.
Optimization of the Use of Post-Industrial Recycled Multilayer Plastic Packaging (MPP) as Asphalt Modifier
(University of Waterloo, 2023-04-27) Qabur, Ali; Baaj, Hassan; El-Hakim, Mohab
The quality of road infrastructure significantly impacts the safety and comfort of road users and the country's economy. In Canada, 15% of roads are rated poor or very poor, with 108,000 km in poor condition, costing drivers CAD 3 billion annually. The cost of pavement maintenance and repairs can be high while investing in sustainable pavement design and maintenance is crucial to ensure longevity and safety. Researchers have investigated using thermoplastic additives, including recycled plastics, to improve pavement performance. Using multi-layer packaging plastics (MPP) additives has become a potential solution to enhance asphalt pavement materials. The primary components of MPP are Polyethylene (PE), Polyester (PET), Nylon (NY), and Metalized Polyester (METPET). Incorporating MPPs into asphalt mixtures minimizes plastic waste generation while conserving virgin aggregate and asphalt cement. The MPP stream from the plastic industry can contribute significantly to this endeavour, allowing for a more controlled and superior output than post-consumer plastics. This approach provides a sustainable solution for both the plastic and asphalt industries with the added benefit of enhanced pavement performance. In Canada and the rest of the world, MPP waste is a growing concern due to its increasing volume over the past two decades, resulting in significant environmental and economic consequences. Recent studies have shown that the individual components of MPP, such as PE and PET, can be successfully used as asphalt modifiers, highlighting the potential for MPP to be used as an asphalt additive. However, a comprehensive study is lacking to evaluate MPP as a viable asphalt additive. This study aims to address this gap in the literature by evaluating the feasibility of using MPP as an asphalt modifier through wet and dry methods., Several sub-objectives were set to achieve this objective. These sub-objectives included the development of a laboratory-scale method for producing MPP powder, which can provide significant benefits for research, development, and education. The study then evaluates the physical, thermal, rheological, and storage properties of the MPP-modified binder at different MPP concentrations in asphalt cement (PG 58–28). The following tests were used: Differential Scanning Calorimeter (DSC), Thermogravimetric Analysis (TGA), Superpave Dynamic Shear Rheometer (DSR), Rotational Viscosity (RV), and Environmental Scanning Electron Microscopy (ESEM). The results from thermorheological testing indicate that incorporating MPP has a solid potential to improve permanent deformation resistance at high temperatures. Concentrations of less than 4% of MPP additives also offer adequate permanent deformation. The study also uses the wet method to investigate the effect of MPP additives on the low-temperature performance of asphalt binders and mixtures. As thermal cracking may have a significant impact on the structural integrity of asphalt pavements, the following tests were used to evaluate the low-temperature properties of modified materials: Thermal Gravimetric Analysis, Differential Scanning Calorimeter, Dynamic Shear Rheometer, Bending Beam Rheometer (BBR), Tensile Strain Restrained Specimen test (TSRST), and Complex Modulus test. It was observed that the chemical composition of MPP influenced the asphalt binder's physical and performance properties. At low temperatures, results show that MPP additives at all dosages increase stiffness, affecting the Superpave Continuous PG and BBR ΔTc parameter. While MPP additives can increase asphalt mixtures' stiffness, they may also reduce their resistance to thermal cracking, demonstrating that the MPP modification percentage should be limited to below 4% by the weight of the binder. Moreover, the study investigated the potential of using a high concentration of MPP pellets to enhance asphalt mixtures using the dry method. The following tests were used: Complex Modulus Test, Moisture-Induced Damage Test, British Pendulum Skid Resistance Tester, Indirect Tensile Cracking Test (Ideal-CT), and Hamburg Wheel Tracking Test (HWTT). The results show that incorporating MPP additives significantly improves resistance to softening at higher temperatures, fracture resistance, rutting resistance, load-carrying capacity, and skid resistance while reducing susceptibility to moisture damage. A more sustainable solution can be promoted by incorporating MPP additives into asphalt mixtures using wet and dry methods. The study highlights the need for increased efforts to address the growing MPP waste issue and promote sustainability and circular economy principles. The research has demonstrated that MPP waste can be upcycled to reduce plastic waste and conserve virgin materials such as asphalt cement, aggregate and plastic additives. The study's findings provide valuable information for policymakers and industries to develop sustainable strategies and regulations to address the MPP waste issue. Thus, repurposing plastic waste and promoting a circular economy is possible through a holistic approach and stakeholder collaboration. However, further research and testing are needed to determine MPP additives' long-term durability and effectiveness in asphalt mixtures under various environmental and traffic conditions. In summary, this study offers valuable insights into the potential of repurposing plastic waste to enhance pavement performance through a comprehensive evaluation of MPP as an asphalt modifier. The laboratory-scale method for producing MPP powder presents significant benefits for research and education.
Optimizing the Performance of Asphalt Mixes with High Reclaimed Asphalt Pavement Content Using Rejuvenators
(University of Waterloo, 2023-01-23) Liao, Hui; Baaj, Hassan; Tavassoti, Pejoohan
Reusing reclaimed asphalt pavement (a.k.a., RAP) has become a routine in the production of asphalt paving materials. Theoretically, RAP is a hundred percent recyclable material since its main components are high-quality, graded aggregates coated with durable asphalt binder. Unfortunately, due to the presence of the aged asphalt binder, most agencies only approve a limited percentage of RAP, either less than 20% to 30% of RAP (by weight of the total mix) or less than 25% of RAP binder replacement (by weight of the total binder content), to be incorporated in new asphalt mixes. For decades, pavement researchers have shown great enthusiasm for promoting the RAP rate in asphalt mixes. One of the most promising approaches is to use rejuvenators to restore the aged asphalt binder to a comparable or even better performance than the virgin asphalt binder. However, there is still a lack of knowledge and practice in using rejuvenators in producing sustainable and durable recycled asphalt mixes. The gap is not only limited to the type of rejuvenators to be used, but also to the optimal dosage, compatibility with virgin and RAP binder, stability under the elevated temperature atmosphere, mix design and manufacturing process, and uncertainties about the long-term performance of the revitalized high RAP mixes. As a result, this research was initiated to investigate the use of rejuvenators for optimizing the performance of asphalt mixes with higher RAP content. This study used seven commercial rejuvenators provided by various suppliers, as well as materials collected at local asphalt plants and refineries for the experimental work, which included six bio-based oils, one petroleum-based oil, one processed RAP, graded virgin aggregates, and two virgin asphalt binders. A sequential screening methodology was applied to evaluate the rejuvenating efficacy of these rejuvenators and a soft binder using various binder and mix tests and data analysis tools. In the first part of this research, rejuvenated binder blends with different RAP binder ratios (25%, 50%, and 75%) and rejuvenator dosages (0%, 5%, and 10%) were prepared to select candidate rejuvenators with better restoration capacities in terms of reducing the viscosities at mixing and compaction temperatures as well as recovering the continuous performance grade (PG) temperatures, non-recoverable compliance, and crossover temperature measured binder testing using the Dynamic Shear Rheometer (DSR) and the Bending Beam Rheometer (BBR). Four bio-based rejuvenators were selected in the first stage and used for dosage optimization through the blending chart method and the response surface modelling (RSM) method. The blending chart method assumes a linear relationship between the rheological index and two variables, rejuvenator dosage and RAP binder ratio. Therefore, the optimal rejuvenator dosage can be determined when the rejuvenated binder blend resembles the same rheological index as a target virgin binder. Meanwhile, the response surface model was built based on a two-level factorial design, which involved the different rheological indices as the responses and the rejuvenator dosage and RAP binder ratio as the two factors. This method can verify the linear relationship and then the model can be used to calculate the optimal dosages. From the results, the blending chart method was proved to be reliable because most of the rheological indices were expected to have a linear relationship with the rejuvenator dosage and the RAP binder ratio. Furthermore, the recommended indices, the low PG temperature based on m-value (PGLm) and the crossover temperature (Tcross), exhibited the potential to ensure that the rejuvenated binder blends have adequate cacking resistance without compromising the permeant deformation resistance at high temperatures. In the mix testing phase, the Hamburg Wheel-Tracking (HWT) test results revealed concerns about increased permanent deformation and moisture susceptibility due to the additions of rejuvenators in high RAP mixes at both test temperatures, 44°C and 50°C. However, the rejuvenated high RAP mixes outperformed the control mix (with 20% RAP), particularly at the higher test temperature. The cracking test results obtained from the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) indicated that the addition of rejuvenators or replacing the base binder with a softer virgin binder was beneficial in improving the cracking resistance; however, more testing results, preferably from plant trial mixes, are needed for statistical analyses. Nonetheless, the rejuvenated high RAP mixes achieved decent high-temperature stability and acceptable cracking resistance, especially after an extended oven conditioning period. The dynamic modulus test was used to investigate the effect of increased RAP content with the use of a rejuvenator (or a soft binder) on mix rheology at a variety of temperature and loading frequency combinations. The measured modulus and phase angle data were analyzed using two master curve models and several time-temperature-dependent shifting equations. Additionally, the long-term performance of the asphalt mixes was assessed by comparing test results obtained from samples before and after the long-term oven aging (LTOA) protocol. The high RAP asphalt mix with the addition of a rejuvenator showed the most stiffness increase after long-term aging; however, it retained relatively better flexibility and temperature sensitivity compared to other mixes. According to the findings of this study, using rejuvenators in asphalt mixes with a high RAP content can produce a recycled HMA with balanced rutting and cracking performance and long-term sustainability. Whereas in the high pavement in-serve temperature range, extra care should be taken for moisture susceptibility.
Pavement Performance Prediction Using Machine Learning and Instrumentation in Smart Pavement
(University of Waterloo, 2022-09-19) Kang, Jianqi; Ghafurian, Moojan; Baaj, Hassan
The optimization of pavement Maintenance and Rehabilitation (M&R) planning and costs has been historically proven as a complex task. In recent years, Artificial Intelligence (AI) and Machine Learning (ML) applications in pavement engineering data analytics have been gaining momentum. These advanced techniques have shown promising results in civil engineering and transportation asset management. Therefore, designing a smart pavement framework that relies on the actual pavement responses and in-service condition can help with utilising the ML approach toward better understanding the performance of pavements. To implement the concept of “Smart Pavement”, constructing an interactive pavement pilot section that provides the necessary data feedback to improve the decision-makings of M&R would be needed. This thesis focuses on some aspects of the design of in-situ pavement monitoring and the applying selected machine learning techniques for pavement performance prediction. In order to design an effective pavement instrumentation plan, a literature review was conducted to identify and evaluate the major in-situ monitoring devices and previous case studies. Innovative technologies of Structural Health Monitoring (SHM) were also discussed as a part of the sensory system. A potential pilot section was identified by the Region of Waterloo, for which the pavement structure and technical details were retrieved. Based on the results from the literature review and the evaluation of the proposed section details, a preliminary instrumentation layout has been proposed. Next, the interaction between the proposed embedded sensors and surrounding pavement structure under traffic loading was further studied to evaluate the effect of pavement instrumentation on actual structural responses. Therefore, a series of finite element analysis (FEA) scenarios were defined, and modelling was conducted using ABAQUS to quantify the artefact impacts of the sensors on the pavement responses. Based on the FEA results, high stress- and strain-concentration areas were located which can be used to optimize the design of sensor layout, leading to capturing representative critical pavement responses. Consequently, sensor spacing criteria were suggested to avoid device interference for the response measurement. Furthermore, it would be informative to know how, and which AI/ML methods have been previously used for pavement performance prediction purposes. A systematic literature review iii was conducted indicating that majority of studies used Artificial Neural Network (ANN) of which the prediction process is unexplainable to predict International Roughness Index (IRI) resulting in high prediction accuracies (R2 >= 0.9). A Decision Tree (DT) model and a Random Forest (RF) model were developed using the most commonly used input data retrieved from the Long-Term Pavement Performance (LTPP) database to predict IRI. Finally, after the pruning process, the DT model and RF model resulted in a cross-validation accuracy (R^2) of 0.846 and 0.859, respectively. The single tree from the DT model is less complex than the trees from the RF model. Further studies on machine learning model development should be conducted to refine prediction accuracy. Finally, recommendation for future data collection standards from pilot sections were provided to help with developing a pavement response database that can overcome the inconsistencies in the existing LTPP database and potentially improve the reliability of the future pavement performance modelling.
Sustainable Alternative Materials in Unbound Granular Layers of Pavement Structures
(University of Waterloo, 2017-05-02) Schneider, Adam C.; Baaj, Hassan
In Part 1 of this thesis, reclaimed cement concrete (commonly referred to as recycled concrete aggregate or RCA) and reclaimed asphalt pavement (RAP) are investigated as potential alternative construction materials for Granular B Type II subbase fill. Ontario Provincial Standard Specification (OPSS) 1010 currently allows the common use of processed reclaimed construction materials in a variety of road base, subbase and asphaltic concrete layers, with the notable exception of Granular B Type II, which at present may only include 100% crushed bedrock, talus, iron blast furnace slag or nickel slag. As more restrictions are placed on zoning and approvals for new natural aggregate extraction sites in Ontario, there is a need to better understand the performance of materials such as RCA and RAP as economically beneficial potential aggregate sources for granular base and subbase fill layers. An experimental program was created to assess and analyze the performance characteristics of a series of different subbase test mixtures incorporating RCA and/or RAP, either pure or blended with crushed bedrock, and the impact of the inclusion of these materials when compared to a conventional 100% crushed bedrock test mix meeting OPSS 1010 requirements for Granular B Type II. The performance characteristics to be assessed were field compactibility, gradations before and after field compaction, physical properties, standard and modified Proctor tests, California Bearing Ratio (CBR), permeability, resilient moduli and lightweight deflectometer (LWD) resilient moduli. Field testing programs conducted at Quarry 1 in Ottawa, Ontario and Quarry 2 in Burlington, Ontario indicate that the subbase test mixtures meeting OPSS Granular B Type II gradation requirements and incorporating different proportions of crushed rock, RCA and/or RAP exhibit similar field rolling compactibility relative to 100% crushed rock. Grain size analysis testing showed some aggregate breakdown in multiple test mixes, with only minimal increases in material passing the 75 µm sieve, which is crucial to preserving permeability and drainage characteristics. Tests using a lightweight deflectometer (LWD) were subject to substantial variability but indicated that mixes using elevated levels of RCA (50% and 100%) can potentially have lower in-situ moduli compared to the other blends tested. Laboratory tests indicate that high replacement levels of RCA can be used in subbase materials as a substitute for 100% crushed rock while maintaining good water permeability characteristics and similar or higher resilient moduli in blends incorporating RCA and/or RAP. CBR testing results were similar across all test blends incorporating crushed rock and RCA, but also indicated that the inclusion of 30% RAP can potentially reduce the bearing capacity of the granular material by approximately 30-40% in comparison to all other blends which do not contain RAP. Based on the overall results of this study, RCA and RAP appear to be capable of successfully substituting for natural aggregates in Granular B Type II in a range of compositional proportions. It is recommended that test sections should be completed on highway contracts with subbase mixture blends incorporating RCA and/or RAP in order to verify their performance in pavement structures in the field. In Part 2 of this thesis, foam glass lightweight aggregates (LWA) are investigated as a potential pavement engineering design alternative in order to mitigate roadway loading impacts upon underlying subgrade soils while promoting the sustainable and economical use of recycled waste glass. Foamyna Canada Inc. supplied the Centre for Pavement and Transportation Technology (CPATT) with two foam glass lightweight aggregate materials, designated in this thesis as LWA-A and LWA-B. Physical properties testing was carried out by CPATT, including grain size analysis, crushed particle content, flat and elongated particle content, Micro-Deval abrasion resistance, cyclic freezing-and-thawing resistance and resilient modulus testing procedures. These procedures were conducted in order to evaluate the LWA materials against locally applicable standards, namely Ontario Provincial Standard Specification document OPSS 1010 as currently used by the Ministry of Transportation of Ontario (MTO). The laboratory testing detailed in Part 2 indicates that both LWA-A and LWA-B have a very consistent and repeatable gradation with a high percentage of coarse aggregates. Both foam glass materials have very high crushed particle contents and very low flat and elongated particle contents. Micro-Deval abrasion resistance, freeze-and-thaw resistance and resilient moduli were also excellent for both materials, while relative density testing indicated LWA material specific gravity values which were substantially lower than that of water. However, it was found that the gradations of these two tested materials do not satisfy the existing requirements of OPSS 1010, which were developed for natural aggregates and, as currently constituted, may not be appropriately adapted to artificial lightweight aggregates. The coarse nature of the LWA materials would be highly beneficial to ensure the stability of the granular layers and prevent upward capillary water movement into other layers of the pavement structure. Pavement design calculations were carried out using the AASHTO 1993 empirical design procedure and found that utilizing foam glass LWA as a lightweight subgrade replacement fill material can result in substantially leaner pavement structures as compared to the use of conventional expanded polystyrene (EPS) geofoam blocks as an artificial subgrade. A life-cycle cost analysis (LCCA) procedure carried out on these pavement designs showed that the use of foam glass LWA as a lightweight fill material underlying pavement can result in overall cost savings of over 30 percent relative to pavement structures which are underlain by EPS geofoam. Overall, the two tested LWA materials showed excellent physical and mechanical characteristics, and would be suitable for use in pavement structures as innovative lightweight and environmentally friendly alternatives to natural aggregate materials.

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