In the asphalt highway industry, a large number of innovative materials and technologies are explored in order to evaluate their suitability in the design, construction and maintenance of pavements. Billions of tonnes of concrete are extensively consumed in the construction of various structures including buildings, bridges, dams, roads, and others. For constructing the above-mentioned structures, massive amounts of construction and demolition (C&D) waste are generated. A sustainable solution has become highly required and an urgent priority in the asphalt industry to solve various problems including lowering the consumption of virgin materials, decreasing waste materials in landfills and reducing environmental problems, and the utilization of recyclable waste materials, especially recycled concrete. This research is conducted to investigate the possibility of using coarse recycled concrete aggregate (CRCA) in asphalt mixtures. Mix design of HMA mixtures is performed for CRCA at various percentages 15%, 30%, and 60%. After determining optimal asphalt content (OAC) of different mixtures, the stiffness resistance of Ontario Superpave asphalt mixtures is evaluated. Depending on the dynamic modulus test results, the rutting susceptibility and fatigue performance of different mixtures are also estimated. At high temperatures, the obtained results indicate that the use of CRCA can increase asphalt pavement resistance to rutting susceptibility compared to the control mixture. However, this resistance decreases with increasing CRCA proportion in the asphalt mixture. At low temperatures, asphalt mixtures including CRCA have a lower stiffness than the control mixture. This leads to minimizing fatigue and low-temperature cracking. The findings also revealed that the utilization of CRCA in the asphalt mixtures appears to be highly successful.
In this paper the interface shear fatigue performance is investigated based on a new fatigue test protocol, which includes both cyclic shear and normal static compressive load. Several asphalt structure types are tested at five temperatures (from -10°C to 50°C) and three normal stress levels (from 0 MPa to 0.50 MPa). Based on fatigue tests at three different shear amplitude levels unique fatigue functions of the layers’ interface were identified. It was found that the interface shear fatigue performance is highly dependent on normal stress state and increases with increasing normal stress. This is a direct consequence of the enhanced friction, adhesion, and interlock at the shear interface. Observing the fatigue lives at different test temperatures, the best resistance was observed at lowest temperature. From a practical viewpoint, it is highly recommended to perform the test without normal stress application, since this can better reflect the research and practice experience, while keeping the testing protocol to a reasonable level of complexity.
The need for viscoelastic characterization of hot mix asphalt (HMA) is increasing as advanced testing and modelling is incorporated through mechanistic-empirical pavement design and performance based specifications. Viscoelastic characterization includes measurement of the mixture stiffness and relative proportion of elastic and viscous response. The most common method is to measure the complex modulus, where dynamic modulus represents the stiffness and the phase angle represents the relative extent of elastic and viscous response. Determination of phase angle from temperature and frequency sweep tests has been challenging, unreliable, and prone to error due to a high degree of variability and sensitivity to signal noise. There is also a large amount of historical dynamic modulus data that is either missing phase angle measurements or has poorly measured phase angle data that inhibits their use in further evaluation. This paper evaluates the robustness of phase angle estimation from stiffness data for asphalt mixtures. The objectives of the study are to: (1) evaluate phase angle determination from the slope of log-log stiffness master curve fitted with a generalized logistic sigmoidal curve and compare it with lab measurements and the Hirsch model; (2) assess the effect of measured and predicted phase angle on mixture Black space diagram; (3) evaluate the effect of using predicted phase angles on S-VECD fatigue analysis, particularly on damage characteristics curves and fatigue coefficients; and (4) evaluate the impact on LVECD pavement fatigue performance evaluation due to the use of predicted phase angles. Three sets of independent mixtures were evaluated in this study comprising a wide range of mixture conditions.
The results indicate a good agreement between measured and predicted phase angle values in terms of shape and peak master curve values. In terms of magnitude, the values from both matched very well for a certain sets of mixtures and subsequently manifested in similar performance predictions. However, for other sets of mixtures a considerable difference was observed between measured and predicted phase angle values as well as S-VECD and LVECD results. The differences may be attributed to the use of different types of LVDTs (loose core versus spring loaded). Another possible explanation of the difference could be the contribution of plastic strain, which may create a difference in phase angles of 1 to 2 degrees.
For performance based specifications and design processes, a number of cracking related index parameters have been proposed for asphalt mixtures in recent years. A number of these parameters have been developed to utilize results from fracture tests. This study conducted a comprehensive evaluation of various fracture index parameters including fracture energy, Illinois flexibility index, stress intensity factor and toughness index. Over 200 tests from 61 distinct test data sets representing 21 asphalt mixtures are included. The focus of this study is on low temperature cracking and all indices were evaluated using test results from the disk shaped compact tension (DCT) fracture tests conducted at low temperatures.
The objective of this study was to determine if there is a relationship between various fracture index parameters as well as to determine typical measurement variability associated with each parameter. Comparisons were made between different indices and correlations were determined for the mix rankings provided by individual indices. The results indicate that fracture energy successfully captured the mix rankings and showed strong correlation with other indices. In order to better capture post-peak softening behavior of asphalt mixtures the flexibility and toughness indices have been utilized, however these parameters were found to have high variability. A new index called fracture strain tolerance (FST) has been proposed that was shown to provide the same level of distinction between mixtures as the flexibility and toughness indices while having considerably lower variability. Finally, several areas were identified for future extension of this research.
This study investigated the feasibility of using a monotonic direct tension test in the AMPT with small scale specimens to evaluate the crack properties of the asphalt materials. Ten loose asphalt mixtures collected from the FHWA’s Accelerated Loading Facility (ALF) test lanes combining various recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) percentages and warm mix (WMA) technologies were tested at three loading rates and two aging conditions. Various mechanical parameters and indexes were developed to analyze the experimental data. The laboratory monotonic testing results were compared to and statistically correlated to the ALF field cracking performance.
The coefficients of variation from the experimental results indicated that the monotonic test has satisfactory repeatability. Test loading rates were found to have significant impact on the behavior of the test materials, and an actuator rate of 10mm/min is considered to be ideal for all tested materials, including both short-term oven aging (STOA) and long-term oven aging (LTOA) conditions. Aging conditions were also found to dramatically influence the monotonic testing results. The experimental results illustrated that the components (percentages of RAP/RAS and binder PG) of the asphalt mixtures and the warm mix technologies have clear effects on the monotonic testing, indicating the test is capable of differentiating such asphalt mixtures. The parameters of the total fracture energy and the total energy divided by the inflection point slope from the laboratory monotonic test were found to have very strong correlations with the field performance. As a general conclusion, this study shows that the monotonic direct tension test in the AMPT is a very promising tool to evaluate the crack properties of asphalt mixtures due to the ease in the sample preparation, compatibility with the AMPT, strong correlation with field performance and feasibility for testing field specimens.
Current methods and criteria for asphalt mix design and quality assurance testing are unable to discern the true impact of recycled materials, such as reclaimed asphalt pavement, recycled shingles, ground tire rubber, re-refined engine oil bottoms, or products aimed at enhancing performance such as polymer modified binders, fibers, or even warm- mix asphalt technologies. There is an urgent need to implement reliable tests to assess the cracking resistance of asphalt mixtures. This study used test specimens compacted to Ndesign in four simple tests: the Cantabro test, a modified version of the Texas overlay test (OT), the semi-circular bend (SCB) test, and the indirect tensile (IDT) test from which IDT strength and two other index parameters were obtained. Relationships between results from these tests and the fatigue cracking of the FHWA’s Accelerated Loading Facility (ALF) test lanes were used to assess how well test methods could differentiate actual performance. The study also examined variability data for test results and how that impacted the utility of the tests to discern mixtures from one another. Results of this study indicate that the IDT Nflex factor and the Cantabro test provide the strongest relationship to fatigue cracking in the field and are able to detect differences among common mixture variables. Both tests are simple, quick, and have very low costs to implement.
Bloomington Road, Regional Highway 40 in the Regional Municipality of York, serves as a major artery for vehicles accessing Highway 404. The section under review between Kennedy Road and Highway 48 was built in 1969 and rehabilitated with an innovative pavement design in 2005.
Prior to rehabilitation, the asphalt surface was severely oxidized with extensive thermal cracking, however, the longitudinal and transverse profiles of the roadway were in relatively good condition and there was no sign of major structural failures. Rehabilitation of the roadway consisted of Cold In-Place Recycling (CIR), a Heavy-Duty Asphalt Binder Course (HDBC) Hot Mix Asphalt (HMA), and a 6.7 mm rut-resistant fine-graded Stone Mastic Asphalt (SMA).
This paper provides a review of the design and construction details for the pavement lifts, as well as material and process selection details. Special consideration is given to the curing of the CIR and the rut resistance of the SMA lift. This paper also presents a long-term field performance evaluation of the rehabilitated pavement section with quantified in-situ performance by means of field observations, laboratory evaluations of retrieved pavement specimens, and semi-automated pavement performance data survey collected by York Region over twelve years of in-service pavement life.
Evaluation of the moisture damage of HMA is normally conducted on loose aggregate coated with binder or on HMA compacted samples; both methods having their respective disadvantages. Those tests are empirical and are susceptible to give misinterpretation of moisture damage. The complex modulus test for asphalt mixtures, also known as the dynamic modulus, characterizes the mixtures Linear Visco-Elastic (LVE) properties. This paper presents a method used at LCMB to evaluate the moisture damage of HMA samples based on LVE measurements. Two reference mixtures and three mixtures with glass aggregates were tested. One set of samples contained hydrated lime as an anti-stripping additive. First, the LVE properties of the samples were evaluated in a dry condition. Then, the samples were saturated with water and cured into a water bath at 60 deg C for 14 days and evaluated again.
Overall, complex modulus test is very effective at evaluating the moisture damage of asphalt samples. This method has multiple advantages and many analysis options, which make it very interesting to evaluate moisture damage. Moreover, it was found that hydrated lime is a very effective anti-stripping additive. For some of the mixtures with anti-stripping agent, water soaking had little effect on the LVE properties.
There is no consensus among state highway agencies as to the appropriate binder specifications required for adequate quality control and acceptance of modified binders. Supplemental tests have been adopted in addition to standard Performance Grade (PG) tests and are often referred to as “PG+” procedures. The Multiple Stress Creep and Recovery (AASHTO M332) test has been proposed to replace the AASHTO M320 for PG grading of binders. However, some agencies are concerned that asphalt binder formulation will change after adopting the new system, while others are unsure how to relate the current M320 grades to the new S, H, and V grades.
In this study, testing of a large number of binders was completed and correlations between results of “PG+” test and MSCR tests were performed. Regarding the MSCR test, results show that the %R parameter is a good candidate to detect the presence, and potentially the quantity, of elastomeric modification. However, using universal limits for the MSCR %R parameter that are dependent on Jnr values in not practical nor useful since current binder formulations are controlled differently by agencies. Furthermore, no logical equivalency of M320 PG grades to M332 traffic grades was identified, so changes to binder formulations are anticipated.
Premature cracking of flexible pavements is a very common problem in Canada. Nowadays, it is common to use several types of additives and modifiers to asphalt binders and asphalt mixes to improve their performance and increase the service life of flexible pavements. In order to mitigate pavement cracking, the asphalt mixes used in the pavement structure need to have a high resistance to fatigue or thermal cracking according to their position in the pavement structure. Several studies reporting on the use of fibers in asphalt concrete have been found in the literature. The objective of this project is to study the impact of the addition of Pulp Aramid Fiber (PAF) to Hot Mix Asphalt (HMA) in terms of mix design and indirect tensile strength.
The optimum asphalt content of the fiber mixes is first determined and then the impact of fiber on their volumetric properties is investigated. Finally, the behavior of PAF in HMA is characterized by indirect tensile testing at different conditions. PAF mixes showed better ductility, even at lower temperatures, than the control mix. Therefore, PAF would lead to an improvement of the resistance to low temperature cracking and would delay crack propagation in the mix.
Nova Scotia Transportation and Infrastructure Renewal (NSTIR) implemented its pavement management system (Highway Pavement Management Application or HPMA) in 2008. NSTIR conducts annual pavement condition surveys on their highway network. Data collected includes International Roughness Index (IRI), which is used to calculate a Roughness Index (RI). Surface distress data is also collected to calculate a Distress Index (DI). The RI and DI are combined into an overall Pavement Quality Index (PQI).
In 2016, NSTIR initiated a project to review their pavement prediction models. Differences in historical data trends were noted during the initial model review. These differences were thought to be a result of technological advancements in data collection equipment.
The study examined the existing roughness and distress indices to determine if and/or how changes in data collection technology have impacted the measured pavement condition. The investigation included a review of the historical roughness and distress data. Based on this data review, changes were made to the roughness and distress models to better reflect current NSTIR data and conditions. A feedback analysis was then conducted on the prediction models to conduct performance modeling on the HPMA. This paper details the data investigation and updated models.
Alberta Transportation has completed rehabilitation of a number of highway sections using Cold In-place Recycling (CIR) and Full Depth Reclamation (FDR) over the years. In order to better understand the mechanism responsible for the formation of transverse cracks (specifically to see if transverse cracks are reflecting from the underlying pavement) and the susceptibility of the recycled material to moisture induced damage, Alberta Transportation retained Tetra Tech to undertake pavement inspections and analysis of selected projects rehabilitated using CIR and FDR.
A total of five highway segments rehabilitated with CIR and one highway segment rehabilitated with FDR were included in the study. The study included a review of background information, visual crack mapping, pavement inspection using Ground Penetrating Radar, asphalt pavement coring, determination of moisture content in the CIR portion of the cores, and visual assessment of the cores to identify the progression and type of cracks. The key objectives were to investigate the performance of the pavements rehabilitated with CIR in terms of transverse crack formation and moisture susceptibility.
This paper discusses the completed evaluation and findings from the study and further expands on Alberta Transportation’s experience with CIR, as presented at the 2016 CTAA Conference.
The British Columbia Ministry of Transportation and Infrastructure (MoTI) has been using 100 percent Reclaimed Asphalt Pavement (RAP) to pave numerous side roads in its network for more than 15 years with mixed results. The RAP is typically transported off site and recycled by adding a rejuvenator and processing the material through a pugmill. The cold recycled mix is then transported to site and placed using conventional paving equipment as a wearing surface – a surfacing layer of Hot Mix Asphalt (HMA) is not placed.
Although the BC MoTI has been using this procedure for over a decade, no study to evaluate the addition rate of the rejuvenator, mix design, recycling process, or testing to determine the quality of the recycled mix was ever completed. The crushed granular equivalency or structural layer coefficient of the recycled mix was also never developed.
This paper will document the findings of a laboratory program undertaken to evaluate the optimum addition rate of the rejuvenator, curing period prior to the placement of the recycled mix, and compaction criteria, as well as the structural layer coefficient and crushed granular equivalency of the recycled RAP.
A case history of several previously completed projects using cold recycled RAP pavement are also presented.
Asphalt binders produced at refineries are becoming stiffer due to an ever-increasing demand for more expensive lighter and heavier fraction products such as gasoline, jet fuel, and lube oils. To increase output of lighter fractions and heavy gas oils, refineries have gone through upgrades producing higher amounts of stiffer asphalt binders such as Vacuum Distillation (VD) tower, Solvent De-Asphalting (SDA), and Residuum Oil Super critical Extraction (ROSE) unit bottoms. Materials used to soften/repair stiff asphalt binders are known as fluxes. Through recent work at Iowa State University, great potential was seen for epoxidized plant oil materials as fluxes/rejuvenators. Within this work two epoxidized plant oil products derived from soybeans, EBS and EMS were manufactured and used for modifying three stiff asphalt binders produced from VD tower, SDA and ROSE units. A full Superpave binder investigation found that improvement in low temperature performance was greater than improvement in high temperature performance for the SD and ROSE unit bottoms when using either EBS or EMS. It was also found that substantial decreases in costs, fuel usage, and emissions could be gained through the use of EBS and EMS in the production of asphalt mix.
The Regional Municipality of York, in collaboration with Metrolinx (an agency of the Government of Ontario), has implemented Bus Rapid Transit (BRT) lanes along the three most heavily travelled roads in York Region. To enhance visibility and assist motorists when navigating this new transit system, a special red-coloured asphalt mixture was employed as a surface layer. The colour was achieved by using a selected aggregate bland, colouring pigment, and specially formulated asphalt mixture.
This paper provides information on steps employed in the design of coloured asphalt mixture such as: 1) selection of performance graded asphalt cement suitable for the Region’s climatic conditions and traffic loadings, 2) designing an aggregate blend to match the desired colour, ) performing a volumetric analysis for the special Hot Mix Asphalt to meet physical requirements of Superpave 12.5 FC2, and 4) performance testing to capture the impact of pigment on the mixture’s strength and durability at different in-service temperatures. Performance testing was performed at the Centre for Pavement and Transportation Technology located at the University of Waterloo. Production and paving experience with the coloured asphalt mix are also included in this paper, as well as field performance in terms of manual and automated distress survey.
Currently in progress, the “Regina Bypass” highway project involves the construction of approximately 45 km of a new four-lane highway (greenfield), the rehabilitation of more than 18 km of Highway 1 (brownfield), and 5 km of reinforcement works on an existing section. The project is being realized using a “Design-Build-Finance-Operate-and-Maintain” (DBFOM) approach and it will be operated by the concessioners group until late October 2049. Taking into account the specific physical and climatic constraints involved, as well as the concession’s duration, flexible pavements have been designed using several innovative concepts such as a mechanistic pavement design approach to the structural pavement design, the use of engineered asphalt mixes, the use of on-site recycling process for existing sections, and the installation of performance monitoring stations.
This article provides a summary of the numerous laboratory tests required for the study of the engineered asphalt mix formulations specifically developed for this project, and it describes the follow-up program that will measure their performance with time.
Flooding has been identified as the most frequently occurring natural hazard in Canada. Extreme weather events, such as floods and extreme precipitation events, are increasing in intensity and frequency under climate change. The impact of flooding on asphalt pavements has become a rising concern, since pavements are designed based on historical data, which do not adequately reflect current and future climate. Therefore a comprehensive understanding of the flooding impacts o pavements is of great importance for improving their resilience.
The objective of this study is to establish an assessment framework for the impacts of flooding on asphalt pavements through fragility analysis, and conduct case study to illustrate the approach. Flood characteristics, pavement damage patterns, damage components, and performance impact factors are investigated. Thirty-six extreme precipitation scenarios with various magnitudes, durations, and numbers of event cycles are loaded to two typical asphalt pavement structures in Southern Ontario by using MEPDG. Then, a probabilistic pavement fragility modeling method is developed for generating fragility functions, which integrate flood hazards, pavement structure, pavement performance, and damage states. Results show that the loss of pavement life is not negligible due to extreme events. Fragility functions and curves are able to demonstrate the probability of exceeding certain pavement damage given flood hazards.
American and European refiners have been going through phases of revamping and rationalization to maximize the flexibility in crude oil supply while matching their production models and refining tools. For users of asphalt, this has created concerns about the quality and consistency of the delivered asphalt binders, especially as the current specifications appear insufficient to ensure satisfactory performance of the finished products.
In this context, the search for relationships and correlations between asphalt properties and the performance of the asphalt mixtures and the pavement has become very relevant. The study presented here was dedicated to identifying and quantifying such relationships. It focused on asphalt mixes made with unmodified asphalts. It was based on a standard mix design with one type of aggregate, and involved 14 paving grade asphalts from various origins. The characterization of asphalt mixes covered various performance characteristics from resistance to rutting and fatigue to thermal cracking.
The compositional analysis of binders included the most advanced fractionation method SAR-AD™ and a chemometrics analysis using a new software to identify and develop the correlations. Both were developed by the Western Research Institute (WRI).
Significant correlations were found tying binder chemical composition metrics to binder mechanical characteristics to asphalt mix characteristics.
The eco-efficiency analysis developed by BASF offers a versatile tool to evaluate and visualize advantages and disadvantages of a product and its use in terms of economy and ecology. The entire life cycle of the product, including raw materials manufacture, energy consumption, end use and disposition, is evaluated. This tool allows BASF to select cost competitive products that are the most compatible with sustainable development principles.
In this study, we applied the eco-efficiency analysis to the preventive maintenance of existing roadways, comparing three different treatments: asphalt emulsion based microsurfacing, hot mix and polymer modified hot mix overlay. Results of the analysis clearly demonstrate that microsurfacing provides a better balance between cost-effectiveness and environmental impact than thin hot mix overlay technologies. The analysis also suggests that even a minute improvement in durability of microsurfacing (e.g. with a higher latex usage in the asphalt emulsion) would have rather significant improvement in the economy and ecology with this treatment.
This paper provides a first step towards understanding the mechanisms of crack propagation and behavior of cracked asphalt pavements, leading to modeling of a reliable prediction of pavement performance. The growth of an existing crack and the rate of propagation of such a crack can be characterized by applying fracture mechanics.
The paper presents results of a laboratory testing program designed to apply the fracture mechanics approach to asphalt pavement characterization. Three-Point Bending tests were carried out to investigate the effect of boundary conditions, initial crack depth, and response of crack propagation to rate of loading on asphalt concrete. In addition, the effect of asphalt mixture components on the fracture behavior and resistance of asphalt layers to crack propagation has been investigated. Fracture mechanics parameters determined and discussed in this study include fracture toughness and fracture energy parameters.
The fracture energy of asphalt concrete mix dramatically increased when crushed dolomite stone coarse aggregate was used. Fine aggregate from crushed screening increased fracture toughness of a mix by 33%. Soft asphalt was found to decrease the fracture toughness by more than 50%.
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