Menu
As part of the social responsibility, SEERO team contributed to multiple studies with multiple academic institutions around the world to produce research studies and published them in peer-reviewed journals and highly reputation conferences.
H Sadeq, T Sayed
Journal of Transportation Engineering 142 (12), 04016062
The use of roundabouts is gaining popularity in North America for their safety, capacity, and environmental benefits. Studies have shown that roundabouts can significantly reduce injury collisions compared to stop control and traffic signals. As more roundabouts are constructed, there will be an increased need for a detailed analysis of their safety performance. Traditional road-safety analysis of roundabouts has relied on the use of historical collision records. This approach offers a less-complete understanding of roundabouts safety and their effects on the behavior of drivers, pedestrians, and cyclists. This paper represents a case study where automated video-based traffic conflicts analysis is used to diagnose safety issues at a roundabout in Vancouver, British Columbia, Canada. Traffic conflicts are automatically identified and analyzed to develop an in-depth understanding of the behavior of road users and the causes of traffic conflicts. Conflicts contributing factors were identified and safety countermeasures are presented.
HT Eid, OA Alansari, AM Odeh, MN Nasr, HA Sadek
Canadian geotechnical journal 46 (4), 438-453
The behavior of shallow foundations resting on laterally and (or) vertically confined sand has been investigated using physical and numerical modeling. The models were designed to simulate the frequently constructed raft foundations that are surrounded by sheet-pile walls to support excavation sides of sand underlain by a rock bed. Laboratory tests were carried out utilizing a square foundation model surrounded by rigid steel walls with different depths, resting on sand that was underlain by a rough rigid layer. Varying sand-layer thicknesses and relative densities were utilized. A threedimensional finite element analysis was conducted to verify the physical-model test results and to infer the performance of full-scale foundations. Based on the results of the experimental and numerical analyses, charts are presented to estimate the enhanced bearing capacity of square foundations resting on confined sand. These charts are presented in terms of bearing capacity of the surface foundation resting on extended sand, sand relative density, wall width to foundation width ratio, and rigid layer depth. Charts are also presented to estimate settlement reductions due to the bearing sand lateral and (or) vertical confinement.
H Sadek, S Lissel
Construction and Building Materials 41, 977-989
In this study, the results from tests on a total of eight squat concrete masonry walls under simulated seismic load are reported. The first specimen is an Unreinforced Masonry (URM) control wall and one was reinforced with steel-ladder shaped Bed Joint Reinforcement (BJR). Three walls were reinforced with different configurations of Geogrid material and the last three were reinforced with different configurations of Glass Fibre Reinforced Polymer (GFRP) reinforcement. No vertical reinforcement was provided. The performance of the walls under horizontal cyclic loading is presented in this paper showing the enhanced seismic performance: energy dissipation and in-plane flexural strength provided by the various types of BJR. The significance of this study is that it examines both FRPs and a new material, Geogrid, along with a new configuration of BJR, grid shape.
M Alfarra, M Sadeq, H Sadek
Qatar University Press
This paper introduces the constructability and economic feasibility study of using one of the proposed two types of permanent shoring system for a highway project in Qatar. The cast-in-situ cantilever retaining wall and the contiguous piles wall were suggested and designed to be used as a permanent retaining system at a multi-level intersection. In this study, the construction complexities of using the cantilever retaining wall system are illustrated and compared to the contiguous piles wall. Besides, the impact on the Right-of-Way (ROW) of the road, excavation process, traffic circulation, and existing utilities are discussed. The paper summarizes the difference in the required construction materials and excavation quantity for the proposed shoring systems at the same retained elevation. Furthermore, the design of both systems is performed based on the local and international guidelines and regulations of the shoring system design in Qatar. The study has shown that both suggested systems are providing the same finishing quality while the contiguous piles system is more effective in minimizing economic and site preparation challenges. It also provides safer utilities handling and faster construction sequencing without cost increases.
Q Lv, W Huang, H Sadek, F Xiao, C Yan
Construction and Building Materials 206, 62-70
Asphalt modification technology is diversifying and developing complexity to overcome early permanent deformation and ensure satisfactory performance for asphalt concrete pavements. The Hamburg Wheel Tracking Device (HWTD) test has been reported to be successful in assessing asphalt mixtures’ rutting performance. This study includes a comprehensive investigation of the effects of different additives at various contents upon the HWTD testing results of asphalt mixtures. According to the degree of their improvement of the rutting performance in the HWTD test, additives were classified into three categories: (1) the first grade including linear styrene–butadiene–styrene (SBS), branched SBS and Gilsonite; (2) the second grade including high-density polyethylene, and polyphosphoric acid; and (3) the third grade including crumb rubber. Additionally, it was found that higher dosages of modifiers do not necessarily result in the improvement of Hamburg performance, and an optimal content exists for most additives. After the extensive mix testing, the dynamic shear rheometer (DSR) testing results were correlated to the HWTD test results in two categories: polymer modified asphalt and non-polymer modified asphalt. It was found that the compliance value Jnr3.2 from the Multiple Stress Creep Recovery (MSCR) test did not underestimate the rutting resistance of polymer modified asphalt compared to non-polymer modified asphalt as the current rutting factor G*/sin δ did. Jnr3.2 was more reliable than G*/sin δ in characterizing the anti-rutting performance of asphalt mixtures no matter they were polymer modified or non-polymer modified. However, different criteria for Jnr3.2 should be adopted for the polymer modified asphalt and non-polymer modified asphalt respectively.
J Jiang, F Ni, F Wu, H Sadek, Q Lv
Construction and Building Materials 196, 284-294
Since the semi-circular bending (SCB) test has been widely used to evaluate the fatigue properties of asphalt mixtures, it has been modified in this paper by adding a certain length of rest period in each cyclic loading sequence to evaluate the healing potential of different asphalt mixtures. The digital image correlation (DIC) method was utilized to characterize the tensile strain at the bottom of specimens during the healing-based cyclic SCB test. The influence of notch depth of the specimen (0 mm, 15 mm and 25 mm) and the length of the rest period (0 s, 0.4 s, 0.8 s and 1.2 s) on the fatigue and healing behaviour were carefully evaluated. The fatigue life (Nf), total dissipated energy (Gsum), secant modulus (Ms), average deformation growth rate (Dr) and average tensile strain (εr) during the cyclic load with or without rest period were analysed. Test results show that the inserted notch reduces the fatigue life and deformation of specimens, while can hardly change the load-sensitivity and secant modulus of the specimen. Most performance recovery happens within the rest period of 0.8 s. So it is better to conduct the healing-based cyclic test with non-notched SCB specimen and 0.8 s rest period. Additionally, it is found that asphalt mixtures with modified binder present both better fatigue and healing properties than asphalt mixtures with neat asphalt, while the stone matrix asphalt mixture presents similar fatigue property but much better healing potential than one dense graded mixture with the same binder.
HA Sadek, EA Masad, O Sirin, H Al-Khalid, MA Sadeq, D Little
International Journal of Pavement Engineering 15 (6), 495-511
The State of Qatar is experiencing tremendous growth in infrastructure including road network and highways. The current methods used in design of asphalt pavements in the State of Qatar are empirical and might not be suitable for the design of long-lasting pavements. Given the significant increase in traffic, road authorities in the State of Qatar have been considering the use of mechanistic-empirical methods in the design and analysis of asphalt pavements. This study documents the results of a study in which the mechanistic-empirical pavement design guide (M-E PDG) software was used in the design of asphalt pavements with input parameters that were carefully selected to reresent local materials and climatic conditions. The selection of material properties was based primarily on specifications and design guides in the State of Qatar and on published literature about these materials. The mechanistic-empirical method was also used to assess the benefits of adopting the concepts of perpetual pavement design and also to compare the performance of pavement structures in which various bitumen grades, granular bases and chemically stabilised sub-base were used. A life-cycle cost analysis was carried out to determine the design with the highest net present value among the various options investigated. It is expected that the outcomes of this study would promote the use of mechanistic-empirical methods in the State of Qatar and the region. Inevitably, this will require significant efforts to calibrate material and damage prediction models used in the M-E PDG for more accurate representation of material properties and measured pavements performance.
H Sadek, E Masad, H Al-Khalid, O Sirin
Construction and Building Materials 126, 227-244
Fatigue cracking is one of the most serious distress modes affecting the serviceability of asphalt pavement structures. The inherent variability of asphaltic materials exhibited in fatigue test results, especially for specimens acquired from field pavements, makes the task of accurately predicting the material’s fatigue characteristics rather difficult. The problem is further exacerbated by the combined impact of a large number of factors, including loading conditions, material heterogeneity, ageing, construction quality and others. For these reasons, notable uncertainty is associated with the predicted fatigue life from laboratory tests based on the use of phenomenological models, which adopt deterministic input parameters despite the varying levels of uncertainty embedded in them. To investigate the effect of inherent uncertainty associated with asphalt mixtures on their fatigue life prediction, a probabilistic analysis approach is evidently needed. In this study, probabilistic analysis was applied to the fatigue life prediction model deduced from the viscoelastic continuum damage theory, based on testing various types of asphalt mixtures. The outcome of the analysis is a newly developed approach with the ability to predict the fatigue performance of asphalt mixtures at more consistent and reliable levels than current practice permits.
Q Lv, W Huang, M Zheng, H Sadek, Y Zhang, C Yan
Construction and Building Materials 238, 117674
Aggregate gradation is a key characteristic affecting the asphalt mix rutting resistance. The relationship between mix gradation and rutting behavior has been comprehensively studied, but only a few studies have incorporated the testing results from the Hamburg Wheel Tracking (HWT) test. This study used HWT test results to discuss the influence of four mix design variables, namely asphalt binder content, 4.75 mm key sieve passing, coarse particle gradation variation (>4.75 mm) and fine particles gradation variation (<4.75 mm) on the mix rutting resistance. A total of 26 asphalt mixes were tested using HWT test at 50 °C. Fine Aggregate (FAc) parameter derived from Bailey method was applied to quantitatively describe the gradation characteristic and was correlated with the creep slope from HWT tests. The results showed that both excessive and inadequate asphalt binder contents will impair the rutting performance. Increasing the mix 4.75 mm passing ratio from 20% to 35% slowly increases the rutting depth, with the passing ratio exceeding 41%, the mix exhibits significantly reduced rutting resistance and stripping behavior is observed. Mix skeleton with a uniform gradation in each size shows the minimum rutting resistance because smaller particles could damage the integrity of the mix skeleton by pushing the coarse aggregate open. Skeleton composed by 13.2–9.5 mm aggregates outperforms the skeleton composed by 9.5–4.75 mm aggregates. A finer gradation in aggregate fine fraction (<4.75 mm) has a positive influence on the rutting resistance as the HWT creep slope negatively correlates with the mix FAC parameter (R2 = 0.73).
H Sadek, M Sadeq, E Masad, H Al-Khalid, O Sirin
Journal of Transportation Engineering, Part B: Pavements 145 (3), 04019024
Fatigue damage is one of the major distress modes that have a critical impact on the performance and serviceability of asphalt pavements. High variability in testing results poses a challenge for predicting the fatigue life of asphalt mixtures using conventional deterministic modeling approaches. This study examined the efficacy of using a probabilistic approach for the analysis of the viscoelastic continuum damage (VECD) and fatigue life of fine aggregate mixtures (FAM) that were prepared using one hot-mix asphalt (HMA) and three types of warm-mix asphalt (WMA). The FAM mixtures were subjected to oscillating stress-controlled fatigue tests. The results highlighted the differences between the probabilistic and deterministic VECD approaches in representing and predicting fatigue life. In addition, the results demonstrated the advantage of the probabilistic VECD approach in providing more reliable predictions of fatigue life that account for uncertainty in determining the model parameters. The probabilistic analysis results showed that the WMA mixtures tested in this study had less variability but shorter fatigue life than the control HMA mixture.
Hussain U Bahia, Husam Sadek, M Ziaur Rahaman, Zachary Lemke, Dan Swiertz, Signe Reichelt, LLC Bitumix Solutions
Wisconsin. Dept. of Transportation
The objectives of this research project included: 1. Develop laboratory short- and long-term aging protocols that will simulate field aging effects measured on plant-produced mixtures from field strip by comparing mixture and extracted binder properties to those of laboratory-produced mixtures, and 2. Verify the effects of softening oils and polymers used to adjust binder grades on results of short- and long-term aging protocols developed in this study. In addition to these objectives, to develop the laboratory short- and long-term aging protocols, a study on the effect of reheating and aging procedures was conducted at the beginning of the The analysis of the study results led to the following findings:
• Based on the oven comparison and pre-heating effects results call for the standardization of mixture handling and aging procedures to minimize possible influence of variation in mixture temperature. Size of containers used for sampling, condition of container (open versus closed), and checking distribution of temperatures within the oven are important items that should be included in standard sampling, handling, and aging of field produced mixtures.
• Mixtures produced in laboratory had comparable volumetric properties to plant-produced mixtures. However, it is noted that methods used for measuring Gmm could be variable and highly operator dependent. A careful look at details for measuring Gmm, and developing a more consistent protocol, is highly recommended.
• Properties at high temperatures (MSCR) and intermediate temperatures (LAS) of binders extracted and recovered from plant-produced mixtures are significantly different than properties of binders recovered from lab-produced mixtures. The same properties are also different than original binders collected from site. These differences could be due to solvent used in extraction as well as interaction with aggregates. This is particularly important for new MSCR parameters. It is highly recommended that this issue of solvent used in extraction and recovery be addressed to avoid disputes between suppliers and agency.
• In general, correlations between HWT and SCB-IFIT tests results of lab- and plant-produced mixtures are acceptable. It is therefore not recommended to change number of aging hours or oven temperature in the laboratory short-term aging to simulate plant short-term aging.
• The Flexibility Index (FI) parameter is highly sensitive to mixture aging and magnitude of FI is controlled by post-peak slope during test. However, change in P200 content, AC% or Dust to Binder Ratio values in plant-produced mixes does not appear to affect resulting FI for either binder grade.
• The eight blends prepared with different oils and additives to target PG58-34 resulted in binders with different properties and characteristics (%R and Jnr) which could affect performance of mixtures prepared with these blends. SCB-IFIT results showed that mixtures with REOB oil have the lowest FI values at all aging levels, but also the lowest aging rates when compared to the mixture with no oils or with bio-oils. The use of bio-oil significantly improved FI values at different aging levels, but also increased aging rate of FI. The mixtures with no oils showed similar FI results and aging rates to mixtures with bio-oils.
• The collective results from the field samples and oil modification of this study confirm that long-term oven aging of 14 hours (LTOA-14) is too severe for asphalt mixtures and not suitable to distinguish between mixtures. The use of 6 hours is therefore recommended as the standard long-term aging procedure for asphalt mixtures.
H Sadek, E Masad, O Sirin, H Al-Khalid, K Hassan
Journal of Performance of Constructed Facilities 29 (5), 1-14
The population and economy in the State of Qatar have been increasing in the past 5 years. Accordingly, traffic loading has also increased rapidly, which affected the performance of existing roads and highways. This high traffic loading merits consideration of the design and construction of long-lasting pavements that require minimal maintenance. The Transport Research Laboratory (TRL) in collaboration with the Public Works Authority (PWA) of Qatar constructed a field experiment that consisted of six different pavement sections in order to investigate the influence of using different materials and asphalt mixture designs on performance. This paper presents a comprehensive study for the field evaluation of the performance of these trial sections. The evaluation involved the use of the falling weight deflectometer (FWD) and a vehicle equipped with instruments for measuring permanent deformation and cracking. These field measurements were complemented with laboratory measurements on field cores: the dynamic modulus, flow number, and semicircular bending tests. The results revealed that the increase in temperature between winter and summer in Qatar reduced the stiffness of asphalt mixtures by about 80%. The sections in which polymer-modified bitumen was used had the lowest temperature susceptibility. Moreover, the results showed that the bitumen and aggregate type significantly affected the stiffness and the trial sections’ resistance to rutting and fracture.
II Idris, H Sadek, M Hassan
Journal of Materials in Civil Engineering 32 (9), 03120004
Reflective cracking is one of the major forms of deterioration in pavements and is very common when hot-mix asphalt (HMA) overlays are constructed over a base with discontinuities in its surface. This issue has not received proper attention compared with classical fatigue cracking. However, it is a major concern during the selection of asphalt mixture surface courses for pavements with an underlying cracked base. This work identified the most appropriate testing device for investigating the resistance of asphalt mixtures to reflective cracking in the laboratory. An in-depth review of the available literature was conducted and 17 reflective cracking testing devices were evaluated, among which best three were chosen based on their availability, ease of use, variability, repeatability of the test results, and field validation. It was concluded that the Hamburg wheel tracking tester (HWTT), the wheel reflective cracking (WRC) apparatus, and the upgraded Texas Transportation Institute (TTI) overlay tester are the best available devices to examine resistance to reflective cracking in the laboratory.
R Taha, O Sirin, H Sadek
The LJMU 13th Annual International Conference on Asphalt, Pavement Engineering and Infrastructure
H Sadek, E Masad, O Sirin, H Al-Khalid, D Little
5th Eurasphalt & Eurobitume Congress, 13-15
The review of the current pavement designs and development of new designs for the State of Qatar are needed because of the tremendous economic growth and the significant increase in traffic loading. The use of the conventional Marshall Design method might not be the best approach to design mixtures that can withstand the increase in traffic loading. In order to assess the long-term performance of different pavement designs, six site trials were constructed in the south of Qatar. The objective of the trial sections were to demonstrate changes that could be made to the current design standards and the influence of these changes on material properties and performance. This paper presents part of a study for monitoring the performance of the trial sections. The dynamic modulus and the FWD tests were conducted to evaluate the influence of mix design, binder type and aggregate source on the performance of the trial sections. The results showed that variation in temperature between summer and winter times in Qatar reduced the stiffness of mixtures by around 80%. In addition, sections with polymer-modified binder had the lowest temperature susceptibility. The authors will continue to monitor the performance of these sections using mechanical and field tests in order to develop guidelines for mixture designs in the State of Qatar.
I Giwa, H Sadek, F Zaremotekhases
Construction and Building Materials 280, 122420
The Hamburg Wheel-Tracking Test (HWTT) has remained a very robust method for characterizing asphalt mixtures due to its ability to simulate field loading conditions. Despite the popularity of the HWTT, there is no standardized step-by-step procedure for analyzing HWTT data according to AASTHO T 324. This has resulted in the proliferation of plausible approaches for analyzing HWTT data. This study identifies and investigates the merits and limitations of available HWTT analysis approaches. An online survey conducted shows that the Iowa DOT approach is the most popular methodology adopted for HWTT analysis. Moreover, other approaches like the Novel Three-Parameter approach, Combined Franken-Power approach, Third-Order Curvature approach, and some other algorithm-based approaches are shown to be useful in accurately analyzing HWTT data. Based on the evaluated analysis methods, recommendations are made to eliminate subjectivity, reduce variability in HWTT results, and obtain result parameters that can effectively discriminate between asphalt mixtures.
H Sadek, MZ Rahaman, Z Lemke, HU Bahia, S Reichelt, D Swiertz
Journal of Materials in Civil Engineering 32 (1), 04019313
Short-term oven aging (STOA) is used in current practice to simulate typical aging of asphalt mixtures during plant production and field construction. This study compares the volumetrics and performance of laboratory-produced asphalt mixtures and corresponding plant-produced mixtures to examine whether STOA simulates plant short-term aging. Eight plant-produced mixtures with varying levels of binder performance grade, binder content, filler content, and traffic design levels were tested for rutting and cracking resistance using Hamburg wheel-tracking (HWT) and semicircular bending (SCB) tests, respectively. The eight mixtures were duplicated in the laboratory and subjected to 2 h of reheating and 2 h of oven aging before testing. The eight lab-produced mixtures had comparable volumetric properties to the plant-produced mixtures, and the performance results showed a relatively high level of equality between plant- and lab-produced mixtures even when the properties of their extracted and recovered binders at high and intermediate temperatures are found to be significantly different. Based on the findings of this study, the use of the outlined STOA procedure is considered sufficient to represent standard plant production aging.
Z Lemke, H Sadek, D Swiertz, S Reichelt, HU Bahia
Transportation Research Record 2672 (26), 124-133
Reheating and oven-aging procedures of plant-produced asphalt mixtures in laboratories are important topics to consider as performance testing of mixtures becomes more popular among agencies. Differences between laboratory equipment and procedure could significantly affect performance properties. The objective of this study is to investigate the influence of sample size, oven type, and variation in reheating/aging temperatures on the results of two performance tests on plant-produced mixtures. A selected mixture was tested for volumetric properties and performance using Hamburg wheel-tracking (HWT) and semi-circular bending (SCB-IFIT) tests. Results show that reheating mixtures uncovered and in smaller containers could significantly reduce the time to achieve aging temperature, and could make the process more efficient and consistent. In addition, aging using three different oven types showed that temperature within ovens can vary significantly depending on the location of the sample inside the oven, which affects the time required to reach the target temperature, and thus may also influence the aging of the sample. The mixture volumetric properties show that the effect of various heating conditions is marginal. Using the developed reheating/aging procedure of this study, the results of the HWT and SCB-IFIT tests showed no substantial effect of oven type on rutting and cracking resistance. The overall results indicate that there is a need to standardize the conditions of reheating, sample geometry, and to verify uniformity of temperature in ovens. Such standardization can further reduce variability and thus should be part of the AASHTO/ASTM standard procedures for quality control, or of laboratory equipment calibration procedures.
R Taha, O Sirin, H Sadek
OMICS International
H Sadek, MZ Rahaman, Z Lemke, HU Bahia, D Swiertz
Construction and Building Materials 237, 117456
The Superpave Performance Grade of an asphalt binder can be improved by adding different combinations of polymers and low-temperature modifiers. Although using various modifiers is not new, their effect, in particular softening oils, on long-term aging is not yet well understood. The objective of this study is to evaluate the effect of two widely-used oils to adjust binder grades on volumetrics, workability and fatigue cracking resistance of mixtures subjected to short- and long-term aging. Eight combinations of softening oils and polymers were used to prepare PG 58-34 binders. The mixtures prepared with these combinations were oven-aged for six and 14 h and used to compare their Flexibility Index (FI) results following Semi-Circular Bending Illinois FI test (SCB-IFIT) procedure. In addition, the effects of binder composition and aging on the compaction effort were assessed using the Superpave Gyratory Compactor (SGC) data. Furthermore, extracted and recovered binders of these mixtures were tested following the Linear Amplitude Sweep (LAS) test at intermediate temperature. Overall results indicate that oils used and aging susceptibility of the eight mixtures affected FI results differently. There is a good relationship (R2 = 83%) between the FI values and the absolute value of the LAS-B parameter of the extracted and recovered binders. This finding shows that FI sensitivity to aging is at least initially driven by the binder properties. The main finding from the analysis of the LAS-B parameter is that ΔTc measured for the 20-hr Pressure Aging Vessel (PAV) aging cannot be assumed to represent long-term oven aging of mixtures exceeding six-hours of oven aging at 135 °C.
H Sadek, E Masad, O Sirin, H Al-Khalid, K Hassan
3rd International Conference on Transportation Infrastructure
Asphalt mixtures have been designed in the past in the State of Qatar to safeguard against permanent deformation associated with high temperatures. These mixtures are typically designed to have low content of unmodified binder. Consequently, there is a concern based on field observations that theyare susceptible to fatigue cracking. During the pasttwo years, a comprehensive study was conducted in Qatar to evaluatethe performance of full-scale trial sections. These sections involve the use of six different asphalt mixtures in the base course. This paper reports on the evaluation of fatigue resistance of asphalt cores that were recovered from the sections by using a continuum damage mechanics approach. The analysis hasfocused on comparing the dissipated pseudo-strain energy (DPSE) and crack growth index (R (N)). Results are used to develop guidelines for the design of fatigue-resistant mixtures in Qatar and to relate the mixture design to the structural design in order to optimise performance.
F Zaremotekhases, H Sadek, M Hassan, C Berryman
Construction and Building Materials 319, 126035
The use of Warm-mix asphalt (WMA) and reclaimed asphalt pavement (RAP) technologies provide an environmentally-friendly and cost-effective approach to produce new asphalt mixtures. This study’s primary objective is to examine the mechanical performance of asphalt mixtures containing RAP using various WMA technologies. In this study, the impact of utilizing 0%, 25%, and 35% RAP contents on the performance of varying WMA mixtures against rutting, fatigue cracking, and moisture damage are evaluated. For this purpose, the rutting performance of the asphalt mixtures and recovered binders were investigated using a loaded wheel tracker (LWT) and multiple stress creep recovery (MSCR), respectively. Further, asphalt mixtures and recovered binders’ cracking performance were evaluated using Semi-Circular Bending (SCB) and linear amplitude sweep (LAS) test, respectively. The findings indicated that WMA mixtures containing 35% RAP have an enhanced performance against permanent deformations. Besides, the cracking resistance is improved by incorporating a higher percentage of RAP and WMA technologies. Overall cracking resistance performance of WMA-RAP mixtures is observed to be better compared to HMA-RAP mixtures. Additionally, the LAS test outcomes show that incorporating RAP materials and WMA technologies is associated with improved fatigue life of the WMA-RAP mixtures.
H Sadek
University of Liverpool
The population and economy in the State of Qatar have been increasing significantly in the past 10 years. Accordingly, traffic loading has also increased rapidly, which merits consideration of the design and construction of long-lasting pavement structures that require minimal maintenance. This study started with an investigation of the feasibility and performance of the current asphalt pavement materials and structures being used in the country. This investigation utilised the analysis approach implemented in the Mechanistic-Empirical Pavement Design Guide (ME PDG) software. The results evidenced how effective it is to replace the conventional unmodified 60-70 Pen bitumen with polymer-modified PG76-10 bitumen for pavements in Qatar and other countries in the region with similar climatic conditions. In addition, the results showed that the use of perpetual pavement structures is a viable option economically and that they are much more accommodating of increase in traffic loading, without causing excessive damage, than conventional pavement structures. The study also concentrated on the assessment of the long-term performance of different full-scale perpetual trial sections by conducting several field tests. The field performance evaluation results showed slightly low resistance to rutting, high IRI values, to some extent, and low stiffness during summertime when the temperature is high. These distresses and deteriorations are expected given the huge traffic loading and the big difference in temperature between seasons in Qatar. Then several field cores, field mixtures, and laboratory mixtures were tested and evaluated in order to assess the performance of different asphalt concrete mixtures against rutting, fracture, temperature susceptibility and fatigue damage. The conducted tests were useful to characterise and assess the performance of the mixtures against several major distresses. The results indicated that resistance of asphalt concrete mixtures to rutting was iii mainly affected by the bitumen grade, aggregate source and aggregate gradation. A well-designed mixture that uses polymer-modified bitumen (PMB) can achieve the high rut resistance of asphalt mixtures either with Gabbro or limestone aggregates. The use of polymer-modified bitumen reduced the temperature and frequency susceptibility on the stiffness and rut-resistance. According to these results, it is obvious that rutting and cracking would not be major distresses for asphalt mixtures in Qatar if the mixtures were designed following a Superpave mix design with the appropriate content of polymer-modified bitumen. However, given the current mixture design system in Qatar, which utilises very low bitumen content, fatigue damage or cracking in general is a main distress, and its characterisation should be investigated in depth. The traditional methods to interpret fatigue tests data are not sufficient to characterise and evaluate mixtures against fatigue damage. Therefore, two advanced fatigue characterisation approaches were performed on the raw data obtained from the fatigue test of specimens prepared from different mixtures. The analysis of the fatigue tests focused on calculating the dissipated energy (DE) and obtaining damage characteristics curves following a comprehensive viscoelastic continuum damage (VECD) approach. The test results showed that the use of the VECD approach has major advantages over obtaining DE results only. However, the predicted fatigue life (Nf) for each asphalt mixture was affected by the uncertainty associated with fatigue tests as well as with model parameters. Therefore, it was important to develop a probabilistic analysis approach that accounts for the uncertainty and the variability associated with fatigue tests and analysis, respectively. To that end, a novel probabilistic analysis approach has been proposed in the last chapter of this study for predicting the performance of asphalt mixture against fatigue damage. The VECD characterisation approach was used in the development of this probabilistic analysis model. The random variables (RVs) of the fatigue life (VECD-Nf) model (|E * |LVE, a, b and α) iv were generated following normal distribution functions. However, it is suggested that more specimens should be tested in the future to specify the true distribution functions for the RVs. In conclusion, it is clear that the fatigue life results of the probabilistic analysis approach were much more consistent and reliable than those of the deterministic analysis approach. This probabilistic approach coupled with VECD results is very practical and useful for engineers and will be beneficial to predict fatigue cracking resistance of asphalt mixtures in the field.
F Zaremotekhases, H Sadek, M Hassan, C Berryman, MI Hossain
Tran-SET 2020, 185-194
Nowadays, reclaimed asphalt pavement (RAP) is becoming more popular in producing new asphalt mixtures since it is a cost-effective and environmentally-friendly approach. However, there are some negative impacts of using RAP in new mixtures, especially with high RAP content. Previous studies show that the mixtures containing high RAP content have poor fatigue and cracking performance. Warm-mix asphalt (WMA) technologies are used to counter the negative effects of RAP on cracking resistance of asphalt mixtures. In this paper, the current specifications used in the south-central states (i.e., Arkansas, Louisiana, New Mexico, Oklahoma, and Texas) and previous regional studies conducted on the use of RAP and WMA technologies are discussed. Based on these specifications, an overview of the challenges and limitations of producing mixtures containing high RAP content and WMA technologies is presented. The objective is to identify deficiencies that currently exist in these specifications toward the implementation of these technologies.
A Al Assi, H Sadek, C Massarra, CJ Friedland
Airfield and Highway Pavements 2021, 49-60
Fatigue cracking has a significant effect on the flexible pavement’s performance and service life. Previous studies have utilized several testing techniques to explore and investigate different fatigue life prediction models and approaches. Among these approaches is the viscoelastic continuum damage (VECD) approach, which is mainly used for stress and strain-controlled fatigue tests. However, several studies found that there are significant variabilities in fatigue testing data and VECD results. Recently, few studies showed promising results for predicting fatigue life utilizing the VECD approach probabilistically. However, the proposed probabilistic VECD (PVECD) approach has some limitations, assumed arbitrary distribution functions for the random variables of the fatigue life model, and added complexity to the VECD analysis by incorporating a probabilistic analysis procedure. This study objective is to identify the main challenges of implementing the P-VECD approach and discuss the opportunities to improve it and make it more implementable by pavement engineers.
H Sadek, E Masad, H Al-Khalid, O Sirin
Bituminous Mixtures and Pavements VI, 343
The population and economy in Qatar have been expanding significantly in the past six years. Accordingly, Qatar is encountering huge development in infrastructure. The existing mix design methods have been developed in the past to protect against rutting given the high temperatures in Qatar. However, these mixtures might be susceptible to fatigue damage. During the last three years, a comprehensive study was conducted for the evaluation of performance of full-scale trial sections. These sections involve the use of six different asphalt mixtures in the base course. The aim of this work is to conduct fatigue tests and to use the Viscoelastic Continuum Damage (VECD) approach in order to characterise the resistance of the sections against fatigue cracking. Results revealed that the use of VECD approach has major advantages; however, the uncertainty associated with fatigue tests as well as models and their parameters have substantial influence on the predicted fatigue life.
H Sadek, E Masad, O Sirin, K Hassan, H Al-Khalid
2nd Middle East Society of Asphalt Technologist (MESAT) Conference
The review of the current pavement designs and development of new designs for the State of Qatar are needed because of the tremendous economic growth and the significant increase in traffic loading. The use of the conventional Marshall Design method might not be the best approach to design mixtures that can withstand the increase in traffic loading. In order to assess the long-term performance of different pavement designs, six site trials were constructed in the south of Qatar. The objective of the trial sections were to demonstrate changes that could be made to the current design standards and the influence of these changes on material properties and performance. This paper presents part of a study for monitoring the performance of the trial sections. The dynamic modulus and the FWD tests were conducted to evaluate the influence of mix design, binder type and aggregate source on the performance of the trial sections. The results showed that variation in temperature between summer and winter times in Qatar reduced the stiffness of mixtures by around 80%. In addition, sections with polymer-modified binder had the lowest temperature susceptibility. The authors will continue to monitor the performance of these sections using mechanical and field tests in order to develop guidelines for mixture designs in the State of Qatar.
C Massarra, MHH Rahat, G Wang, H Sadek
Heliyon, e11239
Human activities significantly contribution to the yearly generated plastic wastes. Moreover, the enormous increase in face masks and face shields caused by the emergence of the COVID-19 pandemic has doubled the generated plastic wastes. Although there is an added benefit of using plastic waste in construction, the cost associated with their application, specifically the face mask, has not been addressed. This paper presents a simplified and rapid estimation of the cost associated with the collection, processing, and application of face masks in hot-mix asphalt (HMA) pavements. Two scenarios, mask modified asphalt pavement and conventional asphalt pavement, are considered. The total cost is based on market price and prices from waste management facilities and plastic processing companies. Life Cycle Cost Analysis (LCCA) is used to evaluate the long-term costs of mask modified asphalt pavement and conventional asphalt pavement. Results show that no significant difference in initial total cost between the two scenarios for pavement sections with lengths less than 500m and the number of lanes less than 6. The difference in total cost begins with lengths greater than 500 m for 5 and 6 Lanes. Despite the higher initial costs for the mask modified asphalt pavement, the LCCA shows that there is a 29% maintenance cost reduction over the 40 years life cycle of the asphalt pavement. The use of LCCA shows the benefit of the selection of the most cost-effective strategy and how the use of mask modified asphalt pavement over the conventional asphalt pavement can save money over the life cycle of the asphalt and improve rutting and stiffens.
A Al Assi, H Sadek, C Massarra, M Sadeq, CJ Friedland
Construction and Building Materials 306, 124853
Pavement industry concerns have been increasing in the past decades towards fatigue cracking due to its negative impact on asphalt pavement performance. Therefore, several studies were conducted to model and characterize asphalt mixture fatigue life and number of cycles to failure (Nf) to achieve the designer’s goal ensuring the asphalt pavement serviceability, durability and to reduce the cost. Viscoelastic Continuum Damage (VECD) approach with incorporating probabilistic analysis (P-VECD) was proposed by several researchers to characterize the fatigue cracking of asphalt mixtures reliably. Although the probabilistic VECD studies attract great attention for characterizing the fatigue crack of asphalt mixtures, the VECD-Nf model random variables (RVs) are defined by using many arbitrary assumptions. Furthermore, the proposed approaches are very complicated, which added computation complexity to the VECD mode. Therefore, the prediction of asphalt mixtures’ fatigue life is needed in a reliable and simple process. This study focuses on developing a user-friendly analysis tool that determines the Nf following the VECD approach with incorporating probabilistic analysis. To achieve this goal, the proper distribution function for each RV in the VECD-Nf model is defined, a simple analysis tool is developed using MATLAB App Designer, and previous studies data for Hot-Mix Asphalt (HMA) and Fine Warm-Mix Asphalt (F-WMA) mixtures are re-analyzed using the developed P-VECD analysis tool. By using the P-VECD analysis tool, deterministic VECD analysis, probabilistic VECD analysis, and the prediction of the fatigue life of asphalt mixtures will be possible for technicians and engineers in the asphalt community.
II Idris, H Sadek, M Hassan, C Berryman, MI Hossain
Tran-SET 2020, 173-184
Reflective cracking is common distress when hot-mix asphalt (HMA) overlays are constructed on top of a pre-cracked base. Cracks on existing base gradually propagate upward because of traffic loading and/or temperature variation, reach surface course, and result in reflective cracking. Previous studies demonstrated that Texas Transportation Institute overlay tester (OT) could effectively simulate the effect of temperature variation, which is considered as the leading mechanism causing reflective cracking in the field. In this study, the effectiveness of using the OT test setup to mimic the field and evaluate the performance of various HMAs against reflective cracking is assessed based on various aspects found in the literature. It was concluded that OT is the most suitable equipment to study thermally induced reflective cracking in the laboratory. Additionally, potential modifications to improve the OT setup is proposed, which is expected to provide a more representative performance evaluation of mixtures against reflective cracking.
II Idris, E Hemphill, H Sadek
Airfield and Highway Pavements 2021, 34-44
The Texas Transportation Institute Overlay Tester (OT) is the most popular equipment to measure the reflective cracking performance of the asphalt mixtures in the laboratory. However, there is a high level of variability associated with the number of cycles to failure (NOT) determined from this test, and it has been a challenge in dependably predicting the reflective cracking performance of asphalt mixtures. The main goal of this study is to identify the reasons for high variability in OT testing data and results. A thorough literature review of recent studies regarding this issue has been conducted, and the potential causes of variability have been categorized based on different phases of OT testing, including testing procedure, data analysis, and reporting results. Finally, the study concludes with recommendations to help minimize these factors causing variability of the OT results and increase repeatability and thereby increase the overall effectiveness and credibility of OT test.
H Sadek, M Hassan, F Zaremotekhases, MR Mousa
Louisiana. Department of Transportation and Development
In general, research funding departs from short-term objectives if the research results are not implementable. Planned and documented technology transfer efforts work to incorporate research findings and evidence-based interventions into real life. However, many research studies in different areas and fields were completed successfully without a real impact on society or undocumented and untracked implementation efforts. Documentation and tracking the technology transfer efforts of research studies are essential throughout the life-cycle of any project. Considering this issue, there is a need for formal guidelines for documenting and tracking the technology transfer efforts to be used by the Southeast Transportation Consortium (STC) and other State Highway Agencies (SHAs). The review of the literature of this project (Task 1) primarily documented the different practices by several agencies for tracking and documenting the technology transfer efforts. An online survey was developed to identify successful examples of guidelines for documentation and tracking of research implementation efforts currently developed/used in different state departments of transportation (DOTs), agencies, organizations, and institutions. The reviewed literature and the online survey results provided the research team of this project with valuable information and a list of the best practices by SHAs and other agencies for documenting and tracking research implementation efforts/activities. The overall technology transfer process of research findings encompasses different interacting domains. The review of the literature indicated that these domains are categorized differently based on the nature of the research itself. As an outcome of this project, the research team has developed formal guidelines to guide any funding agency tracking and monitoring their projects and the Technology Transfer (T2) efforts.
H Sadek, M Hassan, C Berryman, MI Hossain, F Zaremotekhases
Transportation Consortium of South-Central States
The production of Warm-mix asphalt mixtures in conjunction with reclaimed asphalt pavement (RAP) has received considerable interest in recent years for economic and environmental reasons. The primary objective of this project is to enhance the performance of asphalt mixtures containing RAP in Region 6 using different WMA technologies. In this project, the effect of utilizing 0%, 25%, and 35% RAP contents on the performance of different WMA mixtures against rutting, moisture damage, and fatigue cracking are evaluated. The effects of the WMA technologies on the rutting performance of the asphalt mixtures and recovered binders were investigated using loaded wheel tracker (LWT) and multiple stress creep recovery (MSCR), respectively. Further, the influences of these technologies on the cracking performance of the asphalt mixtures and recovered binders were evaluated using Semi-Circular Bending (SCB) and linear amplitude sweep (LAS) test, respectively. Based on the results, WMA mixtures containing no RAP have a lower value of the Jnr compared to the HMA control mixture. This is an indication of the better performance of the WMA mixtures against the permanent deformation. Moreover, findings from the LWT test completely agree with the results from the MSCR test. On the other hand, the fracture resistance is found to be enhanced with the incorporation of a higher percentage of RAP and WMA technologies. Overall fracture resistance performance of WMA-RAP mixtures is observed to be better compared to HMA-RAP mixtures. Moreover, the results of the LAS test show that the incorporation of RAP materials and WMA technologies is associated with improved fatigue life of the WMA-RAP mixtures.
H Sadek, M Hassan, C Berryman, M Hossain, I Idris
The primary objective of this project is to propose a laboratory setup to test and evaluate an asphalt mixture layer on top of a simulated Cement-Treated Base (CTB) layer against reflective cracking. An in-depth literature review on the experimental studies that were conducted throughout the world to investigate the resistance of asphalt mixtures to reflective cracking was conducted. Texas Transportation Institute (TTI) Overlay Tester (OT) was found to be the most appropriate equipment to study thermally-induced reflective cracking in the laboratory, and thereby was selected to be modified and used to assess the performance of asphalt mixtures on top of a pre-cracked CTB layer. Four different asphalt mixtures and two types of stabilized bases were successfully prepared in this study. The reflective cracking performance of the laboratory-produced asphalt mixtures was evaluated using both the modified and conventional OT setup at two different test temperatures. The attempt to modify the conventional OT setup for better mimicking field reflective cracking was unsuccessful because of the inability to establish a bonding between the top and bottom layers of the composite OT specimens. The repeatability of the collected data was acceptable since COVs were below 30%. Results of the conventional OT testing showed that decreasing the test temperature from room to low temperature resulted in the asphalt mixtures to change their behavior from “soft crack-resistant” mixtures to “tough crack resistant” mixtures. On the other hand, no observable effect of changing binder type and RAP content was found when the specimens were tested in conventional OT setup.
A Al-Tawalbeh, M Sadeq, H Sadek
Qatar University Press
Upon the design of any pavement structure, three fundamental external design parameters have to be considered throughout the design process: the characteristics of the subgrade, traffic loads, and environmental conditions. This paper focuses on the main challenges being faced to estimate site-specific traffic loading for a pavement design due to the lack of accurate and recent traffic data. A case study for a pavement structural design process for an actual expressway project in the State of Qatar is discussed in this paper. This case study goes through traffic loading calculations inputs; the Average Daily Traffic (ADT), Truck Factor (TF), as well as Heavy Good Vehicle Percentage (HGV%). The challenges of calculating these site-specific traffic loading inputs are discussed through investigation of the accuracy in traffic loading estimation using Qatar Strategic Transport Model (QSTM), and how the model can be incorporated in the design. Besides, limited available Wight-In-Motion (WIM) surveys have been discussed and the paper ends with the conclusion that rich availability of traffic data enhances the accuracy of the pavement structural design. It affects significantly the value engineering practice, and results in sustainable pavement sections.
H Sadek, H Al-Khalid, E Masad, O Sirin, K Hassan
Sustainability, Eco-efficiency, and Conservation in Transportation Infrastructure Asset Management
Asphalt mixtures have been designed in the past in the State of Qatar to safeguard against permanent deformation associated with high temperatures. These mixtures are typically designed to have low content of unmodified binder. Consequently, there is a concern based on field observations that theyare susceptible to fatigue cracking. During the pasttwo years, a comprehensive study was conducted in Qatar to evaluatethe performance of full-scale trial sections. These sections involve the use of six different asphalt mixtures in the base course. This paper reports on the evaluation of fatigue resistance of asphalt cores that were recovered from the sections by using a continuum damage mechanics approach. The analysis hasfocused on comparing the dissipated pseudo-strain energy (DPSE) and crack growth index (R (N)). Results are used to develop guidelines for the design of fatigue-resistant mixtures in Qatar and to relate the mixture design to the structural design in order to optimise performance.
Ramzi Taha, Okan Sirin, Husam Sadek
Journal of Civil & Environmental Engineering
More than 15 million tons of aggregates are imported each year to Qatar from neighbouring countries. Large quantities of waste materials (around 20 million tons/year) from excavation waste, demolition rubble and reclaimed asphalt pavement (RAP) are being generated. The main objective of this paper is to present the results on the use of combined excavation waste (EW) and RAP aggregates in the construction of road bases and sub-bases. Physical and chemical properties were determined. Different combinations of both materials were subjected to compaction and California Bearing Ratio (CBR) testing in accordance with Qatar Construction Specifications. Results indicated that, for the materials tested, it is not feasible to use excavation waste, RAP aggregates or a combination of the two materials in road bases and sub-bases. The materials failed to meet some Qatari standards such as Los Angeles abrasion, liquid limit, plasticity index and CBR specified for road construction.
II Idris, H Sadek, AM ASCE, M Hassan, F ASCE
Journal of Materials in Civil Engineering
Reflective cracking is one of the major forms of deterioration in pavements and is very common when hot-mix asphalt (HMA) 6 overlays are constructed over a base with discontinuities in its surface. This issue has not received proper attention compared with classical 7 fatigue cracking. However, it is a major concern during the selection of asphalt mixture surface courses for pavements with an underlying 8 cracked base. This work identified the most appropriate testing device for investigating the resistance of asphalt mixtures to reflective crack-9 ing in the laboratory. An in-depth review of the available literature was conducted and 17 reflective cracking testing devices were evaluated, 10 among which best three were chosen based on their availability, ease of use, variability, repeatability of the test results, and field validation. 11 It was concluded that the Hamburg wheel tracking tester (HWTT), the wheel reflective cracking (WRC) apparatus, and the upgraded 12 Texas Transportation Institute (TTI) overlay tester are the best available devices to examine resistance to reflective cracking in the laboratory.
M Sadeq, H Al-Khalid, E Masad, O Sirin
Construction and Building Materials 109, 8-16
Fatigue cracking is one of the crucial distresses in asphalt pavements that affect its service life and rehabilitation process. The resistance of asphalt mixtures to fatigue failure in the laboratory experiments is influenced by several factors such as temperature, loading frequency, loading mode, sample type and geometry. This study focused on the evaluation of fatigue performance of different types of warm mix asphalt (WMA) mixture and comparing them with a hot asphalt mixture (control mixture). Warm fine aggregate mixtures (W-FAM) were fabricated using three different WMA additives: Advera, Sasobit, and Rediset which were short-term aged in the laboratory. Then, the W-FAM specimens were exposed to shear stress oscillation test by applying damaging stress level in the dynamic mechanical analyser (DMA) to examine the material fatigue resistance. The test results were analysed using the viscoelastic continuum damage (VECD) approach. The W-FAM exhibited lower dissipated pseudo-strain energy (DPSE) than the control mixture. However, there was no statistical significant difference between the W-FAM and control mix in terms of the number of cycles to failure resulted from the VECD analysis.
M Sadeq, E Masad, H Al-Khalid, O Sirin, L Mehrez
International Journal of Pavement Engineering 19 (10), 857-864
Warm-Mix Asphalt (WMA) is a widely used product, which proved a contribution to the reduction in asphalt mixing and compaction temperatures. This reduction leads to lower fuel consumption and smoke emission in asphalt plants. Most of the characterisation of binders used in WMA has focused in the past on measuring linear viscoelastic properties and associated Superpave parameters. Several studies have shown that the average stresses and strains of the asphalt mixture remain mostly within the linear viscoelastic response. However, localised strains in the binder phase of the mixture could reach values high enough to induce nonlinear viscoelastic and viscoplastic deformations. Therefore, this study focuses on an experimental and analytical evaluation of linear, nonlinear viscoelastic and viscoplastic responses of selected binders modified for use in WMA. The first part of the paper analyses the linear viscoelastic material properties and their ability to evaluate permanent deformation resistance. Then, the non-recoverable creep compliance parameter obtained from the Multiple Stress Creep Recovery (MSCR) test is analysed to assess the nonlinear response and permanent deformation of asphalt binders. The paper utilises a nonlinear plasto-viscoelastic (NPVE) approach to assess and quantify the nonlinear plasto-viscoelastic response of binders by separating the recoverable and irrecoverable strains measured in the MSCR test. Two WMA additives were included in this study by mixing them with polymer-modified and unmodified asphalt binders. Analysis of results showed that the NPVE approach captured a higher percentage of recovery than the NLVE approach. However, binder’s performance evaluation and ranking did not change by adopting the NPVE approach. The nonlinear viscoelastic parameters provided insight on the behaviour of asphalt binders mixed with WMA additives during loading cycles. Sasobit showed higher influence than Advera on binders in resisting permanent deformation by increasing the recoverable strain during the unloading phase.
M Sadeq, E Masad, H Al-Khalid, O Sirin, D Little
8th RILEM international symposium on testing and characterization of sustainable and innovative bituminous materials
Warm-mix asphalt (WMA) additives are environmentally friendly and cost-effective products that lower the viscosity of bituminous binders to allow reduction of mixing and compaction temperatures in asphalt mix production. In this study, two WMA additives were used; Sasobit® and Advera®. Both were mixed in the lab with unmodified 60/70 Pen and modified PG 76-22 binders. Strain oscillation and viscosity measurement tests were performed to determine the rheological properties of the binder with and without WMA additives. Different ageing processes were performed in this study; half and full short-term ageing using the Rolling Thin Film Oven (RTFO) procedure, and long-term ageing using the Pressurized Ageing Vessel (PAV) procedure. Test results have shown that the addition of Sasobit® increased the stiffness of both binders and changed PG grade by one unit up (6 °C PG grade). Also, Sasobit® presented better rutting resistance in modified and unmodified binders than Advera®, while both WMA additives decreased the fatigue cracking resistance. Multiple Stress Creep Recovery (MSCR) test was also conducted on both unaged and RTFO aged binders. Modified binder with Sasobit® and Advera® exhibited the same performance of the original binder after complete short-term ageing. However, Sasobit® increased the potential of rutting resistance in the unmodified binder more than Advera® did. The viscosity measurements revealed that adding Sasobit® to modified or unmodified binders lowered the viscosity more than Advera® did. These measures were considered as preliminary data required for further studies on the effect of WMA additives on the resistance of bituminous binders to fatigue cracking.
M Sadeq, E Masad, H Al-Khalid, O Sirin
6th international conference bituminous mixtures & pavements, 27-32
Warm-Mix Asphalt (WMA) technology is widely used in the paving industry due to its impact on reduction of asphalt mixing and compaction temperatures. Characterisation of WMA in the past had focused on evaluating the linear viscoelastic properties and associated Superpave specifications. In this study, evaluating the nonlinear viscoelastic responses of different WMA technologies is introduced. A comparison was made to show the difference in permanent deformation resistance of each binder type. Two WMA additives were tested after mixing them with modified and unmodified binders. The tests were conducted using a Dynamic Shear Rheometer to perform oscillatory and multiple stress creep recovery (MSCR) tests. Resistance to permanent deformation was evaluated using the rutting factor and irrecoverable creep compliance. The results showed that Sasobit stiffened the asphalt binder and increased its resistance against permanent deformation. On the other hand, Advera’s effect was almost negligible on both binder types.
MAS Sadeq
The University of Liverpool (United Kingdom) ProQuest Dissertations Publishing, 2017. 28016983.
Warm mix asphalt (WMA) is a relatively new technology that allows asphalt mixtures to be mixed and compacted at lower temperatures than the conventional hot mix asphalt (HMA). Previous WMA investigations have predominantly been limited to basic performance indicators and properties, especially in the Middle East region. Implementing the WMA technology in the asphalt pavement industry in the State of Qatar requires investigation of material properties and performance under the prevailing climatic conditions in the country. This study provides a fundamental material evaluation of WMA material damage using advanced testing and analysis approaches. The results led to a conceptual understanding of the impact of WMA additives on asphalt materials’ performance. It was found that Sasobit is the most effective WMA additive, as it increases the material’s (bitumen and mastic) stiffness, enhances resistance to rutting, and causes a reduction in the ageing effect on fatigue.
The study also evaluated the impact of ageing on WMA material damage. Fine Aggregate Mix (FAM) samples were placed in an accelerated weathering machine that was controlled to simulate the climatic condition in Qatar (UV light and heat). The samples showed significant changes after ageing in the weathering instrument. The aged FAM samples were then subjected to repeated creep and recovery testing and the performance of the material at different ageing levels was studied. The results showed that the Sasobit mix had the highest ability to recover damage induced during the loading period. The results showed a high correlation between the recovery modulus of the material and the reduced damage captured during the unloading. In order to further characterise damage, air void sizes in the asphalt mixture before and after adopting the repeated creep and recovery test were examined by scanning them using the X-Ray CT system. The air voids of the control mix (without any WMA additives) showed a remarkable change after the repeated creep and recovery test; however, all WMA samples had lower air void sizes and minor changes after testing. The CT imaging also confirmed that ageing using the UV light has an insignificant impact on air void changing before and after the repeated loading test. The results confirmed the benefits of implementing the WMA technology in the asphalt industry in the State of Qatar. This is particularly the case for Sasobit, which showed significant improvement in the performance testing results in comparison with the control mix and other WMA additives.
M Sadeq, CW Huang, E Masad, H Al-Khalid, O Sirin
Road Materials and Pavement Design 22 (9), 1986-1999
This study presents two approaches for evaluating damage and recovery characteristics of asphalt mixtures. The first approach focuses on determining damage by extracting recoverable viscoelastic strain that has no damage and comparing it with the strain response of a material that has damage. The second approach is based on identifying the capacity of asphalt mixtures to recover some of the damage that may occur during creep loading. The advantage of these approaches is that they utilise experimental data to extract damage and recovery responses, without detailed mathematical modelling of material behaviour. The developed approaches are used to analyse the behaviours of fine aggregate mixtures (FAM) incorporating warm mix additives. The results show that these mixtures vary in their damage and recovery characteristics. For example, Sasobit FAM experienced the highest damage among mixtures, but it also had the highest recovery. Ageing was found to reduce the differences among mixtures in terms of resistance to damage, but it had less effect on the differences in their healing potential.
B Vajipeyajula, E Masad, KL Roja, M Sadeq, K Rajagopal
Road Materials and Pavement Design 22 (4), 910-924
The goal of this study is to model the creep and recovery response of fine asphalt mixtures using a thermodynamically consistent nonlinear viscoelastic model. The model considers asphalt mixture to consist of two constituents: aggregate structure incorporating the asphalt–aggregate interface and asphalt binder. The efficacy of the model is evaluated using the response of warm fine aggregate mixtures (WFAM). These materials were produced using a polymer-modified binder of PG 76-22 and three warm mix additives (Sasobit, Advera and Rediset). Unaged and aged samples were subjected to creep stress levels of 75 and 400 kPa followed by rest periods. The model was quite successful in capturing the material behaviour as a single set of parameters were derived from the prediction of shear and normal stress responses for both 75 and 400 kPa stress levels. The presented model offers a unique feature in modelling the energy storage and dissipation of each of the two constituents. As such, one can examine the effect of changes in individual material properties on the material response and performance.
M Sadeq, EA Masad, H Al-Khalid, O Sirin
Advances in Materials and Pavement Performance Prediction, 97-100
This study documents the use of high-resolution X-Ray Computed Tomography to characterise air void distribution in Fine Aggregate Mixtures (FAM) prepared using Warm Mix Asphalt (WMA) additives (W-FAM). Specimens were imaged before and after subjecting them to repeated creep and recovery test. The produced images were digitally analysed to measure the air voids size in the samples and changes that occurred due to testing. While the same compaction effort was used to prepare all specimens, mixes prepared using WMA additives had less percentage of air voids than the control mix. In general, the increase in percentage of air voids happened in specimens that had larger air voids prior to loading. In addition, there was more changes in air voids in the original (control) specimens than the W-FAM specimens.
SA Mohammed, M Eyad, AK Hussain, S Okan, M Ilaria, MN d’Eurydice
7th International EATA ( European Asphalt Technology Association) Conference
Several climatic conditions affect the ageing of asphalt pavements. Intense sunlight, high air temperature, and humidity during summertime expedite the ageing of the asphalt materials and deteriorate the performance of road pavements. This study evaluates the feasibility of using an accelerated weathering system for laboratory ageing of asphalt materials. The ageing system and protocol are based on control of temperature and UV light exposure. The system was used to age the Fine Aggregate Mixtures (FAM) that were prepared with Warm Mix Asphalt (WMA) additives. The efficacy of the ageing protocol was evaluated by examining the changes of viscosity and stiffness of FAM using a Low Field Nuclear Magnetic Resonance (NMR) and a Dynamic Shear Rheometer (DSR), respectively. The accelerated weathering conditions were programmed to simulate the climatic condition of the State of Qatar. After ageing, the FAM samples were visually assessed, and no cracks or degradation were observed. The results were able to show that aged samples of all mixes had higher viscosity and stiffness compared to unaged ones. The properties of the Sasobit mix were the least affected by the ageing protocol.
A Abu-Odeh, M Sadeq, E Masad, SR Geedipally, M Ko
Transportation Research Board 96th Annual MeetingTransportation Research Board
The fatality rate in Qatar is significantly higher than many of the best performing nations in the world. Severe single-vehicle rollover crashes are predominant in the country. Vehicle tires failure (such as tread separation and blowouts) and incorrect tires use significantly contribute to loss of control and rollover accidents. This paper presents experimental testing and finite element simulation result to identify the causes of tire failures. The results indicate that balloon tires have limited endurance threshold compared to typical SUV tire and the prolong exposure to heat reduces the life of both types of tires.
A Al-Tawalbeh, O Sirin, M Sadeq, H Sebaaly, E Masad
Case Studies in Construction Materials 17, e01580
The dynamic modulus (|E*|) of asphalt mixtures is one of the most important inputs in Mechanistic-Empirical (ME) pavement analysis and design. Several models have been developed to predict the dynamic modulus based on mixture volumetrics and material properties. This study aimed to calibrate and validate two commonly used models (i.e., Hirsch model and Alkhateeb model) for predicting the dynamic modulus of asphalt mixtures in Qatar. Based on the study outcomes, the Hirsch model was found to have a high prediction performance of asphalt mixture moduli before calibration with a coefficient of determination (R2) of 87.2 % between predicted and measured values. This R2 value improved slightly after calibration to 89.2 %, Alkhateeb model, on the other hand, had a coefficient of determination of 70.8 % before calibration, which also improved to 89.2 % after calibration. The moduli predicted by the Hirsch model before and after calibration were employed in this study to perform a mechanistic-empirical analysis of the performance of various typical pavement sections in Qatar. According to the findings, the percentage change in the predicted fatigue damage due to the use of the calibrated Hirsch model reached more than 50 % with an average value of 17.33 %, while the percent change in rutting reached 14 % with an average value of 3.65 %. These results highlight the importance of using locally calibrated models for the dynamic modulus in order to improve performance predictions.
Ilaria Menapace, Eyad Masad, Mohammed Sadeq
Eighth International Conference on Maintenance and Rehabilitation of Pavements
This paper aims to evaluate the suitability of using warm mix asphalt (WMA) technology in countries with hot climates such as Qatar. For this purpose, an original and two WMA binders were investigated before and after aging. A new aging protocol that takes into account the combined effect of UV radiation, oxygen and typical summer day and night temperatures registered in Qatar is here proposed. The parameters were chosen in order to simulate the weather conditions in Qatar. The microstructure of the exposed binder surface was investigated with atomic force microscopy (AFM) and compared with the unaged surface. This evaluation is more accurate than previously used microstructural evaluations based on the observation of asphalt binder after Rolling Thin Film Oven (RTFO) and Pressure Aging Vessel (PAV) aging. In the proposed method, the exposed surface is directly observed and any rearrangements of the binder components after aging (i.e. during heat treatment to obtain a smooth surface) is prevented. Profound changes in the microstructural features were observed due to aging. Each binder presented a different microstructure of the aged surface and the common feature among the different binders was the disappearance of the bee-like structures. Degradation of the binder surface was correlated with chemical reactions caused by UV radiation and oxygen. Moreover, the effect of a relatively high temperature during the aging process may have aggravated the damage, due to the synergic effect of many factors. This may be the reason of the short service life of pavements in Qatar.
KL Roja, H Yamani, M Sadeq, E Masad
Case Studies in Construction Materials, e01708
Qatar roads are experiencing heavy traffic loads due to the rapid increase in the country’s population and construction projects over the past two decades. Considering the demand for high-performing, sustainable, and cost-efficient pavements, emphasis has been placed on using different asphalt modifiers and recycled materials in pavement layers. These modifiers/recycled materials change asphalt mixture properties, and consequently, influence pavement performance. The main objective of this study is to evaluate the performance of pavement sections that incorporate various types of asphalt mixtures and are subjected to traffic levels that range from 5 to 200 million equivalent single axle loads (ESALs). The analysis of pavement performance was conducted via three methods: Australian pavement design method implemented in Circly software, perpetual pavement design using PerRoad software, and a simplified mechanistic-empirical pavement design method (MEPD) that utilizes performance models used in AASHTOWare. The outcome of these analyses was the selection of suitable combinations of asphalt mixtures as well as the optimization of pavement layer thicknesses for different traffic loads. The results highlighted that the use of a high-stiffness mixture incorporating modified asphalt (PG 82E-10) in the wearing course should be used with caution in high traffic load sections (≥100 million ESALs). These stiff layers could be susceptible to cracking when the underneath asphalt layers have much less stiffness (50–70% less stiffness). However, in the medium traffic level (10–50 million ESALs) sections, pavement performance improved by using a stiff mix incorporating a PG 82E-10 binder in the wearing course layer. In addition, the use of crumb rubber (CR) modified asphalt reduced the material cost of a pavement section relative to the use of polymer-modified binder. The results show that it is desirable to use French EME (Enrobés à Module Elevé) mix in the base course layer for heavy traffic roads as this mix help to reduce pavement layer thicknesses and overall material cost. The outcomes of the analysis showed that the rutting thresholds commonly used in MEPD method are too restrictive (low thresholds) for heavy-duty pavements in Qatar hot climate. It is recommended to increase the rutting thresholds for such pavements.
