DEVELOPMENT OF HIGH MODULUS ASPHALT CONCRETE MIX DESIGN TECHNOLOGY FOR USE ON ONTARIO’S HIGHWAYS

Asphalt pavement is subjected to external loads including mechanical loading induced by traffic and thermal loading induced by thermal variations. The last decades have witnessed a significant rise in number of heavy vehicles especially commercial trucks with higher axle loads on rural and arterial roads in Ontario. Consequently, by increasing the number and amplitude of traffic loading and severe environmental condition, servile life of asphalt pavements has been adversely affected. In many cases, premature distresses were occurred before expected service life of asphalt pavements reaches to its end. On the other hand, new pavement materials, design procedures and construction technologies have been developed worldwide. One of these technologies is “Enrobé à Module Élevé- (EME)” or “High-Modulus Asphalt Mix”. EME is a type of asphalt concrete that represents high modulus/stiffness, high durability, superior rutting performance and good fatigue resistance. This type of mix was developed in France in the 1980’s. EME is a very good option to be used in lower and upper binder courses in the pavement structure which are subject to the highest levels of tensile and compressive stresses. EME offers several advantages over conventional binder course materials including reducing the thickness of the pavement structure with improved service life and reduction in raw materials consumption. Despite the excellent performance at higher and intermediate temperatures, traditional EME mixes would be very susceptible to low-temperature cracking which is associated to using very hard grade asphalt binder. In addition to the cold climate condition, some other aspects such as traffic volume, vehicle attributes, properties of raw materials, construction methods, and testing standards are specific to Ontario. Based on the aforementioned reasons, adopting EME technology will be beneficial to Ontario’s highways. However, development of a suitable EME mix design procedure in Ontario cannot be a duplicate copy of the French method, or any other methods used in other countries or jurisdictions. This study, funded by the Highway Infrastructure Innovation Funding Program (HIIFP-2015), aims to introduce a new approach to EME mix design that contributes to good performance at high, medium and low temperatures. This could be achieved by using premium aggregate particles with dense structure (high packing density), along with utilizing high quality asphalt binder with precise content in the mix. A performance-based mix design approach is developed for EME mix design in Ontario which is a modified version of Superpave mix design procedure. Compressible Packing Model (CPM) was used for the first time to optimize the packing density of aggregate particles for two categories of mixes (12.5 mm and 19 mm Nominal Maximum Aggregate Size (NMAS)). Three types of modified asphalt binders were also considered: PG 88-28, PG 82-28 and PG 58-28 + modifiers (Elastomer additives). In addition to measuring compaction ability (compactibility) of the developed mixes, several thermo-mechanical testing methods were designated to be used in this study to evaluate the performance of asphalt mixes at different levels. Results of this study showed that the CPM-obtained gradation limits were within the grading control points of EME mixes recommended by French specification. The asphalt mixes had higher compactibility than the conventional mix, and, EME 19 was more compactible than EME 12.5 although it had less binder content than EME 12.5. Complex modulus test results illustrated that the mixes had high modulus values, and that the values of EME 19 were generally higher than those of EME 12.5. Hamburg wheel track rutting test results showed both mix types had superior rutting performance. Fatigue performance of developed mixes was assessed using four-point bending beam fatigue test at different strain levels to develop fatigue curves. The test results showed that the minimum strain level to meet 1,000,000 cycles of fatigue life (ε6) was more than 300 μm/m for all the mixes. Additionally, Thermal Stress Restrained Specimen Test (TSRST) results showed that the cracking temperatures of the developed mixes were less than -25˚C; and that EME 12.5 performed slightly better than EME 19. Binder microstructure and rheological properties were assessed using environmental scanning electron microscope (ESEM) and dynamic shear rheometer (DSR) equipment respectively. Two springs, two parabolic elements and one dashpot (2S2P1D) rheological model is used to model and compare the viscoelastic behavior of the binders as well as the mixes. ESEM test results showed that microstructure of PG 88-28 binder was the densest and connected with thicker fibril size. PG 58-28 + Elastomer additives had highly intertwined structural network with the thinnest fibril size among the binder types. 2S2P1D results showed it is a powerful tool for modeling highly polymer modified asphalt binders as well as EME mixes. According to developed master curves the mixes’ moduli have followed the same pattern as for the binders’ although phase angles’ patterns were different. Correlations were found between the binders’ microstructures and their rheological properties. Binders with denser structure and stronger bonds showed to have lower phase angles. Although binders with more intertwined structural network had higher modulus particularly at higher frequencies. The EME mix design approach was validated by using the second source of aggregate materials and PG 82-28 asphalt binder. The SGC compactibility test results showed that the mixes were more compactible than the conventional Superpave mix. According to the rutting test results, the mixes had almost not rut after 20,000 wheel passes on the submerged specimens at 50°C (rut-depth < 1 mm). In addition, the developed mixes with the second source of aggregates had relatively higher fatigue resistance where ε6 values were greater than 550 μm/m for both EME 12.5 and EME 19. TSRST results also depicted that the cracking temperatures of both mixes were below -30°C

UTILIZATION OF WASTE PLASTIC BOTTLES IN ASPHALT MIXTURE

Nowadays, large amounts of waste materials are being produced in the world. One of the waste materials is plastic bottle. Generating disposable plastic bottles is becoming a major problem in many countries. Using waste plastic as a secondary material in construction projects would be a solution to overcome the crisis of producing large amount of waste plastics in one hand and improving the structure’s characteristics such as resistance against cracking on the other hand. This study aimed to investigate the effects of adding plastic bottles in road pavement. Marshall properties as well as specific gravity of asphalt mixture containing different percentages of plastic bottles were evaluated. Besides, Optimum Asphalt Content (OAC) was calculated for each percentages of plastic bottles used in the mix. The stiffness and fatigue characteristics of mixture were assessed at OAC value. Results showed that the stability and flow values of asphalt mixture increased by adding waste crushed plastic bottle into the asphalt mixture. Further, it was shown that the bulk specific gravity and stiffness of mixtures increased by adding lower amount of plastic bottles; however, adding higher amounts of plastic resulted in lower specific gravity and mix stiffness. In addition, it was concluded that the mixtures containing waste plastic bottles have lower OAC values compared to the conventional mixture, and this may reduce the amount of asphalt binder can be used in road construction projects. Besides, the mixtures containing waste plastic showed significantly greater fatigue resistance than the conventional mixture

Stiffness modulus of Polyethylene Terephthalate modified asphalt mixture: A statistical analysis of the laboratory testing results

Stiffness of asphalt mixture is a fundamental design parameter of flexible pavement. According to literature, stiffness value is very susceptible to environmental and loading conditions. In this paper, effects of applied stress and temperature on the stiffness modulus of unmodified and Polyethylene Terephthalate (PET) modified asphalt mixtures were evaluated using Response Surface Methodology (RSM). A quadratic model was successfully fitted to the experimental data. Based on the results achieved in this study, the temperature variation had the highest impact on the mixture's stiffness. Besides, PET content and amount of stress showed to have almost the same effect on the stiffness of mixtures. The optimal amount of PET was found to be 0.41% by weight of aggregate particles to reach the highest stiffness value. (C) 2014 Elsevier Ltd. All rights reserved

Biochar removes volatile organic compounds generated from asphalt

© 2020 Elsevier B.V. Volatile organic compounds (VOCs) emission not only cause the environmental pollution, but also severely threaten human health as they are known to be toxic and carcinogenic. This study investigates the effects of biochar on removing the VOCs emission from asphalt. The biochar was obtained from the pyrolyzed productions of pig manure, waste wood and straw biomasses. Molecular model for the adsorption of the VOCs was developed and used to measure the adsorption energy and heat. The VOCs removal model was built and used to determine the VOCs removal mechanism in the asphalt. The results showed that biochar could remove alkanes, polycyclic aromatic hydrocarbons (PAHs) and sulphide compounds because of its intrinsic carbon negativity and porosity. Furthermore, source of the biochar was an influential factor on the adsorption of the VOCs compounds. Based on the results, waste wood-based biochar had the best adsorption performance which could be related to the amorphous carbon, graphite and its porous structure. Also, it shows that biochar has the great potential to be used as VOCs inhibitors

Nano-scale analysis of moisture diffusion in asphalt-aggregate interface using molecular simulations

Presence of moisture can weaken the asphalt-aggregate bond and result in aggregate stripping and moisture damage in asphalt mixture. This study investigates how the moisture affects the asphalt-aggregate bond and simulates moisture distribution of nano-scale in asphalt-aggregate interface. Effects of aggregate type (basalt, dolomite and limestone minerals), humidity and hydraulic pressure on moisture diffusion in asphalt-aggregate interface are studied. Diffusion coefficient (D), radial distribution function (RDF), contact angle (CA), free volume (FV) are calculated through molecular dynamic simulations. Polarizability of moisture in the asphalt-aggregate interface was measured using density function theory (DFT). Nano-scale moisture migration model in the asphalt-aggregate interface is built for the first time. The results show that D depends more on the hydraulic pressure than humidity and aggregate type which represents the significance of hydraulic pressure on the moisture diffusion. In addition, the aggregate type has significant effects on RDF, CA and FV. DFT results indicate that polarizability of moisture changes for different types of aggregate and hydraulic pressure values. In the asphalt-water-aggregate interface, the asphalt competitively interacts with moisture and ions from minerals through intermolecular forces

Effects of pyrolysis parameters on physicochemical properties of biochar and bio-oil and application in asphalt

Adoption of renewable energy sources such as biomass has been increasing worldwide. In this study, fast pyrolysis as an acceptable and viable method to get renewable bio-oil and biochar is used. Different temperatures and N flow velocities were used in the fast pyrolysis process to evaluate the pyrolysis yield of biochar and bio-oil. The waste wood and pig manure were utilized to prepare biochar and bio-oil. X-ray fluorescence, X-ray diffraction, high-pressure liquid chromatograph, Micro confocal laser Raman spectrometer, Fourier transform infrared spectrometer, and dynamic shear rheometer were used to measure the chemical compositions, structure, and pyrolysis yield of biochar and bio-oil. The obtained results indicate that pyrolysis temperature increases the purity of inorganic oxide in biochar and N flow velocity promotes the yield of carbon in biochar. The increase of N flow velocity would increase the acid property of bio-oil and damage the products yield of bio-oil. It was also observed that biochar could remarkably alter the fundamental performances of petroleum asphalt including penetration, softening point, ductility, viscosity, and complex modulus. The most important is that the upgraded bio-oil can be used to replace partly or fully the petroleum asphalt which is a promising biomass application