Sand Asphalt Research Articles

The effect mechanism of microwave enhanced aggregates on the microwave heating performance of asphalt mixtures

The use of microwave enhanced material as aggregate for asphalt mixture has emerged as a crucial focus in improving the microwave heating performance of asphalt mixture. However, there is a marginal diminishing effect in microwave heating, which limited further improvement in the microwave heating property of the asphalt mixture. In order to explain the mechanism of the marginal diminishing effect, a three-phase (microwave enhanced aggregate, ordinary aggregate, asphalt sand) microscopic model of asphalt mixture was established using MATLAB and COMSOL based on the random aggregate placement and finite translation algorithm. The distribution of electromagnetic field, temperature field and the heat transfer efficiency were analyzed to investigate the mechanism of microwave enhanced aggregates influencing microwave heating efficiency. The results show that the microwave enhanced aggregate changes the heating efficiency of non-microwave enhanced phases (ordinary aggregate, asphalt sand) as follows: firstly, the change of electromagnetic fields distribution may affect the electromagnetic loss power of non-microwave enhanced phases. The other is that the heat transfer rate from microwave enhanced aggregate to the non-microwave enhanced phase will affect the heating efficiency of asphalt mixture. However, it was found that the self-generated heat of non-microwave enhanced phase accounts for over 80% of its internal energy increment. The heat transfer rate of microwave enhanced aggregates decreased as its substitute amount increased. The decrease in impedance matching of asphalt mixture with air and heat transfer efficiency are the two main reasons for the marginal diminishing effect of asphalt mixture containing microwave enhanced aggregates.

A Fractional Creep Constitutive Model Considering the Viscoelastic-Viscoplastic Coexistence Mechanism.

In order to improve the accuracy and universality of the nonlinear viscoelastic-plastic mechanical behavior characterization method of asphalt mixture, a new criterion for the division of the creep process of materials was established based on the strain yield characteristics, and the coexistence mechanism of Viscoelastic-Viscoplastic strain was proposed in the subsequent yield phase; then, a viscoelastic element was constructed in the form of a parallel connection of two fractional viscoelastic elements based on fractional calculus theory, and its mathematical equations were derived; with novel viscoelastic elements, a constitutive model characterizing the whole creep process of asphalt mixtures was developed and its analytical expression was derived. The laboratory short-term creep test of Cement and Asphalt Mortar (CA mortar) and the simulation test data of asphalt mixtures from the references were used to verify the constitutive model. The results show that the creep constitutive model of asphalt mixture established in this paper has excellent fitting accuracy for different phases of the creep process of asphalt mixture under different stress levels, where the minimum fitting correlation values R2 for CA mortar, asphalt mixture (applied to pavement engineering), and asphalt sand are 0.9976, 0.981, and 0.979, respectively. Therefore, this model can be used to provide a theoretical reference for the study of the characterization of the mechanical behavior of asphalt materials.

Evaluation Method and Influence Law of UV-Cured Polyurethane on the Self-Healing Performance of Asphalt and Asphalt Mixtures

To explore the effect of UV-curable polyurethane (UV-PU) on the self-healing performance (SHP) of asphalt and asphalt mixtures, this article conducted research in this area of the evaluation method and influenced the law. polyurethane (PU), Styrene-Butadiene-Styrene Block Copolymer (SBS Ι-C) and 70# asphalt and asphalt mixtures were introduced as the example of comparison. A method for evaluating the SHP of asphalt, sand asphalt mixture, and medium particle asphalt mixture using the healing index (HI) as an evaluation index was proposed, and the healing performance of various materials under different healing conditions was tested and analyzed. The research results indicate that, HI based on asphalt complex shear modulus (HIA), HI based on sand type asphalt mixture (AC-5) flexural tensile strength (HIAC-5), and HI based on medium grained asphalt mixture (AC-16) bending stiffness modulus (S) HIAC-16 can effectively reflect the SHP of asphalt, AC-5, and AC-16 under different healing conditions, and can be used as an evaluation indicator for SHP. The asphalt SHP is related to the asphalt type and the degree of initial loss and is highly correlated with the healing time. Compared to other asphalt types, the sensitivity of UV-PU or PU modified asphalt to initial loss is lower than that of SBS Ι-C modified asphalt, but higher than 70# asphalt. Under the same light healing time and initial degree of loss, the SHP of UV-PU modified asphalt AC-5 and AC-16 is significantly superior to other types of asphalt mixtures. Compared to asphalt, the self-healing time of AC-5 grade AC-16 is longer. The SHP of AC-16 is highly correlated with the loss degree associated with the initial S. The larger the initial loss degree of the S, the greater the loss rate of the HI.

Effect of waste PET and CR as sand replacement on the durability and acoustical properties of semi dense asphalt (SDA) mixtures

Construction materials research is consistently striving to improve sustainability, in the reduction of virgin materials by use of otherwise landfilled materials of the same purpose. Crumb rubber (CR) from end-of-life tires and polyethylene terephthalate (PET) from post-consumer liquid containers are two of the most commonly circulating forms of waste in the urban environment. This study investigated the replacement of semi-dense asphalt (SDA) sand by untreated mechanically shredded CR and PET, at 2.5 and 5.1% respectively by total mass of aggregates. The mixtures were evaluated by compactability, indirect tensile strength (ITS), fracture energy (FE), water sensitivity by ITS ratio (ITSR%), surface texture and acoustic absorption tests. After compaction, the CR and PET samples experienced an elastic rebound effect, which resulted in the air voids being higher than expected. Also, the PET samples required more compaction energy. The ITS, FE and ITSR% were significantly reduced with CR replacement, while the PET mixture performed similar to the control, especially in FE. The sound absorption was related more to the air voids than the material type, although the absorption coefficients of the SDA was not found to be significant. The CR reduced the texture level of the pavement significantly in comparison to the control, while texture level remained the same for the PET mixture, despite a difference in the porosity. Further studies were performed using a mixture replacing PET by aggregate volume at 5.1%, comparing it to the control SDA in terms of low temperature cracking and permanent deformation at 50 °C. While the compactability of the PET mixture was now similar to that of the control, the resistance to cracking and permanent deformation was lower. Although the PET mixture had some interesting ductility properties, the replacement of sand by CR and PET is not recommended, and the more common use as asphalt mixture modifiers with fairly low addition contents of around 1% is more sound.

Stress concentration in the vicinity of road сoating cracks

The article presents the results of a computer analysis of the stress-strain state of a multilayer asphalt pavement under the influence of traffic loads. Based on the finite-element model of coating deformation, a study was made of the mechanical behavior of the system considered for various structural schemes for the existence of vertical cracks in various layers of the structure under the action of vertical transport loads. The effects of stress concentration in the system due to high-gradient deformation fields and structural imperfections of the multilayer coating were found.
 Multi-layer asphalt roads are one of the most common construction projects. Based on a review of the tasks of science about their strength and durability, these structures can be attributed to significantly complex types of building systems. This is primarily due to the multi-parameter nature of the factors that determine their design, material properties, types of loads and the impact on them, as well as their operating conditions. Therefore, designers of road structures and specialists who are involved in the theoretical modeling of the mechanical behavior of layered massifs during operation have to take into account many additional factors that complicate their work. These include the most important design and operational features of these systems, which significantly affect the nature of the distribution of stress and strain fields, as well as their intensity. First of all, they include special structural schemes of the road and pavement. It is a multilayer three-dimensional package having disproportionately different sizes along each direction.
 Hidden (as well as obvious) vertical cracks and horizontal delamination of the structure, sometimes permissible under operating conditions, can be added to the design model of a structure. Such violations of the continuity of the system also lead to discontinuity of the displacement functions, which further worsens the system’s performance and complicates the task of its modeling.
 The materials of the coating layers, which include asphalt concrete, cement, crushed stone, sand, soil, and others, also bring particular specificity to the work of the road structure. All of them differently resist tensile, compression and shear, and asphalt concrete is also elastic-viscous - plastic material, whose properties are largely dependent on temperature.

Strain Sweep Fatigue Testing of Sand Asphalt Mortar to Investigate the Effects of Sample Geometry, Binder Film Thickness, and Testing Temperature

This study evaluated the viscoelastic fatigue behavior of binder using strain sweep fatigue testing of cylindrical sand asphalt mortar (SAM) samples. The SAM samples can represent the realistic film thickness (such as 10–70 μm thick) of the binder in mixtures, while testing repeatability-efficiency can still be met as a result of the use of a standard sand as a load carrier between binder films. A proper testing protocol is still under development, and one of the unknowns in the field is a set of testing conditions that can provide repeatable and case-sensitive test results. Toward that end, SAM samples with different dosages of binder in three geometries were tested at varying temperatures in this study. A PG 64-34 binder was used, and a strain sweep test using a dynamic shear rheometer was conducted to compare the test results from the different cases. Four parameters resulting from the SAM testing were examined: two accounting for material linear viscoelastic behavior and two accounting for fatigue damage characteristics. The parameters were incorporated with statistical analyses to quantitatively evaluate data variability and sensitivity influenced by the binder film thickness, SAM specimen geometry, and testing temperature. The coefficient of variation was less than 20% for all the cases, which indicated the validity of the SAM method attempted in this study. Results also indicated that fatigue behavior was independent of the SAM geometries used in this study, while binder film thickness and testing temperature significantly affected test results.

Asphalt Deck Pavement Design for Concrete Bridge under Frost Climate in the North Sea Region

A prefered waterproofing system and bearing course mixtures for asphalt pavement deck were designed to determine a suitable waterproofing system and material/structure combination optimize proposal for Qingdao Bay Bridge, which was built under the frost climate of Shandong province, through a general analysis on the disease type and the damage mechanism of asphalt deck pavement. Based on the laboratory test results, the test section construction and long-term pavement performance observation, a comprehensive comparison and analysis about five types of waterproofing system(Synchronous Seal coat+ Asphalt Sand, Polymer Modified Bituminous Waterproofing Sheets, Priming Coat+Asphalt Rubber Membrance+Protection Board, Polymer Modified Emulsified Asphalt Waterproof coating, Gussasphalt)were made in terms of waterproof effect, workability, quality reliability and long-term performance. Furthermore, the asphalt deck pavement were proposed to be designed on the basis of the layer performance-related concept, and regarded as the system engineering. The construction effect indicates that both the multi-purpose layer (waterproofing high modulus asphalt sand) and the deck pavement structure are adapted to the evidence temperature difference and windy characteristics during the construction. It also shows the excellent workability and quality reliability.

Study on Creep Behavior Of Asphalt Mixture Based on Discrete Element Method

A three-dimensional (3D) microstructure-based discrete element (DE) model was developed to study the creep behaviour of high viscoelastic asphalt sand (HVAS) with the uniaxial compression creep tests. The three-point bending creep tests of asphalt mortar were carried out in order to obtain the parameters of the Burger model, to determine the transformation method of macroscopic parameters and microscopic parameters of the model in theory, to obtain the parameters used in the discrete element model, and then establish the discrete element analysis model for the asphalt mixture. A 3D-DE digital specimen was composed of coarse aggregates, asphalt mortar and air voids, which could also take gradation, irregular shape, random distribution of aggregate and air voids into consideration, and the boundary conditions of the model were set through the simulation of the uniaxial compression creep tests. An accurate and extensive mapping model of HVAS was built by 3D-PFC (Particle Flow Code), which can provide a simple alternative to the laboratory tests. This method can simulate a series of numerical examples based on different stress levels, coarse aggregate homogenizations, mortar homogenizations and temperatures in a single factor method. Comparison of results of laboratory and numerical tests shows that the 3D-PFC-viscoelastic model can reflect the creep mechanical behaviour of asphalt mixture accurately. It provides the theoretical basis and auxiliary means for analysing the mechanical properties of asphalt mixtures using PFC software. The research on creep behaviour of the asphalt mixture by numerical simulation opens up a new way for the research on creep behaviour of the asphalt mixture, it is of considerable theoretical value and has broad application prospects.

Effect of Aggregate Gradation on Rutting of Thin Asphalt Overlay

Permanent deformation (rutting) of asphalt pavements has a major impact on the service life of pavements. Rutting reduces the performance of the pavement and produces serious hazards for highway users. Due to the axle loads incensement, and high local summer temperature, rutting became the major distress in flexible pavements for many countries. Recently, thin asphalt overlay (TAO) is recommended as a significant remedy technique for deteriorated pavements. Aggregates are one of the main structure materials asphalt paving mixtures, whereas, aggregate properties remarkably effected on the asphalt pavements performance. Aggregate gradation is representing the significant feature of aggregates that affecting permanent deformation of traditional hot mix asphalt (HMA) thick pavement layers. The aim of this study is to examine the influence of aggregate gradation differences on rutting features of modified TAO mixtures that comprising waste polymers. The evaluation process included the preparation of polymer modified asphalt (PMA) comprising two types of additives, namely, Crumb Rubber Modifier (CRM) and Low-Density Polyethylene (LDPE). CRM and LDPE in the form of fines that have a particle size under 250 um were used as additives to liquid neat asphalt, individually and collectively by weight of virgin asphalt; i.e., PMA included 15.0% of CRM and (2.5. %, 5.0%, 7.5% and 10.0% of LDPE. Three types of aggregate gradations were used, i.e. 12.5, 9.5 and 4.75mm, Nominal maximum aggregate size, (NMAS). The Superpave mix design system was adopted in volumetric proportioning of prepared mixtures, while Wheel Tracking (WT) test was used to determine the rut depth characteristics for prepared mixtures. about 30 asphalt concrete specimens were prepared to forecast the TAO behavior concerning permanent deformation for wearing course type III A and B according to State Corporation of Roads and Bridges in Iraq, while for 4.75mm, NMAS (sand asphalt layer) an abroad specification was used. Results demonstrated that the aggregate gradation plays a vital role in increasing permanent deformation for several type of TAO mixtures. Also, the addition of CRM by 15% to the neat asphalt led to an increase in the resistance of the mixture to permanent deformation. Moreover, PMA with LDPE became hardener (higher viscosity) which led to increase binder stiffness, whereas a consequent is stiffening the mixture. Therefore, optimizing aggregate gradation with PMA including waste polymers can limited the rutting occurrence distinguishably

Investigating the Effect of AC Overlays Reinforced with Geogrid and Modified by Sasobit on Rehabilitation of Reflective Cracking

In this paper, the effect of asphalt overlays, which were reinforced with geogrid, modified by sasobit and combination of them on the rehabilitation of reflective cracking, is studied. The laboratory tests were conducted under dynamic loading in bending mode to investigate reflective cracking retardation compared to reference samples. The results illustrated that in a certain range of variables, temperature variations, and sasobit percentages are the most effective parameters on fatigue life and other responses. Another effective variable was the type of interlayer in asphalt slabs. Furthermore, it has been found that the combination of samples (modified by sasobit, reinforced with geogrid and a 3cm sand asphalt layer) (1SP.G.SA & 2SP.G.SA) had a better performance such as improving fatigue life and reducing crack propagation in all loading and temperature conditions compared to the reference samples. Based on the image processing results, the process and shape of crack growth vary greatly at different temperatures. Generally, at low temperatures (20 °C) and frequencies, the cracks grow from bottom to top, and the width of them gets smaller. However, with increasing the temperature and loading frequency, the top-down cracks are also observed, which is due to the reduced resistance of the asphalt resulting from the reduction of adhesion and the fastening between the aggregate and bitumen.

How to Achieve Efficiency and Accuracy in Discrete Element Simulation of Asphalt Mixture: A DRF‐Based Equivalent Model for Asphalt Sand Mortar

The clump‐based discrete element model is one of the asphalt mixture simulation methods, which has the potential to not only predict mixture performance but also simulate particle movement during compaction, transporting, and other situations. However, modelling of asphalt sand mortar in this method remains to be a problem due to computing capacity. Larger‐sized balls (generally 2.0–2.36 mm) were usually used to model the smaller particles and asphalt binder, but this replacement may result in the mixture’s unrealistic volumetric features. More specifically, replacing original elements with equal volume but larger size particles will increase in buck volume and then different particle contacting states. The major objective of this research is to provide a solution to the dilemma situation through an improved equivalent model of the smaller particles and asphalt binders. The key parameter of the equivalent model is the diameter reduction factor (DRF), which was proposed in this research to minimize the effects of asphalt mortar’s particle replacement modelling. To determine DRF, the DEM‐based analysis was conducted to evaluate several mixture features, including element overlap ratio, ball‐wall contact number, and the average wall stress. Through this study, it was observed that when the original glued ball diameters are ranging from 2.00 mm and 2.36 mm, the diameter reduction factor changes from 0.82 to 0.86 for AC mixtures and 0.80 to 0.84 for SMA mixtures. The modelling method presented in this research is suitable not only for asphalt mixtures but also for the other particulate mix with multisize particles.

Fatigue characterization of binder with aging in two length scales: sand asphalt mortar and parallel plate binder film

Fatigue-cracking resistance of asphaltic materials and flexible pavements is strongly related to the properties of the binder under aging and its interaction with aggregate particles, which are small-scale physical-mechanical characteristics of components. Currently, there are binder test methods including the AASHTO TP 101 that are widely used to evaluate fatigue characteristics of asphalt binder. Despite the scientific leap for predicting and characterizing binder fatigue behavior in pavements, there are opportunities to better mimic the true state of the binder subjected to fatigue loading in pavements. This study attempted fatigue damage characterization using sand asphalt mortar (SAM) specimens, which are anticipated to better represent the realistic geometry (such as micrometer thick film) of binder in mixtures than typical binder fatigue tests that use 2-mm thick parallel plate specimens, while testing repeatability-efficiency can still be met due to the use of standard Ottawa sands as a load carrier between binder films. Multiple fatigue-related tests (i.e., time sweep and amplitude sweep) were conducted on both 2-mm thick binder specimens and SAM specimens by varying the level of aging to investigate the effects of binder length scale and aging on fatigue cracking behavior. The laboratory procedure to fabricate SAM specimens was presented with the testing repeatability, which supports the validity of the method. It was observed from the fatigue testing results that SAM testing could capture the microcracking and macrocracking phases more distinctively and sensitively than conventional binder fatigue testing, particularly with the influence of aging. These test results and findings imply that the SAM can be considered a proper solid phase to evaluate the properties and damage characteristics of binders and mastics under various conditions.

KAJIAN BAHAN TAMBAH ATERNATIF SERAT ECENG GONDOK TERHADAP CAMPURAN LATASIR SAND SHEET KELAS A SPESIFIKASI SEKSI-6 2010 BINA MARGA

Asphalt sand layer (Latasir) is a layer of road construction consisting of coarse aggregates, fine aggregates, fillers and hard asphalt, which are mixed, spread, and compacted in hot conditions at certain temperatures. In this study is the use of water hyacinth fiber in a mixture of thin layer sand sheet sand grade grade A. The purpose of this study was to determine the process of making test specimens with ingredients added to water hyacinth fiber and the process of testing specimens with ingredients added to water hyacinth fiber. The test was carried out by adding water hyacinth fibers in the sand sheet class A latasir mixture. And with the addition of water hyacinth fiber variations of 0.6%, 0.9%, 1.2% taken from asphalt content. The final result of this research was Marshall evaluation which was obtained for the effect of the addition of water hyacinth cellulose fiber in this study showed an increase in Marshall stability value of 27.29% with a mixture of 1.2% water hyacinth, plastic fatigue (Flow) decreased by -23 , 89% with a mixture of 0.9% water hyacinth, cavity filled in the mixture (Void in the Mix) increased by 18.65% with a mixture of 1.2% water hyacinth, cavity filled with asphalt (Void Filled With Asphalt) decreased by -8.74% with a mixture of 1.2% water hyacinth, cavity in aggregate (Void In Mineral Aggregate) increased by 7.80% with a mixture of 1.2% water hyacinth, and Marshall Quotient increased by 71.78% with a mixture of 0.9% water hyacinth. These results indicate that water hyacinth fiber can be used as an ingredient to add a mixture of latasir sand sheet class A specifications of clan development. Keywords: sand sheet class A sandflies, Marshall Test Index, water hyacinth fiber, stability, flow, Marshall Quotient.

AAUQ Asphalt Mixtures Using Carbide Lime for Low Traffic Paths in Manaus - AM

The asphalt pavements of the residential streets and outskirts of Manaus city are usually made of Hot Machined Asphalt Sand (AAUQ), which is ideal for low traffic roads, not only for the flow of vehicles and use of materials, but also for the economic viability of the project. In this research we used the waste originated from acetylene gas production in factories of the Industrial District, Cal de Carbureto in the composition of asphalt mixtures of type AAUQ, replacing the usual filler, Portland cement. These mixtures were mechanically evaluated with respect to the Diametral Compression Tensile Strength, Resilience Module and Fatigue Life tests, and it was found that the alternative filler presents superior results when compared to the usual used in the asphalt plants of the City.

Сonceptual Fundamentals for Technology of Sand Disperse-Reinforced Asphalt Concrete

A problem of efficient resource usage in road branch continues to be one of the most complicated issues and requires an intensification in investigation process pertaining to possibilities for production of road construction materials of low resource intensity with high physical and mechanical properties. Technogenic wastes of the Belarusian enterprises are rather various and they need a detailed investigation. Application of such methods as IR spectrometry, probe microscopy, study of of geometric characteristics of particles and fibers make it possible to determine more active centres and reveal micro-defects that influence on strength of adhesion bond at the boundary of “fiber – binder” and physical and mechanical properties of ready-mixed asphalt concrete. Nature of basalt fiber presupposes mainly physical character of adhesion interaction at the boundary of phase separation. An increase of technogenic waste activity to enhance adhesion contacts up to chemisorption level is possible only due to preliminary fiber processing which includes cleaning, removal of foreign inclusions, etching, drying, probable sorting-out and fluffing. Industrial approbation of such technological process is not possible without development of a corresponding module or a plant. Disperse reinforment causes changes in composition and technology of sand asphalt concrete. An increase in specific surface of an aggregate, necessity of uniform distribution of fiber in terms of volume determine the required need in a binder, procedure and regimes for component mixing. Grain composition of the aggregate can be represented by crush screening and natural sand of mixture of these materials. Requirements to properties of sand disperse-reinforced asphalt concrete are formed on the basis of operational conditions and layer arrangement of the material in the design of a surface dressing. The disperse-reinforced sand asphalt concrete can perform functions of a superfine protective layer, a levelling layer or a crack stopping layer which is resistant to fatigue crack formation.

Vibration experiment of CTCP-CRCP composite pavement under heavy traffic

The accelerations of sandwich-type composite pavements consisting of cross-tensioned concrete pavement (CTCP), asphalt sand (AS) stress-absorbing layer, and continuously reinforced concrete pavement (CRCP) layers from the top to the bottom were measured under different traffic loads. First, the acceleration spectra of double plates of composite pavements were measured under axle loads of 100, 200, and 300 kN using an embedded accelerometer. The universal mean of the acceleration ratio of CTCP to CRCP was defined as the stress-absorbing ratio of the AS layer as obtained through statistical analysis of the test data. A frequency spectrum was obtained for the pavement under each vehicle load by using Fourier transformation. Test results show that the maximum acceleration of CTCP and CRCP in composite pavements was 0.022, 0.039, and 0.059 ms−2 and 0.01, 0.015, and 0.025 ms−2 under vehicle loads of 100, 200, and 300 kN, respectively. The corresponding mean stress-absorbing ratio of the AS layers was 3.38, 3.15, and 3.46. The results suggest that the proposed composite pavement is suitable for roads with heavy traffic because its stress-absorbing layer can effectively reduce the pounding caused by heavy loads on the pavement.

Research of Method for Solving Relaxation Modulus Based on Three-Point Bending Creep Test.

A method was developed for solving the relaxation modulus of high viscosity asphalt sand (HVAS) based on the three-point bending creep test, and was verified by comparison with experimental results. In this method, firstly, a transcendental equation was obtained by the convolution, and then equations were obtained by Taylor’s formula, which were solved by Mathmatica to obtain the relaxation modulus by Newton’s method. Subsequently, the laboratory investigations of the viscoelastic parameters of the Burgers model for the HVAS by three-point bending creep tests were carried out. In addition, the method was verified by comparing the relaxation moduli with the indoor relaxation experiments. Results showed that the numerical calculation and the test data were in good agreement, and the relaxation characteristics of the HVAS were reflected more accurately. The method can be used to study the relaxation characteristics of the asphalt mixtures effectively. In addition, this study provides a research basis for road crack prevention.

Reflective cracking reduction by a comparison between modifying asphalt overlay and sand asphalt interlayer: an experimental evaluation

ABSTRACT Reflective cracking is a frequent type of distress in asphalt concrete (AC) pavements that decreases pavement service life in a newly constructed AC overlay. In this study, natural zeolite and hydrated lime were added to crumb rubber modified (CRM) asphalt binder in order to assess their effects on reducing propagation of reflective cracks in composite pavements. CRM asphalt binder containing these additives was used in both AC overlay and sand asphalt interlayer to investigate crack propagation in the composite specimen under dynamic cyclic loading. The results show that asphalt interlayer modification is more effective than AC overlay modification (using CRM binders containing additives) in controlling reflective cracks. In other words, sand asphalt interlayer modification is more capable of absorbing the energy of crack propagation and, consequently, delaying the crack propagation. The results also indicated that simultaneous modification of both the interlayer and overlay significantly decreases reflective cracking potential. With respect to the significant role of additive type in crack propagation delaying, the results show that CRM binders containing natural zeolite are more efficient in crack mitigation compared to CRM binders containing hydrated lime.

Evaluation of factors affecting tack coat bond strength

Different types of distress occur in asphalt concrete pavements due to lack of bonding between existing old layer and overlay. Therefore, this paper evaluates the bonding strength between sand asphalt mixture as overlay and roller compacted concrete (RCC) as the existing layer. Four types of tack coat including crumb rubber modified (CRM), grade 60/70 binder, cationic slow-setting (CSS), and cationic rapid-setting (CRS) emulsion were considered, with 200, 400, and 600 g/m2 dosages. Different RCC surface temperatures including 0, 25, and 60 °C were chosen to evaluate the effect of ambient temperature on the bonding strength. Results showed that CRM and 60/70 binders have higher bonding strength in comparison to emulsions. The bonding strength at 0 °C for all types of tack coat was significantly lower than other temperatures. The optimum application rates of 200 g/m2 and 400 g/m2 were selected for the CSS and CRS emulsified binders respectively. The optimum application rate for the 60/70 and CRM binders was selected as 600 g/m2.

Heavy oil upgrading using magnetic molybdenum disulfide catalyst

In this work, the magnetic molybdenum disulfide catalyst (Fe3O4@SiO2@MoS2) was prepared and evaluated as a dispersed catalyst for the viscosity reduction of Canadian oil sand asphalt. The flower-like MoS2 formed and some Fe3O4@SiO2 particles were deposited on the surface of MoS2. The catalytic reaction was carried out at 400°C and hydrogen pressure of 15 MPa. The results showed that the viscosity of the liquid product at 50°C dramatically decreased from 4660 mPa·s to 76.9 mPa·s and the degree of viscosity reduction reached 98%.