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Asphalts often have filler particles added to improve their mechanical properties. Three distinct filler particle fractions were produced by a planetary high-energy ball mill from limestone aggregates (2.36–4.75 mm). Their particle sizes and shapes were studied by binary image processing and related to milling time and aperture size. The relaxation properties of asphalt mastics prepared with fillers of various sizes and shapes were investigated at a constant strain. Insights into the effects of particle size and shape on mastic relaxation behavior were gained by single regression analysis (SRA) in conjunction with grey relational analysis (GRA). The results show that particle size distributions had noticeable local differences in their slopes and spread, while particle shape distributions showed a narrow range of variability for the studied shape descriptors. Based on stress relaxation curves, fine particles were found to cause binders to become stressed more rapidly than coarse particles. Modified mastics showed much faster stress relaxation than corresponding base mastics at stage I, and exhibited higher stable stress levels than base mastics at stage II. A stress relaxation model was established and found to agree well with experimental data, indicating that mastic relaxation properties can be effectively modeled. Furthermore, the SRA coupled with GRA can provide a simple and effective approach to predicting the effects of particle size and shape on mastic relaxation behavior.

The performance of asphalt can be improved using various additives, such as SBS (styrene-butadienestyrene) and crumbed rubber (CR). This paper investigated the influence of CR particle size and SBS structure on the properties of CR/SBS modified binders. CR/SBS composite modified asphalts were obtained by mixing asphalt, CR of various particle sizes, and SBS copolymers with various molecular structures, and were then subjected to conventional measurements, rheological characterization, and thermal storage tests. The results demonstrated that larger CR particles enhanced rutting and fatigue resistance but reduced low-temperature cracking resistance and storage stability. Modified asphalt containing 20 wt% styrene showed the best rheological properties, followed by those with 30 wt% and 40 wt% styrene. Meanwhile, SBS copolymers with lower styrene contents showed better thermal storage stability. Addition of larger CR particles and lower-styrene SBS copolymers increased rutting and fatigue resistance, while smaller CR particles and lower-styrene SBS copolymers benefited low-temperature cracking resistance and stability. The combination of CR and SBS copolymers has a synergistic effect on asphalt’s rheological properties, thereby lowering the amounts of additives required and improving the cost-effectiveness of CR/SBS modified asphalt.

The application of asphalt with low penetration in warm areas to improve rutting-resistance has attracted great interest in recent years. Deoiled asphalt (DOA) and slurry, by-products of solvent deasphalting and fluid catalytic cracking respectively, are utilized with low value-added. The objective of this work was to prepare paving grade asphalt by blending various proportion of FCC slurry with DOA. The effect of chemical composition on viscoelastic characteristics of the blend was investigated and special emphasis was placed on the linear viscoelasticity and viscous flow behavior as well as on empirical tests. The results revealed that SARA fractions of the blends are close to asphalt and are compromise between DOA in which the content of asphaltenes is high and slurry in which is rich in aromatics. Also, SARA fractions have a significant influence on the rheological properties of the blends. Asphaltenes have been proved to enhance the moduli of asphalt and low penetration blends have demonstrated high rutting and deformation resistance especially at high temperatures. Taking into account the balance between workability and in-service performance, application of the 40 wt% slurry in DOA is highly recommended. It is indicated that a more inferior aging resistance with the increase of slurry in DOA. As a result, it is a highly effective and meaningful way to utilize DOA and FCC slurry.

The rheological properties and storage stability of CR/SBS modified asphalt have been investigated in this study. Crumb rubber (CR) as well as SBS was blended with asphalt having different chemical composition to prepare CR/SBS modified asphalt by high-shear mixer. Linear viscoelastic and viscous measurements, fluorescence microscopy as well as storage stability tests were performed on unmodified and CR/SBS modified asphalt. The results revealed that the addition of CR/SBS to asphalt produces a remarkable improvement in viscoelastic characteristics and viscosity compared with neat asphalt. Consequently, an enhanced resistance to permanent deformation is expected in road. Crumb rubber replacing parts of SBS to produce CR/SBS modified asphalt is feasible because failure temperature, moduli and viscosity undergo a significantly increase when the dosage of SBS exceeds 1%. The chemical composition of base asphalt for this special modification is crucial. In other words, moderate asphaltenes and high aromatics are suggested in order to achieve desired rheological properties. CR/SBS modified asphalt appears obvious phase separation at the storing period resulting from coalescence of SBS particle at the top of sample and sedimentation of rubber particles at the bottom. Thus, CR/SBS modified asphalt must be used swiftly after which has been produced owing to its poor storage stability. Anyhow, crumb rubber could be an alternative for reducing use of virgin SBS from economic and environmental point of view.

Recycled-polymer modified asphalt has been extensively used in road construction, especially the recycled tire scrap rubber-modified asphalt (TSRMA). However, the main problem during the application of TSRMA is poor storage stability which finally affects the service performance of the pavement. The objective of this work is to evaluate viscous properties, storage stability and morphology of TSRMA and to reveal the relationship of microstructure with rheological behavior and storage stability. With this aim, two different penetration grade asphalts were modified by rubber particles with various mean diameter in a four-paddle mixer at 170 °C. Steady state flow measurements, frequency sweep tests in linear viscoelastic region, storage stability tests as well as fluorescence microscopy were carried out on mixes. Rheological evaluation reveals that the addition of tire scrap rubber to asphalt lead to a significant increase in viscosity at 60 °C, improving rutting or permanent deformation resistance. Furthermore, the increase in particle size causes an enhancement in viscosity and the steady flow behavior tend to turn into non-Newtonian fluid with increasing particle size and temperature. Storage tests presented that the viscosity of samples obtained from the bottom section of a tube are always higher and the difference also becomes significant as the increase of rubber particles size, tending to poor stability. Fluorescence microscopy shows that dispersed particles in asphalt are the elongated features or strip-type and the aspect ratio (length/diameter) increases with particle size. In addition, smaller particle tend to be unobvious in matrix under microscopy view, indicating improved compatibility between rubber and asphalt.

Fatigue cracking is caused by repeated traffic loads and environmental conditions (temperature, ageing, etc.); it predominantly initiates within the mastic phase in the form of micro-cracks. In this sense, bituminous mastics (comprised of a binder, filler and entrapped air) play a significant role in the anti-fatigue performance of asphalt mixes. In this paper, the effects of filler particle size and ageing on the fatigue behaviour of bituminous mastics were evaluated. Prior to this, the rheological properties of the studied samples were evaluated using physical tests and frequency sweep tests. Moreover, the mastic morphology and filler distribution inside a bituminous matrix were characterized by Scan Electronic Microscope (SEM). The results revealed that ageing had a greater effect than filler particle size on the rheological behaviour of SBS-modified bituminous mastics, especially for mastics containing coarse filler particles. According to the ageing responses derived from log-log fatigue law plots, aged mastics containing coarse filler particles had higher slopes (represented by coefficient B) and lower intercepts (identified by coefficient A) than un-aged mastics. However, opposite fatigue behaviour was observed with fine filler granules, where coefficient B slightly decreased while coefficient A slightly increased after ageing. In addition, mastic morphology and filler dispersion inside a bituminous matrix were characterized by SEM, providing insight to possible relationships between morphological characteristics and fatigue performance.

Crumb rubber (CR) modified asphalt always presents very poor storage stability. In addition, CR modified asphalt is often prepared with a large amount of CR powders to obtain superior performance, but this modification results in increased instability. In this context, the use of polyphosphoric acid (PPA) was proposed to alleviate these issues. The influences of PPA content and asphalt composition on the properties of CR modified asphalt and its microstructure were studied by conventional test, rheological test, thermal storage test and attenuated total reflection Fourier transform infrared spectrometer (ATR-FTIR) characterization. It was found that the rheological behaviors of CR modified asphalt were improved by adding PPA. PPA also improved the storage stability by increasing the viscosity of CR modified asphalt at the storage temperature. Moreover, asphalt composition also has an influence on the properties. High asphaltenes content increases the rutting resistance and low temperature cracking resistance but reduces the fatigue resistance, while high resins content helps increase the storage stability. ATR-FTIR characterization results demonstrated that PPA/CR modification is both a chemical and a physical process. The adsorption peak area ratio (PAR) value derived from ATR-FTIR can indicate the degree of PPA/CR modification from the microscopic perspective. The relationship between the PAR value and PPA content helps determine the acid concentration of modified asphalt. In conclusion, PPA/CR modification is very promising for its potential in improving the storage stability and the rheological behaviors of CR modified asphalt.