Styrene-butadiene-styrene (SBS) modified asphalt has been used in many road projects for its good performance at high and low temperatures. However, there was no final conclusion whether SBS could change the chemical structure of asphalt binders. The objective of this study was to analyze the impact of SBS on the molecular agglomeration behavior of asphalt binders by means of molecular simulation techniques. Two types of modifiers (SBS, MAH-g-SBS) were added into two asphalt models. Results of simulation show that three types of SBS all have impact on the molecular agglomeration behavior of asphalt binders. The impact of modifiers is largely dependent on the molecular structure of asphaltenes. The molecular agglomeration of asphalt with longer asphaltene alkane side branches is more regular. The agglomeration structure of asphalt molecules is more susceptible to SBS when the asphaltene alkane side branches are longer. The difference of influence on asphalt binders among two types of SBS is small.

Physical properties of different fibers (mineral, cellulose, or carbon fiber) and their stabilizing and reinforcing effects on asphalt mortar performance were studied. Scanning electron microscopy was used to study the effect of fiber’s microstructure on asphalt mortar’s performance. Laboratory tests of mesh-basket draindown and oven heating were designed and performed to evaluate the fibers’ asphalt absorption and thermostability. A cone penetration test was used to study the flow resistance of fiber-modified asphalt mortar. Results showed that fiber can form a three-dimensional network structure in asphalt, and this network can be retained at high temperature. This network of fibers favors the formation of a thick coating of mastic without asphalt draining down. Cellulose fiber possessed a greater effect on asphalt absorption and stabilization than did the other fibers (mineral and carbon fiber). A dynamic shear rheometer was used to evaluate their rheological properties and rut resistance. Results indicated that fiber can effectively improve the rut and flow resistance of asphalt mortar. However, the bending beam rheometer results demonstrated that the addition of fiber had negative effects on the creep stiffness and creep rate of asphalt mortar.

Cold recycled asphalt mixtures (CRAM) are a cost-effective and environmentally-friendly way to reuse reclaimed asphalt pavement (RAP). This paper evaluates the rheological properties and microstructure of mineral filler-asphalt mastic, mineral filler-residue mastic, and cement-residue mastic. Then, based on the premise of using 100% RAP with a gradation that was determined experimentally, the effects of emulsified asphalt and cement on the porosity, indirect tensile strength, tensile strength ratio, dynamic stability, and mechanical properties of CRAM were evaluated. It was found that the rheological properties and cohesive coefficient of the cement-residue mastic varied differently to those of the first two types of mastic and the results show that the addition of cement can greatly improve the interfacial bonding between binders and fillers in the mastic, thereby improving the water damage resistance and high-temperature stability of CRAM. The relationships between cement content and the dynamic modulus and phase angle of CRAM are different to that for emulsified asphalt obviously. In addition, under certain conditions, the properties of CRAM can meet the requirements of relevant technical specifications for its application to subsurface layer of pavement. Hence, the use of 100% RAP in CRAM may be feasible.

The influence of the addition of one commercial wax, Sasobit, on two base asphalts was investigated as it relates to asphalt binder performance. Rheological effects of the wax were studied using a dynamic shear rheometer. A Fourier transform infrared (FTIR) spectrometer equipped with a Golden Gate attenuated total reflectance (ATR) apparatus was used to investigate the changes in chemical composition before and after addition of the wax. The surface free energy of the asphalt binders was determined by measurement of the static contact angle. Results showed that the addition of the wax enhanced the deformation resistance of the asphalt binders. The FTIR-ATR spectra showed that there was an increase only in the absorbance peak of the methylene group between 750 and 680 cm−1 with the addition of the wax. This indicates that there was no interaction between the asphalt and the wax. The wax can reduce the surface free energy of the binders and may increase the wetability of aggregates by asphalt binders.

Hansen solubility parameters (HSPs) of six bitumens were determined using the method of three-dimensional turbidimetric titration ( Fmax ) . Compatibility between styrene-butadiene-styrene (SBS) block copolymer and different base bitumens were experimentally evaluated by the softening point difference and intrinsic viscosity. By comparing the difference between the HSP of SBS and bitumen with the results of compatibility evaluations, it was found that HSP has a very good agreement with results of compatibility evaluations between bitumen and SBS, which can be used to predict the compatibility of SBS-modified bitumen. Dispersive forces ( δd ) play a dominant role in HSP of bitumen. Polar interactions ( δp ) and hydrogen bonding ( δh ) forces have negative effects on compatibility between SBS and bitumen. Closer δd between SBS and bitumen, and lower δp and δh of bitumen improves the compatibility of SBS-modified bitumen. By comparing distribution of nonpolar components of six kinds of bitumens with dispersi...

Crumb rubber modified bitumen (CRMB) has been widely used in pavement construction and provides an effective way to recycle waste tires and helps alleviate the “black pollution” problem. There are no current specifications regarding the appropriate mixing and compaction temperatures of the CRMB mixture. There is a direct relationship between the mixing and the compaction temperatures of the CRMB mixture and the viscosity of the CRMB mastic. In this study, we first prepared CRMB using crumb rubber powder and penetration grade 70 neat bitumen, then prepared the CRMB mastic using CRMB and fillers (limestone mineral powder and cement). Finally, we used the CRMB mastic and aggregate to make mixture specimens. The best air void of the specimens was subsequently used to demarcate the viscosity of the CRMB mastic, and the construction temperatures (including the mixing temperature and the compaction temperature) were calculated based on the viscosity of the CRMB mastic from the viscosity–temperature curves. Test results indicated that the best viscosity of the CRMB mastic was 2.7 ± 0.2 Pa·s and 3.9 ± 0.3 Pa·s that corresponded to the mixing and compaction temperatures, respectively.