Thermoplastic polyurethane elastomers (TPUs) are widely used in a variety of applications as a result of flexible and superior performance. However, few scholars pay close attention on the design and synthesis of TPUs through the self-determined laboratory process, especially on definite of chemical structures and upon the influence on properties. To investigate the properties of synthesized modifier based on chemical structure, firstly each kind of unknown structure and composition ratio of TPUs was determined by using a new method. Furthermore, the thermal characteristics and mechanical properties of modifiers were exposed by thermal characteristics and mechanics performance tests. The experimental results indicate that TPUs for use as an asphalt modifier can successfully be synthesized with the aid of semi-prepolymer method. The linear backbone structure of TPUs with different hard segment contents were determined by micro test methods. The polyester-based TPUs had thermal behavior better than the polyether-based TPUs; conversely, the low temperature performance of polyether-based TPUs was superior. Most importantly, it was found that the relative molecular mass of TPUs exhibited a weak effect on the mechanical properties, whereas the crystallinity of hard segment showed a significant influence on the properties of TPUs.

The objective of this study is to expose the effect of a variety of variables including three reclaimed asphalt pavement (RAP) contents, two warm mix asphalt (WMA) additives and a rejuvenating agent (or lack of) on the performance of WMA containing (WMA–RAP) materials. A laboratory study was conducted to evaluate the performance of WMA–RAP mixtures through rutting, bending and freeze-thaw splitting tests. Analysis of variance (ANOVA) was performed to analyse the significant effect of the variables on the performance. The tests results showed that the increased RAP content led to an increased rutting resistance and the decreased resistance to low-temperature cracking and moisture damage. The addition of the rejuvenating agent into the WMA–RAP mixtures can significantly improve the low-temperature cracking and moisture resistance. The ANOVA results showed that the RAP content had a significant effect on the rutting and low-temperature cracking resistance, and moreover, the rejuvenating agent (or lack of) had a large effect on the low-temperature cracking and moisture resistance.

The objective of this study aims to investigate the performance of thermoplastic polyurethane elastomers (TPU)-modified asphalt, with special focus on the influence of polyurethane synthesis parameters upon the performance of base asphalt. In this study, the TPU modifier was incorporated into base asphalt to prepare TPU-modified asphalt by using a self-determined laboratory process. The properties of polyester-based TPU and polyether-based TPU modified asphalt with different contents was analyzed by the base performance tests. The Fourier transform infrared spectroscopy (FTIR), fluorescent microscope, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal gravity (TG), dynamic shear rheology (DSR), and bending beam rheology (BBR) tests were conducted to expose chemical, microstructure, and rheological properties of the asphalt binders, respectively. The results indicated that the modified asphalt with 5% TPU modifier exhibited a favorable performance in terms of the penetration, ductility, softening point, and rotational viscosity, respectively. The isocyanate and polyol reacted to form carbamate in the TPU-modified asphalt, and moreover the isocyanate and aromatic compounds reacted to form halohydrins in the asphalt. Large particles contained in the polyester-based TPU-modified asphalt increased obviously with the increase of C_h (Hard segment content) and r (Isocyanate root index, molar ratio between NCO and OH) value, the fracture mode of it subjected to external load indicated a typical brittle fracture. The content of MDI in the synthesized polyurethane modifier was an important factor affecting the high-temperature stability of the modified asphalt. The polyester-based TPU modifier had a better high temperature performance than the polyether-based TPU modifier. The polyether polyol chain segment showed a greater flexibility as compared to polyester polyol; the addition of polyether polyols can be effectively offset of MDI chain rigidity as r ≤ 1 and C_h < 40% leading to the improvement of the viscoelastic property of asphalt. When C_h = 40% and r = 0.95, the polyether-based TPU-modified asphalt exhibited the same high-temperature grade as the polyester-based TPU-modified asphalt, whereas the polyether-based TPU-modified asphalt showed obviously higher low temperature grades. The polyester-based TPU with C_h = 40% and r = 1 can be used as a modifier to increase the durability of asphalt binders.

The grout pressure in the shield tunnel tail void during synchronous grouting is the key to controlling ground settlement and restraining the segment. However, the circumferential, longitudinal, and radial distribution of grout pressure considering the temporal variation in grout viscosity has not been well explored yet. In this study, a theoretical model of grout pressure distribution and dissipation considering the temporal variation in Bingham grout viscosity was established. The simulation results of the pressure model were verified by field-measured data. The results showed that the radial and longitudinal distributions of grout pressure considering the temporal variation in grout viscosity were closer to the field-measured data. The impacts of the main parameters on the pressure distribution and dissipation were analyzed. Compared with the effect of the shield tail void thickness, tunnel radius and yield shear stress have greater effects on grout pressure during the circumferential filling phase. During the longitudinal and radial diffusion phases, the increase in soil porosity and permeability coefficient was conducive to grout diffusion. The increase in the grout viscosity reduces the pressure loss during the grout flow process. The results of this research can provide a theoretical basis for the grout design process in shield tunnels.