Study Investigating the Influence of Warm-Mix Asphalt Additives on Rutting and Fatigue Performance of Nano-Modified Asphalt Binders

The current study investigates the synergized effect of a nanomaterial and two warm mix additives asphalt (WMA) additives on different properties of asphalt binders. The study used an optimal percentage of 2% for nano-Al2O3; two WMA additives were used in different concentrations. The results revealed that the addition of WMA additives increased the softening point of nano-Al2O3 modified asphalt binder. Penetration and ductility results showed a decrease after the introduction of WMA additives. The viscosity of nano-Al2O3 modified asphalt binders showed a reduction after the introduction of WMA additives. Rutting evaluation was done by using the superpave rutting parameter and multiple stress creep and recovery (MSCR) test. The fatigue performance of the asphalt binders was measured using the superpave fatigue parameter and linear amplitude sweep (LAS) test. Results showed that the introduction of WMA additives improved the rutting and fatigue performance of nano-Al2O3 modified asphalt binders. The introduction of WMA additives enhanced the aging performance of the nano-Al2O3 modified asphalt binders.

Characterising the linear viscoelastic behaviour of an injection moulding grade polypropylene polymer

The linear viscoelastic behaviour of an injection moulding grade polypropylene is studied using theoretical and computational methods. Polypropylene has a variety of engineering applications as a component. However, it commonly exhibits viscoelastic deformations. This paper analyses the creep and recovery responses of the BJ368MO polypropylene copolymer using the Burgers and generalised Maxwell models. Within the linear viscoelastic regime, an experimental creep strain at $20\ \text{MPa}$ 20 MPa is used to determine the rheological constants of the models. These constants (springs and dashpots) are determined using a nonlinear least-squares curve fitting of the experimental creep. Then they are used to predict the creep and recovery responses of the polymer at three different stresses, $10\ \text{MPa}$ 10 MPa , $12.5\ \text{MPa}$ 12.5 MPa and $15\ \text{MPa}$ 15 MPa . The experiments are made using tensile specimens designed according to the ASTM D638-14standard. The theoretical evaluations are made using the creep and recovery equations derived from their constitutive. Whereas COMSOL Multiphysics software is used during the finite element (FE) analyses. The results of the theoretical and FE calculations are verified using creep and recovery experiments. Based on the validation analyses, both viscoelastic models showed lower deviations from the experimental results when a computational approach is used. In addition, the viscoelastic models are compared by evaluating the residuals of the creep and recovery strain predictions. The theoretical analyses showed better predictions at $12.5\ \text{MPa}$ 12.5 MPa and $15\ \text{MPa}$ 15 MPa stresses when the generalised Maxwell model is used. However, the improvements are attributed to the recovery predictions. When FE is used, the Burgers model showed lower mean absolute percentage errors (MAPEs) in all creep and recovery predictions. The model has a minimum of 6.37% error at the $10\ \text{MPa}$ 10 MPa stress and a maximum of 8.23% error at the $15\ \text{MPa}$ 15 MPa . By comparison, the generalised Maxwell model showed a minimum of 9.24% error at $12.5\ \text{MPa}$ 12.5 MPa and a maximum of 12.8% error at $15\ \text{MPa}$ 15 MPa stresses. The novelty of this paper is on predicting the creep and recovery behaviour of the polymer using the FE and theoretical approaches in the linear viscoelastic regime. The findings suggest that the FE analyses using the Burgers viscoelastic material model provide better predictions, with all calculated errors falling below 10%.

CREEP COMPLIANCE OF VISCOELASTIC MATERIALS AT CONSTANT TEPERATURE

Experiments were carried out to investigate the separate roles of the hydrostatic and deviatoric components of stress tensor (using the first and the second invariant and The results were expressed in term of stress dependent shear compliance in the time temperature region of the tests (up to seconds at of the Relaxation). was found to increase in magnitude with increasing both hydrostatic and deviatoric components of stress. caused a shift in the magnitude of and caused an increase in with time. The difference between the shear compliance in creep and recovery was found to decrease with and increase with . All the different effects mentioned above could be rationalized by the idea of the time dependent free volume. If the free volume increases with time by increasing this could explain the difference in the effect of and on and explain why creep is less than recovery

Investigating the influence of carbon nanotube on the performance of asphalt binder

The purpose of this study aims at investigating the impact of multi-walled carbon nanotubes (MWCNT’s) on the properties of low viscosity grade asphalt binder. Asphalt binder with viscosity grade-10 is selected as the control binder and later it is modified with different percentages of MWCNT’s (0.5–2.5%). Penetration, softening point, ductility and rotational viscosity test were employed for evaluating the effect of MWCNT’s on basic physical properties of modified asphalt binder. Dynamic Shear Rheometer (DSR) is used for evaluating the rheological properties of the base and modified bitumen, for both aged and unaged bitumen. Based on the conventional and basic rheological tests, it was seen that the addition of MWCNT’s improved the high-temperature performance of modified bitumen. Multiple Stress Creep and Recovery (MSCR) test results revealed that the addition of MWCNT’s improved the creep and recovery of modified binders for both stress intensities (0.1 kPa and 3.2 kPa) which confirms that the modified binder is more rut resistant. Moreover, it was observed that there was a significant improvement in the aging resistance of the asphalt binder due to addition of MWCNTs. However low temperature performance of MWCNTs was not encouraging. Also, MWCNTs addition to asphalt binder was found to be stable under high-temperature storage condition. Overall, there is a significant amount of improvement using MWCNTs in the base asphalt binder.