To understand the long-term performance degradation of asphalt, ultraviolet (UV) photo-oxidation has been used to accelerate the aging process. Three types of asphalt binders extracted from reclaimed asphalt pavements (RAPs) and one extracted from fresh hot-mix asphalt (HMA) were aged under continuous UV exposure and UV/moisture/condensation exposure. After accelerated aging tests, the weight percentage of oxygen (WPO) in all samples were measured by using energy-dispersive X-ray (EDX) spectroscopy. The testing results indicate that the aging rates of the asphalt binder under both UV and UV/moisture/condensation are fast at the beginning and stabilize after a certain period. Experimental results were also modeled by two classic asphalt aging models, namely, the fast rate–constant rate (FRCR) and nonlinear differential dynamic (NDD) models. Although the NDD model exhibits acceptable agreement with the experimental results from both the UV aging and UV/moisture/condensation aging samples, the FRCR model fits the UV/moisture/condensation aging better and thus is recommended for future UV/moisture/condensation aging performance prediction. Additionally, although exposed under UV for the same time, the WPO in samples after UV/moisture/condensation aging were lower than those in samples after continuous UV aging. This indicates that condensation and moisture reduce the UV-induced photo-oxidative aging rate.

Given the continued challenge of dispersion, for practical purposes, it is of interest to evaluate the impact of multi-walled carbon nanotubes (MWCNTs) at different states of clustering on the eventual performance properties of cement paste. This study evaluated the clustering of MWCNTs and the resultant effect on the mechanical and electrical properties when incorporated into cement paste. Cement pastes containing different concentrations of MWCNTs (up to 0.5% by mass of cement) with/without surfactant were characterized. MWCNT clustering was assessed qualitatively in an aqueous solution through visual observation, and quantitatively in cement matrices using a scanning electron microscopy technique. Additionally, the corresponding 28-day compressive strength, tensile strength, and electrical conductivity were measured. Results showed that the use of surfactant led to a downward shift in the MWCNT clustering size distribution in the matrices of MWCNT/cement paste, indicating improved dispersion of MWCNTs. The compressive strength, tensile strength, and electrical conductivity of the composites with surfactant increased with MWCNT concentration and were higher than those without surfactant at all concentrations.

Multifunctional polymer-based composites have been widely used in various research and industrial applications, such as flexible and stretchable electronics and sensors and sensor-integrated smart structures. This study investigates the influence of particle coalescence on the mechanical and electrical properties of spherical nickel powder (SNP)/polydimethylsiloxane (PDMS) composites in which SNP was aligned using an external magnetic field. With the increase of the volume fraction of the SNP, the aligned SNP/PDMS composites exhibited a higher tensile strength and a lower ultimate strain. In addition, the composites with aligned SNP showed a lower percolation threshold and a higher electrical conductivity compared with those with randomly dispersed SNP. However, when the concentration of the SNP reached a certain level (40 vol. %), the anisotropy of the effective material property became less noticeable than that of the lower concentration (20 vol. %) composites due to the change of the microstructure of the particles caused by the coalescence of the particles at a high concentration. This work may provide rational methods for the fabrication of aligned composites.

This study examines the merits of applying a biomodifier (Bio-binder, Sustainable Infrastructure Material Lab, NC A&T State University, Greensboro, North Carolina) as a fog sealant on the surface of bituminous materials to delay aging specifically caused by ultraviolet (UV) radiation during pavement service life. This study uses four types of bituminous-based materials: an asphalt binder [Performance Grade (PG 64-22) and three types of crack sealants with varying polymer content and different viscosities. Materials were prepared in small samples on aluminum plates and aged under continuous UV and UV/moisture/condensation conditioning. Changes in the chemical characteristics of the materials were then analyzed using Fourier-transform infrared spectroscopy and energy-dispersive X-ray spectroscopy. The results show that the oxygen uptake of bituminous materials after exposure to UV aging are significantly lower in specimens covered with Bio-binder compared with uncoated ones. The complex modulus and creep compliance were measured using a dynamic shear rheometer. The complex modulus for asphalt binder samples showed an increase that could be due to partial diffusion of the biomodifier in the specimens. However, in sealant samples in which the Bio-binder was removed prior to performing the experiments, the shear modulus showed a significant decrease, indicating that the sealants covered with Bio-binder remained softer compared with the uncovered samples. The results also showed a higher nonrecoverable creep compliance and a lower percent recovery at 3.2 kPa strain rate for specimens coated by Bio-binder compared with the samples with no coating, showing that the fog sealant can effectively improve properties of the sealant samples. Overall, the findings demonstrate that Bio-binder can be a promising candidate to be used as a fog sealant for bituminous binder and crack sealants to delay UV aging.

In this work, the effect of ultraviolet (UV) radiation on samples of asphalt binder mixed with crumb rubber is studied. Two sets of samples are characterised using a PG 64-22 neat binder with different percentages of rubber particles being 0, 16.6, and 20.0 wt.%. One set of the samples was stored at ambient temperature (called the unaged set) and the other was inserted inside an accelerated weathering tester for 100 h (called the UV-aged set). Thermal conductivity, chemical indices, rheology, and morphology of both sets of samples are tested using the flash method, differential scanning calorimeter (DSC), Fourier-Transform Infrared Spectroscopy (FTIR), dynamic shear rheometer (DSR), and Scanning Electron Microscope (SEM), respectively. Results show that the addition of rubber leads to a reduction of specific heat for the rubber-modified binders. Specific heat capacities of the three UV aged samples are larger than those of their unaged counterparts, and the 16.6%-aged has the highest value. FTIR spectra of the three unaged samples are very similar, whereas distinct changes occur after UV exposure. The normalised absorbance of the peak associated with S = O group increases and the peak for the aliphatic group decreases after UV aging, showing some evidence of oxidation due to UV aging. Use of crumb rubber in the binder decreases the thermal conductivity and 20.0 wt.% sample is even less conductive compared to the 16.6 wt.%. At all temperatures above 25°C, aged samples have lower thermal conductivity than the unaged ones, except neat binder which is opposite. Rheological measurements show that the complex modulus of the samples increases with the addition of rubber particles and also after aging. However, 16.6% rubber-modified sample shows the least increase in modulus after aging. Microscopic morphology shows that UV radiation causes cracks in both neat and rubber modified binder. Smaller cracks are seen to form, and the cracked pieces are stuck together in the rubber modified binders, whereas less cohesion between the cracks is observed in the neat binder.