Journal of Materials in Civil Engineering

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 $680{\text{cm}}^{-1}$ 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.

The effects of ultraviolet (UV) radiation on degradation of bitumen have received much attention from both academic and industrial points of view. However, quantitative evaluations of bitumen photo-oxidation in pavements have apparently not been determined. In this study, the effects of photo-oxidation of bitumen were investigated by exposing pressed thin films of bitumen. The data for thermal aging only were compared with corresponding data for photo-oxidation from exposure to UV radiation. The levels of aging were evaluated by following increases in the carbonyl functional group, and increases in viscosity. The results indicated that both thermal and UV aging occurred during exposure in the UV radiation oven test for thin bitumen films of both unmodified and SBS-modified bitumen. UV aging had a significant effect on bitumen properties, particularly when the bitumen film thickness was less than $150\mu \text{m}$ . Results also showed that the level of UV irradiation intensity had a significant influence on the level of photo-oxidation of the bitumen.

Hansen solubility parameters (HSPs) of six bitumens were determined using the method of three-dimensional turbidimetric titration $\left(F_{\text{max}}\right)$ . 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 $\left({\delta }_d\right)$ play a dominant role in HSP of bitumen. Polar interactions $\left({\delta }_p\right)$ and hydrogen bonding $\left({\delta }_h\right)$ forces have negative effects on compatibility between SBS and bitumen. Closer ${\delta }_d$ between SBS and bitumen, and lower ${\delta }_p$ and ${\delta }_h$ of bitumen improves the compatibility of SBS-modified bitumen. By comparing distribution of nonpolar components of six kinds of bitumens with dispersive forces $\left({\delta }_d\right)$ , the results showed that dispersive forces $\left({\delta }_d\right)$ do not apparently correlate with the colloidal instability index of bitumen.

Wearing courses of porous asphalt concrete (PAC) are widely used in The Netherlands for noise reducing purposes. Because these mixtures have a very high void content $\left(>20\mathrm{\%}\right)$ , they are sensitive for damaging effects of climate and traffic. Especially, aging is a major concern because it makes the mixture brittle and prone to raveling. In order to be able to do meaningful tests and analyses based on laboratory produced specimens, it is important to mimic field aging as well as possible. This paper describes the results of an investigation in which the effects of well known short-term and long-term laboratory aging procedures on the rheological characteristics and chemical composition of binders, are compared with the rheological characteristics and chemical composition of field aged binders. The results obtained on field aged binders are also compared with the results of laboratory aging protocols in which a special weatherometer was used. The results clearly show that none of the laboratory procedures is capable of simulating long-term field aging. At best 2 years field aging could be simulated. Furthermore, the study showed that the way bitumens are aged in the laboratory affects the chemical composition of the binder. The paper also discusses the effect of aging on the mechanical characteristics of bituminous binders in porous asphalt concrete. It is shown that due to aging, the binder will start to behave brittle at temperatures above $0°\text{C}$ . Furthermore, it is shown that aging increases the tensile strength of the binder and the bituminous mastic (mixture of bitumen and filler). The strain at break however decreases as a result of aging. Fatigue testing showed that aging initially increases the fatigue resistance of the binder. However long-term aging occurring in the field after a period of more than 7 years results in a significant decrease of the fatigue resistance. Although not discussed in detail, the results show that aging reduces the stress relaxation capacity of the binder. This will negatively influence the behavior of the binder in case temperature stresses occur together with traffic induced stresses. Also, the healing capacity will be negatively influenced by aging.

Three kinds of organomodified montmorillonites (OMMTs), OMMT1, OMMT2, and OMMT3, were prepared by using different organic modifiers. Nanocomposites of bitumen and three kinds of OMMTs were prepared by melt blending. X-ray diffraction (XRD) analysis was used to evaluate the degree of intercalation or exfoliation of OMMT and its dispersion in the bitumen. The effect of OMMTs on the physical and aging properties of the modified bitumen was studied. XRD results show that OMMT1-modified bitumen had an intercalated nanostructure, while OMMT2- and OMMT3-modified bitumens formed an exfoliated nanostructure. Compared with OMMT1-modified bitumen, the OMMT2- and OMMT3-modified bitumens showed a higher value of softening point and viscosity, and the better resistance to aging was due to the formation of exfoliated structure in the OMMT2- and OMMT3-modified bitumens. OMMT2 improved the aging resistance more remarkably than OMMT3, which can be attributed to the physical differences of the organic modifiers.

In the past decades, montmorillonite nanoclay has been used successfully to strongly improve properties of polymers. Similar improvements to nanoclay modified bitumen were expected, so the montmorillonite nanoclay was adopted to modify bitumen. To understand the interaction with bitumen, it was of fundamental importance to know the composition of organic surfactant on montmorillonite nanoclay. Two organically modified montmorillonite (OMMT) nanoclays available in the market were studied to characterize the composition of the surfactant through X-ray photoelectron spectrometry and simultaneous differential scanning calorimetry and thermogravimetric (DSC-TG) analysis. From the measurements it could be concluded that there was a difference between the surfactants. One surfactant was composed of two states of nitrogen: quaternary ammonium and probably amine or nitrile. The other surfactant only contained quaternary ammonium. In general, $\text{C}\text{C}$ bonds could be detected very well for the two surfactants and there were no other functional groups, such as carboxylic, hydroxyl, ketone, etc. However, it was unclear if the surfactants had $\text{C}\text{C}$ bonds. DSC-TG analysis indicated that the two OMMTs showed very different thermal behavior, but at temperatures below $200°\text{C}$ no problems were expected.

Increasing dynamic shear modulus of asphalt binder is one effective measure of improving modulus of asphalt mixture at high temperature. Dynamic shear modulus of asphalt binder may improve through modifying asphalt with polymer or decreasing asphalt grade. In this study, the solvent deasphalting art of producing the hard-grade asphalt demanded crude oil of high quality and decreased the performance of asphalt at low temperature, adopting the technology of blending the hard modifier with the high-grade asphalt reached the criteria of defining the hard-grade asphalt, i.e., dynamic shear modulus is over 10 kPa at the temperature of $60°\text{C}$ (10 rad/s), phase angle is less than 70°, and performance grade achieves 76-22. The results of mix performance tests indicated that the dynamic modulus of the mixture with the hard-grade asphalt at high temperature increased significantly, the antirutting ability also improved notably, while the bending resistant ability at low temperature and the antifatigue ability were slightly inferior to those mixes with the styrene butadiene styrene modified asphalt (PG70-28).

Most asphalt mixture rheology studies were limited to condition tests and condition-evaluation indices, which cannot describe the changes in mechanical properties along with changing external conditions. The full-temperature–full-frequency master curves of rheological functions for asphalt mixtures were obtained by dynamic shearing test and time-temperature-shift formulation. The Christensen-Anderson-Marasteanu rheological model and morphology theory were combined to obtain the morphological characteristics of the rheological master curves. These morphological parameters can better describe the pavement performances of asphalt mixtures.

In the asphalt mixtures, although asphalt is predominantly considered the binder holding the aggregates together, the actual product used to connect aggregate particles is the asphalt-mineral filler mastic which consists of the asphalt and mineral filler. The characterization of asphalt-mineral filler mastic is essential to improve the understanding of the response and performance of asphalt concrete pavements. It is also important to understand the high- and low-temperature properties of asphalt-mineral filler mastic. In this paper, the parameters of the viscous component of the repeat creep stiffness $G_v$ were evaluated using a dynamic shear rheometer; and the creep stiffness modulus $S$ was determined using a bending beam rheometer. The effects of filler/asphalt ratios $F/A$ (on a weight basis) on the high-temperature and low-temperature properties of different asphalt-mineral filler mastics were studied. The results showed that the rheological behavior of asphalt-mineral filler mastics are nonlinear, and follow an exponent function model. The curve can be separated into three components: the slowly changing phase, the transitional changing phase, and the fast changing phase. To more easily understand the two straight line models, we calculated the $F/A$ of the inflection point in the curve and determined that the optimal range of $F/A$ is 0.9–1.4 to balance the high-temperature and low-temperature properties from the aspect of interacting models of asphalts and mineral fillers. Furthermore, the approach to get the optimal $F/A$ ratio was discussed.

A laboratory investigation of the interactions between granites and asphalts based on rheology is described. In this study of asphalt-filler interactions, the rheological properties of asphalt mastics using different granite powders and different filler-asphalt ratios were measured using a dynamic shear rheometer. Statistically significant relations between the rheological properties of the granite-asphalt mastics and the moisture stability of granite-asphalt mixtures were found. Aggregate factors that influence the moisture stability of asphalt-aggregate mixtures were obtained, and the selection criteria for selecting granite aggregates for use in roads were developed; these could be useful as a reference for practical application.