Springer Science and Business Media LLC

In the United States, each year over 100 million tons of asphalt pavement material is reclaimed due to its multifold benefits. The use of reclaimed asphalt pavement (RAP) in preparing new asphalt concrete saves money, safeguards the environment, reduces waste in landfills, conserves other natural resources, and increases the durability and longevity of pavements. However, a high percentage of RAP in asphalt concrete can lead to developing premature failure of asphalt pavements due to fatigue cracking. On the other hand, the use of softening agents in asphalt binders can resolve these problems. To this end, two waste products, namely, waste cooking oil (WCO), and engine bottom oil (EBO) along with a commercial rejuvenator were evaluated in this study. The efficacy of these softening agents in aged asphalt binders has been investigated at micro- and macro-levels. Three types of Performance Grade (PG) binders, namely, PG 64-22, PG 70-22, and PG 76-22, each collected from two different sources, were blended with 25% RAP binders and different percentages (0%, 15%, and 20% by the weight of the binder blend) of the selected softening agents. Selected Superpave tests, the Atomic Force Microscopy (AFM)-based PeakForce Quantitative Nanomechanical Mapping (PFQNM™), and Fourier Transform Infrared Spectroscopy (FTIR) analyses were done on the unrejuvenated and rejuvenated binders. It was found that the rejuvenators improved the flow behavior of the RPA-modified binder samples. The AFM test results showed that the micro-level modulus and deformation values of rejuvenated binders were significantly less than those of their unrejuvenated counterparts. Similarly, distinct peaks were conformed in the FTIR peaks for EBO and WCO-modified binders. The EBO or WCO helped to reduce the RAP-blend binder’s viscosity (e.g., lower mixing and compaction temperatures) and increase its rate of relaxation rates (e.g., improved thermal cracking resistance). Experimental data suggest that 10% EBO or WCO has similar beneficial effects in terms of improving 25% RAP-blended binders’ fatigue and thermal cracking resistance compared to the commercial rejuvenator, whereas WCO was more effective in reducing stripping potential than EBO. The findings of this study will help pavement professionals in selecting suitable rejuvenators for the construction of pavements with high RAP contents.

There is interfacial interaction between asphalt binder and other components of asphalt mixture, including mineral fillers and aggregates, which has significant influence on the service properties and service life of asphalt mixture. The usually used mineral fillers and aggregates mainly consist of various mineral crystals, such as SiO2, Al2O3 and CaO crystals. In this study, the interface models of asphalt and these three mineral crystals were established via Molecular Dynamic simulation to investigate their interaction effect at the molecular and atomistic scale. Additionally, the effect of temperature change on the interaction strength was analyzed according to the service temperature of asphalt mixture. The findings showed that Al2O3 surface formed stronger adsorption effect with asphalt than CaO surface, while weak repulsion effect was observed between α-quartz surface and asphalt. Due to the increase of model temperature, the polar components of asphalt moved toward the surface of Al2O3 and CaO crystals but non-polar components moved away from their surface, particularly saturate molecules. In the process of model cooling, the adsorption effect of asphalt with Al2O3 and CaO crystals showed a reduction trend. For α-quartz crystal, with the increase of model temperature, asphalt molecules presented repulsion interaction with its surface except for aromatic fraction, which was subsequently reinforced due to the decrease of model temperature.

Standard Rolling thin film oven (RTFO) test at 163°C for 85 minutes has been investigated and revised to represent the short-term aging of the warm mix asphalt (WMA) binder which is mixed and aged at lower temperature. Because of wide mixing temperature and variation in duration of storage and paving time, field short-term aging differs significantly. To simulate the reduced aging of WMA binders in the laboratory, series of RTFO tests were conducted on two binders at three different temperatures and for four aging periods. Short-term oven aging (STOA) of mix was performed for the same time duration at those three RTFO aging temperatures. A RTFO aging model was developed correlating the rheological properties of STOA mix. Following the aging model developed in this study aging temperature and duration can be selected for RTFO testing to simulate aging effect that a binder experiences in STOA of mix. It is observed that the change in aging index of binder follows a linear relationship with aging time, and the rate of change of the aging index changes linearly with temperature. This study also affirms that STOA of mix exhibits more sensitivity to temperature than that of RTFO aging of binder. Investigation of plant and laboratory mix depicts that very small portion of mix aging occurs during mixing phase however, main portion of short-term aging occur during the storage of plant mix or oven aging of laboratory mix. Because of wide mixing temperature RTFO aging test protocol need to be adjusted.

Additives are used to improve the properties of asphalt mixtures. One such additive is nanomaterials, which are very popular due to their unique characteristics. This study investigated the effects of graphene nanoplatelets (GNPs) on the performance characteristics of hot-mix asphalt (HMA). Bitumen was modified at 0.1, 0.3, and 0.5% (by weight of the bitumen). Based on bitumen tests, a 0.5% nanographene content was selected. Repeated load axial (RLA), indirect tensile strength modulus (ITSM), and indirect tensile fatigue (ITF) tests were performed to assess the mixtures’ performance characteristics. To evaluate their moisture sensitivity, indirect tensile strength and compressive tests were carried out in both wet and dry conditions. Scanning electron microscopy (SEM) indicated that the nanomaterials were appropriately mixed in the bitumen. The results showed a decrease in final deformation and an increase of 15, 36, and 54% in the stiffness modulus at 5, 25, and 40 °C, respectively. The fatigue life of modified asphalt mixtures was improved by 55% compared to conventional mixtures. Raising the tensile strength ratio (TSR) in the indirect tensile test promoted the performance of the modified sample compared to conventional ones and led to a decline in their moisture sensitivity. The modified sample’s ITS in dry and wet conditions rose by 23% and 38%, respectively compared to conventional samples.

In soil mechanics, water is an important constituent of soil. Hence, presence of water may alter the properties of soils significantly. Geotechnical properties of fine-grained soils are very close related to consistency limits. The present study was aimed to investigate the effect of calcium and chloride based stabilizers i.e. eggshell powder (ESP) and sodium chloride (NaCl) on plastic properties of randomly distributed polypropylene fiber (PPF) reinforced fine grained soil. A statistical method namely, The Taguchi technique was applied to produce trial conditions for experiments and optimization. A series of consistency limits tests was conducted on parent and treated soil in laboratory. ESP (3%-9%), NaCl (2%-6%) and PPF (0.05%-0.15%) by total dry weight of solid mixture were taken for the preparation of specimens and air entraining admixture (AEA) was also used in the experiments. Series A (W+0% AEA), Series B (W+0.05% AEA) and Series C (W+0.15% AEA) were used as the mixture liquid. Experimental results showed that the most effective material to decrease the plasticity index of the samples were PPF, ESP and NaCl for series A, series B and series C respectively. The values of plasticity index for series A, series B and series C in optimized conditions were found 1%, 3% and 1% respectively.

The objective of this study was to investigate the potential performance improvement of asphalt mixtures by changing the source of aggregates and the number of design gyrations during the mix-design process. Two surface course mixtures were produced in the laboratory using common Michigan’s aggregates and polymer modified binders. Their linear viscoelastic behavior was evaluated in the laboratory, together with the resistance to rutting, fatigue, and thermal cracking. The same characterization was performed on two mixtures designed with aggregates of better quality, a higher level of compaction (i.e., design gyrations), and the same binder type. Results were used for a direct comparison of thermal cracking susceptibility and for calibrating the rutting and fatigue cracking models of the Mechanistic-Empirical Pavement Design Guide (MEPDG). Results showed that the resistance to all the major pavement distresses improved sensibly. Moreover, it was observed that the presence of aggregate of better quality together with the application of higher compaction level did not affect the binder quantity of the enhanced mixtures (± 0.2%) which could be a major economic concern for State Departments. The results of this research could lead to a revision of the Superpave mix-design criteria currently adopted by the Department of Transportation.