Nano-scale analysis of moisture diffusion in asphalt-aggregate interface using molecular simulations

Comparative evaluation of moisture susceptibility of modified/foamed asphalt binders combined with different types of aggregates using surface free energy approach

Investigation of the solution effects on asphalt binder and mastic through molecular dynamics simulations

The proper disposal of steel slag has always been a great challenge for the metallurgical industry in China and around the world. In this work, the steel slag aggregate (SSA) was surface pretreated (PSSA) and applied into asphalt mixture. The adhesive behavior between the bitumen and five different types of aggregates (i.e., limestone, diorite, diabase, SSA, PSSA) were evaluated based on the contact angle and binder bond strength tests. The pavement performance of three asphalt mixtures which contain normal aggregate, SSA and PSSA respectively, was analyzed by Marshall stability test, wheel-tracking rutting test, low-temperature bending creep test and water sensitivity test. The results showed that surface modification can improve the surface properties of SSA, reduce its contact angle with bitumen, and eventually lead to the improvement of adhesion between them. In addition to the satisfied low-temperature properties, PSSA was found to significantly improve the anti-rutting property and reduce the water sensitivity of asphalt mixture. This work is expected to promote an alternative application for recycling of SSA in pavement engineering.

Waste plastics have a significant impact on natural resources and the environment. The focus is on the interfacial adhesion behavior of three types of waste plastics-polyethylene (PE), polypropylene (PP), and Poly acrylic (PA)-with neutral silica (SiO2) aggregates, as well as the influence of graphene oxide (GO) on the asphalt-water-aggregate interface performance. The validity of the molecular dynamics simulations was assessed based on fundamental thermodynamic properties of asphalt, including density, glass transition temperature, cohesive energy density, and solubility parameters. The diffusion patterns of the four asphalt components on the SiO2 aggregate surface were analyzed using the mean square displacement (MSD), diffusion coefficient, and relative concentration distribution. The bonding strength between various waste plastics and the asphalt-aggregate interface was quantified by calculating the adhesion work. The results indicate that van der Waals forces and electrostatic forces play a crucial role in the adhesion between asphalt and minerals. The adhesion work between aged asphalt and aggregates is highest when PE plastic is added, lowest when PP plastic is added, and intermediate when PA plastic added. Upon introducing water molecules at the asphalt-aggregate interface, the interfacial adhesion work decreased significantly, indicating that water molecules exert a substantial negative impact on interfacial adhesion performance. However, after coating the aggregate surface with graphene oxide, the adhesion work at the asphalt-water-aggregate interface increased significantly, suggesting that graphene oxide enhances water damage resistance by improving interfacial polarity. This study provides molecular-level theoretical support for the recycling of waste plastics in asphalt-based materials and for the optimization of interfaces. Molecular dynamics simulations were performed using Materials Studio software with the COMPASS II force field. The Nose thermostat and Berendsen isobaric thermostat were used to control temperature and pressure, respectively, to maintain constant temperature and pressure conditions throughout the simulation. In non-bonded interaction calculations, electrostatic forces were calculated using the Ewald method, and van der Waals forces were calculated using the Atom Based method, with a cutoff radius of 15.5Å. The simulations were conducted using NVT and NPT ensembles, with all simulations set to fine computational precision. The constructed model was first subjected to geometric optimization (100,000 iterations), followed by annealing treatment (10 cycles with a temperature change gradient of 100K), and then the ideal molecular structure of the model was obtained through NPT ensemble simulations.

Asphalt mixture workability and effects of long-term conditioning methods on moisture damage susceptibility and performance of warm mix asphalt

Moisture damage of asphalt mixtures is a major distress affecting the durability of asphalt pavements. The loaded wheel tracking (LWT) test is gaining popularity in determining moisture damage because of its ability to relate laboratory performance to field performance. However, the accuracy of LWT’s “pass/fail” criteria for screening mixtures is limited. The objective of this study was to evaluate the capability of the LWT test to identify moisture susceptibility of asphalt mixtures with different moisture conditioning protocols. Seven 12.5 mm asphalt mixtures with two asphalt binder types (unmodified PG 67-22 and modified PG 70-22), and three aggregate types (limestone, crushed gravel, and a semi-crushed gravel) were utilized. Asphalt binder and mixture samples were subjected to five conditioning levels, namely, a control; single freeze–thaw-; triple freeze–thaw-; MiST 3500 cycles; and MiST 7000 cycles. Frequency sweep at multiple temperatures and frequencies, and multiple stress creep recovery tests were performed to evaluate asphalt binders. LWT test was used to evaluate the asphalt mixture samples. Freeze–thaw and MiST conditioning resulted in an increase in stiffness in the asphalt binders as compared with the control. Further, freeze–thaw and MiST conditioning resulted in an increase in rut depth compared with the control asphalt mixture. The conditioning protocols evaluated were effective in exposing moisture-sensitive mixtures, which initially showed compliance with Louisiana asphalt mixture design specifications.

Interfacial adhesion properties and debonding mechanisms in rejuvenated asphalt mixtures

Interfacial adhesive behaviors between SBS modified bitumen and aggregate using molecular dynamics simulation

In this work, the influences of moisture intruded into the asphalt-aggregate interface have been investigated at the atomistic scale. The molecular interactions of asphalt with limestone and granite were studied using molecular dynamics (MD) simulations and the mineral surface components of limestone and granite were detected using the hyperspectral image technique. Relative concentration and radial distribution function (RDF) were employed for the characterization of asphalt component aggregations on aggregates surface. Adhesion work and debonding energy were also evaluated to investigate interface energy variations in asphalt-aggregate systems. MD results showed that the presence of interfacial moisture modified asphalt nanostructure and affected the aggregation state and distribution characteristics of asphalt components near aggregate surface. The study also demonstrated that the external moisture that intruded into the interface of the asphalt-aggregate system can decrease the concentration distribution of the asphalt components with powerful polarity on aggregate surface, reduce the adhesion works of the asphalt-aggregate interface, and decline the water damage resistance of asphalt mixture.

Chemo-physical analysis and molecular dynamics (MD) simulation of moisture susceptibility of nano hydrated lime modified asphalt mixtures

Research on the crack resistance of semi-flexible pavement mixture based on meso-heterogeneous model

Effect of aggregate type on the fatigue durability of asphalt mixtures

Natural factors related to the differential heating of aggregates exposed to microwaves

In this study, the effects of aggregate type on the coefficient of thermal expansion of self-consolidating concrete (SCC) produced with normal and lightweight (porous) aggregate (SCLC) were investigated. In experiments, three aggregate types, gravel, volcanic tuff, and diatomite, were used. Different combinations of water/cement ratio and superplasticizer dosage levels were prepared for the SCC and SCLC mixtures. Thermal tests were performed to accurately characterize the coefficient of thermal expansion (CTE) of SCC and SCLC aged 28 days using the dilatometer. The CTEs of SCC and SCLC were defined by measuring the linear change in length of concrete specimens subjected to a range of temperatures from 20°C to 1000°C. The results, in general, showed that SCLC has a lower CTE than that of SCC above 100°C. Moreover, CTE values of SCC and SCLC were decreased with increase in porous structure. The aggregate type has significant influence on the thermal properties of SCC.

This paper aims at evaluating the compressive strength of structural sand lightweight aggregate concrete (LWC) by the non-destructive ultrasonic pulse velocity method. To this end, a comprehensive experimental study was carried out involving more than 70 different compositions tested between 3 and 180 days with mean compressive strengths ranging from about 30 to 80 MPa and density classes from D1.6 to D2.0. The influence of several factors on the relation between the ultrasonic pulse velocity (UPV) and compressive strength was examined, including the type and binder content, type and volume of aggregates. It is found that lightweight and normal weight concretes (NWC) are affected differently by mix design parameters. NWC is more affected by the volume of aggregate and the dispersion effect caused by concrete heterogeneity tends to be lower in LWC. The prediction of the concrete's compressive strength by means of the non-destructive UPV test is analysed. Based on the dependence of the UPV on the density and elasticity of concrete, a simplified expression is proposed to estimate the compressive strength, regardless of the type of concrete and its composition. High correlation coefficients were obtained taking into account several results for different types of aggregates and concrete compositions.