Tao Bai

Macroscopic fatigue tests, mesoscopic finite element simulations, and microscopic molecular dynamics simulations were composed to study the damage and failure of drainage asphalt mixtures in multiscale. The applicability of the fatigue models fit by strain, stress, and the linear fitting slope of the indirect tensile modulus curves were compared. The mesoscopic damage and failure distribution and evolution characteristics were studied, considering the single or coupling effect of traffic loading, hydrodynamic pressure, mortar aging, and interfacial attenuation. The microscopic molecular mechanism of the interface adhesion failure between the aggregate and mortar under water-containing conditions was analyzed. Results show that the fatigue model based on the linear fitting slopes of the indirect tensile modulus curves has significant applicability for drainage asphalt mixtures with different void rates and gradations. The damage and failure have an obvious leap development when traffic loading increases from 0.7 MPa to 0.8 MPa. The hydrodynamic pressure significantly increases the stress of the mortar around the voids and close to the aggregate, promoting damage development and crack extension, especially when it is greater than 0.3 MPa. With the aging deepening of the mortar, the increase rate of the damage degree gradually decreases from the top to the bottom of the mixture. With the development of interfacial attenuation, the damage and failure of interfaces continue increasing, while that of the mortar increases first and then decreases, which is related to the loading concentration in the interface and the stress decrease in the mortar. Under the coupling effects, whether the cracks mainly generate in the mortar or interface depends on their damage degrees, thus causing the stripping of the aggregate wrapped or not wrapped by the mortar, respectively. The van del Waals force is the main molecular effect of interface adhesion, and both acidic and alkaline aggregate components significantly tend to form hydrogen bonds with water rather than asphalt, thus attenuating the interface adhesion.

A custom enhanced and modified Rice test setup was utilised in this laboratory study to assess and quantify the moisture sensitivity of hot-mix asphalt (HMA) under hydrodynamic pressure testing. The hydrodynamic pressure was simulated by repeatedly alternating the pumping and vacuum suction forces, which separately represented the positive and negative pore pressure on the HMA under a hypothetical combined action of moving vehicles and moisture effects. The overall research approach involved the following sequence of work activities: freeze-thaw and Hamburg wheel track testing for hydrodynamic pressure simulative effects, X-ray fluorescence analysis for stripped and suspended material identification followed by the development of the anti-stripping test (i.e. the enhanced/modified Rice test setup) and sensitivity analyses. In the study, laboratory validity of the new anti-stripping test was preliminary and successfully demonstrated through moisture sensitivity evaluation and analyses of various HMA with different types of aggregates (limestone, diabase, and basalt), asphalt binders (AH-70, SK-70, and styrene-butadiene-styrene (SBS)), and fillers (limestone mineral powder, hydrated lime, and brake pad waste (BPW) powder). For the aggregates, the rank order of superiority in terms on moisture resistance was found to be basalt (best) followed diabase and lastly limestone (poorest). As theoretically expected, the SBS-modified asphalt binder out-performed the AH-70 and SK-70 asphalt binders in terms of resistance to moisture damage, while the BPW powder demonstrated superiority over the other fillers, with the limestone mineral powder being the poorest.

The paper presents a new insight into the assessment of unsaturated slope stability under rainfall using the probabilistic method. The rainfall infiltration, correlation length of soil properties, and the cross-correlation between different shear strength parameters are taken into consideration to examine its influences on the stability status of spatially variable soil slope. The factor of safety and the failure probability are simultaneously used to estimate the slope. Results show that coarse grained soil slope is influenced most by the short term rainfall with high rainfall intensity, while the fine grained soil slope influenced most by the long term rainfall. There exists a threshold value of rainfall intensity for different type of soil. The slope would suffer the minimum danger as its constructed soil possesses strength parameters with small correlation length and variation coefficient. And in addition, the failure probability grows bigger when the correlation coefficient between the cohesion strength and friction angle increases.