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The deformation behaviour of the asphalt concrete (AC) depends on the loading state and the temperature, accompanied by a large number of microcracks. In this study, the deformation and failure behaviour of the AC under uniaxial compression were investigated by the acoustic emission (AE). Both the stress–strain relationship and the energy dissipation were employed to analyse the macroscopic deformation of the specimen at low and medium temperatures. The AE parameters including count, energy and amplitude were measured in real-time during the loading process. The damage morphology of specimens was characterised by the failure location with the AE technology. Results show that with the rise of the temperature, the strength of AC specimens gradually decreased, which leads to a lower capacity in storing strain energy. The dissipative energy is greatly affected by the damage degree of the specimen. Both the event count and amplitude increased rapidly when the specimen failure occurred. The AE parameters are relatively sensitive to the deformation failure of asphalt mixtures influenced by the temperature. Furthermore, the results also imply that the AE method used in the present study to characterise the deformation failure in pavement engineering is more scientific and precise. [ABSTRACT FROM AUTHOR]

The Monte Carlo simulation (MCS) has been developed to estimate the strength distributions of heterogeneous materials influenced by different factors. The method presents a statistical correlation between the macroscopic properties and the non-uniform characteristics at meso scale. This study proposes an extensive MCS to investigate the influence of the aggregate morphology on deformation behaviour of unbound granular materials (UGMs) based on a real aggregate library and the discrete element method. Two indexes, elongation index (EI) and flatness index (FI), were used to evaluate the morphological characteristics of 3D aggregates rebuilt by the X-ray CT technique. Furthermore, repeated load triaxial tests of UGMs were simulated by 50 MCS samples. The effects of shapes and sizes of aggregates on deformation behaviours were statistically analysed. The results show that the deformation behaviour is dependent on the size and the EI distribution, but insensitive to the loading frequencies and FI distribution. [ABSTRACT FROM AUTHOR]

In order to build an appropriate prediction model of pavement friction coefficient attenuation, the effects of aggregate texture, on a basis of texture scanning and pavement testing of the dynamic friction coefficient, traffic volume, and rock characteristics on pavement slide decay resistance were studied, and the accuracy of the developed prediction model of friction coefficient was thereafter compared and analysed. First, based on the tire-pavement dynamic friction analyzer independently developed by the research group, accelerated loading tests under different traffic conditions were conducted by the orthogonal test method, and the dynamic friction coefficient of pavement during the abrasion process was recorded. At the same time, the non-contact laser profile measurement system was used to collect three-dimensional micro-texture data of coarse aggregate surface at different abrasion stages, and characteristic parameters such as height, wavelength, and shape were calculated. Second, the factors such as traffic volume and rock characteristics were incorporated, and the algorithms such as multiple linear stepwise regression, feedforward neural network, and random forest regression were adopted to develop estimation models of pavement friction. The results showed that the model constructed based on only texture feature parameters poorly represented pavement skid resistance. After introducing the two indicators of total traffic volume and rock type, the correlation coefficients of the model significantly improved, reaching 0.63, 0.58, and 0.82 respectively, indicating that the latter two factors have significant effects on the anti-skid attenuation of pavement. Moreover, the above three models can achieve satisfactory prediction results. In addition, when a large sample size can be obtained, a random forest algorithm is recommended to acquire higher prediction accuracy of pavement friction coefficient attenuation. [ABSTRACT FROM AUTHOR]

To reveal the fracture damage of asphalt mixture, an image-based numerical approach is proposed in this study considering the distribution of aggregate and asphalt mortar. Both digital image processing technique and discrete element method are applied to simulate the inhomogeneity of specimen and its fracture evolution at low temperature. At the same time, the acoustic emission (AE) activities are measured in laboratory to be compared with the micromechanical responses of numerical models. Results indicate that the developed method is suitable for modelling the numerical specimen of asphalt mixture, taking into account the size gradation and morphology of aggregates in the two-dimensional image. The numerical results of asphalt mixture have a good agreement with that of laboratory tests in cracking distribution and statistical probability. Cracks first appear on the aggregate–mortar interface, located in the upper and middle parts of the specimen, and then the brittle shear failure gradually propagates along the surface. Cumulative probabilities of both AE ringing counts and microfracture number follow the Weibull distribution. The numerical model has a significant advantage in the fracture evolution of asphalt mixture because the eccentric loading is unavoidable in laboratory tests due to personal and mechanical errors. [ABSTRACT FROM AUTHOR]

The cumulative permanent strain of subgrade soils plays an important role in the pavement structure design and long-term pavement performance maintenance. In Southern China, the hot and humid climate increases the risk of becoming a saturated condition for subgrade soils. The saturated subgrade soils will generate significant cumulative permanent strain under long-term cyclic loading compared with unsaturated soils. This study investigated the impact of the moisture content, number of cyclic loading, deviatoric stress and confining pressure on the evolution of the cumulative permanent strain for subgrade soils by using long-term cyclic (10,000 cycles) triaxial tests. The test results indicated that the cumulative axial permanent strain increase with the increasing moisture content, as well as the increasing number of cyclic loading and deviatoric stress but decreases with the increasing confining pressure. In order to predict the permanent deformation of subgrade soils in Southern China, a new model for predicting the permanent deformation of subgrade soil, which contains number of cyclic loading, initial bulk stress, octahedral shear stress and saturation, was proposed and validated. [ABSTRACT FROM AUTHOR]

This study aims at developing an efficient and accurate methodology to estimate the resilient modulus of subgrade soils. First, a new resilient modulus model incorporating stress dependence and moisture dependence was proposed. Second, prediction models were developed to conveniently and accurately determine model parameters of SWCC and resilient modulus model. In order to characterise the moisture dependence of subgrade soils, the matric suction was added into the proposed model. The matric suction was measured by the pressure plate test and the soil-water characteristic curve (SWCC) was used to determine the matric suction value at any given moisture contents. In order to develop prediction models for model parameters of SWCC and resilient modulus model, the laboratory experiments and multiple regression analysis were conducted on 22 soil samples. A series of performance-related soil properties were measured and used to develop the coefficients prediction models. The developed coefficients prediction models using the performance-related soil properties have high R-squared values and were validated by comparing the measured and predicted values of resilient modulus. Therefore, when the basic physical properties of soils were obtained, the resilient modulus can be predicted for the subgrade soils at any given matric suctions and stress states. [ABSTRACT FROM AUTHOR]