Rutting is a major distress occurring in the service life of the asphalt pavement, especially in hot weather areas. A laboratory-produced specimen is widely used for rutting performance evaluation which may not be completely represented by the field situation. The objective of this study is to evaluate the rutting performance of field specimens from the Chongqing highway by utilizing the Hamburg wheel-tracking test (HWTT) and dynamic modulus test. Different test conditions were conducted on the HWTT by investigation of the actual local weather condition. The results showed that rutting depth was different under different test conditions, and 10000 loading cycles were recommended as the maximum loading cycles. Particularly, several factors that influence the rutting depth were investigated, and the specimen height of 6 cm is more appropriate for the HWTT. Additionally, different test conditions were proposed as the HWTT test condition for different asphalt concrete (AC) layers in the Chongqing area. Rutting contribution of each AC layer to the pavement structure was analyzed. Moreover, the dynamic modulus at 54.4°C, 5 Hz and 54.4°C, 1 Hz could effectively represent the rutting performance of the asphalt mixture, and the dynamic modulus test is recommended for the rutting performance evaluation of the full-thickness AC layer.
Dynamic modulus is a key parameter in the pavement structure design and analysis. A haversine loading waveform is the most widely recommended waveform in the laboratory to obtain the dynamic modulus of asphalt mixtures by test protocols, which may not completely represent all field loading conditions. e aim of this study is to investigate the suitable vertical compressive stress pulse waveforms at different depths under different pavement structures and to obtain the best fitting waveforms by using the least squares method. Specifically, the vertical compressive stress of different pavement structures was calculated by utilizing a threedimensional finite element program incorporating with the measured wheel loads. e results revealed that the vertical stress pulse waveforms at different depths in asphalt layer were different within different pavement structure combinations. Generally, the square waveform fitted the vertical stress pulse waveform better for the shallow depth of the surface layer. e haversine waveform became more suitable while the depth increased. e bell waveform was better when the depth went deeper (i.e., 10 cm). In addition, the method of choosing waveforms at different depths of different pavement structures was provided, and the equation of calculating wavelength was recommended. Moreover, dynamic modulus under different loading waveforms were analysed through laboratory test, and the process for obtaining dynamic modulus of asphalt layer in any depth was presented.
The aim was to study exogenous GB on cold resistance of Phoebe microphylla. Taking one-year-old Phoebe microphylla seedlings as materials, effects of different concentrations (50. 100. 150 mmol•L -1 ) exogenous GB on cold resistance of Phoebe microphylla under low temperature. Under low temperature stress, foliar spraying of different concentrations GB significantly decreased malonaldehyde (MDA) content, Relative conductivity, and increased chlorophyll, Soluble protein, Soluble sugar, peroxidase (POD), superoxide dismutase (SOD) activities in Phoebe microphylla. Among 3 kinds of GB concentrations, 150 mmol•L -1 GB was the best for Phoebe microphylla on cold resistance. A certain concentration GB preprocessing mitigates the harm of low temperature stress on Phoebe microphylla seedling, and improves their ability of cold resistance.
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