A Study of Influence of Temperature on Crack Propagation Behavior of Asphalt Concrete
The fracture resistance of asphalt materials significantly influences the service life of asphalt pavements and consequently affects the maintenance and rehabilitation costs of the pavement network. Therefore, there is significant interest in understanding the mechanism of fracture in asphalt pavements and in developing analysis tools that would lead to the selection of asphalt materials with increased fracture resistance. Study of cracking behavior of asphalt mixtures should be conducted in a micro-scale level to have a real simulation of crack propagation. Using SIEMENS SOMATOM plus X-ray CT (computerized tomography) and multi-functional testing rig, a dynamic observation of cracking propagation of hot mix asphalt was conducted in this research. Failure process under compressive pressure was recorded using CT images and CT numbers. The direct responses in density change of Marshall Samples under a CT-compressive process are change of CT numbers. Cracking propagation in the samples can be clearly observed and failure mode and stress-strain behavior can then be simulated. The tests reported provide important theoretical fundamentals to study the cracking behavior and failure mechanism of asphalt mixtures Under the influence of temperaturet.
Development of a new yielding criterion: The Yeh-Stratton criterion
Abstract A new criterion responsible for the first yielding of a material is presented: the Yeh-Stratton criterion (the Y-S criterion). The Y-S criterion requires three yield strengths in simple tension, compression and torsion. It can be shown that the Y-S criterion is applicable to a brittle material as well as to a ductile material. The yield surface of the Y-S criterion is bounded and compatible in the σ-τ plane, the σ1-σ3 plane and the σ1-σ2-σ3 plane. It also predicts the angle of failure.
Full-scale measurements of SO2 gas phase concentrations and slurry compositions in a wet flue gas desulphurisation spray absorber
Abstract Two measurement campaigns were carried out at ENERGI E2's Asnaes Power plant, unit 5. The unit has a capacity of 620 MW e and is equipped with a wet flue gas desulphurisation (FGD) plant employing a counter-current spray absorber with five spray levels. In the first campaign, the power plant was firing Orimulsion ® with 2.85 wt% S resulting in a flue gas concentration of SO 2 exceeding 2000 ppmv. In the second campaign, the fuel applied was a low-S blended coal and the SO 2 concentration in the raw gas was around 400 ppmv. A novel probe for in situ sampling of gas phase concentrations in wet FGD spray absorbers was developed and applied for measuring axial profiles of the SO 2 gas phase concentrations in the absorber. The expected decrease in SO 2 concentrations along the height of the absorber was found in the spray section (from height 26.5 to 36.2 m) whereas the SO 2 concentration above the holding tank and below the gas inlet was quite low probably due to long local residence times in the region. Horizontal variations, due to somewhat different flow conditions near the column wall were investigated and the SO 2 concentrations were found to be higher near the wall. Measurements at different gross loads showed that the SO 2 gas phase concentration at a given position inside the absorber was roughly linearly related to the L/G ratio in the measuring interval. Turning off one of the lower spray levels, while burning coal with low S content, did not lower the overall removal efficiency of the absorber. However, the SO 2 gas phase concentration inside the lower part of the absorber was increased by a factor of 2–3. Measurements of slurry pH at different positions showed a decrease of approximately 0.5 units from the upper to the lower part of the absorber. The full-scale measurements provide a detailed set of experimental data for validation of mathematical models of a wet FGD spray absorber.