Advances in Civil Engineering

Considering the great contribution of subgrade modulus to the overall performance of roads or railways, it is crucial to provide the best prediction of resilient modulus for their foundations. Incorporating the seasonal variation of moisture content, the resilient modulus variation of unsaturated soils will be accurately predicted. This paper aims to introduce and discuss the knowledge about resilient response of unsaturated soils and emphasize the effects of humidity. A literature review on resilient response of unsaturated soils is presented based on the previous studies. The affecting factors (i.e., wetting and drying, moisture content, and matric suction) were discussed. The prediction model development of the resilient response of unsaturated soils was presented. The limitations and advantages of the model were analyzed and compared. It reveals that the current models were limited regarding stress conditions, moisture content, matric suction, and soil types, and further studies are still needed to achieve a better understanding of resilient response of unsaturated soils.

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To improve the essential properties of soil, stabilization proved to be more significant in overcoming the limitations of the desired soil. The improvement of soil properties will not only enhance the mechanical properties rather it will help in preventing dust and erosion formation. In this study, a set of tests are carried out to examine the strength characteristics of subgrade soil blended with ethylene vinyl acetate (EVA) and cement. EVA contributes almost 14% mass to the global waste, requiring bigger lands for its disposal; therefore, in order to promote a green environment and to bring an economical waste management system, an investigation of using EVA in the soil stabilization techniques is attempted. Soil specimens are investigated with and without the inclusion of EVA and cement. For this purpose, EVA was mixed with soil at a percentage level of 3, 6, and 9% whereas the cement was mixed at a percentage level of 4, 6, and 8%. To examine the combined effects of EVA and cement, the specimens were tested for compaction, direct shear, unconfined compression, triaxial, XRD, porosity, and permeability tests. All the soil samples were cured at 7, 14, and 28 days followed by the standard testing procedure. When cement was added to soil up to 4, 6, and 8% at a constant level of EVA (9%), cohesion was increased by 37, 42, and 46% while the unconfined compressive strength (UCS) was increased by 76, 81, and 84% for the same mixes. From the statistics, it clearly evident that the percentage increase caused by the addition of even 3% EVA to the cemented and uncemented soil specimens is very significant regarding cohesion and compressive strength. Porosity and permeability of soil containing both EVA (9%) and cement (8%) were decreased by 37% and 77%, respectively.

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In order to address the influence of aging on the performance degradation of SBS-modified asphalt, a composite modification of SBS-modified asphalt by nano-zinc oxide (nano-ZnO) and Trinidad Lake asphalt (TLA) was proposed. Several tests were conducted after adding nano-ZnO and TLA to SBS-modified asphalt, including a rotary film oven test (RTFOT), ultraviolet aging (UV), and the pressure aging vessel test (PAV). The conventional physical index, rheological index, and four-component content of SBS-modified asphalt before and after three aging modes were tested, and the characteristic functional groups in SBS-modified asphalt were tracked and analyzed by Fourier transform infrared spectroscopy (FTIR). The results show that the effects of aging on the rheological properties of SBS-modified asphalt are clearly reduced by adding different proportions of nano-ZnO and TLA in the process of thermal oxygen aging and the ultraviolet aging test, and the antiaging ability of SBS-modified asphalt is clearly improved. To improve the conventional performance and rheological properties of SBS-modified asphalt, an incorporation ratio of 3% nano-ZnO + 25% TLA was proposed. At the same time, the increased rate of heavy components and the change index of the colloidal instability index in the SBS-modified asphalt under the blending ratio were significantly lower than the blank SBS-modified asphalt samples in the same aging mode. FTIR spectra also showed that SBS-modified asphalt performance deterioration were mainly caused by long-term aging and ultraviolet aging. The addition of nano-ZnO and TLA effectively reduced the increase of carbonyl groups and the breakage of the C=C double bond in butadiene and synergistically improved the comprehensive aging resistance of SBS-modified asphalt. Therefore, the use of this modification is an effective method to solve the aging problem of SBS-modified asphalt.

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Accidental loads such as explosion and vehicle impact could lead to failure of one or several load-bearing members in the structures, which is likely to trigger disproportionate progressive collapse of overall structures. Prestressed concrete (PC) frame structures are usually at great risk of collapse once load-bearing members fail, because the members in PC frame structures are usually subjected to much more load than those in common reinforced concrete (RC) frame structures. To investigate the progressive collapse behaviors of PC frame structures, five one-fourth reduced scaled frame substructures were fabricated and collapse tests were conducted on them. Influence of span-to-depth ratios of frame beams and prestress action modes on the collapse performance of PC frame structures was discussed. Experimental results indicated that PC frame substructures with different prestress action modes, including bonded prestress and unbonded prestress, presented different collapse resistance capabilities and deformability. Tensile force increment of the unbonded prestressing strands almost linearly increased with the vertical displacement of the failed middle column. Catenary action is one of the most important mechanisms in resisting structural collapse. Prestressing strands and longitudinal reinforcing bars in the frame beams benefited the formation and maintaining of catenary action. The ultimate deformability of the PC frame structures was tightly connected with the fracture of prestressing strand. In addition, a calculation method of dynamic increase factors (DIFs) suitable for PC frame structures was developed, which can be used to revise the design collapse load when static collapse analysis is conducted by the alternative path method. The DIFs of the five substructures were discussed on the basis of the proposed method; it revealed that the DIFs corresponding to the first peak loads and the ultimate failure loads for the PC frame substructures were less than 1.49 and 1.83, respectively.

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Taking the 220 kV transmission line as the prototype, a test model of the double-span tower-line system with a scale ratio of 1 : 20 was proposed on the basis of dynamic similarity theory. 14 different working conditions including zippered, simultaneous, entire, and local ice-shedding were controlled and realized by use of the program-controlled mode. The displacement transient responses of transmission line under these ice-shedding conditions were analyzed in detail. The results show that the variation laws of the ice-shedding dynamic-load coefficient and the jump height with the velocity, quantity, and position of the ice-shedding are obtained, which can provide references for the design of the transmission tower-line system.

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This study introduces an eddy current thermography technique that can be used to detect and evaluate steel corrosion in a reinforced concrete structure. The rate of surface temperature changes in reinforced concrete is proposed as a means to characterize the degree of steel bar corrosion. The rate of surface temperature changes increased gradually with an increase in the corrosion degree. The influence of structural parameters on the rate of the temperature change was analyzed in detail. The results indicated that the rate of surface temperature change increased with a decrease in the concrete cover depth and with an increase in the humidity of the concrete, and this was affected by the diameter of the internal steel bar. Concrete cover was the most significant factor that affected the rate of the surface temperature change, except for the corrosion degree. The variations in the surface temperature of reinforced concrete can be explained using the law of electromagnetic induction and the electrochemical property change of corroded steel bar. This research provides a reliable basis for real-world applications and is helpful to understand the application scope of eddy current thermography technology for the quantitative detection of steel corrosion.

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