Deterioration Of Shaft Lining Concrete Under Freezing Construction And Its Evaluation

The massive concrete in freezing vertical shaft wall continually accumulated its heat and increased its temperature because of intense hydration after pouring. Meanwhile, affected by inner and freezing temperature, the outer and inner shaft wall showed large difference in temperature, and the temperature of different parts of the wall changed rapidly with the age.In order to reveal the relationship between early temperature conditions and crack development of the shaft wall and figure out the influence of freezing construction environment on functions of shaft wall concrete, we relied on the Ordos Neng Hua commissioned projects of Dagon Mining Group and worked on deep freezing vertical concrete shaft wall through field measurement, theoretical research, numerical deduction, etc. We dynamically analyze the distribution of temperature field as well as its temporal and spatial variation during the early development of shaft wall concrete under the circumstance of freezing construction. The results are as following:1. By measuring early temperature variation of shaft and freezing wall during pouring process of massive concrete, we researched on the temperature variation of the measuring points of shaft and freezing wall and made models of early shaft wall temperature field theory under conditions of freezing construction. And we dynamically deducted the early temperature field changing process of shaft and freezing wall with different constructions to reveal the distribution of early temperature field as well as temperature variation of shaft and freezing wall under freezing construction. The results indicated that the temperature variation of 0-28d shaft wall can be divided into 5 stages:temperature increasing sharply stage (0-ld), temperature descending quickly stage (1-3d), temperature dropping slowing down stage (3-7d), transitional stage of the temperature dropping rate (7-14d), and stage of steady descending speed of temperature (14-28d).2. We designed the frozen environment simulation test machine based on the temperature field analyzing theory and heat conduction principle. By utilizing ultrasonic wave detection, scanning electron microscopy and other methods, we researched on the early damaging development and deterioration process of concrete structures under mimic conditions of freezing construction and acquire the micro-characteristics of different parts of the structures with age as well as its performance degradation to unveil the damaging process and degradation mechanisms of concrete with age growing. We found that influenced by low temperature, the early-stage cold-end concrete had a low hydration rate and was damaged severely with a damaging factor reaching 0.32. Comparatively, the early-stage hot-end concrete had a high hydration rate, and thereby was only damaged slightly with a damage factor of about 0.09.3. By experiments of uniaxial compressive strength, splitting tensile and acoustic emission, we worked on the strength growth and performance development status of concrete structures under mimic conditions of freezing construction to reveal its mechanical properties and strength damaging in different ages and different parts, as well as its acoustic emission properties in the process of uniaxial loading. The results showed that the early damage caused by freezing construction had great influence on the mechanical properties of the concrete, with a large slope of stress-strain curve and limited mechanical properties. Early damage has far more effects on concrete structure’s tensile properties than compression properties.4. Based on damage characteristics of concrete, we constructed temporal and spatial relationships between damage and the parts, age and temperature of shaft wall and quantitatively assessed the damage of different parts of shaft wall. We found that the outer wall had the largest damage with a damage factor of around 0.14, while the inner shaft wall had a damage factor of about 0.024 and the central shaft wall 0.07.In this thesis, we relied on engineering practice and researched on the influence of early-stage temperature conditions of freezing construction on shaft wall performances to reveal the damage variation and degradation mechanisms of shaft wall concrete during development. It provides the phenomenon of crack formation and breaking of early-stage freezing vertical shaft wall with new scientific and theoretical basis, which is important for better engineering practice.