Freeze-thaw environment of precast concrete crossties and effect of vibration on fresh materials

concrete;tie;crosstie;sleeper;rail seat area;freeze-thaw;temperature;relative humidity;saturation;rheology;vibration;acceleration;flatbed;image analysis;hardened air

Castaneda, Daniel I.

关键词: concrete;    tie;    crosstie;    sleeper;    rail seat area;    freeze-thaw;    temperature;    relative humidity;    saturation;    rheology;    vibration;    acceleration;    flatbed;    image analysis;    hardened air;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/92745/CASTANEDA-DISSERTATION-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

High performance concrete is typically designed to achieve high strength and low permeability. These suppositions lead practitioners to install high performance concrete in outdoor environments assured that members will remain durable over scores of years. One such outdoor environment is in railroad lines where timber ties (alternatively known as crossties or sleepers) are being replaced with high performance concrete crossties. Additionally, concrete crossties are being installed in burgeoning high speed rail networks across the United States of America. It has been observed, however, that these high performance concrete crossties are subject to multiple deterioration mechanisms including freeze-thaw damage. This early degradation in critical transportation infrastructure necessitates a better understanding of the durability of high performance concrete in wet, wintry climates. In particular, the concrete crossties have been found to degrade at the rail seat area where the crosstie is physically joined to the rail. Among several failure mechanisms, including abrasion and hydraulic pressure cracking, it is hypothesized that the dense configuration of the rail line, pad, clips, and crosstie leads to pooling of water at the underside of the pad. This stagnant water sits atop the concrete crosstie at the rail seat area and can permeate into the material leading to scaling and freezing-thawing damage in colder climates.In this study, the resiliency of high performance concrete crossties against freezing-thawing damage is assessed in a collaborative effort with researchers at Kansas State University and the University of Illinois at Urbana-Champaign. In this dissertation, specifically, the extent of internal moisture and temperature fluctuations of instrumented crossties installed in ballast is examined. Half-space approximations are applied to predict the fluctuation of internal conditions as affected by external environmental conditions. Additionally, this dissertation also examines the stability of chemically entrained air bubbles in fresh concrete when the fresh material is subjected to varying time and degree of vibration. The propagation and attenuation of the vibratory peak acceleration as a function of distance from the vibrating source and the volume content of aggregate is studied and compared against the extent of air loss and aggregate segregation as evidenced in polished, 2-dimensional sections.Summarily, the mutual instances of critical moisture saturation and freezing temperatures in concrete crossties are experimentally measured and predicted. The predictive models are modified to create a concrete crosstie freeze-thaw susceptibility index based on historical weather data. This susceptibility index better informs owners of concrete crosstie infrastructure of environmental design criteria for freezing-thawing damage potential. The vibratory experimental results lend insight into rheological phenomenon that can to enhanced guidelines for the consolidation of non-conventional concrete that optimizes compaction while mitigating the loss of entrained air and aggregate segregation. Taken together, these two research thrusts enhance the civil engineering community’s understanding of the durability and resiliency of high performance concrete exposed to cold climates.