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Abstract:
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External sulfate attack is a complex process that can result in concrete structures deteriorating prematurely . This dissertation describes a comprehensive evaluation of factors influencing external sulfate attack and includes both laboratory and field investigations . Significant emphasis was placed on evaluating the sulfate resistance of mortar and concrete containing high -calcium fly ash (Class C fly ash as per ASTM C 618 ) . This investigation showed that these fly ashes generally reduced the sulfate resistance of mortar and concrete , but that sulfate resistance was possible through the incorporation of other supplementary cementing materials (silica fume and ultra fine fly ash ) into these mixtures . Another key area of emphasis in this project was the correlation between accelerated laboratory tests and outdoor exposure site performance . The behavior of concrete exposed to various sulfate salts (sodium , magnesium , and calcium ) was evaluated , both in static immersion tests and in outdoor sulfate trenches . It was found that the distress outdoors was exacerbated by physical sulfate attack , especially when concrete was exposed to sodium sulfate . It was found that lowering the water -tocementitious ratio (w /cm ) and incorporating appropriate dosages of suitable supplementary cementing materials improved resistance to both chemical and physical forms of sulfate attack . Lastly , a comprehensive study of bridges throughout Texas discovered concrete structures suffering from possible external sulfate attack . The use of analytical techniques such as x -ray diffraction (XRD ) and scanning electron microscopy (SEM ) were used throughout the study to determine the presence of hydration products that may form with mortars and concrete specimens . Findings from this research will be implemented in specifications in Texas for the use of Class C fly ash use in concrete in areas that may have sulfate soils and groundwater . |