Browsing by Subject "Concrete--Deterioration"
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Item Laboratory and field evaluations of external sulfate attack(2007-12) Drimalas, Thanos, 1980-; Folliard, Kevin J.; Thomas, Michael D. A.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.Item Laboratory testing and investigations of delayed ettringite formation(2004-12-18) Drimalas, Thanos, 1980-; Folliard, Kevin J.Delayed ettringite formation (DEF) in concrete structures has recently damaged structures in the state of Texas, which has caused the state to investigate this new type of premature concrete deterioration. The research described in this thesis is part of a comprehensive research project, TxDOT Project 4085. The work described in this thesis focuses primarily on DEF, but also investigates the interplay between DEF and alkali-silica reaction. Significant accelerated laboratory testing was performed, and parallel exposure blocks were cast to evaluate realistic exposure conditions. The research included materials from throughout the state of Texas. The effects of material composition and dosage on DEF were investigated, and several mitigation measures were identified that can prevent DEF-induced expansion, even when concrete is heated above 70 °C. The key findings from this research have been implemented by TxDOT in new state specifications to prevent DEF in prestressed concrete elements.