Investigation of the damaging effects of exposure to deicing chemicals on Portland cement materials

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2003-01-01
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Nelsen, Daniel
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Civil, Construction, and Environmental Engineering
Abstract

This study was designed to partially replicate winter environments and to empirically observe the damaging potential of each of the five different deicing chemicals to Portland cement materials in winter environments. These chemicals were sodium chloride, calcium chloride, potassium acetate, and Geomelt. Paste and concrete samples were exposed after 7 days optimal curing to one of these chemicals in either wet-dry or freeze-thaw simulated environments. Physical deterioration of these samples was analyzed measuring unit weight loss, change in compressive strength, and visual scaling. Chemical deterioration was investigated using x-ray diffraction (XRD) to identify formation of new phases, scanning electron microscopy (SEM) to observe microstructural changes, and ion penetration testing (IPT) to determine the magnitude of Cl−, Na+, and K+ ions with varying depth within deicer-exposed concrete samples. CaCl2 solutions caused the most damage to both paste and concrete. In freeze-thaw conditions, concrete strength decreased by more than 60%. Geomelt, an acidic solution derived from agricultural waste, caused consistent mass loss in nearly all environments. Sodium chloride and potassium acetate were relatively benign in causing physical deterioration. The use of a corrosion inhibitor in one of the CaCl2 solutions delayed the onset of damage in freeze-thaw samples, but may not have been effective at reducing the ultimate damage to CaCl2-exposed samples. XRD identified the occurrence of two new diffraction peaks in CaCl2-exposed samples occurring at approximately 8.35A and 4.00A. No other significant chemical phase changes were identified. SEM revealed considerable precipitation of Cl− and Ca2+ ions around void perimeters and along cracks surfaces in CaCl2-exposed samples and to a lesser degree on NaCl-exposed samples. IPT identified Cl− and K+ concentrations greater than 4 times that of control samples at depths exceeding 1.2 inches in samples exposed to chloride deicers and potassium acetate, respectively. These high ionic concentrations may exacerbate chemical interaction, crystal growth, or other phenomena like corrosion of reinforcement or alkali-silica reactions.

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Wed Jan 01 00:00:00 UTC 2003