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Significant factors on steel corrosion in chloride contaminated reinforced concrete and time-to-corrosion cracking were investigated in this study. Sixty specimens were designed with seven admixed chloride contents, three concrete cover depths, two reinforcing steel bar diameters, two exposure conditions, and a typical concrete with water to cement ratio of 0.45. Corrosion current density (corrosion rate), corrosion potential, ohmic resistance of concrete and temperature were measured monthly on these specimens using both the 3LP and Gecor devices. Metal loss measurements were performed in accordance with ASTM G1-90, method C3.5, after specimens cracked. The actual corrosion weight loss of the steel reinforcing bars was then compared to the result obtained from the corrosion rate measurement devices. An interaction model for characterizing the dynamic corrosion process was developed based on the five-year corrosion database. The model demonstrates that the corrosion rate is a function of chloride content, temperature at reinforcement depth, ohmic resistance of concrete, and corrosion time after initiation. A time-to-corrosion cracking model was suggested based on a corrosion-cracking conceptual model and critical mass of corrosion products. The model predicted times to corrosion cracking are in good agreement with the observed times to corrosion cracking of the cover concrete. / Ph. D.

As stagnant water contacts copper pipe and lead solder (simulated soldered joints), a corrosion cell is formed between the metals in solder (Pb, Sn) and copper. If the resulting galvanic current exceeds about 2 µA/cm², a highly corrosive microenvironment can form at the solder surface, with pH <2.5 and chloride concentrations 11 times higher than bulk water levels. Waters with relatively high chloride tend to sustain high galvanic currents, preventing passivation of the solder surface and contributing to lead contamination of potable water. If the concentration of sulfate increased relative to chloride, galvanic currents and associated lead contamination could be greatly reduced, and solder surfaces were readily passivated. Mechanistically, at the relatively high concentrations of lead and low pH values that might be present at lead surfaces, sulfate forms precipitates while chloride forms soluble complexes with lead. Considering net transport of anions in water, a chloride-to-sulfate mass ratio (CSMR) above 0.77 results in more chloride than sulfate transported to the lead anode surface, whereas the converse occurs below this CSMR. Bicarbonate can compete with chloride transport and buffer the pH, providing benefits to lead corrosion. Although orthophosphate is often an effective corrosion inhibitor, tests revealed cases in which orthophosphate increased lead and tin release from simulated soldered joints in potable water. Phosphate tended to increase the current between lead-tin and copper when the water contained less than 10 mg/L SO₄²⁻ or the percentage of the anodic current carried by SO₄²- ions was less than 30%. Additionally, nitrate in the potable water range of 0-10 mg/L N dramatically increased lead leaching from simulated soldered pipe joints. Chloramine decay and the associated conversion of ammonia to nitrate during nitrification could create much higher lead contamination of potable water from solder in some cases. In practical bench-scale studies with water utilities, the CSMR was affected by the coagulant chemical, blending of desalinated seawater, anion exchange, and sodium chloride brine leaks from on-site hypochlorite generators. Consistent with prior experiences, increasing the CSMR in the range of 0.1 to 1.0 produced dramatic increases in lead leaching from lead-tin solder connected to copper. / Ph. D.

This study was made to compare rates of reactions between thionyl chloride, sulfuryl chloride, and chlorosulphonic acid, separately, with various types of hydrocarbons.