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From page 237... ... 235 5.1 introduction This chapter of the Guide provides essential information for addressing corrosion of reinforcing steel in conventionally reinforced concrete structures. The focus is on controlling and mitigating corrosion for extended durability and service life. Read the entire page →
From page 238... ... 236 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Deicing salts applied during winter months generally contain chlorides. Chloride solutions penetrate existing cracks and diffuse through the concrete cover to the reinforcing steel, initiating corrosion. Read the entire page →
From page 239... ... 237 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES Over time, the corroding area (anode) Read the entire page →
From page 240... ... 238 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 5.2.3 Corrosion Cells Once the chloride concentration at the depth of the reinforcing steel exceeds threshold levels, the passive oxide film will begin to degrade, and corrosion may be initiated. Chlorides act similarly to a catalyst in the corrosion process: the chlorides are involved in the corrosion reaction, but they are generally not consumed by the corrosion reaction itself, such that a single chloride ion can be responsible for the corrosion of many atoms of iron. Read the entire page →
From page 241... ... 239 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES On a localized basis, corrosion cells can be formed as a result of differences in chloride concentration at various locations along a single bar. Read the entire page →
From page 242... ... 240 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE reinforcing steel embedded in adjacent environments with abruptly different corrosion potentials. This difference in corrosion potential (voltage) Read the entire page →
From page 243... ... 241 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES 5.3.1 Chloride Contamination Destruction of the protective oxide film on reinforcing steel is most often caused by the presence of elevated levels of chloride ions. Read the entire page →
From page 244... ... 242 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Non-chloride-bearing salts, including calcium magnesium acetate, magnesium acetate, and calcium acetate, lower the freezing temperature of water and can be used for ice control. However, magnesium-bearing solutions cause severe paste deterioration by forming brucite and noncementitious magnesium silicate hydrate (Lee et al. Read the entire page →
From page 245... ... 243 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES existing structure is not corroding, some of the techniques used on new structures, such as applying sealers and membranes, may also be used on the existing structure. Read the entire page →
From page 246... ... 244 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Figure 5.10. Options for preventing or delaying corrosion initiation. Read the entire page →
From page 247... ... 245 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES 5.4.1 Existing Structures Options for protecting structures from corrosion and extending their service life are much more limited when dealing with existing structures, as many of the physical parameters are already defined and cannot be changed or easily altered. Read the entire page →
From page 248... ... 246 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 5.4.2 Levels of Corrosion Protection for Existing Structures 5.4.2.1 Selecting an Active Corrosion-Protection Strategy for Reinforced Concrete Structures The selection of the appropriate level of corrosion protection is based on many factors, such as the level of chloride contamination and carbonation, amount of concrete damage, location of corrosion activity (localized or widespread) , the cost and design life of the corrosion-protection system, and the expected service life of the structure (Ball and Whitmore 2005) Read the entire page →
From page 249... ... 247 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES 5.4.2.2 Cathodic Protection Cathodic protection provides proven corrosion protection and is intended to effectively stop ongoing corrosion activity. Read the entire page →
From page 250... ... 248 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE current and potential values similar to the OA4 anodes. The two high-voltage anodes and the OA4 anodes provided higher current and generated more negative potential values, indicating better corrosion protection, than ordinary anodes. Read the entire page →
From page 251... ... 249 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES polarization may be significantly less than the NACE 100-mV depolarization criteria for cathodic protection. Read the entire page →
From page 252... ... 250 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE matrix included black bars, electrochemically treated black bars, stainless steel bars, and titanium bars, each subjected to salt solution. Because of time constraints, testing was terminated after 26 cycles consisting of 4 days of wet cycle and 10 days of dry cycle for a total duration of 1 year. Read the entire page →
From page 253... ... 251 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES Falls, Ontario. Read the entire page →
From page 254... ... 252 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE tABLE 5.2. corroSion PotentiAL meASurementS Time Since Treatment Untreated (Control) Read the entire page →
From page 255... ... 253 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES As part of the rehabilitation, which also included enlargement and strengthening of the abutment, the cracked and spalled concrete was removed. Read the entire page →
From page 256... ... 254 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE The current output, shown in Figure 5.17, appears to be strongly related to temperature. Its magnitude varied considerably with temperature on an annual basis, with the mean current density gradually reducing year by year. Read the entire page →
From page 257... ... 255 Chapter 5. Read the entire page →
From page 258... ... 256 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE The anodes were inserted around the perimeter of the repair area between 600- and 700-mm centers (Figure 5.19) Read the entire page →
From page 259... ... 257 Chapter 5. CORROSiON OF STEEL iN REiNFORCED CONCRETE BRiDGES this trial, with a mean current density of around 1.4 mA/m2 over the 10-year period. Read the entire page →

From page 237...

... 235 5.1 introduction This chapter of the Guide provides essential information for addressing corrosion of reinforcing steel in conventionally reinforced concrete structures. The focus is on controlling and mitigating corrosion for extended durability and service life.