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MATERIALS SELECTION & DESIGN Corrosion and Remediation for Bridges in Mexico FIGURE 2
occur more readily. Concrete core sam- ples are broken in half in the laboratory and the freshly exposed concrete is sprayed with a solution of 0.15% phenol- phthalein in ethanol. A pink or purple color corresponds to a pH of 10 or higher. When the solution does not change color, it indicates that the sample has a pH of 10 or less, which indicates carbonated concrete. 1\ [PW]TL JM VW\ML \PI\ \PM ÅMTL QV^M[-
Visual inspection and detection of hidden corrosion defects by sounding: (a) Mezcala Bridge, (b) corrosion damage at La Unidad Bridge, and (c) cracking in the columns of the Dovali Jaime Bridge.
TABLE 1
Corrosion potential with respect to CSE7 Corrosion Condition (mV) Potentials more positive than –200
Potentials between –200 to –350 Potentials more negative than –350
Corrosion Risk
There is a >90% chance of no reinforcing steel corrosion
It is uncertain that there is corrosion A 90% chance that the steel is corroding
barrel. Special care is taken to avoid contamination per the ASTM C42 stan- dard.9
The cores are used for chloride
and carbonation testing. They are taken in areas where there is deterioration, and also where concrete appears to be in good condition. Use of a rebar locator enables the samples to be taken close to the rein- forcing steel and allows the depth of cover to be measured.
Evaluation of Chloride Penetration The chloride ion content can be mea-
sured as a percentage by weight of the concrete per the AASHTO T 260 stan- dard.10
The percentage of chloride ion
content by weight of concrete is mea- 68 MATERIALS PERFORMANCE November 2012
sured using the revised Strategic Highway Research Program (SHRP) chloride analysis procedure. A chloride ion con- tent <0.030 wt% of concrete is consid- ered to be below the threshold for chlo- ride-induced corrosion of the reinforcing steel. If the chloride levels climb above this threshold, the reinforcing steel may lose its passive layer and could initiate corrosion activity.
Evaluation of Concrete Carbonation Carbonation of concrete occurs when
the pH of the concrete diminishes to values between 9 and 10. When this oc- curs, the layer of iron oxide, or passive layer, disappears, allowing corrosion to
tigations were carried out using system- I\QK WZOIVQbML IVL MNÅKQMV\ XZWKML]ZM[ to minimize the risk of leaving any relevant components out of the bridge evaluations.
Results and Discussion
Visual Inspections and Soundings
Figure 2 shows images of the visual
inspections and soundings on the Mez- cala, La Unidad, and Dovali Jaime Bridges. The Mezcala Bridge did not appear to
have damage, but the Dovali Jaime and La Unidad Bridges had cracks, rust stains, spalled concrete cover, and exposed steel. The detection of hidden corrosion defects by sounding corroborated the visual in- spection. The Mezcala Bridge sounding evaluation did not reveal any damaged or delaminated areas. Sounding defects were positive in some components of the Dovali Jaime Bridge as well as the La Unidad Bridge, including corrosion- induced cracking of concrete.
Electrical Resistivity Evaluation of Concrete
The resistivity measurements per-
formed on the concrete structures of the Mezcala Bridge were on average >20 S¤ KU