Highway Bridge Restoration

Structure Characteristic

The structure consists of three concrete arches, two piers, two abutments, sidewalk wing walls and parapets. In addition, the structure is supported on the concrete encased rigid frame.

Problems Incurred:

The roadway was extensively deteriorated.  The arches showed signs of deterioration as evidenced by a number of leaking cracks and joints.  This condition has also indicated a failure of the deck membrane.  In addition to roadway and arch deterioration movement of the four wing walls required underpinning.  The integrity of the sidewalls was questionable.  Therefore they were ear marked for demolition. However the removal of the sidewalls necessitated demolition of the coping and parapets which were in sound condition.

Inspection / Evaluation:

Essentially a visual examination revealed the majority problems. However core samples were extracted to identify and evaluate the overall integrity of the sidewalls concrete; and establish the methods and material for restoration. Cores were examined visually and microscopically according to details. Air content and parameters of air-void system were determined.

Test Results:

Prior to testing it was appeared that the bridge side-walls required demolition and replacement.  This was as discussed necessitated removal and replacement of the coping and parapet which were in sound condition.   However, after excavation and exposure of the inside of the west sidewall a thorough visual inspection was performed and in conjunction with the results of the core samples it was determined that the sidewalk could be repaired using alternate means.

Causes of Deterioration:

The condition of deterioration damage and disrepair is primarily attributed to the continuous and arduous use of the structure.  With the necessity to keep open this bridge for vehicular and pedestrian traffic maintenance was minimal and major repair and restoration was all but prohibitive.  However cracking and spalled concrete over the years required some remedial repairs.  The pre and post-testing program clearly revealed what is common on most patching and pressure injection repairs.   Core samples show a distinctly un-bonded or poorly bonded patch to the existing concrete and pressure injected cracks were only partially filled causing them to open–up or new cracks to occur. It is common knowledge that physical properties of patching material are often very different from the existing undisturbed concrete. At the interface perimeter between old and new a high differential in electro-chemical potential is created. This accelerates corrosion in adjacent steel reinforcement and consequently the early demise of the concrete patch and surrounding area. As observed throughout this structure.

Repair Process Execution:

Preparation required sandblasting and power washing of the concrete sidewalls. The Resident Engineering Consultant identified location of cracks marked them on survey drawings and recorded the length and the width of the defects.   Two major materials were recommended to use for vacuum impregnation repairs on this project: MMA and Low viscosity high modules Epoxy Sealer and Crack Filer. Epoxy Sealer. There are two commonly used methods to verify the level of success of the repairs - Impact-Echo testing and control coring. 75 mm and 100 mm cores were taken every 15 meters of discrete cracks. All specimens subjected to testing produced average of 91.25% of the polymer penetration.   The compressive strength of three samples through the cracks increased from 0-800 psi to the average of 3084 psi which is more than enough for the concrete gravity sidewalk.  Borders between old concrete and patching repairs were sealed up with the repair polymer.