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.

Grout Joints

Structure Characteristics

The structure was constructed with reinforced concrete slab beams and columns. The in-fill between four exterior columns one at each corner of the tower and two intermediate is 8 inch concrete masonry units (CMU).  The exterior façade is comprised of a setting bed overlaid with ceramic tile.  The original building plans indicate that the tile setting bed should be 5/8 inches.  Test results using impact echo have found the setting bed varying from 1.7 to 2.7 inches. The total façade thickness varied due to the inconsistency in the setting bed thickness.

Problems that Prompted Repair

Significant areas of mosaic tile were un-bonded from the grout base. In limited and random sections tile fell leaving gaping holes in the façade.  Furthermore damage with regard to the structural integrity of the façade was evidenced by the loss of bond of the grout base to the CMU in-fill and the concrete columns.  This loss of grout bond resulted in profile protuberance throughout the entire face of the both tower mosaics.  In isolated areas the grout matrix was compromised and disintegrated causing a build up in the protruded areas making it impossible to reestablish a level surface profile.  Grout joints on both towers were severely weathered and on the greater portion of the surface area the grout was missing disintegrated and or friable.

The façade’s poor condition increased the probability that the tile and grout could loosen the mechanical bond and sections would shear from the face of the tower posing grave concern for public safety.

Inspection / Evaluation Methods

 The de-lamination survey was performed by sound with a rebound hammer.  The destructive testing entailed opening an area of the wall at the handrail anchorage and a hollow area on the north tower.  A 4 inch core was taken to evaluate the composite construction of the façade. Subsequently, testing team made a condition assessment specifically to evaluate the extent of damage and deterioration of the tile grout base and setting bed using non-destructive impact echo technology. 

Causes of Deterioration

 The mosaic tile façade was exposed to the harsh climate of winds rain and high temperature for nearly 50 years and the tile grout joints deteriorated.  This continuing process of deterioration and disintegration of the grout resulted in moisture intrusion leading to the loss of integrity of the grout base and eventually of the tile bond and grout base to the substrate.

Repair System Selection

Restoration of the tile façade required a combination of conventional and specialty techniques.  It was essential to the overall repair program to first replace damaged and missing tile and re-grout tile joints. Upon completion of the tile rehabilitation the façade was pinned with stainless steel anchors followed by the bonding of the tiles to the grout base along with the re-bonding of the grout base to the CMU and concrete column substrate. The tile and grout base were re-bonded with special resins and portland cement filler using the vacuum injection and impregnation process.

Repair Process Execution

Due to the numerous areas of damaged and missing tile all openings were grouted flush to the tile surface as a temporary means of sealing the surface to accommodate the vacuum process. Further missing and deteriorated grout in the tile joints was re-grouted to assist in providing a seal where the joints were porous or friable. Stainless steel mechanical anchors were installed on a two-foot grid pattern over the entire surface of both towers.  It was necessary to install the anchors after the damaged and missing tile areas were restored to secure the composite façade and realign the profile of the façade where possible. The vacuum process was then used to secure any questionably un-bonded original tiles fill de-lamination in the setting bed and fill and seal cracks.  Upon completion of the vacuum injection all previously repaired areas that exhibited damaged or missing tiles were removed and new tile was installed.  With the completion of the tile replacement and restoration the entire face of both mosaics was cleaned and hand polished with compounds and lamb’s wool buffers.

Arches

Structure Characteristics: The roadway was extensively deteriorated.  The arches showed signs of deterioration as evidenced by a number of leaking cracks and joints.  This condition 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.

Damage: 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 determine to establish the methods and material for restoration.

Inspection and execution: Prior to testing it was appeared, that the bridge sidewalls required demolition and replacement.  As discussed this has 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.

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 spilled 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 executions: Contract documents included the demolition and replacement of the bridge sidewalls coping and parapet. However core samples and a thorough visual inspection during the excavation and exposure of the inside west sidewall determined that process of vacuum injection / impregnation of concrete repair.Vacuum process on FDR Drive Reconstruction Project where vacuum grouting delivered a specialty concrete mix to the forms without any traffic closures.  The implementation of Balvac Process averted the demolition of the bridge coping and parapet walls which were in relatively sound condition.

Preparation required sandblasting and power washing of the concrete sidewalls. The 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.

Chimney Rehabilitation

Scope: The scope of work for repairing team included supplying all labor, equipment and materials to remove and replace all the deteriorated mortar joints (inside and out) and strengthening the chimney to accommodate the new loads created by the cell antennas.

Structure Details: After a century of natural deterioration, the chimney was in very poor condition, with existing joints badly deteriorated - in some cases, completely through the wall.

Repairing system: Extensive re-pointing of interior and exterior joints was carried out to stabilize and restore the integrity of the chimney, along with the bricks at the top 4 feet so degraded they required replacement. The challenge in doing this was not only rebuilding the unique architectural shape for historic purposes, but also finding a source for the same type and color of brick. An extensive search of the United States found only one manufacturer who still had the materials available.

A structurally efficient, easy-to-install, and cost-effective strengthening option was achieved by using an externally bonded carbon-based FRP strengthening system that would increase the shear and flexural capacity of structural elements. The thin carbon FRP plates were bonded to the inside face of the chimney, serving as vertical tension reinforcement. The continuous FRP laminate plates were installed in single, 30.5-m (100-ft) long pieces extending through the chimney’s full height. Since carbon FRP is only a quarter of the weight of steel, the plates were easily handled by workers inside a small diameter work area (only two workers could fit in the structure) and added only minimal weight to the structure.

Cantilever repairing

Problem: At the main terrace level of the structure, strengthening is required including bonded post-tension tendons parallel to the cantilever girders, and un-bonded tendons in the transverse direction.

Structure Details: The tendons start at points near the bottom of the existing concrete members and gradually rise up to the top of the existing beams at mid-span. This created a lifting effect, or positive bending moment, on the cantilevers when the tendons were stressed. Special care was required during construction to prevent damage to architectural features and landscaping.

Repairing Methodology: The strengthening plan has called for steel channel beams to be bolted to each side of the master level concrete joist which is directly above the four 'T'-shaped mullions. These channels ensured that the beam has sufficient strength to achieve the proper transfer of forces from the living room to the master terrace. Like the post-tension cables at the main level, these channels are hidden in the floor cavity.

Another aspect of repairing team’s work involved repair and strengthening of the master level parapet walls. These walls have experienced significant cracking due to the cantilever deflections. Three 14-foot-long FRP (fiber-reinforced polymer) bars were epoxy-grouted into narrow grooves which are cut into each of two parapet walls. In addition to the new bar reinforcement, a significant amount of epoxy crack injection repair was performed by VSL on the parapet walls. Because of the pristine nature of falling water's setting, restoration and repair activities were conducted with care to minimize the environmental impact on the stream, the falls and the landscape. Protective canvas and shielding along with regular cleanup were used during the project to keep the nature.

Deck Repairing

Structure Details: The deck is 8 in. thick, 2-way, post-tensioned, flat slab. The column-strip post-tensioning in the E-W direction was inadequate. A repair was developed using a heavily-reinforced gunite beam added to the underside of the slab column strip.

Problem: After the repair, de-lamination between few beams and slab was noticed. An NDT investigation (pulse velocity test), concluded that approximately 30 percent structure may have more than 40% de-lamination. The engineering firm then recommended more NDT inspection utilizing impact echo. Of the 133 beams tested, 105 have showed some de-lamination, and 19 had 33% or more de-laminated.

Repairing Methodology: The first phase of the repair included an in-depth and in-situ load testing of the existing slab under various conditions that existed and strengthened with FRP sheets. A load testing procedure was proposed to provide a non-destructive demonstration of the performance of structural components, utilizing hydraulic jacks to induce force equivalent to those resulting from distributed loads.

Test results indicated that the beam in the E-W direction with a minimum of 70% bond performed well. A span with no beam demonstrated poor performance. Results also showed CFRP strengthened slabs (after removing the Gunite beams) were satisfactory. Accordingly, 19 locations E-W beams would remove and the slab would be strengthened with CFRP sheet. Typical span in the N-S direction were found to be acceptable without additional upgrade. External steel-framing was installed reducing the clear span, and additional steel supports were installed under the cantilever slabs. At steel support points, "pancake" jacks were permanently installed to engage the steel frame.FRP Solution Restores Strength to Skyway Double Tee Beams. Engineers discovered the presence of numerous hairline cracks in the precast concrete guide-way beams that support the monorail track nearly a year after the last segment of the Skyway was completed. An investigation revealed that excessive un-bonding of the pre-stressing tendons had taken place and caused cracks in 63 of the 500 beams. While the condition was a cause for concern, it posed no immediate danger to the Skyway. However, temporary supports were installed while a determination was made on how to repair these cracks. Engineers had developed five different repair scenarios to address the problem. Repair strategies were evaluated based on a ranking system that considered durability, maintenance, aesthetics, and cost. After careful review, the repair strategy selected involved injection of the cracks and the application carbon fiber reinforced polymer (FRP).Repairing team had injected all of the cracks, grinded, and pressure washed the beams. The FRP system was externally bonded onto the ends of the deficient beams to restore the strength lost due to the un-bonded strands. Since ensuring the continued operation of the Skyway was important to the JTA, Structural Preservation Systems developed a strategy to complete the repairs and upgrades during the evenings and weekends. 

Strengthening of pre-heater tower

Problem: An inspection by plant personnel revealed the cracking in the concrete frame of a 326-ft-tall, 7-level pre-heater tower. On-site plant engineers deemed the cracking significant, as the structure supports critical manufacturing process equipment. A structural engineering consulting firm was retained to evaluate the extent of the problem and formulate a repair plan. The firm mobilized at the site in less than 24 hours and performed an initial structural safety assessment. A comprehensive structural evaluation indicated that the structure required strengthening.

Repairing Methodology: After considering structural capacity and serviceability requirements, durability issues, the high-temperature operating environment, constructability, and an aggressive construction schedule, the team recommended a retrofitting consisted of bonded post-tensioning in internal holes which are drilled in the beams. This solution was quite extraordinary, as it required precision-drilling horizontal holes up to 87 ft long in the beams of the elevated frame structure, without cutting existing embedded reinforcement. Nondestructive impulse radar/rebar locator testing was used to locate existing embedded reinforcing steel, as well as to monitor the drilled holes' trajectory. This process helped in ensuring proper tendon alignment and preventing damage to embedded steel. The cored holes served as post-tensioning ducts. The repairs were executed quickly and under challenging circumstances, including working high on the exposed structure through a cold winter with severe wind conditions. The unique retrofit resulted in a structure that is stronger, more serviceable, and more durable than the original tower.