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.

Repairing Concrete Slab

Problem: About 934 steel reinforcing bars of the concrete slab were cut or damaged, compromising the structural capacity of the concrete slab.

Repairing Methodology: After evaluation of the structure, consulting team selected carbon fiber reinforced polymer (CFRP) -- paper-thin fabric sheets bonded to concrete members with epoxy adhesive -- to strengthen the loads. The solution came in the form of approximately 15,000 square feet of CFRP on both the top and underside surfaces of the reinforced concrete slabs. CFRP has a tensile strength approximately 10 times that of steel.  Also, because only a portion of the hotel was closed for the rehabilitation, safety of the customers and employees was paramount. By the time team arrived at the site, new interior wall partitions were being installed. Because of the nature of the CRFP strengthening repair work, some of the partitions had to be removed. Repairing team had to expedite the design, installation and development of detailed as-built drawings for the CFRP as other contractors were working to finish each floor.

Post tensioned tendons

Structural Details: In this building, the post-tensioned (PT) tendons act similar to beams running through the concrete slab. When the tension is removed from the cables of the PT tendons are locked-off, the result is similar to the floor losing its support beams. The typical solution to this situation is to place shoring under the affected areas to replace the support. However, in this case, shoring to support the adjacent bays would interfere with the tenants' business operations.

Our Approach: Because of the project constraints, it is possible only if at some place shoring directly under the slab opening, not under adjacent slabs, as that would result to less capacity similarly the cables were de-tensioned. This required the design team to create a phasing plan in which they determined which cables were allowed to be de-tensioned and in which order. This lock-off phasing plan allowed the crews to de-tension individual PT tendons, while maintaining the structural integrity of the entire floor system. The project was phased in small sections in order to minimize disruption to the existing businesses and most of the work was performed at night. Once the tendons were re-tensioned, the crews would begin the concrete demolition for the next lock-off phase. The total square footage of the project area was 3,600 square feet. 

Structural Conservation

Scope of work: The scope of work included supplying labor, equipment and construction materials to remove and replace all the deteriorated mortar joints (inside and out) and strengthening of the chimney to accommodate the new loads created by the cell antennas. 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. Extensive re-pointing of interior and exterior joints was carried out to stabilize and restore the integrity of the chimney; with the bricks at the top 4 feet so much degraded that 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.

Our Approach: 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 laminated plates were installed in single, 30.5-m (100-ft) long pieces extending to the chimney’s full height. Since carbon FRP is only a quarter 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.

Old deteriorated structure to New office space

Structure Characteristics: Structure was constructed of cast-in-place conventionally reinforced concrete beam and slab system. The structure was exposed to road salts and moisture from the environment for years, and the resulting corrosion-induced deterioration had compromised the structural integrity of the floor system. The deterioration had also resulted in concrete deterioration of the pre-cast façade panels.

 Our Approach: The renovation of the tenant space and old bus terminal into new office space prompted the repair project. Structural restoration work included: 45,000 square feet of strip patch full slab replacement; 3,000 square feet of beam repair; 500 square feet of column repair; expansion joint replacement; sealant work; structural strengthening; hot applied waterproofing membrane; and 190,000 square feet of deck coating.

Power plant's cooling tower

Problem: Deterioration, corrosion of embedded steel, and water leakage through the shells.

Structural Details: The towers that need repairs are about 370ft high above the normal ground level with the diameter of 248ft and repairs can only be carried out during scheduled outages to avoid disruptions in the area’s power supply.

Testing: Using visual inspection, hammer sounding throughout both towers, and laboratory testing of core samples, investigators identified the types and extent of concrete deterioration. In addition to the spalling, corrosion, and leakage already noted, cracks were found in the support columns and ring beams at the bases of the towers.

Challenges in repairing: Providing access to the interior and exterior of the towers to allow thorough inspection and repair was difficult. Careful structural analysis was required to maintain the towers structural integrity while repairs were under way. Repair materials had to be evaluated and selected for their ability to withstand the unusual conditions within the towers.

Our Approach: Repair crew removed the deteriorated concrete from the tower shells with pneumatic chipping hammers and filled the created voids with dry-mix shot-crete. They sealed the cooling tower’s interior surfaces with water and vapor proof epoxy coating. They cleaned out cracks in the supporting columns and ring beam and sealed them with epoxy. Meticulous quality control testing and inspection during repairs helped ensure the project’s success. 

Parking Garage needs major repairing

Task: To perform the repairing of concrete, replace expansion joints, and install a urethane deck coating on the condominium's parking garage.

Structural Details: The garage was designed with an elevated flat slab with banded post tension cables running over the column lines in two directions.

Problem: Deterioration of the mono-strand post tension cables because of the lack of proper coverage over the cables had allowed water infiltration.

Initial Survey: An initial Survey of the post-tension cable system was conducted. The initial phase of the survey examined the condition of the high and low points of the topside and underside of the slab to determine positive and negative reinforcement. Technicians also looked to see if water had infiltrated the bottom of the sheathing. While on the surface it was apparent that only 2 cables were broken, careful investigation located 9 others that were broken or close to breaking. Ultimately, it was determined that 7 main cables needed to be repaired, 8 anchors had to be replaced, 5 add-ons were required, and 108 anchor pockets needed cleaning and trimming.

Out Approach: The repair suggested is to be consisted of greasing and re-sheathing of the unbroken exposed strands, full length cable repairs, replacement of extensively corroded anchors with excessive slippage and loss of section, and cleaning and trimming of anchor pockets. Additionally, it has been recommended that sacrificial anodes should be placed every 20 to 24 inches per square foot area and the reinforcing bars treated with a corrosion inhibitor (except in areas where leads from the anodes tied onto the bar). The skill of the crew is a deciding factor for success of repairing by keeping concrete removal to a minimum level and the prompt delivery of materials.

Load Capacity of cast-in-place Slab

Task: the structural floor required an upgrade from a live load capacity of 100 PSF (pounds per square feet) to new load of 25 PSF of super-imposed dead load and 150 PSF of live load.

Structure Details: Floor of the structure consists of a one-way cast-in-place slab on precast pre-stressed joist system, simply supported on continuous cast-in-place concrete beams with precast pre-stressed soffits running between columns of the structure.

Our Approach: Rapid Load Testing has been used to evaluate the in-place strength of the loose floor components and to develop an optimized and economical strengthening solution. On the basis of load test, we concluded that slab was strengthened enough to bear up new loads but the joist should be rated to 125 PSF of live load and the beam for 135, all greater than the theoretical load.

An externally bonded carbon FRP strengthening system was recommended consisting of multiple plies of FRP strips attached to joists soffit to increase the positive bending moment capacity and additional FRP strips were wrapped around the joists at each end to anchor the FRP strips. The beams were strengthened to improve their positive and negative moment capacity by installing FRP strips the soffit of the beam for positive moment and on top of the slab for negative moment. On top of the slab, the required amount of FRP for beam upgrade was equally divided and installed of each side of the column in the direction of the beam.

Raker Beam (Basketball Court)

Problem: Cracks were observed on the beam during its construction phase only and on in-depth investigation it has been revealed that it requires additional tension reinforcement.

Structure Details: It was a 16,000 seat capacity new basketball arena and the raker beams that required strengthening were at the second level.

Our Approach: An optimum solution consisting of an external post-tensioning system and externally bonded FRP reinforcement was recommended. The external post-tensioning system was composed of high strength T-headed steel bars and special steel cross heads for anchorage. The post-tensioning system provided vertical and horizontal "clamping" forces that actively engage this reinforcing system and reduce beam cracking and deflection.

Installation: Core holes were drilled through existing transverse beams to install the vertical T-headed bars. To avoid damage to existing steel bars, small areas were chipped open on the topside of the beams prior to coring. Locations of the core holes were then adjusted to minimize damage to existing steel reinforcement. At less deficient locations, externally bonded FRP system was used to provide the additional tensile reinforcement. To address issues related to FRP development length and anchorage requirements, bonded concrete block was cast-in-place on the underside of each raker beam. At locations where pre-cast concrete tubs were already installed on the raker beams, a special jacking system was used to lift the tubs during strengthening installation. To achieve this, several hydraulic jacks were operated simultaneously to avoid overstressing the precast concrete elements.

Increasing serviceability age of bridge

Problem: Deterioration in the pre-stressed strands of the bridge coupled with extensive cracking and spalling of the concrete.

Task: To increase the life of both the bridges

Our Approach: A carbon fiber system was designed to restore the flexural strength of the beams and to optimize the high strength of the carbon fibers an innovative method for post-tensioning of carbon fibers was used which has been used only six times worldwide till then. In addition to strengthening all the affected beams, the bridge bearings were repaired and aligned, the deck drainage was redesigned and replaced, the deck was waterproofed, and a new wearing course was placed on the bridge. All the deteriorated concrete was removed and replaced with a polymer-modified repair mortar and the exposed mild steel was coated with an anticorrosion coating.

Repairing Advantage: Carbon fibers which were used were non-corrosive and very suited for moisture laden climate over bridge, the ability of repaired system to relieve strain from the existing tendons and the plates to be used can be attached to concrete beams by mechanical and chemical means.

Precaution and Monitoring: After the completion of the repairs, the two bridges will be monitored for a period of at least two years for load-rating, stress and strain patterns, and deflections to determine the long-term effectiveness of the repairs.

Furnace foundation

Problem: Deterioration of the concrete used in foundation wall as well as corrosion of reinforced steel bars. Also include corroded vessel anchor bolts, failed sluiced trench water nozzles and warped railroad rails. Areas undergone repair commonly experienced failure too.

Structural Details: Furnace is around 64 year old structure which include foundation wall, coke drum support structure and coke railroad sluiceway trench.

Cause: The structure was subjected to extreme environmental service include high temperature, chemical attack, water erosion, railroad car impact and thermal shock. This led 

to the cracking, spilling and delaminating of concrete along with corrosion in steel members.

Our Approach: On the basis of the testing of the structure, it has been revealed that structure could support and integrate new concrete materials. Use of high-grade, shrinkage compensating repair concrete along with high capacity mechanical anchors was recommended.

The repairing approach includes wire-line-saw cutting of massive reinforced concrete and use of precast concrete segments involving post-tensioning anchorage and fastening, installation of waterproofing membrane systems and quick setting cementations backfill. Regarding the size of precast structure, each independently reinforced segment was evaluated with shipping load weight and size restrictions, dictating that only the sidewalls could be economically precast and transported to the site. Additional details regarding joint grouting, reworking the wash-down system and waterproofing and backfilling were detailed as the working conditions were not that favorable. 

Corrosion spoiling Cooling tower

Problem: Corrosion in the steel used in column, lintel and beam as well as cracking, rust staining and delaminating of concrete surface.

Structural Details: The hyperbolic cooling tower of power plant which is 450 feet long and 360 feet diameter having column and lintel beam in slip form. It was subjected to intermittent dry and wet conditions and therefore was susceptible to corrosion.  It is low cost comparative to mechanical draft cooling tower.

Cause: The water which is in use has presence of chloride in it and can easily corrode embedded steel in concrete. Once there is crack in the concrete, there is more possibility of intrusion of chloride and oxide along with the air causing delaminating and rust staining of the concrete.

Our Approach: To improve the life of cooling tower, corrosion induced deteriorated concrete need to be removed including cleaning and protection of the reinforced steel and re-stabilizing original concrete. At each repair site the concrete was chipped and the exposed steel needs to be sandblasted and coated with a protective layer and concrete is re-filled by grouting with fiberglass jackets. Because of the height of the structure, the magnitude of challenges in protecting the private and public property surrounding the area was huge and to be dealt with rig-type of platform system to work for.