Completed Research 1995 to 2006

Theme 5 Projects (1999-2002):
FRPs and Integrated Sensing for Structural Rehabilitation

THEME 5 OVERVIEW

(All project descriptions are provided as proposed in 1998 as part of the NCE mid-term review)

Smart Patch Technology (T5.1)
Project Leader: Dr. Roderick Tennyson, University of Toronto

This now-completed project focused on the use of fibre optic sensors in FRPs applied in the form of reinforcing patches to concrete structures.
A fully cured FRP patch is essential to realize its full strength potential. In addition, the FOS provides a measuring device for monitoring strains in the patch and at the patch/concrete interface to ensure structural integrity of this reinforcement. The FOS also permits the field engineer to assess the structural loads applied to the concrete structures and assess potential failures.

This research project involved developing the technology for embedding FOS in the form of short fibre Bragg gratings (FBG) and long gauge fibre optic sensors into/on the reinforcing FRP patch. Test data were obtained and used to address the optical performance of the FOS and to demonstrate the effectiveness of FRP smart patches. Smart refers to the FOS monitoring of the health or integrity of the patch and concrete structure.

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FRP Rehabilitation and Strengthening of Concrete Structures (T5.2)
Project Leader: Dr. Pierre Labossière, Université de Sherbrooke

The proposed program is a continuation of the work accomplished during the first phase of ISIS and is divided into the following components [Neale, K.W., et al., 1997]:

1. Confinement of Concrete Columns with FRPs: Numerical models will be developed that will take into account the nonlinear behaviour of concrete, and will also be expanded to include the effects of combined axial and lateral loads. Testing of columns with square or rectangular sections will be carried out to provide data to validate the models.
2. Strengthening of Reinforced Concrete Beams with FRPs: Modelling and experiments are planned to evaluate the effects of non symmetrical loads and of torsion on beams externally strengthened with FRPs.
3. FRP Reinforcement of Concrete Slabs: Extensive numerical modelling of the test results already obtained will be undertaken.
4. Development of the Smart Patch Technology: Tests will be conducted on cruciform FRP specimens into which FOSs have been integrated. This will lead to the development of "ideal" configurations for smart patches that could be prefabricated before installation on a construction site. In addition to the cruciform specimens, FOSs will be installed at the interface between FRP sheets and concrete surfaces. The specimens will be submitted to debonding tests, under static and cyclic loads, and propagation of the delamination during the loading will be investigated.
5. Field Applications of FRPs and FOSs to Reinforced Concrete Structures: Practical applications will continue to be sought in order to demonstrate the potential benefits of the FRP repair and strengthening techniques.
6. Durability of Concrete Structures Repaired or Strengthened with FRPs: This research involves the testing of various FRPs and concrete elements exposed to exterior climatic conditions at the Sherbrooke exposure site. Accelerated aging conditions, which so far have been limited to wet dry cycles, will be expanded to include a number of water solutions representative of different aggressiveness conditions. FOSs will be integrated into some of the specimens to assess how measurements can be affected by the environmental conditions.
7. FRP Repair and Strengthening of Prestressed Concrete Beams: This project is already in its initial stages. Numerical modelling aspects are currently being investigated and will be pursued further. Laboratory testing will be carried out.

See Quebec Schools Field Demo
See Champlain Bridge Field Demo

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The proposed research will focus on the FRP repair of reinforced concrete columns and beams damaged by reinforcement corrosion [Bonacci, JR, et al., 1996; Neale, K.W., et al., 1998]. Of the two member types, columns are more naturally suited to repair with external FRPs. Perimeter wrapping of the damaged area provides confinement which can compensate for loss of reinforcement and damage to concrete. The research proposed here will build on this basic knowledge by establishing the monitoring capabilities to be integrated with the wrap and by evaluating the effectiveness of various repair schemes using FRP wraps.

Specific goals for the column smart wrap system development are (1) to evaluate the effectiveness of the smart wrap system on a variety of cross section geometries, (2) to perfect the "smart" technology in which transmitted data are used to monitor column load carrying capacity and remaining service life over time, (3) to install fully functional smart wraps for purposes of field demonstration, and (4) to move toward commercialization of the proven smart wrap system for service life extension. The second of these objectives requires analysis of test data and development of analytical models to establish the interrelationships between the rate of corrosion, local expansion at reinforcement elements, overall section expansion, lateral restraint to expansion, and load carrying capacity. The other three objectives depend, to some extent, on technologies being developed within other projects or themes of the ISIS Network, including assessment of post repair corrosion rates, availability of continuous real time long gauge FOS demodulation, and development of durable microelectronic components for demodulation and transmission of monitoring data.

Scientific goals of the proposed new sub project in rehabilitation of flexural members are: (1) to provide the technology required to extend the service life of corrosion damaged flexural members with minimal member patching and without removing dead loads, (2) to conduct laboratory structural testing to demonstrate the effectiveness of proposed repair schemes, and (3) to establish simple, accurate analytical methods for determining load and deflection capacity of externally reinforced concrete beams. If the technology for distributed long gauge FOS becomes readily available during the course of this research, the use of these sensors for detection of debonding will be investigated.

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The main objectives of this project are as follows: (i) to determine the effect of confinement by FRP wraps on corrosion of chloride contaminated, steel reinforced concrete columns; (ii) to evaluate the efficiency of using penetrating corrosion inhibitors in conjunction with FRP wraps for treating corroding columns; (iii) to develop a corrosion monitoring system for use with wrapped columns in the laboratory and field; (iv) to work with repair consultants and identify suitable cases for the field evaluation of the FRP wrap and corrosion monitoring system; and (v) to collaborate with other ISIS projects concerned with FRP repairs of corrosion damaged concrete.

Laboratory testing will include small scale testing of concrete cylinders as well as corrosion monitoring of the reinforced concrete columns manufactured under ISIS project T5.3. Concrete cylinders will be cast with embedded electrodes configured to optimize corrosion rate measurements by linear polarization techniques. The set up will also be designed to permit macrocell corrosion currents to be measured (between the working and counter electrodes). Different systems, including embeddable silver/silver chloride half cells and manganese reference electrodes, will be evaluated. The mild steel working electrode will be placed in chloride contaminated concrete to initiate corrosion. The other electrodes (reference and counter) will be placed in the same specimen but will be in a concrete environment without admixed chlorides. After selected periods of corrosion cylinders will be repaired using FRP wraps possibly in combination with other treatments such as penetrating inhibitors. Corrosion rates will continue to be monitored in the repaired cylinders, which will be exposed to a range of environments. At the end of testing the electrochemical corrosion measurements will be calibrated against gravimetric corrosion determined for the working electrodes.

In addition to the tests on small scale specimens, corrosion measurements will also be made on larger reinforced concrete columns subjected to accelerated corrosion tests. Small three electron probes will be installed in a series of reinforced columns cast as part of the ISIS T5.3 project. These will be monitored periodically using linear polarization techniques to determine the corrosion rate of steel within the columns before and after repair. Both commercially available probes and probes manufactured at the University will be evaluated to determine the most stable system under the severe conditions used for the column testing [Pantazopoulou, S.J., et al., 1996].

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One concern about the behaviour of FRP sheets bonded to concrete and subjected to low temperatures is that the thermal expansion of carbon FRP sheets is only one tenth that of concrete. This difference in thermal expansion will induce thermal stresses that may cause deterioration of the repair system. Furthermore, freeze thaw action may deteriorate the bond between FRP sheets and concrete. These concerns about the effects of a cold region's environment are widespread in the engineering community, and FRP sheets will not be used to a great extent in Canada until these concerns are allayed [Green, M.F., et al., 1997; Soudki, K.A., et al., 1996]. Thus, the major focus of this project is to examine the behaviour of FRP repair systems in cold region environments. A related aspect of this work involves the effects of corrosion on the repair system.

The following specific objectives are proposed: (i) examine the effects of freeze that on the bond of FRP sheets to concrete beams; (ii) test the resistance of FOSs to freeze thaw and low temperature exposure; (ii) test the resistance of concrete cylinders, strengthened for GFRP wraps, to freeze thaw and low temperature exposure; (iv) examine the viability of repairing concrete beams and columns, damaged by freeze thaw action and corrosion, with FRP sheets; (v) develop an improved system for prestressing concrete beams with FRP sheets; and (vi) study the long term, low temperature behaviour of concrete beams prestressed with FRP sheets.
Each of these objectives will be pursued by a separate research task. The first task is to subject the flexural bond specimens (100 x 150 x 1220 mm) to freeze thaw action for 50 to 300 cycles. At the end of the freeze thaw conditioning, the beams will be tested in flexure. The second task is to instrument small scale beams (100 x 150 x 1220 mm) and columns (150 x 300 mm) with FOSs, subject them to freeze thaw and low temperature exposure ( 18°C), and then test the specimens to failure. If the FOSs do not show adequate performance, their design will be modified and the tests repeated until a reliable product is developed. The third task is an extension on earlier work on concrete cylinders wrapped with CFRP sheets. GFRP sheets will be wrapped around the cylinders and subjected to freeze thaw and low temperature exposure. After the cold regions conditioning, the cylinders will be tested to failure in axial compression.

In the fourth task, larger scale concrete columns and beams will be tested. The concrete columns (300 x 1200 mm) will be corroded by exposing them to environmental conditions (e.g. wetdry cycles, temperature extremes) conducive to corrosion. To damage the columns further, they will be subjected to freezing and thawing cycles. After the initial damage period is complete, these specimens will be wrapped with instrumented FRP sheets. To arrest the corrosion process, electrochemical chloride extraction will be applied to some of the specimens before wrapping the FRP sheets. After the repair, the columns will be subjected to freeze thaw cycles and low temperature exposure. Continuing corrosion in the columns and strain in the FRP sheets will be monitored over time. The corrosion rate in the columns repaired with electrochemical chloride extraction and FRP sheets will be compared to the corrosion rate in the columns repaired with only FRP sheets. At the end of corrosion monitoring, the columns will be tested to failure in axial compression. Large scale beams (200 x 400 x 5000 mm) will be corroded and subjected to cold region conditions in a similar manner to the large scale columns.

A preliminary anchorage system for FRP sheets was developed as a collaborative effort between Queen's University and the Royal Military College of Canada. In task five of the project, the anchorage system will be refined to make it more efficient at applying prestress to the FRP sheets. Once a more efficient system is developed, large scale beams will be prestressed with FRP sheets and monitored at both low temperature ( 30°C) and room temperature over time to examine the time dependent effects of prestress in a cold region environment.

A final task that covers the whole range of the research project is the development of analytical models to predict the behaviour of FRP strengthened concrete structures in cold regions. These models will include degradation of concrete due to freeze thaw effects, the damaging effects of corrosion, and stresses induced by thermal incompatibility of materials.

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This project will examine the use of FRP wraps to confine (and monitor) corrosion in reinforced concrete beams when exposed to aggressive environments. The focus will be on the combined effect of wet dry cycles in the presence of de icing chemicals, freeze thaw cycling and steel reinforcement corrosion on beams repaired with FRP wraps [Soudki, K.A., et al., 1997]. The main goals are to develop smart FRP wraps for corrosion monitoring of repaired concrete beams, and develop smart FRP wraps for wet dry environments in the presence of de icing salts. The specific objectives of the research are to: (i) examine the viability of FRP repair system to maintain the structural integrity of reinforced concrete beams experiencing steel reinforcement corrosion; (ii) investigate different FRP wrap configurations for confinement of corrosion; (iii) examine the use of sensing on FRP wraps to monitor corrosion rates; (iv) examine the combined effects of low temperature or wet dry exposure and corrosion on FRP repairs; (v) examine the long term effect of sustained loads and corrosion on FRP repairs; and (vi) determine the effect of wet dry cycles on the bond between FRP wraps and concrete.

Reinforced concrete beam specimens (200 x 400 x 5000 mm) contaminated with variable chloride levels (one to three percent) will be corroded and repaired with FRP sheets. The beams will be subjected to accelerated corrosion by means of impressed current or natural corrosion by means of ponding. The specimens will be repaired with FRP sheets by continuous or intermittent wrapping. Particular attention will be paid to developing anchorage schemes that will resist spalling of the concrete cover due to continued corrosion of internal reinforcement. Half the specimens will be repaired prior to corrosion and the others will be repaired after moderate corrosion. The performance of the FRP repairs will be monitored over a period of two years. Some of the specimens will be subjected to freeze thaw cycles, wet dry cycles, and electrochemical extraction to investigate the effect on corrosion rate. In addition, other specimens will be subjected to combined corrosion and sustained service loading to examine stress corrosion. The corrosion rates will be measured using a number of electrochemical measurement techniques. The internal corrosion measurements will be related to the measured strain gauges mounted externally on the FRP wraps. This will enable precise quantification of the expansive stresses resulting from reinforcement corrosion. At the end of corrosion exposure, the specimens will be tested to failure.

Another part of the research involves examination of the bond between FRP and concrete when subjected to severe environmental conditions. Small scale beams (100 x 150 x 1200 mm) will be pre cracked and strengthened with GFRP and FRP sheets. Some specimens will be specially constructed to study the effect of bond between the FRP sheets and concrete. All the specimens will be exposed to wet dry cycles (100 to 300 cycles) in the presence of de icing chemicals. After completion of the exposure, the beams will be tested to failure. The deliverable will be an understanding of the bond mechanism of FRP and concrete and the effects of exposure to adverse conditions.

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The proposed research program aims to establish close collaborations with various construction sectors to investigate the feasibility and potential of using FRPs and intelligent sensing technologies in practical rehabilitation applications [Alexander, J.G.S., et al., 1996]. The proposed program is divided into four independent projects with FRP/intelligent sensing as a common feature.

1. Repair and rehabilitation of slab column connections in concrete structures. This will involve: (i) assessing the feasibility of strengthening existing slab column connections in concrete structures using smart FRP rehabilitation technologies; (ii) examining the behaviour of strengthened connections under extreme loading conditions; (iii) assessing the performance of rehabilitated structures under long term loading and various service conditions, including the fire performance of structures; and (iv) assessing the performance of intelligent sensing technologies in retrofitted structures.
2. Strength and seismic rehabilitation of masonry structures. The objectives are to: (i) study the out of plane and in plane behaviour of unreinforced masonry walls strengthened by FRPs; (ii) investigate the seismic behaviour of retrofitted unreinforced masonry walls; (iii) study the moisture effects on the rehabilitation schemes; and (iv) develop the optimum rehabilitation system for masonry structures.
3. Fatigue repair and strengthening rehabilitation of steel structures. This research will consist of: (i) examining the behaviour and stress distribution of steel structures repaired using FRP patches; (ii) performing small scale tests on steel plates for fatigue repair performance and strength enhancement; (iii) studying the feasibility of composite overlays on steel structures, such as composite repairs for the stress corrosion cracks of buried pipelines; and (iv) conducting field application and remote monitoring of rehabilitated steel structures, such as steel bridges, pipelines and steel mining equipment.
4. Member strength and connection integrity repair and retrofit of wood structures [Dorey, A.B., et al., 1996]. The proposed research is to: (i) study the behaviour and develop design criteria for the rehabilitation of wood members using FRP patches; (ii) investigate the feasibility of using FRP wrapping technology in connections to provide the integrity of wood frame structures; (iii) develop a moment connection by using FRP wraps for wood frame construction; and (iv) assess the long term performance of strengthened wood members and connections under various environmental conditions to determine the most economical FRP matrix.

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The main objective of the proposed project is to develop cost effective, high performance sprayed FRP composites (based on durable polymeric matrices and reinforced with high performance chopped, non metallic fibres in a 2 D random fashion) for repairs and rehabilitation of concrete structures [Banthia, N., et al., 1996]. The proposed project is divided into three distinct tasks as described below:

(i) Understanding and Optimizing the Process of Spraying
One of the major difficulties with the spray process is the low resulting in place fibre volume fraction. Increasing the fibre dosage rate is a challenge and earlier attempts to incur fibre volume fractions greater than about 15 percent have not been successful. Better shooting techniques must be investigated to incorporate higher fibre volume fractions exceeding 50 percent. What constitutes an optimal fibre volume fractions from the performance point of view, however, is not known and must be determined.
Another problem with the process when electrically conducting fibres (such as pitch precursor carbon) are used is the electrical charge imparted to the fibres during shooting. Due to this charge, the movement of fibres in the stream occurs in a divergent manner rather than in a desired convergent manner. Some possible ways of dealing with the problem include adding decharging additives and/or electrically charging the substrate. Both must be investigated.

Finally, the process characteristically incorporates high fibre rebound, which is partially why the fibre volume fractions in the in situ composite remain low. To this end, the mechanisms of rebound must be studied and measures taken to reduce the rebound.

(ii) Comprehensive Laboratory Assessment of Sprayed FRPs in Repairs
Based on a preliminary understanding and assessment of the technique in actual repairs, a more extensive and systematic laboratory investigation will be undertaken. Reinforced concrete specimens with various reinforcement details will be tested with and without the SFRP coating and also with and without an induced damage. Improvements in flexural, compressive, and shear performance will be investigated. This laboratory assessment will also include tests for durability characteristics such as creep, fatigue, impact and long term performance under deleterious chemical and physical environments. A comprehensive model based on modified constitutive formulation will be developed. Fibre optic sensors will be embedded for strain measurements in order to gain experience with them for their eventual deployment in the field. One of the objectives here will be to compare the performance of sprayed FRPs with the traditional unidirectional wraps. On identical specimens, the two will be applied and then compared for both mechanical and durability performance.

(iii) Field Assessment of Sprayed FRPs in Repairs and Strengthening
Once sufficient experience has been gained with the technique and influence of the various parameters has been understood, some real structures will be repaired and strengthened using the technique. The use of the fibre optic sensors will be made for long term monitoring. One of the issues that needs to be addressed for field application is the portability of the equipment. Some modifications will be necessary to the equipment in this regard, and this will be investigated.

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Few applications for FRP reinforcement of new structural elements have reached commercial development or common use in any significant way. One technology for aramid reinforced glued laminated timber (glulam) beams exists but has met limited acceptance in the marketplace, especially in Canada. Improving the ductility of timber connections for seismic performance is another possible application. The immediate potential seems, however, to be for FRP reinforcement by retrofit.

The potential for different types of fibre reinforcement will be investigated. Aramid, glass and carbon fibres all offer specific benefits. Bonding technology, specific to each product, is even more critical with timber because of its hygroscopic behaviour and the very high strains which develop through seasonal cycles of moisture content. The behaviour of bonded joints and the rules governing transfer or anchorage length will be investigated experimentally, taking into account the effects of moisture cycles.

The apparatus developed in the first phase of this project, essentially the drying unit and the technique for obtaining moisture cycles, will be used in the next phase. The apparatus for shear evaluation of bonded anchorage to concrete, developed at the Université de Sherbrooke, seems to be a promising device and technique for evaluating bond lengths with wood. Initial results during the first phase seem to confirm this. This avenue will continue to be investigated.

The program, therefore, will include the following elements:
(i)  Reinforcement in bending and shear with differing fibre composites. (ii) Glulam and sawn timber. (iii) Applicability of advanced sensing devices. (iv) Effects of moisture, both of degree and cyclic history. (v)  Apparatus effects, appropriate test protocols to establish bond length requirements. (vi) Strength, stiffness, fracture mode and ductility effects.

See Quebec Schools Field Demo
See Eustis Bridge Field Demo

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Many masonry structures suffer serviceability problems. The traditional solution was to repoint the mortar joints since the majority of cracking would be along these weak lines. More recently, a stronger but less sightly solution has been to fill the cracks with epoxy grout. Post tensioning of structures has also been utilized, where holes have been drilled through the masonry, tendons laid and post tensioned, with the anchors subsequently covered to restore the masonry to its original appearance.

CFRPs offer at least three further approaches for repair. In the first instance, where the appearance of the structure can be changed, the cracks could be filled with grout and the masonry wrapped with CFRP sheets. With subsequent coating and painting, the masonry appearance would be lost, but the integrity of the structure restored. In the remaining two approaches, where retention of appearance is important, the masonry could be repaired through filling of cracks, and coating with CFRP sheets from the non visible side of the masonry (requires access to this side). Alternatively, post tensioning with CFRP can be employed to close cracks and strengthen the structure. The advantage of this latter approach over post tensioning with steel is the better durability of CFRP and the reduction in the labour required to provide the durability.

The proposed program will have two strands. In the first, a field demonstration will be developed with Canadian Pacific Rail on masonry piers for railway bridges. These structures will be rehabilitated through the first approach above. The second strand will involve laboratory work to determine the level of strength enhancement that can be achieved for the second method above. This method would be particularly useful to repair walls which have cracked from foundation settlement, or moisture expansion of the masonry. The third method is an extension of the current thrust on post tensioning for new masonry structures.

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The main objective of this research project is to evaluate the short-term and long-term behaviour of FRP-reinforced structures. These structures include existing steel-reinforced concrete structures retrofitted with FRP or new concrete structures in which FRP provides primary or secondary reinforcement. The main focus of the research is concrete columns and slabs. In addition, new innovative techniques will be developed and tested to enhance structural properties of concrete elements.

The use of FRPs in concrete structures is primarily aimed at producing more durable and in the long-run, more economical structures. Although in some instance, FRP may replace reinforcing steel, in most cases it will serve a unique purpose such as in producing corrosion-free structures.

The goals of the research will be achieved by testing of large-scale components for structural characteristics and small-scale specimens for durability. Analytical work to develop conceptual models to predict the behaviour of FRP-reinforced structures form an integral part of this study. Experimental data will be used to calibrate the analytical models. The work builds on research obtained from various ISIS Canada and other research projects. It involves structural testing of square and circular columns and slabs, and durability tests on FRP-concrete bonds. The main emphasis in column specimens will be confined provided by FRP and in slab specimens enhancement of one-way and two-way shear capacity is the main focus.

Results from tests on circular columns are available from previous research. All of these columns can be considered as half-scale to full-scale models. In addition, several other investigators have also reported tests on circular columns. However, data from FRP-reinforced square or rectangular columns are very limited. Therefore, repair and retrofitting work is being conducted on square columns. An innovative technique involving specially designed FRP reinforcement and expansive cement has been conceptually developed to enhance the shear resistance of concrete slabs.

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There is a large number of reinforced concrete buildings that are gravity load designed with adequate lateral load resistance. Many of these existing structures were designed to the then-available codes of practice that may have been upgraded over the years. Due to the high cost of replacement, many old structures are still in service far beyond their design life. Earlier codes did not include seismic provisions, or may have specified lower levels of seismic loads. Gravity load designed structures may behave in non-ductile manner with undesirable modes of failure.

The design approach of codes before the 1970s was to provide adequate strength to resist the specified lateral forces. Recent codes began to focus on details of member design and reinforcement to achieve overall ductility or deformability as well as strength requirements. During recent earthquakes, such as the 1994 Northridge and the 1995 Hanshin-Awaji (Kobe) earthquakes, reinforced-concrete buildings designed to earlier codes or prior to the seismic design requirements did not behave well due to inadequate lateral load resistance capacity an limited ductility. The vulnerability of many existing structures may be due to non-ductile detailing which cases undesirable modes of failure. The shear failure of beam-column joints and bond slip of beam bottom reinforcement has been observed in many recent earthquakes and normally results in brittle and catastrophic failure of the structure. By eliminating these types of brittle failures, the structure is given the opportunity for ductile behaviour. Analytical and experimental studies have shown that it is possible to rehabilitate the beam-column joint region using steel jackets to upgrade their shear resistance.

Fibre-reinforced polymers offer an excellent potential as a rehabilitation material for concrete structures as an alternative to steel jackets. They are lighter, stronger, and non-corrosive, and provide an attractive alternative to the traditional techniques to eliminate the brittle shear failure in joints.

The objective of the research is to develop a viable rehabilitation system using FRPs for beam-column joint by improving their strength and ductility. The rehabilitation scheme is expected to improve the behaviour of existing nonductile joints when subjected to earthquake ground motion. The research program is experimental and analytical with plans for the development of simple design procedures for the practising professionals and code type applications.

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FRP Rehabilitation of Nuclear Reactor "Field Application" (T5.11)
Project Leader: Dr. Kenneth Neale, Université de Sherbrooke FRP

Gentilly-1, the first nuclear plant at Gentilly, Quebec, became operational in May 1972 and was operated intermittently until 1978, after which it was partially decommissioned. International (IAEA) and Canadian (AECB) guidelines are being followed to provide monitoring and surveillance programs which ensure conditions at the site continue to meet safety requirements. While it was originally to be maintained for 40 years after decommissioning, plans are now being progressed to extend this maintenance period to 100 years. AECL and ISIS are carrying out a testing program to determine the strength and durability characteristics of the concrete containment structure.

After the testing program is completed, AECL will decide if the strength of the structure needs to be enhanced. Innovative FRP technology will be used for this purpose and, otherwise, to improve the durability and appearance of the building.

See Field Demo

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Completed Research 1995 to 2006