Restoration and Rehabilitation FRP Wrapping

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1 Restoration and Rehabilitation FRP Wrapping (Rehabilitation of a Power Plant Structures Affected by Earthquake & Tsunami at Port Blair, Andaman) M.Karthikeyan, B.E., M.B.A., F.I.E, K.Thiagaraj B.E., 156 Abstract: The RCC members of various structures such as jetty pile caps, column and beam-column junctions of the over head water tank and Diesel Generator (DG) main building of a 20MW power plant located at Port Blair, Andaman, were severely affected due to the recent earthquake and subsequent tsunami. Sea water had entered into the power plant to a height of 1.20 m and receded after a few minutes. The damaged structures have been rehabilitated with epoxy jointing and wrapping of Fiber Reinforced Plastic (FRP) laminates followed by epoxy grouting. The condition assessment of rehabilitated structures including Diesel Generator Foundations is studied with ultrasonic test and core sampling and subsequent testing. The data obtained by these tests indicate that the integrity of concrete in DG foundations, beam-column junctions of over head water tank and DG main building and jetty pile caps was good, which shows the efficiency of epoxy injection and wrapping of FRP laminates with grouting at the joints. This paper describes the details of the rehabilitation work carried out on the damaged structures and also the condition assessment of the same using non destructive test techniques. The test results, evaluation, interpretation and recommendations are also presented in this paper. On the fateful morning of 26th December 2004, like many parts in Asia, the island of Little Andamans in the Bay of Bengal has experienced an earthquake followed by Tsunami, the water level rising by about 3.0 m. The power plant structures of M/s.Surya Chakra Power Corporation Ltd (SPCL),located at Bambooflat (South Andamans) in Port Blair were affected in the earthquake and tsunami. The SPCL has got four diesel generators of 5 MW each which produces 20 MW power. Due to tsunami, the sea water entered into the Power plant to a height of 1.20 m, and receded after a few minutes. The jetty pile caps of the water pumping station, column and beam junctions of the over head water tank and DG main building have been severely damaged due to earthquake. The damaged structural elements have been classified based on the extent of damage. The opinion given by the experts are to demolish and reconstruct. This power station is the main source of power supply to Port Blair and hence any delay would cause lot of disturbances. The authors suggestion to rehabilitate with FRP materials was accepted by the management and the work was carried out as detailed below The damaged structures were rehabilitated with epoxy jointing, wrapping of FRP laminates followed by epoxy grouting. The soundness of the concrete in DG foundations was assessed using ultrasonic test and core sampling and testing. The rehabilitation work scheme was proposed and carried out by M/s. Hitech Structural Repairs & Rehabilitation Systems, Chennai and the condition assessment of the strengthened members was carried out by Structural Engineering Research centre (SERC), Chennai. This paper outlines the details of rehabilitation work carried out on the damaged structures, condition assessment by NDT techniques, interpretation of test values and recommendations. Description of the Structures M/s. Suryachakra Power Corporation Limited, Andaman has set up a power plant of 20 MW capacity (4 x 5 MW) which consisted of main building, over-head water tank, jetty pump station and diesel engine generator foundations etc., during The dimensions and other details of each unit are given below. All the structure where founded on pile foundation which is mandatory in Andaman Islands Diesel Engine Generator (DG) Foundations There are four DG foundations and each supports a DG which produces 5 MW of power. The over all size of the DG foundation is 9700 mm x 4000 mm in plan and the height is 2700 mm at engine side, and 2290 mm at generator side. On the top of the DG foundation block, diesel engine and generator are placed. The foundation block of the DG has been supported over 14 piles of 400 mm dia. Tor steel reinforcement and M20 grade concrete are used for the DG foundations. Jetty Pump Station Pile caps The jetty pump station is located in the sea, which is about 150 meter away from the main DG building. The pump house is constructed over pre-cast beams and the pre-cast RCC beams are supported over six pile caps. The dimension of the pile cap is 1000 mm x 1000 mm with 700 mm thick. All the supporting piles are 750 mm dia. and are constructed with torsteel reinforcement and M20 grade concrete. Over Head Water tank The over head water tank is constructed with four columns of size 400 mm x 400 mm with intermediate connecting beams of size 300 mm width and 500 mm depth. The columns are placed at 7300 mm apart and intermediate beams are provided at a height of 3850 mm from the plinth beam. The capacity of the overhead water tank is 50,000 liters. The

RESTORATION & REHAB: CASE STUDY columns are supported over pile caps of size 1900 mm width, 700 mm breadth and 800 mm depth. The pile caps are supported over two piles of 400 mm dia.

Beam-Column and junctions of the DG Main Building The over all dimension of the DG main building is 34950 mm x 16500 mm. The longer length of the building lies in North - South direction.

The size of the columns is 750 mm x 400 mm and the height is 10.60 m. The center to center distance between the columns is 7500 mm and the two rows are placed at 16500 mm apart.

There are connecting beams placed in masonry work both at south and north side of the building. These beams are connected to the main columns. The dimension of the connecting beams is 400 mm x 300 mm.

2 RESTORATION & REHAB: CASE STUDY columns are supported over pile caps of size 1900 mm width, 700 mm breadth and 800 mm depth. The pile caps are supported over two piles of 400 mm dia. All the RCC members of the over head tank are constructed using torsteel reinforcement and M20 grade concrete. Beam-Column and junctions of the DG Main Building The over all dimension of the DG main building is mm x mm. The longer length of the building lies in North - South direction. There are twelve major RCC columns in the DG main building and are placed in two rows having six columns in each row. These six columns are placed in North-South direction. The size of the columns is 750 mm x 400 mm and the height is m. The center to center distance between the columns is 7500 mm and the two rows are placed at mm apart. An EOT crane is being operated in the DG main building and the crane girder is supported over the columns at 7.00 m level. There are masonry walls constructed around the DG main Building. There are connecting beams placed in masonry work both at south and north side of the building. These beams are connected to the main columns. The dimension of the connecting beams is 400 mm x 300 mm. All the RCC members are constructed with Torsteel reinforcement and M20 Grade concrete. Fig.2 Damaged column beam junction of over head water tank Investigation Approach and Rehabilitation Visual Observation and Documentation A detailed visual inspection was carried out on all RCC structural members referred to this investigation. Photographic documentation of the damaged members was also carried out. A few typical photographs given in Fig.1 to 4 indicate the extent of damage in Jetty pile caps, over head water tanks and beam-column junctions of the DG main building due to earthquake and tsunami. Fig.3 Damaged column of over head water tank at plinth level Fig.1 The damaged jetty pile caps 157 It was observed that the jetty pile caps were affected mainly due to tsunami effect. Other Beam-column junctions were damaged mainly due to earthquake. Based on the visual observation, it was noticed that the cause of damage on the beam-column junctions of the over head water tank was due to earthquake and magnified due to lack of confinement of re-bars at the joints. The main reinforcements of the con- necting beams were bend out side the stirrups of the main column. The damage in beam-column junction of DG main building was due to construction joints. The beams were connected separately after the columns were executed. It was also noticed vertical cracks in the columns at plinth level of over head water tank (Fig.5) and a split in the connecting beam at the pile cap level. Based on the experience gained and also from the available literatures, the damages of the structural components have been classified and described in Table-II. The rehabilitation methods were selected Fig.4 Damaged column beam junction of main DG building

for the distressed members depending upon the extent of damages. Repair and retrofitting Having classified the damage severity, the next step was to propose a suitable repair methodology.

damage severity, it was proposed to rehabilitate the jetty pile caps with epoxy mortar and epoxy grouting, and for beam-column joints with wrapping of FRP laminates followed by epoxy grouting.

3 for the distressed members depending upon the extent of damages. Repair and retrofitting Having classified the damage severity, the next step was to propose a suitable repair methodology. In the recent years, the application of epoxy injection, epoxy mortar and Fiber Reinforced Plastics construction materials, especially for repair and retrofitting purposes, based on the level of damage severity, it was proposed to rehabilitate the jetty pile caps with epoxy mortar and epoxy grouting, and for beam-column joints with wrapping of FRP laminates followed by epoxy grouting. Concrete Jacketing to the columns of the over head water tank at plinth level was proposed for strengthening. The properties of epoxy and FRP laminate are given in Table-II & III and rehabilitation procedures are described below. - Applied polymer modified mortar over the joints and fixed entry ports (nipples) at different levels for epoxy grouting. - The nipples were spaced at a maximum distance of 400 mm center to center and the second row was staggered. - After 24 hours, epoxy injection was started from the lowest nipple and continued till the epoxy reaches to the next nipple fixed above. This process was repeated for all the pile caps and the nipples were sealed only after the cracks were completely filled. - After drying, the nipples were removed. The finishing work of the pile caps was carried out with epoxy mortar (Fig.6). The integrity of the repaired pile caps were checked by ultrasonic test. Descriptions Viscosity Pot life Tack Free Values 1500 to 2000 Cps (for resin) 650 to 850 Cps (for hardener) Minimum of 45 minutes 3-4 Hrs Minimum compressive 50 N/ mm 2 Minimum flexural strength 35 N/ mm 2 Table-II Specifications of epoxy Thickness, mm Ultimate Strength, N/mm 2 Modulus of Elasticity, N/mm Table-III Properties of FRP laminate Jetty Pile caps Fig.6 Rehabilitated jetty pile cap Beam-Column junction of Over head water tank (OHWT) and DG main building Jacketing of columns of OHWT 158 The following steps were followed to repair the pile caps - Chipping off the broken concrete, loose mortar etc., present at the damaged junctions - The cracks were cleaned thoroughly with compressed air / water jet and surface dried (Fig.5) - Inserted reinforcement bars perpendicular to the cracks - Applied one coat of epoxy over the cleaned area. (on dry surface) Fig.5 Cleaning and removing of particles in jetty pile cap Concrete jacketing is a popular method of column retrofit. This involves addition of a thick layer of reinforced concrete (RC) in the form of a jacket, using longitudinal reinforcement and closely spaced ties This method is comparatively straightforward and increases both strength and ductility. Cracks were found in all the columns at the column pile caps junctions of the over head water tank. Hence, Jacketing to the columns at plinth level was undertaken by providing additional reinforcement. The concrete mix used for the jacketing was M20. The following steps were followed to strengthen the columns of OHWT over the pile caps. Necessary supports were made to the structures by providing props. For the purpose of uniformity and quantity measurements, the concrete up to the main reinforcement was removed. The exposed reinforcements were thoroughly cleaned mechanically and compressed air / water jetting were used to remove all loose rust and other particles. The exposed rods were treated with an anticorrosion coating and the coating was allowed to cure for the period specified by the supplier. Main reinforcement of 12 mm dia. at 100 mm centre to centre and 8 mm dia. stirrups at 150 mm centre to centre were placed. The main reinforcements were inserted into the pile caps to a length of 150 mm and grouted with epoxy. After positioning the reinforcements, shuttering was provided all

4 159

RESTORATION & REHAB: CASE STUDY around the columns. M20 grade concrete was poured to a height of 1200 mm with a cover of 50 mm all around (Fig.7) to make the column size as 600 mm x 600 mm. Fig.

7 Jacketing to the coloumns at plinth level of OHWT 160 FRP Wrapping at Column Beam Junctions The damaged column beams joints were strengthened by wrapping FRP laminates.

Necessary supports were provided to the structures by props. Removal of damaged cover concrete in the columns and the extent of removal depend on the severity of the damage.

5 RESTORATION & REHAB: CASE STUDY around the columns. M20 grade concrete was poured to a height of 1200 mm with a cover of 50 mm all around (Fig.7) to make the column size as 600 mm x 600 mm. Fig.8 Cleaning and removing of particles from damaged column beams junction of over head water tank Fig.7 Jacketing to the coloumns at plinth level of OHWT 160 FRP Wrapping at Column Beam Junctions The damaged column beams joints were strengthened by wrapping FRP laminates. This is relatively a highly efficient material and requires careful surface preparation for this application. The steps involved for retrofitting of these structures are as follows. Necessary supports were provided to the structures by props. Removal of damaged cover concrete in the columns and the extent of removal depend on the severity of the damage. The broken and loose concrete were removed by chipping. Surface cleaning was done with compressed air / water jet to remove the loose particles (Fig.8). Necessary stirrups were provided at the joints to ensure the confinement. One coat of epoxy was applied over the surface and when it was tacky, epoxy mortar was applied to bring the joint to shape, and also nozzles were inserted at vulnerable points in all directions at different levels for epoxy grouting. After 24 hours, the FRPs were wrapped in two layers by applying epoxy coating on each layer so that bonding between the layers is ensured. After 24 hours, epoxy grouting was carried out from the bottom nozzle so that the epoxy flows out smoothly through the nozzle above and making sure that the voids inside were filled properly. The grouting was continued till the epoxy was reached to the top nozzle and then the nozzle was sealed. This process was continued for all the nozzles. After the epoxy grouting, one coat of epoxy was applied over the surface Fig.9 Rehabilitated column beam junction of over head water tank Fig.10 Rehabilitated column beam junction of main DG building and epoxy mortar was applied to the columns to have the regular cross section. Fig.9 & 10 show the rehabilitated column beam junction of the over head water tank and DG main building respectively. Assessment of Structures and Discussions For the purpose of assessing the condition of the struc-

S.No Structural components Description Damage level 1 Jetty pile caps 2 3 Beam- column junctions of over head water tank Beam-column junctions of DG main building tures, ultrasonic test and core

6 S.No Structural components Description Damage level 1 Jetty pile caps 2 3 Beam- column junctions of over head water tank Beam-column junctions of DG main building tures, ultrasonic test and core sampling and testing were conducted. Ultrasonic scanning is a recognized non-destructive test method to assess the homogeneity and integrity of concrete. The test conforms to BS: 4408 and ASTM C: 597 and also IS: Part (1) Ultrasonic Pulse Velocity test is basically a wave propagation test and consists of transmitting ultrasonic pulses of khz frequency through a concrete medium and measuring the travel time of ultrasonic pulses for known or measured length. The length divided by time gives the velocity which can be correlated to concrete quality. Based on correlation graphs, approximate estimation of concrete compressive strength can also be made with a variation of + 20%. UPV values can also be suitably interpreted to assess qualitatively the condition of concrete with regard to homogeneity, uniformity and integrity etc. Table - IV shows the guidelines for qualitative assessment of concrete based on UPV test results. Diesel Generator (DG) Foundations Fine cracks, spalling of concretes, de-lamination of plastering Cracks in beam-column junctions, spalling of concrete cover, dislocation of re-bars, vertical cracks in column Cracks in beam-column junctions, spalling of concrete cover, dislocation of re-bars 4 Diesel Generator Foundations No visible cracks Table-IV Damage classification Moderate damage (Grade-2) Substantial to heavy damage (Grade-3) Substantial to heavy damage (Grade-3) Negligible damage (Grade-1) low. This low velocity may be due to the interface between the pre-cast beams and the pile caps. A perfect filling was made between pre-cast beams and pile caps by grouting. The obtained test data indicates that the concrete integrity and the efficiency of filling the joints by grouting were good. The foundation block was divided into well-defined grid points and the spacing was 300 mm in vertical direction and 300 mm in horizontal direction for conducting the ultrasonic test. The ultrasonic test was carried out by direct and semi direct methods of transmission. The scanning was performed by direct method in East West direction and semi direct method was adopted in South direction. The path lengths were measured for calculating the pulse velocity. It was observed from the test data that the Ultrasonic Pulse Velocity (UPV) was more than 4.00 km/sec in majority of locations and less than 4.0 km/sec in a few locations. This low velocity may be attributed because of weakness of pulses due to presence of minor voids along the path length. However, the UPV values of core samples are 4.18 km/sec and above, indicate that the concrete quality in the DG foundations is good. Jetty Pump Station Pile Caps The rehabilitated Jetty pile caps were well divided by marking grid points for conducting ultrasonic test to assess the efficiency of epoxy injection in terms of integrity with parent concrete. Ultrasonic test was conducted on six pile caps i.e. concrete holding the individual pre-cast support beams. Direct transmission method was conducted both in North- South and East-West directions for all the six pile caps. Fig.11 shows the UPV test in progress. In general, it has been observed that the Ultrasonic Pulse Velocity (UPV) was more than 4.20 km/sec and only in a few points the velocity was Fig.11 Ultrasonic test on rehabilitated jetty pile cap in progress Over Head Water Tank The column and beams junction of the over head water tank which were rehabilitated with wrapping FRP laminates followed by epoxy grouting were well divided by marking grid points. Ultrasonic test was conducted by direct transmission method. The test was conducted both in North- South and East-West directions. It has been observed that the velocity in all the locations was above 3.45 km/sec, which indicates that the concrete integrity of the rehabilitated junction was satisfactory. From the SERC experiences, it has been observed that the UPV values measured on the RCC members wrapped with FRP, varied only up to 5 % (for one or two layers). Further scanning was performed on the columns beyond the junctions and very low velocity values were observed. Epoxy grouting for the columns and also for the beams were suggested and executed. The test data on the rehabilitated locations indicates that the concrete integrity was good. Column and Beam Junctions of the DG Main Building Ultrasonic test was performed by direct transmission method. The test was conducted both in North- South and East-West directions. It has been observed that the velocity in all the locations was above 3.50km/sec, which indicates 161

testing. The cores can be tested for compressive strength. Core sampling was done from four DG foundations using 75 mm dia drill bits. Fig.

7 that the concrete integrity at this rehabilitated junction was satisfactory. Core Sampling and Testing The ultrasonic pulse velocity test gives only the indirect evidence of concrete quality whereas a more realistic assessment on concrete can be made by core sampling and testing. The cores can be tested for compressive strength. Core sampling was done from four DG foundations using 75 mm dia drill bits. Fig.12 shows the core sampling in progress. Fig.12 Core sampling from DG foundation in progress The extracted concrete core samples were dressed to the required length and capping was done by using sulphur compound. Compressive strength of the samples was obtained by standard test procedure Correction factor was applied for the individual core samples according to the direction of core extraction and also for their length / diameter ratio. Estimation of concrete core samples equal to cube compressive strength is determined according to IS Table- V indicates the physical properties of concrete core samples. From the table, it has been found that the compressive strength of the concrete varies from N/mm2 which satisfies the requirement for M 20 grade concrete used in the construction. Summary of Findings The visual inspection and documentation of the distressed structures of SPCL due to earthquake and tsuna- mi were carried out. Based on this, rehabilitation methods were selected to strengthen the structures. The repair and strengthening were carried out depending on the severity of damage, either by epoxy injection or by wrapping FRP laminates followed by epoxy grouting, or both. The condition assessment of the structures was carried out by UPV test and core sampling and testing. The conclusions arrived are as follows. - Based on visual observations, no visible cracks were noticed in all the four diesel generator foundations. - It was noticed that the UPV values in DG foundations are generally good and greater than 4.0 km/sec. - The compressive strength of core samples of DG foundations is varied from N/mm2 - The UPV values of the rehabilitated jetty pile caps are above 4.20 km/sec. - Ultrasonic test was conducted only in two levels from the rehabilitated column beam junctions of the over head water tank. The data obtained from UPV test on these two levels indicate that the concrete integrity was good. Further scanning was performed on the remaining portions of the columns and beams showing loss of integrity and epoxy grouting for all the columns in full length, and for the beams, 1.20 meter on either side of the beamcolumn junction was proposed and carried out. - The UPV values of rehabilitated column beams junctions of the main DG building indicate that the concrete integrity is good except in a few points in column beam junction. These points were re-grouted. Concluding Remarks The UPV values of the DG foundations are greater than the acceptable limits, and low velocity values were observed in a few locations, which may be due to minor voids along the path. The compressive strength of concrete core samples from the DG foundations meets the requirement of M20 grade concrete. From these values, it may be concluded that these foundations were not affected due to earthquake and tsunami. Hence, it was recommended to use these foundations for operating diesel generators. It has been observed from the UPV values that the concrete integrity of the rehabilitated jetty pile caps, column beam junctions of the over head water tank and DG main building indicate that the concrete integrity was good. 162

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