Doordarshan tower of height 300m, which consists of 255m RCC portion and 45m steel tower, is located at High power Transmitter (HPT) campus at Rameswaram. It is 1.5 km from Rameswaram railway station and 2.5 km from bus stand. This tower serves for high power transmission of 10 KW to cover a distance of 40 km as primary coverage and 150 km as secondary coverage. In addition to Doordarshan transmission, All India Radio FM transmission of 100W is also broadcast through TV tower.
- General profile of tower
2.1 RCC Tower
The shape of the RCC tower of height 255m is in the form of Frustum of a right circular cone with external diameter of 24m with wall thickness 500mm at ground level and external diameter of 6.9m with wall thickness 200mm at 247.5m level. RCC shaft of height 7.5m accommodates machine room and top capping slab for anchoring the base plate & bolts of Steel tower. At 255m level, the shaft external diameter is 6.5m with wall thickness 200mm. There are 5nos RCC cantilever platform located at 40m, 80m, 105m 210m and 247.5m level in which 40m and 210m platforms are cut platforms with 120® axis.
2.2 Steel Tower
45m height of free standing cantilever steel tower has been constructed over a RCC tower of height 255m. Base dimension of steel tower at 255m is 3.5mx3.5m (Centre to centre), 2.09mx2.09m at 276.5m and 0.79mx0.79m at 300m level. Indian Standard Angles (ISA) have been used with 200x200x20mm at the base and 130x130x12mm at top. There are two landing platforms located at 276.5m level and 300m level. The platforms are provided with 6mm thick chequered plates. Horizontal and diagonal bracings are connected to increase the stiffness and lateral stability of steel tower. Thickness and size of the splicing plates varies based on forces on the joints and strength of the plates. Steel ladders for fixing RF cable & antenna are also connected to the main member of the tower.
- Investigation of Tower
This tower was constructed in the year 1992-1995. After this construction no repair and rehabilitation including protective coating was carried out over a period of 20 years. As this tower is 0.5 km from seashore, the external surface is not only subjected to heavy wind but also exposed to corrosive nature. Rate of corrosion in Rameswaram has been identified “severe” (MMP 0.002-0.02) according to Corrosivity and Durability Maps of India. Due to Spalling, Delamination of concrete and deterioration of external surface of tower structure, investigation was carried out by Structural Engineering Research Centre (SERC) & Anna University, Chennai for RCC Portions. A team of IIT MADRAS also investigated for condition assessment of steel tower. As per the advice and recommendations of Anna University, Chennai & IIT MADRAS, the specified items got considered in preparation of the estimate for Rehabilitation and Strengthening of 300m tower work. The work was carried out by Civil Construction Wing of All India Radio & Doodarshan through lowest tenderer M/s Standard Rehabilitators Pvt Ltd, Neyveli.
- Erection of Specially Designed Suspended Moving platforms for repairing RCC portions
Specially designed four Nos. suspended moving platforms of capacity 2 tons were provided around the external surface of the RCC Tower for carrying out the repair and protective coating work. The platform moved vertically from 0 to 247.5m high and it was controlled by double motored power winch. Steel wire ropes of dia 12mm with breaking load of 92kN were used for hoisting the platforms. These wire ropes are connected through 2 nos of pulleys to the brackets made of RS Joists at 247.5m level. Ends of the RS Joists are anchored horizontally in to the shaft wall by means of special types of high strength friction grip anchor bolts. Complete assembly of moving platforms such as Lifting machine, chain, and rope was thoroughly examined and tested by Southern Engineering Corporation, Madurai and safe operation was ensured.
- Rehabilitation Techniques / Methods
5.1. Surface Preparation
5.1.1. Chipping of Loose concrete
Power driven chisel, hammer and wire brushes were used to chip off loose concrete at spalled, delaminated and damaged portions on the external surface of the RCC Tower. Concrete surface externally visible good, but making hollow sound was checked thoroughly and the entire loose and weak concrete particles were removed. The depth of patches varied from 10 mm to 60mm depending upon the damage of the surface. It was found that 80% of the patches were between 0 and 40m, 20 % of patches were between 40 and 80m. A total number of 495 patches were identified, chipped and exposed for further treatment. Above 80m, percentage of patches was considerably less.
5.1.2. Sand Blasting
The purpose of sand blasting is to clean the prepared concrete surface by removing all loose, lightly sticking and protruding materials including foreign materials, loose concrete particles, aggregates and exposed reinforcement etc. so as to provide a good bond with the applied repair material. Coarse sand was used for sand blasting operation. Air compressor of 75 HP capacity, spray gun for sand and other related accessories were used. Coarse sand was fed in to the non-tilting, non-rotating (Stationary) cylindrical hopper, which was connected to the hose pipe and it was pumped with mechanical diesel driven air compressor to the required surface to be cleaned. Sand blasting as well as air blasting operation cleaned the chipped off concrete surface and exposed reinforcement.
5.1.3. Cleaning the surface with Water Jetting
After sand blasting operation, the surface was cleaned thoroughly with water using water jetting equipment of capacity 150 bar pressure. Around 25 KL of water has been used to wet and clean the surface area of 13750 sqm.
5.2. Applying Construction Chemicals & Protective Coating
5.2.1. Applying Alkaline based Rust Converter – Sika® Rustoff 100
After sand blasting process and cleaning the surface with water, Rust converter / rust remover cum passivator was applied on reinforcement surface with brush and spraying method. Further rusting was prevented using this rust converter. Sika® Rustoff 100, a single component liquid, has been used as a rust converter.
Coverage: Generally 1 Kg of liquid covers 3 sqm area in two coats.
However depending on the diameter of reinforcements and degree of contaminations, consumption will differ. After this treatment, reinforcements were allowed to dry for 24 hours to receive further anticorrosive rebar coating (Sikadur® – 32).
5.2.2. Applying Epoxy based anticorrosive rebar coating – Sikadur® – 32
Sikadur® – 32 was used to protect the reinforcements from attack of chloride and other chemicals and further corrosion was prevented. Sikadur® – 32, solvent free, epoxy based, two components bonding agent (Part A&B). It was applied on the reinforcement by brush coating. This passivating coat provides excellent weather resistance and anticorrosive coating for steel and reinforcement.
Coverage: 110g / running metre for 10mm dia rod.
5.2.3. Applying Epoxy based Bond coat – Sikadur®-32 LP
After application of anticorrosive rebar coating, a structural bonding agent, Sikadur® – 32 LP in the form of epoxy was applied on the concrete surface. According to laboratory investigation bond strength of Sikadur®-32 LP is lower than the tensile strength at 14 days. But it enhances greater bond strength than the tensile strength of concrete. It is pre-packed in plastic container with 2 kg of part A (resin in white colour) and 1kg of part B (hardener in black colour). The colour on mixing both parts has become light grey. After mixing, smooth consistency has been ensured and applied to the prepared substrate by spraying.
Coverage: 0.3 to 0.5kg per sqm depending on substrate condition.
5.2.4. Filling the patches with Microconcrete – Sikarep microcrete-4
It is cement based pre-packed single component, factory designed pourable, chloride free, Non shrink, free flow and self compacting in specified proportion of aggregate and other chemicals. It is supplied in bags of 30 kg from manufacturer. The application was done by Guniting method. Sikarep Microcrete- 4 was deposited in to the hopper and it was conveyed through the hose to the guniting nozzle by means of Air from the compressor having a capacity of 75 HP, 1600 CFM and 11.6 kg / sq.cm pressure. A water hose of diameter 20 mm to withstand 20kg sqcm pressure was connected to the nozzle of the guniting equipment. Water and microconcrete powder ratio of 0.14-0.16 was maintained. The concrete was applied with pressure on the treated area of tower surface from 0 to 255m height. Self compaction was also achieved before being finished the surface. Thickness of concrete varied from 10 mm to 60 mm depending upon the depth of the patches and the average thickness was 18mm. Curing was done to make the surface hardened and achieve the desired strength.
Consumption: 2000kg / cum.
5.2.5. Filling the patches with Epoxy Mortar – Sikadur ®-41
Sikadur®-41 is a solvent free, three components (Part A- resin in white colour, Part B- Hardener in black colour & Part C-Sand colour powder) thixotropic mortar based on a combination of epoxy resins and selected quartz aggregate. It is used for both multipurpose repair and adhesive mortar. This is to be applied in thin layers to the damaged concrete surface by trowel. It has bonding and excellent mechanical properties.
During the process of chipping of concrete on tower surface, the depth varied from 10 mm to 60 mm. Shallow depth up to 10 mm has been finished with epoxy mortar. Where the depth exceeds more than 10 mm the damaged concrete surface treated with bond coat has been finished with microconcrete first and then followed by epoxy mortar.
Consumption: 2kg / sqm (1mm thickness)
5.2.6. Drilling of holes and epoxy Grouting – Sikadur®-52
12 mm diameter holes with 30mm deep were drilled 500mm centre to centre on the shaft surface from 0 to 255m where micro / environmental crack appeared. 10 mm diameter PVC nozzles were inserted in the 12mm diameter holes through which epoxy was injected and thereby sealed the cracks effectively and made the inner surface of concrete impervious and non porous. Low viscous Epoxy was injected using grouting tanks and Nozzle gun. After injection grouting, the nozzles were sealed using epoxy mortar. Epoxy injection grout of Sikadur®-52 was used. The advantages of this injection grout are non shrink, flowable; effective in sealing cracks, excellent bonding with almost all building material and good chemical resistant.
5.2.7. Cutting of V-Grooves and filling it with Epoxy Mortar
Where the visible cracks have been noticed at the construction joints and other locations, V-grooves of size 10mm width and 10mm deep were cut and finished with epoxy mortar along the surface of cracks.
5.2.8. Application of Concrete Penetrating Corrosion Inhibitor- Sika® FerroGard -903
Generally corrosion Inhibitors are used as admixtures in concrete or mortar. It effectively prevents rusting of embedded reinforcement. Rate of corrosion in Rameswaram (Mandapam Camp) has been identified as “severe” (MMP 0.002-0.02) and salinity is 246 mg / cum per day as per table-1(average climatic and pollution parameters at the exposed station) of Corrosivity and durability maps of india from corrosion science and engineering division, Central Electro Chemical Research Institute, Karaikudi, India.
Sika® FerroGard -903, corrosion inhibitor has been applied on the external surface of 255m RCC tower after the surface was finished with microconcrete and epoxy mortar prior to IPN Coating system. Sika® FerroGard -903 penetrates the concrete and forms a protective layer on the reinforced steel.
Consumption: 0.25 Litre / sqm
5.2.9. Interpenetrating Polymer Network coating system (IPN) on concrete surface
IPN coatings are effective surface coating for RCC structures to prevent carbonation, ingress of water and aggressive chemicals due to bad environmental conditions. It protects and makes the surface impermeable to organic and inorganic chemicals. Adhesion to concrete is excellent and it increases the life of the structure.
The entire external concrete surface of the tower was finished with priming coat, Middle coat and top coat. Each coating system consists of Part-A (resin) & Part-B (hardener). Mixing of part A and B was done in the container to get uniform consistency and it was applied on the surface by airless spraying equipment. The dry film thickness (DFT) was maintained 65-70 microns for primer, 100-110 microns for middle coat and 50-60 microns for the top coat. IPN system was procured from Krishna Conchem Products, Mumbai.
Consumption: 0.2 Litre / sqm for each coat.
- Fixing Fibre Reinforced Polymer (FRP) Handrails on platforms
Existing RCC handrails on all platforms were severely damaged due to corrosion of reinforcements which resulted in spalling of cover concrete. The damaged RCC handrails were dismantled and replaced with FRP handrails. These FRP handrails were fixed using Stainless steel anchor bolts of “Hilti” with base plates. The handrails have been provided with 65x65x5mm heavy duty vertical post, 1000mm centre to centre. Each panel has been provided with horizontal rail of high rigidity and safety and panels were interconnected. The top horizontal rails and mid rails were provided with 75x40mm and 50mm diameter respectively. The kick plate (bottom horizontal rail) was provided FRP material with omega section. Two nos. of 400mm depth FRP sheet of omega section with 3mm thickness were provided with gaps in between them.
- Dismantling of Old Steel tower of 45m height
Condition assessment of old steel tower of height 45m over RCC tower of height 255m was studied & investigated by IIT MADRAS and suggested to dismantle all the structural elements of tower except the bottom legs which were grouted in to the RCC Capping slabs of depth 1m and anchored with circular base plates using 20nos of 32mm diameter bolts for each leg. In order to avoid major disturbance to RCC capping slab, the existing bottom legs were utilized for erection of new steel tower. Accordingly entire structural elements of tower were dismantled and weighed actually. The scrap materials were taken out only after erection of new tower.
- Fabrication and erection of New steel Tower of 45m height
Fabrication and erection of steel Tower is based on approved drawing number 4267 / E / DD-5(R3). New steel tower of 45m height was constructed over RCC tower of height 255m. The material of the tower was procured from JSPL & SAIL. The entire process of fabrication, pre-erection and hot dip galvanization was done at Manali, Chennai. A tower consists of steel column at 4 corners. Each column consist of 4 nos Indian Standard Angles (ISA equal sections) placed back to back to form a built up section. ISAs were used for erection of tower with maximum size of 200x200x20mm and minimum size of 130x130x12mm. ISMCs were used for erection / construction of platforms. Two landing platforms have been provided with railing at 276.5m and 300m level. Floor of the platforms were provided with Chequred plate of 6mm thickness. Ancillary structural elements viz steel ladder, antenna fixtures, vertical cable rack/ tray, pipe strands and lightning arrestors were also connected to the tower. Additionally Aviation lights of “Binay” make was fixed on the top of the tower. All the connections of structural members were used corrosion resistant stainless steel fasteners conforming to IS 1367(Part 14, section I, II) 2002 of grade A4- 80 (Austenite group 4 and tensile strength 8000N / sqmm.
- Protective coating to Steel tower
Structural members of the tower were given Hot dip galvanization treatment. Minimum thickness of galvanisation coating was maintained above 120 microns and average mass of zinc coating on fabricated structural steel was observed above 850g / sqm as per test reports. After galvanisation treatment, structural steel members were finished with 2 coats of polyurethene paint conforming to IS 13213:1991 of DFT 70 microns over a base coat of epoxy redoxide zinc phospate primer conforming to IS 14506:1998 of DFT 110 microns.
The Managing Director: The key-man for the success of every project is the Managing Director of the Company Mr.K.Selvamani, graduated from College of Engineering, Guindy, Madras (Anna University) with Honours Degree and A fellow of Institution of Engineers and Institution Valuers and a Member of Indian Concrete Institute, Builders Association of India, Association of Licenced Engineers & Architects and American Concrete Institute.
After his early entry in M/s.Larsen & Tubro Ltd, ECC Construction group as a Planning Engineer and in a foreign construction company M/s.Eastern Ltd, in Sharjah, UAE, Baghdad at Iraq he stepped into Entrepreneurship. Having started a Firm in 1986, reconstituted the same as a Pvt.Ltd Company Standard Rehabilitators Pvt.Ltd in 2010.
On choosing the special field of ‘Repair and Rehabilitation of high-rise industrial structures’ the Company became “A LEADER” in execution of such works in almost all Government Projects all over India.
The Managing Director is always ‘enthusiastic’ in implementing ‘Innovation’ in the method / technology of execution. In recognition of his hard work he was honoured with (1) “Indian Industrial Excellence Award-2013”, (2) International Achievers Award-2013 and “Indian Business Leadership Award”.
The Director / Technical: Mr.Vignesh Selvamani, Director / Technical is a Civil Engineer and made his Master Degree in UK in the Special field of ‘Rehabilitation of Civil Structure” .
Rigidly adopting the path of his father, the Managing Director, he has become capable of executing the projects independently and proved ‘second to none’ within a very short period of 5 years.
The entire credit of having completed the above Rameswaram Project goes to Mr. Vignesh Selvamani, who handled the project independently right from the day of ‘start’ till the day of “successful delivery”. The magic behind his success was that he deployed the right persons to the right job at the right time. Being a young man of 32 he is enthusiastic in taking up more and more challenging projects.
This major and Risky Rameswaram Project was well planned and completed most efficiently and successfully by engaging the devoted team of Engineers and specially trained and highly skilled crew of Standard Rehabilitators Pvt. Ltd and by deploying sophisticated / imported equipments and plant & machinery.