SHAHAD TEMGHAR WATER AUTHORITY THANE

2009

Structural condition assessment report

PREPARED BY

M/S TANDON AND ASSOCIATES

S T E M W A T E R A U T H O R I T Y, T M T A D M N B U I L D I N G , 1 S T F L R , O P P O U N I O N B A N K O F I N D I A W A G L E A G A R T H A N E ( W )

INDEX

1. Methodology of inspection, testing and cost estimation2. List of structures 3. List of non destructive tests carried out4. Observations5. Recommendations6. Discussion7. References8. Appendix A-Repair methods9. Appendix B-Necessity of repairs10. Appendix C-Load testing procedure

1 Methodology of Inspection, testing and cost estimation

All the sites were visited with STEM officials and experts. During these visits various structures were inspected.

The overall structural system was studied. All visual signs of distress were studied and noted. The crucial members were identified for various equipment testing.

Visual observations/distress mapping is carried out as per following procedure

1 Layouts of the structures are prepared based on available drawings or site measurements. These layouts are prepared from the point of view of identification of elements. Wherever available, photocopies of existing drawings are used

2 Following distress is documented

a. Structural cracksb. Corrosion cracksc. Spalling of concreted. Reinforcement corrosione. Reinforcement bucklingf. Leakageg. Deflectionh. Structural steel corrosion and reduction in thicknessi. Joint failure in structural steel strutures

Non destructive testing is carried out as per scheme finalised after visual observations

The cost estimates are prepared based on the measurements of repairs required. As BMC DSR is found to be realistic and covering most of the items ,it is used for costing

2 List of structures

The structural condition of following structures were assessed

Shahad intake structure - This includes the intake screen structure, Sump and Pump house, anchor blocks, transformer room, staff quarters located in the premises

1. Intake structure consists of two screens and RCC support structure with wing walls. Overall dimensions of the structure: 20x5x10mNWL (top of weir crest): 3.5MLDL: 2.5m

2. The sump/pump house structure is RCC structure with raft foundation. Sump at bottom level (+1.3): 35x10x2mWeir top level: +3.5 MtrsGround level: +11.0 MtrsLarge cantilever beams are taken from +13.5 to +17.0 level to accommodate the pump house Pump House 25x17x7.5mType of Roofing: Steel roof truss with sheeting

Gantry girder capacity: 10 ton The electrical room: 25x10m with lower stilted floor with transformer on upper floor. Type of construction: RCC structure.

3. The residential building:Type of construction: RCC frame structure Size: 10x10m with two floors. (The lower floor is stilted. On upper floor apartments are constructed)

Pipeline bridge on Ulhas riverType of Structure: Structural steel truss bridge supported on Concrete PiersSpacing of piers: 40m C/C Width of bridge: 7.5 mHeight of bridge: 3.2 m HFL of river: 12.765m Total length of bridge: 180 m

Pipeline bridge on Waldhuni NallaType of Structure: Structural steel truss bridge supported on Concrete PiersSpacing of piers: 35 m C/C Width of bridge: 7.5 mHeight of bridge: 3.2 m HTL of river: 3.25 m LTL of river: 0.125 mTotal length of bridge: 35 m

BPT for STEM in KalyanType of construction: RCC structure with 400mm thick wall with strip circular footing. Diameter of the circular tank: 45 mWater height: 6 mGround level: 23.48m. FSL is at 27.0m tank bottom RL is 21.0mWalk way: 1.5 m height along the circumference of the tank at the top

Pipeline bridge on Ulhas river near Saravali Type of Structure: Structural steel truss bridge with RCC deck slab supported on Concrete PiersSpacing of piers: 40 m C/C Width of bridge: -- mHeight of bridge: 3.2 m HFL of river: 9.5 m HTL of river: 3.6 mLTL of river: -- mTotal length of bridge: 417 mTemghar water treatment plant - This includes anchor block on inlet pipe, inlet channel, flash mixer, channels to clariflocculator, channels to filter, rapid sand filters and filter house, pure water channel, chlorine contact tank , pure water sump, pumping station, electrical substation

Pipeline bridge on Ulhas river near Anjur Type of Structure: Structural steel truss bridge supported on Concrete PiersLength of bridge: 800 m

Chairs supporting the raw water and pure water pipeline

Chair/Saddle details

Type Location Number Details

RCC Chair Raw water 125 1800mmdia line

RCC Chair Pure water 49 Pure water to thane MBR

RCC Chair Pure water 251 2mx1.5m (ht)size

RCC Chair 82 2mx1.5m (ht) size

RCC Chair 1121 Pile foundation 400 mm

Saddle UCR 1167 Rising main on 1800 mm dia

Pure water Thane MBR 657 1530 mm dia line

Expansion joints

Type Diameter Number

C1 1800 31

C1 1500 11

C1 200 39

Valve chambers

Nos 1 19

Size 2m X 2m 1.2m X 1.2m

Meter room

Size location Type of construction

4mx3m Mankoli

3mx2.7m Anjur Bridge

MBR for STEM near Mankoli

Type of Construction: RCC

Capacity: 13 ML(for Mira Bhayandar)

Size:48x48 m

Foundation: Raft

Capacity: 15 ML(for Thane)

Size:60 m diameter

Foundation: Raft

MBR for Bhiwandi

Type of Construction: RCC

Foundation: Raft type resting on made up UCR masonry platform

Bridge for Pipeline to Bhiwandi This bridge is provided for crossing the BMC pipe linesType of Structure: Structural steel truss bridge supported on Concrete Piers

Elevated Sump at PatlipadaType of construction-RCC ground resting tankSize-18.5x18.5x3m Pump room 26x7 m ht 6m- 2noMBR at Patlipada

Type of Construction: RCC elevated water tank supported on column braced at intermediate levels

Capacity: 4 ML

Size :32x32x4 m

Foundation:Raft foundation

Capacity: 5 ML

Type of Construction: RCC elevated circular water tank supported on column braced at intermediate levels

Size :44 m dia

Foundation:Raft foundation

Pipeline Bridge near Murda Type: 400 dia pipe directly spanning the nalla with support system of 2 piles with pile cap (Originally the pipe was encased in concrete for protection and strength purpose)

Pipeline Bridge near Rai

Type: 400 dia pipe directly spanning the nalla.

Supports: Laid on the culvert support of the road.

Pipeline Bridge near Morva

Type: 400 dia pipe supported by structural steel truss Type Bridge

Supports: 2 piles with pile cap.

3. List of non destructive tests carried out

i) Rebound hammer test

The test is performed as per IS 13311(part 2). In this test the rebound number is measured, which is correlated to compressive strength of concrete.

Spring-driven mass strikes surface of concrete and rebound distance is given in R-values. Surface hardness is measured and strength estimated from calibration curves.Equipment detailsMake-‘Proceq’ Switzerland

Methodology of test

Plaster is removed at test locations

For testing smooth, clean dry surface without any defect like honeycombing, crack or hollow sound is selected

Area of approx 300x300 mm is rubbed with carborandum stone to remove loosely adhering scales etc

In this area points at approximately 30 mm apart are selected in grids

By holding the rebound hammer at right angles to the surface of the concrete member 12 readings are taken at selected points

Abnormally high and low results are neglected and average of balance readings is worked out

Corrected rebound number is worked out after considering moisture, carbonation ,test location ,direction of test

Compressive strength of concrete is obtained from graph

Statistical analysis is carried out for this set of values

ii) Ultra sonic pulse velocity test

This test is performed as per 13311(part 1). In this test, the velocity of ultrasonic waves through concrete is measured, and is related to concrete quality.

It operates on principle that stress wave propagation velocity is affected by quality of concrete. Pulse waves are induced in materials and the time of arrival measured at the receiving surface with a receiver. Ultrasonic pulse velocity is influenced by elastic modulus and strength of concrete.

Methodology of test Plaster is removed at test locations For testing smooth ,clean dry surface without any defect like honeycombing, crack

or hollow sound is selected Area of approx 300x300 mm is rubbed with carborandum stone to remove loosely

adhering scales etc Two points are marked on the opposite faces of the concrete members for direct

transmission of ultrasonic pulses Grease is applied as a coupling medium to ensure proper contact of the transducers

with concrete surface so that ultrasonic pulse is transmitted through the medium without much disturbance

Both the transducers are held at correct test locations by applying constant pressure and ultrasonic pulses are transmitted through the concrete

The velocity is calculated from the readings

Following is the criteria as per IS code

Sr no Ultrasonic pulse velocity(km/sec) Concrete quality grading

1 Above 4.5 Excellent

2 3.5 to 4.5 Good

3 3 to 3.5 Medium

4 Below 3 Doubtful

iii) Carbonation test

Principle- Carbonation is one of the two main causes of corrosion of steel in concrete, the other one being chloride attack. As the result of the interaction of carbon dioxide gas in the atmosphere with the alkaline hydroxides in the concrete, the carbonation process effectively drops the pH of the concrete to a level where the steel will corrode. The carbon dioxide dissolves in water to form carbonic acid, which can migrate to the reinforcing steel if the concrete cover is low or if the concrete is of poor quality (open pore structure, low cement content, high water cement ratio, or poor curing of the concrete). Carbonation is more common in old structures, Methodology: Phenolphthalein is a type of pH indicator which will indicate the change of pH on a freshly exposed concrete surface. The indicator is simply sprayed on the surface to be checked. The indicator will change to pink in uncarbonated concrete and remain colourless when sprayed on

carbonated (low pH) concrete. If the concrete test area is very dry, a light misting with water will help show the colour.By spraying the indicator along a core drilled from the top surface down to the reinforcement bar it can be readily seen how far the carbonation has progressed and therefore the outlook for corrosion, which will only occur after carbonation reaches the reinforcement bar. Care should be taken to prevent drilling and coring dust from contaminating the surface to be tested.

iv) Profometer tests

a) Cover test- This test is performed to find out the concrete cover in structural member.

b) Rebar locator- This test is performed to find out the reinforcement dia in structural member.

c) Location of steel reinforcement in RC structures by non-destructive tests

v) Half cell potentiometer test for corrosion

Corrosion test - This test is performed to find out corrosion in steel

Ref code: ASTM C 876

Objective of test: To find out the probability of corrosion of steel inside concrete

Principle- When concrete is permeable and non uniform, atmospheric oxygen and water can penetrate up to rebars. Their varying concentrations give rise to potential cathode and anode sites in the concrete body. Electrons from anode are transferred to cathode facilitating formation of hydroxyl ions which in turn diffuse back to anode to get associated with ferrous ions there. Due to this, iron at anode gets converted to ferrous oxide and hydroxide which may be termed as corrosion products

The possibility of corrosion by above process is detected by half cell potentiometer test by measurement of e.m.f. generated in the corrosion cell which is the driving force in above reaction. For this purpose external cathode is provided in the form of copper rod and copper sulphate solution half cell. Any point on the reinforcement bar inside the concrete body functioning as anode when connected electrically to cathodic half cell generates e.m.f which is measured by connecting a milli voltmeter in the circuit. Thus the presence of corrosion process gets detected

Operation- the half cell potentiometer consists of a rigid tube which contains a copper rod immersed in a copper sulphate solution. This is connected to a voltmeter and another live wire connection comes through voltmeter to connect it to rebar. To start the experiment firstly the live wire is connected to a rebar of the test specimen and the rigid tube is put on the surface of concrete and the reading of voltmeter is taken. Reading gives the potential difference between the electrodes. From the value of the potential difference, corrosion status inside the concrete can be predicted

A sponge dipped in soap solution is used between the rigid tube and concrete surface for proper electrical contact.

Corrosion risk by half cell potentiometer

Probability of active corrosion Cu-Cuso4 electrode Silver-silver chloride electrode

>95 percent More negative than-350 mV

More negative than-700mV

50 percent -200 to -350 mV -500 to -700 mV

< 5 percent More positive than-200mV

More positive than-500mV

vi) Core test

A core of 65/95 mm dia is extracted from the structure and the compressive strength of concrete is tested.

Drilled cylindrical core is removed from structure. Tests may be performed on core to determine compressive strength

Methodology of test

The reinforcement is detected at planned location with the help of rebar locator to avoid cutting of reinforcement

The core cutting equipment is fixed at the planned location and extracted up to a length of approx 250mm maximum

The cores are transported to the laboratory and kept submerged in water for 24 hours

The cores are removed from water and cut to the required l/d ratio of 2 exactly perpendicular to the longitudinal axis. Both the ends are prepared by grinding

A thin layer of plaster of Paris is applied to ends to ensure proper contact. Now the cores are tested for compression test

Correction factor for diameter is applied

Estimation of cube strength- As per IS 516, the equivalent cube strength is calculated by the formula

Equivalent characteristic cube strength=1.25*fc*k where k=0.87+0.13*((l/d)-1)

Based on the above, formula the estimated equivalent cube strength of concrete is worked out which shall be equal or more than the acceptable value of 85 % of the characteristic compressive strength as per the acceptance criteria of IS 456

vii) Chemical test

This test is performed to find out chloride, sulphate content and pH of concrete.

Chloride content- whenever there is chloride in concrete there is increased risk of corrosion of embedded metal. The higher the chloride content, the greater the risk of corrosion

As per IS 456 the maximum total acid soluble chloride content expressed as kg/m3 of concrete shall be 0.6 for reinforced concrete

Sulphate content- the excessive amount of water soluble sulphates can cause expansion or disruption of concrete. The total water soluble sulphate content of the concrete mix, expressed as SO3, should not exceed 4 % by mass of the cement in the mix

pH of the concrete sample- the pH of freshly prepared concrete is around 12 and hence it is highly alkaline in nature. Carbonation of concrete by attack from atmospheric carbon dioxide will result in reduction of alkanity of the concrete and increase the risk of reinforcement corrosion.

viii) Ultrasonic thickness gauge test for structural steel

This test is done on structural steel members to find out the in situ thickness of the member.

This test is carried out on structural steel members of columns, beams, trusses and also on plates to measure the in situ thickness of the structural steel member

The measured thickness of the members then are compared with standard steel sections to determine whether there is any reduction in thickness of members

Methodology of test:

The area of approx 50mm x 50mm is cleaned and loosely adhering scales etc are removed using emery paper or wire brush

Grease/oil is applied as coupling medium to ensure proper contact of the transducer to the steel surface

Transducer is held at the test location by applying constant pressure and ultrasonic pulse is transmitted.

The machine displays the thickness of steel in mm in between the testing after every 20 to 25 tests ,the test is carried out on the steel plates of known thickness for calibration

4 Observations

I) Shahad intake structure – a) Shahad pumping station

Severe corrosion is observed in structural steel support system for pumps. The steel sections are very much reduced in thickness.

RCC columns are having reinforcement corrosion . at some places the concrete spalling is observed . corrosion of reinforcement is observed in columns ,beams and slabs.

b) Electrical transformer room

The terrace slab is showing signs of heavy corrosion of reinforcement

Reinforcement corrosion has occurred in slab to a large extent

The slab is showing leakages

c) Residential building

The columns, beams and slabs are showing heavy cracking and spalling of concrete.

Terrace slab is leaking and shows signs of heavy distress

All structural members are showing signs of heavy distress

There are structural cracks observed in columns, beams and slabs

Corrosion of steel is observed in all the structural members

There are leakages in the terrace slabs

The beams and slabs are showing deflections

II) Pipeline bridge on Ulhas riverMajor corrosion in bottom structural steel membersThe thickness of corroded members is reducedTruss members and connection plates are showing varying degree of corrosion

III) Pipeline bridge on Waldhuni NallaSevere corrosion is observed in bottom members. The thickness of the member is heavily

reduced.The joints are heavily corroded and the plates are reduced in thicknessAccess staircase members are severely corroded . there is complete reduction of thickness

of members. Due to heavy reduction of thickness the staircase is broken

IV) BPT for STEM in KalyanMinor structural cracks are observed in the wall of the tankReinforcement corrosion is observed in walkway slabSome concrete spalling is observed in the walk way slab

V) Pipeline bridge on Ulhas river near Saravali Corrosion is observed in bottom membersThere is some reduction in thickness of bottom membersThere is slight reduction in thickness of truss members

Some truss members and connections are lightly rusted

VI) Temghar water treatment plant – The inlet channel sides are eroded and the reinforcement is exposed. There is cracking and minor spalling in columns of channels and flash mixerLeakages are observed in channels, clarriflocculator and filter wallsHeavy distress is observed in CCT Pure water sump shows signs of major distress

VII) Pipeline bridge on Ulhas river near Anjur Bottom members of bridge are showing major corrosionTrusses and connections have varying degree of rusting

VIII) Chairs supporting the raw water and pure water pipelineChairs have varying degree of distress at various locationsUCR masonry chairs are needed to be replaced with concrete.The chairs were checked for tilting by measuring the levels and found OK

IX) MBR for STEM near Mankoli13 ML 48x48 m tank is showing heavy distress in top slab and side walls.

X) MBR for Bhiwandi The bottom slab of tank is showing severe leakagesLeakages are also observed in side wallsSome cracking is observed in top slab

XI) Bridges for Pipeline to Bhiwandi There is some corrosion in the bottom membersConnections are showing minor corrosion

XII) Elevated Sump at PatlipadaLeakages are observed in bottom slab at some locations

XIII) MBR at PatlipadaLeakages are seen from the side walls of tank

XIV) Pipeline bridge near Murda At present, the pipeline is supported on pile caps at both endsThe encasing of concrete is completely lostThe pile caps are in distressed condition

XV) Pipeline bridge near Rai At present, the pipeline is supported on pile caps at both endsThe encasing of concrete is completely lostThe pile caps are in distressed condition

XVI) Pipeline bridge near Morva The existing pipe bridge is severely corrodedThe pile caps are cracked

5 Recommendations

I) Shahad intake structure – a. Shahad pumping station:

Based on the available sizes an analysis of the structure was carried out. It is felt that the structure does not have capacity for any additional loading. Looking to the existing distress it has suffered, it is necessary to repair the structure so prevent further decay.Severe distress is observed in structural steel support system for pumps/motor which needs to be strengthened completely and coated with anticorrosive coating.RCC structure cracks shall be grouted and sealed Polymer modified mortar shall be used for replacement of lost concrete

b. Electrical transformer roomThe terrace slab is showing signs of corrosion of reinforcement. It is recommended to repair the damaged slab Cracks in beams and columns shall be repaired by groutingSpalled concrete shall be removed and repaired with polymer modified mortar.

c. Residential buildingThe columns, beams and slabs are showing heavy cracking and spalling of concreteTerrace slab is leaking and shows signs of heavy distressAll structural members are showing signs of heavy distressIt is recommended that the structure should not to be used Pipeline bridge on Ulhas river

Major corrosion is observed in bottom structural steel members. These members should be strengthened by addition of plates Truss members and connection plates are showing different stages of corrosion-Slightly corroded members may be thoroughly cleaned and strengthened if required and coated with anti corrosive coating

II) Pipeline bridge on Waldhuni Nalla

Severe corrosion is observed in many membersAccess staircase is broken. Many members are severely rusted.Considering condition of present bridge which is found to be severely distressed and major repairs strengthening is required for proper functioning of the systemIt is not recommended to use the structure for augmentation scheme.

III) BPT for STEM in Kalyan

Structural cracks in RCC members shall be grouted The spalled and loose concrete shall be replaced with Polymer modified mortar

IV) Pipeline bridge on Ulhas river near Saravali

Corrosion is observed in bottom structural steel members. These members should be replaced with suitable new members

Truss members and connection plates are showing different stages of corrosion-Slightly corroded members may be thoroughly cleaned and strengthened if required and coated with anti corrosive coating.

V) Temghar water treatment plant –

Inlet channel-

Structural cracks in RCC members shall be grouted Polymer modified mortar shall be used for replacement of spalled concrete

Flash mixerThe RCC columns of flash mixer should be encased after removal of spalled concrete and cleaning of rust of reinforcement

Channels to clarrifloculatorThe supporting columns show minor spalling which should be repaired with polymer modified mortarLeakages are observed in the side wall of the water channel which should be grouted

ClariflocculatorWalls are clariflocculator has leakages at some locations. These shall be grouted the side channel wall and bottom slab is having leakages which shall be grouted

Settled water channelColumns concrete is spalled at few locations which should be repaired with PMMThere are leakages in the side wall of channel which should be groutedFilter house and filterWalls of the filter have leakages at some locations which should be grouted. Access walkway concrete is spalled at some locations which should be repaired with polymer modified mortar

Pure water channel/chlorine contact tank/pure water sumpThe structure is in heavily distressed condition. It may not be advisable to use the structure

VI) Pipeline bridge on Ulhas river near Anjur

Corrosion is observed in bottom structural steel members. These members should be strengtherned with suitable new members/platesTruss members and connection plates are showing different stages of corrosion-Slightly corroded members may be thoroughly cleaned and strengthened if required and coated with anti corrosive coating

VII) Chairs supporting the raw water and pure water pipeline

Structural cracks in RCC members shall be grouted Polymer modified mortar shall be used for replacement of lost concreteThe UCR masonry chairs are in distressed condition and shall be completely replced with pile supports

VIII) MBR for STEM near MankoliFrom visual observations and NDT testing it is observed that the structure is heavily distressed condition. There are large cracks at some locations which are causing heavy leakages of water. The top slab has heavy distress.Considering all these aspects it is not recommended to use the structure.

IX) MBR for Bhiwandi From visual observations and NDT testing it is observed that the structure is heavily distressed condition. There are cracks in walls which are causing leakages of water. The bottom slab has leakages. Considering all these aspects it is not recommended to use the structure.

X) Bridges for Pipeline to Bhiwandi Corrosion is observed in bottom structural steel members. These members should be strengthened with suitable new members/platesTruss members and connection plates are showing different stages of corrosion-Slightly corroded members may be thoroughly cleaned and strengthened if required and coated with anti corrosive coating

Elevated Sump at Patlipada Structural cracks in RCC members shall be grouted The spalled and loose concrete shall be completely removed The surfaces shall be thoroughly cleaned and scrappedThe corroded reinforcement shall be cleaned of rust completely. If there is appreciable loss of material then new reinforcement shall be weldedThe reinforcement shall be coated with anticorrosive systemBonding coat shall be applied.Polymer modified mortar shall be used for replacement

XI) MBR at Patlipada Structural cracks in RCC members shall be grouted The spalled and loose concrete shall be completely removedThe surfaces shall be thoroughly cleaned and scrappedThe corroded reinforcement shall be cleaned of rust completely. If there is appreciable loss of material then new reinforcement shall be weldedThe reinforcement shall be coated with anticorrosive systemPolymer modified mortar shall be used for replacement

XII) Pipeline bridge near Murda

In existing condition the pipe is supported on pile caps at both endsThe encasing of concrete is completely lostThe pile caps are in distressed condition.

The pile caps should be repaired with grouting and polymer mortarIt is proposed to provide new steel box to support the pipeline

XIII) Pipeline bridge near Rai

In existing condition the pipe is supported on pile caps at both endsThe encasing of concrete is completely lostThe pile caps are in distressed conditionThe pile caps should be repaired with grouting and polymer mortarIt is proposed to provide new steel box to support the pipeline

XIV) Pipeline bridge near Morva

The existing pipe bridge is severely corrodedThe pile caps are in distressed conditionThe pile caps should be repaired with grouting and polymer mortarIt is proposed to provide new steel box to support the pipeline

All the structures shall be subjected to load testing to ascertain the strengthening achieved.

6 Discussion

Reasons for distress and control techniques -All concrete in service is subjected to loads and attack by environmental factors. In almost all cases penetration of water and aggressive chemicals is the primary reason for the distress. Deterioration is caused by corrosion of reinforcing bars (carbonation, chloride ingress), sulphate attack, and alkali silica reaction

Corrosion

Once the water enters into the structure and the reaches reinforcement – corrosion starts. Concrete

has a pH of approximately 12.5, and this provides a protective environment for the steel

reinforcement because a thin film of passivating iron oxide forms over the surface of the steel.

However, two processes lead to a breakdown of the passivating film and initiation of corrosion:

An acidic environment develops when carbon dioxide from the air mixes with water in the concrete

pores (carbonation) that removes the passivating layer.

The passivating layer can become permeable due to the presence of chloride ions that penetrate

into the concrete from marine environments and chloride in sand and aggregates.

The corrosion of reinforcements has resulted to be one of the most frequent causes of their

premature failures, which can set in, as early as 3 months depending on the surroundings.

Carbonation

Carbonation is a process in which carbon dioxide from the atmosphere diffuses through the porous

concrete and neutralizes the alkalinity of concrete. The carbonation process will reduce the pH to

approximately 8 or 9 in which the oxide film is no longer stable. With adequate supply of oxygen and

moisture, corrosion will start.

The reaction of Ca (OH) 2 with CO2 takes place by first forming Ca (HCO3)2 and finally CaCO3, the

product precipitates on the walls and in crevices of the pores. This reduction in pH also leads to the

eventual breakdown of the other hydration products, such as the aluminates, C-S-H gel and

sulfoaluminates.

The relative humidity with which the pore solution is in equilibrium greatly affects the rate of

carbonation.

Consequently carbonation occurs at a maximum rate between 50 and 70 percent relative humidity.

In addition to atmospheric conditions, carbonation rate is also influenced by the permeability of the

concrete, and the cement content of the concrete. Cement content of approximately 15 percent

produces a concrete relatively resistant to carbonation.

The two most common causes of reinforcement corrosion are (i) localized breakdown of the passive

film on the steel by chloride ions and (ii) general breakdown of passivity by neutralization of the

concrete, predominantly by reaction with atmospheric carbon dioxide.

Sulphate attack- The sulphate attack on concrete on concrete manifests itself in the form of

expansion, cracking, loss of mass and disintegration. Expansion and cracking is generally associated

with the product ettringite formed due to reaction between sulphate ions and the hydration

products C3A present in Portland cement paste.

Future precautionsCorrosion of the reinforcement steel bars is one of the main reasons for deterioration of concrete structures. In high corrosion risk areas, it is important to use a corrosion control system for long term durability and provide effective cathodic protection to the reinforcement steel in projects. This includes sacrificial coatings, sacrificial anodes, bulk anodes, etc.The selection of an appropriate cathodic protection system requires expert knowledge, and depends on the existing condition of the steel, surrounding environmental conditions, the type of structure, and the durability required. For example, very critical structures in an aggressive climatic zone require far better and robust techniques to arrest the progress of corrosion.

For improved resistance to sulphate attack a reduction in porosity is important. Addition of mineral admixtures, such as fly ash, ground blast furnace slag and silica fume is beneficial.

7 References IS 13311 (Part 1): 1992, Non-Destructive Testing of Concrete – Methods of Test, Part – 1,

Ultra Sound Pulse Velocity, Bureau of India Standards.

IS 13311 (Part 2): 1992, Non-Destructive Testing of Concrete – Methods of Test, Part – 2, Rebound Hammer, Bureau of India Standards.

CPWD Handbook on Repair and Rehabilitation of RCC Structures, Central Public Works Department (CPWD), Government of India, New Delhi, 2002.

IS 456 –2000 Plain and reinforced concrete- code of practice(fourth revision)

IS 516-1959 –Method of test for strength of concrete

8 Appendix A-Repair methods

There are various of strengthening and repairs . A brief description of various methods is as follows

Polymer modified mortar-used for old hardened concrete for repairing defects on exposed concrete surface only. For large repair areas with thickness more than 50 mm it is desirable to use appropriate reinforcing mesh fixed with U nails.

Epoxy mortar-These mortars consist of resing ,hardener and silica sand and are applied over an epoxy bonding coat. These mortars attain strength in few hours.They have very high strength and abrasion resistance, water resistance and can be used in few milimeter thick overlays

Shot crete-it is pneumatically applied concrete or mortar placed directly on to a surface. If required reinforcing mesh is used.

Plate bonding –MS plates and connected to the concrete sections by using epoxy adhesives. Bolts used for holding the plates in position also act as shear connectors.

RCC Jacketing- reinforced concrete jacket increased the member size. It increases the member stiffness.

Fibre wrap technique-Woven fabric pre-soaked in specially formulated epoxy and applied over prepared surface after application of epoxy primer.

Crack filling with cement grout-cracks in concrete members are grouted using cementitious grouts by pumping

Crack filling with epoxy grout-small structural cracks in concrete are grouted by pumping epoxy in to the crack.

Preplaced aggregate concrete-It is concrete made by forcing grout into the mass of aggregate densely prepacked.

Dry packing –It consists of cement and sand (1:2.5) with just enough water to be able to form a ball by hand. It is immediately packed into place, before bond coat has dried ,and shaped by hammer

Foundation rehabilitation-It is done by shoring the underpinning the work . piles , micropiles or jacked pile are used for strengthening. Injection with cement or chemicals to strengthen the surrounding soils may be done.

Cathodic protection-It is provided by having a sacrificial anode to protect the steel .

9 Appendix B -Necessity of strengtheningIt is recommended to do the strengthening of the civil structures

Load test of structure pre and post strengthening is recommended

Post strengthening the life of the structures will be 7-10 years with normal routine maintenance .

It is suggested to do structural audit yearly and based on it required maintenance should be done. This will he helpful in further enhancement of life of structures

There are two typical categories

Structures in highly distressed condition structures showing progressive deterioration

1) Highly distressed structures-There are structures which are showing heavy distress and may lead to failure. This may lead to disruption of normal functioning of the system leading to emergency.

Some of the structures which seem to be in very critical condition are as follows

Shahad pumping station – The steel support structure on which pumps are erected is in highly corroded condition.

The thickness of steel members is greatly reduced. The strength of supporting system for pumps is greatly reduced.

This may lead to failure of support system of collapse of the pumps. This will lead to stoppage of the pumping and emergency repairs will have to be taken for restoration of raw water pumping

Waldhuni pipe line bridge-

Access staircase is already collapsed

There is heavy corrosion in all members of the bridge. The thickness of the members is greatly reduced.

If not immediately attended, there may be partial or complete failure of the bridge which may lead to failure of the raw water pipeline causing disruption in supply of raw water to the treatment plant at Temghar

Mankoli MBR-

It is not being filled to full level because of heavy leakages and hence, full capacity is not utilised. There is heavy distress in side walls.

There are chances of side wall failure which may cause the MBR to be non-functional.

Bhiwandi MBR-

It is showing leakages from bottom slab. There is heavy distress in side walls. The top slab of MBR is showing signs of distress.

There are chances of side wall failure which may cause the MBR to be non-functional.

The leakages at bottom may cause instability of the stone masonry platform foundation leading to total failure of tank and its foundation

Bridges at Morva, Rai, Murda

At all these locations, the pipe was simply spanned across nalla. The pipe was encased in concrete. In the present situation, the encasing is completely lost. The bridge is in very dilapidated condition. The failure of supporting structure will result in disruption of pure water supply to MBMC.

Temghar water treatment plant

Chlorine contact tank and pure water sump are in heavily distressed condition. The top slab of CCT has already started collapsing. There can be major accident and disruption of water supply if the matter is not attended immediately

2) Structures showing progressive deterioration-Other structures like Ulhas Bridge, Saravali, Anjur and Bhiwandi bridges have signs of partial distress but showing signs of progressive deterioration due to corrosion. If not attended immediately, they may become highly distressed.

The roof slab of transformer room at Shahad is having leakages and corrosion of reinforcement is observed. If not attended, it may lead to increased leakage over electrical transformers, which is risky. Increased corrosion of reinforcement may also lead to collapse of slab.

Flash mixer columns for monorail and connection beams are showing corrosion cracks and if unattended may lead to disruption of functioning of the mixer

Chairs supporting the pipe line are in varying degree of distress. If kept unattended, there is chance of failure leading to damage to pipeline.

10 Appendix C-Load Test Procedures

All the structures shall be subjected to load testing to ascertain the strengthening achieved. A brief guideline is given below .

Load test report should contain the following information

Table of Contents Introduction Description of Structure Instrumentation Procedures Load Test Procedures Preliminary Investigation of Test Results Modeling, Analysis, and Data Correlation Results Conclusions and Recommendations References

IntroductionInformation in brief about the structureDescription of StructureLocation Structure Type Span Length(s) Skew if anyRoadway/Structure Widths Connections Stringer Deck type Abutments bearings. .Structural materials.Comments Instrumentation ProceduresThe primary goal of the instrumentation plan is to measure the live-loadresponse behavior of the main truss members and to determine the load distributioncharacteristics of the floor system. Based on the construction details of the superstructure obtain the stiffness parameters. Evaluation of these parameters is necessary to accurately assess the load effect on each component due to an applied load condition.

Load Test MethodDescription of the vehicle including the load, positions of load, no of lanes, path of travel etc shall be givenPreliminary Investigation of Test ResultsA visual examination of the field data shall be performed to assess the quality ofthe data and to make a qualitative assessment of the bridge’s live-load response.Modeling, Analysis, and Data Correlation

A 3 D finite element model of superstructure should be defined based on realistic conditions of site. Loading of the model should be of test vehicle. Comparision of computed and measured strains shall be made. Various stiffness terms shall be modified through a parameter identification process until best fit correlation the measured and computed strain is obtained. This way the model is calibrated to the field measurements and further evaluation is done.

Dynamic Load testing of Bridges

1. IntroductionDynamic load testing is an important part of the acceptance process for new bridges complement to static load tests, dynamic tests yield useful information about the actual behavior of the bridgeunder traffic. This information is usually difficult to obtain analytically, because of the complexity of the actual structure. The effect of pavement deterioration on the dynamic response of the bridge is of particular importance for the management of the structure. This information can be easily and realistically obtained from a dynamic test, and thereafter used by the highway authorities to organize the pavement maintenance.

2. Dynamic Load TestingThe purpose of the dynamic load test is to determine the controlling parameters of the dynamic behavior of the bridges. The main dynamic characteristics of the structure are the fundamental vibration frequency, the dynamic amplification factor and the logarithmic decrement. These properties are usually not analyzed in detail in the design phase of small and middle sized structures. Some parameters, such as the logarithmic decrement or the dynamic amplification factor, can only be roughly estimated at the time of the design. However, these quantities are relatively easy to obtain experimentally, and can give valuable information for the exploitation and maintenance of the bridge.

3. MethodologyDynamic load testing is performed by exciting the vibration of the bridge and by measuring its properties after the excitation has ceased. Several methods are available for the excitation of the bridge, in particular: eccentric rotating masses, impact of a heavy weight and passage of a loaded truck. This last method is often preferred for the dynamic load testing of bridges because it gives, along with reasonably accurate values of the above mentioned quantities, a good approximation of the effect of the actual traffic on the structure. By varying the speed of the truck on the bridge, the full range of traffic speeds can be investigated. Furthermore, this method is easily implemented while some of the other ones necessitate more complicated installation procedures. The measurements are taken and recorded by a dynamic data acquisition system with integrated Fast-Fourier Transform (FFT) analyzer, allowing an immediate interpretation of the results during the test. Absolutedisplacement sensors are used for the measurements, and therefore only components with a relatively high frequency (larger than 0.2 Hz) are recorded. The static influence line of the truck passing on the bridge is then added to obtain the complete dynamic influence line.

4. ResultsBecause a lot of information is gathered in the course of dynamic load testing, the results are usually presented graphically. First, the dynamic influence line of the bridge subjected to the passage of atruck is drawn for all travel speeds, with and without plank. This allows a simple visual determination of the dynamic amplification factor . The natural frequency of the bridge is obtained from acceleration spectra performed by the FFT analyzer. The logarithmic decrement is obtained from the

decay of the bridge free oscillations, after the truck has left the bridge, or at least when it is far enough from the instruments.For testing of bridges following code should be followed-Guidelines for Load Testing of Bridges (IRC:SP-51) Author : Indian Roads Congress (IRC), Ministry of Road Transport & Highways (MORTH, formerly MOST)

Strain gauges for strain measurement during load testing

Strain is the amount of deformation of a body due to an applied force. More specifically, strain (e) is defined as the fractional change in length.

Definition of Strain

Strain can be positive (tensile) or negative (compressive). Although dimensionless, strain is sometimes expressed in units such as in/in or mm/mm. In practice, the magnitude of measured strain is very small. Therefore, strain is often expressed as microstrain ( ), which is E x 10-6.

When you strain a bar with a uniaxial force, as depicted in the figure defining strain gauge above, a phenomenon known as Poisson strain causes the girth of the bar, D, to contract in the transverse, or perpendicular, direction. The magnitude of this transverse contraction is a material property indicated by its Poisson's ratio. The Poisson's ratio (v) of a material is defined as the negative ratio of the strain in the transverse direction (perpendicular to the force) to the strain in the axial direction (parallel to the force), or . For example, Poisson's ratio for steel ranges from 0.25 to 0.3. The Strain GaugeWhile there are several methods of measuring strain, the most common is with a strain gauge. A strain gauge's electrical resistance varies in proportion to the amount of strain placed on it. The most widely used gauge is the bonded metallic strain gauge.

The metallic strain gauge consists of a very fine wire or, more commonly, metallic foil arranged in a grid pattern. The grid pattern maximizes the amount of metallic wire or foil subject to strain in the parallel direction (shown as the "active grid length" in the Bonded Metallic Strain Gauge figure). The cross sectional area of the grid is minimized to reduce the effect of shear strain and Poisson strain.

Bonded Metallic Strain Guage

It is very important to properly mount the strain gauge onto the test specimen. This ensures the strain accurately transfers from the test specimen through the adhesive and strain gauge backing to the foil. A fundamental parameter of the strain gauge is its sensitivity to strain, expressed quantitatively as

the gauge factor (GF). Gauge factor is the ratio of fractional change in electrical resistance to the fractional change in length (strain):

The gauge factor for metallic strain gauges is typically around two.

Ideally, the resistance of the strain gauge would change only in response to applied strain. However, strain gauge material, as well as the specimen material to which the gage is attached, will also respond to changes in temperature. Strain gauge manufacturers attempt to minimize sensitivity to temperature by processing the gauge material to compensate for the thermal expansion of the specimen material intended for the gauge. While compensated gauges reduce the thermal sensitivity, they do not remove it completely. For example, consider a gauge compensated for aluminum that has a temperature coefficient of 23 ppm/°C. With a nominal resistance of 1000 GF = 2, the equivalent strain error is still 11.5 /°C. Therefore, additional temperature compensation is important.

Measuring Strain

In practice, the strain measurements rarely involve quantities larger than a few millistrain ( x 10-3). Therefore, measuring strain requires accurate measurement of very small changes in resistance. For example, suppose a test specimen undergoes a substantial strain of 500 . A strain gauge with a gauge factor GF = 2 will exhibit a change in electrical resistance of only 2·(500 x 10-6) = 0.1%. For a 120 gauge, this is a change of only 0.12 .

Quarter-Bridge Circut

Alternatively, you can double the sensitivity of the bridge to strain by making both gauges active, although in different directions. For example, the Half-Bridge Circuit figure illustrates a bending beam application with one bridge mounted in tension (RG + R) and the other mounted in compression (RG - R). This half-bridge configurati

on, whose circuit diagram is also illustrated in the Half-Bridge Circuit figure, yields an output voltage that is linear and approximately double that of the quarter-bridge circuit.

Half-Bridge Circuit

Finally, you can further increase the sensitivity of the circuit by making all four of the arms of the bridge active strain gauges and mounting two gauges in tension and two gauges in compression. The full-bridge circuit is shown in the Full-Bridge Circuit figure below.

Full-Bridge Circuit

The equations given here for the Wheatstone bridge circuits assume an initially balanced bridge that generates zero output when you do not apply strain. In practice however, resistance tolerances and strain induced by gauge application will generate some initial offset voltage. This initial offset voltage is typically handled in two ways. First, you can use a special offset-nulling, or balancing, circuit to adjust the resistance in the bridge to rebalance the bridge to zero output. Alternatively, you can measure the initial unstrained output of the circuit and compensate in software.

With this in mind, there are several types of commonly measured strain (in order of relative popularity):

Bending Strain -- resulting from a linear force (FV) exerted in the vertical direction.

Axial Strain -- resulting from a linear force (Fa) exerted in the horizontal direction.

Shear Strain -- resulting from a linear force (FS) with components in both the vertical and horizontal direction.

Torsional Strain -- resulting from a circular force (FT) with components in both the vertical and horizontal direction.

Choosing the Right Type of Strain Gauge

The two primary criteria for selecting the right type of strain gauge are sensitivity and precision. In general, if you use more strain gauges, (a full-bridge circuit rather than a quarter-bridge) your measurement will respond more quickly and be more precise. On the other hand, cost will also play a large part in determining the type of strain gauge you select. Typically, full-bridge strain gauges are significantly more expensive than half-bridge and quarter-bridge gauges. For a summary of the various types of strain and strain gauges, please refer to the Strain Gauge Summary table below.