Warwanti WTP Condition Assessment Report

7/26/2019 Warwanti WTP Condition Assessment Report

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WARWANTI WATER TREATMENT PLANT

2014

Structural condition

assessment reportPREPARED !

M"S TAND#N AND ASS#$IATES

L A T % R $ I T ! M % N I $ I P A L $ # R P # R AT I # NTA L & D I S T& L AT % R ' M A ( A R A S ( T R A


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INDEX

1. Methodology of condition assessment

2. List of structures3. List of non destructive tests4. !servations". #onclusion$. %easons for distress&. Methodology of re'air(. %eferences


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1 Methodology of Condition Assessment

All the sites were visited and structures were visually inspected.

The overall structural system was studied. All visual signs of distress were studied and

noted. The crucial members were identified for non destructive testing .

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

Following distress is observed specifically

a. Structural cracksb. Corrosion cracksc. Spalling of concreted. einforcement corrosione. einforcement bucklingf. !eakage

g. "eflectionh. Structural steel corrosion and reduction in thicknessi. #oint failure in structural steel structures

$on destructive testing was carried on various members of all structures

2 List of structures

A layout plan of %arwanti %T& showing all the structures is given in anne'ure A

(verall the system is composed of

Aeration fountain

)nlet channel

Flash mi'er

C!F

filter house

&ure water sump


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The structural condition of following structures were assessed

*. Aeration fountain+. )nlet channel,. Flash -i'er. C!F. Chemical house0. Filter 1ouse2. &ure water sump

3. List of non destructive tests carried out

i) Rebound hammer test

The test is performed as per )S *,,**3part +4. )n this test the rebound number is

measured5 which is correlated to compressive strength of concrete.

Spring6driven mass strikes surface of concrete and rebound distance is given in 6

values. Surface hardness is measured and strength estimated from calibration

curves.Eui!ment details-ake67&roce89 Swit:erland

Methodology of test

&laster is removed at test locations

For testing smooth5 clean dry surface without any defect like honeycombing5 crack or

hollow sound is selected

Area of appro' ,;;',;; mm is rubbed with carborandum stone to remove loosely

adhering scales etc

)n this area points at appro'imately ,; mm apart are selected in grids


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)t operates on principle that stress wave propagation velocity is affected by 8uality of

concrete. &ulse waves are induced in materials and the time of arrival measured at

the receiving surface with a receiver. =ltrasonic pulse velocity is influenced by elastic

modulus and strength of concrete.

Methodology of test &laster is removed at test locations

For testing smooth 5clean dry surface without any defect like honeycombing5

crack or hollow sound is selected

Area of appro' ,;;',;; 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

>rease 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


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. Chemical house

The CC sections of this chemical house shows various signs of distress as porosity5

hollowness5 paint peeling5 fungus 5 loose pocket plaster5 seepage marks on walls and slab

area due to leakage from the tank. The tank top slab is showing ma@or distress .


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& Reasons for distress

All concrete in service is sub@ected to loads and attack by environmental factors. )n almost allcases penetration of water and aggressive chemicals is the primary reason for the distress."eterioration is caused by corrosion of reinforcing bars 3carbonation5 chloride ingress45sulphate attack5 and alkali silica reaction

Corrosion

(nce the water enters into the structure and the reaches reinforcement corrosion starts.

Concrete has a p1 of appro'imately *+.5 and this provides a protective environment for the

steel reinforcement because a thin film of passivating iron o'ide forms over the surface of

the steel. 1owever5 two processes lead to a breakdown of the passivating film and initiationof corrosionB

An acidic environment develops when carbon dio'ide from the air mi'es with water in the

concrete pores 3carbonation4 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 fre8uent causes of their

premature failures5 which can set in5 as early as , months depending on the surroundings.

Carbonation

Carbonation is a process in which carbon dio'ide from the atmosphere diffuses through the

porous concrete and neutrali:es the alkalinity of concrete. The carbonation process will

reduce the p1 to appro'imately or D in which the o'ide film is no longer stable. %ith

ade8uate supply of o'ygen and moisture5 corrosion will start.

The reaction of Ca 3(14 + with C(+ takes place by first forming Ca 31C(,4+ and finally

CaC(,5 the product precipitates on the walls and in crevices of the pores. This reduction in

p1 also leads to the eventual breakdown of the other hydration products5 such as the

aluminates5 C6S61 gel and sulfoaluminates.

The relative humidity with which the pore solution is in e8uilibrium greatly affects the rate of

carbonation.

Conse8uently carbonation occurs at a ma'imum rate between ; and 2; percent relative

humidity. )n addition to atmospheric conditions5 carbonation rate is also influenced by the

permeability of the concrete5 and the cement content of the concrete. Cement content ofappro'imately * percent produces a concrete relatively resistant to carbonation.


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The two most common causes of reinforcement corrosion are 3i4 locali:ed breakdown of the

passive film on the steel by chloride ions and 3ii4 general breakdown of passivity by

neutrali:ation of the concrete5 predominantly by reaction with atmospheric carbon dio'ide.

Sulphate attack6 The sulphate attack on concrete on concrete manifests itself in the form of

e'pansion5 cracking5 loss of mass and disintegration. ?'pansion and cracking is generally

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

hydration products C,A present in &ortland cement paste.

' Re!air MethodologyCement grouting

* -aterial>routing shall normally be performed with a mi'ture of neat &ortland cement and water.

(ther additives and admi'tures may be added to improve the impermeability5 strength5 etc.

on the approval of the ?ngineer. The si:e of the particles and the consistency of the grout

must be suited to the passageways it must follow. $eat grout will not flow freely into holes

smaller than about three times the largest cement particle. ?'cept in large cavities where


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thick mortar can be placed5 the sand should all pass the +6mesh sieve and have a large

portion passing the ; and the *;; mesh sieves. The proportions of (rdinary &ortland

Cement to sand will depend upon the si:e of the spaces to be filled and will vary from a neat

grout to about *B* mi'. The amount of water to be added depends upon the consistency

re8uired. >routs with as little as *0 litres of water per bag of cement could be handled and it

should seldom be necessary to use more than , to ; litres of water per bag of cement.%here necessary and approved by the ?ngineer5 admi'tures to &ortland cement grout

mi'tures may be added for delaying the setting time5 increasing flow ability5 minimi:ing

segregation and shrinkage.+ &reparationsThe surface shall be cleaned with wire brush and compressed air5 * m dia and *; to +;;

mm deep holes along the length of the cracks at a spacing of ;; mm may be drilled by wet

drilling using rotary percussion drills and nipples inserted in these holes., &roportioning5 -i'ing and ?8uipment for >routingThe cement grout shall be mechanically mi'ed using a system of power6driven paddles of

high speed centrifugal pump. The grout pump to be used shall permit close control of

pressures to allow a fle'ible rate of in@ection with minimum clogging of valves and ports.The most satisfactory e8uipment for in@ecting grout is a pump of the double6acting fle'ible

reciprocating type giving a steady flow. The grout pump shall be so placed as to reduce the

waste in cleaning lines. )t is preferable to add ; percent or more of the mi'ing water into the

mi'er before adding the dry ingredients and then the remaining water. A continuous supply of

grout is preferable to an intermittent one. Consistency of the grout may be determined by

trials starting with thin grout i.e. about ; litres of water per bag of cement and progressively

decreasing the water content to about * litres per bag of cement.%here the mi'er and pump are combined in one unit5 the dry material shall be screened

before mi'ing. )f the mi'er and pump are in separate units5 the grout shall pass through a

screen before it enters the pump. Application1ighest practical pressure within the limits *;;6;; k&a should be used in order to force the

surplus water from the grout. As the pressure may be distributed hydraulically over

considerable areas5 vigilance must be e'ercised to prevent damage or needless waste of

grout. >routing is to be done by attaching a packer 3consisting of e'pansible tube of rubber4

to the end of the grout supply pump through the holes and nipples.&ressure shall be steady to ensure a continuous flow of grout. >routing shall not be

continued till the hole consumes mi' at the rate of not less than ,; litres in +; minutes or

until refusal at the grouting pressure of ;; k&a at any hole until refusal. Should the grout

escape from an ad@acent nipple5 it should be plugged or capped. Any seam5 crack or @oint

through which grout escapes shall be caulked with epo'y mortar as soon as thick groutappears. Cleaning of ?8uipmentAfter completion of each grouting operation or temporary shutdown5 it is advisable to force

clear water through the pump until the discharge line shows no colour5 after which the pump

covers shall be removed and the valve chambers thoroughly cleaned.


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References

)S *,,** 3&art *4B *DD+5 $on6"estructive Testing of Concrete -ethods of Test5&art *5 =ltra Sound &ulse Velocity5 overnment of )ndia5 $ew "elhi5 +;;+.

)S 0 +;;; &lain and reinforced concrete6 code of practice3fourth revision4

)S *06*DD -ethod of test for strength of concrete


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Warwanti WTP Condition Assessment Report

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