Maintenance and Repair Strategies of buildings

8/18/2019 Maintenance and Repair Strategies of buildings

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Unit III

Maintenance and Repair Strategies

Maintenance and

Rehabilitation of Structures10 PSE E04


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Denition

• Maintenance – to keep a structure ell so that it doesn!t get

da"aged

• Repair – to restore a da"aged structure

• Retrotting – to strengthen a structure

• Rehabilitation – to return a structure to a useful state b# repair$

alteration$ and "odication


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E%a"ple for Rehabilitation

• Situation& – ' bea" has spalling of concrete

• 'nal#sis&

– (he cause of the proble" is anal#sed

• Proble"& – Spalling of concrete due to corrosion of steel

reinforce"ent)

• Solution& – *orrosion protection is "ade and then patch is

pro+ided)


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E%a"ple for Retrotting

• Situation& – ' bea" has cracks at the base

• 'nal#sis&

– (he cause of the proble" is anal#sed• Proble"&

– De,ection has occurred due to insu-cient crosssection of the bea")

–

*racks ha+e appeared due to large de,ection• Solution&

– Increase the cross.section of the bea" b# /acketing


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acets of Maintenance

1) Planned MaintenanceE%ecuted to keep the structure in useful

condition$ as scheduled at the ti"e of design ofa structure

E%a"ple& hite ashing$ cleaning$ inspection

2) Pre+enti+e MaintenanceE%ecuted to pre+ent failure hich "a# recur

ithin the life of a structureRecurring planned "aintenance

E%a"ple& cleaning$ hite ashing$ a+oidingater stagnation


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acets of Maintenance

3) Predicti+e MaintenanceE%ecuted hen "inor da"ages are noticed so

as to pre+ent their progression)

E%a"ple& routing of "inor cracks4) *orrecti+e Maintenance

–.E%ecuted hen a structure is da"aged to bringit to an acceptable standard

–.Repair orks –.E%a"ple& treat"ent for rising da"p


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I"portance of Maintenance

• (hree co"ponents of a structure&

– *i+il engineering co"ponents

– Mechanical co"ponents

– Electrical co"ponents

• 'll the co"ponents undergo ageing) (he# need "aintenance)


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• Maintenance keeps up a building!sappearance and e%tends its life

• Maintenance ensures properfunctioning and e-cienc# ofe5uip"ents ithin the structure

• Maintenance ensures the usabilit# ofa structure under hu"an acceptableconditions


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• Maintenance ensures that historicplaces ill be in a t state to behanded o+er to future generations

• Maintenance ill reduce need forrepair$ hich ill in turn reduceaste and energ#

• Maintenance is cheaper than repairor rehabilitation


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Maintenance costs at +arious ages

of a structure


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E%a"ple for i"portance of

Maintenance

• Regular inspection enables

– (i"el# identication of deterioratedbuilding ele"ents due to eathering like

loose "osaic tiles$ plaster of e%ternalalls and spalled concrete

– '+oid threatening to public safet#

–

'+oid the need of large repair orks


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Pre+enti+e "easures on +ariousaspects

• In residential structures6usuall# R*structures7

– '+oid8"ini"ise design and construction

errors – Pro+iding appropriate drainage facilities

– Periodic cleaning

– 9isual inspection – Periodic technical inspection


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• In industrial structures6steelstructures7

– *athodic protection

– Multi.la#er protecti+e coatings

– Periodic inspection


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• In h#draulic structures

– *ontrolling a5uatic eeds

– Monitoring the ater 5ualit#

– *ontrol of silt for"ation

– Sur+e#ing the solid deposition

– '+oid cracking of the lining and e+entual

eruption of concrete slabs throughproper design and construction


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• In roads

– Re"o+al of loose "aterial on thesurface

– Relling of s"all holes ith the base andsub.base "aterial

– ood drainage b# "aintaining theshoulder drains

– Prohibition of tra-c on shoulders


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• Seis"ic Strengthening 6hen seis"ic:one is upgraded7

– Modication of roofs and ,oors

– Inserting ne alls

– Strengthening e%isting alls

– Strengthening reinforced concrete

"e"bers – Strengthening of foundations


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*auses of deterioration6R* structures7

• ;ased on the properties of thestructure

– Per"eabilit#

– 9oids

– Micro cracks

– Macro cracks


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*auses of deterioration6R* structures7

• ;ased on the en+iron"ental conditions

– Penetration of ater

– Penetration of aggressi+e che"icals

– *arbonation – *hloride ingress

– Sulphate attack

–

'lkali . silica reaction – ree:e . tha e


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'ssess"ent procedure fore+aluating a da"aged structure

• *ondition sur+e# 6*P=D7

– E%a"ination of a structure of concrete for the purpose ofidentif#ing and dening area of distress

– Undertaken so as to pro+ide fruitful outco"e at opti"u"

eistor# of a pro/ect fro" its inception to co"pletion and

subse5uent life is recorded

• Periodic structural inspections are carried out basedon the folloing fre5uenc#&

– e+er# 10 #ears for buildings here at least ?0@ of its,oor area is used solel# for residential purposes

– e+er# A #ears for all other buildings

– 's per Singapore ;*'


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Bb/ecti+es of *ondition Sur+e#

• (o identif#

– *auses of distress

– Sources of distress

• (o assess – (he e%tent of distress

– (he residual strength

– Its rehabitabilit#

• (o prioritise the distressed ele"entsaccording to seriousness for repairs

• (o select and plan e


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Stages of *ondition Sur+e#

• Preli"inar# Inspection

• Planning

• 9isual Inspection

• ield and laborator# testing


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Preli"inar# Inspection

• (o assess and collect – ;ackground histor# of the distressed

structure

– Cotes and records of earlier repairs$ if an# – 'll other possible infor"ation

– Practical restrictions

–

Safet# re5uire"ents for assess"ent – 'ppro%i"ate ti"e re5uired for

assess"ent


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Planning

• Preparation of eld docu"ents – Draings

– loor plans

– =orksheets for recording data

• rouping of structural "e"bers – ;ased on position

– ;ased on e%posure

– ;ased on protecti+e nishes pro+ided

• *lassication of da"age – *os"etic repair

– Supercial repair

– Patch repair

– Principal repair

– Ma/or repair


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9isual Inspection

• ualitati+e "ethod of e+aluation ofstructural soundness

• uick scan of the structure to assess its

general state of health• Record of +isual inspection is essential for

preparation of bill of "aterials for repairite"s

• *a"era$ binoculars$ "agnif#ing glass$gauge for crack idth "easure"ent areused


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i"itations of 9isual Inspection

• Di-culties in the conduct of a +isual inspection – So"e of the "ain structural ele"ents in a building

"a# ha+e been co+ered up b# architectural nishes

• Professional /udge"ent to deter"ine hichareas should be e%posed for inspection

• Reference is "ade to structural la#out plans todeter"ine the critical structural ele"ents

•

=ithout proper /udge"ent$ the inspectionould not be e


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(esting (echni5uesProperty under

investigation

Test

Insitu concrete strength Rebound >a""er (est

Ultrasonic Pulse 9elocit#

=indsor Probe

BF8*'PB test

*ore cutting and testing

oad test


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=indsor Probe


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=indsor Probe

• Penetration resistance e5uip"ent

• unpoder actuated dri+er$ hardened allo#probe$ loaded cartridges$ depth gauge and

accessories• Dri+er res the probe into the concrete

• E%posed length of probe is "easured b#depth gauge

• Da"age "a# be caused in slender "e"bers

• Cot a


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=indsor Probe


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=indsor Probe


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=indsor Probe


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BF test


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*'PB test


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BF8*'PB test

• E5uip"ent is designed to specied geo"etr#to pro+ide results that closel# correlate toco"pressi+e strength of concrete

•

(his correlation is achie+ed b# "easuring theforce re5uired to pull a steel disc or ring$e"bedded in fresh concrete$ against a circularcounter pressure placed on the concretesurface concentric ith the disc or ring)

• or hardened concrete$ an e%pandable steelring is used


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BF8*'PB test


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• *#lindrical cores are cut b# rotar#cutting tool ith dia"ond bits

• 'ppearance of the core is recorded

• *ore is soaked in ater$ capped ith"olten sulphur to "ake its endsplane

• *ore is then tested in "oist condition


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• (ests conducted on the core

– Strength

– Densit#

– Depth of carbonation

– *he"ical anal#sis

– =ater8gas per"eabilit#


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investigation

Test

*he"ical 'ttack *arbonation test

*hloride test

Sulphate test


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*arbonation test

• 'i"& – (o deter"ine depth of concrete a indicator of concrete

• Inference&

– *hange in colour of concrete to pink indicates that the concrete is ingood health

– Co colour change indicates that concrete is a


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*hloride test

• Rapid chloride test kit G 4

– Recent co""ercial testing instru"ent

– Sa"ples are collected fro" +arious

depths6e+er# A""7 b# drilling – Podered sa"ples6about 1)Ag7 are "i%ed

ith special chloride e%traction li5uid

– Electrical potential of the li5uid is "easured

b# chloride.ion sensiti+e electrode) – ro" calibration graph$ chloride content is

deter"ined


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*orrosion prone ocations based on*he"ical 'nal#sis

6Source& I*H$ Hune 1??7

Test Results Interpolations

p> +alue *hloride content

J 11)A 9er# lo Co corrosion

J 11)A J 0)1A@ b#eight of

ce"ent

*orrosion prone

K 11)A J 0)1A@ b#eight ofce"ent

Increased risk ofcorrosion


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investigation

Test

*orrosion Potential'ssess"ent

*o+er."eter8 Profo"eter"easure"ent

>alf cell Potentio"eter

Resisti+it# Meter

Per"eabilit# 6 =ater and'ir7

* t


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*o+er "eter sur+e#6*o+er"aster L Profo"eter7

• 'i"&

– (o deter"ine e%isting co+er thickness

– (o identif# the location and dia"eter of

rebar

• Principle& – Con destructi+e pulse.induction

– Digital "ethod


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Profo"eter

I t t ti f * (hi k


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Interpretation of *o+er (hickness

Sur+e#

Test Results Interpolations

*o+erthickness

*o+er concrete5ualit#

Re5uired ood Relati+el# no

corrosion prone

Re5uired ;ad *orrosion prone

9er# less ood *orrosion prone


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>alf cell Potentio"eter

* i Ri k b > lf ll


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*orrosion Risk b# >alf cell

Potentio"eter

Half cell potentiometerreading (mV)

Probability ofcorrosion

being active*u G *uSB4Electrode

Sil+er G Sil+erchloride

electrodeK .3A0 K . 00 J ?A@

.200 to .3A0 .A00 to .00 A0@

J .200 J .A00 K A@


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Resisti+it# Measure"ent


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Resisti+it# Measure"ent

• 'i"&

– (o deter"ine the resistance of concrete

• Procedure& – Fnon current applied beteen to

outer probes 100 "" apart

– 9oltage drop beteen to inner probes

A0 "" apart is "easured andresistance +alue R in oh".c" isdeter"ined

*orrosion Risk fro"


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*orrosion Risk fro"Resisti+it#

Resistivity (ohm-cm) Corrosion ProbabilityJ 20000 Cegligible

10000 to 20000 o

A000 to 10000 >igh

K A000 9er# high

*orrosion probabilit# based on


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*orrosion probabilit# based onResisti+it# and Potential diigh intensit# corrosion Gfull# anodic

o 6highconducti+it#7

>igherpotential

gradient

>igh rate of corrosion

Modied igg Per"eabilit# test


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Modied igg Per"eabilit# test6Porosiscope.Plus7

Modied igg Per"eabilit#


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Modied igg Per"eabilit#test

• 'i"& – (o deter"ine the air or ater per"eabilit# of the surface la#er

of the concrete)

• Procedure&

– In both the air and ater per"eabilit# test$ a hole of 10 ""dia"eter is drilled 40 "" deep nor"al to the concrete surface

– ' plug is inserted into this hole to for" an airtight ca+it# in theconcrete

– In the air per"eabilit# test$ the pressure in the ca+it# isreduced to GAA kPa using a hand operated +acuu" pu"p and

the pu"p is isolated – (he ti"e for the air to per"eate through the concrete to

increase the ca+it# pressure to GA0 kPa is noted and taken asthe "easure of the air per"eabilit# of the concrete

Modied igg Per"eabilit#


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Modied igg Per"eabilit#test

– =ater per"eabilit# is "easured at a head of 100""

– ' to.a# connector is used to connect this to as#ringe and to a hori:ontal capillar# tube set 100

"" abo+e the base of the ca+it# – =ater is in/ected through the s#ringe to replace all

the air and after one "inute the s#ringe isolatedith a ater "eniscus in a suitable position

–

(he ti"e for the "eniscus to "o+e A0 "" istaken as a "easure of the ater per"eabilit# ofthe concrete


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investigation

Test

ire Da"age 'ssess"ent Di


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Di


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Di


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Di


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N.ra# Di


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investigation

Test

StructuralIntegrit#8Soundness'ssess"ent

Ultrasonic pulse +elocit#

I"pact Echo (est

Radiograph#


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Radiograph#

• 'i"& – (o deter"ine the location and si:e of reinforce"ent

– (o check for the e%istence of +oids

– (o deter"ine the areas of poor co"paction

–

(o check for +oids in grouting in prestressing ducts• Procedure&

– Photograph is taken$ shoing details of the inside of aconcrete "e"ber

– a""a ra#s used for ele"ents upto A00 "" thickness and

high energ# N.ra#s used for ele"ents "ore than A00 ""thickness

– Safet# precautions ha+e to taken against usage of ga""ara#s and N.ra#s


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*onclusion

• In "a/orit# of cases$ the causes of proble"s are bedue to

– oer co+er thickness

– Per"eable co+er concrete

– >igh chloride le+els – 'lternate etting and dr#ing

• 'll possible factors be noted during anin+estigation$ so that unusual features of theen+iron"ent or the concrete can be identied andthe necessar# solution is sought

• (he re"edial solutions "a# range fro" "ini"alpatch repair to drastic replace"ent


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• Reference & – >andbook on Repair and Rehabilitation

of R** buildings$ *P=D

Maintenance and Repair Strategies of buildings

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