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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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Maintenance and Repair Strategies
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Maintenance and Repair Strategies
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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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Maintenance and Repair Strategies
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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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Maintenance and Repair Strategies
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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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I"portance of Maintenance
• 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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I"portance of Maintenance
• 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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Maintenance and Repair Strategies
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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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Pre+enti+e "easures on +ariousaspects
• In industrial structures6steelstructures7
– *athodic protection
– Multi.la#er protecti+e coatings
– Periodic inspection
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Pre+enti+e "easures on +ariousaspects
• 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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Pre+enti+e "easures on +ariousaspects
• 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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Pre+enti+e "easures on +ariousaspects
• 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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Maintenance and Repair Strategies
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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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Maintenance and Repair Strategies
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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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Maintenance and Repair Strategies
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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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Maintenance and Repair Strategies
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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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*ore cutting and testing
• *#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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*ore cutting and testing
• (ests conducted on the core
– Strength
– Densit#
– Depth of carbonation
– *he"ical anal#sis
– =ater8gas per"eabilit#
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*ore cutting and testing
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*ore cutting and testing
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(esting (echni5uesProperty under
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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(esting (echni5uesProperty under
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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(esting (echni5uesProperty under
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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(esting (echni5uesProperty under
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