Reconstruction and maintenance of concrete and

reinforced conctrete structure

Examples of desintegration of visual concrete and

corrosion of reinforcement – small thickness of cover,

low-quality of concrete (weak concrete), carbonation of

concrete

Examples of desintegration of visual concrete and

corrosion of reinforcement – small thiskness of cover,

low-quality of concrete (weak concrete)

Carbonation of concrete pH < 11 – alkaline of concrete –

increasing the possibility of corrosion of reinforcement

high moisture of environments small thiskness of cover =

drop out of cover, breaking-out and follow corrosion of

reinforcement

corrosion of reinforcement - small thiskness of cover,

in-leak

Effect of corrosion of reinforcement

moisture

Expansion of capacity of

bar by corrosion

Increased effects of adverse of environment

reinforced bar

Pressure till 30 Mpa

(cause = expansion of

capacity)

Carbonation of concrete

Plan of electrochemical

corrosion

Conta

min

ated

concr

ete

by

chlo

ride

Rough defects during realization of reinforced of column – found

during demolition of structure

Examples of disturbance

(desintegration) reinforced

elements after earthquake (Taiwan)

Examples of desintegration of visual

concrete and corrosion of reinforcement –

small thiskness of cover, low-quality of

concrete (weak concrete) Examples of desintegration

(disturbance) of concrete by agressive

material

Low-class stairs element prepare in factory

Examples of roof from finish 19th

century

Examples of using anchor elements independance on bearing reinforcement

Variations of make-up sheare reinforcement

Examples of realisation reinforcement of

older reinforced concrete structure

steel profile

sheare reinforcement

Defect of reinforcemet of reinforced conctrete structure

Reinforcement of rod elements

Transversal

reinforcement of

column from steel

profile

Diagonal brace in

place of stirrup

Bracing of opposite

vertical bar by wire

Substitution of brace by loop

Transversal reinforcement

of column circuit section

brace in column with polygon

section

Unsuitable shape of brace

Continuous roof slab

with reinforcement by

lower surface

Using bearing

reinforcement of

bracket as brace

Incorrect reinforcement of roof

slab by loop in dilatation

Large distance

of brace

Incorrect storage sheare

reinforcement

Insufficient anchorage of

reinforcement ahead support Examples of defects realisation

reinforced concrete structure

Different shape of brace use in strucrure from year 1929

Incorrect location of bearing

reinforcement

Insufficient contact of

reinforcement of column by

overlap

small thiskness of cover

Incorrect make-up

reinforcement in

frame corner

Incorrect make-up

sheare

reinforcement and

reinforcement in

dilatation

Examples of defects realisation reinforcement of older reinforced

concrete structure

Incorrect make-up

reinforcement

Incorrect anchor

logitudinal reinforcement

in block foundation

Incorrect anchor

reinforcement above

support

absent anchor

reinforcement

absent

reinforcement of

frame joint with

haunch

Failures of concrete structure

-Tension and shear cracks, branching of cracks, crushing of concrete and exfoliation of surface

layers, exfoliation of covering layers, buckling of reiforcement and failure of covering, over strain

(deformation) of structure, carbonatation, increase (expansion) of porosity, changing pH, corrosion

of reinforcement

- Technological cracks – cause concrete shrinkage

- High tepmetrature during fire – 800°C till 60 min – disturbance (destruction) of surface layer, when

the covering is min. 15 mm – no changing of load bearing capacity

- from 1000°C till 1200°C – marked (extremly) deformation, cracks and

surface desintegration to depth 30 – 50 mm

- from 1400°C and 60 min and more loss of stability and load bearing

capacity, total desintegration

- rapid cooling of surface layers of concrete by water – desintegration

of layers and large decrease of cohesion between steel and concrete

- Bending moment while rise of cracks rectangular crossection with 0,8 – 1,15% of reinforcement

running at cca 100 MPa. Rise of cracks wider than 1,5 – 2 mm show, that strain is near by yield

limit

- During rise of cracks decrease bending rigidity – increase of deformation

- Desintegration of concreate by chemically effect is manifested rise crystallic new formation or

leach part of cement stone

Failures of concrete structure

- Reduction pH under 9,6 increase dangerous of corrosin of reinforcement

- Number, length and density of cracks on bending element (beam,…) are depend on number and

way of reinforcement. Increasing of ratio of reinforcement – increasing density of cracks (smaller

width, shorter than case with smaller reinforcement)

- Slope (inclination) of crack in bending beam depend on dominant strian of crossection (shear and

normal strain)

Chracteristic failures of vertical concrete structure

Failure of tension reinforced

concrete elements

Ten

sile

cra

cks

Lar

ge

dis

tance

of

stir

rup

Ver

tica

l te

nsi

le c

rack

s

Failure of concrete and reinforced concrete centric press elements

a) Concrete elements b) Reinforced concrete elements obli

que

crac

ks

Mas

siv

e p

iers

colu

mn

Poss

ibil

ty o

f buck

ling m

ain

rein

forc

emen

t

hai

rlin

e

wra

pp

ed c

olu

mn

Svislé prvky namáhané mimostředným tlakem vertical elements subjected to excentric compression

Failure of vertical elements subjected to excentric compression

Sta

tic

pla

n

Sta

tic

pla

n

Ten

sile

cra

ck

Cru

shin

g o

f co

ncr

ete

Incorrect

location of

reinfocement

Different

qaulity of

concrete

Initiative

deflection

of

column

Tensile

crack

Crushing

of

concrete

Deterioration

and drop of

surface layer

1. start crack 2. Failure of column on failure limit

3. Lightly

reinforcement column

4. mediumly

reinforcement column 5. hardly

reinforcement column

Failure of bearing rod elements subjected to bending moment –

dependence of ratio of reimforcement

Concrete wall (press) elements - Lightly reinforcement

Rise of surface technological

cracks in massive wall

Plan of

reinforcement of

element

Part of

larger

shrinkage

Part of smaler

shrinkage

normal strain

from shrinkage

Plan of deformation

of element –

shrinkage influence

Original size

Real

deformation –

rise of cracks

(tension strain)

teoretical

deformation –

ideal plasticity

Failure of monolitic concrete

wall in middle part by hairline

Course of moisture in time

Course of primary proportional

shortening in time

Course of strain from shrinkage

Rise of cracks – cause =

shrinkage of surface layer

Interaction wall –

roof = shaer tension

Failures caused by effect of

volume change of

temperature and shrinkage –

wrong location of stiffening

construction in load bearing

system

Shrinkage of roof slab

Stiffening core Frame structure

volume change of temperature

Stiffening core, walls Reinforced

concrete

roof

column

Effect of temperature (Straining of

stiffening structure) summer

winter

Effect of shrinkage of roof structure

Straining of roof structure

Straining of

stiffening

structure

Straining of

stiffening

structure

Chracteristic failures of horizontal concrete structure

Failure by

bending moment

Failure by

sheare

Dominate

bend

Spectrum of gradient

of cracks in

dependence on

dominate straining

Failure of beam with

haunch - critical load

Dependence of direction and

characrek of cracks on load

Lightly reinforcement beam

mediumly reinforcement beam

hardly reinforcement beam

Dimension and density of cracks on bending beam –

influence of reinforcement ratio

Characteristic failure of beam slab

Lightly reinforcement slab

hardly reinforcement slab

Tensile cracks

Vie

w f

om

bas

e (l

ow

er)

Characteristic failure of two-way slab

Cracks in two-way

slab, immovable

support by 4 side

(from base

(lower))

View overhead View overhead Cracks in roof slab

by reach ultimate

strength, (from

base (lower))

A) Lift of corner

of floating slab

(deflection about

35% larger than B

B) Prevention lift of corner Ordering of reinforcement resistent on torsion

moments in corner of slab

torsion

moments

Cracks in direction main reinforcement

Tensile cracks in part of

concrete cover of two-way

slab (in part of support is

smallr shrinkage of concrete

from

bas

e (l

ow

er))

Technological cracks rise in places

and direction of main bearing

reinforcement

Cracks caused by effect of

temperature

tensile cracks (in attic) sheare cracks (in attic)

Cracks caused by shrinkage and verical load

Cracks in hardly reinforcement element caused by shrinkage

Cracks in lightly reinforcement element caused by

shrinkage

Technological cracks in beam

caused by shrinkage

Maintenance of failure surface of concret structure

Reinforcement disturbed by corrosion

Removing of failure layer of concrete

1- carbonization of concrete

2- corrosion of reinforce

High pressure water jet (HPWJ)

Repaire by technology of air-placed concrete

3- layer of failure concrete, 4-

original reinforcement, 5- basis

treated by HPWJ, 6- additing

reinforcement, 7- air-palced

concrete, 8- adhesive bridge, 9-

maintenance material, 10-

impregnation

Protection of reinforcement before

corrosion

Clean reinforcement

Reinforcement with layer of

impregnation matrial

Using adhesive bridge on

surface concrete

Local repaire of concrete

Maintenance of concrete column, pier and wall

Passive cracks – corrosion of reinforecement and speeding of degradation of concrete – water vapour penetration concrete in larger depth

– depth filling, grouting, sheathing

grouting by polymer resin using for maintenance of cracks smaller than 1 mm, else need using resin with filling mass

grouting by epoxy resin are limitation by temperature of structure and surrounding, weather, moisture of structure and time

limit for working of resim after additing of accelerator

Polymercement mortar and concrete

Maintenance mortar (strength in tension with bending till 10 MPa, strenght in pressure till 60 MPa, modulus of elasticity till 30 000

MPa)

Additing of polypropylen fiber decrease rise of technological cracks and failures of surface concrete maintenance layer by effect of

shrinkage, water and frost

Steel-fiber-reincorced concrete (increase strength in tension with bending, higher ductility, strength in pressure, decrease water

permeability and decrease resistance against rise cracks)

Repaire mortar – markendly higher cohesion with basis than normal mortar about 70 till 100 %)

Horizontal structure – additional switching by prestress free cabel

Transversal bracing concrete element

pin

Cement mortar

Angel iron strap

Strap before welding preheating from

500 till 700 °C,

After cooling on normal temperature –

steel structure prestress masonry

Cement

mortar

Strengthening of

concrete column

and wall

concrete, Air-

placed concrete

Additing main

reinforcement

Additing strrup

Additing

strengthening

reinforcement

concrete, Air-placed

concrete

reinforced concrete

prefabricated

element

Grouting (cemet,

epoxy mortar)

Strengthening

steel profile

Cemet mortar

Welding steel

column

Influence of creep for distribution normal strain in

strenghtening cocrete column

Str

ain

aft

er s

tren

gth

enin

g

Str

ain a

fter

str

ength

enin

g –

long t

ime

afte

r re

alis

atio

n

Month

Original

concrete

New

concrete

year

Month

Month

Month

year

age

of

concr

ete

Diagram of work – carbonic fiber, polyester, aramid and

glass fiber

polyester

glass aramid carbon

steel

steel

polyester glass

aramid

carbon

Tensile

strength Modulus

of

elasticity

steel

Epoxy stick

Examples of strengthening by carbonic fabric(cloth), lamella CFRP

Maintenance of horizontal and roof concrete structure

Bending beams

Welding additing

reinforcement

Extending of section and

additing of

reinforcement, water

jetting surface

Extending of section and

additing of reinforcement,

water jetting surface

Supplying of failures

part of beam by new,

reinforcement

Strengthening by

steel profile and steel

diagonal

additing stick

reinforcement

pin

pin

Anchor plate

1 - Cement mortar (grouting epoxy resin)

2 - Hole – filling by cement mortar (grouting epoxy resin)

3 - Anchor pin

Strengthening of

beam by stick

reinforcement

additing angel profile

reinforcement

maitenance of reinforced concrete slabs

Epoxy resin

Strengthening by

reinforced cocrete layer

Loop from reinforcement

Channel in lower

surface

Guarantee of cohesion

by loop in thin slab

Guarantee of

cohesion by loop in

thick slab

Guarantee of cohesion

by thorn in thick slab

pin

Guarantee of

cohesion by

loop welding by

pin

hollow, filling by cem. mortar

Steel net

concreting hollow, filling by

cem. mortar

Zesílení betonových ohýbaných prvků uhlíkovými lamelami

strengthening of concrete bending elements by carbonic lamella

"Zesílení" ohýbaných nosníků (průvlaků) dodatečným podepřením

strengthening of bending beam by additing support

1 New supports of beam

2 Prestressing cable

3 Steel loop

4 Steel crossbeam

5 Steel tie

6 secondary beam

7 secondary column