DURABILITY of CONCRETE STRUCTURES - DEUkisi.deu.edu.tr/halit.yazici/DURABILITY/Part-I_(143_slides)hy.pdf · BS 7543: Guide to durability of building elements, products and component

1

DURABILITY of CONCRETE

STRUCTURES

Prof. Dr. Halit YAZICI

Part- I

2

GENERAL KNOWLEDGE

- CONCRETE STRUCTURES SHOULD CONTINUE TO PERFORM

ITS EXPECTED FUNCTIONS (STRENGTH & SERVICEABILITY)

DURING THEIR SERVICE LIFE WITHOUT MAJOR REPEATED

REPAIRS

- ARTIFICIAL CONSTRUCTION MATERIALS ARE USUALLY

UNSTABLE. THEY ARE LIABLE TO CONVERT TO THEIR

ORIGINAL FORMS.

- NATURAL MATERIALS (MILLIONS YEARS OLD) ARE MORE STABLE.

EXAMPLE: NATURAL STONE

EXAMPLE:

IRON OXIDE ENERGY

STEEL RUSTING

IRON OXIDE

3

SYMBOLS OF DURABILITY

ST. SOPHIA (ISTANBUL)

SERVICE LIFE :

537 AC COMPLETION DATE

(941 YEARS CHURCH + 422

YEARS MOSQUE & MUSEUM)

PYRAMIDS

(CHEOPS, KHEFREN,

MYKRENOS)

4500 YEARS OLD

EGYPTIAN PROVERB:

MANKIND IS AFRAID of TIME

TIME IS AFRAID of PYRAMIDS

The Pantheon, called the Temple of the Gods, is one of the greatest engineering wonders of the Roman Empire.

Built in 128 A.D. by Emperor Hadrian, the Pantheon held the world record for the largest dome diameter (43.2m) for almost 1800 years.

Romans made concrete by mixing lime and volcanic ash found in regions around the Gulf of Naples, especially from near the modern-day town of Pozzuoli.

SYMBOLS OF DURABILITY

6

GENERAL KNOWLEDGE

ARTIFICIAL STONE (CONCRETE OR REINFORCED CONCRETE)

NEGATIVE FACTORS DETERIORATION

SERVICE LIFE

PERFORMAN CE Time

Minimum

Before repair

After repair

Before repair

After repair

INITIAL

FINAL

7

BS 7543: Guide to durability of building

elements, products and component

Monumental Constructions, Bridges,

Dams, etc. 100 4

Normal Buildings, Public Buildings 50 3

Demontable Construction elements,

Prefabricated beams, columns, etc. 25 2

ENV 1991-1 = BS 7543 Minimum

service life (year) Example Class

Temporary Buildings 1-5 1

8

Relationship between durability and performance

9

Durability of concrete • Durability of concrete may be defined as the ability of concrete to resist: − weathering action, − chemical attack, and − abrasion while maintaining its desired engineering properties. • Different concretes require different degrees of durability depending on the exposure environment and properties desired. − For example, concrete exposed to tidal seawater will have different requirements than an indoor concrete floor.

10

PHYSICAL & MECHANICAL

DETERIORATION of REINFORCED CONCRETE by

EXTERNAL & INTERNAL FACTORS

CHEMICAL & BIOLOGICAL

CORROSION of REINFORCEMENT

CRACKS SPALLINGS, POP-OUTS

LOSS of STRENGTH & RIGIDITY

DEFORMATIONS

CHANGE OF PORE STRUCTURE, INCREASE in PERMEABILITY

ACCELERATION of DETERIORATION PROCESS

11

PHYSICAL & MECHANICAL FACTORS

CAUSES of MASS LOSS

CAUSES of CRACKS

WEARING, EROSION,

CAVITATION FIRE, HIGH TEMPERATURES

EXCESSIVE LOADING, REPEATED LOADING, FATIQUE LOADING, IMPACT LOADS

FREEZE-THAW, DE-ICING AGENTS, WETTING & DRYING, CHANGE of LENGTH & VOLUME

12

CHEMICAL & BIOLOGICAL FACTORS

-SULFATE ATTACK

-DEF

-THAUMASITE ATTACK

-ASR and ACR

-DELAYED REACTIONS of CaO & MgO

-CORROSION of REINFORCEMENT

I. GROUP

HYDROLYSIS, WASHING OUT

II. GROUP

IONIZATON REACTIONS WITH AGGRESSIVE CHEMICALS

III. GROUP

PRODUCTS of REACTIONS of EXPANSIVE NATURE

REPLACEMENT of Ca++ IONS with

Mg++ in CSH

REMOVAL of Ca++ IONS by

FORMATION of SOLUBLE or UNSOLUBLE PRODUCTS

13

14

PRINCIPLES of CONCRETE DESIGN

FACTORS

WORKABILITY

SLUMP, MIN. ENERGY for COMPACTION, COHESIVENESS, NO SEGREGATION, MIN. BLEEDING, HOMOGENIETY

OPTIMIZATION

PROBLEM

ECONOMY EFFECTIVE USE of SOURCES

STRENGTH CONCRETE CLASS (PROJECT)

DURABILITY IMPERMEABILITY + EXPECTED SERVICE LIFE

15

COMBINED ATTACKS

Example: Sea water effect

(Physical+Mechanical+Chemical+Biological effects)

Trigger effect of one attack over others

Mechanical Attack

Cracks

Chemical Attack

Increase in permeability

16

IN MOST CASES;

THE DIFFUSION OF WATER &/OR HARMFULL CHEMICALS &/OR GASES ARE NECESSARY FACTORS FOR CONCRETE DETERIORATION

17

DIFFUSION

PERMABILITY of CONCRETE

DURABILITY

18

19

Why durability problems? • Concrete − Hydrated Cement Phase (HCP) − Aggregate phase − Interstitial Transition Zone (ITZ) • Gel pores, Capillary pores, Air voids • Permeability and porosity • Aggressive species − Moisture, Sulphates, Chlorides, Carbon dioxide, Oxygen, Alkalies etc.

20

CEMENT

COMPLEX COMPOUNDS OF CEMENT

EARLY AGE STRENGTH

LATE & STEADY STRENGTH DEVELOPMENT

DURABILITY PROBLEMS (SULFATE ATTACK)

LOW HEAT OF HYDRATION

HYDRATION OF C3S AND C2S

TOBERMORITE

21

Influence of compound composition on properties of cement

Development of strength of

pure compounds according to

Bogue

Compound composition limits for

cements of ASTM C150

22

PERMEABILITY of CEMENT PASTE

MAJOR FACTOR PERMEABILITY

of CONCRETE PERMEABILITY of CEMENT PASTE

WATER IN

WATER OUT

Aggregate (no

pores)

Cement paste (porous nature)

23

24

PORE STRUCTURE of CEMENT PASTE

CAPILLARY PORES

GEL PORES

GEL PARTICLES CSH + CAH, etc. HYDRATED COMPONENTS + Ca(OH)2 + UNHYDRATED CEMENT + PORES.

25


Calcium silicate hydrate gel

26


27


Crytals of Ca(OH)2 CSH (W/C=0.6, 5 days curing at

24ºC)

28


Ca(OH)2

29


Hexagonal Crystal Structure of Monosulfate Hydrate & Ettringite

30


Ettringite (C3A.3CaSO4.32H2O).

31


Ettringite

32


Ettringite

33


Monosulfate (C3A.CaSO4.12H2O).

34


Thaumasite & Ettringite solid solution

35


Thaumasite

(CaSiO3.CaCO3.CaSO4.15H2O).

36

37

PORE DISTRIBUTION of CEMENT PASTE

•COMPACTION

PORES

•ENTRAINED AIR

•CAPILLARY PORES

•GEL PORES

38

39


•COMPACTION

PORES

•ENTRAINED AIR

•CAPILLARY PORES

•GEL PORES

10-

10

Effective on

Durability

Gel Pores

Capillary Pores

Entrained air

Compaction Pores

10-8

10-6

10-4

10-2

40


•COMPACTION

PORES

•ENTRAINED AIR

•CAPILLARY PORES

•GEL PORES

10-

10

Gel Pores

Capillary Pores

10-8

10-6

10-4

10-2

Effective on

Durability

Entrained air

Compaction Pores

41


•COMPACTION

PORES

•ENTRAINED AIR

•CAPILLARY PORES

•GEL PORES

10-

10

Capillary Pores

Entrained Air

10-8

10-6

10-4

10-2

Effective on

Durability

Gel Pores

Compaction Pores

42


•COMPACTION

PORES

•ENTRAINED AIR

•CAPILLARY PORES

•GEL PORES

10-

10

Compaction Pores

10-8

10-6

10-4

10-2

Effective on

Durability

Gel Pores

Entrained air

Capillary Pores

43

PERMEABILITY of CEMENT PASTE

QUANTITY DURABILITY,

APPEARANCE,

HEALTHY

ENVIRONMENT

GEL PORES: (~28% of CEMENT PASTE, (15-20 A°

DIAMETER, DIAMETER OF WATER MOLECULES)

NOT DANGEROUS

CAPILLARY PORES: (~ 0-40% of CEMENT PASTE,

INTERCONNECTED WEB TYPE of DISTRIBUTION, ~1.3 DIAMETER)

DANGEROUS

TYPE, DIAMETER (CLOSED, CONNECTED, CAPILLARY ETC.)

DISTRIBUTION

CRACKS

PERMEABILITY OF CONCRETE

Permeability is important because:

1. The penetration of some aggresive solution may result in leaching out of Ca(OH)2 which adversely affects the durability of concrete.

2. In R/C ingress of moisture of air into concrete causes corrosion of reinforcement and results in the volume expansion of steel bars, consequently causing cracks & spalling of concrete cover.

3. The moisture penetration depends on permeability & if concrete becomes saturated it is more liable to frost-action.

4. In some structural members permeability itself is of importance, such as, dams, water retaining tanks.

PERMEABILITY OF CONCRETE

The permeability of concrete is controlled by capillary pores. The permeability depends mostly on w/c, age, degree of hydration.

In general the higher the strength of cement paste, the higher is the durability & the lower is the permeability.

46

DEVELOPMENT of HYDRATION

60 ml Water

% 0 Hydration

% 50 Hydration

% 100 Hydration

40 ml Cement

3.7 ml empty capillary pores

33.5 ml Capillary water

12.0 ml Gel water

30.8 ml Solid products of

hydration

20.0 ml unhydrated

cement

Hydrated cement

7.4 ml empty capillary pores

7.0ml Capillary water

24.0 ml Gel water

61.6 ml Solid products of hydration

Hydrated cement

42.8% Hydrated cement

85.6%

47

DEVELOPMENT of HYDRATION

Free water

48

HYDRATION OF CEMENT COMPONENTS

49

HYDRATION OF CEMENT COMPONENTS

50

MATURITY of HYDRATION DEPENDENT on W/C RATIO

ALLOWABLE min. VALUE of PERMEABILITY (USA BUREAU OF RECLAMATION WORK)

1.510-11 m/s THIS VALUE MAY CHANGE UP TO 1000 TIMES!

0.40 3 DAYS 0.45 7 DAYS 0.50 14 DAYS

0.60 6 MONTHS 0.70 1 YEAR

W/C App. Age required to produce maturity at which capillaries become segmented

>0.70 IMPOSSIBLE

51

DEPTH of HYDRATION

AVERAGE DIAMETER D = 30

UNHYDRATED CEMENT PARTICLE

HYDRATED PART (HARD)

UNHYDRATED PART (SOFT)

5.2

DEPTH of HYDRATION 5.2 after 3 months

WATER

time

52

HYDRATION RATIO of PURE COMPOUNDS OF CEMENT

0.2

0.4

0.6

0.8

1.0

C4AF

C3A

C3S

C2S

1 10 100 180 0

53

COEFFICIENT of PERMEABILITY

20

40

60

120

140

0.2 0.3 0

0.4 0.6 0.5 0.7 0.8

100

80

54

Change of Coefficient of permeability with curing time

days Coefficient of permeability (m/s)

Fresh 2 x 10-6

5 4 x 10-10 6 1 x 10-10

8 4 x 10-11

13 5 x 10-12

24 1 x 10-12

Final 6 x 10-13

Water/cement : 0.70 cement paste

55

APPARATUS FOR MEASURING PERMEABILITY

Water (under pressure)

Specimen

56

57

TRANSPORT MECHANISM OF WATER INTO CONCRETE

Water adsorption of the surface

Pore surface

Water vapour

( a)

Capillary condensation

( b) Splash

water

wetting

Time

Slow Fast

drying

wetting

100

Free surfaces of solids exhibit a surplus energy (surface energy) due to a

lack of binding components to the adjacent molecules.

In cement paste pores,

this surface energy absorbs water vapour

molecules onto the surface

Rela

tive h

um

idty

of

concre

te s

urf

ace

58

59

TRANSPORT MECHANISM OF WATER INTO CONCRETE

(c)

1

3 4

2 Concret

e

1 3

4

2

(b)

Concrete

Immersed Structure

Concrete

1

3

4

2

(a) Capillary Suction

Evaporation Efflorence

1. The transportation of water by capillary suction of hydrostatic pressure

2. The leaking of water and the agressive ions within the water

3. The evaporation or leaving of water from the structure

4. The deposition of aggressive materials and crystalization

60

CONCRETE CRACKS

61

62

CONCRETE CRACKS

FORMATION OF CRACKS IN CONCRETE IS NOT A RARE CASE.

CRACKS ARE FORMED DUE TO DIFFERENT CAUSES & HAVE TYPICAL

CHARACTERISTICS .

THERE IS A TENSILE STRESS PERPENDICULAR TO

THE DIRECTION OF CRACK.

STRESS FORMS DUE TO THE RESTRAINT OF DEFORMATIONS.

63

TYPES & FORMATION of CRACKS

EARLY FROST DAMAGE

FRESH STATE PLASTIC SHRINKAGE

SHRINKAGE

SETTLEMENT CONSTRUCTURAL MOVEMENTS

EARLY STRIPPING OF FORMS

BASE SETTLEMENT

HARDENED STATE

PHYSICAL

SHRINKABLE AGGREGATES

DRYING SHRINKAGE

BLEEDING

CHEMICAL BIOLOGICAL


ALKALI-SILICA REACTION

ACID ATTACK

SULFATE ATTACK

THERMAL

FREEZING & THAWING

TEMPERATURE DIFFERENCES

EARLY TERMAL SHRINKAGE EXT.

INT.

CONSTRUCTURAL (MECHANICAL)

EXCESSIVE LOADING

CREEP

INAPPROPRIATE DESIGN SETTLEMENT OF SUPPORT

CARBONATION DEF

64

Bending Cracks

A A J

I I I

C

K

C

E

F

Rust stains

B

L

M

N

N I

I

D

D

I

H

H

G

G

Cold dilations

C

O

O

O

O

O

Relative Shrinkage craks

Relative shrinkage craks

Late, ineffective dilations

Cold dilation

s

Shear crack

Bonding cracks

K

B

Bending crack

C

G

65

FORMATION of CRACKS & TIMES

Loading, service

conditions Alkali-

Aggregate Reaction

Corrosion

Drying Shrinkage

Early thermal Shrinkage

Plastic Shrinkage

Plastic Settlement

1 hour 1 day 1 week 1

month 1 year 50 years

1 hour 1 day 1 week 1

month 1 year 50 years

66

13.3 CRACK CONTROL

Cracks that may cause corrosion or may influence the apperance of structures should not be permitted.

max 0.4 mm Normal environment, indoors

0.3 mm Normal environment,

outdoors & Humid indoors

0.2 mm Humid environment, outdoors

0.1 mm Aggressive environment,

indoors & outdoors

TS500 /FEBRUARY 2000

TYPES & FORMATION of CRACKS

67

DISADVANTAGES of SHRINKAGE:

2. FORMATION of EXTRA STRESSES IN REINFORCEMENT

SHRINKAGE CRACKS

1. FORMATION of CRACKS

HAZARDS of CRACKS • DECREASE TENSILE STRENGTH

• WITH THE EASIER INGRESS of WATER

• FREEZE-THAW RESISTANCE

• DURABILITY AGAINST CHEMICAL ATTACKS

RESTRAINMENT of SHRINKAGE DEFORMATIONS CAUSE CRACKS.

DECREASES!

68

•HYDRAULIC SHRINKAGE

TYPES OF SHRINKAGE

•THERMAL SHRINKAGE LOSS of PORE WATER

DIFFERENCE of TEMPERATURE – IMPORTANT in MASS CONCRETE

•INSTRICT SHRINKAGE REDUCTION in VOLUME DUE to HYDRATION of CEMENT

•PLASTIC SHRINKAGE BLEEDING < EVAPORATION

•CARBONATION SHRINKAGE

EVAPORATION of WATER in CHEMICAL REACTION

3Ca(OH)2+CO2 CaCO3+H2O

69

•INTERNAL EFFECTS

FACTORS THAT INFLUENCE SHRINKAGE

CHEMICAL COMPOSITION (CaO, MgO & SO3)

CEMENT DOSAGE

HEAT of HYDRATION

QUANTITY of MIXING WATER

MODULUS of ELASTICITY of AGGREGATE

•EXTERNAL EFFECTS

LOW HUMIDITY

SPEED of WIND

HIGH TEMPERATURES

70

•DESIGN DETAILS


AREA/VOLUME RATIO of STRUCTURAL ELEMENTS

V1 = V2

Eva1 < Eva2

71

•DESIGN DETAILS


AREA/VOLUME RATIO of STRUCTURAL ELEMENTS

PERCENTAGE of REINFORCEMENT

UNIFORMITY of REINFORCEMENT PLACEMENT

UNPROPER CONSTRUCTION JOINTS

F1 = F2

RIGHT WRONG

72

•MIX DESIGN

PREVENTIVE MEASURES for SHRINKAGE CRACKS

•OPTIMUM AMOUNT of CEMENT

•MINIMUM AMOUNT of MIXING WATER

•MAXIMUM AMOUNT of COARSE AGGREGATE (GOOD QUALITY)

•CEMENT MINIMUM SHRINKAGE, LOW HEAT of HYDRATION, NOT TOO FINE.

•GOOD CURING

•DESIGN DETAILS SUFFICIENT AMOUNT of REINFORCEMENT,

UNIFORM PLACING

•INCORPORATION of FIBERS ( 0.6 – 0.9 kg/m3 )

73

74

SETTLEMENT CRACKS

Main Causes:

Poor grading, too much mixing water,

unsufficient compaction,

Water & cement mortar

Before Settlement

Reinforcement

After Settlement

Cracks

Coarse aggregate

75

A

PLASTIC SETTLEMENT CRACKS

Subdivision : Over Reinforcement – Deep Sections

Causes: Excess Bleeding – Rapid early drying conditions

Remedy : Reduce bleeding (air entrainment) or revibrate

76

A

B

B


Subdivision : Arching – Top of columns



77

A

B

B

C


Subdivision : Change of depth – Trough & waffle slabs



78

SETTLEMENT CRACKS

79


80

81

CAUSE:

EVAPORATION > BLEEDING RATE

DRYING OF TOP SURFACES

Evaporation

Bleeding

PLASTIC SHRINKAGE CRACKS

BLEEDING

Bleeding is the tendency of water to rise to the surface of freshly placed concrete.

It is caused by the inability of solid constituents of the mix to hold all of the mixing water as they settle down.

A special case of segregation.

BLEEDING

Undesirable effects of bleeding are: • With the movement of water towards the top, the top

portion becomes weak & porous (high w/c). Thus the resistance of concrete to freezing-thawing decreases.

• Water rising to the surface carry fine particles of cement which weaken the top portion and form laitance. This portion is not resistant to abrasion.

• Water may accumulate under the coarse agg. and reinforcement. These large voids under the particles may lead to weak zones and reduce the bond between paste and agg. or paste and reinforcement.

BLEEDING

The tendency of concrete to bleeding depends largely on properties of cement. It is decreased by:

Increasing the fineness of cement

Increasing the rate of hydration (C3S, C3A and alkalies)

Adding pozzolans

Reducing water content

Free Shrinkage, causes volume change, but no stresses

before shrinkage After Shrinkage

Restrained Shrinkage- creates stresses, which may cause cracking

Restrained shrinkage cracking Parallel cracking perpendicular

to the direction of shrinkage

Bleeding and its control Creates problems:

poor pumpability

delays in finishing

high w/c at the top

poor bond between two layers

u causes

u lack of fines

u too much water content

u Remedies

u more fines

u adjust grading

u entrained air

u reduce water content

Causes of Plastic Shrinkage Cracking

water evaporates faster than it can reach the top surface

drying while plastic

cracking

Plastic Shrinkage Cracking-Remedies Control the wind velocity

reduce the concrete’s temperature

use ice as mixing water

increase the humidity at the surface

fogging

cover w/polyethylene

curing compound

Fiber reinforcement

Curing The time needed for the chemical reaction of portland

cement with water.

Glue is being made.

concrete after 14 days of curing has completed only 40% of its potential.

70 % at 28 days.

Curing tips water

do not let it dry

dry concrete = dead concrete, all reactions stop

can not revitalize concrete after it dries

keep temperature at a moderate level

concrete with pozzolans, fly ash requires longer curing

Temperature effects on curing The higher the temperature the faster the curing

best temperature is room temperature

strongest concrete is made at temperature around 40 F.(not practical)

If concrete freezes during the first 24 hrs., it may never be able to attain its original properties.

Temperature effects on curing real high temperatures above 120 F can cause serious damage

since cement may set too fast.

accelerated curing procedures produce strong concrete, but durability might suffer.

autoclave curing.

95


D

Subdivision : Diagonal – Roads & Slabs

Causes: Rapid early drying – Low rate of bleeding

Remedy : Improve early curing

96


D

E

Subdivision : Random – Reinforced concrete slaps

Causes: Rapid early drying – Low rate of bleeding


97

D

E

F


Subdivision : Over reinforcement – Reinforced concrete slaps

Causes: Rapid early drying – Steel near surface


98


99


100


101

EARLY THERMAL CONTRACTION

G

Subdivision : External restraint – Thick walls

Causes: Excess heat generation – Rapid cooling

Remedy : Reduce heat &/or insulate

102

EARLY THERMAL CONTRACTION

G

H

Subdivision : Internal restraint – Thick slabs

Causes: Excess temperature – Rapid cooling

Remedy : Reduce heat &/or insulate

103

LONG TERM DRYING SHRINKAGE

I

I

Subdivision : Thin Slabs (and walls)

Causes: Insufficient joints – Excess shrinkage, inefficient curing

Remedy : Reduce water content, improve curing

104

LONG TERM DRYING SHRINKAGE

Insufficient (late) joints

105

SPALLING (crazing)

J

Subdivision : Against formwork – “fair-faced” concrete

Causes: Impermeable formwork- Rich mixes, poor curing

Remedy : Improve curing & Finishing

106

SPALLING (crazing)

J

K

Subdivision : Floated concrete - Slabs

Causes: Over-trowelling - Rich mixes, poor curing

Remedy : Improve curing & Finishing

CRAZING CRACKS

Crazing (Surface cracks develop)

CRAZING PLASTER CRACKS

109


110


111

L

Rust Stains


Subdivision : Natural – Columns & Beams

Causes: Lack of cover – Poor quality concrete

Remedy : Eliminate causes listed

112

L

M


Subdivision : Calcium chloride – Precast concrete

Causes: Excess calcium chloride – Poor quality concrete


113


114


115


Electrical pillars with corrosion damage in İZMİR

116

ALKALI-AGGREGATE REACTION

N

Subdivision : Damp locations

Causes: Reactive aggregate plus high-alkali cement


117

ALKALI-AGGREGATE REACTION

118

ASR

119

ASR

120

ALKALİ-AGREGA REAKTİVİTESİ

ALKALİ-KARBONAT REAKTİVİTESİ BOZULMASI

ACR

121

DEF (DELAYED ETTRINGITE FORMATION)

122

THAUMASITE FORMATION

Swiss tunnel structures: concrete damage by formation of thaumasite (Romer vd. 2003)

123

LOADING CRACKS

PURE BENDING

PURE TENSION

124

LOADING CRACKS

TORSION

Bending

Bond Cracks

CONCENTRATED

LOAD

SHEAR

125

LOADING CRACKS

SHEAR

126

LOADING CRACKS

SETTLEMENT CRACKS

Settlement of Support

Cracks

127

DURABILITY of CONCRETE

STRUCTURES

Prof. Dr. Halit YAZICI

Part- I

Documents

DURABILITY of CONCRETE STRUCTURES - DEUkisi.deu.edu.tr/halit.yazici/DURABILITY/Part-I_(143_slides)hy.pdf · BS 7543: Guide to durability of building elements, products and component