lecture1 21092011 introduction2011 slides

7/23/2019 Lecture1 21092011 Introduction2011 Slides

1/29

1

1

Shrinkage and Cracking of Concrete:

Mechanisms and Impact on Durability

Bauingenieurwissenschaften Master

Vertiefung in Werkstoffe und Mechanik

21.09-14.12.2011

every Wednesday 10:00-12:00

3 ECTS points

Lecturers: Prof. Dr. Pietro Lura

Dr. Mateusz Wyrzykowski Berlin, Holocaust memorial

Lecture 1

Introduction to the course

Pietro Lura

Concrete & Construction Chemistry

Shrinkage and Cracking of Concrete: Mechanisms and Impact on Durability, ETHZ, fall 2011


2/29

2

3

Welcome

Welcome

This series of lectures, reading assignments, and afinal exam constitute a 3 ECTS points course

Participating students receive a DVD with lectures(ppt and movies) of REACCT, a course with similar

topic held in 2008 at Purdue University

4

Reducing Early-age Cracking ofConcrete Today (REACCT 08)

July 28-29 2008, PurdueUniversity, IN, US

Graduate course (~30students), series of 16*50minute lectures

Instructors Jason Weiss, Dale Bentz and Pietro Lura

All lectures were filmed


3/29

3

5

REACCT 09

13 July 2009, Empa,Dbendorf, Switzerland

International PhD Course, 2.5ECTS points, 41 participants,18*50 minute lectures

Instructors Karen Scrivener,Hans Herrmann, Jason Weiss

and Pietro Lura

6

Contents

Instructor and students

Basics of cement and concrete

Basics of cracking

Course contents

Exam


4/29

4

7

About myself

MSc Civ.Eng., Univ. Brescia, Italy, 1992-1998

(Final Project, NTNU, Norway, 1997)

PhD, Delft Univ., The Netherlands, 1999-2003

Assistant Professor, DTU, Denmark, 2003-2006

Patent examiner, EPO, Germany, 2006-2008

Head of Lab, Empa, Switzerland, from 2008

NIST, Maryland, USA, 2002

Purdue University, Indiana, USA, 2005TU Kaiserslautern, Germany, 2006

610-3 km/h

8

Empa is an interdisciplinary researchand services institution for materialsciences and technologydevelopment within the ETH domainin Switzerland

About 30 research laboratories,900 employees

Concrete / Construction Chemistry

Laboratory, 25 people


5/29

5

9

Concrete & Construction Chemistry Laboratory

1E-3 0.01 0.1 1 10 100 1000

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

Na2SO

4

solution

unaffected

core

hydrotalcite

gypsum

ettringite

monocarbonate

portlandite

calcite

unhyd. clinker

C-S-Hvolume(cm

3/100gcement)

ml Na2SO

4solution added /cm

3hydrated mortar

10

My main research interests

Pietro Lura

(roar!)

AUTOGENOUS

SHRINKAGE

Early-age concrete properties

Plastic shrinkage

Autogenous shrinkage

Internal curing

Thermal dilation Cracking and microcracking


6/29

6

11

Mateusz Wyrzykowski

MSc Civ.Eng., Tech. Univ. of Lodz, Poland, 2000-2005

MSc Thesis at Univ of Padua, Italy, 2005

Software Engineer, Robobat/Autodesk Poland, 2005-2010

PhD, Tech. Univ. of Lodz, Poland 2005-2010

Postdoc researcher, Empa, Switzerland, from 2010

Main research interests:

Modelling phenomena in maturing concrete (early age, transport, shrinkage)

Early age concrete (autogenous shrinkage, properties evolution)

Curing of conrete

Thermal dilation

12

And what about you?

What is your background?

What are your interests?

Why do you follow this course?

What do you expect to learn?


7/29

7

13

Concrete

Sunniberg bridge, photo by M. Romer

14

What is concrete?

Concrete is a heterogeneous system of solid, discrete, gradientlysized, inorganic mineral aggregates, usually plutonic (feldspatho-silicaceous or ferro-magnesian) or sedimentary-calcareous inorigins, embedded in a matrix compound of synthesized poly-basic alkaline and alkaloidal silicates held in aqueous solution andco-precipitate dispersion with other amphoteric oxides, this matrix

being originally capable of progressive dissolution, hydration,reprecipitation, gelation and solidification through a continuousand coexistent series of crystalline, amorphous, colloidal andcryptocrystalline states and ultimately subject tothermoallotriomorphic alteration, the system when first conjoinedbeing transiently plastic during which state it is impressed to a pre-determined form into which it finally consolidates, thus providing astructure relatively impermeable and with useful capacity totransmit tensile, compressive and shear stresses.

Source: Portland Cement Association- http://www.cement.org


8/29

8

15

Definitions

Cement Aggregate Water

+ +

Fresh concreteHardened concrete

Mortar:Max aggregate size 4 mm

Concrete:Max aggregate size 8 mm

= Binder

Winnefeld 2008

16

Importance for the economy

Data for Switzerland:

Cement production 2006 (source: cemsuisse1): 4.2 Mt

Cement import 0.8 Mt

3 cement producers with 7 plants (Holcim, Vigier, Jura)

Market volume of aggregates (source: FSKB2):30 millions m3

Own production aggregates: 90%

Concrete production 2006 (source: FSKB): ca. 20 Mt

Own production concrete: 95%

1. Association of the Swiss Cement Industry

2. Fachverband der Schweizerischen Kies- und Betonindustrie Winnefeld 2008


9/29

9

17

A versatile building material

18

and the most used one

10 km3 of concreteor at least 1.5 m3/ personevery year

~3 Gt Portland cement

produced, causing 5% ofman-made CO2 emissions

(1 t Cement 0.75 t CO2)

Raw materials for cement andaggregate production


10/29

10

19

Sustainability

Durable and densesystems

Cement substitution,alternative binders

Challenges for the future

20

Concretes bad image

Cracks facilitate transport ofharmful substances

Durability of concrete is reduced

Repair needed, often repairof repair

Costs of repair often exceedcosts of original structure


11/29

11

21

Cracks from alkali-aggregate reaction (1)

Some types ofaggregates react withthe alkaline poresolution in concrete

(may take years)

A silica-rich gel is

formed within theaggregates

The aggregates

expand and causeconcrete crackingPictures by A. Leemann

22

Cracks from alkali-aggregate reaction (2)

Pictures by J.-G. Hammerschlag


12/29

12

23

Cracks from sulfate attack

Sulfate-containingwater reacts withaluminate phases incement paste to

produce ettringite

Production of

ettringite causesexpansion andcracking within thecement paste

Pictures by A. Leemann

24

Consequences of cracking - steel corrosion

Cracks are preferredpathways forcarbonation andwater and chlorideions ingress

Steel bars corrodeand the corrosionproducts expand

Expansion causescracking and more

corrosionPicture by R. Loser

Picture from www.cowi.com


13/29

13

25

Consequences of cracking concrete corrosion

HCl solutions are used toprepare metal surfaces ingalvanic plants

HCl solution penetratesthe pre-existing shrinkagecracks and cause deep

corrosion of the concrete

Cracks are enlarged bycorrosion and more HCl

penetrates

Pictures by R. Loser

26

Are all cracks bad?

Cracks are essentialto reinforced concrete

Without cracks,tensile stresses

cannot be transferredto reinforcing bars

Flexural cracks areneeded, but theirwidth needs to becontrolled by design

Giuriani et al. J Struct Eng 1991


14/29

14

27

Hardening of concrete

Hollywood, California, 1953

Plastic phase Setting Hard concrete

28

Solid suspension

Cryo-nanotomography Zingg et al. CCR 2008


15/29

15

29

Setting and hardening process

Ye, Lura, van Breugel and Fraaij CCC 2004

Suspension Threshold of solid percolation Solids fully connected

30

Early-age cracks in concrete

Weiss 2009, after British Cracking Manual


16/29

16

31

Joints vs. random cracking in concrete slabs

Bill Palmerwww.concretenetwork.com/blogs/bill-palmer/2007/07/cracking-up.html

There are only two kinds ofconcrete - concrete thats alreadycracked and concrete thats about

to crack.

32

Early-age cracks in concrete (1)

Photos by A. Leemann, 2008Plastic shrinkage cracking


17/29

17

33


Photohttp://w

ww.aggregateresearch.com/caf/file/newdeckcracking.p

df

Drying shrinkage cracks, approach to a bridge (pilot project with HPC)

34


Photo by R. Loser, 2008

Drying shrinkage cracks, top layer on old concrete


18/29

18

35


Photo by R. Loser, 2009

Drying shrinkage cracks above a door

36


Tokyo Institute of Technology, 2003

Photo by O.M. JensenThermal cracking


19/29

19

37

What causes cracking?

Weiss 1999Cracking

Unrestrainedlength change

Initial length

Restraintstress

38

Stress development (1)

( ) ( )

( ) ( )

SHRdE

d

td +=,

Initial Specimen

Shrinkage Effect

Restraint Effect

0 7 14 21 28

Age of Specimen (Days)

0

4

8

12

Stress BasedOn Hookes Law

Stress In

Specimen

CalculatedTensileStress(MPa)

0 7 14 21 28


0

4

8

12



Weiss 1999


20/29

20

39

Stress development (2)

Creep/Cracking Effect

Stress Relaxation

( ) ( )

( ) ( ) ( )

( )

++=

28

,,

E

tdd

E

dtd

SHR

StressRelaxation( )

( )

( ) ( )

SHRd

E

dtd +=,

Initial Specimen

Shrinkage Effect

Restraint Effect

0 7 14 21 28


0

4

8

12


Stress In

Specimen

Calcu

latedTensileStress(MPa)

0 7 14 21 28


0

4

8

12


Calcu

latedTensileStress(MPa)

Final Stress State

Stress In

Specimen

Weiss 1999

40

Cracking conditions

Stress that develops tomaintain constant length

Weiss 1999Age

Material Resistancei.e., Strength

Age ofCracking

StressLevel


21/29

21

41

Common attempts to reduce shrinkage cracking

Weiss 1999

Material resistance

i.e., strength

Age ofcracking

Age

Stresslevel

( ) ( )

( ) ( )

SHRd

E

dtd +=,

Initial Specimen

Shrinkage Effect

Restraint Effect

42

0

10

20

30

40

50

60

70

0 24 48 72 96 120 144 168 1 92 216 240

Time [h]

Temperature[oC]

=TT

Example - Thermal cracking

Lura and van Breugel 2001

-4

-2

0

2

4

6

8

0 24 48 72 96 120 144 168 192 216 240

Time [hrs]

Stress,strength[MPa]

Stress

Tensile

strengthyoung concrete

older concrete

young concrete

young concrete

older concrete


22/29

22

43

High-Strength Concrete in skyscrapers

Burj Khalifa, 828 m, opened 4.1.2010

First 156 floors made of high-strengthconcrete (ACI definition of HSC: fc>40MPa)

Self-compacting pumpable concrete, cooledwith ice and cast at night

Source of text and figures: Wikipedia, Burj Dubai

44

Benefits of High-Strength Concrete

Higher strength

Higher stiffness

Low permeability

Low shrinkage

Low creep

Scaling and freeze-thaw resistance

Improved abrasion resistance Weiss 1999


23/29

23

45

Misconception #1: HSC has lower shrinkage

Start time matters!

Time (Days)

Shrinkage

Measuredshrinkage

0.30 0.40 0.50 0.60 0.70

Water to Cement Ratio

0

250

500

750

1000

Aggregate volume (70%)

Shrinkage()

0.30 0.40 0.50 0.60 0.70

Water to Cement Ratio

0

250

500

Aggregate volume (65%)Measured at 24 hours

Shrinka

ge()

Time (Days)

ActualSh

rinkage

MeasuredShrinkage

Weiss 2008, after Aitcin 1996

46

Misconception #2: Higher E is always good (1)

Initial Specimen

Shrinkage Effect

Restraint Effect

Initial Specimen

Shrinkage Effect

Restraint Effect

E=

Weiss 1999

Hookes law

Ut tensio, sic visRobert Hooke, FRS

1635 1703


24/29

24

47

Misconception #2: Higher E is always good (2)

Higher Elastic Modulus

(if E , for = )

0 20 40 60 80 100

Compressive Strength (MPa)

0

15

30

45

Te

nsileStress(MPa)

0 20 40 60 80 100

Compressive Strength (MPa)

0

15

30

45

Te

nsileStress(MPa)

Weiss 1999

48

Misconception #3: lower creep is always good (1)

"We can't prevent creep from happening,but if we slow the rate at which it occurs,

this will increase concrete's durability andprolong the life of the structures"


25/29

25

49


Weiss 1999

Creep/Cracking Effect

Stress Relaxation

( ) ( )

( ) ( ) ( )

( )

++=

28

,,

E

tdd

E

dtd

SHR

StressRelaxation( )

( )

( ) ( )

SHRd

E

dtd +=,

Initial Specimen

Shrinkage Effect

Restraint Effect

0 7 14 21 28


0

4

8

12


Stress In

Specimen


0 7 14 21 28


0

4

8

12



Final Stress State

Stress In

Specimen

50


Weiss 1999

Specimenstrength

0 7 14 21 28

Age of specimen (days)

0

4

8

12

Stress basedon Hookes law

Relaxation

i.e., creep

Stress in

specimen

Calculatedtensilestress(MPa)

Specimenstrength

0 7 14 21 28

Age of specimen (days)

0

4

8

12

Stress basedon Hookes law

Relaxation

i.e., creep

Stress in

specimen

Calculatedtensilestress(MPa)

Specimen with lower creep


26/29

26

51

Misconception #4: High early strength is always good

Strength

Reduce rate

Stressdeveloped

Reduce magnitude

Time of drying

Tensilestress Strength

Stress

developed

Time of drying

Tensilestress

Weiss 1999

Reducing cracking potential: shrinkage rate and magnitude

52

Misconception #5: HSC is tougher (1)

Weiss 2008

ClintTough

Toughness

Strength

ArnoldStrong


27/29

27

53

aC

Higher strength is more like glass

00

0 20 40 60 80

Comp. Strength (MPa)

10

15

20

25

30

D-a

Crac

kRatio=

(%)

aC-a0

D-a

Crac

kRatio=

(%)

aC-a0

Misconception #5: HSC is tougher (2)

Weiss 1999

54

Outline of the course (1)

21.09: Introduction (2h)

28.09: Hydration and microstructure development (1h)Powers' model (1h)

05.10: Plastic shrinkage (1h)Shrinkage mechanisms in hard. concrete (1h)

12.10: Autogenous shrinkage (1h)

Drying shrinkage and gradients (1h)

19.10: Influence of aggregate (1h)Residual stress development (1h)


28/29

28

55


26.10: Shrinkage-reducing admixtures (1h)

Internal curing (1h)

02.11: Temperature-induced cracking (2h)

09.11: Residual stresses and cracking practicalcases (1 h)

Transport and durability of cracked concrete (1h)

16.11: Visit of the Concrete and ConstructionChemistry Laboratory, Empa

56


23.11, 30.11 and 7.12: Individual project by students.We will be at ETHZ every Wednesday (or onappointment) for discussion

14.12: final exam, 15-20 min presentation on topic of

project plus 5-10 minutes questions


29/29

57

Acknowledgements

J. Weiss, F. Winnefeld and D. Bentz

(slides, other course material)

A. Leemann, R. Loser, O.M. Jensen,

J.-G. Hammerschlag, M. Romer

(pictures)

58

The beauty of cracks

Doris Salcedo, Shibboleth, Tate Modern, London, 2007

lecture1 21092011 introduction2011 slides

Documents