Construction Materials in civil engineering

(1)

CE 212

Engineering Materials

(2)

Introduction

The structure of materials can be described

on dimensional scales

1. The molecular level

2. Materials structural level

(3)

1. The molecular level

o

Smallest scale (atoms, molecules or aggregation

of molecules)

o

Realm of materials science

o

Particle sizes: 10

-7

– 10

-3

mm

o

Examples:

crystal structure of metals, cellulose

molecules in timber, calcium silicate hydrates in

hardened cement paste, variety of polymers

(4)

o

Atomic models used for description of the

forms of physical structure (regular or disordered)

o

Chemical and physical factors determine material

properties

o

Chemical composition and/or the rate of chemical

reactions determine material properties such as

porosity, strength, durability, etc.

o

Mathematical and geometrical models are employed

to deduce the way materials behave

(5)

2. Materials structural level

–

Up in size from the molecular level

–

Material considered as a composite of different

phases

_{Phase I}

_{Phase II}

• Concrete

• Asphalt

particles such as aggregates distributed in

a matrix such as hydrated cement or

_bitumen

Examples:

• Cells in timber

• Grains in metals

• Concrete

• Asphalt

• Fiber composites

• Masonry - regular composition

Entities within the

material structure

Deliberate mixing of

disparate parts

(6)

o

Particle sizes : 5x10

-3

_{mm (wood cell) - 225 mm}

(brick length)

o

Individual phases of the material can be

recognized independently

o

More general information can be derived from

examination of the individual phases of the

material (Multiphase models allow prediction of

material behavior)

(7)

b) State and properties:

Structure of material is affected

from chemical and physical states of phases. Behavior of

material is affected by properties of phases

Three aspects must be considered while

formulating the models;

a) Geometry:

Particulate or disperse phase scattered or

arranged within the matrix or continuous phase model

considers shape and size distribution and concentration

c) Interfacial effects:

Existence of interfaces between

phases may introduce additional modes of behavior.

(strength: failure of material being controlled by band

strength at an interface)

(8)

3. The engineering level

o

Total material is considered

o

Material is considered as continuous and homogenous

o

Average properties for the whole volume of material

body

(9)

Technical information on materials used in practice comes from

tests on specimens of the total material

Strength and failure tests provide technical information

Deformation tests used in practice

Durability tests

Representative cell:

minimum volume of the material that represents

the entire material system

Dimensions for cells:

10

-3

_{mm for metals – 100 mm for concrete –}

1000 mm for masonry

Isotropic material:

properties same for all directions – unit cell is a

cube

Anisotropic material:

properties change with dimensions – unit cell is a

parallel pipe

(10)

(11)

CONCRETE

A composite of mineral particles (aggregates) distributed in a

matrix of hardened cement paste (mixture of powder cement

and water at the beginning)

Versatile, comparatively cheap and energy efficient

Great importance for all types of construction throughout

the world

Concrete is fresh and plastic at the beginning (throughout

some time after mixing of constituent materials)

Final properties of the hardened state of concrete have

been gained slowly through time

Properties change with time

50-60 % of ultimate strength is developed in 7 days,

80-85 % in 28 days

Increases in strength have been found in 30 year old

(12)

History of concrete is very old

Mixtures of lime, sand and gravels have been found in

Eastern Europe, in Egypt and in Ancient Greek and Roman

times

This dates from about 5000 BC

History of concrete

Similar materials still known as pozzolona

Romans; first concrete with a hydraulic cement (lime +

volcanic ash from near Pozzuoli)

(13)

Roman structures;

Foundations and columns of aqueducts

Fig. 1: www.wonderquest.com/fountain-octopus-enzyme.htm

Fig. 2: http://www.artchive.com/artchive/r/roman/roman_colosseum.jpg

Fig. 3: www.dolceroma.it/images/common/dove/pantheon.jpg

In arches of the Colosseum

(14)

In 1756, John Smeaton

Mixture of burnt clay bearing

limestone & Italian pozzolana

for producing a suitable

hydraulic cement to be used in

construction of Eddystone

(15)

In 1790, James Parker

Patented “Roman cement” from calcareous clay burnt

in a kiln and ground to a powder

In 1824, Joseph Aspdin

Patented “portland cement” an artificial mixture of

lime and clay bearing materials used in repairs of

Thames Tunnel in 1828

In 1890s

improvement in kiln technology reduced the

cost of Portland cement production. Then widespread

production and use started worldwide

(16)

CONSTITUENT MATERIALS OF CONCRETE

Portland Cements

Raw materials;

Clay and calcareous stones

Silica from clay + lime from calcareous stone

(SiO

₂

) (shale) (CaO) (Chalk or limestone)

Al

₂

O

₃

, Fe

₂

O

₃

, MgO, K

₂

O also exist in clay

(17)

Chalk + clay reduced to 75μm or less and mixed

Blend fed into upper end of inclined long (up to 250m), 6m

diameter rotating kiln which is heated to 1500°C at lower end

Cement manufacturing process; simple but involves high

temperatures

20°C _250°C 650°C _950°C 1250°C _1500°C Drying _Preheating decomposition of clay minerals Calcining CaCO₃ CaO + CO₂ Burning or clinkering combination of oxides to produce calcium silicates, calcium aluminates and calcium aluminoferrites Raw materials Clinker Fuel + air 20°C _250°C 650°C _950°C 1250°C _1500°C Drying _Preheating decomposition of clay minerals Calcining CaCO₃ CaO + CO₂ Burning or clinkering combination of oxides to produce calcium silicates, calcium aluminates and calcium aluminoferrites

Raw materials

Clinker Fuel + air

Fig. The processes taking place in a Portland

(18)

At 600°C, CaCO

₃

in chalk decomposes to give quicklime (CaO)

and gaseous CO

₂

Form as a result of these reactions

Fusion reactions start at 1200°C

Calcium silicates, 2CaOSiO

₂

or 3CaOSiO

₂

Calcium aluminates, 3CaOAl

₂

O

₃

Other oxides act as a flux

Clinker particles (a few mm) emerge from kiln

After cooling, 3-4% gypsum (CaSO

₄

2H

₂

O) is added to clinker

Mixture is ground to powder

(2-80μm size), (300m

2

_{/kg specific}

(19)

(20)

(21)

Principle oxides in cement

CaO (lime):C

SiO

₂

(silica): S

Al

₂

O

₃

(alumina): A

Fe

₂

O

₃

(iron oxide): F

Composition;

Four main compounds (phases) formed in fusion process:

Tricalcium silicate: 3CaO.SiO

₂

(C

₃

S)

Dicalcium silicate: 2CaO.SiO

₂

(C

₂

S)

Tricalcium aluminate: 3CaOAl

₂

O

₃

(C

₃

A)

(22)

Each cement grain consists of an intimate mixture of these

compounds. Direct chemical analysis is not possible to determine

the amounts. Instead

BOGUE

formulas are used that were

calculated from the results of oxide analysis.

S

F

A

S

C

S

C

4 .

07

7 .

60

6 .

72

1 .

43

2 .

85 %

₃

=

−

S

=

SO

3

S

C

S

C

₂

2 .

87

0 .

754

₃

%

=

−

F

A

C

2 .

65

1 .

69 %

₃

=

−

F

AF

C

3 .

04 %

₄

=

If A/F > 0.64

S

F

A

S

C

S

C

₃

=

4 .

07 −

7 .

60 −

4 .

48 −

2 .

86 −

2 .

85 S

C

S

C

₂

=

2 .

87 −

0 .

754

₃

F

A

AF

C

F

C

₂

+

₄

=

2 .

1 +

1 .

70 If A/F ≤ 0.64

(23)

Compositions of Portland Cements

Oxides (% by wt)

Range

CaO 60-67

SiO

2

17-25

Al

2

O

3

3-8

Fe

2

O

3

0.5 – 6.0

Na

2

O + K

2

O

0.2 – 1.3

MgO

0.1 – 4.0

Free CaO

0 – 2

SO

3

1 – 3

Principle oxides: CaO & SiO

₂

∼

3 to 1by wt.

Principle oxides: C

₃

S & C

₂

S ∼ 75 – 80 % by wt.

The approximate range of oxide composition that can be expected

for Portland Cements

(24)

Composition of cement depends on quality and proportions of

raw materials (limestone and clay)

Relatively small variations in oxide composition result in

considerable changes in compound composition

Properties of compound cement constituents

Medium

High

Low

High

C

₄

AF

Very slow

Very high

Low

Flash

C

₃

A

High

Low

High

Medium

Slow

C

₂

S

Medium

High

Medium

C

₃

S

Final

Early

Sulfate

resistanc

e

Heat of

hydration

Cementing value

Rate of

reaction

(25)

Typical Portland Cements Oxides (% by wt) A B C D CaO 66 67 64 64 SiO2 21 21 22 23 Al2O3 7 5 7 4 Fe2O3 3 3 4 5 Free CaO 1 1 1 1 SO3 2 2 2 2

Potential compound composition (% by wt)

C3S 48 65 31 42

C2S 24 11 40 34

C3A 13 8 12 2

C4AF 9 9 12 15

Typical or

average P.C High-Early Strength P.C

Low Heat

P.C Sulphate Resisting P.C

(26)

Türk Çimento Standardları

Standard No İsim Notasyon TS 3441 Portland Çimentosu Klinkeri

TS 19 Portland Çimentosu PÇ 32.5 PÇ 42.5 PÇ 52.5 TS 3646 Erken Dayanımı Yüksek Çimento EYÇ 52.5 TS 21 Beyaz Portland Çimentosu BPÇ 32.5 BPÇ 42.5 TS 10157 Sülfatlara Dayanıklı Çimento SDÇ 32.5 TS 10158 Katkılı Çimento KÇ 32.5 TS 26 Traslı Çimento TÇ 32.5 TS 20 Yüksek Fırın Cüruflu Çimento CÇ 32.5 CÇ 42.5 TS 809 Süper Sülfat Çimentosu SSÇ 32.5 TS 640 Uçucu Küllü Çimento UKÇ 32.5 TS 22 Harç Çimentosu HÇ 16 TS 12139 Portland Cüruflu Çimento PCÇ/A

PCÇ/B TS 12140 Portland Kalkerli Çimento PLÇ/A PLÇ/B TS 12141 Portland Silika Füme Çimento PSFC TS 12142 Kompoze Çimento KZÇ/A

KZÇ/B TS 12143 Portland Kompoze Çimento PKÇ/A PKÇ/B TS 12144 Puzolanik Çimento PZÇ/A PZÇ/B TS 23 Çimento Numune Alma Metodları

TS 24 Çimentoların Fiziki ve Mekanik Deney Metodları

(27)

ENV 197-1’e Göre Çimento İçinde Bulunabilecek Malzemeler

(Materials in cement)

Malzeme Kısaltma Sınırlamalar

PÇ Klinkeri K C3S+C2S ≥ % 66.7

CaO/SiO2 ≥ 2.0

MgO ≤ % 5 Granüle Yüksek

Fırın Cürufu S Camsı faz miktarı ≥ % 66.7 _{CaO + SiO}₂_{+ MgO ≥ % 66.7} (CaO + MgO)/SiO2 > 1.0

Doğal Puzolan P Reaktif SiO2 ≥ % 25

Endüstriyel Puzolan Q

Silisli Uçucu Kül V KK ≤ % 5

Reaktif CaO ≤ % 5 Reaktif SiO2 ≥ % 25

Kireçli Uçucu Kül W % 5 ≤ Reaktif CaO ≤ % 15 Reaktif SiO2 ≥ % 25 KK ≤ % 5 Hacim Genl. < 10mm % 5 ≤ Reaktif CaO ≤ % 15 Reaktif SiO2 ≥ % 25 KK ≤ % 5 Hacim Genl. < 10mm Pişirilmiş ŞeyL T σ28 ≥ 25N/mm2 Hacim Genl. < 10mm Kalker L CaCO2 ≥ % 75 Kil miktarı ≤ 1.2 g / 100g

Organik Madde Miktarı ≤ % 0.2 Silis Dumanı D Amorf SiO2 ≥ % 85

KK ≤ % 4

Özgül yüzey (BET) ≥ 15m2_/g

Minör İlave Bileşen F Kalsiyum Sülfat

(28)

TS EN 197-1 Çimento Tipleri ve Kompozisyonları (Types of cement and

compositions)

Çimento Tipi Adı Notasyon K S D P Q V W T L MİB I Portland Çimentosu I 95-100 - - - - - - - - 0-5 II/A-S 80-94 6-20 - - - - 0-5

Portland Cüruf Çimentosu

II/B-S 65-79 21-35 - - - - - 0-5

Portland Silis Dumanı Ç II/A-D 90-94 - 6-10 - - - - - - 0-5

II/A-P 80-94 - - 6-20 - - - - - 0-5

II/B-P 65-79 - - 21-35 - - - - - 0-5

II/A-Q 80-94 - - - 6-20 - - - - 0-5

Portland Puzolan Çimentosu

II/B-Q 65-79 - - - 21-35 - - - - 0-5

II/A-V 80-94 - - - - 6-20 - - - 0-5

II/B-V 65-79 - - - - 21-35 - - - 0-5

II/A-W 80-94 - - - - - 6-20 - - 0-5

Portland Uçucu Kül Çimentosu

II/B-W 65-79 - - - - - 21-35 - - 0-5

II/A-T 80-94 - - - 6-20 0-5

Portland Pişirilmiş Şeyl

Çimentosu II/B-T 65-79 - - - 21-35 0-5

II/A-L 80-94 - - - 6-20 0-5

Portland Kireçtaşı Çimentosu

II/B-L 65-79 - - - 21-35 0-5

II/A-M 80-94 6-20 0-5

II

Portland Kompoze Çimento

II/B-M 65-79 21-35 0-5

III/A 35-64 36-65 - - - - 0-5

III/B 20-34 66-80 - - - - 0-5

III Yüksek Fırın Çimetosu

III/C 5-19 81-95 - - - - 0-5 IV/A 65-89 - 11-35 - - - 0-5 IV Puzolanik Çimento IV/B 45-64 - 36-55 - - - 0-5 V/A 40-64 18-30 - 18-30 - - - 0-5 V Kompoze Çimento V/B 20-39 31-50 - 31-50 - - - 0-5

(29)

(30)

(31)

Özellik Çimento Tipi Dayanım Sınıfı Sınır Kızdırma Kaybı (%) CEM I

CEM III

Bütün Sınıflar ≤ 5 Çözünmeyen Kalıntı (%) CEM I

CEM III Bütün Sınıflar ≤ 5 CEM I CEM II 32.5, 32.5R, 42.5 ≤ 3.5 CEM IV CEM V 42.5R, 52.5, 52.5R SO3 (%)

CEM III* Bütün Sınıflar

≤ 4.0

Cl (%) Bütün tiplert Bütün Sınıflar ≤ 0.10 * CEM III/C %4.5’e kadar SO3 içerebilir.

t _{CEM III % 0.1’in üstünde Cl}-_{içerebilir. Bu durumda Cl}-_{miktarı belirtilir.}

TS EN 197-1 Çimentolarında Aranan Kimyasal Koşullar

(32)

(33)

TS EN 197-1 Dayanım Sınıfları

Dayanım Sınıfı Basınç Dayanımı Sınırları (N/mm

2

)

2G

7G

28G

32.5 -

≥ 16

≥ 32.5, ≤ 52.5

32.5R

≥ 10

-

≥ 32.5, ≤ 52.5

42.5 ≥ 10

-

≥ 42.5, ≤ 62.5

42.5R

≥ 20

-

≥ 42.5, ≤ 62.5

52.5 ≥ 20

-

≥ 52.5

52.5R

≥ 30

-

≥ 52.5

(34)

Hydration

(Cement + Water) paste initially fluid

mixture

Fluidity or consistency remains constant for an

initial period after mixing

Final set (max 10 hours after mixing): Mix is

completely stiff, hardening and strength gain

starts

Initial set (2-4 hours after mixing): Mix starts to

stiffer, fluidity is lost at a faster rate

Rate of strength gain is fast for the first 1-2

(35)

Ra

te

of he

at

output

(J/

kg

/sec)

A

Dormant period

B

C

0.1

1.0

10

100 Time after mixing (hours, log scale)

Ra

te

of he

at

output

(J/

kg

/sec)

A

Dormant period

B

C

0.1

1.0

10

100 Time after mixing (hours, log scale)

Hydration reactions are exothermic

A: High but very short peak lasts only a few minutes

Dormant period: cement is inactive (2-3 hours)

B: Broad peak after final set

(36)

Heat of Hydration

Rate of Heat

Evolution

Time

Stage I

Rapid Heat Evolution

(<15 mins)

Stage II

Dormant Period

Important for transportation (2-4 hrs)

Stage III

Accelerating Stage Begins with initial set

(4-8 hrs)

Stage IV

Deceleration Stage No longer workable

(12-24 hrs)

Stage V

Steady State

I

II

III

IV

V

nucleation dissolution hydrolysis C₃S reacts diffusion control Initial set Final set

(37)

Vicat

apparatus

Typical Setting Times for Portland Cements

(38)

(39)

32 __ 3 2 __ 3

A

3 C

S

H

26 H

C

A

3 C

S

H

C

+

→

Retarding is provided by addition of gypsum which reacts with C

₃

A to form

calcium sulphoaluminate (ettringite)

Hydration compounds involve all four main compounds simultaneously.

Processes are extremely complex and not fully understood. Simplified

description consider the chemical reactions of each of the compounds

individually

1) Initial peak “A” is due to:

Rehydration of calcium sulphate hemihydrate

2 __ __ 2 3 5 . 0 2C S H + H → C S H

(H = H

₂

O)

2) Initial reaction of aluminate phases

6 3

3

A

6 H

C

AH

C

+

→

Very rapid reaction of C

₃

A with water results in a flash set in a few minutes

Calcium sulfoaluminate

(Ettringite)

Relatively slow reaction. Gypsum added (3-4%) used up to after first 24

hours after mixing. Then C

₃

A hydration reaction taken over and ettringite

transform into monosulphate form ( ). This occurs as peak “C”

in cements with C

₃

A>12%

C

3

AC

S

H

16

(40)

3) C

₄

AF reacts similarly over same time scales

Reaction products are similar to C

₃

A products

(has little effect on the overall cement behavior)

4) C

₃

S and C

₂

S react to form bulk of hydrated material after these

initial reactions are completed. They are responsible for most of

properties of hardened cement

CH

H

S

C

H

S

C

6

3

2

₃

+

→

₃ ₂ ₃

+

Most of the main peak “B” is due to this reaction

CH

H

S

C

H

S

C

₂

+

4 →

3

₂ ₃

+

2 (Reaction of C

₃

S - faster)

(Reaction of C

₃

S - slower)

(41)

FLY ASH

(42)

FLY ASH

(43)

aggregate

Transition zone Bulk cement paste

Fracture surface of 24 hour old cement paste, showing C-S-H and ettringite

(44)

Typical hydration product development in Portland cement paste

Calcium silicate hydrate (C-S-H) is responsible for strength and

other properties

After 1 day CSH dominates,

thus; Ca(OH)

₂

production

enhanced

(45)

(46)

Increasing temperature accelerates reactions of hydration.

Reactions stop completely below -10ºC

Fresh cement and water Initial set

Two or three days old

(47)

1)

After mixing fresh cement particles dispersed throughout

mix water as single grains or small

flocs

. Spacing depends on

w/c

Microstructural development during HYDRATION of cement

2)

During dormant period, ettringite is formed at cement

surface as sharp needles or rods.

3)

At the end of dormant period, ettringite from adjacent

cement particles has began to interfere and C-S-H with a

spicular crumpled-foil form has started to appear. Solid

layers of foil are a few molecules thick

4)

During subsequent hydration, a dense continuous gel of

C-S-H is formed between particles, resulting in increasing

strength. Also large hexagonal crystals of CH are formed.

Some larger pores remain unfilled between grains, and fresh

unhydrated cement is left in center of grains.

(48)

(49)

(50)

Structure of hardened cement paste

Residue of unhydrated cement, at center of original grains

Hydrates, mainly calcium silicates (C-S-H); also calcium

aluminates, sulphoaluminates and ferrites

Crystals of calcium hydroxide (calcite)

Unfilled spaces between cement grains, called capillary pores

C-S-H occupy about 75 % of volume of HCP

C-S-H govern mechanical properties

C-S-H structure: from poorly crystalline fibers to crumpled sheet-like network of

colloidal scale

Extremely high specific surface: 100-700 m

2

_/g

(~ 10

3

_{times higher than cement particles)}

Spaces between C-S-H particles: gel pores:

~ 0.5-5nm ~ 27 % of C-S-H weight

Note: Don’t confuse gel pores with capillary pores (on the average about 2 orders

of magnitude larger)

(51)

Strength of hardened cement paste

Strength arise from Van der Waals forces between hydrate

layers

Quantitative estimate of unhydrated cement, hydrated gel

and capillary pores was done by Powers in 1950s.

Important futures of his model are:

1)

Hydration takes place at constant volume

V

_cem+water

= V

_{unh.cem+gel+cap.pores}

2)

Same gel is produced at all stages of hydration regardless of

type of cement and water/cement ratio

Constants are;

a) Chemically combined water: ~23% by wt of cement

b) Relative density of gel solids = 2.43

(52)

Gel occupies (including the pores) a space about 1.8 times

that of unhydrated cement

For too small a space, hydration stops when products grow to

fill this space (complete hydration never occurs)

For too large a space, 100% hydration doesn’t fill the space

(capillary pore)

For hcp in water: at w/c = 0.38 → 100% hydration fills

(53)

(a)

(b)

Composition of hydrated cement paste at the final stage of hydration after

prolonged storage a) in water, b) sealed

(54)

For sealed hcp, self-desiccation occurs at low w/c because

of insufficiency of water, hydration stops before it is

affected by lack of space for gel. Break-even point for w/c

is 0.44.

The curves show the final stage (100% hydration) which is

rarely achieved. Therefore, hcp contains less cement gel and

more unhydrated cement and capillaries than those shown in

the figures

Unhydrated cement, not detrimental to strength, results in

(55)

(56)

Water vapour: in partially filled larger voids

Capillary water:: in capillary pores; bulk water free from attractive forces

of solid surfaces.

In voids > 50nm (large capilleries)

It is free water, and removal does not cause shrinkage

In voids < 50nm (small capillaries)

capillary tension forces dominate and removal of water may result in

shrinkage

Adsorbed water: On solid surfaces under influence of surface attractive

forces up to 5 molecular layers (~ thickness of 1.3 nm) Lost on drying to

30% RH and this contributes mainly to shrinkage

Interlayer water: In gel pores < 2.6nm under influence of two surfaces

very strongly held. Lost on drying at elevated temperatures and/or to 10%

of RH. Causes in considerable shrinkage (Van der Waals forces pull solid

surfaces closer together)

Chemically combined water: combined with fresh cement in hydration

reactions. Not lost on drying. Heating to very high temperatures evolves

this water through decomposition of paste.

(57)

ADMIXTURES

Chemicals added immediately before or during

mixing

Significantly change fresh, early age or hardened

properties to advantage

Used in small quantities (1-2 % by wt of cement)

Plasticizers

Workability aids;

↑

fluidity or workability of concrete at same w/c

Water reducers;

↓

w/c and thus

↑

strength and durability at same

workability

(58)

1)

Normal plasticizers;

based on lignosulphonates or

hydroxycarboxylic acids

2)

Superplasticizers;

modified lignosulphonates or based on

sulphonated melamine or naphtalene formaldehydes

– Great increases in workability (flowing concrete) (segregation

occurs if used with high doses of normal plasticizers or high

water contents)

– Great decreases in w/c (down to 0.2 at normal fluidity) and

thus very large increases in strength (strength or

high-performance concrete)

(59)

Plasticizers adsorbe on cement

particle surfaces, giving slight

negative charges to the

surface and thus particles

repel each other, breaking up

any flocs and causing a better

dispersion and wetting of

particles

This results in increased

fluidity and slight increase in

strength at same w/c ratio

Plasticizers may cause

retardation of setting time and

also may entrain 1-2% air into

concrete

(60)

Accelerators

Increased rate of hardening and enhanced early

strength

May allow early removal of formwork

May reduce curing time for concrete placed in cold

weather

CaCl

₂

is a popular accelerator. It may cause increased

creep and shrinkage

Prohibited in R.C and P.S.C due to corrosion of steel

(61)

Typical effects of calcium chloride admixture on (a) setting times, and

(b) early strength of concrete

(62)

Retarders

Delay setting time

Counteracts accelerating effect of hot weather

(especially for long transportation distances)

Avoids cold joints and discontinuities by controlling

setting in large pours

Sucrase and citric acid and calcium lignosulphonate

(63)

Air entraining agents

Organic materials which entrain controlled amount of microscopic

(less than 0.1mm) bubbles into cement paste of concrete

Bubbles preserve stability during mixing, transporting, placing,

compaction and setting and hardening

Note;

entrained air and entrapped air are different

Air entrainment is done for providing freeze-thaw

resistance to concrete

In winter time, water in capillary pores expands on freezing

resulting in disruptive internal stresses. Successive cycles

of freezing and thawing may lead to progressive

deterioration. Entrained air, uniformly dispersed in hcp with

a spacing factor of not more than 0.2mm, provide a

reservoir for water to expand

Entrained air volumes of 4-7% by vol. of concrete is

(64)

Secondary effects

Increase in workability due to lubricating affect of small air bubbles

About 6% decrease in strength for each 1% of air. However,

improvement in workability may allow to partially offset the loss in

strength by reducing water content and thus w/c ratios

Organic substances reduce surface

tension of water and bubbles form

during mixing

Long chain molecules have hydrophilic

and hydrophobic ends

They align themselves radially on

surface of air bubble with hydrophilic

ends in water and hydrophobic ends in

air. Thus they provide air stability

Air bubble

hydrophobic

hydrophilic

(65)

Cement replacement materials (CRM)

Mineral additives that partially replace portland cement

Could be by-products from other industries (Economically advantageous)

They enhance concrete properties in a variety of ways

Pozzolanic behavior

A pozzolanic material is one which contains active silica (SiO

₂

) and is not

cementitious in itself but will, in a finely divided form and in presence of

moisture, chemically react with calcium hydroxide at ordinary temperatures

to form cementitious compounds

Pozzolanic reaction (Secondary reaction)

(66)

1. Fly ash (pulverized fuel ash);

ash from pulverized coal used to

fire power stations

2. Ground granulated blast furnace slag (ggbs);

slag from scum

formed in iron smelting in a blast furnace, ground to a powder

3. Condensed silica fume;

sometimes called microsilica; very fine

particles of silica condensed from waste gases given off in

production of silicon metal

4. Natural pozzolans;

some volcanic ashes

5. Calcined clay and shale;

clay and shale minerals heat treated

Dictionary definitions:

Pulverize; to reduce to dust or powder, as by pounding or grinding

Smelt ; to melt or fuse (ores) in order to separate the metallic constituents.

Types of Cement Replacement Materials

6. Rice husk ash;

ash from controlled burning of rice husks after

rice grains have been separated

(67)

Typical composition and properties of cement replacement

materials

Fly ash Oxide

Low lime High lime

Ggbs Silica fume PC SiO2 48 40 36 97 20 Al2O3 27 18 9 2 5 Fe2O3 9 8 1 0.1 4 MgO 2 4 11 0.1 1 CaO 3 20 40 - 64 Na2O 1 - - - 0.2 K2O 4 - - - 0.5 Specific gravity, (gr/cm3) 2.1 2.9 2.2 3.15 Particle size (μm) 10-150 3-100 0.01-0.5 0.5-100 Specific Surface (m2/kg) 350 400 15000 350

(68)

High lime fly ash

and

ground granulated blast furnace slag

are not

true pozzolanas. They have certain self-cementing due to high CaO

content. They may be used at high substitution rates (up to 90%)

Low lime fly ash is used at most 40% replacement

Silica fume is used at most 25% replacement (needs superplasticizer

to maintain workability)

Particles of artificial pozzolanas are smooth surfaced and spherical

(69)

Age (days) Com p re ss iv e Stre ngth (N/mm 2 ) 70% P.C + 30% F.A 100% P.C w/c or w/(c+fa) = 0.47 Age (days) Com p re ss iv e Stre ngth (N/mm 2 ) 70% P.C + 30% F.A 100% P.C w/c or w/(c+fa) = 0.47

Pozzolanic reaction and then early strength development is slow

With silica fume, delay is much less due to high surface area and active silica content

At later ages concretes with

cement replacement materials exceed strength of Portland cement only concretes

Slower pozzolanic reaction reduces porosity

Pozzolanic reaction enhances transition zone between

(70)

Aggregates

Disadvantages of hardened cement paste (hcp);

1. Dimensional instability (high creep and shrinkage)

2. High cost

Remedy to disadvantages;

Put aggregates into cement paste → Produce concrete

(71)

Objective;

Use as much aggregate as possible

Use largest possible aggregate size

Use a continuous grading of particle sizes from sand to coarse

stones

Thus;

Void content of aggregate mixture

Amount of hcp required Minimized

Coarse agg.

Fine agg.

(72)

Concrete composite models

a) Two-phase model for describing deformation behavior

Coarse aggregate dispersed in mortar matrix

Coarse and fine aggregate dispersed in hcp matrix

b) Three-phase model for considering cracking and strength

Aggregates + hcp + transition or interfacial zone (∼ 50 μm)

(73)

Types of aggregates

1. According to origin;

a) Natural aggregates from natural sand and gravel deposits and

crushed rocks

b) Specifically manufactured aggregates such as fly ash pellets,

granulated blast furnace slag

2. According to size;

a) Fine aggregate; Particle size from 0 to 4 mm

Ex; natural sand and crushed sand

b) Coarse aggregate; Particle size from 4 to 16 or 32 mm

Ex; gravel, crushed limestone

1. According to origin

2. Accroding to size

3. According to density or specific gravity

Dictionary definition:

(74)

3. According to density or specific gravity;

a) Normal density aggregates; natural aggregates,

Examples; gravels, igneous rocks (basalt, granite), sedimentary rocks

(limestone, sandstone)

• Mineral composition is not that important

• Specific gravities; 2.55 – 2.75 gr/cm

3

• Concrete density; 2250 - 2450 kg/m

3

• Gravels from deposits in river valleys or shallow coastal waters

are directly used after washing and grading, particles are round

• Bulk rock sources (granite, basalt, limestone) require crushing

giving angular and sharp particles

Dictionary definitions:

Igneous; produced under conditions involving intense heat, as rocks of volcanic origin or rocks crystallized

(75)

c) Heavyweight aggregates; minerals like barytes to barium sulphate ore

and steel shots

• To produce high density concrete (3500 to 4500 kg/m

3

₎

(For nuclear radiation shielding)

b) Lightweight aggregates; pumice (a naturally occurring volcanic rock),

artificial lightweight aggregates (sintered fly ash, expanded clay or

shale, foamed slag)

• To produce lower density concretes (less than 2000 kg/m

3

₎

advantages; reduced self-weight, better thermal insulation

• Reduced specific gravity (less than 2.0 gr/cm

3

_{) due to voids}

in particles

• Reduced strength of concrete due to increased porosity

Dictionary definition:

Sintering; to form a coherent mass by heating without melting.

Barytes; a white or colorless mineral (BaSO4); the main source of barium

(76)

Grading or particle size distribution (Why do we need that?)

Properties of aggregates

Overall objective

– To calculate suitable grading

for good workability and stability

(continuous grading → low void

content)

How much sand? How much crushed

(77)

Grading or particle size distribution (Sieve analysis)

– Aggregate samples dried, weighed and passed through a stack of

the sieves

• Sieve sizes in mm (0.25, 0.50, 1, 2, 4, 8, 16, 31.5)

– Weight of aggregate retained on each sieve measured and

converted to percentage retained and then to cumulative

– Then plotted against the sieve size to obtain

grading curve

Sieve

Shaker

0.25 0.5 1 2 4 8 16 31.5 0 10 20 30 40 50 60 70 80 90 100

(78)

Grading curves

Standards for aggregate define limits inside which the

grading curves for coarse and fine aggregate must fall

0.25

0.5

1

2

4

8

16

31.5

0

10

20

30

40

50

60

70

80

90

100

0.25

0.5

1

2

4

8

16

31.5

0

10

20

30

40

50

60

70

80

90

100

(79)

1. Limits for Grading (with square opening) Sieve

size _{0-8 mm} _{0-16 mm} _{0-31.5 mm} _{0-63 mm}

(mm) A8 B8 C8 A16 B16 C16 A32 B32 C32 A63 B63 C63

63 100 100 100 31.5 100 100 100 61 80 90 16 100 100 100 62 80 89 46 64 80 8 100 100 100 60 76 88 38 62 77 30 50 70 4 61 74 85 36 56 74 23 47 65 19 38 59 2 36 57 70 21 42 62 14 37 53 11 30 49 1 21 42 57 12 32 49 8 28 42 6 24 39 0.25 5 11 21 3 8 18 2 8 15 2 7 14 2. Limits for Quality (max. %)

Property Fine Aggregate Coarse Aggregate Deleterious

Substances

1. Clay lumps 2. Soft particles 3. Coal and Lignites 4. Mud and clay

1.00 - 1.00 3.00 0.25 5.00 1.00 0.50 Sulphate Soundness 1. With Na2SO4 2. With MgSO3 15.00 22.00 18.00 27.00

Abrasion 1. Los Angeles 2. Impact

50 45

Freeze and Thaw (DIN 4226) - 4.00

Organic Impurities: The aggregate may give yellow or lighter color in a 3% solution of, NaOH, but not dark colors

Table. Outline of TS 706 Limits for Concrete Aggregates

(80)

Example problem

Determine mix proportions of sand and crushed stone such that fineness modulu

of mixture will be 4.30.

Sieve size

(mm)

Material

Passed (%)

0.25

0.50 1 2 4 8 16

31.5 Sand (%)

18

23

28

48

60

90 100 100

Crushed stone (%)

0

5

40

60

100 Fineness modulus; Sum of the cumulative percentages retained on

the sieves of the standard series

(81)

Fineness Modulus =

---For sand =

(82)

---Mix proportions by vol: a (for sand), b (for crushed stone)

Using law of simple mixtures;

m₁a + m₂b = m_m a + b = 13.33 a + 5.95 b = 4.30 a = 0.63b = 0.37

Sieve size (mm)

Material

Passed (%)

0.25

0.50 1 2 4 8 16

31.5 Sand (0.63)

11.3 14.5 17.6 30.2 37.8 56.7 63 63

Crushed stone (0.37) 0 0 0 0 1.9

14.8

22.2

37 Mixture

11 15 18 30 40 72 85 100

(83)

Limiting grading curves

0.25

0.5

1

2

4

8

16

31.5

0

10

20

30

40

50

60

70

80

90

100

(84)

Grading curves of sand and crushed stone

0

10

20

30

40

50

60

70

80

90

100

0.25

0.5

1

2

4

8

16

31.5

(85)

Grading curve of the mixture (sand+crushed s.)

0

10

20

30

40

50

60

70

80

90

100

0.25

0.5

1

2

4

8

16

31.5

(86)

In case of more than two aggregate fractions

1 =

+

b

c

a

m i i i i

a

P

b

P

c

P

1

+

2

+

3

=

m j j j j

a

P

b

P

c

P

1

+

2

+

3

=

Can be extended to as many equation as number

of size fractions which provides full conformity to

the desired grading curve

Ideal (desired) grading curves

TS 500 grading curve

⎟

⎠

⎞

⎜

⎝

⎛

+

=

max max

4

20 D

d

D

d

P

_i i i

Fuller parabola

i i i

D

d

P

=

100 where;

P

_i

= % passing from i

th

_sieve

d

_i

= opening size of i

th

_sieve

D

_max

= Max particle size

(sieve size through which 100% of

aggregate passes)

(87)

Normal weight aggregates contain pores (typically 1-2 % by volume) Particles can absorb and hold water

Completely (oven dry)

All pores empty Air dryPores partially filled

Saturated surface dry All pores full but no excess water

Saturated or wet excess water

Field conditions Possible only_{in lab. conditions} Field conditions Absorb some of

mix water in fresh concrete

Absorb some of mix water in fresh concrete

No absorbtion

and no addition Add to mix waterin fresh concrete

Aggregate Moisture Conditions

OTHER PROPERTIES OF AGGREGATES

(88)

Amount of water available for cement hydration, i.e. non-absorbed

or free water is of prime importance

Therefore, to ensure the required free water/cement ratio, it is

necessary to allow for the aggregate moisture condition

When calculating the amount of mix water;

If aggregate is drier than SSD, extra water must be added If it is wetter, then less mix water is required

2) Elastic properties and strength

Elastic properties of aggregates have major influence on elastic

properties of concrete

Strength of normal weight aggregates are higher than hcp and do

not have major influence on strength of normal strength concrete

In high-strength concrete (greater than 70-80 MPa), strength of

aggregates and effect of transition zone between aggregate and hcp

become seriously important

(89)

3) Surface characteristics

Surface texture have greater influence on the flexural strength than

on the compressive strength of the concrete (rougher texture results

in a better adhesion)

Surface cleanliness is also important for adhesion (surface should be

kept clear of the materials such as mud, clay etc.)

Better adhesion » stronger

interface

between aggregate and hcp

(90)

Fresh state / early age properties of concrete

Fresh concrete:

from time of mixing to end of time concrete

surface finished in its final location in the structure

Operations:

batching, mixing, transporting, placing, compacting,

surface finishing

Treatment (curing) of in-placed concrete 6-10 hours after casting

(placing) and during first few days of hardening is important

(91)

Main properties of fresh concrete during mixing, transporting,

placing and compacting

• Fluidity or consistency:

capability of being handled and of flowing

into formwork and around any reinforcement, with assistance of

compacting equipment

• Compactability:

air entrapped during mixing and handling should be

easily removed by compaction equipment, such as poker vibrators

• Stability or cohesiveness:

fresh concrete should remain homogenous

and uniform. No segregation of cement paste from aggregates

(especially coarse ones)

Fluidity & compactability known as workability

Higher workability concretes are easier to place and handle but obtaining

higher workability by increasing water content decreases strength and

durability

(92)

Compaction of concrete

(93)

93

Fill concrete into frustum of

a steel cone in three layers

Hand tap concrete

In each layer

Lift cone up

Define slump as downward

Movement of the concrete

Workability measurement methods

1. Slump test

2. Mini-slump test

3. Compacting factor test

4. Vebe test

5. Flow table test

1. Slump test - simplest and crudest test (standardized in

ASTM C 143

(94)

Lift cone up

Define slump as downward

movement of the concrete

(95)

True

Valid slump measurement 0-175 mm

Shear

Mixes having tendency to segregate – repeat test

Collapse

Slumps greater than 175 mm - self-leveling concrete

Consistency grade Slump (mm) Recommended method of compaction Stiff, K1 0 - 60 Mechanical compaction like vibration

Plastic, K2 60 – 130 Mechanical or hand compaction (rodding, tampering) Flowing, K3 130 – 200 Hand compaction or no compaction

(96)

2. Mini-slump test

• Used for workability

testing of cement

pastes

• Mini slump cone is a

small version of slump

cone

• The cone is placed in

the center of a piece of

glass, paste is cast into

cone and then the cone

is lifted to measure the

average spread of paste.

w/b : 0.2 sp:%2

(97)

3. Compacting factor test

(to distinguish between low slump mixes)

Upper hopper

Lower hopper

Cylinder

approx. 1m

1. Concrete is placed in an upper hopper

2. Dropped into a lower hopper

to bring it to a standard state and then allowed to fall into a standard cylinder.

3. The cylinder and concrete weighed (partially compacted weight)

5. The concrete is fully compacted, extra concrete added and then conrete and cylinder weighed again (fully compacted weight)

weight of partially compact concrete

Compacting factor =

(98)

4. Vebe test

Vebe time is defined as the time taken to complete covering of the underside of the disc with concretecontainer

1. A slump test is performed in a container

2. A clear perspex disc, free to move

vertically, is lowered onto the concrete surface

(99)

5. Flow table test

(to differentiate between high workability mixes)

1. A conical mould is used to produce a

sample of concrete in the centre of a 700 mm square board, hinged along one edge

2. The free edge of the board is lifted against the stop and dropped 15 times

Flow = final diameter of the concrete

(100)

Some degree of correlation between the results exist, however the

correlation is quite broad since each tests measures the response to

different conditions

(101)

A) Behavior of fresh concrete after placing and compacting

From placing to final set, concrete is in a plastic, semi-fluid state

Heavier particles (aggregates) have tendency to move down

(SEGREGATION)

Mix water has a tendency to move up

(BLEEDING)

1. Segregation and Bleeding

(102)

A layer of water (~ 2 % or more of total

depth of concrete) accumulates on surface,

later this water evaporates or re-absorbed

into concrete

BLEEDING

Water-rich _pockets Surfacelaitance Mix

water Cement and aggregates

Surface laitance;

water rich concrete layer hydrating to

a weak structure (not good for floor slabs that need to have hard wearing

surface)

Water-rich pockets;

upward migrating water can be trapped under coarser

aggregate particles causing loss of strength and local weakening in transition

zone

(103)

2. Plastic settlement

Horizontal reinforcing bars may put restraint

to overall settlement of concrete

Then plastic settlement cracking can occur

Vertical cracks form along line of the bars,

penetrating from surface to bars

Cracks

Reinforcing

bars

Plan

(104)

On an unprotected surface, bleed water

evaporates.

If rate of evaporation > rate of bleeding,

then surface dries (water content

reduces on surface) and plastic shrinkage

(drying shrinkage in fresh concrete) will

occur

Restraint of walls of concrete causes

tensile strains in near surface region

Fresh concrete has almost zero tensile

strength, thus, plastic shrinkage cracking

results cracking is in fairly regular

“crazing” form

3. Plastic shrinkage

Plastic shrinkage cracking will be increased by greater

evaporation rates of the surface water which occurs, i.e.

with

higher concrete or ambient temperatures, or if

the concrete is exposed to wind

(105)

4) Methods of reducing segregation and bleed and their effects

CAUSES OF BLEEDİNG

Poorly graded aggregate with a lack of fine material

with particle size < 300µm

High workability mixes

REMEDIES

1. İncrease sand content 2. Air entrain concrete as substitute for fine materials Provide high workability with superplasticizers rather than

high water contents

Use very fine materials such as silica fume

(106)

REMEDIES for PLASTIC SETTLEMENT or PLASTIC

SHRINKAGE CRACKS

Revibrate surface region, particularly in large

flat slabs

Apply good curing that stops moisture loss from surface as soon as after placing is possible and for first few days of hardening

(107)

B) Curing

Curing methods

Spraying or ponding surface of concrete with water Protecting exposed surfaces from wind and sun by

windbreaks and sunshades

Covering surfaces with wet hessian and/or polythene sheets Applying a curing membrane, a spray-applied resin seal, to

the exposed surface to prevent moisture loss

Curing; proctection of concrete from moisture loss from as soon after placing as possible, and for the first few days of hardening