Reducing cement paste volume for production of SCC by adding fillers

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Reducing cement paste volume for

production of SCC by adding fillers


Professor Albert K.H. Kwan

Department of Civil Engineering

The University of Hong Kong



Dr. Jaime S.K. Yeung

Score Holdings Ltd.


Introduction


The

complex

shape

of

some

of

today’s

large

scale

infrastructure

demand

the

uses

of

very

large

and

sophisticated

concrete

moulds

and

exceedingly

dense

steel

reinforcement,

which

together

render

concreting

a

formidable

task
.


The

great

difficulties

with

the

placing

of

concrete

through

closely

spaced

reinforcing

bars

into

every

corner

of

the

mould

and

with

the

compaction

of

concrete

placed

inside

confined

space

could

lead

to

unfilled

corners,

honeycombing,

insufficient

steel
-
concrete

bond

and

other

defects
.


To

improve

the

general

quality

of

concrete

construction,

the

use

of

self
-
consolidating

concrete

(SCC)

is

probably

the

best

option
.

Introduction

SCC

has

excellent

ability

to


deform

and

flow
;


fill

up

confined

spaces

and

far
-
reaching

corners
;


pass

through

small

clearances

between

rebars
;

and


achieve

good

consolidation

without

compaction

(or

with

facilitation

of

very

little

compaction

in

some

extremely

difficult

condition)
.


Advantages

of

using

SCC
:


enables

a

highly

automated

concreting

operation

that

allows

reduction

in

the

number

of

concrete

workers

and

improvement

in

site

management
.


Introduction

Advantages

of

using

SCC

(continued)
:


Without

the

need

of

vibration,

the

concreting

speed

can

be

accelerated
.


Without

the

need

of

vibration,

the

noise

generated

can

be

reduced

by

about

90
%

(
8
-
10
dB),

leading

to

the

possibility

of

extending

the

working

hours

to

the

evening

and

even

night

time
.


The

automated

concreting

operation

and

longer

working

hours

would

together

dramatically

speed

up

the

construction
.


The

necessity

to

cast

the

concrete

structure

in

stages

can

be

eliminated

and

the

provision

of

construction

joints

can

be

avoided
.

Introduction


It

is

not

at

all

easy

to

produce

SCC
.

In

order

for

concrete

to

be

classified

as

SCC,

it

should

have

the

following

properties
:

(
1
)

High

workability
;

(
2
)

High

passing

ability
;

and

(
3
)

High

segregation

resistance
.


To

achieve

high

passing

ability

and

high

segregation

resistance,

the

concrete

needs

to

have

relatively

high

cohesiveness


SCC

must

be

designed

to

have

high

workability

and

high

cohesiveness,

which

are

not

easy

to

achieve

concurrently
.

Introduction


The

addition

of

more

superplasticizer

to

increase

the

workability

would

at

the

same

time

reduce

the

cohesiveness
.


Concrete

producers

are

forced

to

increase

the

paste

volume

so

as

to

achieve

both

high

workability

and

high

cohesiveness
.


In

general

a

paste

volume

of

30
%

to

38
%

is

needed
.



quite

large!


What

are

the

problems

with

concrete

with

large

paste

volume

composed

only

of

cementitious

materials

and

water?

(
1
)

High

material

cost


(
2
)

Low

dimensional

stability

(
3
)

High

hydration

heat

generated

(
4
)

High

carbon

footprint

Experimental Program

Materials

Cementitious

Material
:



Ordinary

Portland

cement

(OPC)

of

strength

class

52
.
5
N

+

locally

produced

pulverized

fuel

ash

(PFA)


Relative

densities
:

OPC

=

3
.
16
;

PFA

=

2
.
52


Specific

surface

areas
:

OPC

=

336

m
2
/kg
;

PFA

=

369

m
2
/kg

Fine

Aggregates
:


Crushed

granite

rocks


Nominal

maximum

size
:

5

mm


Relative

density
:

2
.
62



Experimental Program

Materials

Fine Aggregates (continued):


Fineness modulus: 3.26


Water absorption: 0.8%

Coarse Aggregates:


Crushed granite rocks


Nominal maximum size: 20 mm


Relative density: 2.62


Fineness modulus: 6.46


Water absorption: 0.6%


Experimental Program

Materials

Superplasticiser

(SP)
:


Polycarboxylate
-
based


Relative

density
:

1
.
05


Solid

content
:

20
%


Molecules

have

a

comb
-
like

structure

consisting

of

a

backbone

chain

and

a

number

of

graft

chains

Experimental Program

Materials

Filler

1



Limestone

Fines

(LF)


Ground

to

have

fineness

similar

to

cement


Volumetric

mean

particle

size
:

8
.
4


m

Filler

2



Ground

Sand

(GS)


Ground

to

have

maximum

particle

size

of

600


m


Volumetric

mean

particle

size
:

302


m



It

was

expected

that

the

LF

would

intermix

with

the

cement

paste

to

become

powder

paste

with

a

larger

volume

whilst

the

GS

would

intermix

with

the

mortar

portion

of

the

concrete

to

become

part

of

the

mortar

Experimental Program

Mix Proportions (Percentage of Concrete Volume)

Mix

no.
1

LF

content

(%)

GS

content

(%)

Cement

paste

volume

(%)

Fine

aggregate

content

(%)

Coarse

aggregate

content

(%)

W/CM

ratio

A
-
0
-
0
-
0.40

0

0

35

32.5

32.5

0.40

A
-
6
-
0
-
0.40

6

0

29

A
-
8
-
0
-
0.40

8

0

27

A
-
0
-
0
-
0.50

0

0

35

32.5

32.5

0.50

A
-
6
-
0
-
0.50

6

0

29

A
-
8
-
0
-
0.50

8

0

27

Note
:



1. Mixes are identified by the convention: (Series)


(LF content in %)


(GS
content in %)


W/C ratio

2. SP was added until the slump flow reached at least 650 mm or the concrete mix
was showing signs of segregation.


Experimental Program

Mix Proportions (Percentage of Concrete Volume)

Mix

no.
1

LF

content

(%)

GS

content

(%)

Cement

paste

volume

(%)

Fine

aggregate

content

(%)

Coarse

aggregate

content

(%)

W/CM

ratio

B
-
0
-
8
-
0.40

0

8

33

29.5

29.5

0.40

B
-
6
-
8
-
0.40

6

8

27

B
-
8
-
8
-
0.40

8

8

25

B
-
0
-
8
-
0.50

0

8

33

29.5

29.5

0.50

B
-
6
-
8
-
0.50

6

8

27

B
-
8
-
8
-
0.50

8

8

25

Note
:



1. Mixes are identified by the convention: (Series)


(LF content in %)


(GS
content in %)


W/C ratio

2. SP was added until the slump flow reached at least 650 mm or the concrete mix
was showing signs of segregation.


Experimental Program

Mixing, Testing and Casting

Experimental

Procedures


An

electronic

balance

was

used

to

weigh

the

materials

and

a

pan

mixer

was

employed

to

produce

each

batch

of

concrete
.


During

production,

the

cementitious

materials

and

water

were

first

added

into

the

mixer
.

After

a

while

of

preliminary

mixing,

the

fillers,

fine

aggregate

and

coarse

aggregate

were

added

to

the

mixer
.


SP

was

then

added

bit

by

bit

and

the

mixing

was

continued

for

about

10

minutes

until

the

concrete

mix

appeared

wet

with

paste

formed
.

Experimental Program

Mixing, Testing and Casting

Experimental

Procedures

(continued)


Immediately

after

completion

of

the

mixing

process,

concrete

samples

were

taken

from

the

mixer

for

slump

flow

test
,

L
-
box

test

and

sieve

segregation

test
,

which

were

all

performed

within

30

minutes

to

avoid

significant

workability

loss

with

time
.


After

finishing

these

tests,

the

concrete

samples

were

put

back

into

the

mixer

for

remixing

and

then

taken

out

of

the

mixer

for

casting

a

total

of

nine

100

mm

cubes
.

The

cubes

were

cast

on

a

vibration

table
.


At

24

hours

after

casting,

the

cubes

were

demoulded

and

put

into

a

lime
-
saturated

water

curing

tank

controlled

at

a

temperature

of

27

±

2

C

until

the

time

of

cube

compression

test
.

Experimental Program

Mixing, Testing and Casting

Slump

Flow

Test


The

slump

flow

test

for

measuring

the

flowability,

as

stipulated

in

the

European

Guidelines

for

SCC
.


It

is

very

similar

to

the

slump

test

for

conventional

concrete

stipulated

in

BS
1881
:

Part

102
:

1983

and

the

same

apparatus

were

employed
.


Unlike

the

slump

test,

no

tamping

was

applied

when

filling

the

concrete

into

the

slump

cone
.

Slump flow tests for all the concrete mixes

A
-
0
-
0
-
0.4

A
-
6
-
0
-
0.4

A
-
8
-
0
-
0.4

A
-
0
-
0
-
0.5

A
-
6
-
0
-
0.5

A
-
8
-
0
-
0.5

B
-
0
-
8
-
0.4

B
-
6
-
8
-
0.4

B
-
8
-
8
-
0.4

B
-
0
-
8
-
0.5

B
-
6
-
8
-
0.5

B
-
8
-
8
-
0.5

Photos showing no segregation problem with all the concrete mixes

A
-
0
-
0
-
0.4

A
-
6
-
0
-
0.4

A
-
8
-
0
-
0.4

A
-
0
-
0
-
0.5

A
-
6
-
0
-
0.5

A
-
8
-
0
-
0.5

B
-
0
-
8
-
0.4

B
-
6
-
8
-
0.4

B
-
8
-
8
-
0.4

B
-
0
-
8
-
0.5

B
-
6
-
8
-
0.5

B
-
8
-
8
-
0.5

Experimental Program

Mixing, Testing and Casting

L
-
Box

Test


The

L
-
box

test

for

measuring

the

passing

ability,

as

stipulated

in

the

European

Guidelines

for

SCC


Apparatus
:


Note: All dimensions in mm

700

150

600

200

100

gate

2
×

12
ϕ

smooth
bars with
gap = 59 mm
for PL1

3
×

12
ϕ

smooth bars with
gap = 41 mm
for PL2

H
1

∆H
1

H
2

L
-
box ratio = H
1
/H
2

L
-
Box Test


A
-
0
-
0
-
0.4

A
-
6
-
0
-
0.4

A
-
8
-
0
-
0.4

A
-
0
-
0
-
0.5

A
-
6
-
0
-
0.5

A
-
8
-
0
-
0.5

B
-
0
-
8
-
0.4

B
-
6
-
8
-
0.4

B
-
8
-
8
-
0.4

B
-
0
-
8
-
0.5

B
-
6
-
8
-
0.5

B
-
8
-
8
-
0.5

Experimental Program:

Mixing, Testing and Casting

Sieve

Segregation

Test


The

sieve

segregation

test

for

measuring

the

segregation

resistance,

as

stipulated

in

the

European

Guidelines

for

SCC


Apparatus

and

the

test
:


Base receiver

5 mm sieve

Electronic balance

Sample
container

500


mm

15 minutes

Sieve Segregation Test


Experimental Results

Mix

no.

SP

dosage

(litre/m
3
)

Slump

flow

(mm)

L
-
box

ratio

Segregated

portion

(%)

7
-
day

cube

strength

(MPa)

28
-
day

cube

strength

(MPa)

Estimated

adiabatic

temperature

rise (
°
C)

A
-
0
-
0
-
0.40

5.5

660

0.62

7.5

60.3

81.2

48.6

A
-
6
-
0
-
0.40

10.7

675

0.88

6.6

63.5

82.9

40.6

A
-
8
-
0
-
0.40

14.0

650

0.82

5.3

62.5

86.7

38.1

A
-
0
-
0
-
0.50

3.4

640

0.63

4.3

36.6

54.3

44.1

A
-
6
-
0
-
0.50

7.7

675

0.71

4.1

43.6

66.6

36.9

A
-
8
-
0
-
0.50

11.4

710

0.89

6.0

45.1

64.7

34.3

B
-
0
-
8
-
0.40

7.0

700

0.86

5.0

59.9

84.6

45.6

B
-
6
-
8
-
0.40

17.0

780

0.90

8.8

58.5

85.7

38.2

B
-
8
-
8
-
0.40

27.0

705

0.98

6.8

58.4

82.3

35.8

B
-
0
-
8
-
0.50

5.0

690

0.78

4.2

40.0

60.5

41.4

B
-
6
-
8
-
0.50

13.0

730

0.91

4.8

44.0

65.2

34.6

B
-
8
-
8
-
0.50

18.0

775

0.91

3.6

41.1

65.7

32.5

Discussions


With

the

cement

paste

volume

reduced

from

35
%

to

25
%
,

one

immediate

benefit

is

that

the

amount

of

cementitious

materials

to

be

added

can

be

decreased

by

as

much

as

29
%
.


Reduction

of

cementitious

material

by

adding

fillers


Without

the

addition

of

fillers,

a

cementitious

materials

content

of

about

450

kg/m
3

is

generally

regarded

as

the

minimum

for

the

production

of

SCC
.


By

adding

limestone

fines

into

the

paste

to

increase

the

paste

volume,

the

cementititous

materials

content

has

been

reduced

to

320

kg/m
3
.



By

adding

also

ground

sand

into

the

mortar

to

increase

the

mortar

volume,

the

cementitious

materials

content

has

been

reduced

to

300

kg/m
3
.

Discussions


Reduction

of

heat

generation


The

substantial

decrease

in

cementitious

materials

content

due

to

the

reduction

in

cement

paste

volume

would

significantly

decrease

the

heat

generation

of

the

concrete

during

curing
.


The

addition

of

fillers

to

reduce

the

cement

paste

volume

to

25
%

can

lower

the

adiabatic

temperature

rise

by

the

order

of

10

to

16
°
C

at

the

W/CM

ratios

of

0
.
40

and

0
.
50
.

This

will

largely

reduce

the

need

of

costly

temperature

control

for

fresh

concrete

and

the

risk

of

thermal

crack

formation,

especially

in

thick

section

pours
.



SCC

mixes

with

cement

paste

volume

reduced

to

25
%

by

the

addition

of

fillers

may

be

regarded

as

low
-
heat

SCC

and

Green

Concrete
.


Discussions


Theoretically,

reduction

of

the

cement

paste

volume

would

also

decrease

the

shrinkage

and

creep,

and

increase

the

Young’s

modulus

of

the

concrete
.


In

other

words,

the

reduction

of

the

cement

paste

volume

down

to

25
%

would

significantly

increase

the

dimensional

stability

of

the

SCC
.


Hence,

the

problem

with

the

relatively

low

dimensional

stability

of

SCC

due

to

the

large

cement

paste

volume

could

be

overcome

by

adding

suitable

fine

fillers

to

reduce

the

cement

paste

volume
.

Conclusions


To

study

the

feasibility

of

adding

fillers

to

reduce

the

cement

paste

volume

in

SCC,

an

experimental

program,

in

which

two

fillers,

namely,

limestone

fines

and

ground

sand,

were

employed

for

the

production

of

SCC,

has

been

conducted
.


The

limestone

fines,

which

has

similar

fineness

as

the

cementitious

material,

was

added

to

replace

an

equal

volume

of

cement

paste


Whereas

the

ground

sand,

which

has

a

mean

particle

size

of

302


m,

was

added

to

replace

one

quarter

of

its

volume

of

cement

paste

and

three

quarter

of

its

volume

of

total

aggregate
.

Conclusions


With

up

to

8
%

limestone

fines

and

8
%

ground

sand

added,

the

cement

paste

volume

could

be

reduced

to

25
%

while

still

satisfying

the

slump

flow,

passing

ability

and

segregation

resistance

requirements

of

SCC
.


With

the

cement

paste

volume

so

reduced,

the

cementitious

materials

content

could

be

decreased

to

lower

the

material

cost,

carbon

footprint

and

temperature

rise

at

early

age
.


Moreover,

the

shrinkage

and

creep

should

be

decreased

and

the

Young’s

modulus

should

be

increased
.

Conclusions


The

various

problems

associated

with

the

large

cement

paste

volume

in

SCC

could

be

overcome

by

adding

fillers

to

reduce

the

cement

paste

volume
.


SCC

with

fillers

added

to

reduce

the

cement

paste

volume

to

only

25
%

should

be

regarded

as

second

generation

SCC
.

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