High Volume Fly Ash Concrete in Civil Engineering
CIVIL ENGINEERING
MATERIALS LAB
III SEMESTER
3CE4-24
PROPERTIES
OF
HIGH
VOLUME
FLY
ASH
CONCRETE
1
OVERVIEW
INTRODUCTION
PROPERTIES
OF
FRESH
HVFA
CONCRETE
PROPERTIES
OF
HARDENED
HVFA
CONCRETE
CONCLUSION
2
INTRODUCTION
Fly
ash
concrete
is an eco-friendly construction material
in which fly ash
replaces
a
part
of
Portland
cement.
Bu
t
IS:45
6
–
2
0
0
0
and
A
CI:318
allows
r
eplaceme
nt
o
f
OPC
by
Fly ash up to 35%
only
as
binding
material.
H
i
g
h
v
o
l
u
m
e
fly
ash
con
c
r
et
e
is
a
c
onc
r
et
e
whe
r
e
a
replacement
of
about
35%
or
more
of
cement is
made with the usage
of
fly
ash.
3
WHAT
IS
FLY
ASH?
Fly ash is a finely divided
byproduct resulting
from
the
combustion
of
coal in power
plants.
It contains
large
amounts
of
silica, alumina and
small
amount
of
unburned carbon,
which
pollutes
environment.
It is
grey
in
colour
and alkaline in
nature.
The
particle
size
ranges
between
1-100
microns.
The specific gravity
of
FA
lies between 1.9 and
2.8
(generally 3.15 for
Cement)
4
The
surface area is typically
300–500 m
2
/kg,
although
some FA can have a
surface
area as high as
700
m
2
/kg ( around 330
m
2
/kg
for Cement
)
The
mass per unit volume
including
air between
particles ( density ) can vary from 540 to 860
kg/m3.
5
Classification
of
Fly
Ash
Two
classes
of
fly ash
are
defined by
ASTM
C618:
Class
F fly
ash
Class
C fly
ash
This
classification is based on the chemical
composition
of
FA
i.e. the
sum
of
silica, alumina and
iron
oxide
percentages
in the
FA,
being
:
minimum
of
70%
for a
Class
F
minimum
50%
for a Class
C
6
7
SOURCE:
www.caer.uky.edu/kyasheducation/flyash.sht
ml
SOURCE:
www.gradjevinarstvo.rs
ISSUES WITH
OPC
Conventional
Portland
Cement is the
most
consumed
commodity in the
world
after
water.
It
is also the
most
energy
intensive
material
Cement
production
leads
to
high
carbon-dioxide
emission.
CO
2
is
the
primary
green
house
gas that causes global
warming
manufacturing
of
cement accounts for 6 to 7%
of
the
CO
2
that
humans
produce.
It is
produced
by
calcination
of
limestone and burning
of
fossil
fuels
8
WHY
TO
USE
FLY
ASH?
being
a pozzolanic, it
can
actually
replace
a
part
of
Portland
cement
results
in
more
durable
concrete
high ultimate
strength
improves
workability
improves
cost economy
of
concrete
reduction
in
heat
of
hydration
decreases
density
of
concrete
more
environment
friendly
concrete.
9
EFFECT OF
HIGH
VOLUME
OF
FLY
ASH
ON
PROPERTIES
OF
FRESH
CONCRETE
1.
WORKABILITY
2.
SETTING
TIME,
BLEEDING AND
SEGREGATION
3.
HEAT
OF
HYDRATION
4.
DENSITY
10
WORKABILITY
The
inclusion
of
high
volume of fly ash
increases the
workability
as the content of FA is
increased.
The
increment
in
the
slump
height
is about 40%
and 54% with the
inclusion
of
45% and 50%
FA,
respectively.
generally
higher
substitution
of Portland cement by
fly ash
reduces
the water
requirement
for
obtaining a given
workability
11
. Effect
of
fly ash
fineness & %
on
water demand
of
concrete
12
WORKABILITY
reduction
in water
requirement
is
mainly
due to
three
mechanisms:
Fly ash gets
absorbed
on the
surface
of
oppositely
charged
cement
particles
and
prevent
them
from
flocculation,
releasing
large
amounts
of
water,
thereby reducing
the water-demand for a
given
workability.
The
spherical
shape
and the
smooth
surface
of
fly
ash
particles
help to
reduce
the
interparticle
friction and thus
facilitate
mobility
Due to
its
lower
density
and
higher volume per
unit
mass,
fly
ash
is a
more
efficient void-filler
than
Portland
cement.
13
Contributions of enhanced
workability:
Light
weight concrete is easier to pump as pumping
requires
less
energy.
Improved
finishing
Reduced
segregation
and bug
holes
Reduced
Bleeding
Less
sand
is
needed in the
mix
to produce required
workability.
14
Back…
SETTING
TIME
High
volume
of
fly ash
extends both the
initial
and
final setting
time
of
concrete
The
impact
of
fly ash on the setting
behavior
of
concrete
is dependent
on:
composition
and quantity
of
fly ash
used
amount
of
cement
water - to –
cementitious material
ratio
concrete
temperature
15
Effect of FA content on penetration resistance of
setting
concrete
mixture
16
Bleeding and
Segregation
The
inclusion
of
high
volume
of
fly ash in the
mixture
reduces
the
bleeding and
segregation.
Reason:
the
rate
and
amount
of
bleeding
decreases
due
to
the
reduced
water
demand.
The
reduction
of
bleeding
and
segregation
may be
related
to the
lubricating
effect
of
the
glassy spherical
FA
particles.
17
Back…
HEAT
OF
HYDRATION
Both
the
maximum rate
of
heat evolution
and the
cumulative heat evolution
decrease with the
inclusion
of
45%
FA
during the
first
72
hours.
The
inclusion
of
45%
FA
results
in 36%
reduction
in
the cumulative
heat
evolution.
In
addition, the time
of
reaching
the maximum
rate
of
heat
evolution
delays.
18
Effect of fly ash
on
heat of
hydration
19
Source
:
optimizing-the-use-of-fly-ash-in-concrete
– by
Michael
Thomas
(www.cement.org)
Effect of fly
ash
on temperature
rise
20
Source
:
optimizing-the-use-of-fly-ash-in-concrete
– by
Michael
Thomas
(www.cement.org)
Back…
D
E
N
S
I
T
Y
Inclusion
of
high
volume
of
fly ash in
the
mixture
decreases
its
density
which leads to a
reduction
in
the dead weight
of
the constructed
element.
Reason:
This
reduction
in the density
could
be
attributed
to the
lower specific gravity
of
FA
(1.9 to
2.8)
as
compared
to
cement
(3.15)
21
Back…
EFFECT
OF
HIGH
VOLUME
OF
FLY
ASH
ON
PROPERTIES
OF
HARDENED
CONCRETE
1.
COMPRESSIVE
STRENGH
2.
DURABILITY
22
COMPRESSIVE
STRENGH
TEST
5
mixtures
were
considered
, 3
of
them with OPC
and
varying
FA
content, and 2
control
pastes using
100%
OPC or 100%
BC.
conducted
using 40%,
60%
and 80%
FA
replacement
by
volume
of
cement
maintaining the w/b by mass
constant
at
0.42
23
MIXTURE
PROPORTIONS
OF THE
PASTES
24
SOURCE:
Felipe
Rivera,
Patricia
Martínez,
Javier Castro,
Mauricio López “Massive
volume
fly ash
concrete”,
Cement and
Concrete
Composites,
Volume
63,
October
2015
The
cement pastes were prepared in a mechanical
mixer
50-mm
cube
specimens
were cast
(3 specimens
per
age)
At
the age of 24 h, the specimens
were
demolded and
placed in vacuum
sealed
plastic bags in a moist room,
(95 ± 3)%
RH
and (23 ± 2)˚C, until the age
of
testing.
25
26
SOURCE
:
Felipe Rivera, Patricia Martínez, Javier Castro, Mauricio
López
“Massive
volume fly ash
concrete”, Cement
and
Concrete Composites, Volume 63, October
2015
The
compressive strength gain after
3
d,
7
d, 28
d
and 90
d
for each
mixture
The
compressive
strength
of
the
40-F
paste is
similar
to that
of
the OPC paste
at
any
age
while
that
of
the 60-F
paste
is
very
similar
to the BC
paste at early ages (3 d and 7
d)
and
higher at 28 d
and
90
d.
The
compressive
strength
of the
80-F
paste
is
lower
than that of the BC paste at any age; its
strength
can
reach up to 22 MPa at 28 d and 35 MPa at 90
d.
27
28
Source
:
optimizing-the-use-of-fly-ash-in-concrete
– by
Michael
Thomas
(www.cement.org)
Rate
of
strength
gain
The
rate
of
strength
gain in the
FA-F
pastes
increases
with the
replacement
level.
Between
28 d and 90 d, the
strength
gain
of
OPC
paste is similar to that
of
the BC paste but
lower
than that
of
the 80-F paste (≈0.21
MPa/d).
For
the 40-F and 60-F pastes, the
strength
gains
are
the
lowest
(≈0.07
MPa/d
and 0.08
MPa/d,
respectively),
between 28 d and 90
d.
29
Back…
DURABILITY
Abrasion
Resistance
The
mix
containing
70%
FA
exhibits
a
slightly
lower
abrasion
value than
the
concrete
containing
50%
FA
and OPC
concrete
although
70%
FA
exhibits
a
higher
abrasion
value below
a
certain
compressive
strength.
The
abrasion
resistance
is mainly
dependent
on the
compressive strength
of
concrete.
It
is assumed that C-S-H
of
50%
FA
or
OPC
provide
better
cohesion
to
the
aggregate-sand-paste
and
therefore
better
resist
the action
of
surface
shear
forces.
30
Permeability
and Resistance to
Penetration
of
Chlorides
Fly
ash
reduces
permeability
of
concrete to water and
gas
provided
the
concrete
is adequately
cured,
due to
a
refinement
in the
pore
structure.
Through
pozzolanic
activity,
fly ash chemically combines
with water and CaOH
2
– forming additional cementitious
compounds,
therefore
:
it
is
not subject
to
leaching
it decreases
bleed channels,
capillary
channels
and
void
spaces and
thereby
reduces
permeability.
31
With
the
use
of fly ash,
concrete
becomes nearly
impermeable to
c
si
h
g
l
n
o
i
r
fi
i
c
d
a
e
n
s
tl
a
y
n
.
d the
rate
of
chloride penetration
decreases
32
Source
:
optimizing-the-use-of-fly-ash-in-concrete
– by
Michael
Thomas
(www.cement.org)
Alkali- Silica
Reaction
Class
F fly ash is
capable
of
controlling
alkali –
silica
reaction
in
concrete
even
at moderate
levels
of
replacement
(20%
to
30%)
Reason :
concentration
of
alkali
hydroxides
is
reduced
in
the
pore
solution
when fly ash is
present
The
level
of
fly ash
required
to
suppress
expansion
of
concrete
increases
with:
Increased
calcium and
alkali
content
of
fly
ash;
Decreased
silica content
of
fly
ash;
Increased
aggregate reactivity;
Increased
alkali
availability
from
Portland cement
and
environment
33
There
is
low
risk of
concrete expansion occurring in
the
field
when very
high volume
fly ash
concrete
with
50%
or
more
fly
ash
is
used.
34
Source
:
optimizing-the-use-of-fly-ash-in-concrete
– by
Michael
Thomas
(www.cement.org)
Sulfate
Resistance
HVFA
concrete
specimens exhibit
higher
sulfate
resistance. The specimens containing
60%
FA
as
cement
replacement
exhibited
better
performance
in lactic/acetic and sulfuric
acid
FA
induces
three
phenomena
which
improves
sulfate
resistance:
consumes
the
free
lime
resulting
it
unavailable to
react
with
sulfate,
reduces
permeability which
prevents
sulfate penetration,
and
by
replacing
cement,
the
reactive
aluminates
are
reduced.
reduced.
35
Carbonation
and
Corrosion
Resistance
When
concrete
specimens
are
exposed
to
different
methods
of
carbonation,
the
results
show
a
reduction
in
the
carbonation resistance
of
concrete specimens
with
the
inclusion
of
50%
FA
as
cement
replacement.
Therefore
there
is
increase
in the
carbonation
depth
of
concrete
specimens
in
areas
prone
to
carbonation,
particular
attention must
be paid to
ensure
suitable:
concrete mix
proportions,
period
of
moist
curing,
and
depth
of
cover
36
37
Source
:
optimizing-the-use-of-fly-ash-in-concrete
– by
Michael
Thomas
(www.cement.org)
Resistance to Cyclic
Freezing
and
Thawing,
and Deicer
Salt
Scaling
Concrete
can be
resistant
to cyclic
freezing
and thawing
provided:
38
it
has
sufficient
strength
an adequate air
void
system
the
aggregates
are
frost
resistant.
This holds
true for fly ash
concrete
concrete
containing
fly
ash
is less
resistant to scaling when
subjected to
freezing
and thawing
in
presence
of
deicer
salts.
For
fly
ash
concrete
structures
exposed to
de-icing
salts the
following
observations
have been
made:
scaling increases
as the w/cm
increases
scaling
mass loss
increases
with fly ash
content
the
use
of
curing
compounds
reduces
scaling
Back…
C
ON
C
L
USI
O
N
Use
of
high
volume
fly ash
concrete
in construction
is one big
step
in natural
resource
conservation
and it
needs
to be
promoted
all
over
the
world.
In fact,
we
can call high volume
fly ash
concrete
as a
green
concrete, since
it
can
protect
the
environment
from
global warming
and at the
same time
from
pollution.
There
may be
some negativity
attached to it like
slower
construction rates
as it
gains
strength
slowly and gives lower
early
strengths.
But,
the
same can
be
ignored
as the
later
strengths
(90 days or
more)
and durability
of
high
volume
fly ash
concrete
is
much better
than plain
concrete.
39
Clearly
there is no one replacement level best suited
for
all applications.
The
inclusion
of high volume fly ash in the
mixture
causes
:
Reduced
the
heat
of hydration, bleeding,
segregation,
density, but increased workability and setting
time.
Decreased
the mechanical
strength
especially at
early
ages with increasing FA
content.
Increased
durability of
concrete
reduced
resistance against Deicer Salt
Scaling.
40
Product
Comparisons
High
Volume
Fly
Ash
Concrete
Less
energy
intensive
manufacture
Higher
ultimate
strength
More
durable
Uses a waste
by-product
Less global
warming
gases
created
Conventional
Concrete
Energy
intensive
manufacturing
Weaker
ultimate
strength
Less
durable
Uses
virgin
material
More
global
warming
gases
created
43
High Volume Fly Ash Concrete is an eco-friendly alternative in construction, where fly ash partially replaces Portland cement. This material offers several benefits but is limited to specific replacement percentages. Understanding the properties, compositions, and benefits of using fly ash concrete can lead to more sustainable construction practices.
Download Presentation
Please find below an Image/Link to download the presentation.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author. Download presentation by click this link. If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.
E N D
Presentation Transcript
CIVIL ENGINEERING MATERIALS LAB III SEMESTER 3CE4-24
PROPERTIES OF HIGH VOLUME FLY ASH CONCRETE 1
OVERVIEW 2 INTRODUCTION PROPERTIES OF FRESH HVFA CONCRETE PROPERTIES OF HARDENED HVFA CONCRETE CONCLUSION
INTRODUCTION 3 Fly ash concrete is an eco-friendly construction material in which fly ash replaces a part of Portland cement. But IS:456 2000 and ACI:318 allows replacement of OPCby Fly ash up to 35% only as binding material. High volume fly ash concrete is a concrete where a replacement of about 35% or more of cement is made with the usage of fly ash.
WHAT IS FLY ASH? Fly ash is a finely divided byproduct resulting from the combustion of coal in power plants. It contains large amounts of silica, alumina and small amount of unburned carbon, which pollutes environment. It is grey in colour and alkaline in nature. The particle size ranges between 1-100 microns. The specific gravity of FA lies between 1.9 and 2.8 (generally 3.15 for Cement) 4
5 The surface area is typically 300 500 m2/kg, although some FA can have a surface area as high as 700 m2/kg ( around 330 m2/kg for Cement ) The mass per unit volume including air between particles ( density ) can vary from 540 to 860 kg/m3.
Classification of Fly Ash 6 Two classes of fly ash are defined by ASTM C618: Class F fly ash Class C fly ash This classification is based on the chemical composition of FA i.e. the sum of silica, alumina and iron oxide percentages in the FA, being : minimum of 70% for a Class F minimum 50% for a Class C
7 SOURCE: www.caer.uky.edu/kyasheducation/flyash.sht ml SOURCE: www.gradjevinarstvo.rs
ISSUES WITH OPC 8 Conventional Portland Cement is the most consumed commodity in the world after water. It is also the most energy intensive material Cement production leads to high carbon-dioxide emission. CO2 is the primary green house gas that causes global warming manufacturing of cement accounts for 6 to 7% of the CO2 that humans produce. It is produced by calcination of limestone and burning of fossil fuels
WHY TO USE FLY ASH? 9 being a pozzolanic, it can actually replace a part of Portland cement results in more durable concrete high ultimate strength improves workability improves cost economy of concrete reduction in heat of hydration decreases density of concrete more environment friendly concrete.
EFFECT OF HIGH VOLUME OF FLY ASH ON PROPERTIES OF FRESH CONCRETE 10 1. WORKABILITY 2. SETTING TIME, BLEEDING AND SEGREGATION 3. HEAT OF HYDRATION 4. DENSITY
WORKABILITY 11 The inclusion of high volume of fly ash increases the workability as the content of FA is increased. The increment in the slump height is about 40% and 54% with the inclusion of 45% and 50% FA, respectively. generally higher substitution of Portland cement by fly ash reduces the water requirement for obtaining a given workability
12 . Effect of fly ash fineness & % on water demand of concrete
WORKABILITY 13 reduction in water requirement is mainly due to three mechanisms: Fly ash gets absorbed on the surface of oppositely charged cement particles and prevent them from flocculation, releasing large amounts of water, thereby reducing the water-demand for a given workability. The spherical shape and the smooth surface of fly ash particles help to reduce the interparticle friction and thus facilitate mobility Due to its lower density and higher volume per unit mass, fly ash is a more efficient void-filler than Portland cement.
Contributions of enhanced workability: 14 Light weight concrete is easier to pump as pumping requires less energy. Improved finishing Reduced segregation and bug holes Reduced Bleeding Less sand is needed in the mix to produce required workability. Back
SETTING TIME 15 High volume of fly ash extends both the initial and final setting time of concrete The impact of fly ash on the setting behavior of concrete is dependent on: composition and quantity of fly ash used amount of cement water - to cementitious material ratio concrete temperature
16 Effect of FA content on penetration resistance of setting concrete mixture
Bleeding and Segregation 17 The inclusion of high volume of fly ash in the mixture reduces the bleeding and segregation. Reason: the rate and amount of bleeding decreases due to the reduced water demand. The reduction of bleeding and segregation may be related to the lubricating effect of the glassy spherical FA particles. Back
HEAT OF HYDRATION 18 Both the maximum rate of heat evolution and the cumulative heat evolution decrease with the inclusion of 45% FA during the first 72 hours. The inclusion of 45% FA results in 36% reduction in the cumulative heat evolution. In addition, the time of reaching the maximum rate of heat evolution delays.
Effect of fly ash on heat of hydration 19 Source: optimizing-the-use-of-fly-ash-in-concrete by Michael Thomas (www.cement.org)
Effect of fly ash on temperature rise 20 Source: optimizing-the-use-of-fly-ash-in-concrete by Michael Thomas (www.cement.org) Back
DENSITY 21 Inclusion of high volume of fly ash in the mixture decreases its density which leads to a reduction in the dead weight of the constructed element. Reason: This reduction in the density could be attributed to the lower specific gravity of FA (1.9 to 2.8) as compared to cement (3.15) Back
EFFECT OF HIGH VOLUME OF FLY ASH ON PROPERTIES OF HARDENED CONCRETE 22 1. COMPRESSIVE STRENGH 2. DURABILITY
COMPRESSIVE STRENGH 23 TEST 5 mixtures were considered , 3 of them with OPC and varying FA content, and 2 control pastes using 100% OPC or 100% BC. conducted using 40%, 60% and 80% FA replacement by volume of cement maintaining the w/b by mass constant at 0.42
MIXTURE PROPORTIONS OF THE PASTES 24 Cement Fly ash Fly ash Water Mixture ID (kg/m3) (%) (kg/m3) (kg/m3) 1359.7 0 0.0 571.1 OPC 1307.5 0 0.0 549.1 BC 864.4 40 434.5 545.5 40-F 594.0 60 671.7 531.6 60-F 306.4 80 924.0 516.7 80-F SOURCE: Felipe Rivera, Patricia Mart nez, Javier Castro, Mauricio L pez Massive volume fly ash concrete , Cement and Concrete Composites, Volume 63, October 2015
The cement pastes were prepared in a mechanical mixer 25 50-mm cube specimens were cast (3 specimens per age) At the age of 24 h, the specimens were demolded and placed in vacuum sealed plastic bags in a moist room, (95 3)% RH and (23 2) C, until the age of testing.
The compressive strength gain after 3 d, 7 d, 28 d and 90 d for each mixture 26 SOURCE: Felipe Rivera, Patricia Mart nez, Javier Castro, Mauricio L pez Massive volume fly ash concrete , Cement and Concrete Composites, Volume 63, October 2015
27 The compressive strength of the 40-F paste is similar to that of the OPC paste at any age while that of the 60-F paste is very similar to the BC paste at early ages (3 d and 7 d) and higher at 28 d and 90 d. The compressive strength of the 80-F paste is lower than that of the BC paste at any age; its strength can reach up to 22 MPa at 28 d and 35 MPa at 90 d.
28 Source: optimizing-the-use-of-fly-ash-in-concrete by Michael Thomas (www.cement.org)
Rate of strength gain 29 The rate of strength gain in the FA-F pastes increases with the replacement level. Between 28 d and 90 d, the strength gain of OPC paste is similar to that of the BC paste but lower than that of the 80-F paste ( 0.21 MPa/d). For the 40-F and 60-F pastes, the strength gains are the lowest ( 0.07 MPa/d and 0.08 MPa/d, respectively), between 28 d and 90 d. Back
DURABILITY 30 Abrasion Resistance The mix containing 70% FA exhibits a slightly lower abrasion value than the concrete containing 50% FA and OPC concrete although 70% FA exhibits a higher abrasion value below a certain compressive strength. The abrasion resistance is mainly dependent on the compressive strength of concrete. It is assumed that C-S-H of 50% FA or OPC provide better cohesion to the aggregate-sand-paste and therefore better resist the action of surface shear forces.
31 Permeability and Resistance to Penetration of Chlorides Fly ash reduces permeability of concrete to water and gas provided the concrete is adequately cured, due to a refinement in the pore structure. Through pozzolanic activity, fly ash chemically combines with water and CaOH2 forming additional cementitious compounds, therefore : it is not subject to leaching it decreases bleed channels, capillary channels and void spaces and thereby reduces permeability.
32 With the use of fly ash, concrete becomes nearly impermeable to cs ihglnoirf iicdaenst layn. d the rate of chloride penetration decreases Source: optimizing-the-use-of-fly-ash-in-concrete by Michael Thomas (www.cement.org)
Alkali- Silica Reaction Class F fly ash is capable of controlling alkali silica reaction in concrete even at moderate levels of replacement (20% to 30%) Reason : concentration of alkali hydroxides is reduced in the pore solution when fly ash is present The level of fly ash required to suppress expansion of concrete increases with: Increased calcium and alkali content of fly ash; Decreased silica content of fly ash; Increased aggregate reactivity; Increased alkali availability from Portland cement and environment 33
There is low risk of concrete expansion occurring in the field when very high volume fly ash concrete with 50% or more fly ash is used. 34 Source: optimizing-the-use-of-fly-ash-in-concrete by Michael Thomas (www.cement.org)
Sulfate Resistance HVFA concrete specimens exhibit higher sulfate resistance. The specimens containing 60% FA as 35 cement replacement exhibited better performance in lactic/acetic and sulfuric acid FA induces three phenomena which improves sulfate resistance: consumes the free lime resulting it unavailable to react with sulfate, reduces permeability which prevents sulfate penetration, and by replacing cement, the reactive aluminates are reduced. reduced.
Carbonation and Corrosion Resistance When concrete specimens are exposed to different methods of carbonation, the results show a reduction in the carbonation resistance of concrete specimens with the inclusion of 50% FA as cement replacement. Therefore there is increase in the carbonation depth of concrete specimens in areas prone to carbonation, particular attention must be paid to ensure suitable: concrete mix proportions, period of moist curing, and depth of cover 36
37 Source: optimizing-the-use-of-fly-ash-in-concrete by Michael Thomas (www.cement.org)
Resistance to Cyclic Freezing and Thawing, and Deicer Salt Scaling Concrete can be resistant to cyclic freezing and thawing provided: 38 it has sufficient strength an adequate air void system the aggregates are frost resistant. This holds true for fly ash concrete concrete containing fly ash is less resistant to scaling when subjected to freezing and thawing in presence of deicer salts. For fly ash concrete structures exposed to de-icing salts the following observations have been made: scaling increases as the w/cm increases scaling mass loss increases with fly ash content the use of curing compounds reduces scaling Back
CONCLUSION Use of high volume fly ash concrete in construction is one big step in natural resource conservation and it needs to be promoted all over the world. In fact, we can call high volume fly ash concrete as a green concrete, since it can protect the environment from global warming and at the same time from pollution. There may be some negativity attached to it like slower construction rates as it gains strength slowly and gives lower early strengths. But, the same can be ignored as the later strengths (90 days or more) and durability of high volume fly ash concrete is much better than plain concrete. 39
Clearly there is no one replacement level best suited for all applications. The inclusion of high volume fly ash in the mixture causes : Reduced the heat of hydration, bleeding, segregation, density, but increased workability and setting time. Decreased the mechanical strength especially at early ages with increasing FA content. Increased durability of concrete reduced resistance against Deicer Salt Scaling. 40
Product Comparisons Conventional Concrete Energy intensive manufacturing Weaker ultimate strength Less durable Uses virgin material More global warming gases created High Volume Fly Ash Concrete Less energy intensive manufacture Higher ultimate strength More durable Uses a waste by-product Less global warming gases created
