Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Chapter One
1
...
The
geopolymers depend on thermally activated natural materials like Meta
kaolinite or industrial by products like fly ash or slag to provide a source
of silicon (Si) and aluminum (Al)
...

Professor B
...
” 4 The ultimate structure of the geopolymer depends largely
on the ratio of Si to Al (Si:Al), with the materials most often considered
for use in transportation infrastructure typically having an Si:Al between
2 and 3
...

The reaction of Fly Ash with an aqueous solution containing
Sodium Hydroxide and Sodium Silicate in their mass ratio, results in a
material with three dimensional polymeric chain and ring structure
consisting of Si-O-Al-O bonds7 [1]
...

Ordinary Portland cement (opc) is used as the primary binder to produce
the concrete
...
However, it is well
1

known that the production of (OPC) is not only consumes significant
amount of natural resources and energy but also releases substantial
quantity of carbon dioxide to the atmosphere
...
8 billion tons of
the greenhouse gas emissions annually, or about 7% of the total manmade
greenhouse gas emissions to the earth's atmosphere
...
An important investigation in this regard is the
development of high volume fly ash concrete that utilizes up to 60
percent of fly ash, and yet possesses excellent mechanical properties with
enhanced durability performance
...
Fly
ash, one of the source materials for geopolymer binders, is available
abundantly worldwide
...

The production of geopolymer concrete is carried out using the
conventional concrete technology methods The fly ash consists 75% to
80% by geopolymer concrete mass of aggregate, which is bound by a
geopolymer paste formed by the reaction of the silicon and aluminum
within the fly ash and the alkaline liquid made up of sodium hydroxide
and sodium silicate solution with addition of superplasticizer [2]
...
2 Definition of geopolymer concrete
Portland cement concrete industry has grown universally in recent
years the demand for concrete as a construction material has increased
due to increase of infrastructure
...

There are many ways to reduce environmental pollution (carbon
dioxide) caused by the production of Portland cement and by the
increasing of waste material
...

It becomes a serious problem due to inadequacy of land disposal
...
Geopolymer concrete was
actually manufactured by reusing and recycling of industrial solid wastes
and by products
...
Fly ash is used as ingredients
in concrete which enhance the properties of concrete and utilization of fly
ash is helpful for consumption [3]
...
It is well evident that
production of ordinary Portland cement (OPC) not only consumes larger
quantity of natural resources but also emits larger quantity of carbon
dioxide gas to the atmosphere
...
Geopolymer concrete (GPC) is a new innovative ecofriendly material which can be produced by partial replacement of cement
in ordinary concrete by a admixture such as silica fume, Fly ash and
Ground granulated blast furnace slag along with alkaline liquid [4]
...
Hence, it is imminent to find an alternative material to the
existing most expensive most resource consuming Portland cement
...
Concrete can be cast in almost any desired shape,
and once hardened, can become a structural (load bearing) element
...

For example emissions of airborne pollution in the form of gases,
noise, dust, and vibration when operating machinery and during blasting
in quarries, devouring of large quantities of fuel during manufacture and
release of CO2 from the raw materials during manufacture
...
It is an excellent
alternative construction material to the existing cement concrete
...
The advancement of geopolymer
concrete is an important step towards the production of environmentally
4

friendly concrete
...


Geopolymerization involves a heterogeneous chemical reaction between
solid aluminosilicate oxides and alkali metal silicate solutions at highly
alkaline conditions and mild temperatures yielding three dimensional
amorphous to semi-crystalline polymeric and ring structures, which
consist of Si-O-Al and Si-O-Si bonds [3]
...
3 Limitations:
Geopolymer concrete did not harden immediately at room
temperature as in conventional concrete
...
These two limitations of
geopolymer concrete mix was eliminated by replacing 10% of fly ash by
OPC on mass basis with alkaline liquids resulted in Geopolymer Concrete
Composite and are considered as drawbacks of this concrete to be used
for practical application [3]
...
4 Applications of Geopolymer Concrete
According to Davidovits [3], geopolymeric materials have a wide
range of applications in the field of industries such as in the automobile
and aerospace, non-ferrous foundries and metallurgy, civil engineering
and plastic industries
...
Dividovits [3] classified the type of application
according to the Si: Al ratio as presented in table 1
...
For many applications in the civil engineering field, a low Si: Al
ratio is suitable Table (1
...

Table 1
...
5 Advantages:
1- The price of fly ash is low
...

3- Fire proof ie; higher resistance to heat
...

5- Eco-friendly
6- Magnificent properties within both acid and salt environments [3]
...
1) geopolymer concrete

1
...
As per

the present world statistics, every year around 260,00,00,000 Tons of
Cement is required
...

Since the Lime stone is the main source material for the ordinary
Portland cement an acute shortage of limestone may come after 25 to 50
years
...
In addition to the above huge quantity of
energy is also required for the production of cement
...

The Cement production generated carbon di oxide, which pollutes
the atmosphere
...
The waste
7

water from the Chemical Industries is discharged into the ground which
contaminates ground water
...

Waste Fly Ash from Thermal Industry + Waste water from
Chemical Refineries = Geo polymer concrete
...


8

Chapter Two
2
...
The source materials for
geopolymers based on alumina-silicate should be rich in silicon (Si) and
aluminum (Al)
...
The choice
of the source materials for making geopolymers depends on factors such
as availability, cost, type of application, and specific demand of the end
users [5]
...
The silicon and aluminium oxides in the
low-calcium fly ash reacts with the alkaline liquid to form the
geopolymer paste that binds the loose coarse aggregates, fine aggregates,
9

and other un-reacted materials together to form the geopolymer concrete
...
This
component of geopolymer concrete mixtures can be designed using the
tools currently available for Portland cement concrete
...
1
...
Fly ash is removed from the combustion gases by
the dust collection system, either mechanically or by using electrostatic
precipitators, before they are discharged to the atmosphere
...


11

Geopolymer concrete can be manufactured by using the lowcalcium (ASTM Class F) fly ash obtained from coal- burning power
stations
...

Although coal burning power plants are considered to be environmentally
unfriendly, the extent of power generated by these plants is on the
increase due to the huge reserves of good quality coal available
worldwide and the low cost of power need from these sources
...

Therefore, huge quantities of fly ash will be available for many
Years in the future (10)
...
An X-Ray
Fluorescence (XRF) analysis may be used to determine the chemical
composition of the fly ash
...
The content of the
iron oxide usually ranged from 10 to 20% by mass, whereas the calcium
oxide content was less than 5% by mass
...

The particle size distribution tests revealed that 80% of the fly ash
particles were smaller than 50 pm
...


11

2
...
2 Alkaline solutions
The alkaline liquids are from soluble alkali metals usually based on
sodium (Na) or potassium (K)
...
, 1999; Barbosa et
al
...

Palomo et al (1999) concluded that the type of alkaline liquid
played an important role in the polymerization process
...


Figure (2
...
They confirmed that the addition of sodium
silicate solution to the sodium hydroxide solution as the alkaline liquid
enhanced the reaction between the source material and the solution
...

A combination of sodium silicate solution and sodium hydroxide
(NaOH) solution can be used as the alkaline liquid
...

The sodium silicate solution is commercially available in different
grades
...
e, SiO2= 29
...
7%, and water=
55
...

The sodium hydroxide with 97-98% purity, in flake or pellet form,
is commercially available
...
The concentration of sodium
hydroxide solution can vary in the range between 8 Molar and 16 Molar;
however, 8 Molar solutions are adequate for most applications
...
For instance, NaOH solution with a
concentration of 8 Molar consist of 8x40=320 grams of NaOH solids per
litre of the solution, where 40 is the molecular weight of NaOH
...


13

2
...
3 Aggregates
Coarse and fine aggregates used by the concrete industry are
suitable to manufacture geopolymer concrete
...
1
...
The water in a lowcalcium fly ash-based geopolymer mixture, therefore, plays no direct role
in the chemical reaction that takes place; it merely provides the
workability to the mixture during handling
...
However, a small
proportion of calcium-rich source materials such as slag may be included
in the source material in order to accelerate the setting time and to alter
the curing regime adopted for the geopolymer mixture
...


14

Chapter Three
3
...
In the laboratory, the fly ash and the aggregates were first
mixed together dry in a pan mixer for about three minutes
...

The alkaline liquid was mixed with the superplasticizer and the
extra water, if any
...

The fresh concrete could be handled up to 120 minutes without any
sign of setting and without any degradation in the compressive strength
...
Fresh fly ash-based geopolymer
concrete was usually cohesive
...

Alhifadhi [8] was prepared the alkaline liquid one day before
using, and then the alkaline liquid is mixed with superplasticizer prior to
starting of the mixing process
...
After that, the mixed alkaline
liquid with superplasticizer is added to dry materials and mix for another
three minutes
...
1)
...
1) Slump flow test [R29]

3
...
All molds
are prepared before mixing geopolymer concrete as in conventional
concrete
...
As in conventional concrete the casting
process can do it in two or three layers and compacted with vibrator
...
3 CURING

[6]
Heat curing substantially assists the chemical reaction that occurs
in the geopolymer paste
...

The effect of curing time is illustrated in Figure (3
...
The test
specimens were 100x200 mm cylinders heat-cured at 60°C in an oven
...

Longer curing time improved the polymerization process resulting
in higher compressive strength
...
Therefore, heat-curing time need not be more than 24
hours in practical applications as shown in Figure (3
...
2) shows the effect of curing temperature on the compressive strength of
geopolymer concrete
...
3) Effect of curing time on compressive strength of geopolymer concrete

18

Figure (3
...
Higher curing temperature
resulted in larger compressive strength
...

Test data show that the compressive strength of dry-cured geopolymer
concrete is approximately 15% larger than that of steam-cured
geopolymer concrete
...
In laboratory trials, precast products were
manufactured using geopolymer concrete; the design specifications
required steam-curing at 60°C for 24 hours
...
The steam-curing was then
stopped for some time to allow the release of the products from the
formwork
...
This two-stage steam-curing regime did not produce any
degradation in the strength of the products
...
It was found that steam curing at 80 ˚C for a period of 4 hours
provided enough strength for de-moulding of the culverts; this was then
followed by steam curing further for another 20 hours at 80 ˚C to attain
the required design compressive strength
...
Tests have shown that a delay in the start of
heat-curing up to five days did not produce any degradation in the
19

compressive strength
...

This may be due to the geopolymerisation that occurs prior to the start of
heat-curing
...
2)
...
The test specimens (100 mm cubes) were
removed from the molds 24 hours after casting, and cured in ambient
conditions in shade as well as in direct sun-light
...
1):
Table (3
...
4) Fresh geopolymer concrete

In another study, Barber at Curtin University manufactured and
tested the properties of the following geopolymer concrete mixture
developed by the author:
20 mm Coarse aggregates : 700 kg/m3
10 mm Coarse aggregates : 350 kg/m3
Fine sand : 800 kg/m3
Fly ash (Class F) : 380 kg/m3
Sodium silicate solution (A53) : 110 kg/m3
Sodium hydroxide solution (8 Molar) : 40 kg/m3

The workability of the fresh concrete as measured by the standard
slump test was 210 mm
...
The results of the compressive strength test
performed on the test cylinders are as follows in Table (3
...
2) results of compressive strength
Age (days)

Compressive strength (MPa)

3

8

7

18

14

23

28

24

56

32

The above flexibilities in the curing regime of geopolymer concrete
can be exploited in practical applications
...
The curing methods include
oven – curing or steam - curing
...
5)

Figure (3
...
14% CaO fly ash was obtained by curing in steam at 115°F and the
compressive strength decreased with an increase in temperature
...
42% CaO fly ash, Figure (3
...

Vijaya Rangan concluded that curing temperatures and methods
influence the compressive strength of the geopolymer concrete depending
on the types of fly ash
...
6) Effect of curing temperatures and methods on compressive strength
of Geopolymer concrete with 14
...


Table (3
...


24

Figure (3
...
42% Cao fly ash (mix 14 through 18 )
...
8) curing time

Several mixes were prepared to study the effect of curing time on
the compressive strength of the concrete
...


25

Chapter Four
SHORT-TERM PROPERTIES OF GEOPOLYMER
CONCRETE
4
...
Behavior in compression
The behavior and failure mode of fly ash-based geopolymer
concrete in compression is similar to that of Portland cement concrete
...
0024 to
0
...
As expected, the modulus of elasticity increased as the
compressive strength of geopolymer concrete increased
...

This may lead to superior mechanical properties and long-term durability
of geopolymer concretes
...
12 and
0
...
These values are similar to those of Portland cement concrete
...
1
...
The silicon and aluminium oxides in the
low-calcium fly ash reacts with the alkaline liquid to form the
geopolymer paste that binds the loose coarse aggregates, fine aggregates,
and other un-reacted materials together to form the geopolymer concrete
...

This component of geopolymer concrete mixtures can be designed using
the tools currently available for Portland cement concrete
...

Vijaya Rangan was made two geopolymer concrete mixture
proportions used in laboratory studies are given in Table 2
...
For each batch of geopolymer concrete made, 100x200 mm
cylinders specimens were prepared
...

The unit-weight of specimens was also determined at the same
time
...
1)
...
1)
...
Test data show that the
compressive strength increased with age in the order of 10 to 20 percent
when compared to the 7th day compressive strength
...
1)
...
The first batch
was cast in the month of May 2005, while the second batch was cast in
the month of July 2005 and the third batch in September 2005
...
The
average humidity in the laboratory during those months was between
40% and 60%
...


Table (4
...
This test trend
is in contrast to the effect of age on the compressive strength of heatcured geopolymer concrete [5]
...
The Geopolymer concrete was a good workable mix
...
The
increase in percentage of fine aggregates and coarse aggregates increased
the compressive strength up to the optimum level
...
The
compressive strength was found reduced beyond the optimum mix
...

The optimum mix is- Fly ash: Fine aggregate: Coarse aggregate are
1:1
...
3 [9]
...
This observation is in contrast to the
well-known behaviour of OPC concrete, which undergoes hydration
process and hence gains strength over the time [10]
...
[10] concluded that : Several series of tests on
geopolymer concrete were performed
...


The compressive strength of geopolymer concrete does not

vary with the age of concrete
...
Longer curing time improves the polymerisation process
resulting in higher compressive strength
...


Commercially available Naphthalene-based superplasticizer
29

can be utilised to improve the workability of the fresh geopolymer
concrete without resulting in any segregation and degradation in the
compressive strength up to 2% of this admixture by mass of fly ash
...
There is very little difference in compressive strengths of
specimens cured immediately after casting and those sent to curing 60
minutes after casting
...


Water content plays an important role in determining the

compressive strength of geopolymer concrete as well as the workability
of the fresh concrete
...


An increase in the curing temperature increases the concrete
o

compressive strength, especially up to 75 C
...
2
...
These tests are
flexural strength according to ASTM C78 and splitting tensile strength
according to ASTM C496
...
Sofi et al also performed indirect tensile tests
on geopolymer mortar and concrete specimens made using three different
sources of low-calcium fly ash
...
Similar results are reported by Anuradha, et al
...


31

4
...
Unit-weight
The unit-weight of concrete primarily depends on the unit mass of
aggregates used in the mixture
...
When granite-type coarse aggregates were
used, the unit-weight varied between 2330 and 2430 kg/m3
...


4
...
Sulfate resistance
Test results showed that heat-cured low-calcium fly ash-based
geopolymer concrete has an excellent resistance to sulfate attack
...

The visual appearances of the test specimens after soaking in
sodium sulfate solution up to one year revealed that there was no change
in the appearance of the specimens compared to the condition before they
were exposed
...
The specimens soaked in tap water also showed no
change in the visual appearance
...

The change in length was extremely small and less than 0
...

The deterioration of Portland cement concrete due to sulfate attack is
attributed to the formation of expansive gypsum and ettringite which
causes expansion, cracking, and spalling in the concrete
...

The main product of geopolymerisation is not susceptible to
sulfate attack like the hydration products
...
However, presence of
high calcium either in the fly ash or in the aggregates could cause the
formation of gypsum and ettringite in geopolymer concrete [5]
...
5
...
Research data have shown that geopolymeric materials
performed significantly better in acid resistance compared to Portland
cement [3, 8]
...


The visual appearance of specimens after exposure to sulfuric acid
solution showed that acid attack slightly damaged the surface of the
specimens
...


The maximum mass loss of test specimens of about 3% after one
year of exposure is relatively small compared to that for Portland cement
concrete as reported in other studies
...
7, exposure to
33

sulfuric acid caused degradation in the compressive strength; the extent of
degradation depended on the concentration of the acid solution and the
period of exposure
...
7) acid resistance of heat-cured geopolymer concrete [5]

34

Chapter Five
Conclusions
Based on several researches on geopolymer concrete, the following
conclusions are drawn:
1
...


2
...


3
...
Geopolymer concrete specimens took a
minimum of days for complete setting without leaving a nail impression
on the hardened surface
...
The advantages of geopolymer concrete are ; the price of by product
materials are low, better compressive strength, higher resistance to heat,
low permeability, eco-friendly and magnificent properties within both
acid and salt environments
...
The natural materials to be used in geopolymer concrete are , kaolinite,
clays
...
The choise of the source materials for making
geopolymers depends on availability, cost, type of application
...
Geopolymer concrete can be manufactured by adopting the
conventional techniques used in the manufacture of Portland cement
concrete
...
Longer curing time improved the polymerization process resulting in
higher compressive strength
...
of curing time, beyond 24 hrs, the gain in strength is only
moderate
...
The aggregate binder interfaces are stronger in geopolymer concrete
than in the case of Portland cement concrete
...


9
...


36

References:

1
...
I
...
D
...


2
...
Vora , Urmil V
...


3
...
of Civil Engineering Mullana Ambala, Haryana, India
...
A
...


Dhinakaran

and

Mohamed

Ershad,

''Compressive strength of Silica Based Geopolymer Concrete'',
Asian Journal of Applied Sciences, 2013, ISSN 1996-3343
...
B
...
88,
Issue 4, pp
...

6
...
R
...


College, Perundurai
...
G
...
V
...
Venkata Muthyalu ,'' A STUDY ON

PERFORMANCE OF FLY ASH BASED GEOPOLYMER
CONCRETE IN CHEMICAL ATMOSPHERE'',

Pragati

Engineering College, A
...

8
...
A
...
Sc
...


9
...
I
...
D
...
5 No
...

10
...
Wallah, Dody M
...
Sumajouw, and

B
...


Rangan,

COMPRESSIVE

''

FACTORS

STRENGTH

INFLUENCING
OF

FLY

THE

ASH-BASED

GEOPOLYMER CONCRETE'', Civil Engineering Dimension,
Vol
...
2, 88–93,September 2004 ISSN 1410-9530

38



---