ABSTRACT
Traditional cementing materials (OPC) produced a lot of greenhouse gases such
CO2, NOx, SO3 which cause various environmental problem, It has been estimated that
for the production of one ton of cement, about two tons of raw materials (i.e. limestone
and shale) is consumed, and approximately one ton of carbon dioxide (CO2) and nitrogen
oxide (NO) gasses emitted (i.e. 0.87 ton of CO2 and 3 kg of NO). In contrast geopolymers
is ecofriendly cement material that exhibits good mechanical properties, thermal
resistance, highly durability and greenness. Geopolymer is commonly known as
inorganic aluminohydroxide polymer which is synthesized predominantly from silicon
and aluminum rich sources mainly coal ash and GGBS with alkaline liquid. In this work,
geopolymers were synthesize from coal ash derived from Larkra (ASTM class f). The
geopolymers were cured at three different curing conditions (Room Temperature, 60 ℃
and 80 oC) for 7 days. XRF, EDX FT-IR were used to characterize Coal ash,
geopolymers paste and their compressive strength were found out. The results reveled
that compressive strength of geopolymers depends on kOH concentration, curing
conditions and also coal ash to potassium hydroxide and Ca (OH2) mass ratio. Significant
Compressive strength of 0.226 Ksi=1.55 Mpa was obtained with 12M KOH ,coal ash to
potassium hydroxide ratio of 3:1 , 10 % Ca(OH2) at 6OOC
Keywords: Geopolymer, coal ash, alkaline activator, compression strength
CHAPTER-1
INTRODUCTION:
1 .1 Background of the study
A cement is a binder, a chemical ingredient used for construction that groups,
hardens, and adheres to other materials to bind them together [1]. Cement is seldom used
on its own, but rather to bind sand and gravel (cumulative) together. Cement mixed with
fine aggregate produces filling for masonry, or with gravel and grit, produces palpable.
Concrete is the most widely used material in existence and is behind only water as the
planet’s most-consumed resource [2]. Cements are dry powders and should not be
confused with concretes or mortars [3]. Cements acts as the ―glue‖ that gives strength to
structures. Cement is powder materials with water forms paste that hardens slowly [4].
1.2 History of Cement
In 1824, Joseph Aspdin din from Leeds city –England, produced a
powder made from the calcined mixture of limestone and clay [5].
He called it ―Portland Cement‖ because when it hardened it and produced a
material similar to stones from the quarter near Portland Island in UK [6].
1.3 Chemical composition of Portland cement
The chemical composition of Portland cement consist of mainly silica SiO2 alumina
Al2O3, lime Cao, Iron oxide F2O3. Over 90% of Portland cement is composed of oxides,
it may be expressed as [7].
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Table 1.1 Chemical Composition Ordinary Portland Cement.
Ingredients Percentage %
Lime (CaO) 62
Silica (SiO2) 22
Alumina (Al2O3) 5
Calcium sulphate (CaSO4) 4
Iron oxide (Fe203) 3
Magnesia (MgO) 2
Sulphur (S) 1
Total 100
There are a number of drawbacks to Portland cement manufacture [8]. Some of
the major drawbacks are. Consumption of huge amounts of natural resources and energy
.Release of greenhouse gases [9]. Portland cement is poor in mobilization and concrete
made from it are not durable in corrosive atmospheres [10].
1.4 Geopolymer
Geopolymer is also known as inorganic aluminohydroxide polymer [11], which is
synthesized predominantly from silicon and aluminum rich sources such as fly ash and
GGBS [12]. Traditional cementing materials produced a lot of greenhouse gases such
CO2 , NOx, SO3 which cause various environmental problem [13, 14], It has been
estimated that for the production of one ton of cement, about two tons of raw materials
(i.e. limestone and shale) is consumed, and approximately one ton of carbon dioxide
(CO2) and nitrogen oxide (NO) gasses emitted (i.e. 0.87 ton of CO2 and 3 kg of NO) [13].
In contrast geopolymer is ecofriendly cement material that exhibits good mechanical
properties [15], thermal resistance, high durability and greenness[16]. Fly ash are divided
in to two classes according to ASTMC618 [17]. Low calcium class F fly ash, which is
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produced from burning anthracite and bituminous coals and high calcium class C fly ash
which comes from the burning of lignite and sub-bituminous coals. Fly ash, slag and clay
are suitable raw material for the production of geopolymer [18]. The compression
strength of fly ash based geopolymer depend on various factors such alkali solutions,
Si/Al ratio, calcium oxide concentration, temperature, time and different types of
additives [19].
Raw materials used in the synthesis of silicon-based polymers are mainly rockforming minerals of geological origin, hence the name: geopolymer [20, 21]. The
utilization of GPC can reduce CO2 emission up to 80 % compared to OPC concrete by
using industrial byproduct waste materials such as GGBFS and fly ash (FA) as a total
replacement of OPC [22].
1.5 Classification of Geopolymers
According to T.F. Yen geopolymer can be classified into two main groups [23].
1.5.1 Pure inorganic geopolymers
Geopolymers are a kind of inorganic polymeric ceramic made from aluminum and
silicon sources that comprises of AlO4 – and SiO4 tetrahedral units, under highly alkaline
conditions (NaOH, KOH, CsOH = MOH) at room temperatures. They have a broad chemical
composition range, but micro-chemical analyses by EDS in the TEM1 have find the intrinsic
composition to be M2O·Al2O3 ·4SiO2 ·11H2O, anyhow the water content is variable depending
on reactant particle size and specific surface area. This chemically bonded, ceramic-like material
is a rigid, hydrated, aluminosilicate gel that contains group I, charge-ba lancing cations. It results
in an amorphous, cross-linked, impervious, acid-resistant, 3D structure. The term ―geopolymer‖
was introduced by Joseph Davidovits, an organic chemist, during the 1970s [24].
1.5.2 Organic geopolymers
Organic geopolymers are a type of geopolymer that use organic compounds as the
source of reactive silica and alumina, instead of the traditional sources like fly ash or met
kaolin. The organic compound used as the reactive source can come from waste materials
like rice husk ash, sugarcane bagasse ash, or coconut shell ash. Organic geopolymers
have several advantages over traditional geopolymers: Sustainability: Using waste
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materials as the reactive source for organic geopolymers helps to reduce waste and
promote sustainability. Improved properties: In some cases, organic geopolymers have
been shown to have improved mechanical and durability properties compared to
traditional geopolymers [25].
1.6 Basics Requirement of Geopolymer Concrete
Geopolymer concrete requires special handling, and it is difficult to create.
It requires the use of alkalies, such as sodium hydroxide/sodium silicates that can be
harmful to humans. GPC should be cured at 60-70 degree Celsius. The biggest limitation
of geopolymer as an alternatives binder is the lack of enough precursor material such as
fly ash and slag or metakaolin to meet the demand for cement [26].
1.7 Sources of geopolymer
Geopolymers can be made from various materials having alumina-silicates
and the alkaline solutions [27]. Sources materials used are kaolinite, clays[28],
zeolite[29], fly ash [30], silica fumes, slag [31], rice-husk ash [32], red mud [33] etc. The
often used alkaline liquid in geopolymerization is a combination of NaOH/KOH and
sodium silicate [34].
Geopolymerization mostly takes place in few stages where the first step is involved in
the releasing of silicates (SiO2) and aluminates (AlO2) as a starting materials which
activated by alkali and results in geopolymer gel as final yield [10]. The Final properties
of geopolymer concrete is affected by various agents like, Curing temperature, Water
content, Alkali concentration Initial solid content and so on [35].
1.8 Advantage of Geopolymers
Actually geopolymers are ceramic-like materials [36] prepared at lower temperatures by
reacting natural aluminosilicates (clays) or aluminosilicates wastes (fly ash and blast
furnace slag) with alkalis or acids[22]. Setting time 30 to 300 min. Geopolymer concrete
exhibits good strength and durability properties than OPC concrete. Geopolymer concrete
is a potential material for future because it is not only ecofriendly but also possesses
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strength and durability [37]. GPC is also cheaper than Portland cement in terms of the
material cost [22].
It is being used for Railway sleepers, Electric power poles, Road pavement,
Cement mortar, Marine structures, Waste containments. Geopolymer is an eco-friendly
construction material that utilizes zero cement for its production. Geopolymer is also an
environmentally friendly materials[38] that can utilized industrial solid wastes and have
low environmental load and energy consumption which is expected to become a
substitute for OPC [39].
1.9 Ingredients of Geopolymer Concrete
Geopolymer concrete is a type of concrete that is made by reacting aluminate and
silicates bearing materials with a caustic activators[40, 41] , such as fly ash or slag from
iron and a metal and metal production .it can be a suitable substitute for ordinary Portland
cement (OPC) [42].
1.10 Chemistry of Geopolymerization
The process of geopolymerization is a chemical reaction between an alkali
solution and a source material containing alum inosilicate (FA) and gives a three
dimensional polymeric chain and a ring structure consisting of Si-O-AL-O bonds as
reported by scheme. The reactions can occur at room temperature [43].
1.11 Properties of Geopolymer
There are a lot of properties of geopolymer .But here we will discuss few of the main
properties.
1.11.1. Compressive strength
It is one of salient property of geopolymer mortars and concrete .The
strength is different in fly ash geopolymers is mainly due to shape, size distribution,
calcium content and high amorphous micro structure of raw material .The silicon and
aluminum components of FA are activated by alkali solution. Calcium content of FA
mainly played an important role in strength development of geopolymer concrete. Alkali
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concentration also affects the strength of geopolymer concrete. With raise in
concentration of the alkali strength also increases.With increasing in kaolin, compressive
decreases .furthermore the addition of slag also increases the strength of GPC [44].
1.11.2. Durability
Durability of geopolymer means (resistance to chloride, sulfate, acid, freeze thaw,
thermal and efflorescence) depends on the microstructure and movement of ions within
the structure. Geopolymer made up from NaOH was found to be more crystalline and
therefore it will be more stable, apart from this geopolymer made from sodium silicate
activator is amorphous and hence it is considered less stable in acidic medium.
Acid resistance of geopolymer increases with curing temperature. FA based geopolymer
cured at 80 ℃for 10 hours when dipped in HCl solution did not decadence much [44].
1.11.3 Electrical properties of geopolymer pastes
Electrical properties of FA- based geopolymer pastes at different NaOH concentrations
and frequencies were determined by Hanjitsuwan et al .The dielectric constant decreased
and electrical conductivity increased with frequency [45].
1.11.4 Fire retardant property
Geopolymer have low thermal conductivity and which does not release harmful toxic
fumes when placed to firing. Geopolymer concrete are one of the most vital construction
materials which can tolerate a very high temperature. Geopolymer concrete is more
porous and also support of escape of inner steam pressure during firing due to which a
good fire-resistant materials formed [45].
1.11.5 Future prospects of geopolymers
Production of geopolymer cement and concretes having fly ash is a best alternatives to
conventional OPC concrete [46]because of various salient factors including, High early
strength economical and release less carbon also at the same time it reduces waste
generation
In this work geopolymer were synthesized from coal ash derived from Lakhra, alkaline
solutions, sand and aggregates.
Sajjad Ahmad from ICs Uop .