Geopolymer cement is an environmentally friendly alternative to Portland cement that has lower carbon emissions in production. It uses industrial byproducts like fly ash or slag as precursors and reacts them with an alkaline solution to form a binding material. Geopolymer cement cures at room temperature and can develop strength faster than Portland cement in some cases. It performs well in durability tests with less creep and shrinkage compared to Portland cement. Geopolymer concrete made from fly ash or slag precursors activated by an alkaline solution forms a polymer network that provides strength and is more resistant to corrosive environments than Portland cement concrete.

1. Geopolymer Cement
PHYSICAL PROPERTIES & APPLICATIONS OF GEOPOLYMER CEMENT
Saifullah Mahmud 王方 (2093191) | Cement Chemistry | 12-June-2021

2. Saifullah Mahmud 王方 (2093191) | Cement Chemistry
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Abstract
Geopolymer cement is a binding system that hardens at room temperature. It is a more
environmentally friendly alternative to conventional Portland cement. It relies on
minimally processed natural materials or industrial byproducts to significantly reduce the
carbon footprint of cement production, while also being highly resistant to many common
concrete durability issues. Geopolymer cements exist which may cure more rapidly than
Portland-based cements. Geopolymer is one of the most important alternatives to Portland
cement but cannot replace completely. It is used as replacement of cement concrete. In
geopolymer concrete cement is not used as a binding material. Fly ash, silica-fume, or
GGBS, along with alkali solution are used as binders.
Keywords: Geopolymer, Cement, Carbon footprint, Durability.
INTRODUCTION
Portland cement production is a resource-intensive, energy-intensive process that emits
enormous volumes of the greenhouse gas CO2 into the environment. About 2.8 tons of raw
materials, including fuel and other resources, are required to produce one ton of Portland
cement. The de-carbonation of lime results in around 1 ton of CO2 being produced per ton
of cement manufactured. Currently, attempts are being undertaken to promote the use of
pozzolans as a partial replacement for Portland cement. Another class of cementitious
materials, made from alumina-silicate precursors activated in high alkali solution-
geopolymers, has recently emerged. Geopolymer cements are a form of inorganic
cementitious material that is relatively new. They can be utilized as a potential replacement
to some traditional construction materials, such as Portland cement, because they synthesis
under alkali activation and form geopolymers with binding ability. Due to its remarkable
mechanical, chemical, and physical qualities and potential widespread practical application
in civil infrastructure building, waste encapsulation, and sustainable development, this
material has recently been widely explored.

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PRODUCTION OF GEOPOLYMER CEMENT
An aluminosilicate precursor material such as metakaolin or fly ash, a user-friendly
alkaline reagent, and water are required for the production of geopolymer cement. With the
inclusion of a source of calcium cations, such as blast furnace slag, room temperature
hardening is more easily accomplished. Geopolymer cements can be made to cure faster
than Portland-based cements; certain mixtures can reach their full strength in as little as 24
hours. They must, however, set slowly enough to be mixed in a batch plant, either for pre
casting or for delivery in a concrete mixer. Geopolymer cement can also build a strong
chemical connection with aggregates made of silicate rock.
Chemistry: Portland cement vs Geopolymer cement
Left: hardening of Portland cement (P.C.) through hydration of calcium silicate into
calcium silicate hydrate (C-S-H) and portlandite, Ca (OH)2.
Right: hardening (setting) of geopolymer cement (GP) through poly-condensation of
potassium oligo-(sialate-siloxo) into potassium poly(sialate-siloxo) cross linked network.
If a geopolymer compound requires heat setting it is not called geopolymer cement but
rather geopolymer binder.

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CONSTITUENTS
1. Coarse aggregate
2. Fine aggregate - sand or bottom ash can be used
3. Admixture - superplasticizers (naphthalene based or naphthalene sulphonate based)
4. Alkaline activators
a) Alkaline activation is a process of mixing powdery aluminosilicate with an
alkaline activator.
b) It produces a paste which sets and hardens within short duration
c) Alkaline activators commonly used are sodium or potassium hydroxide.
d) They are used in combination with sodium silicate (water glass) or potassium
silicate solution.
e) NaOH and Na2SiO3 are more commonly used as it leads to higher
geopolymerisationrate.
f) K2SiO3 solution rarely used because of high cost and lack of easy availability.
g) Alkali hydroxide is used for dissolution and sodium-silicate solution as binder.
❖ Sodium hydroxide
- dissolved in water to form a semi-solid paste
-higher amount reduces ettringite
-makes crystalline product which is stable in aggressive environment
❖ Potassium hydroxide
-improve porosity and compressive strength
❖ Sodium silicate (water glass)
-available in gel form
-for good pozzolanic reaction it is mixed with NaOH

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❖ Fly ash
-combustion by-product of coal in coal fired power plants
-two classes of fly ash are F and C
OXIDES PERCENTAGE
SiO2 52
Al2O3 33.9
Fe2O3 4
CaO 1.2
K2O 0.83
Na2O 0.27
MgO 0.81
SO3 0.28
LOI 6.23
SiO2/Al2O3 1.5
TABLE1: CHEMICAL COMPOSITION OF FLY ASH

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❖ GGBS
-a mineral admixture of silicates and aluminates of Ca and other bases
-same main chemical constituents as OPC but in different proportions
-improves compressive strength of GPC
CEMICAL
CONSTITUTION
CEMENT (%) GGBS (%)
Calcium oxide 65 40
Silicon dioxide 20 35
Aluminium oxide 5 10
Magnesium oxide 2 8
TABLE 2-CHEMICAL COMPOSITION OF GGBS
❖ Silica fume
-also called as micro silica or condensed silica fume
-produced during manufacture of silicon by electric arc furnace
-another artificial pozzolan

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PROCESS
a) Si and Al atoms in source materials dissolved using alkaline solution.
b) Source materials include fly ash, GGBS, silica-fume.
c) gel formed by applying heat.
d) This gel binds aggregates and unreacted source material forming geopolymer
concrete.
MECHANISM
a) dissolution of Si and Al atoms takes place through the action of OH ions
b) precursor ions condense to form monomers
c) polycondensation of monomers to form polymeric structures
d) this framework formed is called as polyciliate
e) -Silate stands for silicon-oxo-aluminate building unit
f) chains and rings formed and cross linked through Si-O-Al bridge

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TYPES OF GEOPOLYMER
1. Slag based geopolymer
Slag is a mixture of metal oxides and silicon dioxide. A transparent by-product material
formed in the processing of melting iron ore. OPC replacement with slag improve
workability and reduce lifecycle costs. It also increases its compressive strength. Corex
slag, steel slag, iron blast furnace slag are examples
2. Slag based geopolymer
Slag is a mixture of metal oxides and silicon dioxide. A transparent by-product material
formed in the processing of melting iron ore. OPC replacement with slag improve
workability and reduce lifecycle costs. It also increases its compressive strength. Corex
slag, steel slag, iron blast furnace slag are examples.
3. Slag based geopolymer
Slag is a mixture of metal oxides and silicon dioxide. A transparent by-product material
formed in the processing of melting iron ore. OPC replacement with slag improve
workability and reduce lifecycle costs. It also increases its compressive strength. Corex
slag, steel slag, iron blast furnace slag are examples.
4. Slag based geopolymer
Slag is a mixture of metal oxides and silicon dioxide. A transparent by-product material
formed in the processing of melting iron ore. OPC replacement with slag improve
workability and reduce lifecycle costs. It also increases its compressive strength. Corex
slag, steel slag, iron blast furnace slag are examples.

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TEST ON GPC
1. CREEP TEST
-three 150x300 mm cylinders prepared
- placed on creep testing frame with hydraulic loading system
-before loading 7th day compressive strength determined
-load corresponding to 40% of mean compressive strength applied
-strain values measured and recorded
-test conducted at 23οC and relative humidity 40-60%
a) creep of GPC smaller than that of OPC
b) smaller creep due to block polymerisation concept
c) presence of micro-aggregates increase creep resisting function in GPC
d) in OPC creep caused by cement paste
2. DRYING SHRINKAGE TEST
-75x75x285 mm prisms with gauge studs used
-specimens kept in a controlled temperature environment
-temperature at 23οC and relative humidity 40-60%
-shrinkage strain measurements taken on third day of casting concrete
-specimen demoulded and 1st measurement taken
-horizontal length comparator used for measurement
-next measurement taken on 4th day
-further measurements taken till one year

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a) drying shrinkage of GPC is very less
b) ambient temperature cured GPC shows more shrinkage than heat cured GPC
c) excess water evaporates during heat curing reducing dry shrinkage
d) drying shrinkage of GPC at ambient temperature is same as that of OPC
e) GPC undergoes shrinkage of 100 micro strains after one year
f) 500-800 micro strains experienced by OPC
FIGURE 2 - DRYING SHRINKAGE OF HEAT CURED AND AMBIENT CURED
SPECIMEN
FIGURE 3- COMPRESSIVE STRENGTH OF GEOPOLYMER CONCRETE IN
AMBIENT CONDITION

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COMPRESSIVE STRENGTH
-higher compressive strength when heat activated
-slag addition improves compressive strength at ambient temperature curing
• compressive strength of GPC decreased with increasing fly ash content
• it increased with higher aggregate content
• higher strength at lower alkali content
• compressive strength increased with age
• Polycondensation of silica and alumina contribute to high strength
NATURE OF GEOPOLYMER
1. Resistance against aggressive environment
-used in constructing marine structures
-in OPC white layer of crystals formed on acid exposed surface
-in GPC there is no gypsum deposition and no visible cracks
-a soft and powdery layer formed during early stages of exposure which later becomes
harder
-mass loss on exposure to H2SO4 in GPC was 3% and in OPC 20-25%
-higher the alkali content higher the weight loss
-GPC showed better resistance

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2. Behavior of geopolymer at elevated temperature
-high strength loss during early heating period (up to 200ο
C)
-beyond 600ο
C no further strength loss
-no visible cracks up to 600 ο
C
-minor cracks at 800 ο
C
-GPC with more compatability between aggregates and matrix led to less strength loss
3. Bond strength
-very high
-about one third of its compressive strength
-four times than that of OPC
APPLICATIONS
a) PAVEMENTS
-light pavements can be cast using GPC
-no bleed water rises to the surface
-aliphatic alcohol-based spray used to provide protection against drying
FIGURE 5 – PLACING OF PAVEMENT USING GEOPOLYMER CONCRETE

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b) RETAINING WALL
-40MPa precast panels were used to build a retaining wall
-panels were 6m long and 2.4m wide
-these panels were cured under ambient condition
FIGURE 6 – PRECASTE GEOPOLYMER RETAINING WALLS FOR A PRIVATE
RESIDENCE WATER TANKS
c) WATER TANKS
-two water tanks were constructed, one with 32MPa concrete with blended cement and
other with GPC
-autogenous healing occurred in OPC due to calcium hydroxide deposition
-in GPC tank there is little calcium hydroxide
-nominal leaking in tank healed rapidly due to gel swelling mechanism

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FIGURE 7 - INSITU WATER TANKS WITH BLENDED CONCRETE (LEFT) AND
GEOPOLYMER CONCRETE (RIGHT)
d) BOAT RAMP
-approach slab on ground to ramp was made using geopolymer
reinforced with FFRP
-entire constituents remained dormant until activator chemicals were added
FIGURE8 – BOAT RAMP CONSTRUCTED WITH BOTH IN-SITE AND PRECAST
GEOPOLYMER CONCRETE.

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e) PRECAST BEAM
-GPC beams formed three suspended floor levels of GCI building
-beams had arched curved soffit
-water pipes were placed inside them for temperature controlled hydronic heating
of building spaces above and below
FIGURE 9 – GEOPOLYMER CONCRETE BEAM CRANED TO POSITION
ADVANTAGES & DISADVANTAGES
Advantages Disadvantages
I. high compressive strength
II. high tensile strength
III. low creep
IV. low drying shrinkage
V. resistant to heat and cold
VI. chemically resistant
VII. highly durable
VIII. fire proof
I. difficult to create
-requires special handling
-chemicals like sodium hydroxide are
II. harmful to humans
-high cost of alkaline solution
III. Pre-mix only
-sold only as pre-mix or pre-caste
material
IV. Geopolymerisation process is
sensitive
-lacks uniformity

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DISCUSSION ON FUTURE DEVELOPMENT
-more studies and wide scale acceptance for using GPC in precast concrete products
-making GPC more user friendly by using lower amount of alkaline solution
-producing more cost effective geopolymer
-replacing fine aggregate with quarry sand as demand for natural sand is increasing
-studies on fibre reinforced geopolymer concrete for improving flexural strength
CONCLUSION
Geopolymer concrete is a promising construction material due to its low carbon dioxide
emission. High early strength, low creep and shrinkage, acid resistance, fire resistance
makes it better in usage than OPC. Wide spread applications in precast industries due to.
Its high production in short duration. less breakage during transportation. Enhanced
research along with acceptance required to make it great advantage to the industry

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REFERENCES
1. Geopolymer Cement; Environmental Considerations. J Terry Gourley [Nov, 2020]
2. Geopolymer cement and concrete: N.B.Singh, Mukesh Kumar , Sarita Rai [May
2020]
3. Unconfined Compressive Strength of Geopolymer Cement: Sarbajit PandaBikasha
Chandra PandaBikasha Chandra Panda [January 2020]
4. Current development of geopolymer cement with nanosilica and cellulose
nanocrystals : Cut Rahmawati, Sri Aprilia ,Taufiq Saidi, Teuku Budi Aulia
[February 2021]
5. Novel one-part ferro-phosphate geopolymer cement: Aleksandar Nikolov
[December 2020]
6. Utilization of geopolymer cements as supercapacitors: influence of the hardeners
on their properties: Martin Pengou, Bertrand Ngoune, Herve Tchakoute Kouamo,
Charles Péguy Nanseu-Njiki, Emmanuel Ngameni [June 2020]
7. Utilization of Industrial By-Products/Waste to Manufacture Geopolymer
Cement/Concrete: Numanuddin Azad, Samindi M.K. Samarakoon [January 2021]