Geopolymerconcreteppt-.pdf

PHYSICAL PROPERTIES AND APPLICATIONS OF GEOPOLYMER CONCRETE

CONTENTS •

Introduction • Why not OPC? • OPC usage without environmental impact • Why geopolymer concrete? • Constituents • Process and Mechanism • Types of GPC • Test on GPC • Properties • Applications • Advantages and disadvantages • •

Discussion on future development Conclusion

INTRODUCTION •

Geopolymer concrete is an innovative, eco-friendly construction material.

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It is used as replacement of cement concrete.

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In geopolymer concrete cement is not used as a binding material.

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Fly ash, silica-fume, or GGBS, along with alkali solution are used as binders.

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FIGURE 1-GEOPOLYMER CONCRETE

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WHY NOT OPC? •

It is the most consumed commodity in the world after water.

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It is also the most energy intensive material

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Cement production leads to high carbon-dioxide emission.

- 1 ton of CO2 is produced for every 1 ton of cement.

-It is produced by calcination of limestone and burning of fossil fuels

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IS THERE A WAY TO USE OPC WITHOUT ENVIRONMENTAL IMPACT? -replacing some limestone with fly ash and blast furnace slag called as blended cement -using carbon dioxide emission captures and storage(CCS) -accelerated carbonation where CO2 penetrate concrete reacting with Ca(OH)2 in presence of H2O forming CaCO3

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WHY GEOPOLYMER CONCRETE? •

Reduces the demand of OPC which leads CO2 emission.

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Utilise waste materials from industries such as fly ash, silica-fume, GGBS.

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Protect water bodies from contamination due to fly ash disposal.

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Conserve acres of land that would have been used for coal combustion products disposal.

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Produce a more durable infrastructure. 5

CONSTITUENTS •

Coarse aggregate

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Fine aggregate - sand or bottom ash can be used

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Admixture - superplasticizers(naphthalene based or naphthalene sulphonate based)

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Alkaline activators

-Alkaline activation is a process of mixing powdery aluminosilicate with an alkaline activator .

-It produce a paste which sets and hardens within short duration 6

-Alkaline activators commonly used are sodium or potassium hydroxide. -They are used in combination with sodium silicate(water glass) or potassium silicate solution. -NaOH and Na2SiO3 are more commonly used as it leads to higher geopolymerisation rate.

-K2SiO3 solution rarely used because of high cost and lack of easy availability. -Alkali hydroxide is used for dissolution and sodium-silicate solution as binder.

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

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 8

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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 TABLE1:CHEMICAL COMPOSITION OF FLY ASH 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

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-fly ash used in concrete to increase life cycle expectancy -helps in increasing durability -improves permeability by lowering water-cement ratio -spherical shape of fly ash improves consolidation of concrete

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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 TABLE 2-CHEMICAL COMPOSITION OF GGBS CEMICAL

CEMENT(%) GGBS(%)

CONSTITUTION Calcium oxide

65

40

Silicon dioxide

20

35

Aluminium oxide 5

10

Magnesium oxide 2

8

11

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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 -Si and Al atoms in source materials dissolved using alkaline solution. -Source materials include fly ash ,GGBS, silica-fume. - gel formed by applying heat.

-This gel binds aggregates and unreacted source material forming geopolymer concrete

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• MECHANISM -dissolution of Si and Al atoms takes place through the action of OH ions

-precursor ions condense to form monomers -polycondensation of monomers to form polymeric structures

-this framework formed is called as polysilates -silate stands for silicon-oxo-aluminate building unit -chains and rings formed and cross linked through Si-O-Al bridge 14

TYPES OF GEOPOLYMER 

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 increase its compressive strength -corex slag, steel slag, iron blast furnace slag are examples

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

Rock based geopolymer

-MK-750 in the slag based geopolymer replaced by natural rock forming minerals forms this geopolymer

-feldspar and quartz are natural rock forming minerals

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

Fly ash based geopolymer

- improves workability and increase compressive strength -reduce cost of OPC along with CO2 emission

-reduce drying shrinkage -class F fly ash used commonly Alkali activated geopolymer: Heat curing at 60 to 80 οC is done. Into 1:2 aluminosilicate gel fly ash particles are embedded. Slag based geopolymer:It contains silicate, blast furnace slag and fly ash 17



Ferro-silicate based geopolymer

-same properties as that of rock based geopolymers

-has a red colour -high iron oxide content -poly type geopolymer formed by substituting some of the aluminium atoms in the matrix

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TEST ON GPC •

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% 19

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creep of GPC smaller than that of OPC

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smaller creep due to block polymerisation concept

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presence of micro-aggregates increase creep resisting function in GPC

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in OPC creep caused by cement paste

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•

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 21

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drying shrinkage of GPC is very less

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ambient temperature cured GPC shows more shrinkage than heat cured GPC

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excess water evaporates during heat curing reducing dry shrinkage

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drying shrinkage of GPC at ambient temperature is same as that of OPC

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GPC undergoes shrinkage of 100 micro strains after one year

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500-800 micro strains experienced by OPC 22

FIGURE 2 - DRYING SHRINKAGE OF HEAT CURED AND AMBIENT CURED SPECIMEN

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•

COMPRESSIVE STRENGTH

-higher compressive strength when heat activated -slag addition improves compressive strength at ambient temperature curing

Time(days)

FIGURE 3- COMPRESSIVE STRENGTH OF GEOPOLYMER CONCRETE IN AMBIENT CONDITION

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compressive strength of GPC decreased with increasing fly ash content

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it increased with higher aggregate content

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higher strength at lower alkali content

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compressive strength increased with age

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Polycondensation of silica and alumina contribute to high strength

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• MODULUS OF ELASTICITY AND POISSON’S RATIO -modulus of elasticity increased with compressive strength in OPC

-similar trend in GPC but values lower than OPC -GPC cured at elevated temperature yields higher value of E than cured at ambient temperature

-Poisson’s ratio of GPC similar to that of OPC and increased with compressive strength

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TABLE 3 -YOUNG’S MODULUS AND POISSON’S RATIO

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PROPERTIES •

Workability

-increase in NaOH and sodium silicate solution reduce flow of mortar -superplasticizer or extra water can be added to increase workability •

Compressive strength

-it depends on curing time and temperature -it increase with fly ash content

-it increase with fineness of fly ash 29

•

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 30

•

Behaviour of geopolymer at elevated temperature -high strength loss during early heating period(up to 200οC) -beyond 600οC no further strength loss -no visible cracks up to 600 οC -minor cracks at 800 οC -GPC with more compatability between aggregates and matrix led to less strength loss • Bond strength -very high -about one third of its compressive strength -four times than that of OPC 31

APPLICATIONS •

PAVEMENTS

-light pavements can be cast using GPC -no bleed water rise to the surface -aliphatic alcohol based spray used to provide protection against drying

FIGURE 5 – PLACING OF PAVEMENT USING GEOPOLYMER CONCRETE 32

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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 33

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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

FIGURE 7 - INSITU WATER TANKS WITH BLENDED CONCRETE (LEFT) AND GEOPOLYMER CONCRETE (RIGHT)

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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. 35

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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

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ADVANTAGES 

high compressive strength



high tensile strength

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low creep



low drying shrinkage

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resistant to heat and cold

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chemically resistant

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highly durable

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fire proof

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DISADVANTAGES 

difficult to create

-requires special handling -chemicals like sodium hydroxide are harmful to humans

-high cost of alkaline solution 

Pre-mix only

-sold only as pre-mix or pre-caste material 

Geopolymerisation process is sensitive

-lacks uniformity 38

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 39

CONCLUSION •

Geopolymer concrete is a promising construction material due to its low carbon dioxide emission

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High early strength, low creep and shrinkage, acid resistance, fire resistance makes it better in usage than OPC

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Wide spread applications in precast industries due to -its high production in short duration -less breakage during transportation

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Enhanced research along with acceptance required to make it great advantage to the industry 40

REFERENCES •

Aslani (2015); Thermal Performance Modelling of Geopolymer Concrete, Journal of Materials in Civil Engineering

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Shankar H Sanni (2012); Performance of Geopolymer Concrete under severe environmental conditions, International Journal on Civil and Structural Engineering

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Ramujee et al (2014), Development of Low Calcium Fly Ash Based Geopolymer Concrete, IACSIT International Journal of Engineering and Technology, Volume 6

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Lloyd et al (2010);Geopolymer concrete: A review of development and opportunities

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Bakharev, T., (2005(a)), Resistance of geopolymer materials to acid attack, Cement and Concrete Research, 35, pp 658-670. 41