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.

• 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.

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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.

• It is also the most energy intensive material • 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.• Utilise waste materials from industries such as fly ash,

silica-fume, GGBS.• Protect water bodies from contamination due to fly ash

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

combustion products disposal.• Produce a more durable infrastructure.

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CONSTITUENTS

• Coarse aggregate• Fine aggregate - sand or bottom ash can be used• Admixture - superplasticizers(naphthalene based or

naphthalene sulphonate based)• 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

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-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

• 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 PERCENTAGESiO2 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 1.59

-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 CONSTITUTION

CEMENT(%)

GGBS(%)

Calcium oxide 65 40

Silicon dioxide 20 35

Aluminium oxide

5 10

Magnesium oxide

2 811

• 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

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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

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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%

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• creep of GPC smaller than that of OPC• smaller creep due to block polymerisation concept• presence of micro-aggregates increase creep resisting

function in GPC• 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

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• drying shrinkage of GPC is very less• ambient temperature cured GPC shows more shrinkage

than heat cured GPC• excess water evaporates during heat curing reducing dry

shrinkage• drying shrinkage of GPC at ambient temperature is

same as that of OPC• GPC undergoes shrinkage of 100 micro strains after one

year• 500-800 micro strains experienced by OPC

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FIGURE 2 - DRYING SHRINKAGE OF HEAT CURED AND AMBIENT CURED SPECIMEN 23

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

FIGURE 3- COMPRESSIVE STRENGTH OF GEOPOLYMER CONCRETE IN AMBIENT CONDITION

Time(days)

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• 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

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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

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• 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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• 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

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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 CONCRETE32

• 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

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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) 34

• 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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• 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 36

ADVANTAGES high compressive strength high tensile strength low creep low drying shrinkage resistant to heat and cold chemically resistant highly durable 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

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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

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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• Aslani (2015); Thermal Performance Modelling of Geopolymer

Concrete, Journal of Materials in Civil Engineering• Shankar H Sanni (2012); Performance of Geopolymer Concrete

under severe environmental conditions, International Journal on Civil and Structural Engineering

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

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

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

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