012- Sulphuric Resistant Geopolymer

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Indian Journal of Engineering & Materials SciencesVol. 19, October 2012, pp. 357-367

Sulphuric acid resistant ecofriendly concrete from geopolymerisation of blast

furnace slag

N P Rajamanea*, M C Nataraja

b, N Lakshmanan

c, J K Dattatreya

d & D Sabitha

e

aSRM University, Kattankulathur 603 203, India,bDepartment of Civil Engineering, S J College of Engineering, Mysore 570 006, India

cCSIR-Structural Engineering Research Center, Chennai 600 113, IndiadSiddaganga Institute of Technology, Tumkur 572 103, India

eCSIR-National Geophysical Research Institute, Hyderabad 500 007, India

Received 13 July 2011; accepted 11 September 2012

In this study, geopolymer is prepared from ‘ground granulated blast furnace slag’ (GGBS)–a powder from grinding the

by-product of slag waste from blast furnace of steel plants. For comparison, conventional cement, Portland pozzolanacement (PPC) containing fly ash was considered. To achieve simultaneous acidic and sulphate attack, sulphuric acid is usedfor durability studies. The test data indicate that on exposure to 2% and 10% sulphuric acids, the losses in weight, thickness

and strength of geopolymer concrete (GPC) are significantly much less than those for Portland pozzolana cement concrete(PPCC). The GPCs have inorganic polymers of alumino-silicates as binder, generally without any free lime. Therefore,GPCs resist acid attack better than free lime containing conventional concretes containing Portland cement. The bindingaction in GPC is through geopolymerisation of GGBS using alkaline activator solution (AAS) made of sodium hydroxide

and sodium silicate solutions. The geopolymer eliminates use of Portland cement in structural concretes by utilizing theindustrial by-product GGBS, thereby reducing considerably the carbon footprint measured by ‘embodied energy’ and‘embodied carbon’, i.e., ‘CO2e emission’ of concrete.

Keywords: Geopolymer, Sulphuric acid, Portland pozzolana cement, Fly ash, Blast furnace slag powder, Sodium hydroxide,

Sodium silicate

Portland cement, a conventional binder in concretes,has performed satisfactorily in most of the civil

engineering applications1,2. However, this cement is

highly internal-energy-intensive (with high ‘embodied

energy’ contents) and also, its production involves

emission of green house gas of CO22 and concrete

made with this cement were observed to be less

durable in some of the very severe environmental

conditions3,4. These facts have urged engineers to look

for development of alternate concretes. In this regard,

geopolymer concretes (GPCs) have emerged as

potential candidate materials5-12

.

These new concretes utilise industrial wastes in theform of fly ash (FA) and ground granulated blast furnace

slag (GGBS) which are activated by alkaline medium to

produce ambient temperature cured inorganic polymeric

binder (called as geopolymers) in the form of alumino-

silicates. However, in order to make these new concretes

acceptable in practical applications, they should be

shown to possess both adequate strength and durability

characteristics. These aspects were studied in the

extensive investigations carried out at CSIR-SERC,Chennai

13-18. The test results discussed in this paper are

with regards to sulphuric acid resistance of GPC made

from GGBS only. Since the above mentioned industrial

wastes become ‘geopolymeric resource material’, they

can be now considered as by-products, instead of so

called waste. Though the term, ‘geopolymer’ has

become now more common to represent the synthetic

alkali aluminosilicate material (produced by reaction of

a solid aluminosilicate with a highly concentrated

aqueous alkali hydroxide or silicate solution), it is

worthwhile to note that the following nomenclatures are

also reported to describe similar materials: (i) inorganicpolymer19, (ii) low-temperature aluminosilicate glass20-22,

(iii) alkali-activated cement23-25, (iv) alkali-activated

binders26-27

, (v) geocement

28, (vi) alkali-bonded ceramic

29

(vii) inorganic polymer concrete30

, (viii) hydroceramic

31,

(ix) mineral polymers32, (x) inorganic polymer glasses33,

(xi) alkali ash material34, (xii) soil cements35, (xiii) alkali

activated aluminosilicate36

It is seen that ‘geopolymer’ is a versatile binder

being studied by scientists of various backgroundsand expertise, but, having good potential to become

__________*Corresponding author (E-mail:[email protected] )



INDIAN J ENG. MATER. SCI., OCTOBER 2012358

eco-friendly alternate to Portland cement for use incivil engineering applications. But, to understand

various aspects of this new material from the

literature, it is necessary to consider the abovenomenclatures also so that the information available

in various forums is readily utilised. In the presentpaper, more widely used term, ‘geopolymer’ is

adopted for presentation of data and discussion.

Aims of Present Study Since Portland pozzolana cement (PPC) is the most

easily available cement in the market at present, it

was chosen to produce a typical conventional cement

concrete. GGBS based GPC mix was selected based

on the earlier works carried out at CSIR-SERC. The

cylindrical specimens (75 mm dia × 75 mm height)were employed for studying the resistance of

concretes to 2% and 10% sulphuric acid solutions and

100 mm cubes for evaluating compressive strengths.

Besides visual observations, changes in weight and

strength after predetermined exposure periods to acid

were recorded. The sulphuric acid resistance test is a

very severe durability test on concretes since this acid

combines the effects of both acidic and a sulphate

environment simultaneously and therefore, the actual

test duration is much shorter than many otherdurability tests.

GPC being a new material of construction, requiresto be assessed for both strength and durability

characteristics. The GPC utilises industrial by-productof blast furnace slag from steel plants. The test data in

this paper is expected to enable the engineers to

examine the durability aspects of the GPC from

GGBS which is obtained after grinding the slag and

consider them for construction of actual structures.The test data of this study provides a basis for

complete elimination of highly energy intensive

Portland cement from concrete which is the most

widely used construction material. The new concrete

produced from the industrial by-product slag wouldnot only have low carbon footprint with low

‘embodied energy’ and ‘low carbon dioxide

emission’, but also it is more durable material with

higher and faster strength development capability.

Though this paper deals with sulphuric acid

resistance of concretes, it is necessary to look at many

other parameters such as sulphate attack, chloride

diffusion, water absorption, stability of geopolymeric

gel formed, bond strength of GPC with steel bars,corrosion protection to embedded steel, alkalinity

level of matrix formed and flexural and otherstructural behaviour of reinforced concrete sections

are also important. These aspects are covered in many

earlier studies

37-44

. However, we must note that‘geopolymer’ is a very generic word and this can form

from a variety of geopolymeric source materials, suchas fly ash, GGBS, metakaolin, rice husk ash, synthetic

alumina and silica apart from possibility a large

number of activator solution formulations. Therefore,

unlike, Portland cement, careful understanding of

different geopolymeric composites is necessary.

Experimental ProcedureMaterials

Properties of materials are described in Tables 1a-1f.

It may be noted here that any concrete requires fine

aggregates (particles smaller than 4.75 mm) andcoarse aggregates (particles larger than 4.75 mm) so

that a packing of these two inert filler materials

creates minimum space for binder paste in the

concrete mix and this is required from economic point

of view also since binder portion is generally the most

expensive in any concrete mix. The river sand as fine

aggregate and crushed granite stone as coarse

aggregate are very commonly adopted for

conventional concrete mixes and the same were

chosen for GPC mixes. The test data also showed that

the chosen aggregates act satisfactorily as almost inert

filler system in both types of concretes.The fly ash described in Table 1c is Class F and

was obtained from North Chennai Thermal Power

Plant where fly ash is being collected dry through

electrical precipitators.

Preparations of test specimens

The mix proportions (Table 2) were arrived by trial

mixes, so that the satisfactory workability with a

slump cone value of at least 100 mm is achieved and

the mix was easily compactable by a laboratory table

Table 1a—Properties of Portland pozzolana cement (PPC)

Sl.No

Descriptions PPC

1 Fineness (cm2 /g) 306

2 Normal consistency (%) 31

3 (a) Initial setting time (min) 55

(b) Final setting time (min) 100

4 (a) Soundness Le Chatelier expansion (mm) 0.5

(b) Soundness autoclave expansion (%) 0.08

5 Compressive strength (MPa) at 28 Days 56

6 Specific gravity 3

9 Loss on ignition (%) 1.31



RAJAMANE et al.: GEOPOLYMER CONCRETE 359

vibrator. Ingredients were weighed in digital balances;

mixing was done in a pan mixer for a minimum period

of 5 min to achieve the uniformity in the mix. Thefreshly prepared mix was weighed for density and

placed into the steel mould in three layers andcompacted using a laboratory table vibrator. The

specimens were demoulded after 24 h of casting. GPC

specimens were self cured by storing them openly underambient laboratory conditions (temperature 25-35ºC,

relative humidity of 65-85%). The conventional

Portland pozzolana cement concrete (PPCC) specimens

were kept submerged in water for effective curing.

The alkali activator solution (AAS) mentioned inTable 2 is made from the mixture of sodium

hydroxide solution and sodium silicate solution. The

quantity of this liquid AS taken was 55% by weight of

binder which, in the present case of GPC is GGBS.

This binder/AAS ratio of 0.55 provided sufficientworkability to the fresh GPC mix. The AAS can be

considered to be consisting of Na2O and SiO2 besideswater. As Na2O is more important from

geopolymerisation point of view, its content with

reference to geopolymeric binder was computed andthis was found to be about 5% as mentioned in Table 2.

Acid attack test on concrete specimens

The concentrated sulphuric acid (98% concentration

and density of 1.84 g/cc) was used to prepare thesulphuric acid of 2% and 10% concentrations. For this,

following formula was used:

Table 1b—Properties of ground granulated blast furnace slag (GGBS)

Chemical compositionLoss ofignition %

Glasscontent %

Finenesscm2 /g

Specificgravity CaO SiO2 Al2O3 Na2O KO MgO LOI

2.1 85 4000 2.92 40.3 43.4 12.5 0.9 0.6 1.5 2.1

Table 1c—Properties of fly ash

S. No Components IS 3812 (2003)Specifications

Fly ash used

1 SiO2 + Al2O3 +Fe2O3 70% min 98%

2 SiO2 35% min 59%

3 Al2O3 - 31%

4 Fe2O3 - 8%

5 MgO 5% max 0.22-0.34%

6 Total sulphur as SO3 2.75% max -

7 Alkalis as Na2O 1.5 % max 0.54%

8 LOI 12% max 1.05-1.08%

9 CaO - 0.86-1.02%

10 Specific gravity - 2.2

11 Bulk density - 950 kg/m3

12 Fineness (Blaine) - 3435 cm2 /gm

Table 1f—Properties of Sodium hydroxide flakes (SHf)

Property Literature* Present study

Molecular formula NaOH NaOH

Molar mass 39.9971 g/mol 40 (used for computation)

Appearance White solid White solid

Density and phase 2.1 g/cm³, solid 2.1 g/cm³, solid

Solubility in water 111 g/100 mL (20°C) Could easily dissolve 100 g in 100 mL of distilled waterat ambient temperature of 30°C

Melting point 318°C Not determined

Boiling point 1390°C Not determined

Basicity (pKb) -2.43 -Not determined

Exposure to air Highly hygroscopic in nature Observed to be highly hygroscopic

Amount of heat liberated

when dissolved in water

44.45 kJ/mol = 1.1111 kJ/g = 266 calories/gram Not determined

Storage Air tight container (absorbs CO2 from the air) Stored in air tight container

* http://www.answers.com/library/Wikipedia-cid-76614

Table 1d—Properties of aggregates

Sl. No Property Coarse aggregate Fine aggregate

1 Specific gravity 2.72 2.65

2 Water absorption 1.20 % 0.50 %3 Fineness modulus 6.68 2.44 Bulk density 1650 kg/m3 1550 kg/m3

5 Source Crushed granite stone River bed

Table 1e—Properties of sodium silicate solution

Property Literature* Present study

Specific Gravity 1.56-1.66 1.62Na2O 15.5-16.5 16.1

SiO2 31-33 32.1Weight ratio 2.2 2.0Molar ratio 2.2 1.94Iron content, ppm <100 58

*Source : http://www.pqcorp.com (URL4)




R = D1 * [(C1 / C2) - 1] … (1)

where, C1 is %concentration of commercially

available conc. sulphuric acid, D1 is density of conc.

sulphuric acid of concentration C1 (g/mL), C2 is%concentration of desired diluted sulphuric acid for

testing, R is volume of water added per mL of

sulphuric acid of concentration, C1 to get diluted

sulphuric acid of concentration, C2

Thus, it was noted that about 11 mL of 98%

concentrated sulphuric acid (conc. H2SO4) was

required to be mixed with 989 mL of distilled water to

get 1 L of 2% acid solution for test. On the other

hand, 1 L of 10% acid solution is obtained by mixing

58 mL of 98% concentrated sulphuric acid (conc.

H2SO4) with 942 mL of distilled water. The

cylindrical specimens were submerged in acidsolution kept in a plastic tubs such that there was a

minimum of 30 mm depth of acid over the top surface

of specimens. The pH of the solution was monitored

periodically using pH meter and also by titration with

standard alkaline solution. The specimens are taken

out from acid tank at the end of each test period for

visual observation for deteriorations and washed in

the tap water before weighing in digital balance of 0.1

mg accuracy and then testing for compressive strength

in an UTM.

Results and Discussion

Fresh concrete properties

The workability of all the concrete mixes (measured

by Abram’s Slump Cone following the procedure

given in IS:1199) was more than 100 mm which wassufficient for satisfactory compaction by use of table

vibrator. The mixes were also cohesive with almost

zero or very little bleeding. The fresh concrete density

of GPC and PPCC were almost similar (Table 2).

Though setting times of GPC were not measured

explicitly, however, they were found to be satisfactory

for GPC mix by observing that the minimum working

time available for fresh GPC mix was about 45 min

and the demoulding operations could be easily carriedout after 24 h of casting.

Efflorescence in GGBS based geopolymer was not

observed in the present study, though it has beenreported by some workers. But, during study on several

GPC mixes, depending upon the formulation of alkali

activator solution, authors noticed that sometimes,

greenish layer gets formed on surface of test specimens

made of some GPCs. This did not affect the structural

properties of GPCs. OPC based concretes, however,

did not show noticeable efflorescence.

The shrinkage characteristics of the mixes were not

measured directly in the present study. However, by

careful inspection of the different mixes prepared, it

Table 2—Details of concretes

1 Mix Id GPC PPCC

% Fly ash 0 28

% GGBS 100 0

2 Binder composition (% by mass)

% Portland Cement 0 72

3 Binder/ Activator solution 0.55 0.40

4 Activator solution (AS) AAS Water

5 Na2O in AS* as % binder 5.6 0

6 Superplasticiser % Binder 0 1.00

7 Slump, mm 120 115

8 Density, kg/m3 2375 2380

9 Ingredient contents of concretes, kg/m3

Fly ash 0 110

Ground granulated blast furnace slag (GGBS) 428 0

Portland cement 0 283

Binder 428 393Sand 642 814

Coarse aggregate 1070 1015

Activator solution, kg/m3 235 157

Alkali activator solution specific gravity 1.16 1.00

Activator solution, L/m3 203 157

GPC = Geopolymer Concrete, PPCC=Portland Pozzolana Cement Concrete, AAS=Alkali Activator solution




could be observed that the GPC mixes were almost

similar to Portland cement based concrete mixes.

Though some authors had reported noticeable

shrinkage of GPCs, the present formulation of the

GPC mix did not result in exhibition of shrinkage

related effects of the mixes.

Compression strength

The average 28 days compression strength of GPCwas 63 MPa which increased only marginally to 65

MPa at 90 days; corresponding values for PPCCs

were 48 and 74 MPa (Table 3a, Fig. 1a). Thus, GPC

had gained almost its full strength at the end of 28

Table 3a—Test data on concretes

1 Mix Id GPC PPCC

% Fly ash 0 28

% GGBS 100 0

2 Binder Composition (% by mass)

% Portland Cement 0 723 Binder/ Activator solution 0.55 0.40



Compressive Strength, MPa 1 day, fc1d 30 10

7 day, fc7d 44 24

28 day, fc28d 63 48

6

90 day, fc90d 65 74

Rate of strength development

fc1d /fc28d (%) 48 21

fc7d /fc28d (%) 70 50

fc28d /fc28d (%) 100 100

7

fc90d /fc28d (%) 103 154

Table 3b—Test data on concretes1 Mix Id GPC PPCC % Reduction in GPC*

Col(1) Col(2) Col(3)

% FA 0 28

% GGBS 100 02 Binder composition

%OPC 0 72

3 Binder/AS 0.55 0.40



Exposure to 2%H2SO4

30 days 0.1 2.3 96

60 days 2.7 6.3 576 Weight loss (%)

90 days 4.5 8.7 48

30 days 0.02 0.38 95

60 days 0.46 1.05 567 Thickness loss (mm)90 days 0.75 1.44 48

30 days 3.7 17.4 79

60 days 10 31.4 688 Strength loss (%)

90 days 11.1 36.2 69

Exposure to 10%H2SO4

30 days 2 4.4 55

60 days 5.3 21.8 769 Weight loss (%)

90 days 7.2 22.6 68

30 days 0.33 0.73 55

60 days 0.88 3.63 7610 Thickness loss (mm)

90 days 1.19 3.77 68

30 days 15.2 31.6 52

60 days 51.1 77.1 3411 Strength loss (%)

90 days 72.1 82.4 13

Note: Binder/AS ratio in PPCCs is water-binder ratio or water-cement ratioAS= Activator solution for GPC is made from mixture of sodium silicate (molar ratio 2.2) and sodium hydroxide solutions

GPC = Geopolymer cement concrete, PPCC=Portland pozzolana cement concrete% Reduction in GPC = 100*(OPCC-GPC)/OPCC




days where as PPCCs continued to gain considerable

strength after 28 days also (Fig. 1b). It may be noted

that these strength levels are quite adequate when

compared with the minimum structural grade

recommended in IS 456-2000 for ‘extreme’ exposure

condition. In present study, the 1 day strength of GPC

was about 30 MPa which is quite high and hence, the

present GPC may be considered as high early strength

concrete, which is useful in faster construction of

structures since the GPC studied does not require any

external curing and only ambient conditions are

enough for the geopolymerisation reactions and

subsequent strength gain. In contrast, OPC based

concretes need always careful curing through

exposure to moisture or water.

The data in Table 3a and Fig. 1b show that the

GPC has higher ratios of f 1d /f c28d and f 7d /f c28d than

those of PPCC indicating faster rate of development

than PPCC. The strength increase beyond 28 day up

to 90 day in case of PPCC is 54% which is substantial

as compared to this value being only about 3% forGPC, thereby confirming that the GPC develops fast

its ultimate strength compared to PPCC. This is a

useful and desirable property in structural concretes.

Sulphuric acid attack

Figures 2a-2c show a contrast between acid

resistances of GPC and PPCC specimens at for 30, 60

and 90 days of exposure to 2% sulphuric acids and the

difference increases with exposure time. The

percentages weight and strength losses for the mixes

and also estimated thickness loss due to attack by 2%

sulphuric acid increases with increased exposureperiod (Table 3b). At the end of 90 days, the PPCC

specimens were found to be in highly deteriorated

state with almost complete loss of integrity, but, theGPC specimens had almost maintained their integrity

with minor visible distress seen on the surface whenexamined visually, even though there were substantial

losses of strength (Figs 2a and 2b, 3a-3c). The %

strength losses in GPC after exposure of 30, 60 and 90

days to 2% H2SO4 were 3.7%, 10% and 11.1%

(corresponding weight losses being 0.1%, 2.7% and4.5%) respectively and these numbers for PPCC were

quite high at 17.4%, 31.4% and 36.2% (corresponding

weight losses being 2.3%, 6.3% and 8.7%) (Table 3b).

Fig.1a—Compressive strength of concrete mixes

Fig.1b—Compressive strength development

Fig. 2a—Percent weight loss on exposure to H2SO4

Fig. 2b—Thickness loss on exposure to H2SO44

Fig. 2c—Strength loss on exposure to H2SO4




Similar observations can be made in respect of depthof deterioration (thickness loss) also.

The above observations were valid also when the

loss of weight was converted into estimated averagedepth of deterioration due to penetration of sulphuric

acid computed using the following formula:

p = 1 - [{1 - 2 * (T /H1)} * {(1 - (T / R1) ^2}] … (2)

where,

T = estimated average depth of deterioration =Change in radius

H1 = initial height of specimen

R1 = initial radius of specimen before acid exposure

(R1 – T) = radius of specimen after exposure

(H1 – 2 * T) = height of specimen after exposure

P = fractional weight loss = (W1 – W2)/W1 =

weight loss/initial weightW1 = initial weight of specimen before acid exposure

W2 = weight of specimen after acid exposure

W1, W2, H1 and R1 are known, and T can be computed

from above equation. These values are given in Table

3b and Fig. 3a.

After 90 days, the PPCC specimens had typically

external exposure of the coarse aggregate; the

surfaces were rough and yellowish in colour (Figs 3b

and 3c). The expansive nature of chemical reaction

has happened in the PPCC specimens since aperceptible increase in porosity of specimens was

noticed. The free lime available in the hydrated

cement matrix get reacted by acid resulting in

formation of gypsum and also the calcium aluminate

phases of both hydrated and the unhydrated portions

of cement in the matrix also get attacked by sulphate

ions leading to formation of ettringite which is anexpansion creating compound3,4,43. These PPCC

specimens could be considered to have reached their

ultimate level of very existence itself. In contract, the

GPC specimens were almost intact even though

significant strength losses had occurred. This isevident from the estimated depths of deterioration

which were 0.02, 0.5 and 0.8 mm only, for 30, 60 and

90 days of 2% H2SO4 acid exposure for GPC whereas

these numbers for PPCC were as much as about 0.4,

1.1 and 1.5 mm (Fig. 2b).The above observations made on 2% sulphuric acid

are almost similarly valid for attack by 10% sulphuric

acid also (Fig. 2b). Thus, it is clear that GPC had

comparatively very high resistance to sulphuric acid

attack. The reductions in deterioration in respect of

Fig. 3a—Percent reduction of deterioration in GPC relative to PPCC

Fig. 3b—Specimens after exposure to 2% H2SO4

Fig. 3c—Specimens after exposure to 10% H2SO4




weight loss, deterioration depth, and strength loss can

be as much as 48% to 96% if PPCC is replaced by

GPC for 2% acid attack and this range becomes 13%

to 76% in case of 10% acid attack (column 3 in Table

3b, Fig. 3a). This can be attributed to the fact that the

GPCs do not have free lime content in its matrix and

geopolymers themselves are not easily attacked by

acids5.

Even though free lime was not measured in the

present case, published literature indicate that because

of nature of chemical reactions occurring ingeopolymer concretes, possibility of free lime is very

less and instead of calcium silicate hydrate (C-S-H)

gel (which is a binder portion in Portland cement

based matrix) aluminosilicate polymeric system isformed and this involves no evolution of free lime.

Superior acid resistances (particularly to sulphuric

acid) of geopolymer concretes in general have been

reported by many researchers44-45

. The PPCC do

contain free lime content in its matrix due tohydration reactions of Portland cement portion of the

PPC and this free lime and also the hydrated Portland

cement matrix C-S-H gel of the matrix are easily

attacked by acids in general, especially more by the

sulphuric acid 2,43

.

Ecological Analysis of ConcretesEmbodied energy (EE) and embodied carbon

(ECO2e) of concretes were computed to examine the

ecological effects of the concretes47,48

. The EE is the

energy consumed for the raw material extraction,

transportation, manufacture, assembly, installation,disassembly and deconstruction for any product system

over the duration of a product’s life. The embodied

carbon (ECO2e) is the CO2e released for the raw

material extraction, transportation, manufacture,

assembly, installation, disassembly and deconstruction

for any product system over the duration of a product’s

life. The data on EE and EC for the ingredients and the

concretes were taken from the literature47-53

. The

computations are shown in Table 4a and the benefit of

GPC over PPCC are given in Table 4b (Fig. 4).

Table 4a—Ecological analysis of concretes

Type of concrete Data for each material EE ECO2e Cost

GPC PPCC EE ECO2e Cost GPC PPCC GPC PPCC GPC PPCC

Ingredient kg/m3

kg/m3

MJ/kg kgCO2e/kg Rs/kg MJ/m3

MJ/m3

kgCO2e/m3

kgCO2e/m3

Rs/m3

Fly ash 0 110 0.1000 0.0080 1.00 0.00 11.00 0.00 0.88 0.00 110.00

GGBS 428 0 1.6000 0.0830 3.00 684.8 0.00 35.52 0.00 1284.00 0.00

Binder

Portlandcement

0 283 5.5000 0.9300 5.00 0 1556.50 0.00 263.19 0.00 1415.00

SHf 23.5 0 3.0000 0.0150 20.00 70.5 0.00 0.35 0.00 470.00 0.00

SSS 47 0 3.0000 0.0150 12.00 141 0.00 0.71 0.00 564.00 0.00

DistilledWater

164.5 0 0.0100 0.0008 2.00 1.645 0.00 0.13 0.00 329.00 0.00

Activatorsolution

Water 0 157 0.0100 0.0008 0.01 0 1.57 0.00 0.13 0.00 1.57

Sand 642 814 0.1500 0.0051 1.00 96.3 122.10 3.27 4.15 642.00 814.00Aggre-gates Coarse

Aggregate1070 1015 0.0830 0.0048 1.00 88.81 84.25 5.14 4.87 1070.00 1015.00

Processing 2375 2379 0.0140 0.0180 0.50 33.25 33.31 42.75 42.82 1187.50 1189.50Total for concrete 2375 2379 1116 1809 88 316 5547 4545

EE = Embodied energy, ECO2e = Embodied CO2 emitted, GGBS=Ground granulated blast furnace slag, SHf=Sodium hydroxide flakes,SSS=Sodium silicate solution, AS=Activator Solution (water for PPCC)

Table 4b—Benefits of geopolymer concrete (GPC) relative to Portland pozzolana cement concrete (PPCC)

GPC PPCC AdvGPC (%) Remarks

Compressive strength at 28 day, fc28, MPa 63 48 31 GPC is stronger

Embodied energy (EE) MJ/m3 1116 1809 -38 GPC needs lower energy

Embodied carbon dioxide emission (

ECO2e)

kgCO2e/m3 88 316 -72 GPC involves less emission of ‘green house gas’

(GHG)

Cost of per cubic meter (indicative) Rs/m3 5547 4545 22 GPC is costlier on unit volume basis

EE/fc28 MJ/MPa 18 38 -53 GPC needs less energy for unit strength

ECO2e/fc28 kgCO

2e/MPa 1 7 -79 GPC produces less GHG for unit strength

Cost/fc28 Rs/MPa 88 95 -7 GPC is economical on unit strength basis




The EEs of GPC and PPCC were 1116 and 1809

MJ/m3 (Table 4) and thus the GPC was 38% lower in

energy requirement (Fig. 4). The ECs of GPC and

PPCC were 88 and 316 kgCO2e/m3 and thus the GPC

was 72% lower in CO2 emission. Therefore, the GPCcan be considered as more ecofriendly. It may benoted here that the PPCC considered here itself had

28% fly ash and if the conventional concrete is made

of OPC only (which is often the case still in many

projects), the GPC would still look more

advantageous. Because of high cost of AAS, the GPCis found to be about 22% costlier, but, it had much

higher early strengths at 1 day and 7 day there by

offering many construction advantages which are not

accounted here in costing. Moreover, if the present

PPCC is modified and re-designed to possess same

strength as that of GPC at 28 day, the cost of PPCCwould be higher than the present estimate thereby

reducing the difference between the costs of the two

concretes.

However, if 28 day strength is taken as criterion,

the energy required to produce one MPa of concrete

strength is about 18 MJ/m3 only which is 53% less

than required for PPCC. Similarly, the CO2e emitted

to produce one MPa of strength is about 1 kg/m3 only

which is 79% less than that of PPCC (Table 4b, Fig. 4).

Thus, the GPC is ecologically superior to PPCC fromconsideration of energy required for strength also. It

may be concluded here that the GPC is alwaysadvantageous ecologically as compared to PPCC.

Ecological analysis of concretes presented in this

paper can be taken as only indicative in nature and

actual computations needs to consider manyparameters such as transportation costs, etc. It is

worthwhile to note here that geopolymer being a

relatively new binder, it becomes a necessity for

engineers to study the literature published by eminent

scientists before adopting the same in any practicalapplication36,54-56.

ConclusionsThe following conclusions can be drawn from the

study presented in this paper:

(i) It was seen that the geopolymer concrete(GPC) mix could be produced easily using

equipment similar to those available for

conventional cement concretes. GGBS, when

used as geopolymer source material, produced

geopolymer binder due to addition of sodium

hydroxide-silicate based activator solution.

The geopolymers formed in the reactions

produced high grade structural concretes by

self-curing mechanisms only. The strength

level achieved are much more than theminimum grade specified for “extreme”

exposure condition of IS 456-2000.(ii) The GPC is found to be more acid resistant,

since the specimens even after 90 days of

immersion in both 2% and 10% sulphuric acidsolutions, remained almost intact. In contrast,

the Portland pozzolana cement (PPC) based

PPCC specimens had deteriorated with very

obvious external damaged surfaces

accompanied by noticeable bulging. It may berecognised here that PPCC mix has both

pozzolanic fly ash and Portland cement as

binder and this concrete is reported to the

better than OPC based concretes. Therefore,GPC could be considered as superior to bothOPC and PPC concretes from the durability as

well as strength considerations.

(iii) The industrial by-product of GGBS based

GPC of the present study, was found to

possess much higher acid resistance when

measured in terms of loss of weight and

reduction in compressive strength on acid

attack, as compared to PPCC. The test data

presented in this paper confirms that the GPC

is a good candidate material of constructions

from both strength and durabilityconsiderations. It is to be noted here that the 1

day strength of 30 MPa recorded in GPC here

is actually indicative of GPC being a high

early strength concrete since this strength level

is generally very difficult to achieve in

Portland cement based conventional concretes.

The rate of strength development of GPC is

also higher since the ratio of 1 day strength to

28 day strength and also the ratio of 7day

strength to 28 day strength are both much

Fig. 4—Ecological advantages of GPC relative to PPCC

[100 * (PPCC – GPC)/PPCC]




higher than those observed for PPCCs. Thus, itis seen that the GPC offers many advantages in

actual constructions also.

(iv) Since the GPC does not have any Portlandcement, it can be considered as less energy

intensive (i.e., low ‘embodied energy’), incontrast, Portland cement based concrete is

very highly energy intensive material since

Portland cement is one of the very high

‘embodied energy’ which is reported to be

next only to aluminium and steel. Apart fromless energy intensiveness (actually very low

‘embodied energy’), the GPC utilises the

industrial by-product for producing the binding

system in concrete, therefore, GPC should be

considered as highly eco-friendly material of

construction.

AcknowledgementsThe cooperation and help received from the

scientific and technical staff including several student

project trainees of Advanced Materials Laboratory

(formerly Concrete Composites Laboratory), CSIR-

SERC in the preparation of this paper are gratefully

acknowledged.

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