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EXPERIMENTAL INVESTIGATIONS ON THE

EFFECT OF INCORPORATING GEOSYNTHETICS

FIBRES IN GEOPOLYMER CONCRETE (GPCC)

Prof. Ashok W.Yerekar1, Dr. Rajabhau S. Londhe

2, Vikram Khajekar

3

1Assistant Professor and Research Scholar, Department of Civil Engineering, P.E.S. College of

Engineering, Aurangabad; affiliated to Dr. B.A.M.U., Aurangabad; Maharashtra - 431005,(India.)

2Associate Professor, Applied Mechanics Department, Govt. College of Engineering, Aurangabad;

affiliated to Dr. B.A.M.U., Aurangabad; Maharashtra - 431005, (India.)

3P.G.Student, Department of Civil Engineering, P.E.S. College of Engineering, Aurangabad;

affiliated to Dr. B.A.M.U., Aurangabad; Maharashtra - 431005, (India),

ABSTRACT

This paper describes the impact of incorporation of single type Geosynthetic fibres like GGR (Tensar SS40-

Biaxial);having aspect ratio >50 with volume fractions(Vf ) ranging from 0% to 0.8% at an interval of 0.1% by

mass of normal GPC used ; with low calcium fly ash- based GPCC / GPC, samples are cured at constant

temperature of 900C in an Oven & tested for its Compressive( σcu ),Flexural( σcr ),Split tensile( σcys )and Bond

strengths( σbd ) for various mix strengths, which are identified by performing rigorous trials-and-errors during

experimental investigations. These experimental tests were carried out according to test procedures in the

relevant Indian Standards given for OPC wherever applicable and explains the manufacturing and design

methodology by using various ingredients like AAS with 13 Molar NaOH , 2.5 mass ratio with dosage of

Sikament 610 ut.250 Kg (Naphthalene based) as Super-Plasticizer. It has been experimentally revealed that the

inclusion of GGR fibres in to GPC enhances the Mechanical and Elastic properties of GPCC and they are also

compared and verified by various analytical formulae available in the literature. Thus the test results so

obtained may proved that the GPCC is a viable and promising composite construction material for the future

having good performance characteristics and eco-friendly behaviour as well compared to conventional

concretes.

Keywords : Geosynth etically reinforced Geopolymer Concrete (GSRGPC/GPCC), low calcium

Class F Fly Ash , Alkaline Activated Solution, Super- Plasticizer, Molarity, Aspect ratio ,GGR

fibres, volume fractions(Vf ).

I. INTRODUCTION

Today’s world is a concrete world for global construction industries. While in manufacturing process of cement,

the Global cement industries contributes more than @ 1.35 billion tones of Green House Gas (GHG) emissions

annually & approx. 7% of total man made GHG emissions into the earth atmosphere [1-2].Also during the

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manufacturing of cement, a very large amount of CO2 is emitted into the atmosphere. This CO2 emission

increases the temperature and resulted in an increase in the overall Global Warming. Therefore in very near

future, there will be an adverse impact on both cement productions and construction industries. Although the use

of Portland cement is still unavoidable, many efforts are being made in order to reduce the use of OPC in

conventional concretes. J. Davidov its [3] has invented a new technology with its chemistry and terminology

called ―Geopoly mer‖, in which cement is totally replaced by fly ash and activated by alkaline solution.

Geopoly mers thus forms the Three-dimensional disordered frameworks of the tecto- aluminosilicate types with

the general empirical formula as…

M n [- (SiO2) Z -AlO2] n.wH2O……………. (1)

where n is the degree of polycondensation, M is predominantly a monovalent cations [ like K+, Na] though Ca2+

may replace two monovalent cations in the structures[4]. The present experimental investigations are carried out

by the new method of design to produce GPCC matrixes analogous to the OPCC and similar to IS: 10262-2009

as basic method [5].

II. LITERATURE SURVEY

McCaffrey R. [2] suggested three alternatives to reduce the amount of CO2 from Cement Industries...they are (1)

To decrease the amount of calcinide material in the cement, (2) to decrease the amount of cement from the

concrete and (3) to reduce the number of buildings i.e. construction industries those using cement. Mehta, P.K.

[6] also proposed two stages in the production of environmental friendly concrete…(1) A ―short term effort

―also known as an industrial ecology , is an attempt to use fewer natural resources, and to utilize the least energy

and minimizing CO2 emissions and (2) the ―long term view‖ is to reduce the impact of unwanted industrial by-

products by lowering down the rate of natural material consumptions. Thus development of GPC is an

indispensible step towards the production of eco-friendly concrete. GPC is an inorganic compound made up

from alumino- silicates [7] in an amorphous form. GPC technology not only substantially reduces CO2 emission

from cement industries, but also utilizes the waste materials or industrial by-products like fly ash(FA), silica

fume(SF), GGBS etc. The fly ash is one of the reliable basic source material for making GPC, which is

abundantly available worldwide and its usage is very limited [1-5, 8].With silicon (Si) and aluminium (Al) as its

main constituents, the fly ash has found to have great potential as a cement replacing material in concrete & the

concrete made with such an industrial wastes is also eco-friendly. As GPC is the new concrete in global

perspective, the properties of fresh and hardened GPC are yet to be studied systematically. It is observed that the

fresh GPC has stiff consistency and high viscosity [9–11].It is also found that geo-polymerization can make

profitable contributions towards recycling and utilization of waste materials. This technology is, however, still

fairly unknown and predictably viewed with skepticism by most workers in the field of traditional waste

processing techniques [12–14]. Joseph Davidovits, the founder of GPC [9-10] claims that the Egyptian

Pyramids were built by casting GPC on site and reported that this concrete has an excellent mechanical

properties, it neither dissolved in an acidic solutions nor generates any deleterious Alkali-Aggregate-Reaction,

even in the presence of high alkalinity ambiences [7].

Chinda prasirt et al. [15] studied the workability and strength of coarse high calcium fly ash based geopolymer

concrete. Prof B.V. Rangan [16] has proposed the Mix Design procedure for production of fly ash based

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Geopolymer Concrete, where as Anuradha et al. [17] have presented Modified Guidelines for Mix Design of

GPC using IS: 10262-2009. Patankar et al. [18] studied the effect of sodium hydroxide on flow and strength of

fly ash based geopolymer mortar. Theory and applications about the potential use of geopolymeric materials to

immobilize toxic metals have been presented by Van Jaarsveld et al. [19]. The effect of recycled concrete

aggregate on various strengths of geopolymer concrete has been studied by Anuar et al. [20]. Alonso and

Palomo [21] have used metakaolin as a substitute for the fly ash to study the effect of temperature and activator

concentration on geopolymer concrete. Sumajouw et al. [22] have carried out a study on slender reinforced

columns using fly ash-based geopolymer concrete. Bakharev ,T., [23] studied the resistance of geopolymer

material to acid attack, whereas Pernica et al. [24] studied the effect of test condition on the bending strength of

a geopolymer reinforced composite. Vijai et al. [25–27] has studied effect of glass fibres and steel fibres on

various strengths of geopolymer concrete. Sathish Kumar et al. [28] also studied the properties of glass fibre

reinforced geopolymer concrete. Bhowmick and Ghosh [29] studied the effect of synthesizing parameters on

workability and compressive strength of fly ash based geopolymer mortar. Y.M.Ghugal and Bhalchandra [30]

studied the effect of steel fibres on mechanical and elastic properties of high strength silica fume concrete.

Earlier work by D. Hardjito et.al. [31-32] reported that the manufacturing process and effects of various

parameters such as elevated curing temperatures, curing time, ratios of (Sodium silicate/sodium hydroxide), and

admixture dosages are reported on compressive strength of GPC.

III. EXPERIMENTAL PROGRAMME

3.1 Materials

Fly ash-(as cementitious/source material) ASTM low calcium - type F- Fly ash is the residue from the

combustion of pulverized coal collected by mechanical or electrostatic separators from the flue gases of thermal

power plants. The important characteristics of fly ash are its particles are in spherical form, which improves the

flowability and reduces the water demand. The fly ash used in this experimentation is obtained from the silos of

Thermal Power Station situated at Parali -Vaijanath, Dist. Beed, Maharashtra State, India; which is of low

calcium, Class F type. The chemical composition of fly ash is shown in table I, with its specific gravity 2.3,

obtained from test reports of CSRL–STRUCTWEL LAB. Pune PVT. ltd., Maharashtra, India.

Table 1: Chemical Composition of Fly Ash

Sr.No.

Chemical constituents

in % or Type of Test

Percentages

As per Test

Result%

Requirement as per IS:3812-2003 [33]

Part-I Part-II

Siliceous fly

ash

Calcareous

fly ash

Siliceous

fly ash

Calcareous

fly ash

1 Silica content SiO2 61.49 35.0 min. 25.0min. 35.0 min. 25.0min.

2

Alumina content(Al2O3)

Ferric Oxide(Fe2O3) 31.34

---- ---- ---- ----

---- ---- ---- ----

3 Silica+ Alumina +Ferric

Oxide 92.83 70 min. 50min. 70min. 50min.

4 Calcium Oxide(CaO) 1.92 ---- ---- ---- ----

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5 Magnesium

Oxide(MgO) 0.56 5 max. 5max. 5max. 5max.

6 Sulphur Tri –Oxide(SO3) 0.51 3max. 3max. 5max. 5max.

7 Loss on Ignition(LOI) 0.49 5max. 5max. 7max. 7max.

8 Chloride ---- 0.05 max. 0.05 max. 0.05max. 0.05max.

F.A. and C.A:- Locally available Godavari (Paithan) river sand as fine Aggregates and Crushed Basaltic stones

(from stone crushers near outskirts of Aurangabad city of Waluj premises) were used as fine Aggregates and

Coarse Aggregates respectively with C.A. of NMS as 20 mm and 12.5 mm having their physical properties as

shown in Table 2 and their gradings are shown in Table 3 and Table 4 respectively.

Table 2: Physical Properties of Aggregates (FA &CA) [34]

Physical Properties Coarse Aggregates(CA) Fine Aggregates(FA)

CA-I CA-II FA (Sand)

Type crushed Crushed Godavari sand

Maximum size 20mm 12.5mm 4.75mm

Specific Gravity 2.641 2.639 2.563

Water Absorption 0.58% 0.84% 1.58%

Moisture content Nil Nil Nil

Table 3: Gradings of CA {In Saturated Surface Dry- Conditions}

Sr.No.

IS Sieve

sizes in

mm

Cumulative percentage Passing for

CA-I

20mm

CA-II

12.5mm

Combined Aggregates

CA-I :CA-II 65:35

Required grading as

per BIS 383:1970 34]

1 40 100 100 100 100

2 25 100 100 100 ---

3 20 87.50 100 89.90 90-100

4 16 6.80 100 39.42 --

5 12.5 0.40 96.5 35.04 --

6 10 0.00 76.40 27.75 25-35

7 4.75 0.00 0.96 0.35 0-10

8 2.36 0.00 0.00 0.00 ---

Table 4: Grading of FA {Saturated Surface Dry- conditions}[34]

Sr.No. IS Sieve size

designation mm

Cumulative percentage Passing

for Godavari river sand Remarks

1 10 100

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2 4.75 92 FM = 3.74

Confirming to Zone II,

As per IS 383-1970

[34]

Specific Gravity-2.61

3 2.36 84.80

4 1.18 59.90

5 600µ 35.30

6 300µ 10.60

7 150µ 0.62

8 75µ 0.10

Total 374.32

3.2 Alkaline Activated Solution (Aas)

Sodium Hydroxide (NaOH) - (Laboratory Grade):- in flake or pellets/solid form and its cost is mainly varied

according to its purity and its main function is to activate the Sodium Silicate solution hence it is better to use

it within economical purity i.e. up to the purity range from 94% to 96%.The concentrations of NaOH used was

13 Molarity as per previous research[5].

Sodium Silicate (Na2SiO3) Solution - In Gel form (known as Water Glass) with a ratio of oxides between (SiO2

to Na2O ) = 2 was used ;which were silicates which are supplied to the detergent company and textile industries

as bonding agent; same type of silicates were used for this investigation for making Geopolymer concrete. The

Chemical Compositions of both NaOH and Na2SiO3 are presented in Table 5.

Table 5: Chemical Compositions of NaOH and Na2SiO3

Chemical Compositions of

NaOH

(Min. Assay)

Percentages

97%

Chemical compositions

of Sodium Silicate (Na2SiO3)

Solution

Colour-light yellow liquid

Percentages

Carbonate(Na2O3) 2 Na2 O (%) 16.37%

Chloride(Cl) 0.01 Si O2 (%) 34.31

Sulphate(SO2) 0.05 Ratio of Na2O: SiO2 1:2.09

Potassium(K) 0.1 Total Solids (%) 50.68

Silicate(Si2 O3) 0.05 Water content H2 O(%) 49.32

Lead(Pb) 0.ooi Appearance Liquid(Gel)

Zink(Zn) 0.02 Boiling point 102

0c for 40%

aq.soln

Specific gravity 1.16 Specific gravity 1.57

Colour Colourless Molecular Weight 184.04

Preparation of Sodium Hydroxide Solution: -Sample case explained as per [18]

1 Mole of Sodium Hydroxide Solution = [40 gm Flakes of NaOH + Distilled Water] {Since Molecular Weight

of NaOH is 40 = 1 Litre Solution of NaOH} temp.rises to 700 to 80

0C.

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Hence, it is suggested to prepare NaOH Solution 3 days prior to the casting of concrete cubes etc to avoid any

contaminations during the mixing of ingredients of GPC. For e.g. for the preparation of 13M NaOH Solution =

{520gms flakes of NaOH+750 ml water} steered solution and after cooling; add remaining quantity of water to

make one litre complete solution. Always avoid direct contact with skin and eyes to avoid severe burns.

Water:-Potable water which is available in laboratory was used for mixing purposes.

Geosynthetics Fibres (Tensar SS40-Biaxial)-Since Geopolymer cement concrete is more brittle than

conventional concrete, in these investigations Geosynthetics fibres (GGR Types only) are used to convert GPCC

into more ductile or elastic one. Geogrids fibres with aspect ratio (𝐿𝑓/ h𝑓= 35.54/1.27 =28) 28 to 50 is used with

modulus of elasticity (E) in the range of 12000 -18000 MPa {MN/m2} say 15000 MPa, Specific Gravity ranging

from 1.22-1.38, melting point @ 2600C., unit mass or weight/unit area-345-930 g/m

2, thickness ranges from 10-

300 mils or generally 20 mils i.e.0.025 mmx20 = 0.5mm (since 1 mil=0.025mm).

Super-plasticizers: -Sikament 610 ut.250 Kg (Naphthalene based) was used as super plasticizer/ an admixture,

its Quality Assurance Certificate shown in Table 6.

Table 6: Quality Assurance Certificate

Property

Specifications

Actual

Results Test Results

Min Max

Aspect Dark Brown Lump Free

Liquid OK PASS

pH Value 7.00 9.00 8.80 PASS

Specific Gravity 1.15 1.19 1.18 PASS

Solid content (%

by wt.) 30.88 34.13 32.42 PASS

Chloride content,%

by wt. 0.00 0.20 0.00 PASS

AAS Preparations:-For preparing 13 Molarity NaOH solutions: - {500gm water + 520 gm pallets} are used.

For making Alkaline Activator Solution …NaOH is mixed with Na2SiO3 at room temperature, in the ratio of

{Na 2SiO3 to NaOH =2.5} were kept constant [14]. When both the solutions mixed together then both the

solutions start to react .i.e. polymerization takes place: during these, it liberates large amount of heat, so it is

recommended to leave it for 24 hours prior to its use and if it exceeds 36 hours then it terminates to semi-solid

liquid state, so the presently prepared solution should be used within this time; therefore Alkaline Activator

Solution is to be prepared one day before casting both GPCC or GPC sample’s.

Mix Proportion of Geopolymer Concrete. Fly ash, CA, FA are initially mixed together in dry state and then the

liquid component of the mixture i.e. AAS is added to prepare wet mix until it gives homogeneous mix with or

without super plasticizer as per workability requirements. Mix proportions and fibre quantity of geopolymer

concrete per cubic meter are given in Tables 7 and 8 respectively.

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Table 7: Mix Proportion of Geopolymer Concrete per Cubic Meter

Fly

ash

NaOH

(13M) Na2SiO3 FA CA

Extra

water

Total Quantity of Ingredients

(kg)

310 54.25 54.25 744 1387.90 62.00

2612.401

1part 0.175

part

0.175

part

2.40

part

4.4771

part

0.20 part

Proportions [AAS/FA]=105/300

= 0.35

Table 8: Quantity of fibres for Various Mixes

Geosynthetics

(Geo-grids

only) fibre

(%)

0.0 0.1 0.2 0.3 0.4 0.5

0.6 0.7 0.8

Fibre

quantity

(kg/m3)

0.0 2.6

13

5.2

2

7.84 10.45

2

13.06

5

15.67

8

18.286 20.899

Super

plasticizer[as

per actual]

(kg/m3)

0.0 0.1

0

0.2

00

0.22

5

0.370 0.500 0.723 0.981 1.052

3.3 Specimen Preparations and Test Results

For testing the GPC/GPCC , Specimens are casted as per IS Codal requirements like (1) cubes for Compression

tests: size (150x150 x150) mm; (2) Cylinders 150 mm diameter x 300 mm height for Split Tensile tests, (3)

Beams of sizes (100 × 100) mm c/s and 500mm length with two-point loads applied at the middle third of the

span for Flexural strength tests and (4) For Bond Strength samples as per IS:2770-1997; out of which three

specimens each were used to determine the corresponding Compressive Strength ,Split Tensile Strength,

Flexural strength and Bond strength each at 7 days for different grades of GPC/GPCC and the reported

strengths are shown in Table 9. A total of (3x9x4=) 108 and more specimens were tested in this experimental

investigations so as to arrived at the Optimized Grades of GPCC both with and without incorporating

Geosynthetics Fibres- in the form of rectangular pieces of the cube sizes within the cubes /or in the form of

circular discs of cylindrical sizes at proper spacing and strips having beam c/s into the beams of beam length

etc.. {Only Geo-gride type’s fibres were used} and the results are shown in Table 9.

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Table 9: Comparison of compressive strengths (σcu), flexural strengths (σcr ), split-tensile

strengths

(σ cys), and bond strengths (σ bd) for various percentages of Geosynthetics fibres (𝑉𝑓).

Strengths (MPa) Percentage increase in strength

𝑉𝑓 σcu σcr σ cys σ bd σcu σcr σ cys σ bd

0.0 28.90 3.20 3.41 12.10 0.00 0.00 0.00 0.00

0.1 31.50 3.63 3.71 12.40 8.99 13.55 8.80 2.84

0.2 33.60 4.16 4.41 12.80 16.26 30.00 29.32 5.78

0.3 34.50 4.20 4.51 13.40 19.38 31.25 32.26 10.74

0.4 34.68 4.26 4.62 14.10 20.00 33.12 35.48 16.53

0.5 34.72 3.86 4.41 13.60 20.14 20.63 29.33 12.40

0.6 31.50 3.50 3.93 13.30 8.99 9.53 15.25 9.91

0.7 31.40 3.33 3.81 13.01 8.65 3.33 11.73 7.52

0.8 29.35 3.32 3.63 12.96 1.56 3.32 6.45 7.10

All in aggregates were prepared by bringing them in Saturated Surface Dry (SSD) conditions. All the GPCC and

GPC samples were made with mix design procedures as follows and mentioned in [35] all respects as far as

possible.

1. All ingredients of GPCC/ GPC are collected separately and mixed in the Pan Mixture for @ 5 minutes.

2. The Alkaline Activated solution/liquid was then added to dry mixture with actual quantity of super

plasticizers, as necessary for workability and then mixing was done for another 5 minutes so as to obtain a

homogeneous matrix.

3. After this mixing, the flow values /slump values of fresh GPCC/GPC was determined as per slump tests

confirming to the IS: 516-1959[36] same as for OPCC in Concrete Technology.

4. After flow test, the fresh GSRGPC/GPC were placed in corresponding moulds as described in the IS: 516-

1959[36] and compacted by usual methods that are used in OPCC and the test results are shown in Table

no10.

Table 10: Workability, Wet Density, and Dry Density of GPCC Mixes.

𝑉𝑓 (%) Flow

(mm)

Decrease in

flow (%)

Degree of

workability

Density (kg/m3) Increase in Density (%)

Wet Dry Wet Dry

0.0 63.23 0.00 High 2586 2465 0.00 0.00

0.1 59.20 6.37 High 2594 2469 0.31 0.163

0.2 56.43 10.75 High 2620 2478 1.32 0.53

0.3 53.56 15.29 High 2638 2499 2.01 1.38

0.4 50.75 19.73 High 2649 2510 2.44 1.83

0.5 48.10 23.93 Medium 2670 2520 3.25 2.07

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0.6 46.10 27.09 Medium 2674 2530 3.40 2.47

0.7 45.10 28.67 Low 2678 2533 3.56 2.60

0.8 44.80 29.15 Low 2680 2536 3.64 2.88

5 The specimens both GPCC and GPC were left standing for at least 1 hour and then cured at 900C in the

thermostatically controlled oven for 7days.

6 Demoulding was then done after 7 days curing age and then all the specimens were left at room

temperature for @ an hour for cooling and then the specimens were ready for testings.

7 Then, the various types of strength tests were performed as per IS Codal provisions for both GPCC & GPC.

3.4 Analysis of Test Results

The workability of fresh geopolymer concrete is measured by flow table apparatus as per IS: 1199–

1959[37].After making the homogeneous mix, concrete was placed in two layers; each layer should be

compacted 20 times with the tamping rod and then level the top surface. Lift the mould away from the concrete

one minute after completing the mixing operation. Then apply fifteen jolting and measure the average diameter

of subside concrete at minimum six equal intervals expressed as a percentage of the original base diameter.

Examination of Table 10 indicates that the workability of geopolymer concrete including Geosynthetics fibre

reduces with increase in fibre contents. It might be due to viscous nature of geopolymer concrete and uneven

distribution of matrix in the fibres incorporated into it.The maximum decrease in flow is 29.15% at 0.8% of

fibre content. Both the wet and dry densities were recorded throughout the experimental program and the

average values for densities are listed for various volume fractions of fibres. Table 10 shows that the inclusion

of fibres increases the density of concrete due to good particle packing and reduction in air content. The

maximum increase in wet density is recorded to be 3.64 %, whereas it is 2.88% in case of dry density.

Discussion on Mechanical Properties:- The tests on hardened GPCC are carried out according to the relevant

BIS standards wherever applicable. New formulae based on law of mixtures for mechanical properties of GPCC

are proposed in this investigation. The various strengths were calculated and they are compared with the

strengths obtained by using experimental work is presented in Table 9.

Compressive strength is determined by carrying out compressive strength test on cubes of sizes (150 ×

150×150) mm and the same is calculated by

σcu= (P/A)…………………………(2)

From the table 9, it is clearly seen that the compressive strength of concrete increases w.r.t. fibre content up to

0.5% and then it decreases, because higher percentage of fibre content reduces the workability of GPCC. The

maximum increase in compressive strength of GPCC is 20.14% over that of normal GPC. The new expression

for compressive strength in the third degree polynomial in terms of �f is proposed and it is obtained by plotting

the curve, as shown in Graph-1between percentage V f v/s σcu given by the following equation:-

σcu = 27.20 Vf3 -67.26 Vf

2 + 37.12Vf + 28.71……………. (3)

Flexural test is carried out on beams of size (100×100) mm c/s and 500mm length with two-point loads applied

at the middle third of the span. The flexural strength is obtained by using the analysis of law of mixtures

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Graph No.1: Showing Relationship Between Percentage �� % Of Fibres V/S Σcu

Σcr = (PL /B D2) …………..(4)

Table 11: Optimum fibres and Maximum Percentage Increase in Various Strengths

Strengths Vf % Maximum strength

(MPa)

Percentage increase in

Strength (%)

σcu 0.5 34.72 20.14

σcr 0.4 4.26 33.12

σ cys 0.4 4.62 35.48

σ bd 0.4 14.10 16.53

From Table 11, it is observed that the maximum increase in flexural strength is 33.12 % with 0.4% of fibre

contents over that of GPC. The proposed new expression for flexural strength in the third degree polynomial in

terms of �� can be obtained from the Graph 2, given by the following equation:

σcr = 12.98 �f3 – 21.22��

2 + 8.873�� + 3.110……. (5)

Graph No. 2: Showing Relationship between Σcr V/S Vf % Of Fibres

y = 27.20x3 - 67.26x2 + 37.12x + 28.71R² = 0.942

0

5

10

15

20

25

30

35

40

0 0.2 0.4 0.6 0.8 1Cu Poly. (Cu)

y = 12.98x3 - 21.22x2 + 8.873x + 3.110R² = 0.943

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 0.2 0.4 0.6 0.8 1

Poly. (6cr)

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Cylinders of size 100 mm diameters and 300mm lengths are used to obtain Split-Tensile Strength. The Split-

tensile strength is obtained by using,

σ cys = 𝟐𝐏

𝛑𝐝𝐋…………….. (6)

The maximum increase in split-tensile strength is 35.48% with 0.4 % of fibre content over that of normal GPC.

The proposed new expression for split-tensile strength in the third degree polynomial in terms of �� is obtained

from the relationship between �� % v/s Split Tensile Strength (6Cys) as shown in Graph no.3 by the following

equation

Graph No.3: Showing Variation of Split Tensile Strength (Σ Cys) W.R.T. �� % Of Geo-Synthetic

Fibers

Σ Cys = 8.013��3 −16.21�� 2 +

8.202�� + 3.290…. (7)

The bond strength test was carried out according to IS: 2770 [47].In this test a 16mm dia. deformed steel

reinforcing bar was embedded into the Geopolymer concrete cube mixed with fibres, at centre up to depth of

150 mm. The total length of bar is 600 mm. All specimens are tested up to failure of bar matrix interfacial bond.

The peak load at failure of bond and maximum slip is observed. All specimens failed with vertical crack along

the embedded length of bar with cracking sound. The maximum increase in strengths is 16.53% with 0.4% of

fibre content over that of normal GPC. The bond strength has been computed from the following expression:-

σ bd =𝐏

𝛑𝐃𝐋 ...................................... (8)

The proposed new expression for bond strength in the third degree polynomial in terms of �� is given by the

following equation:-

y = 8.013x3 - 16.21x2 + 8.202x + 3.290R² = 0.913

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 0.2 0.4 0.6 0.8 1

Cys Poly. (Cys)

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Graph No.4: Showing Relationship Between Σ Bd V/S %

Σ Bd = 18.82��3

– 37.73��2 + 21.00�� + 10.38…. (9)

Optimum fibre content for various strengths of GPCC are presented in Table 11. The comparison of various

strengths of Geopolymer Concrete Composites obtained by using proposed empirical formulae are presented in

Table 12.

Table 12: - Determinations of Compressive strength (𝟔 cu), flexural strength (𝟔 cr), split-tensile

strength (𝟔 cys), and bond strength (𝟔 bd) for various percentages of Geosynthetics fibres (��)

obtained by applications of proposed equations….

Strengths Percentage increase in strength

by proposed equations

��

%

σ cu

by

Eqn.2

σ cu by

Eqn.3

σ cr

by

Eqn .4

σ cr by

Eqn.5

σ cys

by

Eqn. 6

σ cys

by

Eqn.7

σ bd by

Eqn.8

σ bd by

Eqn.9 σ cu σ cr σ cys σ bd

0.00 28.90 28.710 3.20 3.110 3.41 3.290 12.10 10.38 0.00 0.00 0.00 0.00

0.1 31.50 28.750 3.63 3.118 3.71 3.298 12.40 10.401 0.139 0.257 0.243 0.202

0.2 33.60 28.784 4.16 3.127 4.41 3.306 12.80 10.422 0.257 0.547 0.243 0.405

0.3 34.50 28.820 4.20 3.136 4.51 3.314 13.40 10.443 0.383 0.836 0.729 0.606

0.4 34.68 28.860 4.26 3.145 4.62 3.3225 14.10 10.464 0.522 1.124 0.987 0.810

0.5 34.72 28.900 3.86 3.154 4.41 3.330 13.60 10.484 0.661 1.415 1.215 1.002

0.6 31.50 28.930 3.50 3.163 3.93 3.338 13.30 10.504 0.766 1.704 1.459 1.195

0.7 31.40 28.970 3.33 3.180 3.81 3.346 13.01 10.525 0.906 2.250 1.702 1.396

y = 18.82x3 - 37.73x2 + 21.00x + 10.38R² = 0.935

11.5

12

12.5

13

13.5

14

14.5

0 0.2 0.4 0.6 0.8 1 1.2

6bd Poly. (6bd)

526 | P a g e

Elastic Properties: Elastic properties such as modulus of elasticity, modulus of rigidity, and Poisson’s ratio

are the important parameters in the analysis of structures. These properties are obtained by various methods

available in the literature. As per IS: 456[41], the Modulus of Elasticity is obtained by the formula

Efc =5000√Fcu……………………...(10)

Modulus of Elasticity: The modulus of elasticity is obtained by various methods available in the literature as

given below. Modulus of elasticity of fibre reinforced composites (FRC) can be calculated by using law of

mixtures as suggested by Hannant [38] and Tan et al. [39] as follows:

�fc = (1 − �1�2��) Em + �1 �2 �f Ef… (11)

Where �1=fibre orientation factor (1 for aligned fibres), �2 = efficiency factors (0.98 for all practical purposes),

�f = fibre content (%), Em = modulus of elasticity of matrix (GPa) = 5√σ cu, and modulus of elasticity of fibre

(GPa) = (12 to 18 GPa = 15 GPa). The equation of modulus of elasticity in terms of compressive strength (σ cu)

and specific gravity (�) is also given by Kakizaki et al. [40] as …

�fc = 0.8 × 105(� /2.3)

1.5 x √ (σ cu / 350)…… (12)

Where � = specific gravity of concrete (dry density of composite/1000). As per IS: 456 [41], the modulus of

elasticity is calculated by the formula as �fc = 5√ σ cu, Hence for average value of specific gravity, Eqn.(11)

leads to the following form :

�fc = 4846√ σ cu …….. (13)

The modulus of elasticity obtained by using equations (10) through (13) is shown in Table 13. Help in Tsai

equations [41] based on Micro-Mechanics Analysis can also be used to predict the elastic constants of fibre

composites. The longitudinal (��) and transverse moduli (��) can be evaluated by using following equations:

�� = ��. {1+ (2�����) / (1–����)}……(14)

ET = {1 + (2����) / (1 – ����)………….(15)

Where �� = (�� / ��) – 1 / (��/��) + 2 � …. ….. (16)

�T = (��/��) – 1 / (��/��) +�…………..(17)

where � is the aspect ratio of fibre = (��/h�) & where �� = length of fibre , h� = thickness of fibre.

Table13: Elastic Properties of GPCC.

�� %

Modulus of elasticity (�fc)

Poisson’s ratio

(�)

Equation

(10)

Efc = 5√ σ cu

GPa

Equation (11)

�fc = (1 − �1�2��)

E�

+ �1 �2 �f ��

GPa

Equation (12)

�fc = 0.8 × 105x

(� /2.3)1.5

√ (σ cu

/350) GPa

Equation (13)

�fc = 4846 √ σ

cu GPa

Equation (21)

� =( σ cr / σ cu )

0.0 26.879 28.062 25.505 26.051 0.1107

0.1 28.062 28.053 26.690 27.198 0.1153

0.2 28.980 28.962 27.720 28.090 0.1238

527 | P a g e

0.3 29.368 29.34 28.450 28.463 0.1217

0.4 29.440 29.40 28.708 28.540 0.1228

0.5 29.460 29.407 28.897 27.293 0.1111

0.6 28.062 28.030 27.688 27.209 0.1112

0.7 28.018 27.95 27.694 27.166 0.1060

0.8 27.083 27.010 26.822 26.260 0.1131

Table 14: Modulus of Elasticity and Shear Modulus Using halpin Tsai Equations [41]

��

%

Equation

(16)

�� = (�� /

��)– 1 /

(��/��) + 2

�

Equation

(17)

� T

=(��/��)-1

/(��/��) + �

Equation (14)

��=��.{1+(2�

����) / (1–

����)}

GPa

Equation

(15) �T={1 +

(2����) / (1

– ����)

GPa

Equation

(18)

�� = [1/8

(3��+ 5��)

(GPa)

Equation

(19)

��=1/8(

��+2�T)

(GPa)

Equation

(20)

�fc =(1

−��) ��

(GPa)

0.0 0.0773 0.141 26.879 26.879 26.879 10.079 26.879

0.1 0.0816 0.1493 28.030 28.030 28.030 10.511 28.00197

0.2 0.0848 0.1556 28.948 28.954 28.951 10.855 28.893

0.3 0.0862 0.1582 29.319 29.075 29.166 10.933 29.078

0.4 0.0865 0.1330 29.380 29.396 29.390 11.0215 29.272

0.5 0.0866 0.1580 29.380 29.390 29.386 11.020 29.239

0.6 0.08165 0.1493 27.975 27.986 27.981 10.493 27.813

0.7 0.0816 0.1492 27.918 27.929 27.924 10.472 27.728

0.8 0.0780 0.1423 26.981 26.993 26.989 10.1211 26.773

Modulus of elasticity and shear modulus of randomly oriented fibre reinforced concrete can be predicted using

the following relations:

�� = [1/8 (3��+ 5��) … (18)

GR = 1/8 (��+ 2�T)……, (19)

Where �� and �� respectively are the longitudinal and transverse moduli of fibre composite having the same

fibre aspect ratio and fibre volume fraction . The results obtained by using (12) are modified according to (13) to

have the similar trends with the other results and all they are presented in Table 14; similarly the results obtained

by using equation(18) and(19) are modified by equation(20) as follows:

�fc = (1 −��) ��…………... (20)

The behavior of geopolymer concrete is very complex. So, the modulus of elasticity calculated by various

methods does not match with each other. But it is observed that the modulus of elasticity increases with

incorporation of Geosynthetics fibres up to 0.5% by volume and then decreases with increase in fibre contents

but higher than plain geopolymer concrete. This means that the fibre improves the elastic behavior of

Geopolymer Concrete Composites which is more brittle than GPC.

528 | P a g e

Poisson’s Ratio (�):-The Poisson’s ratio (�) is determined according to Ghugal [43] using strength of material

theory based on flexural strength and compressive strength and is given by the following relation:

� = [σ cr /σ cu ] …………………….. (21)

Table 13: Last Column, Shows the Effect of Geosyn thetics Fibers on Poisson’s Ratio.

V. CONCLUSIONS

1 Geopolymer concrete is a modern invention in the world of concrete wherein the portland cement is 100%

replaced by an industrial waste materials which contributes towards the global warming by eliminating or

decreasing the use of cement and thereby utilization of by-products like fly ash. Geosynthetic fibres are

incorporated so as to increase the ductility of GPC to make it more elastic since GPC is more brittle than CC’s.

From the literature survey on geopolymers, by adopting the currently used concrete technology to manufacture

OPCC, a rigorous trial-error method was adopted to develop a process of manufacturing fly ash-based

geopolymer concrete. The trial-and-error method thus yielded successful results for the manufacture of low-

calcium ASTM Class F Fly Ash based Geopolymer concrete. Thus GPCC is an excellent alternative solution to

the CO2 producing conventional concretes like OPCC.

2 Low-Calcium fly ash-based GPCC has excellent compressive strength and it is suitable for structural

applications [10].

3 It is also observed that Compressive Strength results obtained for GPCC are more than that of GPC similarly

tensile strength of the GPCC are also higher w.r.t the GPC.

4 It is also concluded that the wet and dry densities of GPCC increases continuously with increase in fibre

contents, whereas the workability of GPCC reduced with increase in fibre content. Optimum Geosynthetics

fibre contents for the maximum values of various strengths of GPCC are 0.4%. The maximum percentage

increase in compressive strength, flexural strength, split tensile strength, and bond strength is 20.14%, 33.12%,

35.48% and 16.53% respectively.

5 The proposed analytical equations for modulus of elasticity yielded good result and Poisson’s Ratio also varies

within the limiting specified values.

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