chapter 6 polypropylene fibre reinforced geopolymer...

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CHAPTER 6

POLYPROPYLENE FIBRE REINFORCED GEOPOLYMER

CONCRETE COMPOSITES

6.1 GENERAL

This chapter describes the effect of addition of polypropylene fibres

on the strength characteristics of geopolymer concrete composites. The fresh

and hardened properties such as workability, density, compressive strength,

split tensile strength, flexural strength, impact strength, modulus of elasticity,

water absorption and sorptivity of Polypropylene Fibre Reinforced

Geopolymer Concrete Composites (PFRGPCC) is presented in this chapter. A

comparison on the strength and durability aspects between GPCC and

PFRGPCC is also discussed.

6.2 EXPERIMENTAL PROGRAMME

6.2.1 Parameters of Study

The following parameters were considered in this experimental

investigation:

(a) Volume fraction of polypropylene fibres: 0% , 0.1% , 0.2%

and 0.3%

(b) Age of concrete at time of testing: 1day, 3days, 7 days and

28 days

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6.2.2 Materials Used

Fly ash: Class F dry fly ash conforming to IS 3812-2003 obtained

from Mettur thermal power station of Tamilnadu from southern part of India

was made use of in the casting of the specimens.

Cement: Ordinary Portland Cement (OPC) conforming to

IS: 8112 – 1989, having a specific gravity of 3.15 was made use of, in the

casting of the specimens.

Fine Aggregate: Locally available river sand having a bulk density

of 1693 kg/m3,fineness modulus of 2.75, specific gravity of 2.81 and

conforming to grading zone-III as per IS: 383 - 1970 was used.

Coarse Aggregate: Crushed granite coarse aggregates of 19 mm

maximum size having a fineness modulus of 6.64 and a specific gravity of

2.73 were used. Bulk Density of the coarse aggregate used is 1527 kg/m3.

Sodium Hydroxide: Sodium hydroxide solids in the form of flakes

with 97% purity manufactured by Merck Specialties Private Limited, Mumbai

was used in the preparation of alkaline activator.

Sodium Silicate: Sodium silicate in the form of solution supplied

by Salfa Industries, Madurai was used in the preparation of alkaline activator.

The chemical composition of Sodium silicate solution supplied by the

manufacturers is as follows: 14.7%, of Na2O, 29.4% of SiO2 and 55.9% of

water by mass.

Super plasticiser: To achieve workability of fresh Geopolymer

Concrete, Sulphonated napthalene polymer based super plasticizer Conplast

SP 430 in the form of a brown liquid instantly dispersible in water,

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manufactured by Fosroc Chemicals (India) private limited, Bangalore, was

used in all the mixtures.

Water: Distilled water was used for the preparation of sodium

hydroxide solution and for extra water added to achieve workability.

Polypropylene fibre: Polypropylene fibres having a length of 6

mm and a diameter of 0.02 mm were used and they are shown in Figure 6.1.

These fibres have a density of 910 kg/m3, modulus of elasticity of 3500 MPa

and yield strength of 550 MPa. (Source: Manufacturer’s data)

Figure 6.1 Polypropylene fibres

6.2.3 Preparation of Alkaline Activator Solution

A combination of sodium hydroxide solution of 12 molarity and

sodium silicate solution was used as alkaline activator solution for

geopolymerisation. To prepare sodium hydroxide solution of 12 molarity (12

M), 480 g (12 x 40 i.e, molarity x molecular weight) of sodium hydroxide

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flakes was dissolved in distilled water and madeup to one litre. The mass of

solid NaOH was measured as 354.45 g/ kg in the 12 M NaOH solution

6.2.4 Mix Proportion of PFRGPCC

In case of PFRGPCC mixes polypropylene fibres were added to the

GPCC mix in three volume fractions such as 0.1%, 0.2% and 0.3% by volume

of the concrete. The mix proportions of GPCC and PFRGPCC are given in

Table 6.1.

Table 6.1 Details of mix proportions of PFRGPCC

Mix ID

Fly Ash

kg/m3

OPCkg/m3

FA kg/m3

CAkg/m3

NaOHSolution

kg/m3

Na2SiO3

Solution kg/m3

Extra Waterkg/m3

SPkg/m3

PPfibreskg/m3

GPCC 354.87 39.43 554.4 1293.4 40.56 101.39 55.18 11.83 --

P0.1 354.87 39.43 554.4 1293.4 40.56 101.39 55.18 11.83 0.91

P0.2 354.87 39.43 554.4 1293.4 40.56 101.39 55.18 11.83 1.82

P0.3 354.87 39.43 554.4 1293.4 40.56 101.39 55.18 11.83 2.73

6.2.5 Preparation of PFRGPCC Specimens

The prepared solution of sodium hydroxide of 12 M concentration

was mixed with sodium silicate solution one day before mixing the concrete

to get the desired alkalinity in the alkaline activator solution. Initially Fine

aggregates, fly ash, OPC, coarse aggregates and polypropylene fibres were

dry mixed for three minutes in a horizontal pan mixer. After dry mixing,

alkaline activator solution was added to the dry mix and wet mixing was done

for 4 minutes. Finally extra water along with super plasticizer was added.

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6.2.6 Curing of PFRGPCC Specimens

PFRGPCC specimens were removed from the moulds immediately

after 24 hours since they set in a similar fashion as that of conventional

concrete. All the specimens were left at room temperature in ambient curing

till the date of testing.

6.3 WORKABILITY

All the freshly prepared PFRGPCC mixes were tested for

workability by using the conventional slump cone apparatus. The slump cone

was filled with freshly mixed polypropylene fibre reinforced geopolymer

concrete composite mix and was compacted with a tamping bar in four layers.

The top of the slump cone was leveled off, then the cone was lifted vertically

up and the slump of the sample was immediately measured.

All the mixes were generally cohesive and shiny in appearance due

to the presence of sodium silicate solution. Inclusion of polypropylene fibres

reduces the slump values. Increase in fibre content dosage additionally

reduces the workability of PFRGPCC specimens as shown in Figure 6.2.

220195

180 170

0

50

100

150

200

250

GPCC P0.1 P0.2 P0.3

GPCCP0.1P0.2P0.3

Figure 6.2 Effect of polypropylene fibres on workability

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6.4 DENSITY

Density was calculated by measuring the weight of cube specimens

before subjecting them to compression test. Density of all the mixes is

presented in Table 6.2. Specimens have been given descriptive names,

composed of two terms. Each of these terms gives information about some

aspect of the specimens which is described as follows: The first term

describes the volume fraction of polyproylene fibres in the geopolymer

concrete composite mix. ‘P0’ refers to GPCC specimens without

polypropylene fibres. ‘P0.1’ refers to PFRGPCC specimens containing 0.1%

volume fraction of polypropylene fibres. Similarly ‘P0.2’ and ‘P0.3’ refers to

PFRGPCC specimens containing 0.2% and 0.3% volume fraction of

polypropylene fibres respectively. The second term refers to the age of

concrete at the time of testing A1, A3, A7 and A28 refer to tests conducted at

respective age of concrete in days.

The density of GPCC without polypropylene fibres ranges from

2347 kg/m3 to 2458 kg/m3, density of GPCC containing 0.1% of

polypropylene fibres ranges from 2376 kg/m3 to 2415 kg/m3, density of GPCC

containing 0.2% of polypropylene fibres ranges from 2336 kg/m3 to

2406 kg/m3 and density of GPCC containing 0.3% of polypropylene fibres

ranges from 2299 kg/m3 to 2421 kg/m3 as shown in Figure 6.3. The density of

GPCC and PFRGPCC is found close to that of ordinary Portland cement

concrete. It was found from the test results that for most of the cases,

inclusion of polypropylene fibres in concrete resulted in a marginal decrease

in unit weight.

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Table 6.2 Density of PFRGPCC specimens

Spec. Avg. Weight in kg

Avg.Density kg/m3

P0 A1 8.117 2404.94P0.1 A1 8.087 2396.05P0.2 A1 8.065 2389.63P0.3 A1 7.975 2362.96P0 A3 8.152 2415.31P0.1 A3 8.105 2401.48P0.2 A3 7.945 2354.07P0.3 A3 8.133 2409.88P0 A7 8.028 2378.77P0.1A7 8.078 2393.58P0.2 A7 7.970 2361.48P0.3 A7 8.073 2392.10P0 A28 8.052 2385.88P0.1 A28 8.058 2387.65P0.2 A28 8.005 2371.85P0.3 A28 7.833 2320.99

2280

2320

2360

2400

2440

2480

0 1 2 3 4 5 6 7 8 9 10 11 12

Specimen number

GPCC P 0.1 P 0.2 P 0.3

Figure 6.3 Density ranges of PFRGPCC specimens

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6.5 COMPRESSIVE STRENGTH

6.5.1 Test Specimens

Totally thirty six cubes of size 150 mm x 150 mm x 150 mm were

cast to study the compressive strength of PFRGPCC. Standard cast iron

moulds were used for casting the test specimens. Before casting, machine oil

was smeared on the inner surfaces of moulds. Geopolymer concrete with

polypropylene fibres was mixed using a horizontal pan mixer machine and

was poured into the moulds in layers. Each layer of concrete was compacted

using a table vibrator.

6.5.2 Instrumentation and Testing Procedure

For the evaluation of compressive strength, all the PFRGPCC cube

specimens were subjected to a compressive load in a digital Compression

Testing Machine with a loading capacity of 2000 kN. Specimens were tested

as per the procedure given in Indian Standards I.S.516. The maximum load

applied to the specimen was recorded. The compressive strength of the

specimen was calculated by dividing the maximum load applied to the

specimen by the cross-sectional area.

6.5.3 Results and Discussion

The effect of addition of polypropylene fibres in different volume

fractions and age of concrete at the time of testing on the compressive

strength of geopolymer concrete composite has been investigated and

presented. Test results of compressive strength are presented in Table 6.3. At

the age of 1 day, PFRGPCC specimens gained 9 % to 15 % of its 28 days

compressive strength. Similarly at the age of 3 days PFRGPCC specimens

gained 37% to 40% of its 28 days strength and at the age of 7 days PFRGPCC

specimens gained 49% to 53% of its 28 days strength as shown in Figure 6.4.

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Table 6.3 Compressive strength of PFRGPCC specimens

Spec. Avg. Ultimate load in kN

Avg. Compressive Strength

MPaP0 A1 175.2 7.79P0.1 A1 82.1 3.65P0.2 A1 111.7 4.96P0.3 A1 131.7 5.85P0 A3 279.6 12.43P0.1 A3 208.6 9.27P0.2 A3 221.5 9.84P0.3 A3 259.4 11.53P0 A7 446.1 19.83P0.1A7 436.2 19.39P0.2 A7 438.6 19.49P0.3 A7 465.4 20.69P0 A28 861.4 38.28P0.1 A28 887.2 39.43P0.2 A28 876.9 38.97P0.3 A28 875.6 38.92

20% 9% 13% 15%

12%14% 12% 14%

20% 26% 25% 24%

48% 51% 50% 47%

05

1015202530354045

0 0.1 0.2 0.3

Volume fraction of polypropylene fibres in %

28 days7 days3 days1 day

Figure 6.4 Gain in compressive strength with age

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As the age of concrete increases from 1 day to 28 days,

compressive strength also increases for all the mixes. From the test results it

can be seen that, the 28 days compressive strength of geopolymer concrete

composites containing polypropylene fibres was slightly higher than those of

GPCC without polypropylene fibres. The increase in compressive strength

due to addition of polypropylene fibres is not much significant and it was only

about 3%, 1.82% and 1.66% for 0.1%, 0.2% and 0.3% volume fraction

respectively with reference to GPCC mix without polypropylene fibres as

shown in Figure 6.5.

3.00

1.82 1.66

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0.1 0.2 0.3

Volume fraction of Polypropylene fibres in %

Figure 6.5 Gain in compressive strength due to PP fibres

6.6 SPLIT TENSILE STRENGTH


Totally eighteen cylinders with a diameter of 150 mm and 300 mm

length were cast to evaluate the split tensile strength of PFRGPCC. Standard

cast iron moulds were used for casting the test specimens. Before casting,

machine oil was smeared on the inner surfaces of moulds. Geopolymer

concrete with polypropylene fibres was mixed using a horizontal pan mixer

machine and was poured into the moulds in layers. Each layer of concrete was

compacted using a table vibrator.

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In order to evaluate the splitting tensile strength of polypropylene

fibre reinforced geopolymer concrete composites, all the cylinder specimens

were subjected to split tensile test in a 2000 kN digital Compression Testing

Machine. Specimens were tested as per the procedure given in Indian

Standards IS.5816. The maximum load applied to the specimen was recorded

and the split tensile strength of the specimen was calculated.


The effect of various factors such as addition of polypropylene

fibres in different volume fractions and age of concrete at the time of testing

on the split tensile strength of geopolymer concrete composite has been

investigated and presented. Test results of split tensile strength are presented

in Table 6.4.

Table 6.4 Split tensile strength of PFRGPCC specimens

Spec. Avg. Ultimate load in kN

Avg. Split tensile Strength

MPaP0 A7 86.4 1.22P0.1A7 97.0 1.37P0.2 A7 100.0 1.41P0.3 A7 101.5 1.44P0 A28 188.3 2.67P0.1 A28 190.0 2.69P0.2 A28 204.8 2.90P0.3 A28 211.2 2.99

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Within 7 days, PFRGPCC specimens gained 51%, 49% and 48% of

its 28 days split tensile strength for volume fraction of 0.1%, 0.2% and 0.3%

respectively as shown in Figure 6.6. As the volume fraction of polypropylene

fibres increases from 0% to 0.3%, the split tensile strength also increases as

shown in Figure 6.7.

46% 51% 49% 48%

54% 49% 51% 52%

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 0.1 0.2 0.3


28 days7 days

Figure 6.6 Gain in split tensile strength with age

13

1618

1

9

12

0

4

8

12

16

20

0 0.1 0.2 0.3

Volume fraction of polypropylene fibre in %

7 days

28 days

Figure 6.7 Gain in split tensile strength due to PP fibres

The improvement in the split tensile strength at 28 days was found

to be 1%, 9% and 12% for volume fractions of 0.1%, 0.2% and 0.3%

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respectively. Once the splitting occurred and continued, the polypropylene

fibres that bridges across the split portions of the geopolymer matrix acted

through the stress transfer from the matrix to the fibres and, thus, gradually

supported the total load. The stress transfer improved the tensile strain

capacity of the PFRGPCC specimens thereby increasing the split tensile

strength over the unreinforced control GPCC specimens. The increase in split

tensile strength may be also due to the role of polypropylene fibres to resist

cracking and spalling across the failure planes.

Based on the test results, using least square regression analysis, an

equation for predicting the 28 days split tensile strength of polypropylene

fibre reinforced geopolymer concrete composites in terms of the split tensile

strength of plain GPCC and percentage volume fraction of fibres (Vf) is

obtained and given in Equation (6.1).

fts = ft + 1.028 Vf (6.1)

where, fts = 28 days split tensile strength of PFRGPCC

ft = 28 days split tensile strength of GPCC without fibres

Vf = Percentage volume fraction of polypropylene fibres.

The split tensile strength of PFRGPCC predicted from the proposed

analytical equation was compared with the experimental results as shown in

Table 6.5. It was found that a good correlation was obtained between the

experimental results and those got from the equation. It can be seen that the

proposed equation predicts the split tensile strength of PFRGPCC well with

good accuracy.

126

Table 6.5 Comparison of experimental and analytical results

Volume fraction of fibres in

%

Split tensile strength MPa Analytical /

Experimental Experimental Analytical

0 2.67 2.67 1.00

0.12.73 2.77 1.022.63 2.77 1.052.71 2.77 1.02

0.22.90 2.88 0.992.94 2.88 0.982.85 2.88 1.01

0.32.99 2.98 0.992.95 2.98 1.013.03 2.98 0.98

6.7 FLEXURAL STRENGTH


Totally eighteen prisms of 500 mm x 100 mm x100 mm were cast

to study the flexural strength of PFRGPCC. Standard cast iron moulds were

used for casting the test specimens. Before casting, machine oil was smeared

on the inner surfaces of moulds. Geopolymer concrete with polypropylene

fibres was mixed using a horizontal pan mixer machine and was poured into

the moulds in layers. Each layer of concrete was compacted using a table

vibrator.

6.7.2 Instrumentation and testing procedure

Flexural strength of polypropylene fibre reinforced geopolymer

concrete composites was determined using prism specimens by subjecting

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them to two point loading in Universal Testing Machine having a capacity of

1000 kN. Specimens were tested as per the procedure given in Indian

Standards IS.516. The maximum load applied to the specimen was recorded

and the flexural strength of the specimen was calculated.


The effect of addition of polypropylene fibres with different

volume fractions and age of concrete at the time of testing on the flexural

strength of geopolymer concrete composite has been investigated and

presented. Test results of flexural strength are presented in Table 6.6.

Table 6.6 Flexural strength of PFRGPCC specimens

Spec.Avg. Ultimate

load in kN

Avg. Flexural Strength

MPaP0 A7 9.8 3.93P0.1A7 10.3 4.13P0.2 A7 10.8 4.33P0.3 A7 11.2 4.47P0 A28 14.7 5.87P0.1 A28 14.8 5.93P0.2 A28 15.5 6.20P0.3 A28 16.5 6.60

Geopolymer concrete composite specimens harden immediately

and start gaining flexural strength without any need of heat curing. In ambient

curing at room temperature, within 7 days, PFRGPCC specimens gained 67%

to 70% of its 28 days flexural strength as shown in Figure 6.8. As in the case

of split tensile strength, PFRGPCC specimens resulted in significant increase

of flexural strength when compared to control GPCC specimens as shown in

128

Figure 6.9. The flexural strength improves by about 1%, 6% and 12% for

volume fractions of 0.1%, 0.2% and 0.3% of polypropylene fibres

respectively at the age of 28 days. This increase in flexural strength might

have resulted primarily from the polypropylene fibres intersecting the cracks

in the tension zone of the flexure beam. These fibres accommodated the crack

face separation by stretching themselves, thus providing an additional energy

absorbing mechanism.

67% 70% 70% 68%

33% 30% 30% 32%

0

1

2

3

4

5

6

7

0 0.1 0.2 0.3


28 days7 days

Figure 6.8 Gain in flexural strength with age

5

10

14

1

6

12

0

2

4

6

8

10

12

14

16

0.1 0.2 0.3

Volume fraction of Polypropylene fibre in %

7 days28 days

Figure 6.9 Gain in flexural strength due to PP fibres

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6.8 IMPACT RESISTANCE


The impact resistance of the specimens was determined in

accordance with ACI committee 544 recommendations. The test specimen

consists of concrete discs of 150 mm diameter and 64 mm thickness.

Specimens were cast using cast iron moulds as shown in Figure 6.10. In this

investigation, totally twelve geopolymer concrete composite discs were cast

with and without fibres. Three specimens were cast for each volume fraction

of fibre as shown in Figure 6.11 and remaining three discs were cast as

control specimens without any fibres.

Figure 6.10 Specimens with moulds

Figure 6.11 PFRGPCC specimens for impact test

130


Drop weight impact test, also known as repeated impact test, is

conducted for evaluating the impact resistance. The impact test equipment

was fabricated according to standards for testing as per ACI Committee 544.

Specimens were tested as per the recommendations given by ACI

Committee 544.


The effect of addition of polypropylene fibres in different volume

fractions in improving the impact strength has been investigated and

presented. Test results of impact strength are presented in Table 6.7.

Table 6.7 Test Results of impact strength

Spec.First Crack strength (blows) Failure strength (blows)

Spec. 1

Spec. 2

Spec. 3 Avg.

Spec. 1

Spec. 2

Spec. 3 Avg.

GPCC 10 12 9 10 11 13 11 12P0.1 68 70 78 72 98 90 93 94P0.2 116 118 109 114 155 163 158 159 P0.3 120 125 119 121 163 172 165 167

It is observed from the test results, that the specimens without

fibres failed in a brittle manner. Plain GPCC specimens do not have

considerable post crack resistance as it resisted only a few additional blows

after the crack. The increase in number of blows for the first crack and the

ultimate failure is significantly higher in the case of polypropylene fibre

reinforced GPCC specimens. Even for a small addition of fibres the

enhancement in first crack resistance as well as ultimate resistance is quite

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considerable when compared to that of plain GPCC specimens as shown in

Figure 6.12.

10

72

114 121

12

94

159 167

0

30

60

90

120

150

180

0 0.1 0.2 0.3

Volume fraction of fibres in %

First crackUltimate failure

Figure 6.12 Effect of polypropylene fibres on Impact strength

Due to the addition of polypropylene fibres, the first crack

resistance increases by about 7.2 times, 11.4 times and 12.1 times for volume

fractions of 0.1%, 0.2% and 0.3% respectively. A similar trend to that

specified for first crack resistance is observed for ultimate resistance also. For

volume fractions of 0.1%, 0.2% and 0.3% of polypropylene fibres, the

ultimate resistance increases by about 8 times, 13 times and 14 times

respectively. The percentage increase in number of post crack blows

(PINPCB) is about 31%, 39% and 38% for the fibre volume fractions of

0.1%, 0.2% and 0.3% respectively and thus inclusion of polypropylene fibres

considerably improved the ability of concrete to absorb kinetic energy leading

to delayed failure strength.

In Figure 6.13, a comparison of failure pattern in the disc

specimens with and without polypropylene fibres is shown. It can be seen that

the addition of fibres changes the crack pattern from a single large crack to a

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group of narrow cracks, which demonstrates the beneficial effects of fibre

reinforced GPCC subjected to impact loading.

Figure 6.13 Failure pattern of PFRGPCC impact discs

6.9 MODULUS OF ELASTICITY

6.9.1 Specimens and Test Procedure

The modulus of elasticity was determined in accordance with

IS.516. The test specimen consists of concrete cylinders 150 mm diameter by

300 mm height. In this investigation, totally twelve geopolymer concrete

composite cylinders were cast with and without fibres. Three specimens were

cast for each volume fraction of fibre. Three cylinders were used as control

specimens without any fibres added to them. All specimens were loaded in

axial compression, using a digital CTM of capacity 2000 kN. Specimens were

tested as per the procedure given in Indian Standards IS.516.

6.9.2 Evaluation of Modulus of Elasticity

The strains at ten equal load intervals upto an average stress of

(C+1.5) kg/sq.cm were measured and the stress-strain values are listed in

133

Appendix 3. For each volume fraction of polypropylene fibres, a graph was

drawn by plotting the average strains against their corresponding stresses as

shown in Figures 6.14 to 6.17. Then best fit straight line was drawn through

the plotted points. From the best fit straight line equation, the slope of the line

is expressed as modulus of elasticity.

y = 27246xR² = 0.999

0

3

6

9

12

15

18

0.0000 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 0.0007Axial strain

Figure 6.14 Axial stress Vs axial strain for GPCC specimens

y = 28177xR² = 0.999

0

3

6

9

12

15

18

21

0.0000 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 0.0007

Axial strain

Figure 6.15 Axial stress Vs Axial strain for P0.1 Specimens

134

y = 27425xR² = 0.999

0

3

6

9

12

15

18

0.0000 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 0.0007

Axial strain


y = 27301xR² = 0.999

0

3

6

9

12

15

18

0.0000 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 0.0007

Axial strain



The effect of addition of polypropylene fibres on the modulus of

elasticity has been investigated and presented. Test results of modulus of

elasticity are presented in Figure 6.18. Incorporation of polypropylene fibres

in geopolymer concrete does not affect positively the modulus of elasticity.

Elastic modulus of concrete containing polypropylene fibres is slightly higher

than the elastic modulus of concrete without fibres. The elastic modulus

improves by only about 3%, 1% and 0.2% for volume fractions of 0.1%, 0.2%

and 0.3% respectively.

135

27246

28177

2742527301

26600

26800

27000

27200

27400

27600

27800

28000

28200

28400

GPCC P0.1 P0.2 P0.3

Figure 6.18 Modulus of elasticity of PFRGPCC

6.10 WATER ABSORPTION

6.10.1 Test Procedure

The water absorption test has been carried out according to

ASTM C 642-82, to study the relative porosity or permeability characteristics

of PFRGPCC specimens at 28 days. The specimens used for this test were

100 mm cubes as shown in Figure 6.19. The difference between the saturated

mass and oven dried mass expressed as a fractional percentage of oven dried

mass gives the water absorption.

Figure 6.19 PFRGPCC specimens for water absorption test

136


The values of saturated water absorption of the specimen at 28 days

were found out and tabulated in the Table 6.8. The initial absorption values

(at 30 min) for all the concretes were compared with recommendations given

by Concrete Society (CEB). From the test results, it can be seen that the water

absorption values at 30 minutes for the PFRGPCC specimens for all the

volume fractions of fibres were lower than the limit of 3% specified for good

concretes.

The water absorption capacity of PFRGPCC specimens having

0.1% and 0.2% volume fraction of fibres were less when compared with

control GPCC specimens, whereas the specimens having 0.3% of fibres have

higher water absorption capacity as compared to control GPCC specimens.

Within the fibrous specimens, specimens containing 0.2% of polypropylene

fibres performs better by showing lower value for water absorption as shown

in Figure 6.20.

1.96 1.93 1.74

2.57

3.242.78

2.38

3.81

00.5

11.5

22.5

33.5

44.5

GPCC P 0.1 P 0.2 P 0.3

30 minutes immersion 24 hours immersion

Figure 6.20 Water absorption at 30 minutes and 24 hrs

137

Table 6.8 Test Results of water absorption

Spec.Initial weight

g

Weight g

Water absorption

%

Averagewater

absorption %

At 30 minutes

immersion

At 24 hours

immersion

At 30 minutes

At 24 hours

At 30 minutes

At 24 hours

GPCC2291 2331 2362 1.75 3.10

1.96 3.242320 2363 2389 1.85 2.97 2251 2302 2333 2.27 3.64

P0.12343 2383 2402 1.71 2.52

1.93 2.782333 2374 2393 1.76 2.57 2276 2329 2350 2.33 3.25

P0.2

2334 2372 2385 1.63 2.19 1.74 2.382295 2339 2355 1.92 2.61

2273 2311 2326 1.67 2.33

P0.3

2286 2343 2372 2.49 3.76 2.57 3.812277 2343 2371 2.90 4.13

2280 2333 2361 2.32 3.55

6.11 SORPTIVITY

6.11.1 Test Procedure

Oven dried cube specimens of 100 mm size were exposed to the

water by placing it in a pan as shown in Figure 6.21. At certain times, the

mass of the specimens was measured using a balance, then the amount of

water adsorbed was calculated and normalized with respect to the cross

section area of the specimens exposed to the water at various times such as 1,

4, 9, 16, 25, 36, 49, 81and 100 minutes. To determine the sorptivity value,

138

AQ was plotted against the square root of time t .The sorptivity value was

calculated from the slope of the linear relation between AQ and t .

Figure 6.21 PFRGPCC Specimens during sorptivity test


The sorptivity test results of GPCC and PFRGPCC specimens are

presented in Appendix 4. From the test results, cumulative absorbed volume

after time t per unit area of inflow surface is calculated and given in Table 6.9.

When polypropylene fibres were added into the GPCC mix the

sorptivity coefficient decreases as shown in Figure 6.22. This is due to the

decreased porosity in the geopolymer paste and this lower sorptivity value

emphasizes the beneficial effect of adding polypropylene fibres to increase

the durability of concrete. Sorptivity values of specimens containing 0.1% and

0.2% of fibres were too low which indicates that the porosity of concrete is

lesser with lesser number of interconnected pores. These specimens have a

denser structure as compared to specimens containing 0.3% of fibres because

139

P0.3 specimens showed a maximum sorptivity value of 0.1618. This higher

value of sorptivity coefficient is due to larger number of capillary pores.

Table 6.9 Cumulative water absorption

tmin1/2

Q / A in mm

GPCC P0.1 P0.2 P0.3

2 0.8000 0.8000 0.7667 1.0333 3 0.9667 0.9333 0.9000 1.2333 4 1.2000 1.0333 0.9667 1.4333 5 1.3667 1.1667 1.1000 1.6000 6 1.5333 1.2333 1.2000 1.7667 7 1.7667 1.4333 1.3000 2.0000 8 1.9333 1.5333 1.4333 2.1000 9 2.1333 1.6000 1.5333 2.2000 10 2.2667 1.7000 1.6333 2.3667 11 2.4667 1.8000 1.7667 2.5000

0.1861

0.1121 0.1095

0.1618

00.020.040.060.080.1

0.120.140.160.180.2

GPCC P 0.1 P 0.2 P 0.3

GPCCP 0.1P 0.2P 0.3

Figure 6.22 Sorptivity values for PFRGPCC specimens

140

6.12 CONCLUSIONS

Based on the results obtained in this investigation, the following

conclusions are drawn:

Inclusion of polypropylene fibres reduces the slump values.

Increase in fibre content dosage additionally reduces the

workability of PFRGPCC specimens.

The density of GPCC without polypropylene fibres ranges from

2347 kg/m3 to 2458 kg/m3.Density of GPCC containing

polypropylene fibres ranges from 2376 kg/m3 to 2415 kg/m3,

2336 kg/m3 to 2406 kg/m3 and 2299 kg/m3 to 2421kg/m3 for

volume fractions of 0.1%, 0.2% and 0.3% respectively. It was

found from the test results that for most of the cases, inclusion

of polypropylene fibres in concrete resulted in marginal

decrease in unit weight.

The increase in compressive strength due to addition of

polypropylene fibres is not much significant and it was only

about 3%, 1.82% and 1.66% for 0.1%, 0.2% and 0.3% of

polypropylene fibres respectively with reference to GPCC mix

without polypropylene fibres.

As the volume fraction of polypropylene fibres increases from

0% to 0.3%, the split tensile strength also increases. The

improvement in the split tensile strength at 28 days was found to

be 1%, 9% and 12% for volume fractions of 0.1%, 0.2% and

0.3% respectively. The increase in split tensile strength is due to

the role of polypropylene fibres to resist cracking and spalling

across the failure planes.

141

Based on the test results, using least square regression analysis,

an equation for predicting the 28 days split tensile strength of

polypropylene fibre reinforced geopolymer concrete composites

in terms of the split tensile strength of plain GPCC and

percentage volume fraction of fibres is obtained. The split

tensile strength of PFRGPCC predicted from the proposed

analytical equation was compared with the experimental results

and it is found that a good correlation is obtained.

Addition of polypropylene fibres to GPCC resulted in

enhancement of flexural strength. At the age of 28 days, the

flexural strength increases by about 1%, 6% and 12% for

volume fractions of 0.1%, 0.2% and 0.3% of polypropylene

fibres respectively. This increase in flexural strength might have

resulted primarily from the polypropylene fibres intersecting the

cracks in the tension zone of the flexure beam. These fibres

accommodated the crack face separation by stretching

themselves, thus providing an additional energy-absorbing

mechanism.

In case of impact testing, the number of blows at first cracks and

failure, increased considerably in fibrous specimens.

Incorporating 0.1%, 0.2% and 0.3% polypropylene fibres into

the GPCC specimens led to an increase in the number of blows

by 620%, 1040% and 1110%, respectively at first crack and

683%, 1225% and 1292%, respectively, at failure compared to

those of control GPCC specimens. The percentage increase in

number of post crack blows is about 31%, 39% and 38% for the

fibre volume fractions of 0.1%, 0.2% and 0.3% respectively and

142

thus inclusion of fibres considerably improved the ability of

concrete to absorb kinetic energy.

Incorporation of polypropylene fibres in geopolymer concrete

does not affect positively the modulus of elasticity. Elastic

modulus of concrete containing polypropylene fibres is

marginally higher than the elastic modulus of concrete without

fibres. The elastic modulus improves by only about 3%, 1% and

0.2% for volume fractions of 0.1%, 0.2% and 0.3% respectively.

Water absorption values at 30 minutes for the PFRGPCC

specimens for all the volume fractions of fibres were lower than

the limit of 3% specified for good concretes. The water

absorption capacity of PFRGPCC specimens having 0.1% and

0.2% volume fraction of fibres were less when compared with

control GPCC specimens, whereas the specimens having 0.3%

of fibres have higher water absorption capacity as compared to

control GPCC specimens. Within the fibrous specimens,

specimens containing 0.2% of polypropylene fibres perform

better by showing lower value for water absorption.

The addition of polypropylene fibres into the GPCC mix

decreases the sorptivity coefficient. Sorptivity values of

specimens containing 0.1% and 0.2% of fibres were too low

which indicates that the porosity of concrete is lesser with lesser

number of interconnected pores. These specimens have a denser

structure as compared to specimens containing 0.3% of fibres

because P0.3 specimens showed a maximum sorptivity value of

0.1618. This higher value of sorptivity coefficient is due to

larger number of capillary pores.

chapter 6 polypropylene fibre reinforced geopolymer...

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