PVA FIBER - FLY ASH CEMENTITIOUS COMPOSITE: … · Engineered Cementitious Composites (ECC) is a...

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 8, Issue 10, October 2017, pp. 647–658, Article ID: IJCIET_08_10_068

Available online at http://http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=8&IType=10

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

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PVA FIBER - FLY ASH CEMENTITIOUS

COMPOSITE: ASSESSMENT OF MECHANICAL

PROPERTIES

K.V. Wishwesh

Post Graduate Student (Structural & Construction Engg.),

Amrita University, Coimbatore, Tamilnadu, India

K.B. Anand

Professor, Department of Civil Engineering,

Amrita University, Coimbatore, Tamilnadu, India

ABSTRACT

Engineered cementitious composites (ECC) come under the category of high

performance fiber reinforced cementitious composites (HPFRCC), exhibiting high

ductility and strain hardening behavior. ECC generally consumes high volumes of

cement and hence causes harmful impact on environment. This paper is aimed to

highlight the mechanical behaviour of fly ash - cementitious composite incorporating

Polyvinyl Alcohol (PVA) fiber. The PVA fiber volume fraction (Vf) was maintained at

1% of total volume of the composite. Though there is a reduction in compressive

strength with increase in fly ash content, tensile strain capacity of about 1.2 % was

achieved for 20% fly ash replacement for cement. At this flyash replacement level,

higher content of fiber (1.5% and 2%) was tried and at Vf of 2%, tensile strain

capacity of 2.3% could be achieved.

Key words: Fly ash cementitious composite, PVA fiber, fiber volume fraction, ECC.

Cite this Article: K.V. Wishwesh and K.B. Anand, PVA Fiber - Fly Ash

Cementitious Composite: Assessment of Mechanical Properties. International Journal

of Civil Engineering and Technology, 8(10), 2017, pp. 647–658.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=10

1. INTRODUCTION

Concrete serves as the most extensively incorporated material in constructions around the

world. It has advantages like durability, resistance to fire, low maintenance cost and on-site

fabrication. On the other hand it is weak in tension, has volume instability and low ductility.

To overcome the above stated problems high performance concrete (HPC), fiber reinforced

concrete (FRC) were developed. FRC having low fiber volume fraction (<1%) are effective in

reducing shrinkage cracking whereas FRCs with moderate fiber volume fraction (1% - 2%)

display improved mechanical properties like modulus of rupture, impact resistance and

fracture toughness [1]. High performance fiber reinforced concrete (HPFRC) using polymer

PVA Fiber - Fly Ash Cementitious Composite: Assessment of Mechanical Properties


fiber materials like asbestos, steel, nylon, glass etc exhibit strain hardening behaviour. Usage

of steel fiber has drawbacks of corrosion damage and increased density, while using glass

fibers improvement of flexural strength is not achieved. Moreover most HPFRCs require fiber

in large quantities (4% to 20%) by total volume to achieve a tensile ductility of about 1% [2].

Engineered Cementitious Composites (ECC) is a mortar-based composite, reinforced with

specially selected randomly distributed short polymer fibers with a volume fraction of 2% or

less. It has tensile strain capacity of 3-5% which when compared to normal concrete is about

300-500 times [3]. Moreover addition of ECC in reinforced concrete beams enhances flexural

strength, ductility and toughness. These exclusive properties arise due to the interaction

between the cementing matrix and fibers which might be engineered through micromechanics

design [4]. The fibers aid in limiting cracks to micro level. Nevertheless, the realization of

these versatile features is limited by the cost incurred in preparation of ECC. Polymer fibers

utilized in the preparation of ECC is costlier than steel fibers. Introduction of polymer fibers

is done on volumetric basis, as the specific density of the same is about six to seven times

lower than that of steel fibers [8].Therefore ECC can be used in critical regions of a structure

where ductility is of vital importance. In situations when the need to repair and rehabilitate

structures are necessary (as prolonging its life is better than demolishing it), sustainable

special material like ECC will be of utmost importance.

2. LITERATURE REVIEW

Victor C. Li [5] observed that ECC exhibits high tensile ductility several hundred times more

than that of conventional concrete apart from retaining requisite compressive strengths. This

ductile behaviour of ECC can be achieved at lower volumes of fiber content whereas for

FRP’s high fiber volume fraction is required. Victor C. Li and Kanda T [6] recommended not

to use coarse aggregate as they tend to affect the ductile property of ECC. The difference

between ECC and FRC was that after the formation of first crack ECC strain hardens rather

than tension-softening as in the case of FRC. The relatively lesser amount of fiber usage in

ECC (than FRC) makes it suitable for many practical applications. A summary of studies in

the past decade is utlising non-metallic fibres is highlighted in the following sections.

2.1. Role of Reinforcing Index

S.H.Said et al. [7,8] studied the effect of PVA and PE (Polyethylene) fibers on ECC by

varying Reinforcing Index (R.I) ({length of fiber × Volume fraction in % }÷{diameter of

fiber}) and found that as R.I increases compressive strength decreases. In contrast, increase in

R.I increases ultimate load at post-cracking apart from increasing the deflections at ultimate

load and at failure.

2.2. Influence of Fiber Type and Volume

Kolli. Ramujee [9] conducted study on the strength properties of Polypropylene fiber

reinforced concrete by varying the fiber volume fraction (Vf) from 0% to 2%. An increase in

compressive strength and split tensile strength was observed until Vf =1.5% and it decreased

at 2%. P Sravana et.al. [10] assessed the flexural behaviour of Glass fiber reinforced self

compacting concrete slabs by varying Vf from 0% to 0.1% in increments of 0.03%. The

flexural strength of the slabs was not improved. In addition to that they also recognized that

multiple cracks and micro cracks were not formed.

The effect of inclusion of PVA fibres at volume fractions of 0.15%, 0.3% and 0.45% in

concrete were studied by Gayathri and Anand [11]. Significant improvement of mechanical

properties (strength, impact, abrasion resistance) and remarkable reduction in sorptivity and

K.V. Wishwesh and K.B. Anand


shrinkage were observed. Fiber volume fractions of 0.125%, 0.25% and 0.5% were adopted. It

was observed that the optimum Vf was 0.25%, at which compressive, flexural and tensile

strength improved by 10%, 20% and 30% respectively over plain concrete. Shuxin Wang and

Victor C. Li [12] proved that micromechanics can be adopted for the design of ECC. As per

this concept of design PVA-ECC exhibited a tensile strain capacity of 3% along with

achievement of tensile, flexural and compressive strengths greater than 5 MPa, 15 MPa and

70 MPa respectively.

S P Singh et.al. [13] analyzed the variation of strength and flexural toughness of concrete

reinforced with Steel-Polypropylene (PP) hybrid fibers by keeping Vf as 1%. The proportions

of Steel-PP fibers were varied from 100%-0% to 0%-100% by volume. The best performance

of all mechanical properties was achieved at 75%-25% of Steel-Polypropylene fiber ratio. Pan

J L et al. [14] examined the effect of Vf on flexural behaviour of PVA-ECC. The Vf was

varied between 0%-4% while other ingredients were kept constant. It was noticed that as

volume fraction increased ultimate flexure load and corresponding deflection increased.

2.3. High Volume Fly Ash Utilization

En-Hua Yang, Yingzi Yang, Victor C.Li [15] investigated the effect of high volume fly ash to

improve the mechanical properties of ECC by keeping the total Fly ash + Cement (binder)

content constant (by increasing the fly ash content and decreasing cement content). The PVA

fiber Vf was fixed at 2%. It was observed that as fly ash content increased compressive

strength reduced. However, better performance resulted through lesser crack width, drying

shrinkage and enhanced tensile ductility.

2.4. Large Scale Manufacturing

All the above studies were conducted in small scale under laboratory conditions. Gregor

Fischer et.al. [16] designed ECC for large scale processing with better workability

requirements using the concept of Liquefaction effect. This study proved that at adequate

moisture content and with specific extent of external agitation, the cementitious mortar

achieves a condition of liquefaction, which diminishes the mortar viscosity while maintaining

consistency (without segregation).

3. SIGNIFICANCE AND OBJECTIVES OF STUDY

The cost incurred for producing ECC can be reduced by partial replacement of cement with

fly ash. Moreover, the usage of fly ash is expected to reduce PVA fiber-matrix interface bond

and also matrix toughness. This in general will favour attainment of high tensile strain

capacity [3]. Hence fly ash not only reduces the cost but also helps in the formation of

multiple cracks which will be in favour of attaining high ductility. The objectives of this work

are:

To find the optimum percentage replacement of cement with fly ash (with 1% volume fraction

of PVA fiber) at which better mechanical performance can be achieved.

To study the effect of different levels of PVA fiber content on the mechanical properties at the

optimum fly ash to cement ratio.



4. EXPERIMENTAL INVESTIGATION

4.1. Materials

Ordinary Portland Cement : OPC-53 grade of specific gravity 3.15 confirming to IS

12269:1987.

Fine Silica sand of size less than 250 µm with specific gravity 2.65.

Fly ash: Class F fly ash of specific gravity 2.1 conforming to IS 3812:2013(Part II).

PVA fiber : The properties of PVA fiber used in the mix are given in Table 1. It is surface-

coated with a proprietary oil agent (1.2 % by weight)a.

Superplasticizers / High range water reducing admixtures (HRWA) of Polycarboxylate Ether

family was used.

Table 1 Properties of PVA fiber used in the mix b

Type

of

fiber

Specific

Gravity

Length of

fiber(mm)

Diameter

of fiber

(µm)

Aspect

ratio(l/d)

Elongation(%) Tensile

strength

(MPa)

Young's

Modulus

(GPa)

PVA 1.3 6 38 158 7 1317 39 a,b

Based on manufacturer's data

4.2. Mixing and Curing

Materials in dry state were mixed in the mortar mixer for about 2 minutes. Water was then

added gradually and mixed with the materials. This was followed by the addition of super

plasticizer and the entire matrix was mixed for another 5 minutes to attain suitable

workability. The superplasticizer to binder ratio (SP/B) is generally decided based on the

workability requirement consideration before the addition of fiber. Finally the PVA fibers

were mixed with the matrix for 3 minutes. Care was taken when adding the fiber such that it

does not stick to the inner surface of the mixing container. Finally the mortar was placed in

the moulds. All the specimens were water cured for 28 days.

4.3. Specimens

Compressive strength was evaluated by casting three cubes of dimensions 50 mm × 50 mm×

50 mm. Steel moulds with dimensions of 500 mm × 100 mm × 25 mm were used to cast and

prepare beams. Cylinders of dimensions 300 mm × 150 mm were cast for each mix to

determine the split tensile strength. Fig 1 shows the dimensions of the specimen used for

direct tensile test in accordance with E646-07 (ASTM standard) [17].

Figure 1 Dimensions of direct tensile test specimen



4.4. Mix Proportion Details

The control mix proportion for this study is adopted from the study done by Shwan H Said et

al [6] which is shown in Table 2. The 1% fiber volume was incorporated in the mixes after

converting into gravimetric measure (13 kg/m3) using fiber specific gravity. The workability

of ECC was determined and evaluated using flow table test. It was noted that, as fly ash

content increased, the amount of super plasticizer needed also increased in mixes to maintain

the same level of consistency. Flow percentages between 205-220 was maintained before the

addition of fiber which enabled the fiber to get dispersed homogenously in the mix. After the

addition of fiber the observed flow percentage was 95-110. Fig 2a and 2b shows the

workability of mix before and after the addition of fiber. Water to binder ratio (W/B) was

maintained constant as 0.37 for all the mixes. SP/B ratio was maintained between 0.28% -

0.43% to ensure workability.

Figure 2a Flow before adding fiber 2b Flow After adding fiber

Table 2 Mix proportions used for ECC

Mix

Proportions

FA/C

Ratio

Cement

(C)

kg/m3

Fly ash

(F.A)

kg/m3

Sand(S)

kg/m3

Water

kg/m3

HRWA

kg/m3

PVA

fiber

kg/m3

Control

Specimen

(CS)

0 1025 0 656 379.25 2.87 0

ECC 1 0 1025 0 656 379.25 2.87 13

ECC 2 0.25 820 205 656 379.25 3.075 13

ECC 3 0.5 683.33 341.67 656 379.25 3.18 13

ECC 4 0.75 585.71 439.29 656 379.25 4.00 13

ECC 5 1 512.5 512.5 656 379.25 4.40 13

4.5. Testing

ECC cubes were tested to evaluate the compression strength at 28 days of time. The ECC

beams were tested using Universal testing machine of 400 kN capacity under four point

flexural loading. For each beam the deflection was measured using a dial guage which was

fixed at the center as shown in Fig 3. All the above mentioned tests were performed in

accordance with BIS procedures. I-shaped specimens as shown in Fig 4, after 28 days of

curing were used to conduct uniaxial tensile test using UTM of 200 kN capacity as shown in

Fig 5. The rate of loading was maintained as 0.1 mm/min.



Figure 3 Four point loading setup- flexure test

Figure 4 Tensile specimen Figure 5 Tensile testing machine

5. DISCUSSIONS ON HARDENED PROPERTIES

Table 3 Compressive, splitting tensile, flexural and direct tensile strength

Mixture

Avg.

Compressive

strength

(MPa)

Avg.

Splitting

tensile

strength

(MPa)

Modulus

of rupture

(MPa)

Deflection

at the

ultimate

load (mm)

Deflection

at failure

(mm)

Direct

tensile

strength

(MPa)

Control

Specimen

(CS)

49.06 1.34 3.19 0.39 0.61 2.03

ECC 1 50.35 1.72 3.46 1.21 3.11 2.55

ECC 2 43.54 2.08 5.90 1.62 4.52 3.48

ECC 3 37.93 2.00 4.18 1.38 3.53 2.75

ECC 4 31.79 1.91 4.03 1.34 3.24 2.17

ECC 5 25.87 1.58 3.24 1.2 3.09 1.07

5.1. Compressive Strength of ECC

The compressive strength given in Table 3 of the control specimen was 49.06 N/mm2

and that

of ECC 1 was 50.35 N/mm2, i.e., a marginal strength increase by 2.63% when PVA fibers are

added. However, as cement is replaced with fly ash, the compressive strength reduces.

Specimens with fiber were able to hold their shape even after failure when compared with

control specimens. The difference in the failure pattern of the specimens is shown in Fig 6.



Stress-strain relationship for different mix proportions is represented in Fig 7. Compression

strain of 3.38% was observed for ECC1 specimen wheras the same for a control specimen

was 1.53%. This indicates that when fibers are incorporated in the mix it helps in holding the

matrix together (eliminating the brittle failure of the specimen). Maximum compression strain

of 4.96% was observed for ECC 2 specimen.

Figure 6 Failure pattern of cube- a) Control specimen b) ECC 1

Figure 7 Stress- Strain relationship in compression

5.2. Flexural Strength of ECC

Modulus of rupture given in Table 3 was calculated for all the ECC mix proportions from the

maximum load obtained from the test. Results showed that all the mix proportions in which

fly ash was incorporated, showed better flexural strength than the control specimen. ECC 2

showed better performance with a modulus of rupture of 5.90 MPa which is 45.93% greater

than the control specimen. The deflection at the maximum axial load and at failure were 1.62

mm and 4.52 mm respectively. Multiple cracking phenomenon observed predominantly for

ECC 2 is shown in Fig 8. Load Vs deflection graph for the same is shown in Fig 9.



Figure 8 Multiple cracking in beam

Figure 9 Load Vs Deflection curve for various mix

5.3. Splitting Tensile Strength of ECC

The split tensile strength results are given in Table 3. Split tensile strength of ECC 1 was

28.4% more than the control specimen. Maximum splitting tensile strength of 2.08 Mpa was

achieved for ECC 2. The specimens which were incorporated with fiber did not fail in a brittle

manner.

5.4. Direct Tensile Test

Maximum stress and strain was observed for ECC 2 specimen. Strain hardening was not

observed for any of the specimens probably because of low volume of fiber fraction used.

However ECC 2 showed larger strain before failure when compared with the rest of the

mixes. Fig 10 shows the stress-strain graph of the ECC specimens in tension.



Figure 10 Stress-Strain relationship in tension

6. INFLUENCE OF INCREASED IN FIBER CONTENT

From the above mechanical tests, it was observed that ECC 2 (with 1% fiber and 20% flyash

replacement for cement) showed better performance when compared with the rest of the

mixes. Earlier studies by Prijatmadi Tjiptobroto and Will Hansen [18] and Hiemstra and

Sottos [19] have indicated that at higher volume fraction of fiber there will be reduction in

spacing between the microcracks. This, indirectly indicates fiber influence on increasing the

ductility of the composite. Hence for proportions of ECC 2 mix, an increase in volume

fraction of fiber of 1.5 % and 2 % (19.5 kg/m3 and 26 kg/m

3) was tried and details of tests,

results and inferences are discussed in the following sections. Table 4 gives the hardened state

properties of ECC at higher volume fractions of fiber.

6.1. Results and Discussions

Table 4 Mechanical strength values at higher volume fiber fraction

Mixture

PVA fiber Compressiv

e strength

(MPa)

Split

tensile

strength

(MPa)

Modulus

of

rupture

(MPa)

Deflection

at the

ultimate

load

(mm)

Deflection

at failure

(mm)

Direct

tensile

strengt

h

(MPa)

% Vol.

fraction

kg/m3

ECC 2 1 13 43.54 2.08 5.90 1.62 4.52 3.48

ECC 6 1.5 19.5 50.528 2.12 7.6 3.06 7.62 3.57

ECC 7 2 26 53.664 2.31 8.64 3.66 9.06 3.94

The compressive strength of ECC 6 and ECC 7 increased by 16.05% and 23.25% when

compared with ECC 2. Fig 11 shows the stress-strain relationship under compression for ECC

mixes at increased fiber content. Compression strain of 7.14% and 7.88% was observed at 1%

and 2% volume fraction of fiber respectively. Modulus of rupture of ECC 6 and ECC 7

increased by 28.81% and 46.45% respectively when compared with ECC 2. Fig 12 shows the

load vs deflection curve at increased fiber content. Flexural deflection at failure increased

from 4.52 mm to 9.06 mm when fiber volume fraction got increased from 1% to 2%. Hence it

is observed that as fiber content increased the modulus of rupture and ductility of the

specimen increased. An increase of 1.92% and 11.06% was observed in split tensile strength

as the fiber volume increased from 1% to 1.5% and 2% respectively.



Strain hardening behaviour was observed for the ECC 7 mix incorporating 2% volume

fraction of fiber. Fig 13 illustrates the Stress-Strain graph under direct tension. A tensile strain

capacity of 1.98% and 2.3% was achieved for ECC 6 and ECC 7 respectively. This also

proves that as fiber content increases the tensile strain carrying capacity enhances. On the

whole all the mechanical properties - compressive strength, split tensile strength, flexural

strength and direct tensile strength improved as the amount of fiber content added to the mix

increased.

Figure 11 Stress vs Strain graph under compression

Figure 12 Load vs Deflection graph under flexture

Fig 13 : Stress-Strain graph under direct tension



7. CONCLUSIONS

Following conclusions are drawn within the range of materials and test parameters

investigated:

All the mixes incorporating fiber showed better performance than the control specimen during

failure.

The compressive strength of the ECC mixes decreases with an increase in fly ash content.

However even at FA/C=1 compressive strength of 25 MPa was achieved.

At 1% fibre volume fraction, tensile properties (investigated through flexure test, direct tensile

test and split tensile test) was higher for mix with FA/C ratio 0.25.

Strain hardening behaviour was predominantly observed for ECC 7 at 2% volume fraction of

fiber.

As the fiber content increased the formation of multiple cracks increased and spacing between

them decreased indicating the improvement in ductility.

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