Long term strength and durability evaluation of sisal fibre composites

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),

ISSN 0976 – 6316(Online) Volume 4, Issue 1, January- February (2013), © IAEME

71

LONG-TERM STRENGTH AND DURABILITY EVALUATION OF

SISAL FIBRE COMPOSITES

Part-I: CEMENT MORTAR COMPOSITES

G.Ramakrishna*, T.Sundararajan

Department of Civil Engineering

Pondicherry Engineering College

Pondicherry – 605 014

INDIA

*Corresponding author; E-mail: [email protected]

ABSTRACT

In the first part of a two –part paper, the long-term strength and durability evaluation

of sisal fibre cement mortar composites have been investigated. Strength characteristics of

cement mortar composite (compressive, flexural, split-tensile strength) and that of composite

slabs (flexural and impact strength) were determined at various ages (28-120 days) for 1:3

mix, at a constant flow value (110%) for various fibre contents (0.25%-2.0%, by wt. of

cement). The durability of the composites was evaluated by two methods. It is found that the

strength behaviour of the composites (i.e. compressive, flexural and split- tensile) are similar

over the range of parameters and ages and that there is considerable improvement in the long-

term strength. The two methods of evaluation of durability of the composites can be used to

understand the interaction of the matrix and an alkaline medium considered. The above

results are to serve as a reference to understand the role of a pozzolana used in cementitious

mortar composites, being reported in a companion paper.

Key words: Cement mortar Composite Strength, Durability, Impact Strength, Long-term

studies, Sisal Fibres,

I. INTRODUCTION

Studies on natural fibre reinforced cement/cementitious composites and development

of products for various applications in Civil Engineering, have the twin advantages of

ensuring sustainable development and making available materials/ products at affordable

INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)

ISSN 0976 – 6316(Online)

Volume 4, Issue 1, January- February (2013), pp. 71-86

© IAEME: www.iaeme.com/ijciet.asp

Journal Impact Factor (2012): 3.1861 (Calculated by GISI)

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72

cost. If the above advantages have to be actually realized, then, two inherent drawbacks

(‘balling effect’ and ‘embrittlement’ of fibres) have to be addressed scientifically and

comprehensively. Gram [1] was the first to recognize the ‘embrittlement of fibres’ in an

alkaline medium and to identify the mechanisms and investigate various measures to improve

the durability of cement composites with sisal and coir fibres. Subsequently several

approaches have been suggested and investigated [2-16]. From a comprehensive review of

literature on the strength characteristics of natural fibre cement composites it is found that

long-term studies on the strength behaviour of the above composites are rare [17]. Further,

studies on the use of flyash in natural fibre composites and its influence on various

characteristics of composites is also rather rare [17]

Hence, a, comprehensive and exhaustive investigations on the long-term strength,

evaluation of durability and durability of sisal fibre cement/ cementitious composites were

undertaken. The first part of the investigation covering the long-term strength characteristics

and evaluation of durability of cement mortar composites is covered in this paper. The results

from the first part of the investigations is expected to serve as a reference to understand the

role of fly ash in influencing the various characteristics of sisal fibre cementitious mortar

composites, which are reported in a companion paper (i.e. part-II of the paper)

II. EXPERIMENTAL INVESTIGATION

2.1 MATERIALS USED

Ordinary Portland cement (OPC – 53 grade) conforming to IS: 12269 - 1987 [25];

good quality river sand, whose gradation corresponds to Zone – II, as stipulated in IS: 383 –

1997 [26], were used. Good quality potable water available in the campus was used both for

mixing and curing the mortar specimens. Sisal fibres are available abundantly in ‘fully

processed form’ in this part of the region. The salient properties of above materials are given

in Tables 1 to 3.

Table 1: Physical Properties of Cement (OPC-53 grade)

Sl. No. Property Value

1 Standard consistency (%) 29%

2 Initial setting time (min.) 55 min

3 Final setting time (min.) 175 min

4 Soundness 1mm

5 Specific gravity 3.14

6 Compressive strength @

i) 3 days

ii) 7 days

iii) 28 days

28 MPa

38 MPa

56.7 MPa

Note: (i)Sand conforming to the gradation stipulated in I.S. specification for ‘standard sand’ was prepared in

the laboratory and used for determining the compressive strength of cement.

(ii)The sample conforms to the requirements of 53 grade as stipulated in IS: 12269-1987



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Table 2: Physical Properties of Fine Aggregate

Sl.

No.

Property Value/

description

1 Specific gravity 2.48

2 Water absorption 1.4%

3 Rodded bulk density 1.737 gm/cc

4 Fineness modulus 2.5

Note: Procedure is based on IS: 383 – 1997 [26]

Table 3: Physical Properties of Sisal Fibres

Sl.

No.

Fibre-

type

Fibre

length

(mm)

Fibre

diameter

(mm)

Tensile

strength

(N/mm2)

Elongation

(%)

Specific

gravity

Elastic -

modulus

GPa

1. Sisal 180 -600 0.10– 0.50 31 – 221 14.8 1.4 7.83

2.2 PREPARATION AND TESTING OF MORTAR COMPOSITE

Compressive strength, flexural strength and split-tensile strength of cement mortar

specimens and impact and flexural strength of cement mortar composite slabs of 1:3 mix

were determined at four ages (i.e.28, 56, 90 and 120 days of normal curing) and at six fibre

contents (i.e. ranging from 0% to 2.0%) and at a constant flow value (i.e.112.5%). Details of

the workability studies on the various composites are reported elsewhere [18-20]. From the

‘flow curves’ developed by the workability studies, the required water-binder (W/B) ratio

was selected for preparing the mortar, based on the constant flow value (i.e.112.5). No

adjustment was made for the water absorption-capacity of sisal fibres, as the fibres were pre-

soaked (at least for 5 minutes) in fresh water and then used in the mortar for casting various

test specimens. W/B ratio for each combination of mix for a constant flow value of 112.5% is

summarized in Table 4. Altogether there were 7 combinations (1 combination with OPC; 6

combinations with OPC + sisal fibre). Details of elements cast like size of specimen, number

of specimens, total number of specimens cast for each combination of mix etc. is given in

Table 5, for evaluating the flexural strength of beam specimens of the mortar composites.

After casting the mortar beam specimens, they were cured in water for the specified ages and

at the end of the respective curing period, the specimens were first tested for their flexural

strength as per IS 4031 (Part-8) [21]. Compressive strength of the specimens were determined

by using one of the fractured (broken) pieces of the beam specimens (after determining their

flexural strength) and testing them as per IS 4031-Part-8 [21]. Split- tensile strength of

specimens were determined by using another fractured (broken) piece of the beam specimen

and tested by a ‘novel method’ suggested by Hannant [22]. The slab specimens were tested

by the projectile impact test for evaluating the impact strength characteristics [23]. The

usefulness of the above method has been established based on earlier investigations carried

out on a few natural fibre reinforced cement mortar composites and reported elsewhere [23].

To evaluate quantitatively the improvement in the impact resistance characteristics of

composites, a simple parameter called, ‘residual impact strength (Irs )’ has been defined as



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given in eqn.(1), which can also be taken as a ‘measure of ductility’ of the composite

imparted by the fibres incorporated in to the matrix. Using the approach the performance of a

few natural fibre composites has been evaluated and reported elsewhere [23].

Residual impact strength ratio (Irs) =

Table 4: W/B Ratio of Mixes Considered for Strength Studies of Sisal Fibre

Reinforced Mortar (1:3; flow value= 112.5%)

Fibre Content 0 0.25% 0.5% 0.75% 1.0% 1.5% 2.0%

Water/Cement

ratio

0.64 0.64 0.65 0.68 0.70 0.74 0.76

Table 5: Details of Elements Cast for Strength and Durability Studies

(1:3; @ 28, 56, 90, and 120 days)

Sl.

No.

Type of

element

No. of specimens for

strength studies

No. of

specimens

for the

durability

study

Total no.

of

specimens

for the

durability

study

Total no. of

specimens

cast

for the

total

no. of

Mixes

(ie.-7)

A B C D

1. Flexural Beam

(40x40x160mm)

3

3

3

3

-

12

84

2.

Slab

(300x300x18mm)

2

2

2

2

2

10

70

Note: (i) ‘A, B, C, D and E’ indicated in the column below ‘strength’ and ‘durability’

studies indicate the curing ages i.e. 28, 56 , 90 and 120 days, respectively .

(ii) The slab specimens of durability studies were immersed in NaOH solution

(0.1N; pH: 12.5) for 28 days, after 120 days of normal curing in water.

Flexural strength of mortar slab specimens were determined by a four-point loading

system and using the 5kN capacity universal tensile testing machine available in the Dept. of

Civil Engineering. The usefulness of the above method has been established and reported

elsewhere [17, 24]. A computerized data-logging system was interfaced to the above test set-

up for acquiring data and processing them, through a software exclusively developed for the

above purpose. For the above test, slab specimens of size 120x90x20 mm were cut and

removed from the fractured slab specimens obtained from the impact test of slab specimens

of size 300x300x18 mm. The load versus deflection values were obtained through LVDT and

logged on to a computer and a plot of load vs. deflection obtained using the specially

developed software, wherein, the load was measured at the loading position of the specimen

Energy absorbed upto ultimate failure

Energy absorbed at initiation of first crack

…(1)



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used in the test. Along with the above plot, the maximum load and deflection at failure as

displayed in the system were logged on to the computer. From the load –deflection curve,

‘flexural toughness’ (FT) of the specimens were evaluated. The various strength tests

conducted on the various specimens are shown in Fig.1 and 2.

(a) A View of Flexural Testing Machine for Prism Specimens

(b) Test Set –Up for Compressive (c) Test Set –Up for Split- Tensile

Strength of Mortar Strength of Mortar

Fig. 1 : Prism Specimens for Determining the Various Strength Characteristics



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(a) Data Acquisition System

2.3 DURABILITY STUDIES ON SISAL FIBRE CEMENT COMPOSITES

Slab specimens of size 300 x 300 x 18 mm (1:3) were cast under identical conditions

as that of specimens for strength studies. After the specified period of normal curing, the slab

specimens were kept immersed in NaOH solution (prepared at 0.1N) for (another) 28 days.

During the period of exposure in the above alkaline medium, pH of the medium was

maintained constant at (about) 12.0. After 28 days of immersion in the above alkaline

medium, the slab specimens were tested for their impact and flexural strength. To evaluate

the durability of composites identical procedure and experimental set-up used for the case of

normal-cured specimens were used.

‘Irs’ and ‘IT’ of composites before and after exposure in NaOH along with deviation in

the above values computed and expressed as a percentage of relative change in values with

respect to values obtained before exposure, were used to evaluate the durability of the

composites.

(b)Experimental Set-Up

Fig. 2: A View of Experimental Set-up for Flexure Test of Mortar Slab (broken)

(with Data Acquisition system)

Shown in (b)



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III. RESULTS AND DISCUSSION

3.1 COMPRESSIVE STRENGTH

Compressive strength of cement mortar composites (1:3; Vf = 0.25% - 2.0%; @ 28,

56, 90 and 120 days of normal curing) are given in Table 6. Based on the above results,

following inferences are drawn:

(i) Compressive strength of cement mortar composites increases, with increase in

fibre content upto 0.5%, beyond which the strength decreases. The above

phenomenon is found to be independent of age of the composite (i.e. from 28 to

120 days).

(ii) Maximum strength is attained when the fibre content in the composite is 0.5%, for

all the ages considered and that the above strength is 25 – 61% higher than the

plain cement mortar strength (at the corresponding ages).

(iii) Moreover, the maximum strength attained increases with increase in age and that

there is about 44%, 104% and 112% increase in the maximum strength, at the ages

of 56 days, 90 days and 120 days, respectively, over the 28 days strength of the

cement mortar composite at 0.5% ( i.e.26 MPa).

(iv) The maximum long – term strength - gain ratio of the composite is about 2.1

i.e. ratio of the compressive strength @ 120 days (i.e. long-term) to that @ 28

days (i.e. at ‘normal age’).

Table 6: Compressive Strength of Sisal Fibre Cement Mortar Composites

(1:3; constant flow value=112%; @ 28, 56, 90 & 120 days)

Sl.

No.

Compressive

Strength at the Age

of

Compressive strength (N/mm2) at fibre contents of

0% 0.25% 0.5% 0.75% 1.00% 1.5% 2.00%

1 28 days 19.5 23.0 26.0 22.5 20.0 12.0 9.0

2 56 days 30.0 32.5 37.5 33.0 28.0 22.5 19.0

3 90 days 33.0 49.0 53.0 44.5 36.0 30.5 25.0

4 120 days 44.0 52.0 55.0 50.0 41.0 35.0 31.0

3.2 FLEXURAL STRENGTH

Flexural strength of cement mortar composites (1:3; Vf = 0.25% - 2.0%; at various

ages 28 -120 days), are presented in Tables 7. Based on the analysis of the above results

and comparing the compressive and flexural strength behaviour of the composites, following

inferences are drawn:

(i) Flexural strength behaviour of cement mortar composites is similar to that of the

compressive strength, within the range of fibre contents and ages considered.

(ii) Flexural strength of cement mortar composites is also maximum when the fibre

content is 0.5%, for all the ages considered and that the maximum strength is

about 34-53% higher than the corresponding plain mortar strength, over the range

of ages considered.



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(iii) The maximum flexural strength attained (i.e. @ Vf =0.5%) increases with

increase in age and that there is about 16%, 91% and 120% increase in the

strength, at the ages of 56 days, 90 days and 120 days, respectively, over the

maximum strength of the composite (i.e. 4.5 MPa) at 28 days.

(iv) The maximum long-term flexural strength ratio of the cement mortar composite is

2.2, which is nearly the same as that of the compressive strength - ratio of cement

mortar composites under identical conditions.

Table 7: Flexural Tensile Strength of Sisal Fibre Cement Mortar Composites


Sl.

No.

Flexural Tensile

Strength at the Age

of

Flexural Tensile strength (N/mm2) at fibre contents of

0% 0.25% 0.5% 0.75% 1.00% 1.5% 2.00%

1 28 days 3.0 3.5 4.5 3.8 3.0 2.7 2.4

2 56 days 3.4 4.4 5.2 4.6 4.1 3.8 3.3

3 90 days 6.1 7.5 8.6 7.1 6.1 5.6 5.3

4 120 days 7.4 8.8 9.9 9.5 8.6 7.6 6.4

3.3 SPLIT –TENSILE STRENGTH

Split - tensile strength of sisal fibre cement mortar composites (1:3; 28-120 days) are

presented in Tables 8. From the analysis of the above results and on comparing the above

strength behaviour with that of compressive and flexural strengths, following salient

inferences are drawn:

(i) Split - tensile strength behaviour of cement mortar composites is similar to that of

the compressive and flexural strengths, within the range of fibre contents and ages

considered.

(ii) Split-tensile strength of cement mortar composites is also maximum when the

fibre content is 0.5%, for all the ages considered and that the maximum strength is

generally about 20 - 30% higher than the corresponding plain mortar strength,

over the range of ages considered.

(iii) The maximum split – tensile strength increases, with age and that the increase is

about 28%,40% and 54%, over the maximum strength of the composite (i.e.5.0

MPa), at 28 days.

(iv) The maximum long – term split – tensile strength - ratio of cement mortar

composite is 1.6, which is slightly less than that of cement mortar composites in

compression and flexure, under identical conditions.

(v) Ratio of the maximum split-tensile strength to the maximum compressive strength

of the composite under identical conditions, and for various ages, is in the range of

13 to 19%, with an average value of 15.8%. The above (average) ratio indicates

good performance of the composite, under direct tension.



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Table 8: Split –Tensile Strength of Sisal Fibre Cement Mortar Composites


Sl.

No.

Split- Tensile Strength

at the Age of

Split - Tensile strength (N/mm2) at fibre contents of

0% 0.25% 0.5% 0.75% 1.00% 1.5% 2.00%

1 28 days 3.8 4.8 5.0 4.1 3.5 3.0 2.5

2 56 days 5.7 6.1 6.4 5.5 4.8 4.0 3.9

3 90 days 5.7 6.6 7.0 6.5 5.9 4.9 3.8

4 120 days 6.3 7.2 7.7 7.4 6.6 5.7 4.9

3.4 IMPACT STRENGTH OF CEMENT MORTAR COMPOSITE SLABS

3.4.1 NORMAL –AGE BEHAVIOUR (@28 DAYS)

Impact strength characteristics of cement mortar slabs and cement-mortar composite

slabs (@ 28 days) are presented in Table 9. It can be seen from the above results, that the

energy absorbed after initiation of first crack and upto failure is only nominal (i.e. from 9.25

to 10.0 Joules only). Hence, the inherent ductility of the cement mortar slab, which is

reflected in ‘Irs’ value is very less and is equal to 1.08. The ‘above value is taken as the

reference’, to obtain the relative performance of various mortar slabs / composite slabs.

As the fibre content in the cement mortar slab increases, energy required to cause

‘initiation of crack’ and ‘final failure’ goes on gently increasing and that energy absorbed is

maximum @ 2% fibre content, i.e.18.9 and 35.5 Joules, respectively. This shows the ductility

imposed by the fibres on the composite. In terms of energy absorbed there is an improvement

of 2.04 and 3.56 times than the corresponding energy required for the ‘reference mortar slab’.

Residual impact strength ratio (Irs) which is a measure of ductility inherent in the

material, increases gently with increase in fibre content for the cement mortar composites and

is in the range of 1.27 to 1.88 for the above composite, within the range of fibre contents

considered. However, Irs of cement mortar composites, relative to that of the cement mortar

slab (i.e. reference, with Vf = 0%), denoted by ‘Irs’ , ranges from 1.18 to 1.74. This gives the

range of ductility improvement that could be achieved due to incorporation of sisal fibres

(i.e.0.25% to 2.0% in this study), in cement mortar slabs.

3.4.2 LATER - AGE BEHAVIOUR (i.e.. 56 - 120 DAYS)

Impact strength characteristics of cement-mortar slabs at later-ages (i.e. 56-120 days)

are given in Table 9. Based on critical analysis of the above results and on comparing them

with the early-age behaviour, following inferences are presented:

(i) Later-age behaviour of cement mortar slabs are similar to that of early-age

behaviour, with respect to the energy absorbed. However, increase in energy

absorbed is substantial upto 90 days and that the maximum value is reached @

120 days, within the range of ages considered.



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(ii) Maximum energy absorbed for initiation of crack and at failure @ 120 days

are,13.8 and 18.0 Joules respectively, @ 120 days, which is about 1.5 and 1.8

times over the corresponding values of the reference mortar slab.

(iii) In terms of Irs, there is only a gentle variation over the various ages considered and

lies with in a narrow range of 1.20 to 1.30. However, ‘Irs’ of the composites is in

the range of 1.11 to 1.20, (i.e.about 20%) indicating only a marginal improvement

in the ductility of the composite slabs, over the early-age behavoiur, within the

range of later-ages considered.

Table 9: Impact Strength of Sisal Fibre Cement Mortar Composites


Sl.

No.

Fibre

content

(%)

Impact Strength/ Residual Impact strength Ratio at

@28 days 56 days 90 days @120 days

A B C A B C A B C A B C

1 0 9.25 10 1.08 12.5 15 1.20 13.49 17.0 1.26 13.84 18.0 1.22

2 0.25 11.02 14 1.27 15.4 18.8 1.22 16.01 20.5 1.28 16.91 22.5 1.70

3 0.50 13.43 18 1.34 16.01 24.5 1.53 17.18 27.5 1.60 17.35 29.5 2.0

4 0.75 16.19 23 1.42 16.38 29.0 1.77 17.37 32.5 1.87 17.76 35 2.25

5 1.00 17.41 27 1.55 16.66 33.50 2.01 17.61 37 2.10 18.18 40.0 2.53

6 1.50 18.00 31.5 1.75 17.51 38.0 2.17 18.69 41.5 2.22 19.39 45.0 2.68

7 2.00 18.88 35.5 1.88 18.55 42.5 2.29 19.23 45.2 2.35 21.34 54.0 2.88

3.5 FLEXURAL STRENGTH OF CEMENT MORTAR COMPOSITES SLABS

Results of flexural strength evaluated by the four - point loading method using the

broken pieces after conducting the impact test , are given in Table 10, for various ages and

other parameters considered. Based on the above and also comparing the flexural strength of

the composites (i.e. standard specimens), following inferences are drawn:

(i) Behaviour of composite mortar slabs are generally similar to that of flexural

strength of standard specimens of mortar and composites, within the range of

parameters and ages considered.

(ii) Flexural strength of reference mortar slabs (CM 1:3, fibre content = fly ash,

content= 0%) is found to be 3.93 MPa, (at 28 days), which is comparable to the

strength of reference mortar specimens under flexure. However, the strengths are

always lower, at all later-ages. Moreover, the later-age strength of slabs (@120

days) are about 30% lower than the strength of flexural specimens.



81

(iii) Flexural strength of cement mortar composite slabs are maximum at the fibre

content of 0.5% and at all ages, which is also similar to the flexural behaviour of

composite specimens (evaluated by the standard procedure). However, the

maximum strength obtained by the composite slabs are always less than the

maximum strength attained by the specimens (in flexure) at all ages considered.

The above phenomenon may be due to the ‘residual stress’ present in the slab

specimens due to the impact test, conducted earlier.

The primary objective of the above test is to obtain the ‘reference data’ for determining the

‘flexural toughness factor’ (IT) of the composite slabs after exposing them in NaOH and,

hence, to evaluate the ‘durability of the composite’.

Table 10: Flexural Strength of Sisal Fibre Cement Mortar Composite Slabs

Sl.

No.

Flexural Strength at

the Age of

Flexural strength (N/mm2) at fibre contents of

0% 0.25% 0.5% 0.75% 1.00% 1.5% 2.00%

1 28 days 3.93 4.11 3.98 3.41 3.08 2.93 2.29

2 56 days 4.55 4.67 4.77 4.47 4.10 3.57 2.40

3 90 days 4.80 5.10 5.76 5.55 5.25 4.32 3.97

4 120 days 5.26 5.40 5.41 5.34 5.00 4.73 4.40

3.6 DURABILITY OF SISAL FIBRE CEMENT MORTAR COMPOSITE SLABS

3.6.1 EVALUATION OF DURABILITY BASED ON ‘IRS’

Impact strength of cement mortar slabs, cement mortar composite slabs, before and

after exposing them in NaOH medium, are given in Table 11, for various fibre contents.

From a critical evaluation of the above experimental data, following observations are

obtained:

(i) ‘Irs’ values of cement mortar composite slabs increases with increase in fibre content,

after exposure in the alkaline medium, when compared to the Irs value before

exposure and it is found to be independent of the fibre content. ‘Irs’ values of the

above composite slabs after exposure have the same trend as that of slabs before

exposure in the alkaline medium and that it is maximum when the fibre content is

maximum i.e. 2.0% in the cement mortar composite slabs.

(ii) A closer look at the deviation in Irs values above results presents an interesting

scenario, i.e. (i) The deviation in Irs values of all plain mortar slabs, are all negative,

indicating nearly failure of matrix, due to exposure in the alkaline medium; (ii) the

deviation in ‘Irs’ values of all composite mortar slabs are all positive as ‘Irs’ values of

composite slabs after exposure are higher than the corresponding values before

exposure.



82

Table 11 : Impact Strength of Sisal Fibre Cement Mortar Composite Slabs Before and

After Exposure in NaOH

(1:3; Constant flow value =112%; r=200)

Sl.

No.

Fibre

content

(%)

Impact Strength/ Residual Impact strength Ratio Deviation in

Irs Before Exposure After Exposure

A B C A B C

1 0 13.84 18.0 1.30 8.91 10.89 1.22 -6.15

2 0.25 16.91 22.5 1.33 9.9 16.83 1.70 +27.81

3 0.50 17.35 29.5 1.7 10.89 21.78 2.0 +22.35

4 0.75 17.76 35 1.97 11.88 26.73 2.25 +14.21

5 1.00 18.18 40.0 2.20 12.87 32.67 2.53 +20.00

6 1.50 19.39 45.0 2.32 15.84 42.57 2.68 +18.96

7 2.00 21.34 54.0 2.53 16.83 48.51 2.88 +13.83

Note: (i) Energy for one blow = 0.99J (Height of fall = 21cm)

(ii) A- Impact strength at initiation of crack (in Joules)

B – Impact strength at final crack (in Joules)

C- Residual impact strength (Irs)

3.6.2 EVALUATION OF DURABILITY BASED IN FLEXURAL TOUGHNESS INDEX (IT)

Flexural toughness of cement mortar slabs, cement mortar composite slabs, before

and after exposure in NaOH medium are presented in Tables 12, for various fibre contents.

From a closer look of the above, it is seen that IT values of various mortars / composites

exhibit the same trend as that of ‘Irs’ values, with respect to the range of parameters

considered.

Table 12 : Flexural Toughness Index of Sisal Fibre Cement Mortar Composite Slabs

(1:3; Constant flow value = 112% ; r = 200 ; @ 120 days)

Sl.

No.

Fibre

content

(%)

Toughness Energy/Toughness index = {A2/(A1+A2)} Deviation in

IT Before Exposure After Exposure

A B C A B C

1 0 1322 700 0.346 1006.5 368.5 0.268 -22.54

2 0.25 1557 432.5 0.217 790.8 701.2 0.470 +116.58

3 0.50 998.5 434 0.302 198.6 846.7 0.810 +168.21

4 0.75 1361 2388.4 0.637 629.5 1887.5 0.750 +17.73

5 1.00 1319.5 471.2 0.263 848.1 498.1 0.370 +40.68

6 1.50 2413.8 1788 0.425 885.4 2392.0 0.730 +71.76

7 2.00 1347 1846 0.578 325.0 1084.0 0.770 +33.21

Note: (i (A) – Area of the load-displacement diagram upto the pre-cracking stage- (A1)

(B)- Area of the load-displacement diagram after the post-cracking stage-(A2)

(C)- Flexural toughness index –( IT )= {A2/ (A1+A2)}



83

IV. CONCLUSIONS

4.1 STRENGTH BEHAVIOUR OF CEMENT MORTAR COMPOSITES

(i) Compressive, flexural and split-tensile strength behaviour of sisal fibre cement mortar

composites (1:3) are similar over the range of parameters and ages (normal age i.e. at

28 days, and at later – ages upto 120 days), considered. All the above strengths attain

the maximum at identical fibre content in the mortar composite (i.e. sisal fibre content

= 0.50%).

(ii) Maximum compressive strength attained by the cement mortar composite is about 26

MPa [@ sisal fibre content (Vf) = 0.5%), at the normal – age], which is about 25 –

61%, higher than the plain cement mortar strength, for the range of ages considered.

The maximum long-term strength-gain ratio of the cement mortar composite (i.e. ratio

of compressive strength @ 120 days to that at normal age) is about 2.1.

(iii)Maximum flexural strength attained by the cement mortar composite is 4.5 MPa (at Vf

= 0.5), at the normal – age, which is about 30 – 50% higher than the reference mortar

strength and for the range of ages considered. It is found that the long – term

(maximum) flexural strength - ratio is nearly the same as that of the compressive

strength - ratio.

(iv) Maximum split – tensile strength attained by the cement mortar composite is 5.0 MPa

(@ Vf =0.5, at the normal – age), which is about 20 – 30% higher than the reference

mortar strength and for the range of ages, considered. It is found that the long- term

(maximum) split- tensile strength ratio is about 1.6, which is slightly less than the

other two strengths considered.

4.2 IMPACT STRENGTH OF CEMENT MORTAR COMPOSITES

(i) Residual impact strength ratio (Irs) which is measure of ductility inherent in the

material ranges from 1.18 to 1.74, for the cement mortar composite slabs relative to

that of the reference cement mortar slab, at normal-age and the range of sisal fibre

contents considered.

(ii) There is only a marginal improvement in the ductility (as measured by Irs) of the

cement mortar composite slabs, over the early – age behaviour, within the range of

later – ages considered.

4.3 FLEXURAL STRENGTH OF CEMENT MORTAR COMPOSITES

1. Flexural strength behaviour of composite mortar slabs are generally similar to that of

standard specimens (of mortar and composites), within the range of parameters and

ages considered.

2. However, the maximum strength obtained by the composite slabs are always less (

by 30% - average) than that attained by the specimens (under flexure), at all ages

considered, which may be attributed to the ‘residual stress’ present in the slab

specimens by virtue of the earlier impact load subjected on them.



84

4.4 DURABILITY OF SISAL FIBRE CEMENT MORTAR COMPOSITES

(i) Irs and IT values could reflect the changes in the strength due to the interaction

between the matrix and the medium considered (i.e. NaOH) and hence can be used

with confidence to evaluate the durability of the mortar composites.

V. ACKNOWLEDGEMENT

This work reported herein forms a part of comprehensive investigations on the

rheology, strength and durability characteristics of sisal fibre cement and cementitious

composites, carried out by the authors in the Dept. of Civil Engg., Pondicherry Engineering

College, Pondicherry , India. The kind support and co-operation extended by the Principal,

and the Head of Civil Engg. Dept., PEC , in all the endeavors of the authors is recorded with

a deep sense of gratitude. The financial assistance received from Dept. of Science and

Technology, (DST), Govt. of India, has greatly helped to carry out the experimental

investigations reported in this paper, which is gratefully acknowledged

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Documents

Long term strength and durability evaluation of sisal fibre composites