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LONG-TERM STRENGTH AND DURABILITY EVALUATION OF SISAL FIBRE COMPOSITES

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LONG-TERM STRENGTH AND DURABILITY EVALUATION OF SISAL FIBRE COMPOSITES Powered By Docstoc
					   INTERNATIONAL Engineering and Technology (IJCIET), ISSN 0976 – 6308 AND
   International Journal of Civil JOURNAL OF CIVIL ENGINEERING (Print),
   ISSN 0976 – 6316(Online) Volume 4, Issue 1, January- February (2013), © IAEME
                               TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 4, Issue 1, January- February (2013), pp. 71-86
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        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: ramakrishna_grk@rediffmail.com


   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

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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                       28 MPa
                                        ii)     7 days                       38 MPa
                                       iii)    28 days                      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.                 Property                         Value/
                 No.                                                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.    Fibre-      Fibre          Fibre          Tensile      Elongation       Specific   Elastic -
 No.     type      length        diameter        strength         (%)           gravity    modulus
                    (mm)           (mm)          (N/mm2)                                    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].
                                                 Energy absorbed upto ultimate failure
Residual impact strength ratio (Irs) =                                                             …(1)
                                                Energy absorbed at initiation of first crack


        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          0.64        0.64             0.65             0.68         0.70      0.74   0.76
 ratio

           Table 5: Details of Elements Cast for Strength and Durability Studies
                             (1:3; @ 28, 56, 90, and 120 days)
Sl. Type of                    No. of specimens for No. of                       Total no.    Total no. of
No. element                    strength studies     specimens                    of           specimens
                                                    for the                      specimens    cast
                                                    durability                   for the      for the
                                                    study                        durability   total
                               A     B     C    D
                                                                                 study        no. of
                                                                                              Mixes
                                                                                              (ie.-7)
1.    Flexural Beam
      (40x40x160mm)            3        3       3       3        -               12           84

2.    Slab           2                  2       2       2        2               10           70
      (300x300x18mm)

 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

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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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  Shown in (b)




                                (a) Data Acquisition System




                              (b)Experimental Set-Up

  Fig. 2: A View of Experimental Set-up for Flexure Test of Mortar Slab (broken)
2.3    DURABILITY STUDIES ON SISAL FIBRE CEMENT COMPOSITES
                       (with Data Acquisition system)

        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.

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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.               Compressive            Compressive strength (N/mm2) at fibre contents of
 No.            Strength at the Age
                        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
                  (1:3; constant flow value=112%; @ 28, 56, 90 & 120 days)

 Sl.            Flexural Tensile        Flexural Tensile strength (N/mm2) at fibre contents of
 No.           Strength at the Age
                       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
                    (1:3; constant flow value=112%; @ 28, 56, 90 & 120 days)
 Sl.         Split- Tensile Strength   Split - Tensile strength (N/mm2) at fibre contents of
 No.              at the Age 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
                       (1:3; constant flow value=112%; @ 28, 56, 90 & 120 days)

Sl.  Fibre                             Impact Strength/ Residual Impact strength Ratio at
No. content
      (%)
                             @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.



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       (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.            Flexural Strength at              Flexural strength (N/mm2) at fibre contents of
No.                 the Age 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.



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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 4, Issue 1, January- February (2013), © IAEME

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.  Fibre Impact Strength/ Residual Impact strength Ratio Deviation in
     No. content   Before Exposure           After Exposure         Irs
           (%)
                   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.     Fibre        Toughness Energy/Toughness index = {A2/(A1+A2)}                 Deviation in
    No.    content                                                                           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)}


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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 4, Issue 1, January- February (2013), © IAEME

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.



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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 4, Issue 1, January- February (2013), © IAEME

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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