EFFECT OF SULFATE ON THE PROPERTIES OF SELF COMPACTING CONCRETE-2

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EFFECT OF SULFATE ON THE PROPERTIES OF SELF COMPACTING CONCRETE-2 Powered By Docstoc
					  International Journal of Civil Engineering and CIVIL ENGINEERING – 6308
  INTERNATIONAL JOURNAL OF Technology (IJCIET), ISSN 0976 AND
  (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME
                            TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 4, Issue 2, March - April (2013), pp. 270-287
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          EFFECT OF SULFATE ON THE PROPERTIES OF SELF
        COMPACTING CONCRETE REINFORCED BY STEEL FIBER

                                Abbas S. Al-Ameeri1, Rawaa H. Issa 2
                    1
                     (Civil, Engineering/ University of Babylon, Babylon City, Iraq)
               2
                   (Civil, Engineering/University of Babylon, Al-Najaf Al-Ashraf, Iraq)


   ABSTRACT

            The Internal sulfate attack is considered as very important problem of concrete
   manufacture in Iraq and Middle East countries. Sulfate drastically influence the properties
   of concrete. This experimental study is aimed at investigating the effect of internal sulfates on
   fresh and some of the hardened properties of self compacting concrete (SCC) made from
   locally available materials and reinforced by steel fibers. Tests were conducted on fifteen
   mixes, three varied steel fiber contents (0, 0.75 and1.5) (%by Vol.) with five SO3 levels (3.9
   ,5, 6, 7 and 8) (% by wt. of cement). The last four SO3 levels are outside the limits of the Iraqi
   specifications (IQS NO.45/1984). The results indicated that sulfate passively influenced the
   fresh and hardened properties of the plain and the reinforced SCC. However, regarding the
   effect on the hardened properties, the SCC reinforced with steel fiber showed similar to better
   sulfate resistance over plain SCC, the resistance enhanced with increasing steel fiber content.
   The results of the present study refer to that there might be a possibility of using reinforced
   SCC with unacceptable SO3 (with regard to Iraqi specifications) if high steel fiber content and
   long curing period are employed and if the SO3 is limited to 6 (% by wt. of cement).

   Keywords: Self compacting concrete, Steel fiber, Steel fiber reinforced concrete, Steel fiber
   reinforced self compacting concrete, Sulfate attack, Internal sulfate attack.

   1. INTRODUCTION

           Self compacting concrete (SCC) is a concrete which has the ability to flow by its own
   weight and achieve good compaction without external vibration. In addition, SCC has good
   resistance to segregation and bleeding because of its cohesive properties [1]. SCC, like any
   other concrete, is known to be brittle and can easily crack under low levels of tensile force.
   This inherent shortcoming, which limits the application of this material, can be overcome by

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the inclusion of fibers. The steel fiber is the most common fiber type in the building industry.
The mechanical properties of SCC reinforced with steel fibers have been the pivot of
numerous research programs, whereas its durability has not been investigated to the same
extent. One of the durability problems which may encounter the concrete during its service
life is the internal sulfate attack; internal sulfate attack is the major culprit of causing the
deterioration to concretes in middle east countries, particularly in Iraq.
         Internal sulfate attack results from the reaction between sulfates in concrete
ingredients ( water , cement , sand , gravel ) and cement paste, which had calcium aluminates,
and water to form high calcium sulfoaluminate (ettringite). One of the main sources of
internal sulfates that cause damage of concrete structures is the sand used. In the central and
southern regions of Iraq, most sands are contaminated with sulfates mainly in the form of
gypsum. About 95% of the sulfates in sand are in the form of calcium sulfates [2]. Gypsum is
also normally added to cement to retard early hydration, prevent quickset and increase the
efficiency of clinker grinding. The total sulfate in concrete may, therefore, be high enough to
cause internal sulfate attack. This may lead to deterioration and possibly cracking and failure
of concrete structure[3].
         Therefore, an attempt has been made to study the behavior of self compacting
concrete reinforced by steel fiber in the fresh and in the hardened state, in case of exposure to
internal sulfate attack. To shed some light on the potential of the exposure to this kind of
problem in such a concrete is highly requisite, it may illustrate to what extent internal sulfates
can affect the properties of this type of concrete and to what extent can this concrete resist the
sulfate attack.

2. Materials Used

2.1 Cement
   Ordinary Portland cement, which has specific gravity of 3.15 and the SO3 of 2.51, was
used in this investigation. It is conforming to IQS:5 -1984

2.2 Coarse aggregate
  Rounded shape aggregate of size of 10 mm was used and it has the following properties:
Specific gravity of 2.61 and the SO3 of 0.04

2.3 Fine aggregate
   Natural sand conforming to zone III of IQS: 45 – 1984 was used and its properties are
found as follows: Specific gravity 2.56 and the SO3 of 0.37

2.4 Water &Super-plasticizer
   The drinking tap water has been used for both mixing and curing of concrete. A chemical
admixture based on modified polycarboxylic ether, which is known commercially (Glenium
51) was used in producing SCC as a superplasticizer admixture.

2.5 Lime stone powder (LSP)
   This material was used to increase the amount of powder (cement + filler). It has SO3 of 1.9
and its specific gravity was 2.7.




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 2.6 Gypsum
    Gypsum was added to the fine aggregate to obtain the required SO3 content in concrete.
 The added gypsum was natural gypsum rock .It was crushed and ground by hammer to obtain
 nearly the same gradation set of fine aggregate used in the mixes. This gypsum was used as a
 partial replacement by weight of fine aggregate with limited percentages. The following
 equation has been used to control the SO3 contents in the used sand:


        w=
             (R − 0.37% ) S
                                                                            …………. (1)
                   N
  Where:
   : the weight of natural gypsum needed to be added to fine aggregate.
    : the percentage of SO3 desired in fine aggregate.
    : the weight of fine aggregate in mix.
  N: the percentage of SO3 in the used natural gypsum (34.9%).
 2.7 Fibers
     In this work, type of steel fiber having geometry of cylindrical with hooked ends was used.
 The characteristics of the steel fiber ; length, diameter ,tensile strength, specific gravity were
 30mm , 0.5 mm,1100 MPa and 7000 Kg/m3 respectively.

 3. METHODOLOGY

               In order to cover a broad range of SO3 levels ( 3.9 which is within the limits of
 Iraqi specifications[4] and, 5,6,7and 8 which are outside the limits)% by weight of cement in
 concrete, a total of fifteen mixes were made. The mixture was designed according to [5]. Adding
 gypsum as a partial replacement of sand was the adopted procedure to obtain the required SO3
 level in concrete. Fibers were added in quantities ranging from 0 to 1.5 % by volume of the total
 mixture. Moist curing was adopted , the curing time was for four ages (7, 28, 90 and 180) days.
 Table (1) shows the proportions of reference plain mixture.

                        Table (1) Proportions of reference plain mixture
         Cement         Sand      Gravel      LSP         SP
                                                                    w/c          w/p
         (kg/m3)            3
                       (kg/m )         3
                                  (kg/m )         3
                                            (kg/m )     (L/m3)

           425          870        600       129.2       3.35        0.52        0.4

4.FRESH CONCRETE TESTS

        The fresh properties of plain SCC and SCC reinforced by steel fiber were tested by the
 procedures of (European Guidelines for self compacting concrete). In this work three tests
 were used slump flow test, L-box test and V-funnel test.

5. HARDENED CONCRETE TESTS

         The mechanical properties studied are compressive strength, splitting tensile strength,
 flexural strength and static modulus of elasticity. Furthermore, the non-destructive test methods,
 length change test, ultra-sonic pulse velocity test and Schmidt hammer test are used. The

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                                                               IQS:348
compressive strength test was performed in accordance with IQS:348-1992 [6] using 150 mm
                .                                                                IQS:283-1995
cube specimens. The splitting tensile strength test was carried out according to IQS:283
                                                                            IQS:291-1991 [8]
[7] using Ø100 × 200 mm cylinder specimens. The test procedure given in IQS:291
was used to determine the flexural strength using 100 × 100 × 400 mm prisms. The sta     static
                                                   IQS:370
modulus of elasticity was performed according to IQS:370-1993 [9] by using test cylinders of
                              IQS:54
Ø150×300 mm. According to IQS:54-1989 [10] prisms of (75×75×285) mm of concrete was
                                                                         and
used to measure the changing in length due to sulfate action. The UPV and Schmidt hammer
                                  IQS:300
tests were conducted according to IQS:300-1993 [11] and IQS:325-1993 [12] respectively.

6. Results of Tests

6.1 Fresh Concrete Properties
6.1.1 Slump Flow Test
                                                                           values
        Table (2) and Fig. (1) show the results of slump flow tests . The values of (D) represent
the maximum spread (slump flow final diameter), while the values of T50 represent the time
required for the concrete flow to reach a circle with 50 cm diameter. The results of the slump
                            750)
flow range between (486-750) mm, the results of T50 cm range between (2.1     (2.1-5.7) seconds as
shown in Fig. (2). The results indicate that increasing sulfate decrease the slump flow diameter
and increase the time required to reach the diameter of 50 cm (T50), This can be accounted for,
                      ages
during very early stages of hydration, ettringite forms in relatively increased quantities with
increased sulfates content, as a result, relatively large amount of water would be consumed for
the reaction forming ettringite, beside, the roughness of gypsum particles could be another
                                                                    .
reason. Therefore, concrete mixtures tending to be cohesive [13]. Accordingly, the yield stress
value might be increased causing the reduced flowability. Significant decrease in slump flow
                                                           incorporating
diameter and increase in T50 have been observed with incorporating steel fibers in SCC mixes,
adding steel fibers increases the resistance to flow and reduces the flowability due to increasing
the interlocking and friction between fibers and aggregate [14].


                           800                                                                 6
 Slump flow diameter(mm)




                           700                                                                 5
                           600
                                                                                               4
                           500
                                                                                    T50(sec)




                           400                                     Vf%=0                       3                                        Vf%=0
                           300                                     Vf%=0.75                    2                                        Vf%=0.75
                           200                                     Vf%=1.5                                                              Vf%=1.5
                                                                                               1
                           100
                             0                                                                 0
                                 3.9     5      6       7     8                                    3.9      5       6        7      8
                                  Total SO3 (% by wt. of cement)                                      Total SO3 (% by wt. of cement)

                                                          (mm)
                           Fig.(1): Slump flow diameter D (mm                              Fig.(2):Time required to reach a circle
                                                                                                          with50dia


6.1.2 L-Box Test
               Box
       The L-Box with 2 bars was used in this study to assess the passing ability of the
mixes. The Blocking Ratios results (BR=H2/H1) of the tests are summarized in Table (2) &
                                                                  1).
plotted in Fig. (3). The results of the BR ranged between (0.58-1). According to [5], a

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                                                0.8
blocking ratio (H2/H1) of more than or equal to 0.8 represents good passing ability. All
mixtures had a good passing ability with BR ≥ 0.8 except the mixtures (S4F3 and S5F3)
had BR less than 0.8.The results show that the BR decreased with increasing sulfates in
                        se
concrete. This decrease is likely due to increased yield stress and viscosity with the
increasing in sulfates.

                                  1.2

                                        1

                                  0.8
                         BR



                                  0.6                                               Vf%=0

                                  0.4                                               Vf%=0.75

                                  0.2                                               Vf%=1.5

                                        0
                                                 3.9     5       6         7   8
                                                 Total SO3 (% by wt. of cement)



                                                       L
                          Fig.(3): Blocking Ratios for L-box tests


6.1.3 V-Funnel Test
               funnel                                                            self-compacting
        The V-funnel test is used to assess the viscosity and filling ability of self
                                               V
concrete [5] . Table (2) shows the results of V-funnel test. The Tv values ranged between
       12.3).                                         V-funnel
(6.57-12.3). It is clear from the results that the V funnel flow time increased with the
increasing SO3 content in the mixes, confirming that raising sulfate content increases
                               Funnel
viscosity of the mixtures. V-Funnel flow time also increased by incorporating steel fibers in
                                                      test.
mixes. Similar behavior was observed in the T50 test. Besides, the higher the steel fiber
                             time                           ascribed
content, the more the flow-time increased. This can be ascribed to, the increasing in fiber
content leads to increase the friction between the fibers and aggregates and the friction of the
                                                                            V funnel
fibers with each other which could extend the required time to empty the V-funnel

                                            14
                                            12
                                            10
                              Tv(sec)




                                             8
                                             6                                        Vf%=0

                                             4                                        Vf%=0.75

                                             2                                        Vf%=1.5

                                             0
                                                   3.9       5   6         7   8

                                                   Total SO3 (% by wt. of cement)



                                            V-funnel flow time Tv (sec)
                                   Fig.(4): V


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                            Table (2) Results of fresh concrete tests
   Mix       SO3 (%by        Steel Fiber    D (mm)       T50 (Sec)      Blocking Ratio       Tv (sec)
             wt. of          (% by Vol.)                                    (BR)
             cement)
  S1F1             3.9            0           750           2.1                1               6.57
  S1F2                           0.75         681          2.95              0.95              7.68
  S1F3                           1.5          584          4.25              0.84              9.23
  S2F1                            0           745          2.18                1               6.69
  S2F2             5             0.75         675           3.1              0.93              7.86
  S2F3                           1.5          573          4.53              0.82              9.46
  S3F1                            0           729          2.35              0.98               6.8
  S3F2             6             0.75         658          3.37              0.91              8.27
  S3F3                           1.5          555            5               0.79              10.27
  S4F1                            0           699          2.55              0.96              7.22
  S4F2             7             0.75         625          3.71              0.88               8.9
  S4F3                           1.5          518           5.7              0.71              11.53
  S5F1                            0           685          2.73              0.93              7.51
  S5F2             8             0.75         595          4.12              0.83              9.36
  S5F3                           1.5          486          N.a*              0. 58             12.3
*N.a: not applicable

6.2 Hardened Concrete properties
6.2.1 Compressive Strength
          Table (3) and Fig.(5) refer to that there is an optimum SO3 content at which the compressive
strength is maximum. The data in table (5) indicate that the optimum SO3 content for these mixes is
about (5) (% by wt. of cement), beyond this optimum value the compressive strength decreased with
the increase of sulfates content for all SCCs the plain and the reinforced ones, at all ages of
test. at age of 180 days, the percentages of change (increase or decrease) in compressive strength for
SCCs having 5 %, 6 % ,7% and 8 % SO3 content in concrete, were (4.36%, -10.89%,-25.66% and
-36.14%) relative to corresponding reference SCC. While, for SCC reinforced with 0.75 (%by Vol.)
the percentages of change were (5.10%, -5.92%,-23.02% and -33.39%) and for SCC reinforced with
1.5 (% by Vol.), the percentages of change were (4.66%, -3.39%,-19.49% and -29.26%) relative to
their corresponding reference SCC reinforced with 0.75 and 1.5 (%by Vol.) respectively.
          Adding steel fibers decreased compressive strength at low sulfate contents at (3.9 and 5)%.
while, at high sulfate contents(6,7 and 8)% the compressive strength was increased by adding steel
fibers. at age180 days, the percentages of change in compressive strength for SCCs having
3.9%,5%,6%,7% and 8% percent SO3 content in SCC reinforced with 0.75 and 1.5 steel fiber
contents (% by Vol.), were (-2.97%, -2.28%, 2.44%, 0.48%, 1.21%) and (-6.53%, -6.26%, 1.33%,
1.23%, 3.53%) respectively relative to corresponding plain SCC. The improvement in strength refer
to the control of cracking and the mode of failure by means of post cracking ductility as indicated by
AL-Musawee [14].While, the decrease in strength refer to entraining air with incorporating steel
fibers [15]. Moreover, the steel fiber indirectly would contribute to the increment of strength through
delaying the deterioration due to the sulfate action while, the corresponding plain SCC continue to
deteriorate, therefore, there would be a definite difference between plain and reinforced SCC.


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             40                                                                50

             35                                                                45
                                                                               40
  Fcu(MPa)




                                                                   Fcu(MPa)
             30
                                                                                                                        Vf%=0
                                                     Vf%=0                     35
             25                                                                                                         Vf%=0.75
                                                     Vf%=0.75                  30
             20                                                                                                         Vf%=1.5
                                                     Vf%=1.5                   25
             15                                                                20
                   3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                    3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                   Total SO3 (% by wt. of cement)                                      Total SO3 (% by wt. of cement)


             55                                                                55
             50                                                                50
             45
                                                      Vf%=0
 Fcu (MPa)




                                                                               45


                                                                   Fcu (MPa)
                                                                                                                           Vf%=0
             40
                                                      Vf%=0.75                 40                                          Vf%=0.75
             35
                                                      Vf%=1.5                  35                                          Vf%=1.5
             30
             25                                                                30

                  3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                     3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                    Total SO3 (% by wt. of cement)                                     Total SO3 (% by wt. of cement)


                                      c                                                                d

                                                                         strength
     Fig.(5):Effect of increasing SO3 content in concrete on compressive strengt at (a) 7
                            days (b) 28 days (c) 90 days (d) 180 days

6.2.2 Splitting Tensile Strength
        Table (3) shows the average of the results of splitting tensile strength test at 7, 28, 90 and
                                                                    optim
180 days gained from cylinders. Table (3) and Fig.(6), show the optimum SO3 content at which
the splitting tensile strength is maximum. Further increase in SO3 content caused decreasing in
strength. at age of 180 days, the percentages of change in splitting tensile strength for SCCs
                                                                               12.90%,
having 5 %, 6 % ,7 and 8 % SO3 content in concrete ,were (4.95%, -12.90%, -26.88% and
 33.33%)
-33.33%) relative to reference SCC. While, for SCC reinforced with 0.75 (%by Vol.) the
                                                             36.49%)
percentages of change were (3.05%, -10.00%,-31.3%and -36.49%) and for SCC reinforced with
                       ercentages                (8.97%,                          31.86%)
1.5 (% by Vol.) the percentages of change were (8.97%,-2.21%,-23.72% and -31.86%) relative to
their corresponding SCCs reinforced with 0.75 and 1.5 (%by Vol.) respectively. It can be seen,
that both the plain and the reinforced SCC suffered reduction in splitting tensile stren strength with
increased SO3 beyond the optimum value. However, in general, the reinforced SCC showed
better performance than SCC. This reduction can be ascribed to, with high sulfates contents and
                                                                       consequently
continued exposure to water, more ettringite would be formed, consequently the expansion
increased, inducing high tensile stresses and causing decrease in ultimate strength. The existence
of steel fibers restricts the expansion and hence, delays the failure process. The SCC reinforced
with steel fibers and contained 6 % (by wt. of cement) suffered losses at later ages within a
tolerable limits.
        By contrast to the compressive strength, the results of the splitting tensile strength tests,
indicated in Table (3), clearly showed the benefit of steel fibers. Splitting tensile strength
indicated significant increase in strength due to the inclusion of steel fibers. The percent of

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increase in splitting tensile strength was found to be increase with the increase in steel fibers
                                           percentages
content for all mixes. at age180 days, the percentages of increase in splitting tensile strength for
SCCs having 3.9%, 5%, 6%, 7% and 8% SO3 content in SCC reinforced with 0.75 and 1.5 steel
fiber contents (% by Vol.) were (40.86%, 38.32%, 45.56%, 32.35% and 34.19%) and
                                %
(55.9%,61.89%,75.06%, 62.65% and 59.35%) respectively relative to corresponding plain SCC.


                5.5                                                                     6.5

                                                                                        5.5
                4.5




                                                                           ft (MPa)
                                                                                        4.5
 ft (MPa)




                                                         Vf%=0                                                                  Vf%=0
                3.5
                                                         Vf%=0.75
                                                                                        3.5                                     Vf%=0.75
                2.5                                                                     2.5                                     Vf%=1.5
                                                         Vf%=1.5

                1.5                                                                     1.5
                      3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                           3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                       Total SO3 (% by wt. of cement)                                          Total SO3 (% by wt. of cement)

                                      a                                                                        b

                 8.5                                                                     8.5
                 7.5                                                                     7.5

                 6.5                                                                     6.5
     ft (MPa)




                                                                             ft (MPa)




                                                          Vf%=0                                                                 Vf%=0
                 5.5                                                                     5.5
                                                          Vf%=0.75                                                              Vf%=0.75
                 4.5                                                                     4.5
                                                          Vf%=1.5                                                               Vf%=1.5
                 3.5                                                                     3.5

                 2.5                                                                     2.5
                       3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                           3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                        Total SO3 (% by wt. of cement)                                         Total SO3 (% by wt. of cement)

                                          c                                                                  d

 Fig.(6):Effect of increasing SO3 content in concrete on splitting tensile strength at (a) 7
                         days (b) 28 days (c) 90 days (d) 180 days

6.2.3 Flexural Strength
        The flexural strength results for the plain and the reinforced SCC mixes are listed in
Table (3). The optimum SO3 content at which the flexural strength is maximum has been
                                                                              ent
recognized, Fig.(7). The flexural strength decreased with increasing SO3 content beyond the
optimum value. at age of 180 days, the percentages of change in flexural strength for SCCs
having 5 % 6 % ,7 and 8 % SO3 content in concrete ,were (15.60%,-7.80%,-       -24.65% and -
36.17%) relative to reference SCC. While, for SCC reinforced with 0.75 (%by Vol.) the
                               (4.97%,                        38.12%)
percentages of change were (4.97%,-7.18%,-25.97% and -38.12%) and for SCC reinforced
                                                        (3.91%,         23.11%
with 1.5 (% by Vol.) the percentages of change were (3.91%,-7.24%,-23.11% and -32.47%)
                                                          a
relative to their corresponding SCC reinforced with 0.75 and 1.5 (%by Vol.) respectively.
      The fine voids developed over the aggregate surface represent structural breaks in the
continuity and are, at the same time, an opportunity for the accumulation of ettringite,
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                                 microcracks
ettringite forms in voids and microcracks requires less surface energy than forming in bulk
           .
paste [16]. It has been observed by many researchers [16], [17], [18] in damaged concretes,
that the ettringite crystals are usually present in cracks, voids, and transition zone at the
                er
aggregate-binder interface, if concrete is submitted to expansion due to ettringite, fact which
                                          aggregate matrix
leads to an additional stress on the aggregate-matrix interface and hence to microcracks.
Beside, ettringite formed in microcracks, due to expansion pressure will widen these
microcracks. These processes will result in debonding of aggregates/matrix under low applied
stresses, giving rise to prompt failure. The presence of steel fibers will delay these whole
                                                                 microcracks.
processes by restricting the widening and arresting any new microcracks. Thus, reducing the
negative effect of sulfates on concrete.
        Concrete mixes reinforced with steel fibers showed significant improvement in
flexural strength at all ages relative to their corresponding plain concretes. at age180 days, the
          ges
percentages of increase for SCCs having 3.9%,5%,6%,7% and 8% SO3 content in SCC
reinforced with 0.75 and 1.5 steel fiber contents (% by Vol.) , were (60.46%, 45.71%,
61.54%, 57.65% and 55.56%) and (117.91%, 95.86%, 119.23%, 122.35% and 130.56%)
                   ive
respectively relative to corresponding plain SCC. This is mainly due to the increase in crack
resistance of the composite and to the ability of fibers to resist forces after the concrete matrix
has failed. The SCC reinforced with 1.5 % steel fiber and contain 6% (by wt. of cement)
suffered losses within tolerable limits.

                12                                                             14

                10                                                             12
                                                                    fr (MPa)




                                                                               10
     fr (MPa)




                 8
                                                       Vf%=0                    8                                      Vf%=0

                 6                                     Vf%=0.75                                                        Vf%=0.75
                                                                                6
                                                       Vf%=1.5                                                         Vf%=1.5
                 4                                                              4

                 2                                                              2
                     3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                  3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                       Total SO3(% by wt. of cement)                                   Total SO3(% by wt. of cement)
                           a                                                                     b

                13                                                             13
                11                                                             11
                 9                                                              9
                                                                    fr (MPa)
    fr (MPa)




                 7                                     Vf%=0                                                           Vf%=0
                                                                                7
                                                       Vf%=0.75                                                        Vf%=0.75
                 5                                                              5
                                                       Vf%=1.5                                                         Vf%=1.5
                 3                                                              3
                 1                                                              1
                     3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                  3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                       Total SO3(% by wt. of cement)                                  Total SO3(% by wt. of cement)

                               c                                                                  d


Fig.(7):Effect of increasing SO3 content in concrete on flexural strength at (a) 7 days (b)
                             28 days (c) 90 days (d) 180 days

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6.2.4 Modulus of Elasticity
                                  lasticity
        The static modulus of elasticity for all mixes is experimentally determined at ages 28 and
90 days, the results of this test are listed in Table (3). The results listed in Table (3) and plotted in
Fig.(8), show the optimum SO3 content at which the modulus of elasticity is maxi         maximum. The
presence of sulfates up to the optimum value of compressive strength means that more
densification of material occurs. Therefore, the modulus of elasticity of concrete also increases.
Further increase in SO3 content above the optimum, resulted in decrease in elastic modulus of
specimens due to the decrease in modulus of elasticity of the matrix caused by the degeneration
of the interfacial bond strength between bulk cement paste and aggregate. at age of 90 days, the
percentages of change in elastic modulus for SCCs having 5 % 6 % ,7 and 8 % SO3 content in
                                    28.22%        38.76%)
concrete ,were (6.03%,-16.36%,-28.22% and -38.76%) relative to reference SCC. While, for SCC
                                                                        (13.14%,
reinforced with 0.75 (%by Vol.) the percentages of change were (13.14%,-8.57%,-           -22.10% and -
33.60%) and for SCC reinforced with 1.5 (% by Vol.) the percentages of change were (12.96%,   (12.96%,-
                       32.30%)
5.69%, -19.96% and -32.30%) relative to their corresponding reference SCC reinforced with 0.75
                                                                                  on
and 1.5 (%by Vol.) respectively. Steel fibers demonstrated similar impact on elastic modulus as
on compressive strength. However, the increments ,if any, due to incorporating steel fibers were
insignificant. at age 90 days, the percentages of change in elastic modulus for SCCs having
                                                     reinforced
3.9%,5%,6%,7% and 8% SO3 content in SCC reinforced with 0.75 and 1.5 steel fiber contents
                                  0.78%,                                       (
(% by Vol.) , were (-7.01%, -0.78%, 1.65%, 0.92% and 0.81%) and (-8.18%, -2.17%, 3.54%,  2.17%,
2.39% and 1.51%) respectively relative to corresponding plain SCC.


                  29                                                                32
                  27                                                                30
       Ec (GPa)




                  25                                                                28
                                                                         Ec (GPa)




                  23                                     Vf%=0                      26                                      Vf%=0
                  21                                     Vf%=0.75                   24                                      Vf%=0.75
                  19                                     Vf%=1.5                    22                                      Vf%=1.5

                  17                                                                20
                  15                                                                18

                       3.5 4 4.5 5 5.5 6 6.5 7 7. 8
                                                .5                                       3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                         Total SO3(% by wt. of cement)
                                  (%                                                        Total SO3(% by wt. of cement)




                                               oncrete
  Fig.(8):Effect of increasing SO3 content in concrete on modulus of elasticity at (a) 28
                                     days (b) 90 days

6.2.5 Length Change
        Concrete prisms (75×75×285) mm were tested to determine the length change
                                                                                       quite
(expansion) of concrete at ages of 3,7,14,28, 56, 90 and 180 days. From fig.(9) ,it is quit evident
that expansion increased with age and with increasing sulfates content in concrete for both plain
and reinforced SCC, more ettringite formation can be anticipated since more sulfates will be
                                                   expansion
available for the reaction forming ettringite. The expansion can be a direct consequence of the
crack enlargement. Ettringite deposited in rims surrounding aggregate grains, and ettringite
                  a                                              b
deposited in cracks considered as contributing to the overall expansion, through crack
                                 ettringite
development and propagation by ettringite swelling or crystal growth, much less energy is needed
compared to the energy needed for the formation of new cracks in concrete [18] As well, the
                                                                                [18].
transformation of monosulfate to ettringite is well known to cause 2.3 times increase in volume
                                                       .
and thus represents another source for expansion [19]. It can be noticed that the mixtures of SO3
content of 5% had little propensity to expand among the increased SO3 contents of mixtures, this

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content was defined earlier as the optimum SO3 content. In fact, the values of this content were
really close to the expansion values of the reference mixes with SO3 =3.9%. steel fiber played a
crucial role in this test by reducing expansion. Steel fibers provided internal restraint to concrete
                                   cracks
expansion by bridging the micro-cracks and restraining further propagation of those cracks. As a
result, the expansion related stresses will be reduced and by this way, the steel fibers mitigate the
                                It                                            still
effect of sulfates on concrete.It was noticed at high expansion values there still a development in
strength with progressing age. The last mix despite its high expansion at later ages showed
relatively some gain in strength. The occurrence of relatively slow expansion in concrete at later
ages may not lead to concrete deterioration [20].

                              250                                                                                                          250

                              200




                                                                                                                  Expansion *10-6
   Expansion *10-6




                                                                                                                                           200
                              150
                                                                                             Vf%=0                                         150                                                              Vf%=0
                              100                                                            Vf%=0.75                                                                                                       Vf%=0.75
                                                                                                                                           100
                               50                                                            Vf%=1.5                                                                                                        Vf%=1.5

                                0                                                                                                                     50
                                     0       50      100     150          200                                                                               0        50      100     150            200
                                                  Age (Days)                                                                                                              Age (Days)


                                                           a                                                                                                                          b

                               400                                                                                                                         500
                               350                                                                                                                         450
            Expansion *10-6




                                                                                                                                                           400
                               300
                                                                                                                                    Expansion *10-6




                                                                                                                                                           350
                               250                                                               Vf%=0                                                                                                         Vf%=0
                                                                                                                                                           300
                               200                                                               Vf%=0.75                                                                                                      Vf%=0.75
                                                                                                                                                           250
                               150                                                               Vf%=1.5                                                   200                                                 Vf%=1.5
                               100                                                                                                                         150
                                         0    50      100     150                     200                                                                        0        50        100       150     200
                                                   Age (Days)                                                                                                                  Age (Days)


                                                          c                                                                                                                               d

                                                                                       750
                                                                    Expansion *10-6




                                                                                       650

                                                                                       550                                                                                Vf%=0

                                                                                       450                                                                                Vf%=0.75

                                                                                       350                                                                                Vf%=1.5

                                                                                       250
                                                                                             0                100                                            200
                                                                                                           Age (Days)

                                                                                                                  e
 Fig.(9): Effect of steel fibers content on expansion for SO3(a)3.9 (b)5 (c)6 (d)7 (e) 8 (% by
                                          wt. of cement)
                                                       )


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6.2.6 Ultrasonic pulse velocity
        Ultrasonic pulse velocity UPV test was used to evaluate the effects of sulfates on
concrete. The values of ultrasonic pulse velocity for the various types of concrete at (7, 28, 90
and 180 days) are presented in Table (3). The results indicated that there is an optimum SO3
                                                     that
content at which the velocity is maximum, beyond that value, the velocity decreased with the
increase in sulfates content as shown in Fig(10). at age of 180 days, the percentages of
change in pulse velocity for SCCs having 5 %, 6 %, 7% and 8 % SO3 content in concrete,
                         4.93%
were (2.98%, -1.03%,-4.93% and -10.88%) relative to reference SCC. While, for SCC
                                                                                0.88%,
reinforced with 0.75 (%by Vol.), the percentages of change were (2.35%, -0.88%, -4.91%
            %)
and -11.48%) and for SCC reinforced with 1.5 (% by Vol.), the percentages of change were
                    4.86%
(2.55%, -0.58%, -4.86% and -9.72%) relative to their corresponding reference SCC
reinforced with 0.75 and 1.5 (%by Vol.) respectively. The decrease in UPV is due to the
disrupting effect of sulfates on the microstructure of concrete. Introducing steel fibers
                         ltrasonic
negatively affected the ultrasonic pulse velocity. This might be attributed to the increase of
the amount of entrapped air voids due to incorporation of fibers into the mixes. besides, the
fibers inside cube were randomly oriented, when the wave pass through the fibers the wave
  aybe
maybe deflected to other directions rather than pass straight forward to the end of the cube.


                    4                                                                                 4.4

                                                                                                      4.2
                   3.8
 UPV (Km/sec)




                                                                                 UPV (Km/sec)




                                                                                                       4
                                                                                                                                              Vf%=0
                                                            Vf%=0
                                                            Vf%=0.75                                  3.8                                     Vf%=0.75
                   3.6
                                                            Vf%=1.5                                   3.6                                     Vf%=1.5

                   3.4                                                                                3.4
                         3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                                      3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                           Total SO3 (% by wt. of cement)                                                    Total SO3 (% by wt. of cement)


                                           a                                                                                  b


                   4.6                                                                          4.6

                   4.4                                                                          4.4
                                                                         UPV (Km/sec)
    UPV (Km/sec)




                   4.2                                                                                                                         Vf%=0
                                                            Vf%=0                               4.2
                     4                                                                                                                         Vf%=0.7
                                                            Vf%=0.75
                                                                                                                                               5
                                                                                                 4                                             Vf%=1.5
                   3.8                                      Vf%=1.5

                   3.6                                                                          3.8
                         3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                                3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                           Total SO3 (% by wt. of cement)                                                Total SO3 (% by wt. of cement)


                                          c                                                                                 d

 Fig.(10):Effect of increasing SO3 content in concrete on pulse velocity at (a) 7 days (b)
                             28 days (c) 90 days (d) 180 days



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6.2.7 Rebound Number
        The surface hardness of the 150 mm concrete cubes was assessed by the, "Schmidt
rebound hammer test". The rebound number results of plain and the reinforced SCC with
different percentages of SO3 content in concrete at the ages of 7,28,90 and 180 days
are presented in Table (3). There is an optimum SO3 at which the rebound number is
maximum, referring to densification effect due to ettringite formation at the plastic stage.
                                                      decreased
Beyond the optimum value, the rebound number decreased with increased SO3 content as
shown in Fig (11). at age of 180 days, the percentages of change in rebound number for SCCs
having 5 %, 6 % ,7% and 8 % SO3 content in concrete , were (1.44%, -9.86%,      9.86%,-15.62%,-
19.23%) relative to reference SCC. While, for SCC reinforced with 0.75 (%by Vol.) the
   centages                                               17.15%)
percentages of change were (1.07%, -9.66%, -14.72%, -17.15%) and for SCC reinforced with
                                                   (6.48%,                   11.77%)
1.5 (% by Vol.), the percentages of change were (6.48%,-5.93%, -9.17%,-11.77%) relative to
                                 CC
their corresponding reference SCC reinforced with 0.75 and 1.5 (%by Vol.) respectively. This
decrease is ascribed to the detrimental action of sulfates which causes the weakness of
surface. Incorporating steel fiber in SCC, decreased the rebound number for all specimens
                ined
due to the entrained air increase which gave rise to increasing in porosity of the surface.


         33                                                             34
         31                                                             32
         29                                                             30
   R.N




                                                                  R.N




         27                                      Vf%=0                  28                                      Vf%=0

         25                                      Vf%=0.75               26                                      Vf%=0.75

         23                                      Vf%=1.5                24                                      Vf%=1.5

         21                                                             22
              3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                  3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                 Total SO3(% by wt. of cement)                                  Total SO3(% by wt. of cement)


                                a                                                              b

         34                                                             35
         32                                                             33
         30
                                                                        31
   R.N




                                                                  R.N




                                                 Vf%=0                                                           Vf%=0
         28
                                                 Vf%=0.75               29                                       Vf%=0.75
         26
         24                                      Vf%=1.5                27                                       Vf%=1.5

         22                                                             25
              3.5 4 4.5 5 5.5 6 6.5 7 7.5 8                                  3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
                 Total SO3(% by wt. of cement)                                  Total SO3(% by wt. of cement)


                            c                                                                  d

         Fig.(11):Effect of increasing SO3 content in concrete on rebound number at
                           (a) 7 days (b) 28 days (c) 90 days (d) 180 days




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                          Table (3) Results of hardened concrete tests


          Compressive strength (MPa)       Tensile strength test (MPa)       Flexural strength test (MPa)
Mix


         7      28      90       180      7       28      90       180      7       28      90        180
       days    days    days      days    days    days    days     days     days    days    days       days


S1F1    34     43.25     49      50.5    3.385   3.95     4.35     4.65     4.5     5.1      5.4      5.64


S1F2   34.91    44.4     48       49     4.65    5.015    6.44     6.55     7.2    8.25       9       9.05


S1F3   33.1     42     46.57     47.2     5      5.54     7.19     7.25     11     11.7     12.15     12.29


S2F1   35.4    46.65   51.75     52.7    3.55     4.1     4.6      4.88     4.8     5.6       6       6.52


S2F2   33.5    45.11    50.9     51.5     5      5.54     6.72     6.75    7.46     8.7      9.3       9.5


S2F3   34.16    43.6   48.19     49.4    5.21     5.9     7.7       7.9    11.3    11.96    12.45     12.77


S3F1    29      37.1    42.5      45     2.45      3      3.87     4.05     3.9    4.48      4.9       5.2


S3F2    30      38.5     42      46.1     3.4    3.77     5.78     5.895    6.2     7.3     8.22       8.4


S3F3    31      41      44.7     45.6    3.76     4.1     6.83     7.09     9.6    10.37    11.3      11.4


S4F1    23     29.84    34.5     37.54    2      2.39      3        3.4     3      3.55       4       4.25


S4F2    25      31.7   34.67     37.72   2.85    3.124    4.1       4.5    5.09    5.59      6.4       6.7


S4F3   25.5    32.22   35.05      38     3.29    3.69     4.94     5.53     8       8.9      9.1      9.45


S5F1   20.3     24.5   29.74     32.25   1.75    1.96     2.85      3.1     2.7    2.95      3.4       3.6


S5F2   21.33    25     30.12     32.64   2.54     2.9     3.99     4.16     4.2     4.6      5.3       5.6


S5F3    22      26.1   31.65     33.39   3.06    3.232    4.7      4.94     6.9     7.2     8.17       8.3




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Continuous


Mix
         Modulus of
                                  U.P.V (Km/sec)                    Rebound number test
       elasticity (GPa)




        28        90       7       28       90     180       7         28        90       180
       days      days     days    days     days    days     days      days      days      days


S1F1   28.2       30.37   3.88    4.23      4.35    4.365   30.6      31.6      32.5      33.28


S1F2   27.2       28.24   3.84    4.21      4.33    4.338   29.78     30.84     31.2      31.66


S1F3    27        27.89   3.82     4.2      4.31    4.32    28.33     29.13     29.3      29.58


S2F1   29.6       32.2    3.92    4.33      4.47    4.495   31.7      32.5      33.2      33.76


S2F2   29.38      31.95   3.87    4.29      4.44    4.44    30.7      31.45     31.6       32


S2F3   29.25      31.5    3.835   4.26      4.4     4.43    29.47     30.8       31       31.5


S3F1   24.2       25.4    3.77    4.15      4.28    4.32    26.9      27.9      28.73      30


S3F2   24.44      25.82   3.74    4.115     4.23     4.3    26.1       27        28       28.6


S3F3   25.72      26.3    3.72    4.095     4.22    4.295   25.25      26       26.77     27.83


S4F1   20.25      21.8    3.64    3.99     4.108    4.15    24.57     25.7      26.54     28.08


S4F2   20.64       22      3.6    3.97     4.094    4.125   23.61      25       25.6       27


S4F3   21.2       22.32    3.6    3.94     4.075    4.11     23       24.5      25.9      26.87


S5F1    17        18.6     3.5    3.63      3.77    3.89    23.75     24.25     25.3      26.88


S5F2   17.55      18.75   3.49    3.615     3.74    3.84    22.88     23.6      24.8      26.23


S5F3    18        18.88    3.5     3.6      3.75     3.9    22.45      23       24.5      26.1




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7. CONCLUSIONS

1. Overall, slump flow diameter (flowability) and L-Box blocking ratios (passing ability)
    decrease with the increase in sulfates content in concrete with respect to mixtures
    having the reference SO3, similarly, with the increase in steel fiber content of the
    concrete mixtures with respect to plain mixtures. However, steel fibers affected the
    flow ability and passing ability more than the sulfates did.
2. Slump flow time and V-funnel flow time increase with the increase in the sulfates
    content in concrete with respect to mixtures having the reference SO3 and also with
    increase in steel fiber content of the concrete mixtures with respect to plain mixtures.
3. The effect of sulfates and steel fibers together on the fresh properties of the mixtures
    was greater than the effect of each one separately.
4. The optimum SO3 content, at which a higher mechanical properties and little tendency
    to the expanding were obtained, was at SO3 equal to 5 (% by weight of cement).
    Further increase in sulfates content in concrete after this optimum value showed a
    considerable reduction in mechanical properties; compressive strength, splitting
    tensile strength, flexural strength, static modulus of elasticity, U.P.V and rebound
    number, splitting tensile strength was more sensitive to sulfate attack than the other
    mechanical properties. Nonetheless, there was some recovering with advance in age at
    which the affected mixtures retrieve some of their lost strength.
5. Steel fibers decreased compressive strength at low sulfates and increased it at high
    sulfates contents and in the same manner the modulus of elasticity was. Overall, steel
    fibers had a marginal increments on both compressive strength and modulus of
    elasticity compared to the increments in the other mechanical properties.
6. For different SO3 contents in concrete, all steel fiber mixes demonstrated a higher
    splitting tensile strength and flexural strength relative to plain mixes at all curing ages.
    The tensile strength increased as the fiber content increased, however, the increments
    in flexural strength were higher than splitting tensile strength with more than 100%
    increments having been recorded.
7. Increased sulfates contents increased the expansion for all mixes with varied steel
    fiber contents. On the other hand, expansion of steel fiber mixes was less than plain
    mixes. The lowest expansion values were for the highest steel fiber content.
8. For different SO3 contents, pulse velocity and rebound number decreased with
    including steel fiber.
9. The highest steel fiber content 1.5 (% by Vol.) had, in general, best effect on
    hardened properties but the worst on fresh properties of SCC. As well, 0.75% steel
    fiber content was sufficient for achieving satisfying performance in fresh and
    hardened properties of SCC.
10. SFSCCs showed similar to better resistance to sulfate attack than plain SCCs, the
    resistance to sulfates enhanced with increasing fiber content.
11. Self compacting concrete containing SO3 of 6 (%by wt of cement) and reinforced with
    1.5 steel fiber (% by Vol.) suffered losses in strength within tolerable limits in the
    later ages.




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                                           286
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