20320140503015 by iaemedu

VIEWS: 0 PAGES: 19

									 International Journal of Civil              and             (IJCIET), ISSN 0976
INTERNATIONALEngineeringMarchTechnologyCIVIL IAEME – 6308 (Print),
 ISSN 0976 – 6316(Online) Volume JOURNAL OF 132- 150 © ENGINEERING
                                 5, Issue 3,     (2014), pp.
                      AND TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)                                                             IJCIET
Volume 5, Issue 3, March (2014), pp. 132-150
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2014): 7.9290 (Calculated by GISI)
                                                                                    ©IAEME
www.jifactor.com




     MIX DESIGN FOR HIGH STRENGTH CONCRETE WITH PORTLAND
                     CEMENT AND SILICA FUME

                    Samir A. Al-Mashhadi                          Dalya Hekmat Hameed
                          Asst. Prof.                                  M.Sc. Student
                      Babylon University                             Babylon University




 ABSTRACT

         The common method used to design mix with silica fume depends on similarity between
 projects requirements and make trail batches if there was a different. This study aims to build a
 design method for high strength silica fume concrete which covers a compressive strength (41-90)
 MPa, maximum aggregate size (14 to 25) mm, replacement level (5, 10, 15) % by wt. of cement and
 w/c+p (0.22-0.45) and make a trails mixtures to check its validation and modify it. This method
 based fixing cementitious material on (520) kg/m3, it contains tables for select: maximum aggregate
 size, coarse aggregate content, w/c+p and silica fume replacement, air content, and initial dosage of
 SP to produce (50-75) mm slump. The materials content ranges in this method are: cement (442-494)
 kg/m3, sand (444-784) kg/m3, silica fume (26-78) kg/m3, coarse aggregate (1067-1148) kg/m3, water
 (114.4-234) kg/m3, and SP (0.1-2.4) % by wt. of cement.

 Keywords: Silica Fume, Microsilica, High Strength Concrete, Mix Design of High Strength
 Concrete, Compressive Strength.

 1. INTRODUCTION

         The term high strength concrete (HSC) is used to describe concretes that are made with
 carefully selected high quality ingredients, optimized mixture designs, and which are batched, mixed,
 placed, consolidated and cured to the highest industry standards [1]. The objective of any mixture
 proportioning method is to determine an appropriate and economical combination of concrete
 constituents that can be used for a first trial batch to produce a concrete that is close to that which can
 achieve a good balance between the various desired properties of the concrete at the lowest possible
 cost. A mixture proportioning method only provides a starting mix design that will have to be more
 or less modified to meet the desired concrete characteristics. In spite of the fact that mix

                                                    132
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

proportioning is still something of an art, it is unquestionable that some essential scientific principles
can be used as a base for mix calculations [2]. Mix proportions for (HSC) are influenced by many
factors, including specified performance properties, locally available materials, local experience,
personal preferences, and cost [3]. Pozzolans such as silica fume (SF), fly ash, and metakaolin are
introduced as supplementary cementitious materials. These admixtures play an important role as
microfillers and help improve particle-packing density of cementitious system, rheological properties
in fresh state, mechanical properties and durability.
         The American Concrete Institute [4] defines silica fume (SF) as “very fine non crystalline
silica produced in electric arc furnaces as a by-product of the production of elemental silicon or
alloys containing silicon”. SF was first sampled and characterized in the 1950s in Norway and
formally adopted into design codes for concrete during the 1970s. Thereafter its use around the globe
has been considerable. SF was first used in the UK in the early 1980s when major construction
projects in the scrap, waste and marine industries commenced and concretes able to better resist these
aggressive environments were required [5]. SF color varies from light to dark gray depending mainly
on the carbon content. It is usually a gray colored powder, somewhat similar to Portland cement or
some fly ashes containing at least 85% silicon dioxide. SF particles are spherical in shape and
measure about 0.1 µm in diameter, i.e., they are about 100 to 150 times smaller than the average
particle size of Portland cement. The specific surface area of silica fume is approximately (20000 –
30000) m2/kg “as determined by the nitrogen adsorption method”. Silica fume is an extremely
effective material for achieving very high strengths and significant decreases in permeability.
Because of its chemical and physical composition, silica fume is highly effective for achieving high
strength at both early and later ages [6]. It can be used as an admixture or a partial replacement for
cement.
        There is no chart that can be used to drive the mixture ingredient to meet a specified level of
performance for HSC with silica fume and most researchers interested on the effect of SF addition
on the properties of fresh and hardened concrete and the best percentages for better results. The best
approach to design a mix is to start with mixture proportions that have been used successfully on
other projects with similar requirements [4]. Holland [7] put a procedure to select SF concrete mix
proportion depending on concrete mixtures that are used in other projects, These procedures cannot
consider as a method to design HSC with silica fume because most of starting mixes contain fly ash
and slag.
        This study includes a proposal for silica fume high strength concrete mix design with
specified concrete compressive strength. The proposed method is to cover the mix proportioning of
concrete compressive strength in the range of (41-90) MPa, maximum aggregate size (MAS) of (14,
20 and 25) mm and silica fume replacement (5, 10, and 15) % by wt. of cement.

2. EXPERIMENTAL WORK

2.1 Material used
       HSC is obtained by selecting suitable materials, good quality control and proportioning. The
material must be conforming to ACI committee 363R, 1997 [8] requirements.

2.1.1 Cement
        Ordinary Portland cement (type I) was used for making concrete. The chemical and physical
properties of this cement are shown in tables, which comply with the Iraqi Standard Specification
I.Q.S. No.5, 1984 [9] requirements.




                                                   133
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

             Table (1): The chemical and physical properties of cement and silica fume
                                        Physical properties
                                              Cement                       Silica Fume#
                             2
         Specific surface (m /kg)              310*                          25000**
             Specific gravity                   3.15                           2.2
                                    Chemical Composition (%)
                   CaO                         62.20                           1.3
                   SiO2                        20.39                          95.68
                  Al2O3                         4.55                           0.5
                  Fe2O3                         3.81                            -
                  MgO                           2.36                          0.43
                   SO3                          1.97                          0.31
                  L.O.I                         2.41                          1.55
     # Physical properties of silica fume are according to manufacturer.
     * Blain fineness
      ** Determined by nitrogen absorption method

2.1.2 Silica Fume
       The SF used was German production in a powder form, SiO2 content of 95.68%. Detailed
physical properties and chemical composition are also given in Table 1.

2.1.3 Superplasticizrer
       To produce HSC with silica fume a high range water reducer was used. It was based on
polycarboxylic ether and had the trade mark “Glenium 51”. It is a light brown color with 1.1 relative
density.

2.1.4 Aggregate
        The coarse aggregate used was crushed granite with three maximum size (25, 20, 14 ) mm
with specific gravity = 2.65, absorption = 0.6% and dry rodded unit weight (1530, 1537, 1546) for
maximum size (25, 20, 14) respectively. Fine aggregate used was natural sand with specific gravity
= 2.64, fineness modulus = 2.82, sulfate content = 0.3 and absorption = 1.4%.

2.2 Test Program
     Test program consists of fabricating and testing (10 ×10) cm cube compressive strength test
specimens. Different variables were investigated, these variables are:
   1- Six compressive strength ranges (41-90) MPa.
   2- Maximum aggregate size (14, 20, and 25) mm.
   3- Percentage of SF replacement (5, 10, and 15) % by weight of cement.

2.3 Mix design for high strength concrete
       After studying SF as a construction material, its effect on hardened and fresh properties of
concrete, and its reactions inside concrete through the previous studies and mixtures which they were
done to know the effect of this material on some properties of concrete, steps have been developed

                                                134
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

for the design of concrete mix based on the data and recommendations mentioned in previous
studies. These steps were checked to know the validity of them by fabricating trail mixtures and
make necessary adjustments to the proposed design method.
        The principle of this method was fixing the cementitious material and slump in some way to
control the amount of variables. About forty five trail mixes were done to investigate the required
compressive strength and slump.
        In this study, three replacement ratios for the SF (5, 10, 15) % by weight of cement were
used. Appointed a replacement ratio of 15% for the high, 10% for the medium and 5% for the
relatively low compressive strength. It was decided to keep the SF content at not more than 15% by
weight of cement so that the resulting concrete mixes would not be too expensive to produce.

2.4 Work Procedures
       Trails on mixtures selected from previous studies were done to obtain the required
compressive strength and workability. According to that a mixture with proportion (C:F.A:C.A =
1:1.28:2.2) by weight was chosen as a starting mixture.
       A slump (50-75) mm was chosen as an initial slump in this study which is found suitable for
mixing and vibrating the specimens [12]. The cementitious material is fixed on (520 kg/m3) [12].
This proportion used for:-

2.4.1 Determine initial superplasticizer dosage
         About forty five mixes are done to determine the suitable initial dosages for all blends to keep
the slump constant. Because of high water demand of SF due to high surface area it can’t depend on
mixing water to attain the required slump. So an initial dosage of superplasticizer is added to
facilitate mixing, casting, and vibrating of samples. When no plasticizer is used, it has been
suggested that an additional 1 litre/m3 of water should be used for every 1 kg/m3 of SF addition to
maintain constant level of fluidity [24]. In this case the additional water leads to decrease
compressive strength therefore, a high-range water reducing admixture should always be considered
as a necessary ingredient in high-strength silica fume concrete.

2.4.2 Determine w/c+p to give the required strength
        Thirty trail mixes with different (w/c+p, maximum size of aggregate, and SF replacement)
were making to ensure the relationship between each one of them and the resulted compressive
strength.
        Two sets of mixtures were done to determine the suitable w/c+p for a required strength range.
Tables (2) and (3) show the description of mixes and proportion of HSC used in first set which was
the estimated one.
        After production the mixes above and depending on the obtained results, a new set were done
with adjustment in w/c+p to ensuring the required compressive strength and trying to put it in the
safe side. Tables (4) and (5) show the description of mixes and proportion of HSC used in second set.
        These two sets also helped to give the relationship between maximum sizes of aggregate and
compressive strength which were used to check and modify the estimated one.
        Results obtained from the above-mentioned mixtures used in making the necessary
adjustments to some pre-design estimation steps. To complete amendment on the pre-set design
method, a new set of nine mixes were done to investigate if the table (4-3-3) in ACI committee
211.4R which was used to know the recommended volume of coarse aggregate per unit volume of
high strength concrete with fly ash is applicable in this design method [12].




                                                  135
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

                             Table (2): description of mixes in first set
   Group      Symbol                                     description
                A11      Mix with w/c+p = 0.25, MAS = 14mm, and SF replacement = 15%

     A1         A12      Mix with w/c+p = 0.27, MAS = 14mm, and SF replacement = 15%

                A13      Mix with w/c+p = 0.25, MAS = 20mm, and SF replacement = 15%

                B11      Mix with w/c+p = 0.35, MAS = 20mm, and SF replacement = 10%

     B1         B12      Mix with w/c+p = 0.37, MAS = 20mm and SF replacement = 10%

                B13      Mix with w/c+p = 0.35, MAS = 25mm and SF replacement = 10%

                C11      Mix with w/c+p = 0.45, MAS = 20mm and SF replacement = 5%.

     C1         C12      Mix with w/c+p = 0.47, MAS = 20mm and SF replacement = 5%.

                C13      Mix with w/c+p = 0.45, MAS = 25mm and SF replacement = 5%.



                             Table (3): proportion of first set mixtures

                                                                                 HRWR
                                   Sand
   Mix     Cement       SF                    Gravel      water      HRWR        % wt of
                                   kg/m3                                                    w/c+p
 symbol     kg/m3      kg/m3                  kg/m3       kg/m3      liter/m3   cementit-
                                                                                  ious
   A11       442        78         665.6       1144        130.0       10.30       1.8      0.25

   A12       442        78         665.6       1144        140.4       8.58        1.5      0.27

   A13       442        78         665.6       1144        130.0       10.30       1.8      0.25

   B11       468        52         665.6       1144        182.8       2.29        0.4      0.35

   B12       468        52         665.6       1144        192.4       1.72        0.3      0.37

   B13       468        52         665.6       1144        182.8       2.29        0.4      0.35

   C11       494        26         665.6       1144        234.0       0.57        0.1      0.45

   C12       494        26         665.6       1144        244.4            -       -       0.47

   C13       494        26         665.6       1144        234.0       0.57        0.1      0.45




                                                 136
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

                           Table (4): description of mixes in second set
     Group      Symbol                                description
                           Mix with   w/c+p = 0.22, MAS = 14mm, and SF replacement =
                  A21
                           15%
                           Mix with   w/c+p = 0.25, MAS = 14mm, and SF replacement =
       A2         A22
                           15%
                           Mix with   w/c+p = 0.22, MAS = 20mm, and SF replacement =
                  A23
                           15%
                           Mix with   w/c+p = 0.32, MAS = 20mm, and SF replacement =
                  B21
                           10%
       B2         B22      Mix with w/c+p = 0.35, MAS = 20mm and SF replacement = 10%

                  B23      Mix with w/c+p = 0.32, MAS = 25mm and SF replacement = 10%

                  C21      Mix with w/c+p = 0.42, MAS = 20mm and SF replacement = 5%.

       C2         C22      Mix with w/c+p = 0.45, MAS = 20mm and SF replacement = 5%.

                  C23      Mix with w/c+p = 0.42, MAS = 25mm and SF replacement = 5%.



                           Table (5): proportion of second set mixtures
                                                                             HRWR
      Mix      Cement       SF        Sand    Gravel    water     HRWR       % wt of
                                                                                       w/c+p
    symbol      kg/m3      kg/m3      kg/m3   kg/m3     kg/m3     liter/m3   cementi
                                                                              -tious
      A21        442         78       665.6    1144      114.4     12.58        2.2    0.22
      A22        442         78       665.6    1144      130.0     10.30       1.8     0.25
      A23        442         78       665.6    1144      114.4     12.58       2.2     0.22
      B21        468         52       665.6    1144      166.4      3.43       0.6     0.32
      B22        468         52       665.6    1144      182.0      2.29       0.4     0.35
      B23        468         52       665.6    1144      166.4      3.43       0.6     0.32
      C21        494         26       665.6    1144      218.4      1.14       0.2     0.42
      C22        494         26       665.6    1144      234.0      0.57       0.1     0.45
      C23        494         26       665.6    1144      218.4      1.14       0.2     0.42


      These nine mixes differ from previous mixtures whither they designed by using the adjustment
steps from the previous work with inclusion table (4-3-3) in ACI committee 211.4R for selecting
volume of coarse aggregate and table (6-3-3) in ACI committee 211.1R for choosing air content
reduced by one percent [12]. Tables (6) and (7) show the description of these nine mixes and
proportions of them respectively.


                                               137
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

       Table (6): description of mixes used in checking coarse aggregate content and air content
      Group        Symbol                                  description
                    CA1       Mix with w/c+p = 0.22, MAS = 14mm, and SF replacement =15%
        CA          CA2       Mix with w/c+p = 0.25, MAS = 14mm, and SF replacement =15%
                    CA3       Mix with w/c+p = 0.22, MAS = 20mm, and SF replacement =15%
                    CB1       Mix with w/c+p =0.32, MAS = 20mm, and SF replacement =10%
        CB          CB2       Mix with w/c+p=0.35, MAS = 20mm and SF replacement =10%
                    CB3       Mix with w/c+p=0.32, MAS = 25mm and SF replacement =10%
                    CC1       Mix with w/c+p=0.42, MAS = 20mm and SF replacement =5%.
        CC          CC2       Mix with w/c+p=0.45, MAS = 20mm and SF replacement =5%.
                    CC3       Mix with w/c+p=0.42, MAS = 25mm and SF replacement =5%.



        Table (7): proportion of mixes used in checking coarse aggregate content and air content
                                                                              HRWR
        Mix     Cement       SF      Sand     Gravel     water    HRWR        % wt of
                                                                                           w/c+p
      symbol     kg/m3      kg/m3    kg/m3    kg/m3      kg/m3    liter/m3    cementi-
                                                                                tious
       CA1        442        78       784       1067     114.4     13.73         2.4        0.22
       CA2        442        78       689       1067     130.0     10.87         1.9        0.25
       CA3        442        78       743       1114     114.4     12.58         2.2        0.22
       CB1        468        52      612.5      1114     166.4      2.86         0.5        0.32
       CB2        468        52       570       1114     182.0      2.29         0.4        0.35
       CB3        468        52      591.4      1148     166.4      2.86         0.5        0.32
       CC1        494        26       485       1114     218.4      1.14         0.2        0.42
       CC2        494        26       444       1114     234.0      0.57         0.1        0.45
       CC3        494        26       462       1148     218.4      1.14         0.2        0.42

2.5    Mixing Procedures
        The laboratory mixing procedure used in this study was outlined by Holland [7], 2005 and SF
association. The concrete ingredients are mixed in a pan type mixer with 0.1 m3 capacity. Added SF
with the coarse aggregate and some of the water. Batching SF alone or first can result in head
packing or balling in the mixer. Mix SF, coarse aggregates, and water for 1½ minutes. The procedure
is stated in the following:
     1- Add the Portland cement. Mix for an additional 1 ½ minutes.
     2- Add the fine aggregate and use the remaining water to wash in any chemical admixtures
        added at the end of the batching sequence. Mix for 5 minutes, rest for 3 minutes, and mix for
        5 minutes.
                                                  138
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

    3- Add the fine aggregate and use the remaining water to wash in any chemical admixtures
       added at the end of the batching sequence. Mix for 5 minutes, rest for 3 minutes, and mix for
       5 minutes.

2.6 Casting and Curing of Test Specimens
      The molds used were cleaned, assembled and oiled. The concrete was cast in molds in three
layers; each layer compacted by using vibrating table for adequate time to remove any entrapped air.
The concrete surfaces were leveled by trowel, and the specimens were covered with nylon sheets to
prevent evaporation of water for 24 hours. In the second day the specimens were demolded and
put in water for curing at temperature (21-27) oC to the day of testing after 28 day.

2.7 Testing Fresh and Harden Concrete
    a- Slump test
               This test is used to determine the workability of concrete mixture according to ASTM
       143-05 by using standard slump cone. Slump maintained constant at rang (50-75) mm for
       each mix.
    b- Test the relation between slump and superplasticizer dosage
               Four mixes were used to determine the optimum dosage of superplasticizer in which
       there is no increase in slump when increasing the dosage of superplasticizer. The proportions
       of mixtures used for this purpose are shown in table (8).

                Table (8): proportion of mixes for determine optimum dosage of SP
                                                                                    SP
          Mix       cement       SF        Sand         Gravel        Water
                                                                                  % wt of
          No.        kg/m3      kg/m3      kg/m3        kg/m3*        kg/m3
                                                                                  cement
            1         468          52      665.6         1144           156          2
            2         468          52      665.6         1144           156           4
            3         468          52      665.6         1144           156           6
            4         468          52      665.6         1144           156           8
       *MAS = 14 mm

    c- Compressive strength test
               (10×10) cm cubes were cast and tested to determine the compressive strength of
       hardened concrete at age of testing (28 days). The tests were made by a compression testing
       machine according to the BS 1881: Part 116, 1989. The machine which is used in the tests is
       one of the electronic type of 2000 kN capacity. The average of three specimens was recorded
       for each mix.

3     RESULTS AND DISCUSSIONS

3.1 Initial dosage of superplasticizer
        Table (9) shows the initial dosage of superplasticizer which was necessary for mixes
containing different levels of SF to have a constant slump of (50-75) mm, measured according to
ASTM 143-05.
         It can be observed that the mixes incorporating higher SF content and lower w/c+p tended to
require higher dosages of superplasticizer like mixes CA1 and A21 which had maximum dosage of
SP.
                                                139
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

                       Table (9): initial dosage of SP obtained from this study
                       Dosage of                     Dosage of                      Dosage of
         Mix          SP% wt. of        Mix         SP% wt. of        Mix          SP% wt. of
        Symbol       cementitious      Symbol      cementitious      Symbol       cementitious
                       materials                     materials                      materials
          A11             1.8            A21            2.2            CA1             2.4
          A12             1.5            A22             1.8           CA2             1.9
          A13             1.8            A23             2.2           CA3             2.2
          B11             0.4            B21             0.6           CB1             0.5
          B12             0.3            B22             0.4           CB2             0.4
          B13             0.4            B23             0.6           CB3             0.5
          C11             0.1            C21             0.2           CC1             0.2
          C12              -             C22             0.1           CC2             0.1
          C13             0.1            C23             0.2           CC3             0.2

         Mix C12 didn’t need an initial dosage of superplasticizer because it had a sufficient amount
of water (w/c+p = 0.47) to obtain (50-75) mm slump. Generally the dosage range of SP in this work
was (0.1-2.4) % wt. of cementitious materials. The higher demand of superplasticizer with the
concrete containing SF can be attributed to the very fine particle size of silica fume that causes some
of the superplasticizer being adsorbed on its surface [6],[15],[16].
         It is worth adding that mixes incorporating more SF were more cohesive due to the large
increase in surface area which gives a corresponding increase in internal surface forces and less
segregation and bleeding this is in agreement with the findings of Khatri and Sirivivatnanon [16],
Sobolev and Batrakov [17], Bhikshma et al [18] and Nacer [19].
         The effect of condensed SF on the rheology of fresh mortar is generally viewed as a
‘‘stabilizing effect.’’ In other words, the addition of very fine particles to concrete tends to reduce
segregation and bleeding tendencies. Without SF, the finest particles in mortar are those of Portland
cement. Since the sand particles are bigger than the cement particles, the latter act as stabilizers by
reducing the dimensions of channels through which bleed water rises to the surface of mortar. When
very fine particles of SF are added to the mortar, the size of flow channels further reduced because
these fine particles are able to adjust their positions to occupy the empty spaces between cement
particles [20].

3.2 Relation between slump and superplasticizer dosage
        This relation obtained by making four trail mixtures with fixing all variables except SP
dosage which is increased gradually to the optimum dosage. It gives an indication about the suitable
estimation dosage to achieve the required slump because the effect of SP is different from type to
another. Also it helps to know the dosage after which excess additions of SP lead to segregation and
thus the selected dosage will be on the safe side. Table (10) and figure (1) show the results obtained
from this study.




                                                 140
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

                       Table (10): Results of slump test for mixtures includes
                                                                SP % wt. of
       Mix    cement     SF      Sand     Gravel        Water
                                                                cementitious     Slump mm
       No.     kg/m3    kg/m3    kg/m3    kg/m3*        kg/m3
                                                                  materials
        1       468       52     665.6     1144          156         2               80

        2       468       52     665.6     1144          156         4              130

        3       468       52     665.6     1144          156         6              200

        4       468       52     665.6     1144          156         8           segregation

*maximum aggregate size = 14 mm

        The results show an increased in slump with the increased of SP dosage this status may be
analyzed as follows. When water is added to cement, the grains are not uniformly dispersed
throughout the water but tend to form into small lumps or flocs due to van der Waals’ forces,
electrostatic interactions between the opposite charges and surface chemical interactions between the
hydrating particles. These flocs trap water within them causing the mix to be less mobile and fluid.
In the presence of a superplasticizer, deflocculation or dispersion of cement particles occurs due to
adsorption and electrostatic repulsion. This process does not allow the formation of entrapped water
and discourangessurface interaction of the particles[21],[22].




                          Fig. (1): Relation between SP dosage and slump

3.3 Compressive Strength results of silica fume high strength Concrete
        After putting hypothetic procedures for making silica fume high strength concrete, it was
starting to make trail batches for each putting step to ensure it. The first set of mixtures used to
ensure if a suggestion w/c+p are given strength ranges which selected for a certain MAS and level of
SF replacement. Table (11) shows the results of compressive strength obtained from these mixtures
and the ranges which are supposed to be within. The value of strength for all mixtures is average of
three cubes (10 × 10) cm.


                                                  141
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

                         Table (11): compressive strength results of first set
                                                        Compressive        Range of strength
          Mix symbol                w/cm
                                                       strength (MPa)          (MPa)
               A11                  0.25                     81                 80-85
               A12                  0.27                     73                 75-79
               A13                  0.25                     76                 75-79
               B11                  0.35                     70                 68-74
               B12                  0.37                     61                 61-67
               B13                  0.35                     59                 61-67
               C11                  0.45                     52                 50-60
               C12                  0.47                     42                 41-49
               C13                  0.45                     46                 41-49

        All mixtures in the first set satisfy compressive strength range except (B13 and A12).
Maximum strength is (81) MPa obtained from mixture (A11) due to the high replacement of SF, low
w/c+p and small MAS, while minimum strength (42) MPa obtained from mixture (C12) due to low
level of SF, high w/c+p and large MAS.
         It is obvious that the value of strength for most success mixtures is near to lower value of
strength range. For this reason and to provide more safety when designing with making all mixes
check the required strength range, it suggested re-casting the previous set of mixtures but with lower
w/c+p. Table (12) shows the results of compressive strength obtained from second set mixtures and
the ranges which are supposed to be within.

                        Table (11): compressive strength result of second set
                                                      Compressive          Range of strength
          Mix symbol               w/cm
                                                     strength (MPa)            (MPa)
               A21                  0.22                   88                   80-85
               A22                  0.25                   81                   75-79
               A23                  0.22                   79                   75-79
               B21                  0.32                   73                   68-74
               B22                  0.35                   70                   61-67
               B23                  0.32                   69                   61-67
               C21                  0.42                   56                   50-60
               C22                  0.45                   52                   41-49
               C23                  0.42                   49                   41-49

        Results show that all values of compressive strength were higher than first set and more than
the put strength range. This belong to lower w/c+p which inversely proportional with strength. The
higher strength allow amendment to the values of these ranges and makes it higher. Maximum
strength reached to (88) MPa in mix (A21) and minimum strength was (49) MPa in mix (C23).
Mixes (A22 and A23) have the same range of strength and give strength within it although the two
mixes having different MAS this attributed to the effect of reducing w/c+p ratio for large MAS. This
leads to reduce the effect of MAS on strength between two mixes. The same for mixes (B22 , B23)
and (C22 , C 23).


                                                 142
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

        Table (12) shows the results of strength obtained from mixtures which designed by following
steps developed from results of previous mixes. Tables of air content and volume of coarse aggregate
mentioned above were within the steps [12]. The advantage of such mixes is to know if tables
content of the air and coarse aggregate suitable for use in concrete mix design steps developed.

                            Table (12): results of strength for the designed mixes
                                                         Compressive        Designed Range of
          Mix symbol               w/cm
                                                        strength (MPa)       strength (MPa)
             CA1                   0.22                       87                  80-85
             CA2                   0.25                       82                  75-79
             CA3                   0.22                       78                  75-79
             CB1                   0.32                       74                  68-74
             CB2                   0.35                       68                  61-67
             CB3                   0.32                       66                  61-67
             CC1                   0.42                       57                  50-60
             CC2                   0.45                       53                  41-49
             CC3                   0.42                       52                  41-49

         The results of these mixtures are virtually identical to the results of mixtures in the second
set, which means that the tables of content of air and coarse aggregate can be applied. Also it proved
that it is possible to make a change to the pre-set ranges of strength.
         It is clear that SF enhanced compressive strength; the presence of SF in the Portland cement
mixes causes considerable reduction in the volume of large pores at all ages and is therefore
instrumental in enhancing the compressive strength. Also, the pozzolanic reaction of SF reduces the
CH content, which leads to increase the strength. SF changes the orientation of CH crystals in the
zone, resulting in less micro cracking at the transition zone [23].

3.4 Procedures of mix design resulted from this study
        The results obtained from experimental work can be summarized and arranged into steps
which can be easily followed to get the suitable proportion for mixtures according to required
compressive strength.
        The slump value will be fixed on (50-75) mm, this value attained with initial dosage of
superplasticizer because without superplasticizer concrete is difficult to consolidate due to the effect
of SF. Cementitious materials will fix on (520) kg/m3 within limits of cement content for high
strength concrete.

step1. Calculate the required compressive strength
         Required compressive strength determined from below equation [8]:

 fcr =                                                                   …………. (1)

step2. Select maximum size of aggregate
        Depending on required strength table (13) shows the suitable sizes of aggregate for strength
ranges. It should be noted that the ACI committee 318M, 2005 recommendation to determine
maximum size of aggregate are valid.


                                                  143
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

                              Table (13): select maximum size of aggregate
         Required Concrete Strength fcr (MPa)         Maximum Size of Aggregate (mm)
                       90 - 75                                   14 - 20
                       74 - 60                                   20 - 25
                       59 - 41                                   20 - 25

step3. Select optimum coarse aggregate content
        Optimum coarse aggregate selection is relating to the maximum size of aggregate as shown in
table (14). The amount of coarse aggregate per m3 can be determined according to the elect value by
the following equation:

       Weight of coarse aggregate = (coarse aggregate factor x DRUW) ........ (2)

                                  Table (14): volume of coarse aggregate

               Optimum coarse aggregate contents for nominal maximum sizes of
               aggregates to be used with sand with fineness modulus of 2.5 to 3.2
           Nominal maximum size, mm                  14           20                25
         Fractional volume* of oven dry
                                                  0.69           0.725          0.75
            rodded coarse aggregate

    *Volumes are based on aggregates in oven-dry rodded condition as described in ASTM C29
      for unit weight of aggregates.

step4. Select water to cementitious ratio and silica fume replacement
        Depending on the required compressive strength and maximum size of aggregate, w/c+p can
be chosen form table (15). This table also gives the percentage replacement of silica fume for each
range of compressive strength.

                           Table (15): Select w/c+p and SF replacement
           *fcr        SF (% by weight           Maximum size of aggregate (mm)
          (MPa)         of cementitious
          28 day           materials)           14               20                 25
          90 - 83                              0.22               -                -
                             15
          82 - 75                              0.25             0.22               -
          74 - 67                                -              0.32               -
                             10
          66 - 60                                -              0.35             0.32
          59 - 52                                -              0.42               -
                              5
          51 - 41                                -              0.45             0.42
     *fcr′= fc′+1400

step5. Calculate content of water and cementitious material
        As mentioned previously the amount of cementitious material is fixed on (520) kg/m3. So,
after chosen w/c+p and silica fume replacement in step 4, water content can be determine by
multiply w/c+p by 520. While silica fume content per m3 calculated by multiplying the selected


                                                144
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

percentage replacement by 520. The result of 520 minus silica fume content will be equal the cement
content per m3.
step6. Select volume of entrained air required
       Table (16) shows the volume of air entrained for each maximum size used throughout the
study.

                               Table (16): Air content of silica fume concrete
         Nominal maximum aggregate size
                                                           Entrapped Air content %
                     mm
                      14                                            1.38
                          20                                        0.92
                          25                                         0.5

step7. Calculate sand content
       After determining the weights per m3 of coarse aggregate, the cement, silica fume, water, and
the percentage of air content, the sand content can be calculated to produce m3, using the absolute
volume method.

step8. Estimate initial dosage of superplasticizer
        To produce high strength concrete with silica fume, using of HRWR is unavoidable. So table
(17) gives estimation for dosage of HRWR to achieve an initial slump between 50 to 75 mm.

                                      Table (17): Initial dosage of HRWR

              w/c+p            0.22         0.25         0.32     0.35       0.42     0.45
        SP(% by wt. of
                             2.2       1.9         0.5            0.4        0.2      0.1
            cement)
    # These dosages may be changed due to the type of SP

step9. Making trail mixtures
       Trail mixtures are necessary to ensure that all proportion used in concrete production give
the required properties such as slump and compressive strength. The weights of sand, coarse
aggregate, and water must be adjusted to correct for the moisture condition of the aggregates used.
These mixes are essential to chemical admixture dosage to know the exact dosage for a required
slump.

3.5 Examples for silica fume high strength concrete mix design
        Design a silica fume high strength concrete mix to cast bridge girders. Compressive strength
for this concrete was 73 MPa in 28-day. specific gravity = 2.65, absorption = 0.6% and oven dry
rodedd unit weight of coarse aggregate = (1546, 1537, 1530) kg/m3 for MAS (14, 20, 25) mm
respectively. Natural sand was used conforming to ASTM C33 with fineness modulus = 2.83,
specific gravity depending on oven-dry weight of fine aggregate = 2.64, absorption = 1.4% and oven
dry rodedd unit weight = 1680 kg/m3. Specific gravity for silica fume = 2.2 and for cement = 3.15,
moisture content = (0.4, 0.3) % for sand and coarse aggregate respectively.
(This example will repeated for compressive strength = 73 , 56 , 45 MPa)


                                                   145
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

Example 1 for 73 MPa
Example 2 for 56 MPa
Example 3 for 45 MPa
Solution:-
Slump fixed on (50-75) mm as initial slump for all examples.

   step 1:- Determine required compressive strength:
       ( fcr ) for Ex1 =          = 13333 psi ≈ 92 MPa
       ( fcr ) for Ex2 =         = 10580 psi ≈ 73 MPa
       ( fcr ) for Ex3 =         = 8857 psi ≈ 61 MPa

   step 2:- From table (13) choose maximum size of aggregate (MAS) depending on required
       compressive strength:-
       MAS for Ex1 = 14 or 25 mm
      MAS for Ex2 = 20 or 25 mm
      MAS for Ex3 = 20 or 25 mm

   step 3:- Optimum coarse aggregate content for maximum aggregate size from table (14):
       (14 mm) = 0.69 m3/m3 concrete.
       (20 mm) = 0.725 m3/m3 concrete.
       (25 mm) = 0.75 m3/m3 concrete.
       So weight of coarse aggregate per m3 according to Eq. (2):
       0.69 × 1546 = 1067 kg/m3 for (MAS = 14 mm)
       0.725 × 1537 = 1114 kg/m3 for (MAS = 20 mm)
       0.75 × 1530 = 1148 kg/m3 for (MAS = 25 mm)

   step 4:- Although the required compressive strength of laboratory trail mixtures is (92, 73, 61)
       MPa the value of strength to be used in table (15) to select w/c+p will be:-
       92 × 0.9 = 83 MPa for Ex1
       73 × 0.9 = 66 MPa for Ex2
       61 × 0.9 = 55 MPa for Ex3
       So the value of w/c+p for three cases will be:
       0.22, SF replacement = 15% by wt. of cement and MAS=14mm for Ex1
       0.35 (for economical reason), SF replacement = 10% by wt. of cement and MAS= 20mm for
       Ex2
       0.42, SF replacement = 5% by wt. of cement and MAS= 20mm for Ex3

   step 5:- Cementitious material content = 520 kg/m3 for all mixtures.
       Weight of water = Cementitious material content × w/c+p
                        = 114.4 kg/m3 for Ex1
                        = 182 kg/m3 for Ex2
                        = 218.4 kg/m3 for Ex3
       Weight of silica fume = 0.15 × 520 = 78 kg/m3 for Ex1
                             = 0.1 × 520 = 52 kg/m3 for Ex2
                             = 0.05 × 520 = 26 kg/m3 for Ex3
       Weight of cement = Cementitious material content – SF content
                          = 442 kg/m3 for Ex1

                                                146
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

                          = 468 kg/m3 for Ex2
                          = 494 kg/m3 for Ex3

   step 6:- From table (16) the value of air content = 1.38% for Ex1
                                                     = 0.92% for Ex2
                                                     = 0.92% for Ex3

   step 7:- Calculate weight of sand per m3:Volumes of each material used per m3 without sand are
       determine as below:
       Volume of cement =            = 0.14 m3
      Volume of silica fume =            = 0.035 m3
      Volume of coarse aggregate =              = 0.4 m3
      Volume of water =         = 0.114 m3
      Volume of air content =    = 0.0138 m3
      Sum of volumes = 0.703 m3
      Volume of sand per m3 = 1 – 0.713 = 0.297 m3
        Weight of sand = 1000 × 2.64 × 0.297 = 784 kg/m3 for Ex1
      Using the same way, weight of sand = 570 kg/m3 for Ex2
                                          = 485 kg/m3 for Ex3

   step 8:- Estimation dosage of SP is chosen from table (17):-
       2.2 % by wt. of cementitious materials for Ex1= 12.58 L/m3
       0.4% by wt. of cementitious materials for Ex2= 2.29 L/m3
       0.2% by wt. of cementitious materials for Ex3= 1.14 L/m3

   step 9:- Adjust water content:
       Weight of sand (wet) = wt. of dry sand × (1+ moisture content)
                            = 784 × ( 1 + 0.004 ) = 787 kg/m3
       Weight of coarse aggregate (wet) = wt. of dry coarse agg. × (1+ moisture content)
                                          = 1067 × (1 + 0.003) = 1070 kg/m3
       Adjustment wt. of water = wt. of water – wt. of dry sand(moisture – absorption)for sand –
                                  dry wt. of gravel (moisture – absorption)for gravel
                               = 114.4 – 784 (0.004 – 0.014) – 1067(0.003 – 0.006)
                               = 125 kg/m3 for Ex1
                               = 193 kg/m3 for Ex2
                               = 227 kg/m3 for Ex3

   step 10:- Make trail mixes to adjust superplasticizer content to obtain the required slump and
       required strength.

   Hint:-
          In case of not satisfying required compressive strength reduce w/c+p by 0.02 and retry
          trail mixes
          0.2 % by wt. of cementitious materials from SP can increase slump 1 cm
   Table (18) shows the proportions of the mixtures per m3 for the pervious examples and
   compressive strength resulted from them.

                                                 147
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

                       Table (18): Proportions of mixtures for all examples
                  Material             Ex1             Ex2                 Ex3
                Cement (kg)            442              468                494
              Silica fume(kg)          78               52                  26
               Sand, dry (kg)          784              570                485
              Gravel, dry(kg)         1067             1114               1114
                 Water(kg)            114.4             182               218.4
                 HRWR %
                                       2.2              0.4                0.2
              (wt. of cement)
              Comp. strength
                                       64               46                  39
                7 days(MPa)
              Comp. strength
                                       90               67                  58
               28 days(MPa)


4. CONCLUSIONS

       In this work, it was aimed to propose a mix proportioning method for the design of silica
fume high strength concrete with compressive strength in the range of (41-90) MPa. The only
method developed for this proposes depends on a mixture previously used in other project and makes
necessary adjustment on it.
        From the results of the experimental work obtained in this work, the following conclusions
are withdrawn:-

       1- It is necessary to use superplasticizer when introducing SF to concrete in order to keep
          the water ratio at acceptable levels and obtain reasonable and maintainable workability.
       2- Superplasticizer dosages increased with increasing SF replacement level by weight of
          cement.
       3- Fresh concrete mixtures with SF are cohesive and therefore less prone to segregation and
          show no bleeding due to the high surface area of SF.
       4- The resulted mix design has no table to select water content because SF needs high water
          demand which offset with compressive strength. So HRWR was used to obtain the
          required workability.
       5- Table (4-3-3) in ACI committee 211.4R which was used for select volume of coarse
          aggregate for high strength concrete with fly as was valid to use with high strength silica
          fume concrete.
       6- The resulted mix design method gives wide ranges to select compressive strength and
          w/c+p.
       7- For different (MAS) the resulting compressive strength would be in the same range by
          increasing w/c+p. This effect gives an economical benefit.
       8- Table (6-3-3) in ACI committee 211.1R for choosing air content reduced by one percent
          for silica fume concrete with compressive strength over (35) MPa was valid and right
          with resulted mix design.
       9- High range of compressive strength conjugated with high replacement level of silica
          fume and low content of cement and vice versa.

                                                148
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

        10- Fine/coarse aggregate ratio decrease with decreasing of strength due to the increased of
           w/c+p.
        11- With silica fume it can produce high strength concrete even with high w/c+p (equal to
           0.45).
        12- It is possible to design a mix with silica fume by following procedures proposed in this
           study.
        13- Mixing procedures of silica fume concrete need long time to break down the
           agglomeration and to disperse silica fume.

5. REFERENCES

 [1]    Lwin, P. E., and Triandafilou, P. E., 2005, “High Performance Concrete Structural
        Designer’s Guide,” First Edition, Federal Highway Administration’s, March 2005, 128 pp.
 [2]    Aïtcin, P.C., 1998, “High-Performance Concrete,” E & FN Spon, London and New York.
 [3]    Russell, H. G., 2000, “High-performance concrete mix proportions,” Concrete products
        Magazine, issue. June, 2000.
 [4]    ACI Committee 234.R, 2000, “Guide for the Use of Silica Fume in Concrete,” American
        Concrete Institute.
 [5]    Dunster, A., 2009, “Silica fume in concrete,” BRE, Information Paper IP 5/09, 12 pp.
 [6]    Mazloom, M., Ramezanianpour, A. A., Brooks, J. J., 2004, “Effect of silica fume on
        mechanical properties of high-strength concrete,” Cement & Concrete Composites, Elsevier,
        Vol. 26, pp. 347-357.
 [7]    Holland, T. C., 2005, “Silica Fume User’s Manual,” first edition, Federal Highway
        Administration, Washington, 193 pp.
 [8]    ACI committee 363R, 1997, “State of the Art Report on High-Strength Concrete,” American
        Concrete Institute. Detroit, Vol. 81, No.4.
 [9]    Iraqi Specification, No.5/1984, “Portland Cement,” National Center for Construction
        Laboratories and Researches, Baghdad, 2001.
 [10]   ACI committee 211.4R, 1998, “Guide for Selecting Proportions for High-Strength Concrete
        with Portland Cement and Fly Ash,” American Concrete Institute. Detroit.
 [11]   ACI committee 211.1, 2002, “Standard Practice for Selecting Proportions for Normal,
        Heavyweight, and Mass Concrete,” American Concrete Institute.
 [12]   Hameed, D. H., 2010, “ Mix Design for High Strength Concrete with Portland Cement and
        Silica Fume”, M.Sc. Thesis, University of Babylon.
 [13]   ACI Committee 234.R, 2000, “Guide for the Use of Silica Fume in Concrete,” American
        Concrete Institute.
 [14]   Khatri, R.P., Sirivivatnanon, V., 1995, “Effect of different supplementary cementitious
        materials on mechanical properties of high performance concrete,” Cement and Concrete
        research , Vol. 25, No.1, pp. 209– 220.
 [15]   Chakraborty, A. K., Ray, I., Sengupta, B., 2001, “High Performance Concrete for
        Containment Structures,” 16th international Conference on Structural Mechanics in Reactor
        Technology, Washington DC.
 [16]   Khatri, R.P., Sirivivatnanon, V., 1995, “Effect of different supplementary cementitious
        materials on mechanical properties of high performance concrete,” Cement and Concrete
        research , Vol. 25, No.1, pp. 209– 220.
 [17]   Sobolev, K. G., and Batrakov, V. G., 2007, “Effect of a Polyethylhydrosiloxane Admixture
        on the Durability of Concrete with Supplementary Cementitious Materials,” Journal of
        Materials in Civil Engineering, ASCE, Vol. 19, pp. 809-819.


                                                149
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME

 [18] Bhikshma, V., Nitturkar, K. and Venkatesham, Y., 2009, “Investigations On Mechanical
      Properties of High Strength Silica Fume Concrete,” Asian Journal of Civil Engineering
      (building and housing), Vol. 10, No. 3, pp. 335-346.
 [19] Nacer, S., 2005, “Optimization of Silica Fume Content And Water to Enhance Performance
      Of Concrete,” M.Sc. Thesis, Southern Illinois University Carbondale.
 [20] Appa Rao, G., 2003, “Investigations on the performance of silica fume-incorporated cement
      pastes and mortars,” Cement and Concrete Research, Vol. 33, pp. 1765-1770.
 [21] Dransfeild, J., 2003, “Admixtures for concrete, mortar and grout,” advanced concrete
      technology set, part II, Elsevier, chapter 4, pp. 3-36.
 [22] Ramachandran, V. S., 1995, “Chemical admixtures-recent developments,” Concrete
      admixture handbook: properties, science, and technology,” second edition, Noyes
      publications, U.S.A, chapter four, pp. 137-176.
 [23] Larbi, J.A., Bijen J.M., 1990, “Orientation of calcium hydroxide at the Portland cement
      paste-aggregate interface in mortars in the presence of silica fume a contribution,” Cement
      and Concrete Research, Vol. 20, pp. 461–470.
 [24] Sellevold, E. J., 1984, “Review: Microsilica in Concrete,” Project Report No. 08037-EJS TJJ,
      Norwegian Building Research Institute, Oslo.
 [25] P.J.Patel, Mukesh A. Patel and Dr. H.S. Patel, “Effect of Coarse Aggregate Characteristics
      on Strength Properties of High Performance Concrete using Mineral and Chemical
      Admixtures”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4,
      Issue 2, 2013, pp. 89 - 95, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
 [26] Asst. Prof. Mr. Samir A. Al-Mashhadi, Asst. Prof. Dr. Ghalib M. Habeeb and Abbas
      Kadhim Mushchil, “Control of Shrinkage Cracking in End Restrained Reinforced Concrete
      Walls”, International Journal of Civil Engineering & Technology (IJCIET), Volume 5,
      Issue 1, 2014, pp. 89 - 110, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
 [27] Dr. D. V. Prasada Rao and G. V. Sai Sireesha, “A Study on the Effect of Addition of Silica
      Fume on Strength Properties of Partially Used Recycled Coarse Aggregate Concrete”,
      International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 6, 2013,
      pp. 193 - 201, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.




                                              150

								
To top