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DURABILITY STUDIES ON HIGH STRENGTH HIGH PERFORMANCE CONCRETE-2

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DURABILITY STUDIES ON HIGH STRENGTH HIGH PERFORMANCE CONCRETE-2 Powered By Docstoc
					   INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND
   International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
                               TECHNOLOGY February (2013), © IAEME
   ISSN 0976 – 6316(Online) Volume 4, Issue 1, January-(IJCIET)

ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 4, Issue 1, January- February (2013), pp. 16-25
                                                                                  IJCIET
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                         DURABILITY STUDIES ON
               HIGH STRENGTH HIGH PERFORMANCE CONCRETE
                                     Vinod P.a, LaluMangalb, Jeenu G.c*
          a
           Professor in Civil Engineering, College of Engineering Trivandrum- 695 016,India.
                     Phone no.: 91 471 2515617, E-mail:dr_pvinod@rediffmail.com
        b
         Professor in Civil Engineering, T.K.M. College of Engineering, Kollam- 691 005, India.
                      Phone no.: 91 474 2712022,E- mail: lalu_mangal@yahoo.com
                   c*
                     Corresponding author, Associate Professor in Civil Engineering,
            College of Engineering Trivandrum- 695 016, India. Phone no.: 91 471 2515617
                                     E-mail: jeenu_shaj@yahoo.com


   ABSTRACT

           This paper focusses on the influence of aggregate gradation, cement content, micro
   silica and superplasticiser on durability of High Performance concrete (HPC). As the first
   step, an optimum aggregate gradation (for 20 mm size aggregates), derived from packing
   density test results, is proposed. HPC Specimens were tested for initial surface absorption,
   water absorption, sorptivity and chloride ion permeability. The results indicate that for given
   micro silica (MS), there exists a unique superplasticiser (SP) dosage that yields the best
   results and this value increases with increase in micro silica. Comparing mixes with same
   powder content,it is seen that the one having the higher cement content exhibitslesser
   absorption and permeability. The study emphasises the complex inter-relationship between
   the quantities of cement, MS and SP to be used to obtain a durable mix.

   Keywords: Durability, High Performance Concrete, Chloride ion permeability

   1.         INTRODUCTION

          The latest developments in the field of high performance concrete (HPC) attempt to
   make an ecological material with enhanced rheological, strength and durability
   characteristics, by utilizing the components to its full potential[1].Aggregate packing and the
   corresponding particle size distribution, andthe improvement in theproperties of cement paste
   and interfacial transition zone by the use of mineral and chemical admixtures have been found to play
   a paramount role in the behaviour of HPC [2-3]. However, most mix design methods for high strength
   and high performance concrete are not able to optimize the choice of mineral and chemical
   admixtures and their proportioning in the mixtures.

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

        The attacks of deleterious agents cause rapid deterioration of concrete structures
leading to prematurefailure[4-5]. The surface layer of concrete is the first line of defence
against the ingress of aggressive agents and hence, the characteristics of this layer of concrete
determine the rate of transport of the various aggressive substances into the concrete. The
moisture along with chlorides and dissolved oxygen will be absorbed into the concrete cover
by capillary forces depending on the degree of saturation of the concrete, which initiates the
chloride-induced corrosion of the reinforcing steel. Hence an assessment of the rate of ingress
of chlorides has become very important for evaluating the long-term performance of concrete
structures [6-7].
        As the strength and behaviour of HPC is a function of the aggregate characteristics
and mineral as well as chemical admixture content, there is a need to reinvestigate the most
effective particle size distribution and proportion of mineral and chemical admixtures that
would result in optimised performance of HPC.The paper first elucidates the influence of the
aggregate gradation characteristics on the packing density of all in aggregates, to arrive at the
most effective gradation. The combined use of cement, micro silica (MS), and
superplasticiser(SP) on durability of HPC is assessed by conducting initial surface absorption,
water absorption, sorptivity and RCPT.The work reported herein also provides guidelines for
obtaining a flowable HPC mix with slump greater than190 mm (for flowing concrete
according to ASTM C1017-07[8]), having compressive strength greater than 75N/mm2and
that provides enhanced durability characteristics.

2.     MATERIALS AND METHODS

2.1 Materials used
       Coarse aggregate: Crushed quartz aggregates of angular shape and rough texture (size
<20 mm) were used. The specific gravity of coarse aggregate was 2.67.
Fine aggregate: River sand passing through 4.75 mm sieve was used. Its specific gravity and
fineness modulus were 2.55 and 2.64 respectively.
Cement: The chemical composition of cement used (53 grade OPC) is given in Table1.
MS: The chemical composition of MS used is given in Table 1.
SP: Polycarboxylate ether based high range water-reducing admixture with solid content 42
% and specific gravity 1.1 was used.

          Table 1 Chemical composition of cementitious materials (in percentage)

            Compounds                                  Cement        Micro silica
            Silica (SiO2)                               18.10          98.12
            Calcium Oxide (CaO)                         60.30          0.053
            Iron Oxide (Fe2O3)                          4.90            0.52
            Aluminium Oxide (Al2O3)                     4.54            0.29
            Titanium Dioxide (TiO2)                     0.27            0.17
            Magnesium Oxide (MgO)                       0.68            0.15
            Potassium Oxide (K2O)                       0.57              -
            Sulphur Trioxide (SO3)                      3.59              -
            Sodium Oxide (Na2O)                         0.20              -


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

2.2. Gradation of aggregates
        To achieve the most effective particle size distribution that would yield the densest
gradation, packing densities of different aggregate combinations were determined by
separating the all in aggregates into different size fractions and by varying the percentage of
individual fractions. The packing density of each aggregate combination was measured by
weighing a one-litre container filled with aggregates consolidated on a vibrating table for two
minutes [9]. The specific gravity of the aggregate fractions was determined according to
ASTM C127-12 [10]. From the weight of aggregate filling the container, bulk density as well
as solid density was determined using the known values of proportion and specific gravity of
each individual fraction. The aggregate combination that exhibited the highest value of
packing density (presented in Table 2) was used for all subsequent experiments in this study.

                   Table 2 Optimal gradation pattern (for 20 mm aggregates)

                       Particle fractions considered (mm)
                                                                                    Packing
                                                                                    density
 20-12.5   12.5-10     10-4.75   4.75-2.36     2.36-1.18    1.18-0.6    0.6-0.15


   10         10         30          10            10          20          10        0.7951


2.3 Mix proportion
        HPC mixes were proportioned by absolute volume method. To optimise the range of
cement content and water- cement ratio for the targeted compressive strength (75 N/mm2),
trial mixes were made by varying the cement content between 400 and 750 kg/m3 and water-
cement ratios between 0.21 and 0.27. Based on the preliminary results, three cement contents
(450 kg/m3, 525 kg/m3 and 600 kg/m3) and two water-cement ratios (0.23 and 0.25) were
selected. For each cement content and water cement ratio, mixes were proportioned by
varying the MS content from 0% to 25% (in steps of 5%) by weight of cement and SP dosage
from 0.0% to 3.5% (in steps of 0.5%). From these mixes, only those that exhibited slump
higher than 190 mm were considered for further investigation. The mixes are designated as M
followed by the cement content, water-cement ratio and the percentages of MS and SP (Table
3).The concrete is mixed in a tilting concrete mixer of 200 l capacity for about 6 minutes. The
prepared HPC mixes were filled in three layers in steel moulds of standard sizes, each layer
being compacted well using a table vibrator. The specimens were demoulded after 24 hours
and water cured until testing.

2.4 Test procedure
       The rate of water absorption by the surface zone of concrete under a head of 200 mm
between 10 minutes to 2 hours was measured and the multidimensional capillary absorption
of water into concrete was determined as per ASTM C642-06[11]. Sorptivity, which
represents the rate of penetration of water into the pores of concrete by capillary suction, was
measured as per ASTM C1585-11 [12]. The ability to resist chloride penetration was assessed
by RCPT as per ASTM C1202-12 [13].The compressive strength at the age of 3, 7 and 28
days was also determined (ASTM C39-12[14]).


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

3.        RESULTS AND DISCUSSION
3.1 Initial surface absorption
         After 10 minutes of immersion, initial surface absorption values greater than 0.50
ml/m2/s is considered high and less than 0.25 ml/m2/s is considered low. After 120 min,
initial surface absorption values greater than 0.15 ml/m2/s is considered high and less than
0.07 ml/m2/s is considered low[15]. For the set of ingredients used in the present study, the
values of initial surface absorption, after 10 minutes, ranged between 0.00 and 0.17 ml/m2/s
and was zero after 120 minutes, for all except one series (MS=5% and SP=3.5%) of the
investigated mixes. Typical results are given in Table 3. For the very low MS content, a
higher SP dosage would have caused unpacking of the system, resulting in more pore spaces
and consequent higher initial surface absorption. It was also noticed that initial surface
absorption did not bear any relationship with the change in MS dosage or powder content.
The negligibly low values of surface absorption shows that the highly dense aggregate
packing, which was further densified by the successive filling of pores with cement and
micro silica, is very effective in preventing the ingress of water into the cover zone.
     Table 3 Durability characteristics and compressive strength of typical investigated mixes
Mix designation        ISAT         ISAT        Water       Coefficient   Sorptivity      Charge     28 day
                       at 10        at 120     absorption       of                        passed   Compressive
                                                                              3       2
                                                                          ( mm /mm
                        min          min         (%)        Absorption
                                                                             /√min)
                                                                                           (C)       strength
                       (ml/m²/s)   (ml/m²/s)                 (m²/s)                                 (N/mm2)
M-450-0.23-5-1.0       0.167        0.000        1.453      1.94E-09       0.0211         148.5       98.0
M-450-0.23-5-1.5       0.167        0.000        1.000      1.67E-09       0.0252         111.6       95.0
M-450-0.23-5-2.0       0.000        0.000        1.029      8.33E-10       0.0323         130.5       97.5
M-450-0.23-5-2.5       0.167        0.000        1.074      8.33E-10       0.0398         100.8       95.0
M-450-0.23-5-3.0       0.167        0.000        1.179      8.33E-10       0.0477         126.0       81.0
M-450-0.23-5-3.5       0.167        0.167        1.302      1.39E-09       0.0497         125.1       80.5
M-450-0.23-10-1.0      0.000        0.000        1.570      1.59E-09       0.0177         123.3       97.0
M-450-0.23-10-1.5      0.000        0.000        1.300      1.11E-09       0.0202          21.6      101.0
M-450-0.23-10-2.0      0.000        0.000        0.950      8.33E-10       0.0257          68.4      100.0
M-450-0.23-10-2.5      0.167        0.000        0.956      8.33E-10       0.0167          47.7       97.0
M-450-0.23-10-3.0      0.167        0.000        0.972      1.39E-09       0.0236         123.2       98.0
M-450-0.23-10-3.5      0.167        0.000        1.099      1.11E-09       0.0240         125.3       88.5
M-450-0.23-15-1.0      0.000        0.000        1.560      1.91E-09       0.0330         234.0      102.0
M-450-0.23-15-1.5      0.000        0.000        1.284      1.67E-09       0.0391         198.0      102.0
M-450-0.23-15-2.0      0.167        0.000        0.920      1.39E-09       0.0278         143.1      103.5
M-450-0.23-15-2.5      0.000        0.000        0.932      1.11E-09       0.0278          92.0      108.0
M-450-0.23-15-3.0      0.167        0.000        0.835      1.39E-09       0.0252         112.0       95.0
M-450-0.23-15-3.5      0.167        0.000        0.859      1.11E-09       0.0292         178.3       83.0
M-450-0.23-20-1.0      0.167        0.000        2.216       2.5E-09       0.0496         191.7      105.0
M-450-0.23-20-1.5      0.000        0.000        1.008      1.94E-09       0.0430         171.1      107.5
M-450-0.23-20-2.0      0.167        0.000        1.263      1.67E-09       0.0341         155.8      110.0
M-450-0.23-20-2.5      0.167        0.000        1.109      1.67E-09       0.0427         121.6      112.0
M-450-0.23-20-3.0      0.167        0.000        1.014      1.67E-09       0.0458         121.6      111.0
M-450-0.23-20-3.5      0.167        0.000        1.974      1.67E-09       0.0552         174.7       93.5




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

3.2 Water absorption
         High water absorption implies higher pore volume. If pore volume is high and the pores are
interconnected, permeability of the concrete is high and this indicates poor durability. It has been
reported that good concretes have absorption values well below 10% by mass [7,15].Bharatkumar et
al. (2001) [16] have reported water absorption values between 2.5% and 6.8% for fly ash concrete.
Khatib and Clay (2004) [17]obtained values between 4.2% and 5.4% for concrete mixes with
metakaolin as mineral admixture. For the mixes used in the present study, water absorption values
was found to lie in the range of 0.8 to 2.2% (Table 3).
       For all the cement contents considered in the study, mixes with MS dosage 10% exhibited the
least water absorption. Typical results are given in Fig.1. The relatively higher values of water
absorption for the mixes with 20% MS can be due to the unpacking of the granular system as pointed
out by Sobolev (2004)[18]. In addition, all the mixes with cement content 600 kg/m3 showed
relatively higher values of water absorption, possibly due to the higher powder content. It was also
noticed that for a given MS content, there is an optimum value of SP that results in the least water
absorption and this optimum value generally increases with increase in MS (Fig.2). Also, when mixes
with the same powder content was compared, the one with higher cement content exhibited lesser
water absorption. For instance, though the mixes M-450-0.23-20-1.0 and M-525-0.23-5-1.0 had the
same powder content, the one with higher cement content showed lesser water absorption (Fig.3).
Coefficient of absorption, which is a measure of permeability to water for a hardened concrete, was
also computed [16]. Very low values of coefficient of absorption of the mixes investigated in the
present study (Table 3) are quite encouraging and comparable with those reported in the literature for
HPC mixes with mineral admixtures[16]. The slightly adverse effect of larger quantities of fine
particles is evident from the comparatively higher values coefficient of absorption for mixes with 20%
MS. The least values of absorption were generally observed for MS content of 10%, with SP dosage
about 2 to 2.5%.Noticeable increase in water absorption with time was observed in the experiments
for about 90 minutes as illustrated in Fig.4. Thereafter, the absorption rate decreased significantly due
to the saturation of the outer zone of the concrete surface. Based on the present study, for developing
flowable HPC mixes with negligible water absorption, cement content in the range of 450 to 525
kg/m3 with MS content of about 10% and SP dosages of about 2% are recommended.




                      Fig.1 Typical variation of water absorption with cement content
                                       (w/c = 0.23; SP=2.0%)


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




                  Fig.2 Typical variation of water absorption with SP dosage
                          (cement content=525 kg/m3; w/c=0.23)




           Fig. 3 Combined influence of cement and micro silica (powder content) on
                                water absorption (w/c = 0.23; SP=2.0%)



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




              Fig. 4 Cumulative water absorption versus elapsed time relationship
                     (cement=525 kg/m3; w/c=0.23; MS= 15%)

3.3 Sorptivity
        Sorptivity is a function of porosity, pore diameter and continuity of pores within the
concrete matrix and can be correlated to permeability.It has been suggested that for low
permeability concrete, the sorptivity values should be less than 0.1 mm3/mm2 /√min [6]. For
all the HPC mixes investigated in the study, sorptivity values less than 0.055 mm3/mm2 /√min
were observed (Table 3), indicating dense concrete with finer pores and lesser interconnected
network of capillary pores. One of the main reasons is the merit of the chosen aggregate
gradation. Also, the presence of micro silica acting as micro fillers would have helped to
reduce the size of capillary pores of cement paste, causing the pore system to become
segmented through partial blocking. Results from the study as shown in Table 3 also indicate
that the mixes with 10% MS content exhibited the least sorptivity.

3.4 Chloride ion permeability
       The charge passed through the specimen was observed to be less than 450 C for all the
investigated mixes (Table 3). Comparable values have been reported in the literature [19].
The lower the total charge passed through the hardened cement matrix, the higher its
resistance to chloride penetration. The negligibly low values of chloride ion penetrability in
the investigated mixes indicate very high durability. As in the case of water absorption,
comparison of mixes with the same powder content revealed that the mix with higher cement
content exhibits lesser sorptivity and chloride ion penetration. The mixes with higher cement
content (600 kg/m3) exhibited higher chloride ion permeability and this might be due to the
higher powder content.


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

3.5 Compressive strength
        The 3-day compressive strength of all the mixes considered in the present study was
higher than 50 N/mm2 while the 28-day compressive strength varied between 76 N/mm2and
125 N/mm2. About 88% of the 28-day compressive strength was attained within seven days.
Most of the calcium hydroxide released during the hydration of Portland cement would
probably have reacted with the highly reactive micro silica (silicon dioxide content >98%)
within seven days and would have contributed to the development of high 7-day compressive
strength. It was also noticed that though very low water absorption values were observed for
high strength mixes, there was no direct correlation between water absorption and
compressive strength. A similar observation has been reported elsewhere [17].

4.     CONCLUSIONS

The following conclusions are drawn based on the results of the present study:
    • A new gradation characteristics (for 20 mm size aggregates), which is derived from
       the packing density test results, is proposed to obtain concrete that yields acceptable
       level of performance, from workability, strength and durability points of view.
     • The measured initial surface absorption, multi-dimensional water absorption,
       sorptivity and chloride ion permeability values for the HPC specimens, (regardless of
       cement content (450, 525 and 600 kg/m3), water cement ratios (0.23 and 0.25), MS
       content (5 to 20%) and SP dosage (1 to 3.5%)) were significantly lower than the
       values reported in the literature as well as the recommended ones.
     • For the set of ingredients used in the present study and for the ranges of values of
       variables considered, MS should be kept to about 10% and SP to about 2% of the
       cement content to yield the best results.
    • There exists a unique SP dosage that yields the best results, for a given MS content
       and this value increases with increase in MS content.
    • Comparing the HPC mixes with the same powder content has revealed that the
       specimen with higher cement content exhibits lesser water absorption, sorptivity and
       chloride ion permeability.
    • There is a noticeable increase in water absorption with time up to about 90 minutes.
       Thereafter, the rate of absorption decreases significantly.
    • The strength and durability properties were found to be poorly correlated, though high
       strength mixes exhibited extremely low absorption and permeability characteristics.
The study emphasises that there is a complex inter-relationship between the quantities of
cement, MS and SP to be used to obtain a densified mix. It may be noted that findings
obtained in the present study, to a certain extent, are material specific. Also, it is
recommended to perform more studies related to electrical conductivity of concrete,
considering the uncertainties associated with the RCPT.

ACKNOWLEDGEMENT

       Authors express their gratitude to the Kerala State Council for Science, Technology
and Environment (KSCSTE), Government of Kerala, India, for funding this study, which is
part of the sponsored research project on “Investigations on Ultra High Performance
Cementitious Composites”.


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

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20. V.S.Tamilarasan, Dr.P.Perumal and Dr.J.Maheswaran, “Experimental Study On Water
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23. M. Vijaya Sekhar Reddy, Dr.I.V. Ramana Reddy and N.Krishna Murthy “Durability Of
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24. A.S Jeyabharathy, Dr.S.Robert Ravi and Dr.G.Prince Arulraj “Finite Element Modeling
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    International Journal of Civil Engineering & Technology (IJCIET), Volume 2, Issue 1,
    2011, pp. 35 - 39, Published by IAEME




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