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					International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
   INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME
                               TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)                                                       IJCIET
Volume 4, Issue 6, November – December, pp. 116-125
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2013): 5.3277 (Calculated by GISI)                   ©IAEME
www.jifactor.com




    HARMFUL EFFECTS OF RAPIDITE ON STRENGTH OF CONCRETE

                Sameer ul bashir,     Shabbir Ahmad Parray,       Syed Rizwan Shah
                                   B.Tech, NIT Hazratbal, Srinagar



ABSTRACT

        This present paper presents the progress on research of use of rapidite in cold weather
concreting. The project aims at making and studying various properties of cold weather concrete
using admixture called rapidite which is locally available in oils and chemical industries of Kashmir.
The actual compressive strength of concrete depends on the percentage of Rapidite used in the
concrete. In recent years, concrete usage around the world is second only to water .Ordinary Portland
cement is conventionally used as a primary binder to produce concrete. But, the progress of strength
of concrete is a function of temperature. At relatively low temperatures, it gives low strength because
of the freezing action. Thus, In winters, especially in Kashmir where the temperatures are below zero
degree in winters some admixtures need to be added to nullify the effects of cold temperature on the
strength of concrete. Considering the availability and cost of the admixture, Rapidite is mostly used
admixture in Kashmir in winters. This project aims at finding the optimum amount of percentage of
Rapidite at which the strength of concrete comes to be maximum.

Keywords: Cold Weather, Concreting Rapidite, Compressive Strength.

CONCRETE

       Concrete is a composite construction material, composed of cement (commonly Portland
cement) and other cementitious materials such as fly ash and slag cement, aggregate (generally a
coarse aggregate made of gravel or crushed rocks such as limestone, or granite, plus a fine aggregate
such as sand), water and chemical admixtures.
       Concrete is used to make pavements, pipe, architectural structures, foundations,
motorways/roads, bridges/overpasses, parking structures, brick/block walls and footings for gates,
fences and poles. Concrete is used more than any other man-made material in the world. As of 2006,
about 7.5 cubic kilometers of concrete are made each year—more than one cubic meter for every
person on Earth.

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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

       Reinforced concrete, prestressed concrete and precast concrete are the most widely used
types of concrete functional extensions in modern days.
       Concrete solidifies and hardens after mixing with water and placement due to a chemical
process known as hydration. The water reacts with the cement, which bonds the other components
together, eventually creating a robust stone-like material.

PORTLAND CEMENT + H2O + ROCK = HARDENED CONCRETE + ENERGY (HEAT)
COLD WEATHER CONCRETING

        In India certain regions experience sub-zero temperatures in winter. Concrete structures in
such regions undergo cycles of freezing and thawing and there durability is affected due to frost
action. Fresh concrete contains considerable quantity of fresh water which gets converted into ice
lenses at freezing temperature. The ice formation in fresh concrete results in about 9% rise in volume
and causes permanent damage to concrete and structural integrity cannot be recovered even if the
concrete is made to harden later at high temperature. Even during hardening the concrete should be
protected from extremely low temperature hence while concreting in cold weather ensure that the
temperature of fresh concrete is maintained above 0 °C and temperature during first six hrs of casting
should not be less than 5 °C.
        IS 7861 part II defines Cold Weather Concreting as Any operation of concreting done at
about 5°C atmospheric temperature or below.

ACI 306 “Cold Weather Concreting” defines cold weather concreting as a period when for more than
three (3) consecutive days, the following conditions exist:
    • The average daily air temperature is less than 5°C (40°F) and,
    • The air temperature is not greater than 10°C (50°F) for more than one-half of any 24 hour
        period.

What Happens When Concrete Freezes?
  • Pore water in concrete starts to freeze around -1°C (30°F)
  • As some water freezes the ion concentration in the unfrozen water goes up, further depressing
      the freezing point.
  • At around -3 to -4°C (25 to 27°F), enough of the pore water will freeze so that hydration will
      completely stop, and depending on the extent of hydration, and thus the strength of the
      concrete, the forces generated by the expansion of ice (ice occupies ~9% more volume than
      water) may be detrimental to the long term integrity of the concrete.

Objectives of Cold Weather Concreting

The objectives of cold weather concreting are to:
   • Prevent damage to concrete due to freezing at early ages
   • Assure that concrete develops the required strength for the safe removal of forms
   • Maintain curing conditions that foster normal strength development without using excessive
       heat
   • Limit rapid temperature changes in the concrete to prevent thermal cracking

       For every 10°C (18°F) reduction in concrete temperature, the times of setting of the concrete
double, thus increasing the amount of time that the concrete is vulnerable to damage due to freezing


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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

Deleterious Effects
Following deleterious effect may occur due to cold weather concreting
    • Hydration will be hampered
    • Setting time will be prolong
    • Disruption of freshly placed concrete because of freezing
    • Low workability
    • Freezing and thawing effect
    • Improper curing
    • Workmanship is affected
    • Deicing effect

Recommended Practices and Basic Principles

Curing and Protection: Where a specified concrete strength must be attained in a few days or weeks,
protection at temperatures above 10°C (50°F) is required.
Temperature Records: Temperature of the concrete determines the effectiveness of protection,
regardless of air temperature. Maintaining temperature records of concrete in place is essential.
Heated Enclosures: Must be strong enough to be windproof and weatherproof. Combustion heaters
must be vented to the outside to prevent carbonation.
Exposure to Freezing and Thawing: Concrete should be properly air entrained if it will be saturated
and exposed to freezing and thawing cycles during construction.
Slump: All else being equal, lower slump and/or lower water/cement ratio mixes are particularly
desirable in cold weather for flatwork. This reduces bleeding and decreases setting time.
Truck Travel Time: The distance from the plant to the point of placement can have a severe effect on
the temperature of concrete.
Hot Water: While hot water improves setting time of cold weather concrete, after the first few
batches of concrete hot water heaters may not be able to maintain hot water temperature. Later in the
pour, concrete may be cooler than at the beginning of the pour.
Admixtures : Some admixtures, which act as accelerators ,can be used in cold weather concreting so
to increase the rate of hydration and thus decreasing the effect of cold weather on concreting.

RAPIDITE




        Rapidte is a commonly used admixture in Kashmir during winter to accelerate the strength
gain of concrete. It falls under Type C on the basis of ASTM classification i.e., it acts as accelerator.
It also acts as anti freeze, depressing the freezing point of water and hence protecting the fresh
concrete.


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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

Description
       RAPIDITE 2 IN 1 is a specially developed Concrete Set Accelerator, a ready-to-use, liquid
admixture. It accelerates initial setting time (cement-water chemical reaction HYDRATION) of
normal mortar and concrete and acts as anti-freeze within cement concrete. It improves workability
and strength while fastening the hydration of cement. It makes the mix easier to place and speeds
construction by shortening the initial set and curing time. Time and labor are saved, because forms
and other protection can be removed earlier, and finishing can be started.
Uses
       RAPIDITE 2 in 1 is recommended for use during cool and cold weather to accelerate the set
time and reduce the risk of frozen mortar and concrete mixes.

Features/Benefits
   • Accelerates initial set time.
   • Increases compressive strength.
   • Provides Anti –freeze properties.
   • Speeds up hydration of cement.
   • Increases workability of concrete or mortar mix in colder temperatures.

Properties
Color : Lemon-Orange
Appearance : Clear bright Liquid
Relative Density (g/ml) :1gm/ml

EXPERIMENTAL PROGRAM

        In total five castings were done at the Rapidte percentage of 0.5, 1, 1.25, 1.4 and 1.5% by
percentage of cement and the minimum and maximum temperature during the first 24 Hrs after
casting was observed.
        The Temperature during first 24 Hrs after casting along with the results of various tests are
shown in tables below:

         Variation of Increase in 7 day strength and Compaction Factor with Rapidite %
  Temperature during 1st 24Hrs of                  Average increase in 7
                                                                            Compaction factor
           casting (°C)               Rapidite        day strength %
                                          %         150mm       100mm
   Min         Max         Avg.                                             plain    Admixture
                                                     cube        cube
     -1           7           3          0.50          3.6          8          0.77        0.88
     -1           6          2.5         1.00          8.3        16.8         0.74        0.81
     -2           6           2          1.25         106.3       96.2         0.68        0.77
     -4           7          1.5          1.4         -30.2       -26.6
    -2.5         6.5          2          1.50          -22         -20         0.74        0.88




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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

            Variation of Increase in 28 day strength and compaction factorwith Rapidite %

  Temperature during
  1st 24Hrs of casting                Average Increase in 28 day strength %     Compaction factor
         (°C)
                          Rapidite
                            %                              ↑ in        ↑ in
                                     150mm     100mm      Split     Flexural
  Min      Max     Avg.                                                         plain     Admixture
                                      cube      cube     tensile     tensile
                                                        strength    strength
   -1       7       3       0.50        2.6     5.3       2.9         3.2       0.77          0.88
   -1       6      2.5      1.00        5.2     10.4      6.4         6.7       0.74          0.81
   -2       6       2       1.25        38      30.6      53.5       53.1       0.72          0.77
   -4       7      1.5      1.4        -42.6    -26       -12        -21.1      0.73          0.8
  -2.5      6.5     2       1.50       -18      -23      -17.4       -17.5      0.73          0.88


  Variation of Compaction Factor for plain concrete and concret with admixture for different % of
                                             rapidite

           S. No                   Rapidte %                Plain                Admixture
             1                       0.50                   0.77                    0.88
             2                       1.00                   0.74                    0.81
             3                       1.25                   0.72                    0.77
             4                        1.4                   0.73                        0.8
             5                       1.50                   0.73                    0.88


DISCUSSIONS

       In order to study the variation in the rate of gain of strength with respect to the Rapidite
percentage, a comparative study of the test results achieved at different Rapidite percentage is
performed.

Following Variations were studied:

   •     Variation of increase in 7 day strength with Rapidite %
   •     Variation of Increase in 28 day strength with Rapidite %
   •     Variation of split and flexural tensile strength with Rapidite %
   •     Comparison of Avg. Increase in 7 and 28 day strength for 150mm cube
   •     Comparison of Avg. Increase in 7 and 28 day strength for 100mm cube
   •     Variation of compaction factor on adding Rapidite.




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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

The results graphs and tables represent the comparative study:



                                                                                    G1-Variation of 7 day strength with
                                                                                               Rapidite %
                                                                              120
                                               Percent increase in strength   100
                                                                               80
                                                                               60
                                                                               40
                                                                                                                                 150mm
                                                                               20
                                                                                                                                 100mm
                                                                                0
                                                                              -20 0          0.5       1           1.5       2

                                                                              -40
                                                                              -60
                                                                                                   Rapidite %


        From the study of G1 it is clear that the by adding Rapidite the 7 day strength increases when
compared to the plain concrete casted at the same temperature. Also it can be seen that the at the
1.25% there is maximum increase in strength, beyond this value there is a decrease in the strength of
concrete with admixture ,when compared with plain one. Also the 100mm cube shows more increase
in strength when compared with 150mm cube, except at the optimum amount, the increase in
strength of 150mm cube is more than 100mm cube.

                                                                               G2-Variation of 28 day strength with Rapidite
                                               50                                                   %
                                               40
                      percent increase in strength




                                               30
                                               20
                                               10
                                                0
                                              -10 0                                    0.5         1         1.5         2
                                              -20                                                                                150mm
                                              -30                                                                                100mm
                                              -40
                                              -50
                                                                                              Rapidite %




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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

       The G2 also shows same trend i.e, the 28 day strength also goes on increasing upto the
percentage of 1.25, beyond which it decreases.Also the 100mm cube shows more increase as
compared to 150mm cube except at the optimum amount.

                                                                                G3-Variation of split and flexural tensile strength
                                                                                                 with rapidite %
                                                                       60
                    percent increase in split and flexural strengths


                                                                       50

                                                                       40

                                                                       30

                                                                       20                                                             Split tensile
                                                                                                                                      strength
                                                                       10
                                                                                                                                      Flexural tensile
                                                                        0                                                             strength

                                                                       -10 0                   0.5       1        1.5       2

                                                                       -20

                                                                       -30
                                                                                                     Rapidte %



        G3 shows that there is an increase in both split and flexural tensile strengths up to the 1.25%
of rapidite, beyond this value the strength decreases in both the cases. Also the two graphs almost
coincide showing that both strengths increase by equal amounts, flexural strength increasing slightly
more than split strength.

                                                                                       G4-Comparison of Avg. increase in 7 and
                                                                                          28 day strength for 150mm cube
                                                                                       120
                                                                                       100
                                                                                        80
                                                                                        60                                      Avg.↑ in 7 day
                                                                        Syrength MPa




                                                                                        40                                      strength %

                                                                                        20
                                                                                                                                Avg. Average ↑
                                                                                        0                                       in 28 day
                                                                                                                                strength %
                                                                                       -20 0             1              2

                                                                                       -40
                                                                                       -60
                                                                                                     Rapidite %




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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

        G4 shows that although both 7 and 28 day strength for 150mm cube increases and reaches
there maximum at the Rapidite percentage of 1.25% , the increase in 7day strength is 180% more
than increase in 28 day strength.



                                  G5-Comparison of Avg. increase in 7 and 28
                                       day strength for 100mm cube
                               120
                               100
                                 80
                                 60                                                  Avg. ↑ in 7 day
                                 40                                                  strength %
                        %↑




                                 20
                                                                                     Avg. Average ↑
                                  0                                                  in 28 day
                                                                                     strength %
                                 -20 0                 1                2

                                 -40
                                 -60
                                                Rapidite %



       G4 shows the same trend, that although both 7 and 28 day strength for 100mm cube
increases and reach there maximum at the rapidite percentage of 1.25% ,the increase in 7day strength
is 214% more than increase in 28 day strength.which is higher than in case of 150mm cube.



                             G6-Variation of C.F for plain concrete and concret
                                with admixture for different % of rapidite

                                                       Plain        Admixture
                               0.88                                                               0.88
                        0.77                    0.81                                0.8
                                         0.74              0.72 0.77        0.73           0.73




                             1              2                   3               4             5



       G6 shows that the compaction factor always increases when compared with the plain
concrete,thus workability increases by the addition of rapidite.




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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

CONCLUSION

After analyzing the test results following important conclusions are drawn:

   •   All the three strength parameters viz, compressive strength, split tensile strength and flexural
       tensile strength of concrete increase when compared with plain one. The increase in strength
       reaches the maximum value at the Rapidite percentage of 1.25%, beyond which it starts
       decreasing. It must be noted that the avg temperature during the 1st 24 hrs after casting is
       almost constant.

   •   The increase in 7 day strength is much higher than increase in 28 day strength, in case of
       150mm cubes former is 180% more increase and in case of 100mm cubes former shows
       214% more increase. Thus increase in early strength is more significant than increase in
       lateral strength.

   •   The increase in early strength shows that the freezing of fresh concrete was not there, as such
       the admixture also acts as a antifreeze, depressing the freezing point of water and protecting
       the concrete from the affects of freezing in early age.

   •   Adding Rapidte has shown increase in the workability of mix with respect to the plain mix.

   Recommendations

   •   The quantity of Rapidite to be added needs to be carefully controlled as there is a decrease in
       the strength of concrete if the value passes 1.25% by weight of cement. The manual which
       comes with the Rapidite recommends the percentage of Rapidite to be used in the range of 2-
       6%, which in excess of the optimum value of 1.25%. Thus the amount of the Rapidite should
       be limited to the 1.25%.

   •   When concreting is to be done in the period from November to February, Rapidte should be
       used to accelerate the early gain of strength and protecting the fresh concrete from the effects
       of freezing, as Rapidite acts as Antifreeze cum accelerator.

   •   When there is intention of using Rapidite during warm weather for the purpose of early
       removal of formwork, proper performance tests testing should be done to check the behaviour
       of rapidite at the high temperature, as the behavior of a admixture depends on the
       temperature.

   •   Further proper testing should be done to check the compatibility of the Rapidite with the type
       of cement to be used in actual construction.

   •   Admixture should be uniformly distributed throughout the mix, and this best achieved by
       dissolving the admixture in mixing water.

   •   Trial tests should be carried out using the actual constituents of the mix to be used. Also,
       adequate supervision should be provided at the batching stage so as to ensure correct levels of
       dosage of the admixture.


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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME


REFERENCES

   1)   M.S.Shetty, Concrete Technology, Chapters 1- 8,page nos. 1 – 330,
   2)   IS 9103 : 1999, Admixtures : definition, Page nos (23,24).
   3)   IS 456 : 2000, strength of concrete : tests, compressive strength .pages (2-7)
   4)   Abbas S. Al-Ameeri, K.A.Al- Hussain and M.S Essa, “Constructing a Mathematical Models
        to Predict Compressive Strength of Concrete from Non-Destructive Testing”, International
        Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 4, 2013, pp. 1 - 20,
        ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
   5)   Alaa Abdul Kareem Ahmad, “The Effect of Gypsum Compensative on Mortar Compressive
        Strength”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4,
        Issue 3, 2013, pp. 168 - 175, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
   6)   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.
   7)   Dr. Shanthappa B. C, Dr. Prahallada. M. C. and Dr. Prakash. K. B., “Effect of Addition of
        Combination of Admixtures on the Properties of Self Compacting Concrete Subjected to
        Alternate Wetting and Drying”, International Journal of Civil Engineering & Technology
        (IJCIET), Volume 2, Issue 1, 2011, pp. 17 - 24, ISSN Print: 0976 – 6308, ISSN Online:
        0976 – 6316.
   8)   M.Vijaya Sekhar Reddy, Dr.I.V. Ramana Reddy and N.Krishna Murthy, “Experimental
        Evaluation of the Durability Properties of High Performance Concrete using Admixtures”,
        International Journal of Advanced Research in Engineering & Technology (IJARET),
        Volume 4, Issue 1, 2013, pp. 96 - 104, ISSN Print: 0976-6480, ISSN Online: 0976-6499.
   9)   Vinod P, Lalumangal and Jeenu G, “Durability Studies on High Strength High Performance
        Concrete”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4,
        Issue 1, 2013, pp. 16 - 25, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.




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