Strength Evaluation of Steel Fiber Reinforced-Self Compacting Concrete

Strength Evaluation of Steel Fiber Reinforced-Self Compacting Concrete

Abhishek Sachdeva

Assistant Professor

Lyallpur Khalsa College of Engineering Jalandhar, Punjab, India.

Pankaj Singla

Serving as Engineer

Public Works Department (Building & Roads), Punjab, India

Abstract Self-compacting concrete (SCC) offers several economic and technical benefits; the use of steel fibers extends its possibilities. Steel fibers acts as a bridge to retard their cracks propagation, and improve several characteristics and properties of the concrete. Fibers are known to significantly affect the workability of concrete, but to compensate the effect of workability, dosage of super-plasticizer was increased. Therefore, an investigation was performed to compare the properties of normal self-compacting concrete and SCC with steel fiber. SCC [1, 2, 3] was developed in Japan in the late 1980s to be mainly used for highly congested reinforced structures in seismic regions. The main motive was to compare the strength aspects between normal SCC and the fiber reinforced SCC. Fiber content was varied from .35 to 1 percent by weight of cement. The dosage of viscosity modifying agent (VMA) was varied from .1 to .2% by weight of cement. The workability was measured with slump-flow test, L-Box test and V-funnel test. The results indicated that high-volume of fly ash can be used to produce Steel fiber reinforced self-compacting concrete (SFR- SCC), even though there is some increase in the concrete strength because of the use of steel fiber and high-volume of fly ash.

KeywordsWorkability, Volume fraction of Fibers, Split Tensile Strength, Viscosity modifying agents (VMA), Super- Plasticizer.

1. INTRODUCTION

   Cement concrete is the most extensively used construction material in the world. The reason for its extensive use is that it provides good workability and can be molded in any shape. In this modern age, civil engineering constructions have their own structural and durability requirements, every structure are intended to meet this purpose and hence modification in the conventional concrete has become mandatory. The proclivity of present engineers is to target the existing problems associated with concrete and with meager resources, so as to define the new standards and methods.

   Fiber reinforced concrete (FRC) is defined as concrete made with cement containing fine and coarse aggregate and corrugated steel fibers. In FRC, thousands of small fibers are dispersed and distributed randomly in concrete during mixing and thus improves concrete properties. Consequently, it improves tensile and compressive strength, energy absorbing capacity and ductility of concrete. Tests have shown that use of 0.25% – 1% steel fibers by weight of cement can produce concrete with better performance characteristics.

   The present work deals with experimental research of M25 grade Self-Compacting Concrete (SCC) with corrugated steel fibers of 1 mm diameter and 30 mm length at different fiber volume fractions as mentioned above. The dosage of super- plasticizer (Glenium-51) was varied from 1% to 1.6% by weight of cement and that of viscosity modifying agent [4] (VMA) was varied from 0.1% to 0.2% by weight of cement. The effect of steel fibers on the properties of fresh and hardened concrete was investigated and results obtained are presented.

   A. Material Requirements for Concrete

   The constituent materials, used for the production of Self- Compacting Concrete (SCC) shall generally comply with the requirements of EN 206. The materials shall be suitable for the intended use in concrete and not contain harmful ingredients in such quantities that may be detrimental to the quality or the durability of the concrete, or cause corrosion of the reinforcement.

   General suitability is established for cement conforming to EN 197-1. Aggregates shall conform to EN 12620. The moisture content should be closely monitored and must be taken into account in order to produce SCC of constant quality. Suitability is established for mixing water and for recycled water from concrete production conforming to EN 1008. Admixtures used shall comply with EN 934-2: 2000 (including Annex A), where appropriate.

   Finely-divided inorganic material is used in concrete in order to improve certain properties or to achieve special properties. This specification refers to two types of inorganic additions

   (i) nearly inert additions (Type I), (ii) Pozzolonic or latent hydraulic additions (Type II). General suitability as Type I (semi-inert) addition is established for filler aggregate conforming to EN 12620, pigments conforming to EN 12878. General suitability as Type II (Pozzolonic or latent hydraulic) addition is established for fly ash conforming to EN 450, silica fume conforming to EN 13263 ground granulated blast furnace slag conforming to BS 6699.

2. EXPERIMENTAL PROGRAM

   Mix design of M25 of concrete was carried out using NAN- SU method. Ordinary Portland cement of 43 grade conforming to IS 8112 was used. Fine aggregate of fineness modulus 2.57 and specific gravity 2.61 was used along with the coarse aggregate of fineness modulus 6.55 and specific gravity of 2.72 conforming to IS 383. Fly ash was used as a substitute for cement replacement. Steel fibers were varied from 0.35% to 1% by weight of cement. The quantity of super-plasticizer (Glenium-51) was varied from 1% to 1.6% by weight of cement. The properties of steel fibers and fly ash are given in Tables 1 and 2 respectively. The cement content, coarse aggregate, fine aggregate, fly ash content was kept constant for all the mix, the detail of which is given in Table

   1. The details of the mix prepared are given in Table 4. Firstly, the coarse aggregates were added to the mix, and then fine aggregates, cement and fly ash were added and dry mixed for about one minute. Then two-third of water was added to the mix to obtain uniform wet mix. Finally the super plasticizer was added to the remaining one-third water and added to the wet mix. The total mixing time was about five minutes. In case of SFR-SCC, the steel fibers were added to the wet mix by sprinkling uniformly through hands, to avoid balling of steel fibers. Finally the super plasticizer and VMA were added to the remaining one-third water and fed into the mixer. The mixing time for SFR-SCC was increased by one minute to facilitate the uniform mixing of steel fibers. Cubes of sizes 150 x 150 mm for compressive strength and beams of 500 mm x 100 mm x 100 mm for flexural strength were cast. All the specimens were water cured and tested at 3, 7 and 28 days of curing. The workability was measured with the slump cone test, L-box and V-funnel test

      .

      TABLE 4 Detail of Mix

      Mix	Fiber Content (%age of weight of cement)	Super Plasticizer (kg)	Viscosity Modifying Agent (ml)
      SCC	0%	2.5	0
      SFR-SCC .35	.35%	3	250
      SFR-SCC .70	.70%	3.5	600
      SFR-SCC 1.0	1%	4	840

3. TESTS CONDUCTED ON CONCRETE

   In the present work, slump flow, L-box and V-funnel tests have been performed to check the workability of SCC & SFR-SCC. Strength evaluation has been done based on the compressive strength test and flexural strength test for SCC & SFR-SCC. The experimental set up for varios tests and their results are described below:

   1. Workability

      Specifications for the four workability tests performed in the laboratory according to the EFNARC, 2006 are:

      • SLUMP FLOW TEST T500 = 2 -5 sec

        Flow Spread = 650 800 mm

      • V-FUNNEL TEST Time = 6 12 sec

      • L-BOX TEST

        PA = H2/H1 = 0.8 1.0

        The various workability test results for SCC & SFR-SCC are represented in Table 5.

        WORKABILITY TESTS	RESULTS
        	SCC	SFR- SCC .35	SFR- SCC .70	SFR-SCC 1.0
        T50 (sec)	2.6	3.2	3.8	4.1
        Flow spread (mm)	780	720	690	680
        V-funnel Time (sec)	8	10	11.2	12
        L- box PA =H2/H1	1	0.91	.87	0.82

        S.No.	PROPERTIES
        1.	Diameter : 1mm
        2.	Length : 30mm
        3.	Tensile Strengt : 400 MPa
        4.	Appearance : Bright in clean wire
        5.	Modulus of Elasticity : 200 GPa
        6.	Specific Gravity : 7.850

        TABLE 1 Physical Properties of Steel fibers

        TABLE 5 Results for Workability Test

        S.No.	PROPERTIES
        1.	Type : Class F
        2.	Particle Size : 1-100
        3.	Colour : Greyish
        4.	Density : 2200-2400 kg/m3
        5.	Blains Value : 3500-5000 cm2/gm
        6.	Specific Gravity : 2.14-2.42

        TABLE 2 Physical Properties of Fly Ash

        Cement	250 kg
        Fine Aggregates	980 kg
        Coarse Aggregates	730 kg
        Fly Ash	200 kg
        Water	200 liters

        TABLE 3 Constituents of Mix

        T50 (sec)

        4.5

        4

        3.5

        3

        2.5

        2

        1.5

        1

        0.5

        0

        variation of slump flow time for different concrete mixes

        SCC SFR-SCC 0.35 SFR-SCC 0.70 SFR-SCC 1.00

        Type of mix

        Fig. 1 Variation of slump flow time for different concrete mixes

        30.26

        Flow spread (mm)

        variation of Flow Spread for different concrete mixes

        800

        780

        760

        740

        720

        700

        680

        660

        640

        620

        TABLE 6 Compressive Strength Results

        Mix	3 Days	7 Days	28 Days
        SCC	12	15.9	22.5
        SFR-SCC .35	15	16.9	25.6
        SFR-SCC .70	16	18.1	26.6
        SFR-SCC 1.0	18.4	20.4	30.2

        3 DAYS COMPRESSIVE STRENGTH

        35

        30

        25

        20

        COMPRESSIVE STRENGTH (N/mm2)

        15.95

        22.48

        15

        16.98

        25.6

        16

        18.07

        26.66

        18.4

        20.48

        SCC SFR-SCC 0.35 SFR-SCC 0.70 SFR-SCC 1.00

        15

        7 DAYS

        10 COMPRESSIVE

        STRENGTH

        5

        0

        12

        Type of Mix

        Fig. 2 Variation of Flow Spread for different concrete mixes

        28 DAYS COMPRESSIVE STRENGTH

        variation of V funnel time for different concrete mixes

        SCC SFR-SCC 0.35 SFR-SCC 0.70 SFR-SCC 1.00

        14

        Type of mix

        12

        10

        V-Funnel Time 8

        Fig. 5 Compressive strength test results for different concrete mixes

        (sec) 6

        4

        2

        0

        SCC SFR-SCC 0.35 SFR-SCC 0.70 SFR-SCC 1.00

        Type of Mix

        C. Flexural Strength Test

        Flexural strengths tests were performed on beam specimens according to IS 516:1959. Standard beams of size 500 mm x 100mm x 100 mm were subjected to two pints loading till failure of specimen. It was performed after 28 days of curing on a flexural testing machine of capacity 25kN. The

        Fig. 3 Variation of V funnel time for different concrete mixes

        variation of passing ability of different concrete mixes

        1.2

        1

        0.8

        Passing ability 0.6

        (H2/H1) ,mm

        0.4

        0.2

        0

        results are shown in table 7. To obtain load-displacement graphs some beam samples were also tested on a 100 kN capacity servo-controlled computerized flexural testing machine and is calculate by using formula:

        45 P

        Where, Flexural strength, MPa P = Load at failure, N

        TABLE 7 Flexural Strength Results

        <>Mix	28-Days (N/mm2)
        SCC	3.66
        SFR-SCC .35	4.78
        SFR-SCC .70	5.81
        SFR-SCC 1.0	7.24

        SCC SFR-SCC 0.35 SFR-SCC 0.70 SFR-SCC 1.00

        Type of Mix

        7

        7.24

        8

        FLEXURAL STRENGTH (N/mm2)

        Fig.4 Variation of passing ability of different concrete mixes

        6

        5

        5.81

   2. Compressive Strength

   FLEXURAL STRENGTH

   3

   2

   3.66

   4

   4.78

   Cubes compression tests were performed on standard cube of size 150 x 150x 150 mm after 3, 7 and 28 days curing as per IS 516-1959. The compressive strength of specimen is obtained by dividing the load taken by the concrete cube before the appearance of first crack to the area of block. The results are shown in table 6.

   SCC SFR-SCC 0.35 SFR-SCC 0.70 SFR-SCC 1.00

   Type of Mix

   1

   0

   The compressive strength is calculated by the following formula:

   fcu = Pc/A

   Where, fcu = compressive strength of specimen, N/mm2 Pc = Failure Load in compression, KN

   A = Loaded area of cube, mm2

   Fig. 6 Flexural Strength Test results for different concrete mixes

4. CONCLUSIONS

From the results of the workability tests for SCC and SFR- SCC, it can be seen that with the increase in the quantity of fibers the flowing ability and passing ability of the concrete decreases due to interlocking of fibers and hence the time taken by the concrete to reach a particular point increases. Therefore, to enhance the Flowing ability of the concrete, the dosage of the Super Plasticizer is to be increased along with the quantity of the fibers.

It is observed that 3, 7, 28 day compressive strength in case of .35% steel fiber12 is more than that of SCC and same is observed in the case of .70 and 1.00. It has also been observed that with increase in steel fiber the compressive strength also increases i.e. compressive strength of SFR-SCC

.70 mixes at any day is more than that of .35 and compressive strength of SFR-SCC 1.00 mix is more than that of .35 and

.70 mixes. So it is noticed that with increase in fiber content, compressive strength also increases.

The increase in flexural strength for SFR-SCC 1.00, SFR- SCC 0.70 and SFR-SCC .35 is 100%, 61% and 33% over SCC. The maximum increase is for SFR-SCC 1.00.

REFERENCES

1. K. Ozawa, K. Mackawa, M. Kunishima, H. Okamura, Performance of concrete based on the durability design of concrete structures, Proc. of the Second East Asia-Pacific Conference on Structural Engineering and Construction, 1989.

2. EFNARC, (2005), The European guidelines for self compacting concrete, specification, production and use, May 2005.

3. H. okamura, M. ouchi, Self compacting concrete, Journal of advanced concrete technology, vol. 1, pp 5-15, 2003.

4. K.H. Khayat, Z. Guizani, Use of viscosity-modifying admixture to enhance stability of fluid concrete, ACI Material Journal, vol. 4, pp. 332-341, 1997.

5. G. DE Schutter, Guidelines for testing fresh self-compacting concrete, pp. 2-18, 2005.

6. S. Deepa Shri, R. Thenmozhi, An experimental investigation on the flexural behavior of SCC ferrocement slabs incorporating fibers, International Journal of Engineering Science and Technology, Vol. 4 pp. 2146-2158, May 2012.

7. M. Sonebi, S. Grunewald, and J. Walraven, Passing ability of Self consolidating concrete, ACI Material Journal, Vol. 104, pp. 162-170, 2007.

8. B. Miao, J.C. Chern, C. Yang, Influence on Fiber content on properties of Self-Compacting Steel Fiber Reinforced Concrete, Journal of Chinese Institute of Engineers, Vol. 26, No. 4, pp. 523- 530,2003.