PUNCHING STRENGTH AN D IMPACT RESISTANCE … · PUNCHING STRENGTH AN D ... was the first high performance fibre reinforced concrete ... fibre reinforced specimens. The SIFCON slabs

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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 4, April 2017, pp. 1123–1131, Article ID: IJCIET_08_04_126 Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication Scopus Indexed

PUNCHING STRENGTH AND IMPACT RESISTANCE STUDY OF SIFCON WITH

DIFFERENT FIBRES Azoom K T

Student, M-Tech Structural Engineering, School of Civil and Chemical Engineering, VIT University, Vellore, Tamil Nadu, India

Rama Mohan Rao Pannem Associate Professor, Centre for Disaster Mitigation and Management Engineering,

VIT University, Vellore, Tamil Nadu, India

ABSTRACT SIFCON contains relatively high volume of steel fibres as compared to SFRC.

Failure patterns of SIFCON slabs are studied in this paper. SIFCON specimens are cast by varying steel fibres and polypropylene fibres in different ranges of volume separately. Research also arrived at a hybrid combination of fibre for slab and studied the properties. Slab specimens of side 60 cm and height 5 cm are adopted for punching shear studies. Cement, GGBS and Sand are taken in the ratio 1:1:2. Water to binder ratio adopted is 0.45 and super plasticizer dosage is found to be 1%. Steel fibres of Length 25mm, diameter 0.5mm and aspect ratio 50 is used. And Polypropylene fibres of Length 24mm, diameter 0.028mm and aspect ratio 857 is used. Key words: Impact, Punching shear, SIFCON, Slurry.

Cite this Article: Azoom K T and Rama Mohan Rao Pannem, Punching Strength and Impact Resistance Study of SIFCON with Different Fibres. International Journal of Civil Engineering and Technology, 8(4), 2017, pp. 1123–1131. http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4

1. INTRODUCTION The development of SIFCON dates back to 1979 when Lankard started investigations on incorporating large amount of fibres into FRC. SIFCON exhibits good strength and ductility compared to conventional FRC with a high volume fraction of steel fibres. The behaviour of SIFCON in compression, tension and flexure are investigated by several researchers with different types of fibres by varying fibre volume fractions and other parameters. Information available regarding the behaviour of SIFCON at application level is limited since SIFCON is relatively a new material. Flexural strength of cementitious based fibrous materials is greater than their uniaxial tensile strength is a known fact. Flexural strength of these materials depends on the specimen geometry and is not a constant. The present research investigates

Punching Strength and Impact Resistance Study of SIFCON with Different Fibres

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structural behaviour of SIFCON slabs, its load deflection behaviour and failure characteristics.

Fibre reinforced concrete (FRC) is normally prepared by mixing fibres with a concrete mix. In FRC, fraction of fibres is limited. Much studies are not carried out regarding the flexural strength of FRC and hence isyet to be exploited. Since ultimate stress required to fail fibre reinforced concrete(FRC) in flexure and tension is governed by fibre volume fraction, aspect ratio, fibre matrix and bond strength, increase in failure stresses can be achieved by increasing these parameters.

Slurry infiltrated fibrous concrete (SIFCON) was the first high performance fibre reinforced concrete (HPFRC). It was developed by Josifek et al. by making use of slurry infiltration technique with high fibre volume content. This matrix was different from normal FRC. In the normal FRC, fibre content usually varies from 1 to 3 % by volume whereas in SIFCON, fibre contents vary in the range 5 to 20 %. It is attained by making use of special manufacturing techniques. The matrix consists of cements and slurry or flowing cement mortar. SIFCON is prepared by infiltrating high fluidity cement slurry with into preplaced fibres. Fibre volume fraction is tremendously increased to obtain improved mechanical properties.

2. EXPERIMENTAL SETUP

2.1. Materials Cement: Zuari OPC 53 grade was used in the experiments. The specific gravity of cement was found using Le Chatelier flask as 3.01. The initial and final setting was found using vicat apparatus as 40 and 340 minutes. GGBS: GGBS of specific gravity 2.85 from JSW was used. Fine Aggregate: Sand passing through 4.75 mm IS sieve was used in the experiments. The sand was found to confine in Zone II after grading. The specific gravity was found to be 2.62. Fibres: Two different fibres are used in this research. Steel fibres of 25mm length, 0.5 mm diameter and 50 aspect ratio is one of the fibre used and its ultimate tensile strength was 395 MPa. Polypropylene fibres of 24mm length, 28-micron diameter and 857 aspect ratio was the second type of fibre used. Super plasticizer: Conplast SP337 complies to IS:9103: 1999 is used as the water reducing admixture.

2.2. Casting of Specimens Mix Proportion of Slurry: Slurry is prepared with Cement, GGBS and Sand in the proportion 1:1:2 by mass. The water to binder ratio is adopted as 0.45. Optimum dosage of Superplasticizer was found as 1 % by marsh cone apparatus. Placing: The specimens of dimensions 60 x 60 x 5 cm were casted for the research. Plywood sheets of 5 cm height were assembled on a floor carpet for casting the required specimens. The gap between plywood and carpet was sealed using cello tapes to prevent any leakage of slurry. Other specimens were casted with standard dimensions.

SIFCON specimens with Steel Fibres were prepared by pouring slurry into required quantity of steel fibres. Steel fibres were spread into the mould layer by layer and Slurry was poured over the fibres in each layer. Hand tamping was provided to assure penetration of slurry through fibres. This process was repeated till the mould got completely filled.

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SIFCON specimens with Polypropylene Fibres were prepared in a different way. All the components for slurry and polypropylene fibres were mixed thoroughly in a mechanical mixer and the mix prepared was poured directly to the mould.

2.3. Nomenclature

Table 1 Specimens with steel and polypropylene fibres

Designation Volume of fibres S1 6% S2 8% S3 10% S4 12%

Designation Volume of fibres P1 0.7% P2 1.0% P3 1.3% P4 1.6%

Control specimen: M30 concrete was used as control specimen and denoted by CS. Hybrid specimen: 10% steel fibres and 1.3% polypropylene fibres were used for this specimen.

2.4. Curing Specimens after demoulding were water cured for 28 days. Specimens were coated with white paint after curing to get a clear visibility of crack patterns.

2.5. Testing of Specimens The test setup for testing the casted specimens is shown in the figure below.

Figure 1 Experimental setup for punching

Punching Strength and Impact Resistance Study of SIFCON with Different Fibres

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Punching test was carried out using loading frame. A frame was used for supporting the specimen (ISMC75). The frame was kept over I-Girders on loading frame. Specimen was kept over this frame as simply supported. Hydraulic jack was kept in inverted position. The load was distributed to the specimen through proving ring and a 10 x 10 cm plate. A deflection gauge was fixed at bottom of specimen. Hydraulic jack was of 500 kN capacity and proving ring of 200 kN capacity. The load was applied in increments of 0.08kN (1 division of proving ring). The load and corresponding central deflections for initial crack and at failure were observed and recorded.

3. RESULTS AND DISCUSSIONS

3.1. Punching Shear The results after testing the specimen are tabulated below. The values in the table represent the average of punching shear strengths, load and deflection obtained for various specimens. It is observed that there is an increase in punching shear with the increase in fraction of fibres.

Table 2 Punching shear test results

Designation First crack load (kN)

Deflection at first crack (mm)

Failure load (kN)

Deflection at failure load (mm)

CS - - 2.56 - S1 10.8 5 20.4 8.13 S2 1.92 5 22.8 9.13 S3 5.6 4.18 23.2 18 S4 11.28 5.09 24 10.93 P1 2 2.45 4.24 9.85 P2 3.6 3 4.4 9 P3 2 4 5.6 11 P4 3.12 4 5.6 11

Hybrid 6.88 4.28 8 14.28 The slab specimens reinforced with higher volume fraction of fibres behaved better than

those containing lower volume fractions of fibres. The maximum punching shears and deflections were observed for the slab reinforced with 12% of Steel fibre and with 1.3% of polypropylene fibre by volume in respective categories. The increase from first crack load to ultimate load is ranging between 1.92 to 24 kN for Steel fibre and 2 to 5.6 for polypropylene SIFCON slabs indicates the excellent load carrying capacity of SIFCON slab specimens in punching shear.

Figure 2 Punching shear of SIFCON

CS S1 S2 S3 S4 P1 P2 P3 P4 Hybrid

First crack 0 10.8 1.92 5.6 11.28 2 3.6 2 3.12 6.88

Failure load 2.56 20.4 22.8 23.2 24 4.24 4.4 5.6 5.6 8

0

5

10

15

20

25

Punc

hing

shea

r (N

/mm

2 )

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Slab with 12% volume fraction of fibre show higher stiffness than others in case of steel fibre reinforced concrete and with 1.3% volume fraction of fibres in case of polypropylene fibre reinforced specimens. The SIFCON slabs sustained greater deflections till ultimate stage apart the fact that they carried higher loads. Crack pattern is observed to be similar in almost every SIFCON slabs. First crack originated at the centre and propagated radially towards the edges and corners.

Figure 3 Central deflection of SIFCON slab with Steel fibres

Figure 4 Central deflection of SIFCON slab with Polypropylene fibres

Figure 5 (a) Crack patterns of slabs with steel fibres

-505

1015202530

0 5 10 15 20

Punc

hing

valu

e (N

/mm

2 )

Deflection (mm)

S1 S2 S3 S4 Hybrid

0

2

4

6

8

10

0 2 4 6 8 10 12 14 16Punc

hing

valu

e (N

/mm

2 )

Deflection (mm)

P1 P2 P3 P4 Hybrid

Punching Strength and Impact Resistance Study of SIFCON with Different Fibres

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Figure 5 (b) Crack patterns of slabs with polypropylene fibres

Initially formed cracks widened with higher loads along with the formation of new cracks. The new cracks were formed near the point of application of punching load and were accumulated up to a particular distance from the loading point. The influence of this distance was inferred to increase with increase in volume fraction of fibres in slab specimens. A few cracks are observed on the top surface. The SIFCON slab specimens exhibited superior performance in punching shear. This may be mainly due to the incorporation of higher volume fraction of fibres which leads to crack arresting and crack bridging mechanism in the matrix.

3.2. Impact Resistance Impact values for SIFCON specimens were high. PCC specimens scattered with the impact while SIFCON specimen were intact.

Table 2 Impact resistance values

Specimen Impact resistance

(No of blows) Impact energy (N-m)

First crack Failure Static Dynamic S1 3 24 1231.2 2415.6 S2 4 26 1333.8 2616.9 S3 7 34 1744.2 3422.1 S4 7 40 2052 4026 P1 2 7 359.1 704.6 P2 1 15 769.5 1509.8 P3 2 15 769.5 1509.8 P4 3 28 1436.4 2818.2

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32.6

51.958.6

71

56.5

0

20

40

60

80

CS S1 S2 S3 S4

Stre

ngth

(N/m

m2 )

Steel fibres

32.6

46 43.1

34.1 32.6

0

10

20

30

40

50

CS P1 P2 P3 P4

Stre

ngth

(N/m

m2 )

Polypropelene fibres

2.8

6.6 7.28.4

7.2

0

2

4

6

8

10

CS S1 S2 S3 S4

Stre

ngth

(N/m

m2 )

Steel fibres

2.8

6.02 5.9 5.7 5.8

01234567

CS P1 P2 P3 P4

Stre

ngth

(N/m

m2 )

Polypropelene fibres

Figure 6 Impact energy of SIFCON with different fibres

3.3. Mechanical Properties of SIFCON Characteristic strengths like compressive strength, flexural strength and split tensile strength of SIFCON specimens were much higher compared to PCC.

Figure 7 Compressive strength at 28days

Figure 8 Split Tensile Strength at 28days

CS S1 S2 S3 S4 P1 P2 P3 P4

Static 205.2 1231.2 1333.8 1744.2 2052 359.1 769.5 769.5 1436.4

Dynamic 402.6 2415.6 2616.9 3422.1 4026 704.6 1509.8 1509.8 2818.2

0500

10001500200025003000350040004500

Impa

ct e

nerg

y (N

-m)

Static Dynamic

Punching Strength and Impact Resistance Study of SIFCON with Different Fibres

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2.7

19.623.6

26.630.1

05

101520253035

CS S1 S2 S3 S4

Stre

ngth

(N/m

m2 )

Steel fibres

2.7

13.9 13.411.4 9.46447

5

0

5

10

15

CS P1 P2 P3 P4

Stre

ngth

(N/m

m2 )

Polypropelene fibres

Figure 9 Flexural Strength at 28days

4. CONCLUSIONS Punching shear of the SIFCON slabs is much higher than that of PCC and was up to 9 times

with steel fibres, 2 times with polypropylene fibres and 3 times with hybrid fibres.

Punching strength increased with increase in fibre volume varied from 2 to 12 times in case of steel fibres and from 0 to 27 times in case of specimens with steel fibres.

SIFCON slabs with higher volume of fibre possessed higher deflection zone (dispersion angle).

Impact resistance was also found much higher for SIFCON specimens up to 10 times with steel fibres and 7 times with polypropylene fibres compared to PCC.

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12(1984) 44-47.

[2] Victor. C.Li., Large volume High performance applications of fibres in civil engineering Applied Polymer Science, 83(2002) 660-686.

[3] Schneider. B., Development of SIFON through applications High Performance Fibre Reinforced Cement Composites, (E&FN Spoon, London), 1992.

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[5] Naaman. A E. & Baccouche. M R., Shear response of dowel reinforced SIFCON ACI Structural journal, No. 5, 92(1995) 587–596.

[6] Balasubramanian. K., Kumar. B.H.B., Krishnamoorthy. T.S. & Parameswaran. V.S., Behavior of SIFCON under pure torsion Journal of Structural Engineering, No. 1, 24(1997) 37-40.

[7] IS:9103: 1999., Specification for concrete Admixture, BIS, New Delhi

[8] Sudarsana Rao. H., Ramana. N.V., Gnaneswar. K., Behaviour of restrained SIFCON two way slabs Part-1: Flexure, Communicated to Asian Journal of Civil Engioneering (2007).

[9] Swamy. R.N. and Ali. S. A. R., Punching shear behavior of reinforced slab column connections made with steel fibre concrete ACI Journal, (79-41) (1982) 392-406.

[10] Kuang. T.S. and Morley. C.T., Punching shear behavior of re-strained concrete slabs ACI Structural Journal, No. 1, 89(1992) 13-19.

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[11] Lim. F. K. and Rangan. B. V., Studies on concrete slabs with stud shear reinforcement in vicinity of edge and corner columns, ACI Journal, No. 5, 92(1995) 515-525.

[12] Harajli. M.H., Maalouf. D. & Khatib. H., Effect of fibres on the punching shear strength of slab-column connections, Cement & Concrete Composites, 17(1995) 161-170.

[13] Mansur. M.A., Ahmad. I. and Paramasivam. P., Punching shear strength of simply supported ferrocement slabs, materials in Civil Engineering, No. 6, 13(2001) 418-426.

[14] Ebead. U. and Marzouk. H., Strengthening of two way slabs using steel plates ACI Structural Journal, No. 1, 99(2002) 23-30.

[15] Binici.B and Bayrak.O., Punching shear strengthening of reinforced concrete flat plates using carbon fibre reinforced polymers Journal of Structural Engineering ASCE 129, No. 9, (2003) 1173-1182.

[16] Lovrovich. J. S. and Mclean D. I., Punching shear behavior of slabs with varying spandepth ratios ACI Structural Journal, No. 5, 87(1991) 507-511

[17] Arun Aniyan Thomas and Jeena Mathews, Strength and Behaviour of Sifcon with Different Types of Fibers. International Journal of Civil Engineering and Technology, 5(12), 2014, pp. 25–30.