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Int. J. Struct. & Civil Engg. Res. 2014 G S Sudhikumar et al., 2014

EFFECT OF ASPECT RATIO OF FIBERS ON THE

STRENGTH CHARACTERISTICS OF SLURRY

INFILTRATED FIBROUS FERROCEMENT

G S Sudhikumar1*, K B Prakash2 and M V Seshagiri Rao3

The concrete composites play an important role in the field of concrete. The addition of fibers toconcrete enhances the strength properties and ductility characteristics. Ferrocement is a lightweight and versatile material having high cracking, ductility and fatigue resistance and isadditionally impermeable to make it far superior than reinforced concrete. It is used forprefabricated residential units, marine and industrial structures. Slurry Infiltrated Fiber Concrete(SIFCON) could be considered as a special type of fiber concrete with high fiber content. Thematrix consists of cement slurry or flowing cement mortar. This composite material withstandsblast loading and can be used for pre-stressed concrete beams and safe vaults. Slurry InfiltratedFibrous Ferrocement (SIFF) is a combination of SIFCON and ferrocement and can overcomethe limitations the latter. SIFF can be used for the structures like runways in aerodromes, industrialfloors, etc. This paper deals with an experimental investigation on the strength characteristicsof SIFF using 1% by volume of steel, GI and polypropylene fiber. The aspect ratios of steel andGI fibers used were 25, 38 and 50 and that of polypropylene fiber was 800 and 1600. The resultsindicated that with lower aspect ratios of steel, GI and polypropylene fiber yield higher compressivestrength, a higher energy absorptive material which can result in higher flexural strength,toughness indices and impact strength.

1 Department of Civil Engineering, Channabasaveshwara Institute of Technology, Gubbi 572216, Karnataka, India.

2 Government Engineering College, Devagiri 581110, Haveri District, Karnataka, India.

3 Department of Civil Engineering, JNTU College of Engineering, Hyderabad 500 085, Andhra Pradesh, India.

*Corresponding author:G S Sudhikumar � sudhikumargs@rediffmail.com

ISSN 2319 – 6009 www.ijscer.com

Vol. 3, No. 2, May 2014

© 2014 IJSCER. All Rights Reserved

Int. J. Struct. & Civil Engg. Res. 2014

Research Paper

Keywords:Ferrocement, Fibers, Fiber Reinforced Concrete, Slurry Infiltrated FibrousFerrocement (SIFF), Welded Mesh, Chicken mesh, Compressive strength, Flexuralstrength, Impact strength

INTRODUCTION

Today, concrete fiber composite is the mostpromising and cost-effective material used inthe construction. Many researchers haveshown that the addition of small closely spaced

and uniformly dispersed fiber to concrete

transforms the brittle cement composite into a

more isotropic and ductile material called

Fiber Reinforced Concrete (FRC).

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Int. J. Struct. & Civil Engg. Res. 2014 G S Sudhikumar et al., 2014

In RCC, the strength makeup is in thedirection of reinforcing bars. In a structurewhere the tensile stresses are omni-directional, the reinforcing becomes difficultand expensive. FRC which is made up of thinfibers dispersed randomly in all the directions,imparts strength to its entire volume.

FRC can be used in the preparation ofvarious precast building units such as claddingsheets, window frames, roofing units, floortiles, manhole covers and advancedapplications in highway pavements, air field,machine foundations, industrial floorings,bridge deck overlays, sewer pipes,earthquake-resistant structures and explosive-resistant structures (like MX missile silos, etc.).

Even though the performance of FRC inpavement, air fields, industrial floors andmachine foundations is satisfactory, it hassome limitations. It cannot be employed wherehigh impact, vibration, wear and tear areexpected. Many problems have to be facedduring the construction of FRC, especiallywhen the quantity of fiber used is for beingeffective. For effectiveness, the fibers shouldbe uniformly dispersed in concrete. The fibersif put in bulk along with other ingredients donot disperse, but nest together and is calledballing effect. The balling effect can be reducedto some extent by mixing the fibers and otheringredients in dry form and then adding water.The fibers present in the concrete may blockthe discharge port. Since the flow of FRC islow, the FRC has to be placed near to theplace where it is to be used finally. Its spreadingwith rakes and spades is difficult and laborious.With compaction fibers realign, such that theytend to concentrate more near the surface.Therefore the compaction has to be controlled.

Similar to FRC, the ferrocement has alsomany advantages and its applications arerapidly increasing in the precast constructionindustry. Ferrocement with uses of differenttypes of steel meshes for its construction.Ferrocement also suffer from limitations. Itcannot be employed where high impacts,vibrations, wear and tear are expected. Thestrength of the ferrocement increases with theincrease in steel content. But when thereinforcement is more, the mortar cannot beeasily forced inside without forming voids.Thus, strength of ferrocement reduces.

The fibrous ferrocement, which is acombination of fiber reinforced concrete andferrocement, can overcome all the above saidlimitations to some extent and can beemployed with assurance where high impacts,vibrations, wear and tear are expected. Thefibrous cement is becoming a promisingmaterial for bridge overlays and industrialfloorings where high impacts, high vibrationsand high wear and tear are expected. Thereinforcements used in fibrous ferrocementare of three kinds: The first type ofreinforcement is welded mesh where smallerdiameter bars (approx. 12 G) are kept closelyin both directions and are spot-welded. Thismesh gives stability and shape to the structure.The second type of reinforcement is chickenmesh. This is mesh of similar wires (approx.20 G) which are interwoven to differentopenings. The spacing between the wires ofchicken mesh is small. This is a mesh mainlydistributes the stresses evenly and the crackswill be minimized. The third type ofreinforcement is fiber. The fibers may be ofsteel, carbon, glass, polypropylene, GI, etc.These fibers act as crack arresters and arerandomly distributed in the concrete.

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Int. J. Struct. & Civil Engg. Res. 2014 G S Sudhikumar et al., 2014

Depending upon the shape required, thecage is prepared out of welded mesh andchicken mesh. The cage can be prepared bytying the chicken mesh over the welded meshat regular intervals by using binding wires. Thecalculated quantities of fibers are placed in themould. The mortar is then infiltrated into themould to form SIFF.

MATERIALS AND METHODS

The main objective of this experimentation isto study the strength characteristics of slurryinfiltrated fibrous ferrocement with differentaspect ratios of fibers. The fibers consideredfor the study are Steel Fiber (SF), GalvanizedIron Fiber (GIF) and Polypropylene Fiber(PPF). Fiber content used for steel, GI andpolypropylene fibers was 1%. The aspectratios of steel and GI fibers used was 25, 38and 50 and that of polypropylene fiber was 800and 1600. Different strength parametersconsidered for study are compressivestrength, flexural strength and impact strength.

Ordinary Portland cement of 43 grade andlocally available sand (passing 1.18 mm andretained on 150 micron IS sieve) with specificgravity 2.64 was used in the experimentation.To impart additional workability, a superplasticizer (Conplast SP 430), 1% by weightof cement was used. The welded mesh (WM)used in the experimentation was a squareopening of 25 mm x 25 mm. The Chicken Mesh(CM) used was having a hexagonal openingwith 0.5 mm diameter. The cement mortar witha proportion of 1:1 was used with a watercement ratio of 0.45.

To study the effect of aspect ratios ofdifferent fibers on the strength properties of

SIFF, the compressive strength specimens,flexural strength specimens and impactstrength specimens were casted. Forcompressive strength test, specimens ofdimensions 150 x 150 x 150 mm were cast.For flexural strength test, specimens ofdimensions 100 x 100 x 500 mm were cast.Flexural strength specimens were testedunder two-point loading over an effective spanof 400 mm. The impact strength testspecimens were of 152.4 mm in diameter and63.5 mm thick. An ASTM D1557 drop hammerwas used (drop hammer weighs 4.5 kg andfalls at 457 mm per blow, each blow represents20.2 N-m of energy). The number of blowsrequired to cause the first crack and final failurewere noted.

The required size of welded mesh andchicken mesh were first cut according to themould sizes for compression, flexural andimpact tests. The chicken mesh was tied tothe welded mesh using binding wires at regularintervals. This forms the cage (1 WM + 1 CM).

Fibrous mortar was prepared by mixing therequired percentage of fibers into the cementmortar prepared by replacing cement bypozzolona. This cement mortar was placed inthe mould in which cages are kept. The mortaris then compacted and finished smooth.

The specimens were demoulded after 24 hof casting and specimens were transferred tocuring tank for 28 days. After 28 days of curing,they were taken out of water and were testedfor their respective strengths.

TEST RESULTS

Compressive Strength

Compressive strength test results of slurry

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Int. J. Struct. & Civil Engg. Res. 2014 G S Sudhikumar et al., 2014

infiltrated fibrous ferrocement using steel fiber;GI fiber and polypropylene fiber for differentaspect ratios are tabulated in Table 1. Thevariation in the compressive strength isrepresented graphically in Figures 1 and 2.

Flexural Strength

Flexural strength and toughness indices testresults of slurry infiltrated fibrous ferro cement

using steel fiber; GI fiber and polypropylenefiber for different aspect ratios are tabulatedin Table 2. The variation in the flexural strengthand toughness indices are representedgraphically in Figures 3 to 6.

Impact Strength

Impact strength test results of slurry infiltratedfibrous ferrocement using steel fiber; GI fiber

Table 1: Compressive Strength Test Results of SIFF with Steel Fiber, GI Fiberand Polypropylene Fiber for Different Aspect Ratio

Fiber Description Aspect Ratio Compressive Strength (MPa) Average Compressive

Strength (MPa)

Steel fiber 25 40.89 41.78 41.30 41.33

38 32.00 32.88 33.30 32.73

50 28.44 27.11 29.30 28.29

GI fiber 25 40.00 39.56 39.60 39.70

38 29.33 28.40 30.20 29.31

50 26.20 26.66 26.70 26.46

Polypropylene fiber 800 36.89 37.33 37.80 37.33

1600 24.00 24.40 24.00 24.13

Figure 1: Variation of CompressiveStrength of SIFF

Figure 2: Variation of CompressiveStrength of SIFF

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Int. J. Struct. & Civil Engg. Res. 2014 G S Sudhikumar et al., 2014

Table 2: Flexural Strength Test Results of SIFF with Steel Fiber, GI Fiber andPolypropylene Fiber for Different Aspect Ratio

Fiber Aspect Flexural Average Toughness Indices

Description Ratio Strength Flexural

(MPa) Strength (MPa) I5 Average I5 I10 Average I10

Steel fiber 25 10.00 10.05 7.31 7.35 17.04 17.11

10.32 7.42 17.18

9.84 7.32 17.11

38 8.24 8.11 6.28 6.25 12.96 12.87

8.00 6.31 12.84

8.08 6.16 12.80

50 7.76 7.76 5.38 5.34 10.91 10.55

7.60 5.40 10.23

7.92 5.24 10.50

GI fiber 25 8.88 8.96 6.94 7.00 16.77 16.78

9.20 6.96 16.84

8.80 7.10 16.72

38 7.76 7.65 5.92 5.85 10.56 10.54

7.60 5.76 10.42

7.60 5.87 10.64

50 7.60 7.44 5.22 5.19 9.04 9.14

7.44 5.16 9.18

7.28 5.18 9.20

Polypropylene fiber 800 8.64 8.77 6.34 6.56 16.63 16.64

8.88 6.41 16.58

8.80 6.94 16.70

1600 8.00 8.11 3.91 3.92 7.94 7.88

8.16 4.04 7.81

8.16 3.82 7.88

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Int. J. Struct. & Civil Engg. Res. 2014 G S Sudhikumar et al., 2014

and polypropylene fiber for different aspectratios are tabulated in Table 3. The variationin the impact strength is representedgraphically in Figures 7 and 8.

RESULTS AND DISCUSSION

The following observations were made withreference to the effect of aspect ratio of fiberson the strength characteristics of slurryinfiltrated fibrous ferrocement.

It was observed from the test results that thecompressive strength of slurry infiltrated fibrousferrocement with steel fiber goes on reducingas the aspect ratio of steel fiber increases. A

higher value of compressive strength of 41.33MPa (Table 1) was observed for an aspect ratioof 25 whereas a compressive strength of28.29 MPa (Table 1) was observed with anaspect ratio of 50.

This clearly indicates that slurry infiltratedfibrous ferrocement produced with steel fibersof lower aspect ratio yields better compressivestrength. A similar trend was observed in thecase of slurry infiltrated fibrous ferrocementwith GI fibers. Even the slurry infiltrated fibrousferrocement with polypropylene fiber having anaspect ratio of 800 has indicated acompressive strength of 37.33 MPa (Table 1),

Figure 3: Variation of Flexural Strengthof SIFF

Figure 4: Variation of Flexural Strengthof SIFF

Figure 5: Variation of FlexuralStrength of SIFF

Figure 6: Variation of FlexuralStrength of SIFF

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Int. J. Struct. & Civil Engg. Res. 2014 G S Sudhikumar et al., 2014

Table 3: Impact Strength Test Results of SIFF With Steel Fiber,GI Fiber and Polypropylene Fiber For Different Aspect Ratio

Fiber Aspect First Final First Final First FinalDescription Ratio Crack Failure Crack Failure Crack Failure

Steel fiber 25 1244 1327 25128.80 26805.40 23728.27 26226.33

1188 1312 23997.60 26502.40

1092 1256 22058.40 25371.20

38 1003 1224 20260.60 24724.80 20873.33 24913.33

1041 1253 21028.20 25310.60

1056 1223 21331.20 24704.60

50 871 1032 17594.20 20846.40 17701.93 20334.67

824 986 16644.80 19917.20

934 1002 18866.80 20240.40

GI fiber 25 894 1112 18058.80 22462.40 17600.93 23634.00

823 1194 16624.60 24118.80

897 1204 18119.40 24320.80

38 865 1041 17473.00 21028.20 17506.67 21607.27

823 1032 16624.60 20846.40

912 1136 18422.40 22947.20

50 749 917 15129.80 18523.40 15129.80 18927.40

784 932 15836.80 18826.40

714 962 14422.80 19432.40

Polypropylene fiber 800 568 814 11473.60 16442.80 12375.87 16429.33

619 792 12503.80 15998.40

651 834 13150.20 16846.80

1600 365 512 7373.00 10342.40 8275.27 11561.13

402 594 8120.40 11998.80

462 611 9332.40 12342.20

No. of BlowsRequired to Cause

Impact StrengthRequired to Cause

Average Impact StrengthRequired to Cause (N-m)

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Int. J. Struct. & Civil Engg. Res. 2014 G S Sudhikumar et al., 2014

whereas that of aspect ratio of 1600 hasindicated a compressive strength of 24.13MPa (Table 1).

This may be due to the fact that a fiber oflower aspect ratio can be compacted well withslurry infiltration without producing more voids.Thus it can be concluded that, slurry infiltratedfibrous ferrocement produced with loweraspect ratio of steel fiber or GI fiber orpolypropylene fiber yields a highercompressive strength.

A similar trend was observed in flexuralstrength and toughness indices for slurryinfiltrated fibrous ferrocement produced withsteel fibers or GI fibers or polypropylene fibers.A higher flexural strength of 10.05 MPa (Table2) was observed for slurry infiltrated fibrousferrocement with steel fibers of lower aspectratio of 25. For this case the values of I

5 and

I10 observed were 7.35 and 17.11 (Table 2)respectively. The values of toughness indicesgo on decreasing as the aspect ratioincreases. The slurry infiltrated fibrousferrocement with GI fiber and polypropylenefibers also show a similar trend.

A remarkable improvement is observed in

the impact strength values with the addition of

fibers into slurry infiltrated fibrous ferrocement.

The impact strength also shows a decreasing

trend with increase in aspect ratio of fibers.

This is true for slurry infiltrated fibrous

ferrocement produced with steel fibers or GI

fibers or polypropylene fibers.

This may be due to the fact that, fibers with

lower aspect ratio can fit into the voids thus

producing a dense slurry infiltrated fibrous

ferrocement which can exhibit higher

absorption of impact energy and flexural

energy thus giving rise to higher values of

impact strength, flexural strength and

toughness indices.

Thus, it can be concluded that slurry

infiltrated fibrous ferrocement produced with

lower aspect ratio of steel fibers or GI fibers

or polypropylene fibers yield a higher energy

absorptive material which can result in higher

flexural strength, toughness indices and impact

strength.

Figure 7: Variation of ImpactStrength of SIFF

Figure 8: Variation of ImpactStrength of SIFF

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Int. J. Struct. & Civil Engg. Res. 2014 G S Sudhikumar et al., 2014

CONCLUSION

Following conclusions can be drawn based onthe study conducted on the effect of aspect ratioof fibers on the strength characteristics of slurryinfiltrated fibrous ferrocement.

1. Slurry infiltrated fibrous ferrocementproduced with lower aspect ratio of steelfibers or GI fibers or polypropylene fibersyield a higher compressive strength.

2. Slurry infiltrated fibrous ferrocementproduced with lower aspect ratio of steelfibers or GI fibers or polypropylene fibersyield a higher energy absorptive materialwhich can result in higher flexural strength,toughness indices and impact strength.

3. The performance of slurry infiltrated fibrousferrocement with steel fibers is morepronounced than slurry infiltrated fibrousferrocement with GI fibers or slurry infiltratedfibrous ferrocement with polypropylenefibers.

4. Small addition of fibers into slurry infiltratedferrocement (0% fibers) can enhance thestrength characteristics.

REFERENCES

1. Abdullah and Katsuki Takiguchi (2002),“Strength and behaviour of concreteconfined by ferrocement boxes” Journal ofFerrocement, Vol. 32, No. 4, pp. 304-314.

2. Balaguru P et al. (1992), “Flexuraltoughness of steel fiber reinforcedconcrete” ACI Materials Journal, pp. 541-546.

3. Lillia Robles - Austriaco (2005), “Evolutionof ferrocement” Journal of Ferrocement,Vol. 35, No. 3, pp. 603-610.

4. Neven Krstulovic - Opara, andMohammad Jamal A L - Shannag (1999),“Compressive behaviour of slurryinfiltrated mat concrete”, ACI MaterialsJournal, V. 96, No. 3, pp. 367-377.

5. Rajesh Kumar G (2001), “Behaviour ofhigh strength concrete confined withferrocement shell in addition to lateralties”, Journal of Ferrocement: Vol. 31,No. 3, pp. 213-222.

6. Structural Engineering Research Center(R and D) (2000), Chennai “Experimentalinvestigation on slurry infiltrated fibrousconcrete (SIFCON)”, ICFRC News, No.1, pp. 7-8.

7. Sudarsana Rao H, and Ramana N V(2005), “Behaviour of slurry infiltratedconcrete (SIFCON) simply supportedtwo-way slabs in flexure” Indian Journalof Engineering and Material Sciences,Vol. 12, pp. 427-433.