The challenges posed by the modern structuralrequirements demand materials with increasinglyimproved properties such as strength, stiffness, impactand abrasion resistance. The focus of research shiftedto developing high performance materials in thisdecade. Fibre reinforced concretes prepared withdifferent types of fibres have found many structuralapplications. However, the ductility of fibrereinforced concrete basically depends on the volumefraction of fibres used in the production thoughvarious other factors such as type of fibre, its aspectratio and tensile strength of fibre can also influencethe ductility. Efforts have been made to produce fibrereinforced concrete with fibres up to 6% but wereaffected by difficulties in placing and mixing of highvolume of fibres. Special production methodologiesdeveloped in the modern days to overcome thisdifficulty have lead to the development of anotherhigh performance material called as slurry infiltratedfibrous concrete (SIFCON). SIFCON is one such highperformance material that possesses excellentmechanical properties coupled with greater energyabsorption characteristics. Ever since its invention byDavid Lankard I, SIFCON has attracted manyresearchers and structural engineers. This compositecan be considered as a special fibre reinforcedconcrete. Normally, fibre reinforced concrete contains1-3%fibres by volume, whereas SIFCON contains 6-20% of fibres. The other major difference is in thecomposition of the matrix. In SIFCON, the matrix is

Indian Journal of Engineering & Materials SciencesVol. 12, October 2005, pp. 427-433

I

Behaviour of slurry infiltrated fibrous concrete (SIFCON) simply supportedtwo-way slabs in flexure

H Sudarsana Rao & N V RamanaDepartment of Civil Engineering, JNTU College of Engineering, Anantapur 515002, India

Received 16 November 2004; accepted 30 May 2005

Slurry infiltrated fibre concrete (SIFCON) is one of the recently developed construction material. SIFCON could beconsidered as a special type of fibre concrete with high fibre content. The matrix consists of cement slurry or flowingcement mortar. This composite material has already been used for structures subjected to blast loading, repair of pre-stressedconcrete beams and safe vaults'. This paper presents the information on behaviour of two-way slabs in flexure. Flexure andcyclic load tests have been conducted and compared with fibre reinforced concrete (FRC) and plain concrete slabs. Bothstrength and deflection characteristics have been studied. The results of the experimental investigation indicate that with12% fibre by volume of matrix slabs possess excellent performance among other slabs in all respects.

IPC Code: C04B14/38

made of flowing cement mortar slurry as opposed toaggregate concrete in normal fibre reinforcedconcrete. The casting process is also different for

. I . ., .

SIFCON. In most cases, SIFCON is fabricated byinfiltrating a bed of pre-placed fibres with cementslurry.

Even though, SIFCON is a recent constructionmaterial, it has found applications in the areas ofpavements repairs, repair of bridge structures, safevaults and defence structures due to its excellentenergy absorption capacities'". Due to its extra-ordinary ductility characteristics, it has' a lot ofpotential for applications in structures subjected toimpact and dynamic loading. However, theseapplications can be attempted only after evaluatingthe basic mechanical properties. Since the compositeis relatively new, only limited amount of informationis available regarding its behaviour. Lankard I,

presented the basic properties of SIFCON (preparedwith 12.5% of fibres) such as load-deflection curve,ultimate compressive and flexural strengths, impactand abrasion resistance. Singh et al.', studied thestress-strain behaviour in compression and tension bypreparing SIFCON with 10% volume fraction offibres by adding fly-ash in the matrix. Naman andBaccouche, presented the shear response of dowelreinforced SIFCON. They observed that the shearstrength of SIFCON is 10 times higher than that of theplain matrix. The behaviour of reinforced concretebeams with SIFCON matrix has been studied by

428 INDIAN J. ENG. MATER. SCI., OCTOBER 2005

Naman et al.6 were reported that use of SIFCONeliminates the need of shear stirrups in RCC beams.Utility of SIFCON connections for seismic resistantframes has been investigated by Naman et al.' Thebehaviour of SIFCON under pure torsion has beenpresented by Balasubramanian et at. 8. SIFCON withstraight, crimped and trough shaped fibres has beenprepared and investigated for torsional resistance.Parameswaran et al.9 have studied the flexuralbehaviour of SIFCON beam specimens under cyclicloading and reported that the flexural strength is500% more when compared with plain mortorspecimens and 100% more to that of ferro-cement I

specimens. In most of these works, SIFCON has beenproduced with Drarnix steel fibres are which are veryexpensive and are to be imported. This has inhibitedthe applications of SIFCON in India. For greaterapplications of SIFCON in India, it is essential toproduce SIFCON with locally available fibres. Thepresent paper aims to address this problem. In thisinvestigation, SIFCON has been produced withlocally available fibres, i.e., black steel wire fibres.Because of its excellent energy absorptioncharacteristics, pre-cast SIFCON slabs can have awide range of structural and nuclear engineeringapplications. This paper presents experimental resultsthat describe the behaviour of the SIFCON slabs inflexure under both monotonic and cyclic loading. Inthis work SIFCON slabs are prepared by using locallyavailable fibres for our national applications. Theexperimental investigation is proposed on two-waySIFCQN slabs with simply supported edge conditionsubjected to uniformly distributed loading. Theinvestigation envisages studying the strength andstiffness behaviour of SIFCON slabs up to first crackand ultimate loads under flexure. The results arecompared with slabs made of plain concrete and fibrereinforced concrete.

Experimental ProcedureThe experimental program comprises casting and

testing of nine SIFCON slabs, three fibre reinforcedconcrete slabs (2% fibre) and three plain concreteslabs (M20) simply supported on all four edges. Themix proportions of the various slabs are presented inTable 1. All the slabs are square and are of size 600 x600 x 50 mm. The simply supported edge conditionhas been simulated by supporting the slabs on 10 mmdiameter steel rods. The details of the loadingarrangement are depicted in Fig. 1.

Fig. I-Loading arrangement

wo

Table I-Mix proportions

S.No Size Mix proportion Volume W/C Dosage of Mode offraction of ratio super vibration

fibre plasticizer

600 x 600 x 50 mm Cement and sand 8% 0.45 1.5% Hand tamping(SIFCON) (1: 1 by wt)

2 600 x 600 x 50 mm Cement and sand 10% 0.45 1.5% Hand tamping(SIFCON) (1:1 by wt)

3 600 x 600 x 50 mm Cement and sand 12% 0.45 1.5% Hand tamping(SIFCON) (1:1 by wt)

4 600 x 600 x 50 mm Cement, sand and coarse aggregate 2% 0.5 Table vibrationFibre reinforced concrete (1:1.54:3.17)

5 600 x 600 x 50 mm Cement, sand and coarse aggregate No fibres 0.5 Table vibrationPlain Concrete (1:1.54:3.17)

RAO & RAMANA: BEHAVIOUR OF SLURRY INFILTRATED FIBROUS CONCRETE

MaterialsCement

Ordinary Portland cement of 53 grademanufactured by Birla Company conforming to IS12269 was used. The specific gravity of the cementwas 3.01. The initial and final setting times werefound as 40 min and 340 min respectively.

Fine aggregateLocally available river sand passing through 4.75

mm I S Sieve was used. The specific gravity of thesand is found to be 2.62

Coarse-aggregateCrushed granite aggregate available from local

sources has been used. To obtain a reasonably goodgrading, 50% of the aggregate passing through 20 mmIS sieve and retained on 12.5 mm IS sieve and 50% ofthe aggregate passing through 12.5 mm IS sieve andretained on 10 mm IS sieve was used in preparation offibre reinforced concrete and M20 grade plainconcrete specimens. The specific gravity of thecombined aggregate is 2.6.

FibresThe present investigation aims at producing

SIFCON with locally available fibres so that it iseconomical and viable for Indian applications.Accordingly, black annealed steel wire of 1.0 mmdiameter was used. The fibres were cut to the requiredlength of 50 mm by using shear cutting equipmentgiving an aspect ratio of 50. The ultimate tensilestrength of fibre was 395 MPa. These black steelwires are commercially available and are generallyused for binding the steel reinforcement in RCCworks.

Fig. 2-Mould for casting SIFCON slab specimens

429

WaterPotable fresh water available from local sources

was used for mixing and curing of SIFCON, fibrereinforced concrete and plain concrete slabs.

Super plasticizerTo improve the workability in slurry and concrete

CONPLAST-220 high range water-reducing agent hasbeen used.

Casting of test specimensSteel moulds were used to cast the slab specimens

of required size. Two L-shaped frames with a depthof 50 mm and were connected to a flat plate at thebottom using nuts and bolts: Cross-stiffeners wereprovided to the flat plate at the bottom to prevent anypossible deflection while casting the specimens. Thegaps were effectively sealed by using thin card-boardsand wax to prevent any leakage of cement-sand slurryin SIFCON specimens. The moulds are shown in Fig.2. Initially the steel mould was coated with waste oilso that the slab specimens can be removed easily fromthe moulds. Then the steel fibres are placed randomlyin the mould such that they occupy the entire volumeof the mould. In the mean time cement-sand slurrywas prepared using CONPLAST - 220 which was laterpoured into the mould uniformly over the pre-placedfibres. The details of casting are shown in Fig. 3. Incase of fibre reinforced concrete slabs, fibres are firstmixed in the dry mixture of cement and sand and thenspread over the heap of coarse aggregate. Handmixing was done after adding required quantity ofwater to achieve uniform dispersion of fibres andprevent the segregation or balling of fibres duringmixing. For both FRC and plain concrete specimens,

Fig. 3-Casting of SIFCON slab specimens

430 INDIAN J. ENG. MATER. SCI., OCTOBER 2005

table vibration was adopted. The test specimens werede-moulded after 24 h and were cured for 28 days incuring water ponds. After removing the slabspecimens from the curing pond, they were allowed todry under shade for a while and then they were coatedwith white paint on both sides, to achieve clearvisibility of cracks during testing. The loadingposition on the top and the dial gauge position at thebottom of the slab were marked with black paint.

Loading arrangement and testingThe set-up for loading the slab consists of nine

numbers of RSJs (Rolled Steel Joist) of DoubleHeaded Rail of 460 mm length. These RSJ s wereplaced over the slab as shown in Fig. 1 to get theWhiffle tree arrangement. This arrangement willdistribute the centrally applied load uniformly on theentire slab and was used by earlier researchersworking on RCC slabs10,II. The self-weight of thesejoists was found to be 180 kg, and the same has beentaken in to account in load deflection computations.The loading platform consists of four welded steelbeams in square shape. These steel beams werestiffened using small size steel 'I-sections'. Thisloading platform has been supported by brick-wallson two sides and .the other two sides were supportedwith two steel rods. The load 'was applied throughhydraulic jack and was measured with a calibratedproving ring of 50 tonnes capacity. The verticaldeflections were measured by using dial gauge with aleast count of 0.01 mm. The vertical deflections weremeasured at the centre of the slab specimens. Tosimulate the simply supported condition, steel roadsof 10 mm diameter were placed in between the slabspecimen and platform at the edges.

The load has been applied incrementally. The loadincrement was selected such that there will be asmany number of readings as possible. The load wasapplied in increments of 83.33. kg which correspondsto one unit of proving ring. Deflections have been

Table 2- Details of test results

Nomenclature First crack Ultimate Maximum No. of cyclesload load central(kN) (kN) deflection

(mm)

SIFCON (80/0) 16.6 27.39 9.42 5SIFCQN (10%) 16.6 49.8 ' 10.31 5SIFCON (12%) 21.58 58.93 11.42 5FRC slabs 4.98 9.13 5.8Plain concrete 3.32 6.64 2.68slabs

recorded for each load increment. The load at the firstcrack and the corresponding deflection at the bottomcentre of the slab were recorded. The ultimate' loadand corresponding deflection at the centre were alsoobserved and recorded. Cycling load testing wasconducted on all the specimens after the slab reachedthe ultimate load by releasing the load decrementallyand reapplying the load in increments. The cyclicloading test has been carried out for five cycles. pel

Results and DiscussionThe results of the experimental investigation are

presented in Table 2. The values presented hererepresent the average of flexural strengths, load anddeflection obtained for three specimens in each series.The effect of percentage of fibres on the ultimate loadof the SIFCON slabs is shown in Fig. 4. It is observedfrom Fig. 4 that there is an increase in both first crackstrength and ultimate load due to the increase involume fraction of fibres. The slab specimensreinforced with higher volume fraction of fibresbehaved better than those containing lower volumefraction of fibres. The maximum.first crack load of21.58 kN has been achieved for slabs reinforced with12% volume fraction of fibres. The maximum ultimateload of 58.93 kN has been obtained for SIFCON slabswith 12% volume fraction of fibres which is 115%higher than that of 8% volume fraction. The increasefrom first crack load to ultimate load is rangingbetween 65% to 200% for SIFCON slabs whichindicates the excellent load carrying capacity ofSIFCON specimens. Fibre reinforced concrete (FRC)

in(SI]covafitcoobov

spobcecospS1S1pI1

isondeofFIgr

incrdi

First Crack Load 'Ultimate Load

60

50

40

ZC30

~g 20

10

10 12 14

% of Fibre (By Volume)Fig. 4-Effect of volume fraction or· fibre

RAO & RAMANA: BEHAVIOUR OF SLURRY INFILTRATED FIBROUS CONCRETE 431

0-" 8%fibre ~- .-_ --c

>-,,,.... //C 12%fiber /bd-FRCe Plain //

~

0.:/// d

~

Fig. 5-Load deflection curves of different slab specimens

slab specimens and plain concrete slab specimens havefailed at significantly lesser loads as expected. Thepercentage increase in first crack strength in SIFCONspecimen when compared to FRC specimens is in therange of 230% to 330% for different volume fractionsof fibres. When compared to plain concrete slabspecimens, the first crack load of SIFCON specimensis about 400-550% higher. This confirms the superiorperformance of SIFCON specimens.

It is observed that ultimate strength increases withincrease of fibre content. The ultimate strength ofSIFCON slab specimens is 200-550% higher whencompared to FRC slab specimens with maximumvalues corresponding to 12% volume fraction offibres. The increment when compared to plainconcrete specimens is 300%-790%. From this it isobserved that the SIFCON specimens behave wellover FRC and plain concrete slab specimens.

The central deflection values of various slabspecimens are presented in Table 2. It can beobserved from this table that there is a decrease incentral deflection in SIFCON slab specimens whencompared with the FRC and plain concrete slabspecimens. This is due to the greater stiffness ofSIFCON specimens. The load-defection curves forSIFCON slabs, FRC slabs and plain concrete slabs arepresented in Fig. 5. The superiority of SIFCON slabsis evident from this figure. SIFCON slabs have notonly carried higher loads, but also sustained greaterdeflections till ultimate stage. The ultimate deflectionsof SIFCON slabs are an order higher than those ofFRC and plain concrete slabs demonstrating thegreater ductility of the composite.

It is observed that the crack pattern is almost similarin all the SIFCON slabs. It is observed that the firstcrack originated at the centre and .then propagateddiagonally towards the corner. At higher loads, it is

656055504540

~ 35030C§ 25..J 20

1510

5o

o 2 4 6 8 10 12

DEFLECTION (mm)

observed that already formed cracks are gettingwidened with formation of few new cracks. Thespacing of cracks was decreased with the increasing infibre content for same loading. The reason is the crackarresting mechanism of fibres. The propagation ofcracks was observed to be faster in plain concretespecimens and the failure was almost instantaneousbreaking the slab into four pieces. Whereas the failureof SIFCON slabs is very gradual and the slabs wereintact even after ultimate load is reached. The typicalfailure patterns are presented in Fig. 6 (a-e).

, "

Fig. 6a-Failed specimen depicting crack patterns

Fig. 6b--Failed specimen depicting crack patterns

432 INDIAN J. ENG. MATER. SCI., OCTOBER 2005

Fig. 6c-Failed specimen depicting crack patterns

Fig. 6d-Failed specimen depicting crack patterns

Fig. 6e-Failed specimen depicting crack patterns

Cyclic load testCyclic load test has been performed on the

SIFCON slab specimens' by releasing the load afterreaching the ultimate stage in first cycle and re-

30 I 8% OF FIBER!

10.5

14

25

20

~ 15

~9 10

5

7.5 8.0 8.5 9.0 9.5 10.0

11.5

DEFLECTION (mm)

Fig .7a- Cyclic load-deflection curve for SIFCON slab (8%)

50

40

5230

~2O--I

10

08.0 8.5

I 10% OF FIBER I

,9.0 9.5 10.0

DEFLECTION (mm)10.5 11.0

Fig. 7b--Cyclic load-deflection curve for SIFCON slab (10%)

60

50

40Z::.::~3O

a--120

10

09

I 12% OF FIBER I

10 11 12

DEFLECTION (mm)13

Fig. 7c-Cyclic load-deflection curve for SIFCON slab (12%)

I

RAO & RAMAN A: BEHAVIOUR OF SLURRY INFILTRATED FIBROUS CONCRETE

applying and is continued for five cycles. The cyclicload-deflection curves are presented in Fig. 7 (a-c).These load-deflection curves indicate the capacity andthe performance of SIFCON slabs to with stand thecyclic loading.

ConclusionsThe major objective of this investigation is to

produce SIFCON slabs with locally available fibresfor Indian applications. SIFCON slabs with differentvolume fractions of fibres have been produced andtested under uniformly distributed load. Cyclicloading tests also have been performed. Thesuperiority of SIFCON slabs over fibre reinforcedconcrete slabs and plain concrete slabs has beendemonstrated. Analysing the results obtained fromthis investigation, the following conclusions aredrawn: (i) The load carrying capacity of the SIFCONslabs is much higher than the fibre reinforced concreteand plain concrete slab specimens. (ii) The stiffness ofSIFCON slabs is an order of higher magnitude thanthat of fibre reinforced concrete and plain concreteslab specimens. (iii) The SIFCON slab specimensexhibited greater ductility. Even at the ultimate stage,

433

SIFCON slab specimens were intact while the plainconcrete slab specimens broke into pieces. (iv) TheSIFCON slab specimens behaved well in cyclicloading test. (v) The crack width is much less inSIFCON slab specimens than the FRC specimens ..

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