Construction and Building Materials 25 (2011) 2240–2247

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Construction and Building Materials

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High strength characteristics of cement mortar reinforced with hybrid fibres

Eethar Thanon Dawood ⇑, Mahyuddin RamliBuilding Technology, School of Housing, Building and Planning, Universiti Sains Malaysia, 11800 Penang, Malaysia

a r t i c l e i n f o a b s t r a c t

Article history:Received 24 May 2010Received in revised form 12 November 2010Accepted 14 November 2010Available online 10 December 2010

Keywords:Barchip fibreHybrid fibresHigh strength mortar

0950-0618/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2010.11.008

⇑ Corresponding author.E-mail address: eethar2005@yahoo.com (E.T. Daw

An experimental study was conducted on high strength mortar reinforced with steel fibres and hybridfibres consisting of steel fibre, palm fibre and synthetic fibre (Barchip). The inclusion of fibres was main-tained at a volumetric fraction of 2%. The compressive strength, splitting tensile strength, static modulusof elasticity, shrinkage, flexural strength, and flexural toughness were determined to study the effect ofthe hybrid fibres on the properties of high strength cement mortar (HSCM). The results showed thathybridization of fibres in the quantities 1.5% steel fibres + 0.25% palm fibres + 0.25% Barchip fibres,improved the compressive strength and flexural toughness significantly, and also enhanced the splittingtensile strength and flexural strength of the mortar by about 44% and 140%, respectively.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction mum performance [5]. The addition of flexible fibres (such as palm

1.1. General

In order to obtain more fundamental information, an under-standing of the behaviour of reinforced mortar under differenttypes of load is required due to an increasing number of structuralapplications placing a greater demand on material performance.One of the most practical applications mortar is its use for rehabil-itation and repair of reinforced concrete structures. The inclusionof fibres in concrete or cement mortar considerably improvesstructural characteristics such as flexural strength, impactstrength, tensile strength, ductility and flexural toughness [1,2].Many researchers have studied the different characteristics of fi-bres in concrete or cement mortar. Shah and Namman [3] investi-gated tensile strength, flexural strength and compressive strengthtests on mortar specimens reinforced with steel fibres. It was ob-served that the tensile or flexural strength of steel fibre reinforcedmortar was at least two to three times higher than that of plainmortar, while the corresponding strains and deflections were atleast 10 times higher than that of plain mortar specimens. The con-tribution of steel fibres can be observed significantly after matrixcracking in concrete, in which they arrest the propagating cracks[4]. However, the addition of steel fibres at higher dosages hassome disadvantages in terms of poor workability and higher cost.In addition, the high stiffness of steel fibres in the matrix meansthat voids and honeycombs could be formed during placing as a re-sult of improper compaction at low workability. In order for goodworkability or flow ability of mortar, with good flexural toughness,the addition of two or three different fibre types can yield the opti-

ll rights reserved.

ood).

fibres and synthetic (Barchip) fibres) results in good fresh mortarproperties and a reduction in early age cracking. The beneficial ef-fects of flexible fibres could be attributed to their high aspect ratiosand increased fibre availability (because of their lower densitycompared to steel) at a given volume fraction. Having lower stiff-nesses, these fibres are particularly effective in controlling thepropagation of microcracks in the plastic stage of concrete andtheir contribution to post-cracking behaviour is known to be sig-nificant [6–8]. The hybrid combination of metallic and non-metal-lic fibres can offer potential advantages in improving concreteproperties as well as reducing the overall cost of concrete produc-tion [9]. It is important to have a combination of low and highmodulus fibres to arrest the micro and macro cracks, respectively.

1.2. Research significance

The objective of this study is to investigate the mechanical prop-erties of various fibre reinforced mortars containing individual steelfibres and hybrid fibres consisting of steel fibres, palm fibres andsynthetic fibres (Barchip). The total dosage of fibres was maintainedat a volumetric fraction of 2.0%. A comparative evaluation of varioushybrid fibres mortar was made based on their hardened propertiessuch as; compressive strength, splitting tensile, static modulus ofelasticity, shrinkage, flexural strength and flexural toughness.

2. Materials and mix proportions

2.1. Materials

The cement used in mortar mixtures was Ordinary Portland Ce-ment (OPC) type I from Tasek Corporation Berhad. Silica fume wasobtained from Scancem Materials Sdn Bhd and was used as partial

Table 4Characteristics of steel fibre.

Fibre properties Quantity

Average fibre length (mm) 30Average fibre width (mm) 0.56Aspect ratio (L/d) 54Tensile strength (MPa) >1100Ultimate elongation (%) <2Specific gravity 7.85

E.T. Dawood, M. Ramli / Construction and Building Materials 25 (2011) 2240–2247 2241

replacement for cement. The chemical composition of OPC and sil-ica fume are given in Table 1.

The superplasticizer (SP) used was Conplast SP1000, obtainedfrom Fosroc Sdn Bhd, and was used to establish the desired prop-erties of mixes. The fine aggregate was natural sand, with a fine-ness modulus of 2.86 and a maximum size of 5 mm. The palmfibre was supplied by Fibre-X (M) Sdn Bhd and their characteristicsare presented in Table 2. The characteristics of synthetic fibres(Barchip), which were obtained from Elasto Plastic Concrete PtyLtd., are presented in Table 3. The steel fibre was supplied by Hu-nan Sunshine Steel Fibre Co. Ltd., and their mechanical propertiesare presented in Table 4.

2.2. Mix proportions

The mortar compositions are given in Table 5. A total of elevenmortar mixes were prepared using water-binder (cement + silicafume) in a ratio of 0.43 and the silica fume replacement was 10%.The amount of cement, silica fume, sand and free water were keptconstant. The amount of superplasticizer varied from 1.8% to 2.2%by weight of binder content to maintain appropriate flow abilityfor all the mixes. The mix design of the control mix (M0) was car-ried out according to the absolute volume method given by theAmerican Concrete Institute (ACI 211.1) [10] to achieve the criteriaof flowable high strength mortar. The steel fibres were added to themix according to the volumetric fraction of 2% for the mix (M1).

Table 1Chemical composition of ordinary Portland cement and silica fume.

Constituent Ordinary Portland cement Silica fume% by weight % by weight

Lime (CaO) 64.64 1.0 (max)Silica (SiO2) 21.28 90 (max)Alumina (Al2O3) 5.60 1.2 (max)Iron oxide (Fe2O3) 3.36 2.0 (max)Magnesia (MgO) 2.06 0.6 (max)Sulphur trioxode (SO3) 2.14 0.5 (max)N2O 0.05 0.8 (max)Loss of ignition 0.64 6 (max)Lime saturation factor 0.92 –C3S 52.82 –C2S 21.45 –C3A 9.16 –C4AF 10.2 –

Table 2Characteristics of palm fibre.

Fibre properties Quantity

Average fibre length (mm) 30Average fibre width (lm) 21.13Tensile strength (MPa) 21.2Elongation at break (%) 0.04Specific gravity 2.14Water absorption%, 24/48 h 0.6

Table 3Physical properties of synthetic fibre (Barchip).

Fibre properties Quantity

Average fibre length (mm) 30Average fibre width (mm) 0.52Tensile strength (MPa) 550Young’s modulus (GPa) 8.2Specific gravity 0.92Melting point (�C) 150–165

However, the 2% hybrid mix of fibres was composed of differentamounts of steel and palm fibres in the preparation of mixes M2to M5. Similarly, the hybridization of the three different fibres ofsteel, palm and Barchip fibres were used to prepare mixes M6 toM10. The total amount of hybrid fibres in all mixes was maintainedat a volumetric fraction of 2%.

3. Test methods

All the specimens used for the different tests were cured using awater tank as a normal water curing method with a controlledtemperature of 27 �C ± 2 �C. Three 50 mm cube samples were usedfor each mix to test the compressive strength at various ages (7 and28 days) according to ASTM C109 [11]. The flow test for mixes wasperformed according to ASTM C230 [12] with a targeted flow of150 mm ± 10 mm. The cube specimens were left in the mouldsfor 24 h at 20 �C. The splitting tensile strength was carried out at28 days using 100 mm � 200 mm concrete cylinders according toASTM C496 [13]. Also, for the same curing time, the 150 � 300mm concrete cylinders were used to test the static modulus ofelasticity according to ASTM C469 [14]. The strain was measuredusing the compresso-meter as described in ASTM C469. The spec-imens were placed with the strain-measuring equipment attached,on the lower plate or bearing block of the testing machine. The axisof the specimen was aligned carefully with the centre of thrust ofthe spherically-seated upper bearing block, and then the readingon the strain indicators was noted. However, the specimen wasloaded twice without recording any data. During the first load,which is primarily to seat the gauges, the performance of thegauges was observed. The testing machine was set at the screwtype so that the moving head travelled at a rate of about1.25 mm/min when the machine was running idle. The recordingwas implemented without interruption of loading process, the ap-plied load and longitudinal strain at the point (1) when the longi-tudinal strain is 50 millionths and at (2) when the applied load isequal to 40% of the ultimate load. Testing of the flexural strengthand the toughness indices of the specimens were conducted on40 � 40 � 160 mm samples in accordance to ASTM C348 [15] andASTM C1018 [16], respectively. The sample ages for the latter testswere 28 and 90 days. Consequently, the same specimen size wasused to determine the shrinkage of different mortar mixes accord-ing to ASTM C157/C 157 M-99 [17]. The shrinkage sample test ageswere 28, 90 and 180 days. After de-moulding (24 h after casting),the bases of the comparator, into which the gauge stud on the low-er end of the bar fits, were fixed tightly using proper glue. This holetends to collect water and sand and should be cleaned after everyreading. The reference length (Li) was read and recorded after de-moulding. The specimens were kept in a space so as to be exposedto air curing until the required age for the test (Lx). The shrinkageor length change was determined by the following equation:

L ¼ ðLx� LiÞ=G� � 100

where L is the change in length at x age, in%, Lx is the comparatorreading of specimen at x age minus comparator reading of reference

Table 5Mortar mix proportions.

Index Cement(kg/m3)

Silica fume(Kg/m3)

Water(Kg/m3)

SP(%)

Sand(kg/m3)

W + SP /B Steel fibre(%)

Palm fibre(%)

Synthetic fibre(Barchip) (%)

Flow(mm)

M0 550 55 260 1.8 1410 0.43 – – – 160M1 550 55 260 2.2 1410 0.43 2.00 – – 140M2 550 55 260 2.2 1410 0.43 1.75 0.25 – 140M3 550 55 260 2.2 1410 0.43 1.50 0.50 – 145M4 550 55 260 2.2 1410 0.43 1.25 0.75 – 145M5 550 55 260 2.2 1410 0.43 1.0 1.0 – 150M6 550 55 260 2.2 1410 0.43 1.5 0.25 0.25 140M7 550 55 260 2.2 1410 0.43 1.25 0.50 0.25 145M8 550 55 260 2.2 1410 0.43 1.25 0.25 0.50 145M9 550 55 260 2.2 1410 0.43 1.0 0.50 0.50 145M10 550 55 260 2.2 1410 0.43 1.0 0.25 0.75 145

2242 E.T. Dawood, M. Ramli / Construction and Building Materials 25 (2011) 2240–2247

bar at x age in millimeters, Li is the initial comparator reading ofspecimen minus comparator reading of reference bar at that sametime, in millimeters, and G is the nominal gage length.

4. Results and discussion

4.1. Flowability

The effect of fibres on the flow of the mortar mixes is significant.It is clear from Table 5 that the inclusion of steel fibre in the highstrength cement mortar (HSCM) mixes reduces the flowability. Thecomparison between the control mortar (M0) with the mortar of2% volume of steel fibre (M1) shows that the flow results droppedfrom 160 mm to 140 mm despite increasing the SP dosage from1.8% to 2.2%, respectively. On the other hand, in the mortar mixeswith hybrid fibres, those with a higher amount of palm fibres had abetter flowability. Therefore, with a certain dosage of SP the mixwith 1% steel fibres and 1% palm fibres (M5) has a higher flowabil-ity than that of (M1).

The effect of the inclusion of Barchip fibres was found to be lesseffective on the flowability of mortar than steel fibres. In summary,the effect of palm and Barchip fibres on either the flow or workingcapacity is much smaller than that of steel fibre.

4.2. Compressive strength

The results of the compressive strength for the different mortarmixes are shown in Table 6. The use of a 2% volume of steel fibre(M1) was found to reveal a compressive strength of about 2.6–4%higher than that of the control mortar (M0) for different ages. Thisenhancement in the compressive strength resulted from the bettermechanical bond strength between the fibres and the cement ma-trix which delays micro-cracks formation [11,12]. The increases inthe compressive strength of HSCM reinforced by hybrid fibres were

Table 6Mechanical properties of mortar mixes.

Index Compressivestrength (MPa)(7 days)

Compressivestrength (MPa)(28 days)

Splitting tensilestrength (MPa)(28 days)

ModEc (

M0 42.7 54.3 2.10 33.11M 44.4 55.7 2.62 45.12M 46.1 57.8 2.71 47.83M 46.4 58.4 2.89 44.9M4 43.1 54.9 2.35 42.7M5 42.7 54.4 2.25 41.8M6 47.0 59.3 3.02 50.4M7 43.6 55.2 2.51 47.2M8 45.5 56.6 2.65 48.9M9 41.6 53.2 2.44 40.1M10 41.1 52.8 2.31 38.9

found to be higher than that of the mortar only containing steel fi-bre. The increase in strength for mix M3 with a hybrid fibre contentof 1.5% steel fibre + 0.5% palm fibre by volume was 7.5% higherthan that of the control mortar mix (M0). Whereas the mix con-taining 1.5% steel fibre + 0.25% palm fibre + 0.25% Barchip fibre(M6) had a higher compressive strength than that of the controlmix (M0) by about 9%. This improvement in compressive strengthresulted from the hybridization of the fibre system derived fromdifferent fibre types which offers various restrain conditions [18].

4.3. Splitting tensile strength

The splitting tensile strength results of the HSCM mixes are gi-ven in Table 6. The effect of using a 2% steel fibre content on thesplitting tensile strength is significant. The increase in splittingtensile strength from the inclusion of steel fibre (M1) was foundto be 25% higher than that of the control mortar mix (M0) [19].On the other hand, the hybridization of 1.5% steel fibre with 0.5%palm fibre, or a combination of palm and Barchip fibres, increasesthe splitting tensile strength. Indeed, the percentage increase of thelatter cases was found to be higher than that of the control mix(M0) by about 38% and 44%, respectively. This can be attributedto the ability of the mortar with two fibres to bridge the crackseffectively, thus the micro-mechanical features of crack bridgingare operative from the stage of damage evolution to beyond ulti-mate loading [20]. Fig. 1 illustrates the relationship between com-pressive strength and splitting tensile strength of hybrid fibremortar mixes.

4.4. Modulus of elasticity test

The modulus of elasticity results for all HSCM mixes are pre-sented in Table 6. The comparison between M0 and M1 shows thatthe use of 2.0% steel fibre leads to an increase in the static modulus

ulus of elasticity ,GPa) (28 days)

Shrinkage%(28 days)

Shrinkage%(90 days)

Shrinkage%(180 days)

Reduction inshrinkage (%)

0.0789 0.0897 0.103 –0.0116 0.0144 0.0189 81.70.0283 0.0345 0.0398 61.40.0387 0.0412 0.0489 52.50.0478 0.0522 0.0574 44.30.0587 0.0659 0.0689 33.10.0294 0.0362 0.0392 61.90.0446 0.0472 0.0511 50.40.0378 0.0422 0.0477 53.70.0589 0.0623 0.0687 33.30.0526 0.0567 0.0635 38.3

y = 0.0166x2 - 1.7546x + 48.66R² = 0.9198

52 53 54 55 56 57 58 59 60

Split

ting

stre

ngth

(N

/mm

2 )

Compressive strength (MPa)

0

0.4

0.8

1.2

1.6

2

2.4

2.8

3.2

3.6

4

Fig. 1. Relationship between compressive strength and splitting tensile strength of hybrid fibre cement mortar mixes.

E.T. Dawood, M. Ramli / Construction and Building Materials 25 (2011) 2240–2247 2243

of elasticity. The static modulus of elasticity increased by about36% following the inclusion of steel fibre. This can be due to thefact that steel fibre has a high stiffness resulting in a higher mod-ulus of elasticity for HSM [21–23]. However, the use of 0.25% ofpalm fibres, or 0.5% of palm fibres and Barchip fibres in a hybridcombination, was found to be much more effective. The percentageincrease in the static modulus of elasticity for these cases wasfound to be 44% and 52%, respectively. This is probably due tothe optimization of these percentages of fibres to operate the high-er bond strength behaviour and thus provide a higher modulus ofelasticity [23,24].

4.5. Shrinkage

The shrinkage results for all HSCM mixes are presented in Table6. The results indicate that the steel fibres reduce the shrinkage ofmortar significantly. The reductions in shrinkage shown in Fig. 2,by using various types of hybrid fibres are consistent with the ear-lier results.

The maximum reduction in shrinkage was obtained when 2% ofsteel fibre was added to the mortar mix where a reduction in

0

81.7

61.452.5

44.3

M0 M1 M2 M3 M4 M5

Shri

nkag

e re

duct

ion

%

Fiber Morta

Shrinkage r

Shrinkage re

0

10

20

30

40

50

60

70

80

90

100

Fig. 2. Relationship between the fibre mortar mixes and reduct

shrinkage of about 82% was recorded. On the other hand, the hy-brid of fibres also showed a significant reduction in shrinkage.However, the comparison between M3 and M6 shows that theuse of 1.5% steel fibre + 0.25% palm fibre + 0.25% Barchip fibre re-duces the shrinkage more effectively than using a mix of 1.5% steelfibre + 0.5% palm fibre. In general, it can be concluded that theshrinkage property is affected by the stiffness of the fibres[25,26]. The development of shrinkage for HSCM mixes reinforcedwith hybrid fibres [steel and palm fibre] with different ages is pre-sented in Fig. 3. Whereas, the development of shrinkage for HSCMmixes reinforced with hybrid fibres [steel fibres, palm fibres andBarchip fibres] with different ages is presented in Fig. 4.

4.6. Flexural strength

The flexural strength results of the HSCM are shown in Table 7.The result of the flexural strength of mortar with 2% of steel fibreindicates that the increase in flexural strength is 109% higher thanthat of the control mix. This significant improvement can be attrib-uted to the enhancement in the compactness and toughness matrixin HSCM [27]. However, the results of hybrid fibres indicate that

33.1

61.9

50.4 53.7

33.338.3

M6 M7 M8 M9 M10

r mixes

eduction

duction

ion in shrinkage for high strength cement mortar (HSCM).

M0 M1 M2 M3

Fig. 3. Shrinkage development of HSCM mixes reinforced with hybrid fibres [steel fibres and palm fibres] with different ages.

M0 M1 M6 M7 M8 M9

Fig. 4. Shrinkage development of HSCM mixes reinforced with hybrid fibres [steel fibres, palm fibres and Barchip fibres] with different ages.

Table 7Toughness indices for mortar mixes.

Index Flexural strength (MPa)(28 days)

Flexural strength (MPa)(90 days)

Toughness index (I-5)(28 days)

Toughness index (I-10)(28 days)

Toughness index (I-5)(90 days)

Toughness index (I-10)(90 days)

M0 7.60 9.12 – – – –M1 15.90 17.36 5.05 7.05 8.22 9.44M2 15.92 17.64 5.15 7.67 8.67 9.85M3 17.67 19.22 5.82 8.10 8.62 11.45M4 13.12 14.95 3.84 5.42 6.32 8.63M5 11.65 13.26 3.66 5.28 6.12 7.44M6 18.23 19.67 5.78 8.74 8.73 11.78M7 13.67 15.11 3.97 6.74 6.52 8.73M8 14.06 15.24 4.12 6.93 6.68 8.89M9 12.10 14.15 3.69 6.28 6.34 8.54M10 10.92 12.44 3.48 5.98 5.97 8.14

2244 E.T. Dawood, M. Ramli / Construction and Building Materials 25 (2011) 2240–2247

the increase in flexural strength is much more effective. The in-crease in flexural strength by hybrid fibres containing 1.5% steel fi-bre + 0.5% palm fibre was found to be about 133% higher than thatof the control mortar. The highest increase in flexural strength was140% which was obtained from the mix containing hybrid fibres of1.5% steel fibre + 0.25% palm fibre + 0.25% Barchip fibre. This effec-tive increase in flexural strength possibly resulted from the im-proved compaction and homogeneity of fibre distribution in themortar mixes and the ability of different types of fibre to restrainand bridge the cracks [27]. Fig. 5 shows clearly the effect of theuse of these fibres on different mechanical properties of HSCM.

4.7. Toughness indices

Toughness indices were determined according to ASTM C1018.The indices I-5 and I-10 results are shown in Table 7, Fig. 6 andFig. 7. It can be observed that the use of 2% steel fibre significantlyimproved the flexural toughness. This can be attributed to the abil-ity of steel fibre to arrest cracks at both the micro- and macro-level.At micro-level fibres inhibit the initiation of cracks, while atmacro-level fibres provide effective bridging and impart sourcesof toughness and ductility [28,29]. However, the use of hybrid fi-bres of steel with 0.5% palm fibre or with 0.25% palm fibre + 0.25%

M0 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10

Mec

hani

cal P

rope

rtie

s Pe

rcen

tage

s %

Fiber Mortar mixes

Compressive Strength Flexural Strength

Splitting Tensile Strength Static modulus of elasticity EC

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

Fig. 5. Relationship between the fibre mortar mixes and different mechanical properties for high strength cement mortar (HSCM).

Toughness Index I-5

Toughness Index I-10

M0 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10

Tog

hnes

s In

dex

Fiber mortar mixes

0123456789

1011121314

Fig. 6. Relationship between the fibre mortar mixes and toughness indices of high strength cement mortar (HSCM) at 28 days.

Tog

hnes

s In

dex

Fiber mortar mixes

Toughness Index I-5Toughness Index I-10

M0 M1 M2 M3 M4 M5 M6 M7 M8 M9 M100123456789

1011121314

Fig. 7. Relationship between the fibre mortar mixes and toughness indices of high strength cement mortar (HSCM) at 90 days.

E.T. Dawood, M. Ramli / Construction and Building Materials 25 (2011) 2240–2247 2245

0 1 2 3 4 5 6 7 8

Loa

d (K

N)

Deflection (mm)

M1 (2.0 % steel fiber)

M2( 1.75% steel fiber+0.25% palm fiber)

M3( 1.5% steel fiber+0.50 palm fiber)

M4(1.25% steel fiber+0.75% palm fiber)

M5( 1.0% steel fiber+1.0% palm fiber)

0

1

2

3

4

5

6

7

8

9

10

Fig. 8. Load–deflection curves for hybrid fibres [steel fibres + palm fibres] for HSCM mixes.

0 1 2 3 4 5 6 7 8

Loa

d (K

N)

Deflection (mm)

M1 (2.0 % steel fiber)

M6( 1.5% steel fiber+0.25 palm fiber+0.25% Barchip fibers)"M7 (1.25% stel fiber+0.5% palm fiber+ 0.25% Barchip fiber)"M8(1.25% steel fiber+0.25% palm fiber+ 0.5% Barchip fiber)M9( 1.0% steel fiber+0.5% palm fiber+0.5% Barchip fibers)M10( 1.0% steel fiber+ 0.25% palm fiber+ 0.75% Barchip fiber)

0

1

2

3

4

5

6

7

8

9

10

Fig. 9. Load–deflection curves for hybrid fibres [steel fibres + palm fibres + Barchip fibres] for HSCM mixes.

2246 E.T. Dawood, M. Ramli / Construction and Building Materials 25 (2011) 2240–2247

of Barchip fibre can be considered the most effective. This is due tothe fact that the hybridization contributes to the arresting ofcracks, whereas the flexible fibres (palm and Barchip) improvethe toughness in the post crack zone [30]. The load deflectioncurves for HSCM reinforced by hybrid fibres are shown in Figs. 8and 9.

5. Conclusions

The experimental study on the high strength mortar reinforcedwith various volume fractions of hybrid fibres reveals the followingconclusions:

1. The compressive strength results show that the use of hybridfibres of 1.5% steel + 0.25% palm + 0.25% Barchip gives the high-est increase in compressive strength of cement mortar due to animprovement in the mechanical bonding in the matrix.

2. The hybridization of 1.5% steel fibres with 0.5% of palm fibresincreases the splitting tensile strength by about 38%. Whereasthe hybrid fibres of 1.5% steel + 0.25% palm + 0.25% Barchipincreases the splitting tensile strength and flexural strengthby about 44% and 140%, respectively.

3. Hybridization was also found effective in enhancing the modu-lus of elasticity. Combining concrete mixes with 1.75% steelfibre and 0.25% palm fibre, or 1.5% steel fibre and 0.25% palmfibre and 0.25% Barchip fibre, increased the static modulus of

E.T. Dawood, M. Ramli / Construction and Building Materials 25 (2011) 2240–2247 2247

elasticity by about 44% and 52%, respectively. Consequently,their flexural toughness was significantly enhanced by thehybridization process as a result of the bridging effect fromthe flexible fires in the post crack zone.

4. The shrinkage property was found to be affected by the stiffnessof the fibres, therefore, the mortar reinforced with higher per-centage of steel fibre would reduce the shrinkage significantly.

5. The best hybrid fibres composition derived from this study wasfound to be 1.5% steel fibres + 0.25% palm fibres + 0.25% Barchipfibres.

Acknowledgement

The work described in this paper was a part of first namedauthor’s PhD research program which is supported by a researchgrant and USM Fellowship from the Universiti Sains Malaysia.

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