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KAIWAAN, et al. - Structural Behavior of Kenaf Fibre Reinforced Concrete Beams. pp. 89-95 ISSN:1390-5007

Abdulhai Kaiwaan,

Sayed Javid Azimi,

Sayed Alem Azimi

Structural Engineering Faculty of Afghan International Islamic University. PhD candidate at Civil Engineering

at Delhi Technological University. kaiwaan38@gmail.com. ORCID: 0009-0008-2427-5902

Structural Engineering Faculty of Afghan International Islamic University. PhD candidate at Civil Engineering

at Delhi Technological University. s.javidazimi@gmail.com. ORCID: 0000-0003-2149-7768

Electrical Engineering faculty of Takhar University. alem.azimi@gmail.com. ORCID: 0009-0005-1451-164X

Structural Behavior of Kenaf Fibre Reinforced

Concrete Beams

Comportamiento estructural de vigas de hormigón armado con

bra Kenaf

EÍDOS N

Revista Cientíca de Arquitectura y Urbanismo

ISSN: 1390-5007

revistas.ute.edu.ec/index.php/eidos

Recepción: 19, 11, 2023 - Aceptación: 12, 12, 2023 - Publicado: 01, 01, 2024

Resumen:

Este artículo presenta el efecto de las bras de kenaf

en vigas de hormigón armado. Al investigar el compor-

tamiento estructural de las vigas, se realizó una prue-

ba de exión de cuatro puntos en cinco vigas con-

siderando dos parámetros distintos (i) la disposición

del refuerzo de corte (ii) la cantidad de bras de kenaf

en las vigas antes mencionadas. Las vigas constan

de dos vigas con refuerzo de corte total mediante dos

cantidades de bras de kenaf, 10 kg/m³ y 20 kg/m³,

respectivamente, y otras dos vigas con un 50 % de

mayor espaciado de corte con dos cantidades dife-

rentes de bras de kenaf de 10 kg/m³ y 20 kg. /m³

fueron examinados. Una viga de control está hecha

de bra de kenaf de 0 kg/m³ con refuerzo de corte

total. Los resultados experimentales sugieren que las

vigas con la inclusión de bras de kenaf demuestran

un aumento signicativo en la capacidad de carga,

ductilidad y resistencia al corte. Además, se observó

que el modo de falla cambia del modo de corte al

modo de exión. Además, este estudio opina que las

bras de kenaf son compatibles con RC, lo que arroja

resultados prometedores.

Palabras clave: bra de kenaf, ductilidad, capacidad

de carga, modo de falla.

Abstract:

This paper presents the effect of kenaf bres in

reinforced concrete beams. In investigating the

structural behaviour of the beams, four point bending

test was conducted on ve beams by considering

two distinct parameters (i) shear reinforcement

arrangement (ii) the amount of kenaf bres in the

aforementioned beams. The beams consists of Two

beams with full shear reinforcement by two amount of

kenaf bres, 10kg/m³ and 20kg/m³, respectively and

two other beams with 50% increased shear spacing

with two different amount of kenaf bre 10 kg/m³ and

20 kg/m³ were examined. A control beam is made

of 0 kg/m³ kenaf bre with full shear reinforcement.

The experimental results suggests that beams with

the inclusion of kenaf bres demonstrates signicant

increase on the load carrying capacity, ductility and

shear strength. Moreover, it was observed that the

mode of failure is altered from shear mode to bending

mode. Furthermore, this study opines that kenaf bres

are compatible with RC which yields promising results.

Keywords: kenaf ber, ductility, load carrying capacity,

mode of failure.

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Figure 1. Kenaf ber (cut 30 mm length) Figure 2. Slump test

1. INTRODUCTION

Kenaf is scientically known as

Hibiscus cannabin’s L. and it falls under

the Malvaceae family. It is cultivated in In-

dia, Bangladesh, United States of Amer-

ica, Indonesia, Malaysia, South Africa,

Thailand, parts of Africa, and in specic

parts of southeast Europe for its bre [1].

The cracking phenomenon on concrete

structures, are often caused by low ten-

sile strength, drying shrinkage and plastic

shrinkage. The inclusion of bre increases

the strength load carrying capacity, ductil-

ity, stiffness of structure as well as reduces

the drying shrinkage and plastic shrink-

age. The inclusion of bres also acts as a

crack arrestor and improves the dynamic

and static behaviour of concrete struc-

ture [5]. Although steel bre mitigates the

problem of low tensile strength of concrete

and micro cracks, nonetheless it does not

completely solve the problem as over a

long period of time, steels are susceptible

to corrosion and this will cause sudden

catastrophic failure in concrete structures.

This alone motivates the need of

the use of different type of bres such

as, natural bres which is more copious,

economical and environmental friendly as

compared to synthetic bres [2, 4]. The in-

clusion of natural bres in reinforced con-

crete structures in enhancing the struc-

tural properties are well recognised due to

their low density and high specic strength

which are desirable in concrete structures

[1-4]. The tensile strength of kenaf bre is

between 400-550 MP which is higher than

some natural bre namely sisal and jute

[4]. Owing to the desirable characteris-

tics of kenaf bres, it bets as a potential

candidate to be used as bres in concrete

structures [6]. A similar study was con-

ducted for lightweight concrete using oil

palm shell (OPS) [7]. The present study in-

tends to investigate the inuence of kenaf

bres when added to reinforced concrete

beams as well as its effectiveness of as a

part of shear reinforcement through the in-

crease of shear links.

2. METHODOLOGY

2.1. Preparation of reinforced concrete

beams for testing

Table 1 lists three sets of concrete

mixture proportions for ve beams. Kenaf

bres included in the mixtures are 30 mm

of length with a diameter between 0.1 mm

to 2 mm as shown in Fig. 1. Super-plasti-

cizer was added to achieve the required

slump. The concrete mixture used in the

fabrication of all specimens has a slump in

the range of 95 mm to 105 mm as shown

in Fig. 2.

The loading arrangement and re-

inforcement properties of the beam are

shown in Fig. 3 and Fig. 4. The beams

were initially designed by Euro code 2

with shear reinforcement less than that is

required to cause shear failure. Two ar-

rangements were considered (i) full shear

reinforcement and (ii) reduced in shear

reinforcement (this was carried out by in-

creasing the spacing between the shear

links by 50 %). Subsequently, two amounts

of bres contents were added into the re-

inforced concrete mixture to examine the

effect of kenaf bres in reinforced con-

crete beams. Therefore, ve beams (three

for full shear reinforcement and two for re-

duced in shear reinforcement) were tested

under four point bending test. The beam

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with full shear reinforcement without 0 kg/

m³ bers was considered as the control

beam. The test was carried out on the 56th

day in order to ensure that the reinforced

concrete beams added with kenaf were

fully hardened.

Table1. Mixture of concrete

Ingredients Kg/m³ Kg/m³ Kg/m³

Concrete Mix 1 Mix 2 Mix 3

Kenaf ber 0 10 20

Coarse aggregate 308 308 308

Super plasticizer

(Liter/m³)

5 5 5

Water (Liter/m³) 204 204 204

Fine aggregate

(sand)

848 848 848

W/C ratio 0.4 0.4 0.4

Cement 510 510 510

2.2. Testing.

Static loading test was conducted

using a hydraulic machine under two point

loading. The three linear variable differen-

tial transducers (LVDT) in the actuator was

used to determine the mid-span displace-

ment whilst the load cell indicated the ap-

plied and the load test set-up for beams as

shown in Fig. 3. The cracking of the beams

was marked by numbering all the cracks

and their location.

3. RESULTS AND DISCUSSION

Fig. 6 and Fig. 7 illustrate the load

deection curves of the ve beams. Fig.

6 depicts the load deection curve for full

shear reinforcement with 0 kg/m³, 10 kg/

m³ and 20 kg/m³ amount of kenaf ber. It

could be observed from the load- deec-

Figure 5. Main reinforcement

arrangement & dimensions of the

beam

Figure 4. Loading arrangement and dimensions of the beam

Figure 3 Test set-up

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KAIWAAN, et al. - Structural Behavior of Kenaf Fibre Reinforced Concrete Beams. pp. 89-95 ISSN:1390-5007

tion curves, that the beam without bers

failed at a deection of 8mm and at a load

carrying capacity of 80 kN. On the other

hand, beam with 10 kg/m³ and 20 kg/m³

failed at a deection of 18 mm with a load

carrying capacity of 100 kN, whilst for the

deection of 20 mm, the load carrying ca-

pacity is 107 kN. The load deection curve

demonstrates signicant increase at load

carrying capacity of beam. Moreover, the

beams with reduced shear arrangement

and with 20 kg/m³ failed at a deection of

18 mm and load carrying capacity of 88

kN which suggests a good improvement

in the load carrying capacity by adequate

amount of kenaf ber.

The results from the load deec-

tion curves of Fig. 6 and Fig. 7 are summa-

rized in Table 2 and Table 3, respectively.

Where P

max

characterizes the maximum

strength, P

max,0

characterizes the maxi-

mum strength of the control beam, P

the

ultimate strength, δ

the yield deection, δ

the ultimate deection, μ the ductility and

, the amount of kenaf ber. Table 2 sug-

gests that the peak strength of the beam is

increased to up to 25% for Wk = 10 kg/m³

and 34% for Wk = 20 kg/m³ respectively.

The Table 3 shows that the peak strength

of the beam is reduced in shear reinforce-

ment with 10 kg/m³ shows a 1% increase

in P

max

as compared to the control beam

whist for the 20 kg/m³ kenaf ber, 9%.

However, with reduced shear links dem-

onstrates the potential for kenaf bers to

enhance peak strength to up to 9%.

TABLE 2. Results for beams with full shear

reinforcement

(* this ratio represents the change in maximum

strength, † this ratio represents the change in

residual strength, ‡ this ratio represents the

change in ductility)

(kg/m³) 0 10 20

Max

(KN) 80 100 107

Max

Max,0

* 1 1.25 1.34

(KN) 74 102 116

/PMax† 0.9 1.275 1.45

(mm) 6 12 12

(mm) 8 18 20

μ=δ

/ δ

‡ 1.3 1.5 1.67

TABLE 3. Results for reduced shear

reinforcement beams

(* this ratio represents the change in maximum

strength, † this ratio represents the change in

residual strength, ‡ this ratio represents the

change in ductility)

(kg/m³) 10 20

Max

(KN) 70 88

Max

Max,0

* 1.01 1.09

(KN) 76 78.8

/PMax† 1.085 0.98

(mm) 10 12

(mm) 18 24

μ=δ

/ δ

‡ 1.8 2

Figure 6. Load-deection curves for RC beams with full shear

reinforcement.

Figure 7. Load-deection curves for RC beams with reduced

in shear reinforcement.

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The result obtained opines that the

ber acts appropriately in controlling the

crack propagation of the beams. Presence

of the bres bridge the crack opening, thus

higher load is required to produce similar

deection with the control beam. As the

load increases, more cracks formed in the

KFRC beam. Eventually, the ber starts to

pull out from the matrix which consequent-

ly drops the load carrying capacity. Fail-

ure of the control beam (beam with 0 kg/m³

and full shear reinforcement) occurred

due to the formation of a single crack led

to shear failure of the beam as shown in

Fig. 8. Therefore, bres serve potential

as part of shear reinforcement, which

in turn changes the mode of failure from

brittle (beam without bres) to a more duc-

tile manner (beam with bres). All KFRC

beam have exural cracks distributed over

the entire section of maximum and con-

stant bending moment as shown in Fig. 9,

Fig. 10, Fig. 11 and Fig. 12. The two beams

with normal spacing and with 10 kg/m³

and 20 kg/m³ kenaf ber show high mul-

tiple cracking behaviours than other two

beams with increased spacing. Cracks

widths were measured at every load inter-

val and the crack formations were marked

on the beams. It was observed that the rst

crack constantly appears close to the mid-

span of the beam. The cracks forming on

the surface of the beams were mostly verti-

cal, suggesting failure in exure with KFRC

beams. By enhancing the ber amount the

number of crack increased, and show mul-

tiple cracking failure. It was also observed

that for KFRC beams, the crack widths at

service load were below the maxi- mum al-

lowable value as conformed by Erocode2

for durability requirements.

In this study, the ductility (μ) was

investigated and presented in Table 2

and Table 3. The ductility ratio is taken

in terms of µ=δ

/δ

, which is the ratio of

ultimate to rst yield deection, where

is the deection at ultimate load and

is the deection when steel yields. In

general, high ductility ratios indicate that

a structural member is capable of under-

going large deections prior to failure.

In this investigation adequate ductility is

observed for both beams shear arrange-

ment. The Fig. 6 and Table 2 show ductil-

ity increased up to 50% for Wk = 10 kg/m³

and 67% for Wk= 20 kg/m³ with full shear

reinforcement. Furthermore, signicant in-

crease in the ductility with reduced shear

reinforcement 80% for Wk = 10 kg/m³

and 100% for Wk = 20 kg/m³ as shown

in Fig. 7, and Table 3. This demonstrates

that with the addition of the bers facili-

tates ductile mode of failure.

Figure 8. RC beam with full shear reinforcement without bres

Figure 9. RC beam with full shear reinforcement,10kg/m³ kenaf ber

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4. CONCLUSION

Based on the nding of this study, it

can be concluded that the addition of kenaf

ber consistently enhances the load car-

rying capacity, ductility, and changes the

mode of failure of RC beams from brittle to

ductile manner. This shows that there are

clear benets of adding kenaf bres at both

serviceability and ultimate limit state which

are important for design consideration. The

study indicates that in order to maintain the

workability of the KFRC requires the use of

a cement rich mixture. Furthermore, super-

plasticizer should be added to account for

water absorbed by the bres and to main-

tain the workability of the fresh KFRC. Ke-

naf ber exhibits the ability to control crack

opening and reduce the crack width con-

siderably as compared to RC beam with-

out bres. As sufcient amount of ber was

added the load carrying capacity, ductility

were increased at certain point. The differ-

ence in capacity of the beams with 20 kg/

m³ amount of kenaf ber was signicantly

larger than the difference of the beams with

low kenaf ber 10 kg/m³).

• Kenaf bre showed favourable con-

tribution in improving the strength

and P

max

) and ductility as well

as changing the mode of failure of

NRC beams. The addition of ber at

Vf = 2 % into the beam with SI = 0 %

demonstrates the increase in streng-

th of P

and P

max

up to 31 % and 37 %,

respectively.

• It is also observed that the ductility

ratio is increased; nonetheless only a

certain limit of bre inclusion should

be observed as the inclusion beyond

this limit exhibits poor ductility.

• Mode of failure of beams with an

adequate amount of ber changed

from shear to bending as illustrated

by the beam with SI = 100 % added

ber at Vf = 2 %.

• Cracking pattern indicated that with

a sufcient quantity of ber the mode

Figure 11. RC beam reduced shear reinforcement with 10kg/m³

Figure 12. RC beam reduced shear reinforcement with 20kg/m³

Figure 10. RC beam full shear reinforcement with 20kg/m³

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of failure of beams changes from

shear to bending as illustrated by

adding a minimum bre of Vf = 1 %

Vf = 1.5 % and Vf = 2 % into the

beams with SI = 0 %, SI = 50 % and

SI = 100 % respectively

ACKNOWLEDGMENT

This study is partly funded by the

Ministry of Higher Education, Afghanistan

and University Malaysia Pahang, Malay-

sia, under internal research grant number

RDU 1203108.

5. REFERENCES

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Renewable resource based “all green

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Saee, S., Ishak, Z. A. M., & Abu Bakar,

A. (2011). Kenaf ber reinforced compo-

sites: A review. Materials & Design, 32(8–

9), 4107–4121.

Udoeyo, F. F., & Adetifa, A. (n.d.). cha-

ractristic of kenaf ber reinforced mortar

composite

Lewis, G., & Premalal, M. (1979). Natural

vegetable bres as reinforcement in ce-

ment sheets. Magazine of Concrete Re-

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R. Nicole, “Title of paper with only rst

word capitalized,” J. Name Stand. Ab-

brev., in press.

Zhang, J., Stang, H., & Li, V. C. (2001).

Crack bridging model for bre reinforced

concrete under fatigue tension. Internatio-

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Mohsin, S., Maszura, S., Azimi, S. J., &

Namdar, A. (2014, August). Behaviour of Oil

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