Page 1 of 5

European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online:https://ejbss.org/ P a g e | 813

Flexural behavior of concrete prismsconfined

With FRP composites

P. RAJENDRAN

DEPARTMENT OF CIVIL ENGINEERING

PRIST (Deemed to be University), THANJAVUR.

ABSTRACT

The main objective of this study was to develop a nonferrous hybrid reinforcement system for

concrete bridge decks by using continuous fiber-reinforced polymer (FRP)rebars and discrete

randomly distributed polypropylene fibers. This hybrid system hasthe potential to eliminate

problems related to corrosion of steel reinforcement whileproviding requisite strength,

stiffness, and desired ductility, which are shortcomingsof the FRP reinforcement system in

reinforced concrete structures. The overall study plan includes (1) development of design

procedures for anFRP/FRC hybrid reinforced bridge deck system; (2) laboratory studies of

static andfatigue bond performances and ductility characteristics of the system; (3)

accelerateddurability tests of the hybrid system; and (4) static and fatigue tests on full-scale

hybrid reinforced composite bridge decks. This paper presents the results relating to the

flexural behavior of the polypropylene-fiber-reinforced-concrete beams reinforcedwith FRP

rebars. Test results indicated that with the addition of fibers, the flexuralbehavior was

improved with an increase of ductility index by approximately 40% ascompared to the plain

concrete beams. Crack widths of FRP/FRC were found to besmaller than those of FRP/plain

concrete system and the values predicted by thecurrent ACI 440 equations. Furthermore, the

compressive failure strains of concrete inFRP/FRC beams exceed thestrain of 0.0040

mm/mm.

INTRODUCTION

Fibre reinforced concrete (FRC) has been

widely used for industrial pavements and

small (non-structural) precast elements or

sprayed in tunnels. Besides the

nonstructural elements (pipes, culverts and

other small components), fibre

reinforcementis particularly appealing for

large structural elements. Here steel

fibresmay besuccessfully adopted in

Page 2 of 5

European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online:https://ejbss.org/ P a g e | 814

substitution, at least partly, of the

conventional reinforcement(bars or welded

mesh) to reduce labour costs (since the

conventional reinforcement is placed

manually).

However, the full potential of fibre

reinforced concrete is still not fully

exploited inpractice. This is mainly due to

a lack of specific rules of fibre reinforced

concrete in building codes. In fact, the

existing rules for conventional concrete

can hardly be adopted for fibre reinforced

concrete that is markedly nonlinear since

fibres start working after cracking of the

concrete matrix. While conventional

reinforced concrete keeps a reasonable

linear behaviour until the bars yield, fibre

reinforced concrete has a noticeable

nonlinear response and, depending on the

fibre reinforcement (content and type),

fibre reinforced concrete has a quite

complicated post-cracking softening

behaviour.

Ductility is a structural design requirement

in most design codes. In steel RC

structures, ductility is defined as the ratio

of post yield deformation to yield

deformation which it usually comes from

steel. Due to the linear-strain-stress

relationship of FRP bars, the traditional

definition of ductility cannot be applied to

structures reinforced with FRP

reinforcement. Several methods, such as

the energy based method and the

deformation based method have been

proposed to calculate the ductility index

for FRP reinforced structures.

Due to the linear elastic behavior of FRP

bars, the flexural behavior of FRP

reinforcedbeams exhibits no ductility as

defined in the steel reinforced structures. A

great dealof effort has been made to

improve and define the ductility of beams

reinforced withFRP rebars. To date, there

are two approaches; one approach is to use

the hybrid FRPrebars; that is, pseudo- ductile materials are fabricated by

combining two or moredifferent FRP

reinforcing materials to simulate the

elastic-plastic behavior of the steelrebars.

Belarbi, Chandrashekhara and Watkinsand

Harris, Somboonsong, and Kotested beams

reinforced with the hybrid FRP reinforcing

bars and they found that the ductility index

of those beams could be close to that of the

beams reinforced with steel. This method

has shown some success in the research

studies but has resulted in limited practical

applications because of the complicated

and costly manufacturingprocess of the

hybrid rebars. The other approach is to

Page 3 of 5

European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online:https://ejbss.org/ P a g e | 815

improve the property ofconcrete. ACI 440

recommends the FRP reinforced structures

be over-reinforced anddesigned so that the

beams fail by concrete crushing rather than

by rebar rupture.

Thus, the ductility of the system is

strongly dependent on the concrete

properties.

Alsayed and Alhozaimy found that with

the addition of 1% steel fibers, the

ductilityindex can be increased by as much

as 100%. Li and Wang reported that the

GFRPrebars reinforced with engineered

cementitious composite material showed

muchbetter flexural behaviors. The

ductility was also found to be significantly

improved.

This work presents research result on the

flexural behavior of concrete beams

reinforced with FRP rebars and concrete

containing polypropylene fibers. The

different behaviors of plain concrete

beams and FRC beams are also discussed.

EXPERIMENTAL PROGRAM

A total of 12 beams making 6 testing

groups were investigated. Each testing

group was composed of two similar

beams, one subjected to monotonic

loading and the other subjected to repeated

loading/unloading. The experimental

variables included FRP rebar size (#4 vs.

#8), rebar type (GFRP vs. CFRP), and

plain concrete vs. FRC.

Materials

FRP Rods--three types of commonly used

FRP rods were adopted in this study:

namely the #8 (25mm) glass fiber

reinforced polymer (GFRP), #4 (13 mm)

GFRP, and #4 (13mm) carbon fiber

reinforced polymer (CFRP). The surface

of the GFRP rods is tightly wrapped with a

helical fiber strand to create indentations

along the rebar, and sand particles are

added to the surface to enhance itsbonding

strength. For the #4 GFRP, the pitch of the

fiber strand is about 25.4 mm andhelically

rounded about 60 degrees to the

longitudinal direction. For the #8 GFRP,

thepitch of the fiber strand is 22 mm and

helically rounded about 75 degrees to the

longitudinal direction. The surface of the

CFRP is very smooth. The resin used for

these bars is epoxy modified vinyl-ester

for both GFRP rebar andCFRP rebar.

Based on the information provided by the

manufacturer, the ultimatetensile strengths

for #4 GFRP, #8 GFRP and #4 CFRP are

690 MPa, 552 MPa, and2,069 MPa,

respectively. The elastic moduli are 41

GPa, 41 GPa, and 124 GParespectively.