R. MOHANRAJ et al.: MECHANICAL PROPERTIES OF RC BEAMS WITH AFRP SHEETS UNDER A SUSTAINED LOAD
365–372
MECHANICAL PROPERTIES OF RC BEAMS WITH AFRP SHEETS
UNDER A SUSTAINED LOAD
MEHANSKE LASTNOSTI BETONSKEGA NOSILCA OJA^ANEGA
S PLETIVOM AFRP POD STALNO OBREMENITVIJO
R. Mohanraj
1*
, S. Senthilkumar
2
, P. Padmapoorani
2
1
Civil Engineering, Excel Engineering College, NH544 Salem Main Road, Komarapalayam, Namakkal, Tamilnadu 637303, India
2
Civil Engineering, KSR College of Engineering, KSR Kalvi Nilayam, Thiruchengode, Namakkal, Tamilnadu 637215, India
Prejem rokopisa – received: 2022-04-22; sprejem za objavo – accepted for publication: 2022-05-16
doi:10.17222/mit.2022.481
In this research, an attempt was made to find the permeability of an RC beam with AFRP by making use of the hydraulic con-
ductivity test and a double-ring infiltrometer. Based on the state-of-the-art methodology, three different AFRP samples, Kelvar
29, Kelvar 49 and Kelvar 149, were considered as the laminates to prevent the deflection of the beams. Accelerated corrosion
was carried out using impressed current, and induced corrosion was calculated using the galvanostatic method. In this project,
nine RCC beams were strengthened with aramid FRP sheets. Novel results were obtained using three different layers and three
different patterns of AFRP sheets. Experimental investigation showed that the mechanical properties of the reinforced concrete
beams were enhanced (by 10 %) with Kelvar 149. The durability and corrosion resistance of concrete were achieved due to the
increased number of layers of the AFRP sheet. The entire research shows that three layers of Kelvar 149 allow better perfor-
mance of the concrete specimens. No other results based on the abrasion resistance and hydraulic conductivity of beams with
AFRP laminates are available in the literature.
Keywords: aramid fiber reinforced polymer, kelvar laminates, hydraulic conductivity test, reinforcement corrosion
V raziskavi so avtorji na za~etku posvetili pozornost ugotavljanju prepustnosti (permeabilnosti) oja~anega betonskega nosilca
(RC), ki so ga pred tem oja~ali s polimernimi vlakni iz Aramida (AFRP; angl.: Aramid Fiber Reinforced Polymer). Preizkuse
prepustnosti so izvajali s hidravli~nimi testi prevodnosti in infiltrometrom z dvojnim obro~em. Za preiskave so uporabili tri
razli~ne danes najnaprednej{e vzorce AFRP in sicer Kelvar 29, Kelvar 49 in Kelvar 149 kot laminate za re{itev pove~anja
odpornosti nosilca proti zvijanju. Izvajali so tudi pospe{ene teste korozije z njihovim obremenjevanjem z elektri~no napetostjo
in tokom ter na njihovi osnovi izra~unali inducirano korozijo z uporabo galvanostati~ne metode. Za raziskavo so uporabili devet
RCC nosilcev oja~anih z AFRP. Nov pristop in rezultat so dosegli s tremi razli~nimi plastmi in tremi razli~nimi vzorci pletenja
laminatnih polnil AFRP (pletenih tankih plo{~). Eksperimentalne raziskave so pokazale, da so se mehanske lastnosti oja~anih
betonskih nosilcev izbolj{ale za 100 % pri uporabi laminatov iz Kevlarja 149. Trajnost in odpornost betona proti koroziji se je
pove~ala s pove~evanjem {tevila plasti laminata AFRP. Raziskava je pokazala, da tri plasti laminata iz Kevlarja 149 mo~no
izbolj{ajo lastnosti betonskih vzorcev. V literaturi avtorji niso na{li podatkov o abrazijski odpornosti in hidravli~ni prevodnosti
betonskih nosilcev oja~anih z laminati AFRP.
Klju~ne besede: aramidna vlakna, polimer, kelvar, test hidravli~ne prevodnosti, korozija
1 INTRODUCTION
The durability of concrete is a potential problem gov-
erned by several factors such as low compressive
strength, high chance of clogging and low abrasion resis-
tance under dynamic loading.
1
The use of FRP compos-
ites to strengthen reinforced-cement-concrete (RCC)
beams is becoming increasingly common.
2
For many
reasons, aramid fiber reinforced polymer (AFRP) is
more convenient than steel. The usage of advanced fiber
reinforced polymer/plastics (FRP) composites for rein-
forced concrete beams has grown in popularity in recent
years.
3
This is because the structure:
• may require alteration due to aging,
• corrosion in steel induced by exposure to a hostile en-
vironment may cause it to deteriorate,
• may require strengthening to withstand accidental
loads such as earthquakes, etc.
4
Flexural failure and shear failure are the two impor-
tant failure modes in any flexural member. The former is
a ductile failure and the latter is a brittle failure.
5,6
A duc-
tile failure distributes the stress and alerts the occupants,
whereas a brittle collapse occurs suddenly and is conse-
quently disastrous.
7,8
To strengthen flexural members
against a brittle failure, different strengthening tech-
niques/materials are commonly adopted.
FRP is one of the strengthening materials recom-
mended, instead of steel, for several reasons.
9
Compared
to steel, the FRP material has higher ultimate strength
and lower density, as well as being easier to install and
requiring no interim support until it reaches its full
strength.
10
This material can be easily shaped into com-
plex shapes and cut to the desired length on the job site.
Fibers are normally classified as GFRP, CFRP and
AFRP.
11,12
From a structural standpoint, FRP is primarily
used in two areas. The first is the use of FRP
Materiali in tehnologije / Materials and technology 56 (2022) 4, 365–372 365
UDK 625.843:620.194 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 56(4)365(2022)
*Corresponding author's e-mail:
rsrirammohan@gmail.com

sheets/plates to reinforce structural components using
externally applied FRP.
13
The focus here is on potential
enhancement of the toughness and durability provided by
synthetic macro-fibers, which helps us to develop new
applications of AFRP.
14
Steel has a stronger ultimate
strength but a lower density than aramid FRP, as well as
being easier to install and requiring no interim support
until it reaches its full strength.
Among the above fiber polymers, aramid fiber rein-
forced polymer is interesting and challenging when used
for improving mechanical and corrosion resistance of
concrete specimens.
15–17
However, expanding its use be-
yond the lime-based concrete in historical buildings to
commercially available goods would help us to better
comprehend its potential in its current applications.
Therefore, in this research, aramid fiber reinforced poly-
mer was used for laminated sheets in fresh and hardened
concrete to evaluate the durability and corrosion resis-
tance of concrete.
2 EXPERIMENTAL PART
2.1 Materials
Portland Pozzolana cement of 53 grade was used in
this investigation. The cement was tested as per IS 2720
Part-3. Fine aggregate (FA) for the experimental exami-
nation was obtained locally and used in accordance with
IS: 383-1970. Coarse aggregates are manufactured from
stones by breaking them. A 20 mm aggregate (max.), lo-
cally available for our work, suited the nature of our op-
eration.
18
Coarse aggregates (CAs) were examined in ac-
cordance with the Indian Standard Specifications,
IS:2386-1963. Steel bars of grade Fe 415 (HYSD) with
6-mm, 8-mm and 12-mm diameters were used.
12-mm-diameter bars were utilized as the tension rein-
forcement, while 8-mm-diameter bars were employed as
hanger bars. 6-mm-diameter bars were utilized as shear
stirrups. The cement, sand and coarse-aggregate proper-
ties are displayed in Table 1. Aramid fibers, known un-
der their trademark name Kevlar, have unique and bene-
ficial properties. The brand name Kevlar is owned by
DuPont.
19
Poly-paraphenylene terephthalamide was the
chemical name for Kevlar when it was first developed in
the 1960s.
20
Kevlar has idiosyncratic properties such as
excellent impact resistance and low density.
21
The three
different patterns of the AFRP sheets used in this study
and their properties are listed in Table 2. Kelvar 29 has a
knitted mesh reinforcement shape, Kelvar 49 has a
chicken mesh reinforcement shape, and Kelvar 149 has a
honeycomb reinforcement shape, shown in Figures 1a to
1c.
Table 1: Physical properties of the materials
Physical property Cement FA CA
Specific gravity 3.13 2.66 2.76
Fineness modulus (%) 2.32 3.71 7.42
Water absorption (%) – 0.6 0.5
Consistency (%) 30.5 – –
Initial setting time (min) 34 – –
Final setting time (h) 10 – –
Table 2: Properties of different AFRP sheets
AFRP
patterns
Density
(g/cm
3
)
Tensile strength
(MPa)
Modulus
(GPa)
Kelvar 29 1.44 2920 83
Kelvar 49 1.44 3600 124
Kelvar 149 1.47 3450 174
2.2 Hydraulic conductivity
This is a property that permits fluids to flow through
interconnecting voids, and can be measured in terms of
permeability (k) and infiltration (I). Here, permeability
was measured with a constant head permeameter, and in-
filtration with a double ring infiltrometer.
2.3 Abrasion-resistance test methods
These test methods were used to determine the ravel-
ing resistance (ASTM C1747) and surface wearing
(ASTM C944). A Los Angeles abrasion-test apparatus
was used to determine the toughness and raveling index,
and a rotating-cutter drill press was used to determine
the disintegration and degradation. Cylindrical samples
with a diameter and height of 100 mm were used in these
tests.
R. MOHANRAJ et al.: MECHANICAL PROPERTIES OF RC BEAMS WITH AFRP SHEETS UNDER A SUSTAINED LOAD
366 Materiali in tehnologije / Materials and technology 56 (2022) 4, 365–372
Figure 1: Kevlar patterns: a) Kelvar 29, b) Kelvar 49, c) Kelvar 149

2.4 Flow index
The flow index is a direct measure of the workability
of a freshly prepared concrete mix.
22
The effects of the
change in the aggregate size and change in the fiber
length on the consistency of the flow percentage are
demonstrated in detail in Table 3. The consistency in the
flow percentage of a fresh concrete mix was inversely
proportional to the aggregate size, i.e., the flow index in-
creased with a decrease in the aggregate size. The flow
index of a given fresh concrete mix was also inversely
proportional to the fiber length, i.e., the flow index de-
creased with an increase in the fiber length. The elevated
values of the flow index observed for the aramid-fi-
ber-reinforced polymer mix were high due to the addi-
tion of a viscosity-modifying agent: Eucoplacant-721.
Table 3: Flow index values
Mix ID Conventional
Concrete with
AFRP
Flow (%) 98 111
3 RESULT AND DISCUSSION
3.1 Compressive tests on concrete cubes
As per IS 10262:2009,
12
concrete mix proportions for
M40 grade were designed. This ratio determined the de-
sign procedure using the properties of the materials.
A mix ratio of 1 : 1.01 : 2.92 (cement : FA : CA) was ob-
tained based on the mix design method.
23–25
The
water-cement ratio for this design was 0.41. The com-
pressive test results are shown in Table 4.
Table 4: Compressive tests on concrete cubes
Test
specimen
Grade of
concrete cube
Compressive
strength after
28 d (N/mm
2
)
Average com-
pressive
strength
(N/mm
2
)
1M 40
43.67
43.40 2M 40
42.38
3M 40
44.16
3.2 Hydraulic conductivity
3.2.1 Permeability
Permeability (k) of cylindrical samples was tested, as
shown in Figure 2a, using Equation (1). The samples
were subjected to a vacuum wash before testing to get
more accurate results.
k
QL
Ah t
=
Δ
(1)
Here, Q is the volume of discharge (m
3
), L is the
specimen length (0.1 m), A is the cross-sectional area of
the cylinder (m
2
), h is the water head (m), and  t is the
time interval (s).
R. MOHANRAJ et al.: MECHANICAL PROPERTIES OF RC BEAMS WITH AFRP SHEETS UNDER A SUSTAINED LOAD
Materiali in tehnologije / Materials and technology 56 (2022) 4, 365–372 367
Figure 2: Test set-up for measuring permeability (k) and infiltration rate (I): a) constant head permeameter, b) double ring infiltrometer

3.2.2 Infiltration
Infiltration (I) testing required two cylindrical rings,
one with a diameter of 300 mm (the inner cylinder) and
the other with a diameter of 600 mm (the outer cylinder)
placed over the slab specimen with a length of 1000 mm
and depth of 100 mm as shown in Figure 2b. Initially,
water was poured into the cylinder and then the rapidity
of infiltration of the water was noted using the scale at-
tached, determining the time and depth of the infiltration
into the slab specimen using Equation (2). The values of
the infiltration rate are given in Table 5.
I
V
Dt
i
=
4
2
πΔ
(2)
Here, V is the volume (m
3
) of water added in time  t,
D
i
is the diameter of the inner cylinder and  t is the time
interval (s).
3.3 Accelerated corrosion test and calculation
Corrosion of the reinforced steel was carried out us-
ing the impressed current technique. Beams of 1 m in
length and with a cross-section of 150 mm × 200 mm
were cast for each optimum AFRP mix and the control
mix (the total of 10 samples). The tension reinforcement
was wound with wires at two points so that uniform cor-
rosion was initiated in the rebars.
26
Only the corrosion of
the tension reinforcement was considered for the study.
The test set-up for accelerated corrosion is shown in Fig-
ure 3.
The impressed current technique, applying direct cur-
rent constantly to the steel embedded in the concrete for
a short period, allowed accelerated corrosion, which was
later observed on the steel after inducing electrolytes in
the concrete. The rate of corrosion was accelerated
through the concrete with the help of electrolytes (3 % of
sodium chloride solution). For the provided power sup-
ply, the induced corrosion was determined using
Faraday’s law. If the source current was increased, the
rate of accelerated corrosion was also increased. The
amount of weight loss of steel was calculated using a
gravimetric test, determining the weight loss during cor-
rosion. The source which consisted of an anode and a
cathode was connected to the steel bars and the counter
electrode – stainless steel plates, respectively. The rein-
forcements fabricated for the corrosion acceleration test
are shown in Figure 4.
Current readings were noted every hour using a
multimeter and the average current reading was used in
the calculation as the applied current (I
app
). The beams
were kept in the acceleration corrosion process for 120 h.
Lead wires were connected at two points of each tension
reinforcement to ensure uniform corrosion throughout
the beam. Only the corrosion of the tension reinforce-
ment was considered.
After generating corrosion on the beams, the bars
were retrieved from the beams by fracturing the concrete
and measured using the gravimetric test to determine the
average loss of steel due to induced corrosion. To remove
any rust products, the bars were cleaned using chemical
cleaning and weighed to calculate the steel net weight.
R. MOHANRAJ et al.: MECHANICAL PROPERTIES OF RC BEAMS WITH AFRP SHEETS UNDER A SUSTAINED LOAD
368 Materiali in tehnologije / Materials and technology 56 (2022) 4, 365–372
Figure 3: Accelerated corrosion set-up
Table 5: Hydraulic conductivity test result
Concrete mix k/(cm/s)
Coefficient of variance
(%)
I/(cm/s)
Coefficient of variance
(%)
Conventional 1.31 23.1 0.30 2.3
AFRP concrete 1.12 10.0 0.32 14.6
Figure 4: Reinforcement for the corrosion acceleration test

Following ASTM G-1-90 (ASTM, 1990), the corrosion
test specimens were prepared, cleaned and evaluated.
For the current capacity of the circuit, the current ap-
plied to the fiber specimens was found to be lower than
that of the control specimens.
From Table 6, it can be understood that the conduc-
tance of the fiber specimens was lower compared to the
control specimens, which in turn indicates higher poros-
ity of the control specimens. Thus, it can be concluded
that the fiber has a higher corrosion resistance and it can
effectively be used in an aggressive environment. The
mass loss percentages of the fiber specimens were found
to be lower than that of the control mix without fiber.
In accordance with Faraday’s law, the theoretical
mass of rust (M
th
) was determined with Equation (3):
M
WI T
F
th
app
= (3)
where M
th
is the theoretical mass of rust or mass loss
(g), W is the equivalent weight of steel (27.925 g), I
app
is
the current applied (A), T is the period of induced corro-
sion (s) and F is Faraday’s constant (96487 As).
After the corrosion test, the specimens and rebars
were extracted by breaking the concrete. In accordance
with the gravimetric test (ASTM G1), the actual mass
(M
ac
) of rust was calculated with Equation (4):
M
WW
DL
i
ac
f
=
−
π
(4)
where W
i
is the initial weight of the rebar, W
f
is the
weight of the rebar after corrosion, D is the diameter of
the rebar and L is the length of the rebar.
Assuming that the actual and theoretical mass of rust
were equal (i.e., I
corr
= I
app
) and by equating M
ac
and M
th
,
the equivalent corrosion current (I
corr
) was calculated
with Equation (5):
I
WWF
WT
i
corr
f
=
− ()
(5)
Where,
W
i
– Initial Weight
R. MOHANRAJ et al.: MECHANICAL PROPERTIES OF RC BEAMS WITH AFRP SHEETS UNDER A SUSTAINED LOAD
Materiali in tehnologije / Materials and technology 56 (2022) 4, 365–372 369
Table 6: Accelerated corrosion test results
Beam ID
No. of
Layer
Average I
app
(A)
Initial weight
(g)
Final weight
(g)
Actual weight
loss (g)
Theoretical
weight loss (g)
Actual weight
loss (%)
Conventional – 1.02 2823 2703 120 126.56 4.22
B FRP K29 1 1.19 2858 2665 193 150.11 5.06
B FRP K29 2 1.57 2836 2657 179 97.84 6.24
B FRP K29 3 0.81 2860 2782 78 102.14 2.80
B FRP K49 1 0.73 2835 2767 68 89.60 2.40
B FRP K49 2 0.75 2808 2733 75 95.05 2.67
B FRP K49 3 0.76 2841 2764 77 95.67 2.71
B FRP K149 1 0.77 2853 2775 78 93.63 2.77
B FRP K149 2 0.87 2851 2766 85 107.69 3.02
B FRP K149 3 0.87 2861 2775 86 107.38 3.07
Figure 5: a) Reinforcement details of a beam, b) cross-section of a beam, c) beam failure

W
f
– Final Weight
F – Faraday Constant
W – Equivalent weight of steel
T – The period of induced corrosion
The percentage weight loss (P) was calculated with
Equation (6):
P
WW
W
i
i
=
−
f
× 100 % (6)
3.4 Tests with beams
3.4.1 Experimental work
This experimental task entailed casting M40 rein-
forced concrete (RC) beams with cross-sectional dimen-
sions of (150 × 200 × 1000) mm. Two of 12 mm diame-
ter were placed at the base, at a 160-mm center-to-center
distance, with the top having  2–8 mm and  6mmver -
tical stirrups.
27,28
Single, double and triple-layer AFRP
were three alternative patterns and layer combinations
used to strengthen the beams utilizing AFRP sheets.
29
Totally, ten reinforced concrete beams were cast and kept
in water for curing for 28 d.
3.4.2 Experimental set-up
All the specimens were put through their paces in the
loading frame, and the deflection was measured with a
linear variable differential transformer (LVDT) ma-
chine.
30
They were subjected to the same testing proce-
dures. After the 28-d cure time, the beams had three lay-
ers and three patterns, there were also conventional
beams. The load arrangements for evaluating all sets of
beams included two-point loading, and reinforcement de-
tails are shown in Figures 5a and 5b. The testing of a
beam is shown in Figure 5c.
3.4.3 Beam specification
The length of a beam was 1000 mm, its span was
800 mm, its width was 150 mm, its depth was 200 mm
and the numbers of layers were specified as shown in
Table 6.
3.4.4 Beam results
The performance of the specimens under load was
noted. It was discovered that, with the growing load, the
cracks additionally began to show up, constantly increas-
ing. A few cracks went throughout the beam. The crack
pattern was also noticed. The values of load and deflec-
tion for various volumes of Kelvar 29 and conventional
concrete were examined and listed in Table 7.
Table 7: Deflection of conventional concrete and Kelvar 29
Load
(kN)
Deflection (mm)
Conventional
concrete
Single
layer
Double
layer
Triple
layer
00000
50 0.112 0.090 0.050 0.025
100 1.730 1.001 0.800 0.475
150 4.192 3.002 2.182 1.290
It is seen that the bend followed a straight pattern un-
til the first break load. With the additional increase in
load, numerous cracks were formed, the number of
which increased as a certain load was reached. The out-
comes obtained show improved primary conduct, like
that of FRP. If the number of layers increased, the deflec-
tion against the load decreased.
The values of load and deflection for various volumes
of Kelvar 49 and Kelvar 149 were analyzed, and their
properties are listed in Table 8 and Table 9.I ti sp e r -
ceived that the bend followed a straight pattern until the
first break load. With the additional increase in load, nu-
merous cracks were formed, the number of which in-
creased as a certain load was reached.
Table 8: Deflection of Kelvar 49
Load
(kN)
Deflection (mm)
Single layer Double layer Triple layer
0000
50 0.0925 0.066 0.039
100 1.115 0.978 0.575
150 3.125 2.264 1.390
Table 9: Deflection of Kelvar 149
Load
(kN)
Deflection (mm)
Single layer Double layer Triple layer
0000
25 0.030 0.017 0.005
50 0.046 0.037 0.015
75 0.280 0.230 0.130
100 0.560 0.548 0.292
125 1.890 0.880 0.520
150 1.625 1.264 0.800
4 CONCLUSIONS
The outcomes obtained show an increase in the
strength with the increasing the number of layers. The
deflection against load was lower for three-layer Kelvar
49 and 149. The physical properties of the materials, hy-
draulic conductivity, flow index, compressive strength of
a concrete cube were tested on the beams and the results
obtained are presented.
The aggregate size and fiber length were inversely
linked to the consistency in the flow percentage of a
fresh concrete mix. The increase in the flow index of
aramid concrete compared to the conventional mixes was
due to the addition of a viscosity modifying agent. The
addition of macro-synthetic fibers reduced the perme-
ability and infiltration rate of the test samples. This was
observed to be most significant for a high dosage of long
fibers. The infiltration rate was about 5 times lower com-
pared to the permeability values for the other mixtures.
Concrete mixes containing fiber showed a higher
value of compressive strength than the conventional con-
crete. The maximum increase in the compressive
strength of 22.08 % was obtained for the Kelvar 149 con-
R. MOHANRAJ et al.: MECHANICAL PROPERTIES OF RC BEAMS WITH AFRP SHEETS UNDER A SUSTAINED LOAD
370 Materiali in tehnologije / Materials and technology 56 (2022) 4, 365–372

crete. Concrete mixes containing fiber showed lower val-
ues of water absorption than the conventional concrete,
hence the plugging of pores was better than in the con-
ventional concrete. The corrosion resistance of the AFRP
concrete specimens was found to be higher than that of
the conventional concrete specimens.
The weight loss percentages were higher for the con-
trol specimens when compared with the fiber concrete
specimens. Based on performance, a triple layer is better
than a double layer or a single layer. It was also observed
that the influence of the fiber length was not as substan-
tial as that of the aggregate size. The effect of the sudden
release technique should be further examined. Additional
research is needed for aramid fiber-reinforced polymer
members with different types of concrete (i.e., light-
weight concrete, high-performance concrete, etc.).
Acknowledgements
This research is supported by Excel Engineering Col-
lege and KSR College of Engineering. The author would
like to thank M/s. Modern Builders Pvt. Ltd. for provid-
ing the strands for this research. The author would also
like to thank a number of individuals at the College
Campus for their contribution to this research.
Declarations of interest
My co-author and I do not have any interests that
might be interpreted as influencing the research. "Con-
flict of interest: none".
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