Y. LUO et al.: EXPERIMENTAL STUDY OF THE CHLORIDE-ION PERMEABILITY OF BAMBOO-FIBER-REINFORCED CONCRETE
239–248
EXPERIMENTAL STUDY OF THE CHLORIDE-ION
PERMEABILITY OF BAMBOO-FIBER-REINFORCED CONCRETE
EKSPERIMENTALNA [TUDIJA PERMEABILNOSTI KLORIDNIH
IONOV V BETONU OJA^ANEM Z BAMBUSOVIMI VLAKNI
Yong Luo
1,2
, Mustafasanie M Yussof
1*
, Yiming Jiang
2
, Zhongwei Peng
2
,
Chaoxing Wu
2
, Fangcheng Shi
3
, Yuepeng Chen
3
1
School of Civil Engineering, Engineering Campus, Universiti Sains Malaysia, Penang, Malaysia
2
Smart construction Engineering Center, Fujian Forestry Vocational Technical College, Nanping, China
3
Department of Civil Engineering and Industrial Design, University of Liverpool, Liverpool, UK
Prejem rokopisa – received: 2023-11-15; sprejem za objavo – accepted for publication: 2024-02-09
doi:10.17222/mit.2023.1049
This study investigated the chloride-ion permeability of C30 concrete by adding bamboo fibers with different treatments (un-
treated, treated with calcium hydroxide solution and treated with sodium hydroxide solution) and different dosages. Three test-
ing methods, namely the electric-flux method, AC test method and the RCM method, were used to characterize the concrete. Pa-
rameters such as electric-flux value, AC resistivity and chloride-ion diffusion coefficient were obtained. Results showed that the
surface impurities of the bamboo fibers treated with calcium hydroxide solution were removed and the thermal stability of the
bamboo fibers was improved, which can effectively enhance the chloride-ion permeability of concrete. Compared to untreated
bamboo fibers, the improvement rate was between 14 % and 17 %. Sodium hydroxide is a strong alkaline solution, which can
easily disrupt the structure of bamboo fibers and reduce the resistance of concrete to chloride-ion penetration. The best chlo-
ride-ion permeability was achieved when the bamboo fiber content reached 2 %. The electric-flux method, AC test method, and
the RCM method were mutually validated with good correlation. It is recommended to choose a suitable and simple method for
testing. Bamboo-fiber concrete lays a solid foundation for the future transformation of the civil-engineering industry.
Keywords: bamboo fibers, microstructure, AC resistivity, chloride-ion diffusion coefficient
V ~lanku avtorji opisujejo raziskavo permeabilnosti kloridnih ionov v betonu vrste C30, kateremu so dodani razli~ni dele`i
razli~no obdelanih bambusovih vlaken (neobdelana vlakna, obdelana v raztopini kalcijevega hidroksida in vlakna obdelana v
raztopini natrijevega hidroksida). Karakterizacijo izdelanih betonov so izvedli s tremi razli~nimi metodami: z metodo
elektri~nega fluksa, metodo z izmeni~nim elektri~nim tokom in RCM metodo. S pomo~jo teh metod so dolo~ili vrednodti
elektri~nrga fluksa, upornost izmeni~nega elektri~nega toka in difuzijski koeficient kloridnih ionov. Rezultati preizkusov so
pokazali, da so bile z obdelavo v raztopini Ca(OH)2 odstranjene povr{inske ne~isto~e bambusovih vlaken. Izbolj{ala se je tudi
termi~na stabilnost bambusovih vlaken, kar je u~inkovito zmanj{alo tudi permeabilnost kloridnih ionov v betonu. V primerjavi z
neobdelanimi bambusovimi vlakni sta se vrednosti izbolj{ali za 14 % oziroma 17 %. Raztopina natrijevega luga (NaoH) je
mo~na alkalna raztopina , ki z lahkoto poru{i strukturo bambusovih vlaken in zmanj{a odpornost betona za penetracijo
(prodiranje) kloridnih ionov. Najbolj{o permeabilnost kloridnih ionov so avtorji dosegli pri dodatku 2 %-ov bambusovih vlaken.
Vse tri uporabljene metode preisku{anja so avtorji uspe{no medsebojno ovrednotili in nato priporo~ajo uporabo najprimernej{e
in najenostavnej{e metode. Temelji oziroma podlage iz betonov oja~anih z bambusovimi vlakni so trdna osnova za prihodnjo
uveljavitev njihove uporabe v industriji gradbeni{tva.
Klju~ne besede: bambusova vlakna, mikrostruktura, upornost izmeni~nega toka, difuzijski koeficient kloridnih ionov
1 INTRODUCTION
China, as a developing country, has experienced rapid
development in science, technology, and construction,
achieving remarkable accomplishments and working to-
wards sustainable development.
1,2
However, due to lim-
ited technological capabilities, there is often a risk of
low-quality construction. To expedite construction prog-
ress, many organizations incorporate chlorides into con-
crete, which exacerbates the phenomenon of structural
damage. With its vast territory and abundant marine re-
sources, China has developed numerous coastal tourist
cities with dense coastal constructions. Chloride ions
from the ocean constantly corrode reinforced concrete
structures, resulting in extensive damage. Additionally,
in the cold winters of northern China, the durability of
bridge roads is compromised due to the use of de-icing
salts over an extended period, leading to increased main-
tenance costs and economic losses.
3
Therefore, it is nec-
essary to study the erosion and damage mechanisms of
chloride ions and enhance the chloride-ion permeability
resistance of hydraulic concrete.
As a natural fiber, bamboo offers the advantages of
being environmentally friendly, widely available, and
low-cost. Adding bamboo fibers to concrete can reduce
its porosity and enhance its resistance to chloride-ion
permeability. Currently, there is a lack of research on
bamboo-fiber-reinforced concrete regarding the chlo-
ride-ion permeability, both domestically and internation-
ally. Scholars have conducted studies on the resistance to
chloride-ion permeability by adding other fibers to con-
crete. Jiang et al.
4
found that polyvinyl alcohol (PVA) fi-
Materiali in tehnologije / Materials and technology 58 (2024) 2, 239–248 239
UDK 625.821.5:676.034.26 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(2)239(2024)
*Corresponding author's e-mail:
cemustafa@usm.my (Mustafasanie M Yussof)

bers can improve the resistance to chloride-ion perme-
ability of cement-based composites, but excessive
content can have adverse effects. Wang et al.
5
studied the
chloride-ion permeability of polypropylene fiber-rein-
forced concrete under dry-wet cycle conditions and
found that incorporating a volume content of 0.1 % of
polypropylene fibers yielded the greatest improvement in
the resistance to chloride-ion permeability. Wang
6
dis-
covered that fibers can enhance the resistance to chlo-
ride-ion permeability of concrete, and the better the
hydrophilicity of the fiber, the more pronounced the en-
hancement effect on the resistance to chloride-ion per-
meability. Liu
7
found that an appropriate amount of hy-
brid fibers (volume content of 0.2 % for polypropylene
fibers and 0.3 % for basalt fibers) can effectively im-
prove the pore structure of concrete. The longer the cur-
ing time of concrete, the more significant the improve-
ment effect on the pore structure. Guo et al.
8
discovered
that the chloride-ion concentration of concrete beams
with basalt fibers is lower than that of beams without ba-
salt fibers, with a peak-concentration reduction of ap-
proximately 1 %. Zheng et al.
9
found that incorporating a
volume ratio of 1.2 % basalt fibers reduced the electric
flux of concrete by 442 C and improved the chloride-ion
permeability rating from low to very low. Fan
10
stated
that the chloride-ion permeability of basalt-fiber-acti-
vated powder concrete can be considered negligible.
When the water-binder ratio is 0.22 and the volume con-
tent of fibers is 0.10 %, the resistance to chloride-ion
permeability of basalt fiber-activated powder concrete is
optimized. Kirthika et al.
11
found that the chloride-ion
permeability rate of ordinary concrete is 49% higher than
that of basalt fiber-reinforced concrete. Niu et al.
12
dem-
onstrated that the diffusion coefficient of chloride ions in
C30, C40, and C50 concrete decreases by 77.8 % when
an appropriate amount of basalt-polypropylene fibers are
added, but an excessive fiber content has adverse effects
on the resistance to chloride-ion permeability of con-
crete.
13–17
In summary, different fibers can enhance the resis-
tance to chloride-ion permeability of concrete. However,
very few studies have been conducted on the durability
of bamboo-fiber concrete at home and abroad. Bamboo
fibers possess advantages that synthetic fibers like basalt
fibers and polypropylene fibers do not have. Bamboo fi-
bers are not only environmentally friendly and beneficial
to physical and mental health but also widely available
and extremely low-cost. Nanping of Fujian is called the
"Hometown of Bamboo" and has a large amount of bam-
boo fiber. They offer an opportunity to utilize the resid-
ual waste from bamboo factories. Bamboo fibers possess
advantages that synthetic fibers like basalt fibers and
polypropylene fibers do not have. The world is empha-
sizing sustainable development.
18,19
Well aligning with
this theme, bamboo fibers are not only environmentally
friendly and beneficial to physical and mental health but
also widely available and extremely low-cost. They offer
an opportunity to utilize the residual waste from bamboo
factories. In this paper, flock-like bamboo fibers are first
subjected to a microscopic analysis by optical micro-
scope and thermal analysis, analyzing their chemical
composition and internal characteristics. Then the bam-
boo fibers treated with different methods (untreated,
treated with calcium hydroxide solution and treated with
sodium hydroxide solution), and at different dosages (0,
0.5 %, 1 %, 1.5 %, 2 %, 2.5 %), will be added to C30
concrete for chloride-ion permeability experiments. The
effects of the treatment method and dosage of the
flock-like bamboo fibers on the resistance to the chlo-
ride-ion permeability of concrete will be determined to
provide theoretical references and practical evidence for
the durability performance of concrete.
20
2 RAW MATERIALS AND RESEARCH
METHODS
2.1 Raw materials
Bamboo fiber: Utilizing the advantage of "bamboo
village" in Nanping City, Fujian Province, China, the
waste bamboo fiber from bamboo factories is used, with
an average fiber age of approximately 3–4 years, about
4 cm long. Put the bamboo fibers into calcium hydroxide
solution and sodium hydroxide solution for 5 min, and
then take them out for use. The bamboo fibers were put
into calcium hydroxide solution and sodium hydroxide
solution for 5 min, which were then taken out for use.
Bamboo fibers were put into the drying oven to dry for
24 h, then taken out and spared.
Cement: The volcanic ash-based Portland Pozzolana
Cement P.P32.5 is mainly composed of Portland cement
clinker, 20–50 % volcanic ash admixture, and gypsum. It
has low heat of hydration, good impermeability, and cor-
rosion resistance, poor frost resistance and heat resis-
Y. LUO et al.: EXPERIMENTAL STUDY OF THE CHLORIDE-ION PERMEABILITY OF BAMBOO-FIBER-REINFORCED CONCRETE
240 Materiali in tehnologije / Materials and technology 58 (2024) 2, 239–248
Figure 1: Flock-like bamboo fiber

tance, high shrinkage, low early strength, and rapid
strength development in the later stages.
Crushed stone: In this experiment, crushed stones
with a particle size of 5–40 mm are used as coarse aggre-
gates. They are required to have a hard texture, clean and
rough surface, and well-graded distribution.
Medium Sand: River sand from Nanping, Fujian
province is selected, and its basic theorical performance
parameters are shown in Table 1.
Table 1: Basic performance parameters of sand
Type
Clay con-
tent (%)
Apparent
density
(kg/m
3
)
Bulk den-
sity
(kg/m
3
)
Void ratio
(%)
Fineness
modulus
Sand 2.0 2521 1514 39.9 2.4
Calcium hydroxide: Food-grade calcium hydroxide
with a purity of 95% in white-powder form is used. An
appropriate amount is dissolved in water and stirred to
obtain a solution of calcium hydroxide.
Sodium hydroxide: Food-grade calcium hydroxide
with a purity of 95% in white powder form is used. An
appropriate amount is dissolved in water and stirred to
obtain a solution of sodium hydroxide.
2.2 Mix design
According to the "Standard for Basic Performance
Test Method of Concrete in Building" (JGJ/T 70-2009),
21
the consistency of the concrete is controlled at a range
from 70 mm to 90 mm, and the apparent density should
be greater than or equal to 1900 kg/m
3
. After trial adjust-
ments, the selected laboratory mix for concrete is shown
in Table 2.
Table 2: Baseline mix for concrete
Cement
(kg/m
3
)
Crushed stone
(kg/m
3
)
Bulk density
(kg/m
3
)
Water
(kg/m
3
)
402 1215 598 185
The untreated bamboo fiber, bamboo fiber treated
with calcium hydroxide solution and bamboo fiber
treated with sodium hydroxide solution were separately
added to the concrete at different dosages for experimen-
tation. The specific mix design parameters are shown in
Tables 3 to 5.
Table 3: Mix parameters for concrete with bamboo fiber untreated
Cement
Crushed
stone
Bulk den-
sity
Water
Untreated bamboo
fiber
(kg/m
3
) (kg/m
3
) (kg/m
3
) (kg/m
3
)
Volume
ratio
Dosage
(kg/m
3
)
402 1215 598 185 0 0
402 1215 598 185 0.5 2.01
402 1215 598 185 1 4.02
402 1215 598 185 1.5 6.03
402 1215 598 185 2 8.04
402 1215 598 185 2.5 10.05
Table 4: Mix parameters for concrete with bamboo fiber treated with
calcium hydroxide solution
Cement
Crushed
stone
Bulk den-
sity
Water
Untreated bamboo
fiber
(kg/m
3
) (kg/m
3
) (kg/m
3
) (kg/m
3
)
Volume
ratio
Dosage
(kg/m
3
)
402 1215 598 185 0 0
402 1215 598 185 0.5 2.01
402 1215 598 185 1 4.02
402 1215 598 185 1.5 6.03
402 1215 598 185 2 8.04
402 1215 598 185 2.5 10.05
Table 5: Mix parameters for concrete with bamboo fiber treated with
sodium hydroxide solution
Cement
Crushed
stone
Bulk den-
sity
Water
Untreated bamboo
fiber
(kg/m
3
) (kg/m
3
) (kg/m
3
) (kg/m
3
)
Volume
ratio
Dosage
(kg/m
3
)
402 1215 598 185 0 0
402 1215 598 185 0.5 2.01
402 1215 598 185 1 4.02
402 1215 598 185 1.5 6.03
402 1215 598 185 2 8.04
402 1215 598 185 2.5 10.05
2.3 Test method
Optical microscopy analysis: A small amount of sam-
ple was adhered to a glass slide and changes in the sur-
face structure of the samples were observed to analyze
the similarities and differences.
Thermal analysis: Tests were carried out using a si-
multaneous thermal analyzer with a nitrogen flow rate of
50 mL/min, a heating rate of 100 °C/min, and a tempera-
ture range of 30–1000 °C.
In this study, three methods were used to investigate
the chloride-ion permeability of concrete, i.e., the elec-
tric-flux method, AC test method, and the RCM method.
The research methods are described as follows.
Electric-Flux Method: The resistance to chloride-ion
permeability is characterized by electric flux and refer-
enced to the "Standard Test Method for Long-Term Per-
formance and Durability of Ordinary Concrete"
(GB/T50082-2009).
22
The electric flux test apparatus is
shown in Figure 2. After curing the cylindrical concrete
samples with a diameter of 100 mm and a thickness of
50 mm for a specified time, they are exposed to the air to
dry the surface. The side of the specimens is coated with
sealing material, then placed in a vacuum container for
vacuum saturation. Inside the testing tank, the positive
electrode of the specimen is injected with a NaOH solu-
tion having a concentration of 0.3 mol/L, and the nega-
tive electrode is injected witha3%NaCl solution. A DC
60 V is applied axially, and the current passing through
the specimen is recorded every 5 min for a duration of
6 h. The total electric flux can be calculated based on the
change in current over the 6-hour period.
Y. LUO et al.: EXPERIMENTAL STUDY OF THE CHLORIDE-ION PERMEABILITY OF BAMBOO-FIBER-REINFORCED CONCRETE
Materiali in tehnologije / Materials and technology 58 (2024) 2, 239–248 241

AC-Current Test Method: The test is carried out ac-
cording to the relevant specifications, using a concrete
resistivity tester and a testing tank (Figure 3). The opti-
mization of the resistivity testing apparatus includes: (i)
adopting a new wire connection method, where the con-
nection between the wire and the tester remains the
same, and the connection joint with the copper plate uses
a pure copper alligator clip directly clamped onto the
copper plate, eliminating the use of terminal blocks; (ii)
an additional opening for venting is added at the middle
of the upper part of the testing tank; (iii) sealing is done
using double-sided tape; (iv) a new type of clamping fix-
ture is used. After the specimens are saturated with water
under vacuum conditions, their height and diameter are
measured with an accuracy of 0.1 mm. Then, the speci-
men’s cylindrical sides are coated with silicone sealing
material. Before testing, the specimens are sealed with
strong double-sided tape, fixed with the new clamping
fixture, and tested according to the aforementioned spec-
ifications.
3 RESULTS AND DISCUSSION
3.1 Analysis of the microstructure of bamboo fibers
The enlarged structures of bamboo fibers untreated,
treated with calcium hydroxide solution and treated with
sodium hydroxide solution are shown in Figure 4:
From Figure 4 it can be observed that the untreated
bamboo-fiber surface is covered with a thick adhesive
substance, similar to fructose, making it appear relatively
heavy. In contrast, the bamboo-fiber surface treated with
calcium hydroxide solution no longer shows a thick layer
of adhesive substance, and it appears lighter. Further-
more, the internal connecting structure of the bamboo fi-
ber is clearly visible. In the case of THE bamboo fiber
treated with sodium hydroxide solution, there is no visi-
ble adhering substance on the surface, indicating that the
solution has effectively removed impurities from the
bamboo-fiber surface. However, the internal connecting
structure of the bamboo fiber is not clearly visible, and it
appears loose and fragile.
Analysis of the reasons: The bamboo-fiber surface
contains various impurities, such as sugars and pectin.
23
THE Calcium hydroxide solution is a weak alkaline so-
lution that can remove the adhesive substances from the
bamboo-fiber surface while preserving the internal fiber
structure, maximizing the bonding strength of the bam-
Y. LUO et al.: EXPERIMENTAL STUDY OF THE CHLORIDE-ION PERMEABILITY OF BAMBOO-FIBER-REINFORCED CONCRETE
242 Materiali in tehnologije / Materials and technology 58 (2024) 2, 239–248
Figure 2: Schematic diagram of the electric flux test device
Figure 4: Microstructure of bamboo fibers: a) microstructure of bam-
boo fibers untreated, b) microstructure of bamboo fibers treated with
calcium hydroxide, c) Microstructure of bamboo fibers treated with
sodium hydroxide
Figure 3: Schematic of the main structure principle of the AC mea-
surement test apparatus. 1 – Concrete resistivity tester (1000 Hz, 1V);
2–Wire;3–T esting tank; 4 – Copper mesh; 5 – Concrete specimen;
6 – 3.0 % NaCl solution; 7 – Liquid injection hole
RCM Method: The testing method is carried out according to the rele-
vant specifications.

boo fiber. On the other hand, sodium hydroxide solution
is a strong alkaline solution that not only removes sur-
face impurities but also disrupts the internal fiber struc-
ture of the bamboo, causing it to lose its inherent proper-
ties and, consequently, its ability to enhance the
impermeability of concrete.
3.2 Analysis of the thermal stability of bamboo fibers
From Figure 5 it can be observed that untreated bam-
boo fibers start to lose weight at 100 °C, and their mass
decreases rapidly from 200 °C to 400 °C. After 400 °C,
there is a slow decline until it reaches zero. Bamboo fi-
bers treated with calcium hydroxide solution also experi-
ence a sharp decrease in mass between 200 °C and 400
°C, but after 400 °C, their mass gradually stabilizes, indi-
cating that they have reached a stable state. Bamboo fi-
bers treated with a strong sodium hydroxide solution ex-
hibit a sharp decrease in mass after 200 °C, and their
mass rapidly declines after 400 °C, reaching zero at
around 600 °C.
Reasons for this phenomenon: Untreated bamboo fi-
bers contain numerous impurities, and as the temperature
changes, the quality of the bamboo fibers becomes unsta-
ble, especially in the presence of impurities like sugars
and pectin. In contrast, bamboo fibers treated with cal-
cium hydroxide solution have their impurities removed,
leading to simpler composition and a more robust fiber
structure, resulting in stable mass at later stages. How-
ever, bamboo fibers treated with sodium hydroxide solu-
tion undergo structural changes that disrupt their inher-
ent properties. As the temperature rises, their mass
rapidly decreases to zero, indicating that the internal fi-
ber structure of the bamboo fibers has been compro-
mised, making them unable to withstand temperature
variations.
3.3 The influence of bamboo-fiber treatment methods
on the chloride-ion permeability of concrete
After curing the specimens for 28 d, electric-flux ex-
periments, AC tests, and RCM tests were conducted sep-
arately. For each set of experiments, conduct three tests
and take the average value as the result. Obtaining data
related to electrical flux, electrical resistivity, and chlo-
ride-ion diffusion coefficients for concrete with varying
amounts of bamboo fiber and different treatment meth-
ods. Present this data in the graphical representations as
shown in Figures 6 to 8.
From Figure 6 it can be observed that the electrical
flux of the bamboo-fiber-reinforced concrete treated with
calcium hydroxide solution is lower than that of the un-
treated bamboo-fiber-reinforced concrete, reaching the
minimum values at a bamboo fiber content of 2 %,
which are approximately 1750 °C and 2050 °C, respec-
tively. This represents a reduction of around 14.6 % in
electrical flux compared to untreated bamboo-fiber-rein-
forced concrete. On the other hand, concrete containing
bamboo fibers treated with sodium hydroxide solution
exhibits a higher electrical flux compared to untreated
Y. LUO et al.: EXPERIMENTAL STUDY OF THE CHLORIDE-ION PERMEABILITY OF BAMBOO-FIBER-REINFORCED CONCRETE
Materiali in tehnologije / Materials and technology 58 (2024) 2, 239–248 243
Figure 8: Relationship between different treatment methods and con-
tent of bamboo fiber and diffusion coefficient of chloride ion
Figure 5: Thermal analysis of bamboo at different stages
Figure 7: Relationship between different treatment methods and dif-
ferent content of bamboo fiber and resistivity
Figure 6: Electrical flux of bamboo-fiber concrete with different treat-
ment methods and different incorporation ratios of fiber

bamboo-fiber concrete. The highest electrical flux is
achieved at a bamboo fiber content of 2 %, reaching
4010 C, which is approximately 81 % higher than the
electrical flux of untreated bamboo-fiber concrete. A
lower electrical flux indicates better resistance to chlo-
ride-ion penetration, indicating that bamboo-fiber-rein-
forced concrete treated with calcium hydroxide solution
significantly enhances the resistance to chloride-ion per-
meability. Concrete containing bamboo fibers treated
with sodium hydroxide solution, on the contrary, exhibits
a reduction in its resistance to chloride-ion penetration.
From Figure 7 it can be seen that the AC resistivity
of bamboo-fiber-reinforced concrete treated with cal-
cium hydroxide solution is higher than that of untreated
bamboo-fiber-reinforced concrete. The highest values are
achieved at a bamboo-fiber content of 2 %, which are ap-
proximately 208 ·m and 180 ·m, respectively. This
indicates an increase of around 15.6 % in AC resistivity
compared to untreated bamboo-fiber-reinforced concrete.
Concrete containing bamboo fibers treated with sodium
hydroxide solution, on the other hand, exhibits a lower
AC resistivity compared to untreated bamboo-fiber con-
crete. The highest AC resistivity is achieved at a bam-
boo-fiber content of 2.5 %, measuring 57 ·m, which is
approximately a 66 % reduction in AC resistivity com-
pared to untreated bamboo-fiber concrete. Higher AC re-
sistivity suggests better resistance to chloride-ion pene-
tration, demonstrating that bamboo-fiber-reinforced
concrete treated with calcium hydroxide solution en-
hances the resistance to chloride-ion permeability. Con-
crete containing bamboo fibers treated with sodium hy-
droxide solution, on the contrary, exhibits a reduction in
its resistance to chloride-ion penetration.
From Figure 8 it can be observed that the chlo-
ride-ion diffusion coefficient of bamboo-fiber-reinforced
concrete treated with calcium hydroxide solution is
lower than that of untreated bamboo-fiber-reinforced
concrete. The lowest values are achieved at a bamboo-fi-
ber content of 2 %, which are approximately
2.5 (10
–12
m
2
·s
–1
) and 3 (10
–12
m
2
·s
–1
), respectively. This
represents a reduction of around 16.7 % in chloride-ion
diffusion coefficient compared to untreated bamboo-fi-
ber-reinforced concrete. Concrete containing bamboo fi-
bers treated with sodium hydroxide solution exhibits
higher chloride-ion diffusion coefficients compared to
untreated bamboo-fiber concrete. The highest chlo-
ride-ion diffusion coefficient is achieved at a bamboo-fi-
ber content of 2.5 %, measuring 9.3 (10
–12
m
2
·s
–1
), which
is approximately a 144 % increase in chloride-ion diffu-
sion coefficient compared to untreated bamboo-fiber
concrete. A lower chloride-ion diffusion coefficient indi-
cates better resistance to chloride-ion penetration, indi-
cating that bamboo-fiber-reinforced concrete treated with
calcium hydroxide solution significantly enhances the re-
sistance to chloride-ion permeability. Concrete contain-
ing bamboo fibers treated with sodium hydroxide solu-
tion, on the contrary, exhibits a reduction in its resistance
to chloride-ion penetration.
Based on the analysis above, all three experimental
methods for chloride-ion permeability demonstrate that
the addition of bamboo fibers treated with calcium hy-
droxide solution can improve the resistance to chlo-
ride-ion permeability in concrete. The improvement rate
ranges between 14 % and 17 %, which further eliminates
the errors introduced by individual experimental meth-
ods. Due to the existence of impurities such as pectin on
the surface of bamboo fibers, calcium hydroxide is clas-
sified as a weak alkaline solution. the treatment with cal-
cium hydroxide solution removes these impurities, in-
creases the contact area between the bamboo fibers and
concrete, and enhances the mechanical bond between
them without damaging the fiber structure of the bamboo
fibers. This treatment also reduces the porosity of the
concrete, thus enhancing its resistance to chloride-ion
permeability. Concrete with the addition of bamboo fi-
bers treated with sodium hydroxide solution not only
fails to improve its resistance to chloride-ion penetration
but actually has a detrimental effect. This is because the
sodium hydroxide solution is a strong alkaline solution,
which can easily disrupt the fiber structure. While it re-
moves impurities from the surface of the bamboo fibers,
it also harms the inherent properties of the bamboo fi-
bers. As a result, it not only fails to enhance the con-
crete’s resistance to chloride ions but also reduces its du-
rability.
3.4 The influence of bamboo-fiber content on chlo-
ride-ion permeability of concrete
From Figure 6 it can be observed that the electric
flux of the bamboo-fiber concrete treated with calcium
hydroxide solution and untreated bamboo-fiber concrete
both show a decreasing trend followed by an increasing
trend with an increase in bamboo fiber content. The low-
est values are achieved at a bamboo-fiber content of 2 %,
which are 1750 C and 2050 C respectively. This repre-
sents a decrease of 54 % and 46 % in electric flux com-
pared to the concrete without bamboo fibers. A lower
electric flux indicates better resistance to chloride-ion
permeability, suggesting an optimum bamboo fiber con-
tent of 2 % for the best anti-permeability performance to
chloride ions. The continuous increase in electrical flux
in concrete with bamboo fibers treated with sodium hy-
droxide solution indicates that the strong alkaline solu-
tion has disrupted the bamboo fiber structure, rendering
it ineffective.
From Figure 7 it can be observed that the AC resis-
tivity of the bamboo-fiber concrete treated with calcium
hydroxide solution and the untreated bamboo-fiber con-
crete both show an increasing trend followed by a de-
creasing trend with an increase in bamboo-fiber content.
The highest values are achieved at a bamboo fiber con-
tent of 2 %, which are 208 ·m and 180 ·m respec-
tively. This represents an increase of 177 % and 140 % in
Y. LUO et al.: EXPERIMENTAL STUDY OF THE CHLORIDE-ION PERMEABILITY OF BAMBOO-FIBER-REINFORCED CONCRETE
244 Materiali in tehnologije / Materials and technology 58 (2024) 2, 239–248

AC resistivity compared to the concrete without bamboo
fibers. A higher AC resistivity indicates better resistance
to chloride-ion permeability, suggesting an optimum
bamboo-fiber content of 2 % for the best anti-permeabil-
ity performance to chloride ions. The continuous de-
crease in AC resistivity in concrete with bamboo fibers
treated with sodium hydroxide solution suggests that the
strong alkaline solution has disrupted the bamboo fiber
structure, rendering it ineffective.
From Figure 8 it can be observed that the chlo-
ride-ion diffusion coefficient of the bamboo-fiber con-
crete treated with calcium hydroxide solution and the un-
treated bamboo-fiber concrete both show a decreasing
trend followed by an increasing trend with an increase in
bamboo-fiber content. The lowest values are achieved at
a bamboo fiber content of 2 %, which are 2.5 × 10
–12
m
2
·s
–1
a n d3×1 0
–12
m
2
·s
–1
respectively. This represents a de-
crease of 70 % and 64 % in chloride-ion diffusion coeffi-
cient compared to the concrete without bamboo fibers. A
lower chloride-ion diffusion coefficient indicates better
resistance to chloride-ion permeability, suggesting an op-
timum bamboo fiber content of 2 % for the best anti-per-
meability performance to chloride ions. The continuous
increase in the chloride-ion diffusion coefficient in con-
crete with bamboo fibers treated with sodium hydroxide
solution indicates that the strong alkaline solution has
disrupted the bamboo-fiber structure, rendering it inef-
fective.
Based on the comprehensive analysis of the three dif-
ferent chloride-ion penetration-resistance tests, it is evi-
dent that for both untreated bamboo fibers and those
treated with calcium hydroxide solution, as the bam-
boo-fiber content increases, the resistance to chloride-ion
penetration initially increases and then decreases. The
optimal resistance to chloride-ion permeability is
achieved when the bamboo fiber content is 2 %, which
avoids the errors introduced by individual experimental
methods. Due to the microfiber structure and water-ab-
sorption characteristics of bamboo fibers, they can effec-
tively fill the voids inside the concrete, reduce the poros-
ity of the concrete, and block the permeation channels of
chloride ions, thereby enhancing its resistance to perme-
ability. The water-absorption effect of bamboo fibers
also makes the interior of the concrete more compact, re-
ducing the corrosion effects caused by internal moisture
and blocking the permeation and corrosion of chloride
ions, further enhancing the resistance to chloride-ion per-
meability. In the case of bamboo fibers treated with so-
dium hydroxide solution, their fiber structure has been
disrupted, making them unable to fill the internal voids
of the concrete and losing their bonding function. This,
in turn, reduces the concrete’s resistance to chloride-ion
penetration.
3.5 Correlation analysis of different experimental
methods
To establish a linear relationship between the three
different experimental methods, the resistivity of bam-
boo-fiber concrete was converted to conductivity, and
then summarized with electric-flux and chloride-ion dif-
fusion coefficient, as shown in Table 6. The linear fitting
was performed using the least-squares method to obtain
the linear models for conductivity and electric flux with
respect to the chloride-ion diffusion coefficient (Fig-
ure 9).
From Figure 9 it can be observed that the elec-
tric-flux method, AC test method, and RCM method ex-
hibit a strong correlation. Lower values of electric flux,
electrical conductivity, and chloride-ion diffusion coeffi-
cient indicate better resistance to chloride-ion permeabil-
ity in bamboo-fiber concrete. Additionally, there is a lin-
ear relationship among these variables, indicating the
effectiveness of the three testing methods in evaluating
the resistance to chloride-ion permeability when bamboo
Y. LUO et al.: EXPERIMENTAL STUDY OF THE CHLORIDE-ION PERMEABILITY OF BAMBOO-FIBER-REINFORCED CONCRETE
Materiali in tehnologije / Materials and technology 58 (2024) 2, 239–248 245
Figure 9: Linear models of conductivity and electric flux with respect
to the chloride-ion diffusion coefficient
Table 6: Summary of three experimental results
Bamboo fiber
content
/%
Electric flux method AC current test method RCM method
Electric flux
/C
Permeability
evaluation
Electrical resis-
tivity /(Ù·m)
Electrical con-
ductivity
/(10
–3
Ù
–1
·m
–1
)
Permeability
evaluation
Chloride-ion diffusion
coefficient
D/(10
–12
m
2
·s
–1
)
0 3800 high 75 13.3 high 8.3
0.5 3380 medium 98 10.2 high 6.5
1 2870 medium 130 7.7 medium 5.3
1.5 2460 medium 152 6.6 medium 4.1
2 2050 medium 180 5.6 low 3
2.5 2210 medium 168 5.9 medium 3.8

fibers are incorporated into concrete. Therefore, it is fea-
sible to choose a relatively simple method for testing.
4 MECHANISM ANALYSIS
The permeability of concrete is primarily influenced
by the size of its internal porosity.
24–29
A higher porosity
leads to poorer permeability, while a lower porosity en-
hances permeability. Concrete is composed of materials
such as crushed stones, sand, and cement, and the con-
tact surfaces between different mediums inevitably gen-
erate certain gaps.
30–32
Additionally, the different produc-
tion processes of concrete contribute to a certain
proportion of porosity. Larger porosity negatively im-
pacts the mechanical performance and the resistance to
the chloride-ion permeability of concrete.
33
Bamboo fibers have a diameter of approximately
1–2 mm and a length of about 3–4 cm, exhibiting a cer-
tain tensile strength and ductility. Adding bamboo fibers
to concrete can fill the internal voids of the concrete,
compact its density, and thereby reduce its porosity, im-
proving its resistance to chloride-ion permeability. The
voids that affect the permeability of concrete mainly ex-
ist in the interfacial zone between the crushed stones and
the cement. Due to the strip-like structure of these inter-
facial voids, chloride ions can find pathways for penetra-
tion. The strip-like structure of the bamboo fibers can
bond the voids between the crushed stones and the ce-
ment contact zone, filling and bonding the voids result-
ing from the property differences between different me-
diums. This obstructs the penetration channels for
chloride ions and enhances the resistance to the chlo-
ride-ion permeability of concrete. If the bamboo-fiber
content is insufficient, the internal voids of the concrete
cannot be adequately filled, resulting in an inadequate re-
duction of the porosity, and failing to maximize the im-
provement in resistance to chloride-ion permeability. On
the other hand, excessive bamboo-fiber content lowers
the rigidity and hardness of the concrete, diminishing its
resistance to chloride-ion permeability. Only with an ap-
propriate amount of bamboo fibers can the internal voids
of the concrete be completely filled without affecting the
overall rigidity and hardness, thereby maximizing the
improvement in its resistance to chloride-ion permeabil-
ity.
Due to the presence of impurities such as sugars and
pectin on the surface of bamboo fibers, if bamboo fibers
are directly added to concrete without surface treatment,
during the initial formation of concrete, the bamboo fi-
bers, along with the surface impurities, fill the voids in
the concrete. However, as the subsequent hydration of
cement in concrete progresses, the alkaline environment
inside the concrete will dissolve the sugars and pectin on
the surface of bamboo fibers, creating new voids. This,
in turn, fails to enhance the resistance of concrete to
chloride-ion permeability. Therefore, many researchers
have explored different methods of surface treatment for
bamboo fibers. However, the treatment process is com-
plex and costly. In this study, a calcium hydroxide
solution and sodium hydroxide solution were used for
the surface treatment of bamboo fibers. As the calcium
hydroxide solution is a weak alkaline and less corrosive,
it can remove impurities such as sugars and pectin from
the surface of the bamboo fibers without damaging the
fiber structure internally. The treatment enlarges the con-
tact area between the inner fiber structure of bamboo fi-
bers and the concrete, further enhancing the bonding ca-
pacity of bamboo fibers. This not only strengthens the
bonding between bamboo fibers and different media con-
tact zones in the concrete but also compacts the concrete,
effectively reducing the porosity. At the same time, it
avoids the dissolution of impurities on the surface of
bamboo fibers during the subsequent cement hydration
phase, thus preventing the formation of new voids. This
ensures that the bamboo fibers do not undergo new
chemical reactions with the age of the concrete, posi-
tively impacting the durability of the concrete and en-
hancing its resistance to chloride-ion permeability, with
certain sustainability. On the other hand, a sodium hy-
droxide solution was used for surface treatment, which
effectively removes the impurities on the surface of the
bamboo fibers. However, since sodium hydroxide is a
strong alkaline and corrosive substance, it damages the
fiber structure of the bamboo fibers, resulting in weak
bonding between the bamboo fibers and the voids in the
concrete. As a result, it does not effectively improve the
resistance of concrete to chloride-ion permeability.
5 CONCLUSIONS
This study observes the microstructure of bamboo fi-
bers using optical microscopy and thermal analysis, and
employs the electric-flux method, AC test method, and
RCM method to determine the effect of adding bamboo
fibers to concrete on its resistance to chloride-ion perme-
ability. The following conclusions are drawn:
(1) The surface impurities of bamboo fibers treated
with calcium hydroxide solution are removed and the
thermal stability of bamboo fibers are improved.
(2) The bamboo fibers treated with sodium hydroxide
solution have disrupted their fiber structure. While this
treatment removed impurities from the surface of the
bamboo fibers, it also damaged their inherent properties.
As a result, it not only fails to enhance the concrete’s re-
sistance to chloride ions but also reduces its durability.
(3) Bamboo fibers treated with calcium hydroxide so-
lution not only remove surface impurities but also pre-
serve the fiber structure. Compared to untreated bamboo
fibers, they improve the resistance to chloride-ion perme-
ability in concrete, with an enhancement rate between
14 % and 17 %.
(4) The resistance to chloride-ion permeability of
concrete shows an increasing trend with increasing bam-
Y. LUO et al.: EXPERIMENTAL STUDY OF THE CHLORIDE-ION PERMEABILITY OF BAMBOO-FIBER-REINFORCED CONCRETE
246 Materiali in tehnologije / Materials and technology 58 (2024) 2, 239–248

boo-fiber content, reaching an optimal performance at a
fiber content of 2 %.
(5) The electric-flux method, AC test method, and
RCM method are mutually validating, showing good cor-
relation. It is recommended to choose a suitable and sim-
ple method for testing purposes.
Bamboo fibers have been explored as a potential rein-
forcement material in concrete to enhance its mechanical
properties, sustainability and overall performance. For
future work on bamboo-fiber concrete could include: (i)
material development and optimization – researchers
should focus on optimizing the composition of bam-
boo-fiber concrete to achieve the best balance between
strength, durability and workability; (ii) mechanical
properties enhancement – continued efforts to enhance
the mechanical properties of bamboo-fiber concrete,
such as tensile strength, flexural strength, and impact re-
sistance; and (iii) standardization and guidelines – the
development of industry standards and guidelines for the
use of bamboo fibers in concrete construction to ensure
consistent quality and performance.
Acknowledgment
The authors would like to acknowledge the financial
support from the Nanping Natural Science Foundation
Co-Sponsored Program funded by Nanping Science and
Technology Bureau, Fujian Forestry Vocational and
Technical College (Grant No: N2023J009).
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