Effect of Fiber Content on Mechanical and Microstructural Properties of Alkali Resistant Glass Fiber Reinforced Concrete

Abstract

Owing to the enhanced strength, ductility, and resistance to harsh environments, increasing research attention has been paid to alkali-resistant glass fiber reinforced concrete (ARGFRC). This paper presents ARGFRC experimental studies concerning fiber content on mechanical properties and microstructural characteristics of alkali-resistant glass fiber reinforced concrete. The amount of glass fiber was considered at levels of 0.0, 0.3, 0.5, 0.8, 1.0, 1.3, and 1.5% of the concrete volume. The compression, flexural, impact resistance, scanning electron microscopy, and energy dispersive spectroscopy tests were conducted. The flexural load-deflection curve, flexural strength, flexural toughness index, flexural fracture energy, post-cracking stiffness, post-peak stiffness, and impact resistance energy absorption were obtained. Then the changing law affected by fiber content on these mechanical properties was further analyzed, and the corresponding equation was fitted. When fiber content was 1.5%, the flexural toughness index I5, I10, and I20 values were 4.0, 5.9, and 8.9, respectively, and increased by 3.0~7.9 times. Glass fiber incorporation could increase the ductility and delay the brittle failure when the fiber content reached 0.8%. The largest post-cracking stiffness was calculated as 36.174 kN/mm with a fiber content of 0.8%. The higher the fiber content, the larger the post-peak stiffness of the tested beams. Impact resistance test results demonstrated that the optimum fiber content was 1.3%. As the fiber content increased, the effect of the concrete grout on the fiber packaging decreased from the scanning electron microscopy analysis. The energy dispersive spectroscopy observation proved that adding a certain fiber content did not affect the concrete hydration reaction.

Full text

Research Article
Effect of Fiber Content on Mechanical Properties and
Microstructural Characteristics of Alkali Resistant Glass Fiber
Reinforced Concrete
Chao Wu ,
1
,
2
,
3
Xiongjun He ,
1
,
2
Xia Zhao ,
4
Li He ,
5
Yuan Song ,
6
and Xiuyan Zhang
4
1
School of Transportation and Logistics Engineering, Wuhan University of Technology, Wuhan 430063, China
2
Hubei Province Highway Engineering Research Center, Wuhan 430063, China
3
CERIS, Instituto Superior T´
ecnico, Universidade de Lisboa, Lisboa 1049-001, Portugal
4
Binzhou Polytechnic, Binzhou 256603, China
5
School of Civil Engineering, Guizhou Institute of Technology, Guiyang 550003, China
6
Hubei Communications Planning and Design Institute Co., Ltd, Wuhan 430051, China
Correspondence should be addressed to Xia Zhao; yxzhaoxia@sina.com
Received 9 August 2022; Revised 3 November 2022; Accepted 7 November 2022; Published 21 November 2022
Academic Editor: Mehran Khan
Copyright ©2022 Chao Wu et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Owing to its enhanced strength, ductility, and resistance to harsh environments, increasing research attention has been paid to
alkali-resistant glass ber reinforced concrete (ARGFRC). is paper presents experimental studies concerning the eects of ber
content on the mechanical properties and microstructural characteristics of ARGFRC. e amount of glass ber was considered at
levels of 0.0, 0.3, 0.5, 0.8, 1.0, 1.3, and 1.5% of the concrete volume. e compression, exural, impact resistance, scanning electron
microscopy, and energy dispersive spectroscopy tests were conducted. e exural load-deection curve, exural strength,
exural toughness index, exural fracture energy, postcracking stiness, postpeak stiness, and impact resistance energy ab-
sorption were obtained. en the changing law aected by ber content on these mechanical properties was further analyzed, and
the corresponding equation was tted. When ber content was 1.5%, the exural toughness index I
5
,I
10
, and I
20
values were 4.0,
5.9, and 8.9, respectively, and increased by 3.0∼7.9 times. Glass ber incorporation could increase the ductility and delay the brittle
failure when the ber content reached 0.8%. e largest postcracking stiness was calculated at 36.174 kN/mm with a ber content
of 0.8%. e higher the ber content, the larger the postpeak stiness of the tested beams. Impact resistance test results
demonstrated that the optimum ber content was 1.3%. As the ber content increased, the eect of the concrete grout on the ber
packaging decreased, according to the scanning electron microscopy analysis. e energy dispersive spectroscopy observation
proved that adding a certain ber content did not aect the concrete hydration reaction.
1. Introduction
e development of modern engineering constructions has
generated a high demand for new types of concrete needed
to have improved properties such as strength, fracture,
durability, and sustainability. ere has been a steady in-
crease over the last decades in the use of ber-reinforced
concrete (FRC) in the engineering eld. FRC comprises
hydraulic cement, aggregates, and discrete reinforcing bers
[1]. FRC has received worldwide attention due to its
advantageous material properties, including high initial
crack strength, tensile and compressive strength, toughness,
outstanding impact resistance, and excellent energy ab-
sorption capacity [2–5]. Afroughsabet et al. provided a
comprehensive review of the mechanism of crack formation
and propagation and the mechanical properties of high-
performance FRC [2]. Yin et al. [3] presented the prepa-
ration techniques and the properties of macroplastic bers,
and the eects of macroplastic bers on the fresh and
hardened concrete performances were discussed as well. Yoo
Hindawi
Advances in Materials Science and Engineering
Volume 2022, Article ID 1531570, 19 pages
https://doi.org/10.1155/2022/1531570

and Banthia studied the impact resistance of FRC; the
impact test methods were addressed, and the comprehensive
impact resistance of FRCs subjected to various loading
conditions with dierent bers was investigated [4]. Ahmad
and Zhou discussed the mechanical performances of con-
crete reinforced with natural or synthetic bers. e rec-
ommended ber content addition by weight was up to 1.0%
of the maximum mechanical properties of FRC, while
further addition of bers decreased the mechanical per-
formances due to the lack of workability [5]. FRC’s me-
chanical properties [6–10], such as tensile strength,
compressive strength, exural strength, fracture toughness
[6, 11–13], impact resistance [12, 13], and microstructural
characteristics [14, 15], were investigated. S¨
oylev and
¨
Ozturan concentrated on the mechanical properties of a
low-volume fraction (0.5% steel bers + 0.1% polypropylene,
0.1% glass ber) FRC [6]. e eect of moist curing was
more favorable for compressive and splitting tensile
strengths of FRCs, while this eect was more emphasized in
compressive compared to splitting strength. Dehghan et al.
[7] demonstrated that the compressive strength and drying
shrinkage were not promoted by recycled glass ber rein-
forced polymer and virgin E-glass ber additions at a
substitution level of 5 wt% of the coarse aggregate, while the
splitting tensile strengths were improved in most cases.
Gopalaratnam and Gettu [8] pointed out the suggestions to
improve the toughness characterization while adopting the
four-point bending test on unnotched FRC beams. Fur-
thermore, the equivalent post-cracking strength approach
provided an elegant way to consider energy absorption in
design. Bakhshi et al. [9] evaluated the eects of early age and
ber type on the FRC toughness parameters, including the
back-calculated tensile stress-strain response along with
simulated and tested exural load-deection curves.
Gopalaratnam et al. concluded that the initial crack de-
ection of FRC can vary by as much as an order of mag-
nitude relying on the methodology adopted to measure
deections. e relative magnitudes of the extraneous de-
formation rely upon the test setup and load-carrying ca-
pacity of the FRC beam [11]. Enfedaque et al. depicted more
bers being pulled out of the matrix instead of broken in
aged glass FRC (GFRC) scanning electronic microscope
(SEM) samples, owing to the addition of metakaolin [14].
Yuan and Jia [15] studied the eects of glass ber (GF) and
polypropylene ber (PPF) on the microstructural charac-
teristics of FRC as a function of ber content and water/
binder ratio. e results demonstrated that the water/binder
ratio aected the optimal ber content based on the pre-
liminary analysis of the SEM observation. e improvement
eect of GF on water absorption was superior to that of PPF.
e inuencing factors of the FRC properties have been
explored, such as ber types [12, 15–17], ber content [16],
and ber dispersion. Vafaei et al. investigated the static and
dynamic fracture behavior of high-strength ber-reinforced
seawater sea-sand (SWSS) concrete by conducting fracture
toughness and drop weight impact tests. Polyvinyl alcohol
and polypropylene bers (PPFs) with dierent ber contents
(0.1%–0.5%) were used for reinforcement. Incorporating
PPF improved both the static and dynamic fracture
performances of SWSS FRC [12]. Ghadban et al. studied the
eect of ber type (steel ber and synthetic ber) and
content on the exural performance of FRC for highway
bridges. Steel FRC (SFRC) presented superior exural
performances compared to synthetic FRC. Notwithstanding,
SFRC was susceptible to corrosion and twice as expensive as
synthetic bers [16]. Yang et al. [17] demonstrated that 1.0%
steel ber and 1.0% glass ber presented the best im-
provement eects on the compressive strength and im-
permeability of recycled concrete. Madhkhan and Katirai
[10] used AR glass bers (ARGFs) with three dierent types
of pozzolanic materials in GFRC and found that the
toughness index and modulus of rupture decreased over
time due to aging. Kimm et al. proposed dierent surface
treatments to protect ber-reinforced polymer fragments in
concrete and improve adhesion. A sanded surface of glass
ber polymers increased the average maximum shear stress
by 16%, according to the pull-out tests [18]. Ali et al. [19]
manufactured FRC by incorporating 0.5 and 1.0% volume
fractions of GF, hooked steel ber (HSF), and polypropylene
ber (PPF). FRC pavement with 0.5% HSF, 0.5% GF, 1% GF,
0.5% PPF, and 1% PPF indicated 4%, 18%, 17%, 13%, and
18% lesser carbon emissions of pavement compared to plain
concrete, respectively. Lin et al. [20] studied the coupling
eects of expansive agents (EAs) and GFs on the splitting
strength and fracture properties of SWSS concrete. e
combined usage of EAs and GFs maximally increased the
splitting strength, exural strength, fracture energy, and
initial and unstable fracture toughness indexes by 65%, 75%,
155%, 101%, and 82%, respectively. Saidani et al. [21]
demonstrated that steel, macro-ber, and micro-
polypropylene change the failure types to ductile failures,
thus overcoming concrete’s brittleness issue and improving
its split tensile strength. Çelik and Bing¨
ol [22] investigated
the impact strength and fracture properties of self-com-
pacting concrete reinforced with basalt ber (BF), GF, and
PPF, and it was suggested that the addition of BF, GF, and
PPF all increased the exural strength, impact resistance,
and fracture energy. Surveys conducted by Aghdasi et al.
[23] suggested that steel FRC (SFRC) could be developed for
large-scale structural applications by changing mixture
components and ber volume fractions. Steel bers are one
of the most attractive preferences because they are widely
available and aordable. Conversely, SFRC poses unavoid-
able disadvantages, such as increased self-weight, decreased
workability, ber balling at high contents, and susceptibility
to corrosion. Simultaneously, synthetic bers also have a low
modulus of elasticity, a low melting point, and weak in-
terfacial bonding with cementitious matrixes [24]. ere-
fore, GF is a popular substitute to reimburse for this
vulnerability. Adopting GFRC could signicantly improve
the design of concrete structures, oer endless design
possibilities in architecture, and be more cost-eective than
other alternatives. e distinguished interaction of two basic
materials, concrete matrix and GF, safeguards the good
mechanical properties of GFRC [25].
Despite the signicance and concerns about the behavior
of GFRC, studies on this topic are still quite limited, namely
about the eects of ber volume content on the mechanical
2Advances in Materials Science and Engineering

and microscopy properties of GFRC. e most relevant
issues of earlier investigations in this specic research eld
are illustrated, along with the aspects that still require extra
research eorts and motivate the present investigation.
Arslan [26] analyzed the eects of chopped glass bers’
incorporation on fracture energy and mechanical properties
of normal-strength concrete using crack mouth opening
displacement (CMOD) measurement. ree-point bending
tests were also performed on notched beams produced using
GFRC with 0.5, 1, 2, and 3 kg/m
3
ber contents to determine
the value of fracture energy. GF has been used in concrete for
controlling early-age microcracks (EAMC) in bridge decks.
e experiments illuminated a decrease in compressive
strength and an increase in splitting tensile and exural
strengths of GFRC compared to plain concrete (PC) [27].
Yuan and Jia [15] reported that the content of GF aected
the slump and the exural properties; when the slump
decreased, average residual strength, equivalent exural
strength ratio, toughness, and modulus of rupture increased
with increasing ber content [16]. No exural strength in-
creased with a high ber content of GFRC, while more than
0.50% ber content was added in high-strength GFRC.
Furthermore, fracture energy increased signicantly when
more than 0.25% ber content was used for GFRC [28].
Incorporating chopped GFs with ber volume fractions
between 0% and 2% into ceramic concrete leads to signif-
icant increases in exural strength and direct shear strength,
regardless of the matrix type or ber length [29]. Static tests
in compression, tension, and bending were performed.
Dynamic tests using a modied Hopkinson bar were con-
ducted to gure out how GF aected energy absorption and
tensile strength of the ber-reinforced mortar at a high strain
rate. e experimental results demonstrated that adding GF
signicantly increased energy absorption at a high strain rate
[30]. e eects of alkali-resistant GF (ARGF) volume
fractions of 0.125–0.75% on the exural strength and duc-
tility, restrained shrinkage cracking of lightweight GFRC
were investigated, and ber volume fractions of 0.25–0.5%
were sucient for control of restrained shrinkage cracks and
enhancement of the exural toughness [31]. Incorporating
low-volume fractions of two types of ARGF can control the
cracking that develops due to early age shrinkage on both
standard concrete and SCC in two diverse ways, namely by
reducing the total cracked area and the maximum length of
the cracks. e microscopic study of cracked surfaces veries
the encouraging eect of the presence of dispersed ARGFs
on cracking control [32]. e eects of ARGF with ber
content varying from 0.5 to 4.5% by weight of cement on
dierent strengths (compressive, exural, split tensile, and
bond) of M20 grade concrete were considered [33]. Single
ber model composites of ARGFs and a cementitious matrix
were adopted to interrogate the pull-out behavior under
quasistatic and high-speed loading. Results testied that the
interface between ARGFs and the concrete matrix behaved
normally, without obvious slip-hardening or slip-weakening
eects, in both quasi-static and high-rate pull-out tests [34].
GFRC with and without polymer was used as the benchmark
material to evaluate concrete self-healing enhanced by
crystalline admixture. Results showed a dierence in the self-
healing start between GRC and PGRC samples [25]. Scan-
ning electron microscopy (SEM) photographs indicated that
incorporating metakaolin enabled more bers to be pulled
out of the matrix rather than broken in aged GFRC samples
[14]. us far, studies have highlighted factors associated
with recycled GF used in FRC [7, 35–37]. Zhao et al. in-
vestigated the constitutive model of ARGFRC with four
dierent ber volume contents (0.0%, 0.5%, 1.0%, and 1.5%).
Results indicated the optimal load-bearing capacity of GFRP
(glass ber reinforced polymer) reinforced GFRC beam was
at 1.0% ber content [38]. Le et al. proposed a constitutive
model of FRC by incorporating microcracking and ber-
bridging mechanisms [39]. Yang et al. studied the properties
of ARGF reinforced coral aggregate concrete [40]. Wang
et al. experimentally investigated the properties of graded
GFRC based on the construction of tunnel engineering
applications to avoid partition wall cracking and lining
seepage [41].
e studies reviewed above conrmed the suscepti-
bility of mechanical, durability, and microstructural
properties for GFRC at dierent ber contents. Never-
theless, the information they provided about the behavior
of dierent ber contents was not always and completely
consistent. e following gaps are being highlighted: (i)
Arslan’s experiments [26] claried that the exural
strength of GFRC increased with ber content, whereas
there was a slight downturn for a high volume of ber
content. Meanwhile, in other studies [16, 29], the exural
properties increased with high ber content, and no
exural strength increase was observed by Kizilkanat et al.
[28] when ber content was more than 0.5%. Much un-
certainty still exists about the relationship between ber
content and the mechanical properties of GFRC. e
optimal ber content of ARGFRC is still unclear con-
sidering various aspects of its mechanical properties and
application scenario. (ii) e mechanism by which ber
content aects the SEM and energy dispersive spectros-
copy (EDS) has not been adequately established.
Consequently, this study aimed to fulll the research
gaps mentioned above and better understand the eects of
ber content on the mechanical and microstructure prop-
erties of alkali resistant glass ber reinforced concrete
(ARGFRC). Homoplastically, a systematic investigation of
the compressive strength, exural toughness, and impact
resistance of ARGFRC was experimentally conducted. SEM
and EDS microstructural analyses of ARGFRC were per-
formed as well, which will provide references to the research
and practical engineering applications of ARGFRC in civil
engineering infrastructures.
2. Materials and Methods
2.1. Materials and Mix Proportions. e cement used in the
experiment was ordinary Portland cement with a strength
grade of 42.5R, and the cement stability met the specied
requirements from GB 175-2007 [42]. e apparent sand
density and bulk density were 2710 kg/m
3
and 1600 kg/m
3
,
respectively. e sand porosity was 45.00%, and the stone
powder content was 5.10%. For concrete compressive
Advances in Materials Science and Engineering 3

strength grades ranging from C30 to C55, the requirement
for stone powder content should be less than 7.00% re-
garding JGJ 52-2006 [43]. According to JGJ52-2006 [43] and
the sand sieving properties provided in Figure 1, the sand
neness modulus was 2.9, and the sand particle grading
belonged to region II. Crushed stone per JGJ 52-2006 [43]
has an apparent density, bulk density, porosity bulk density,
crushing index, mud content, and needle-like particle
content of 2700 kg/m
3
, 1420 kg/m
3
, 47.00%, 9.90%, 0.50%,
and 4.00%, respectively. e FMY-1 water-reducing agent
adopted was recommended by GB 8076-2008 [44]. Local tap
water based on JGJ 63-2006 [45] was used.
e GF adopted in the experiment was alkali-resistant
GF (ARGF), a high-performance short-cutting original
wire was used to increase the mechanical performance of
concrete and is applied to concrete and cement mortar.
Compared to other types (plastic shrinkage control,
sprayed yarn, repair mortar, and premixed mortar) of
ARGF, this kind of ARGF was especially used in bridge
concrete structures aiming at controlling and preventing
cracking in concrete. By adding ARGF to concrete, there
are advantages such as eectively improved exural and
impact properties, good processability with the surface
almost out of sight; availability for high volume incorpo-
ration without aecting the workability; no trace on the
surface; homogeneous mixing without requiring additional
water; safe and straightforward operation. e surface
treatment methods of glass ber are generally divided into
heat treatment methods and chemical treatment methods.
Chemical treatment methods of glass ber generally in-
clude acid alkali etching treatment and silane coupling
agent coating treatment. e essence of silane coupling
agent surface treatment is to graft the silane coupling agent
onto the surface of glass ber through chemical bonding.
e treatment mechanism is that the silanol generated after
the hydrolysis of organ silane reacts with the hydroxyl
group on the surface of glass ber to form a stable Si-O-Si
bond. Diluted silane solution (pH �3∼4) was prepared by
using pure silane with 80% ethanol, 10% acetic acid, and
10% aqueous solution. e silane surface treatment
adopted a weight concentration of the diluted silane versus
ARGF of 0.2: 100 in an ultra-mixing machine at 100 rpm for
ve minutes and then a drying process in an oven at 140°C
for 4 h [46]. e ARGF properties presented in Table 1 were
obtained from the manufacturer, Taishan Fiberglass Inc.
is type of ARGF was specially applied in the negative
moment zone of bridge concrete slabs to prevent concrete
cracks. e original ber wire diameter was 14–19 m
according to ISO 1888:2006 [47], the loss on ignition was
0.80–2.0%, in line with ISO 1887:1995 [48], and the
moisture content was less than 0.50% per ISO 3344:1997
[49]. e tensile strength of ARGF was 1700 MPa as per
ASTM D 2343-17 [50]. e specic gravity and softening
temperature of ARGF were 2.68 g/cm
3
and 860°C, re-
spectively. e ber length was 36 mm, and the modulus of
elasticity was 72 GPa.
Specimens were cast according to the code for the design
of concrete structures, with 28 days to reach the target
strength of 40 MPa. In the whole concrete mixture design
process, the mixture design of cement, ne natural aggre-
gate, coarse natural aggregate, and water was 1 : 1.40 : 2.09 :
0.40 [38, 51]. e amount of water-reducing agent was 3.0 kg
per cubic meter of concrete. e volume incorporation of
ARGF content was 0.0%, 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, and
1.5%, respectively. e specic mixture proportion design of
ARGFRC was displayed in Table 2.
2.2. Specimen Preparation and Curing. During the ARGFRC
specimen preparation process, the following two steps were
included in the concrete mixing procedure: (i) Adding
cement, ne natural aggregate (river sand), coarse natural
aggregate (stone), water, and a water-reducing agent to the
concrete mixer to mix for two minutes. (ii) Adding all the
ARGF gradually to the concrete mixer and mixing the fresh
ARGFRC for at least one minute. e ARGFRC mixing
process should guarantee that ARGF is evenly and ran-
domly distributed in the concrete specimens to prevent
ber agglomeration [52]. Due to the slump being 45 mm
Lower Standard Treshold (FA)
Fine Aggregates (Sand)
Upper Standard Treshold (FA)
Lower Standard Treshold (CA)
Coarse Aggregates (Crushed Stone)
Upper Standard Treshold (CA)
1 10 1000.1
Particle Size (mm)
0
20
40
60
80
100
Cumulative Passing Rate (%)
Figure 1: Particle size distribution of the aggregates.
Table 1: ARGF properties.
Property Value
Fiber length (mm) 36
Fiber length to diameter ratio 58
Original wire diameter (m) 14–19
Loss on ignition (%) 0.80–2.00
Moisture content (%) ≤0.50
Specic gravity (g/cm
3
) 2.68
Modulus of elasticity (GPa) 72
Tensile strength (MPa) 1700
Softening temperature (°C) 860
Color White to o-white
4Advances in Materials Science and Engineering

(less than 50 mm), the electronic vibration table was used
for tamping and vibrating the concrete mixture in the steel
specimen mold [52]. e specimen’s surface was covered
with plastic lm immediately after forming. e specimens
were kept static for 1–2 days in a room with a temperature
of 20 ±5°C and a relative humidity greater than 50%, they
were named according to the specimen specication. After
demolding, the specimens were put into a standard curing
room for curing and placed on the support with an interval
of 10–20 mm. e temperature of the standard curing room
was 20 ±2°C, and the relative humidity was above 95%. e
surface of the standard curing specimens was kept moist,
but rinsing the specimens with water was not allowed. e
standard curing periods for compressive specimens were
7–28 days, while the exural and impact specimens’ curing
duration was 28 days [52]. A total number of 42 ARGFRC
cubes (dimension: 100 mm ×100 mm ×100 mm) were cast
to obtain the cubic compressive strength for seven ber
contents and two standard curing periods (7 days and 28
days). Each ber content was prepared with three speci-
mens, and two trial runs were done to achieve the com-
pressive strength of the two curing periods [52, 53].
Twenty-one ARGFRC beams (dimension:
100 mm ×100 mm ×350 mm) with a standard curing pe-
riod of 28 days were prepared to conduct the exural test
per the standard recommended by the American Society for
Testing and Materials Standard (ASTM) C1609/C1609M-
19a [41], each ber content cast with three specimens. As
stated in CECS 13-2009 [52], a total of 42 ARGFRC col-
umns (150mm diameter and 63mm height) were cast to
investigate the impact properties, with six specimens for
each ber content after 28 days of standard curing.
2.3. Test Procedures
2.3.1. Compression Test. A full-automatic pressure testing
machine was adopted to conduct the compressive strength
test regarding GB/T 50081-2019 [53], as demonstrated in
Figure 2. During the test, it shall be loaded continuously and
evenly, and the loading speed should be 0.5 MPa/s∼0.8 MPa/
s. e cubic compressive strength of ARGFRC can be cal-
culated as shown in equation (1) [53].
fcc �F
A,(1)
where fcc �the cubic compressive strength of concrete
(MPa); F�the damage load of the specimen; A�the cross-
section of specimen.
2.3.2. Flexural Test. A four-point bending loading test with a
spreader beam placed on the third point was applied to the
exural test beams to study the exural strength and exural
toughness. As the ARGFRC schematic exural test shown in
Figure 3, the distance from the spreader beam’s left loading
point to the left support of the test beam was 100 mm, and
the support was 25 mm from the test beam end on each side.
e adopted test equipment was a model WEW-1000B
hydraulic universal testing machine (manufactured by
Changchun New Testing Machine Co. Ltd, China). e
range of its display value was 0–1000 kN, the resolution was
0.1 kN, and the loading rate was controlled at 0.05 mm/min.
e exural strength of FRC was calculated according to the
following equations [52–54]:
ff�Fl
bh2,(2)
fcr �Fcrl
bh2.(3)
Where ff�exural strength of concrete; F�damage load of
specimens; l�support span; h�cross-section height of the
specimen; b�cross-section width of the specimen; fcr �initial
crack exural strength of concrete; and Fcr �initial crack load.
e calculation methods for the exural toughness index
were successively put forward by the American Concrete
Institute (ACI) 544.9R-17 [55], Japan Concrete Institute
(JCI) SF4 [56], and ASTM C1018 [57]. e exural
toughness index I5,I10, and I20 was proposed according to
ASTM C1018 [57]. e exural toughness calculation
schematic diagram was illustrated in Figure 4. e O was the
original point, following 1.0, 3.0, 5.5, and 10.5 in multiples of
initial crack deection δcr. On the horizontal axis, points B,
Table 2: ARGFRC mixture proportion design.
Component FC0 FC0.3 FC0.5 FC0.8 FC1.0 FC1.3 FC1.5
Cement (kg/m
3
) 500 500 500 500 500 500 500
Stone (kg/m
3
) 1045 1045 1045 1045 1045 1045 1045
River sand (kg/m
3
) 700 700 700 700 700 700 700
Water (kg/m
3
) 200 200 200 200 200 200 200
Water-reducing agent (kg/m
3
) 3.0 3.0 3.0 3.0 3.0 3.0 3.0
Fiber volume content (m
3
) 0.0% 0.3% 0.5% 0.8% 1.0% 1.3% 1.5%
Note. FC-0.5 indicates 0.5% ber content (by volume) of ARGFRC.
Figure 2: ARGFRC compression test.
Advances in Materials Science and Engineering 5

D, F, and H were determined, with a planimeter to measure
the area of OAB, OACD, OAEF, and OAGH, which could be
named as Ωδ,Ω3δ,Ω5.5δ, and Ω10.5δ, respectively. e exural
toughness index of each specimen was calculated according
to the following Equations [10, 52, 57]:
I5�Ω3δ
Ωδ
,(4)
I10 �Ω5.5δ
Ωδ
,(5)
I20 �Ω10.5δ
Ωδ
.(6)
Aiming to accurately evaluate and compare the energy
absorption, ductility, and strength sustainability of the test
beams, two alternative stiness approaches were utilized:
post-cracking stiness, which considered the beam stiness
after initial cracking until the peak load was reached,
therefore evaluating the nonlinear postcracking behavior.
And postpeak stiness is considered the beam stiness after
the peak load until the maximum midspan deection is
reached (at beam failure), therefore evaluating the nonlinear
postpeak behavior. In this light, postcracking stiness, DPC
is calculated using the following equation [58, 59]:
DPC �Fpeak −Fcr
δpeak −δcr
,(7)
where Fpeak �the measured maximum force; Fcr �the load at
initial cracking; δpeak �the mid-span deection at peak force
(Fpeak); and δcr �the mid-span deection at initial cracking.
Similarly, post-peak stiness, DPP, may be calculated
using the following Equation [58, 59]:
DPP �δult −δpeak
Fpeak −Fd,ult
,(8)
where δult �the maximum midspan deection as deter-
mined from the load-displacement relationship; and Fd,ult
�the load corresponding to the maximum measured
midspan deection that relates to a beam’s ability to recover
and sustain a high-strength, postpeak state.
2.3.3. Impact Test. Self-made test instrumentation was
implemented on the drop hammer impact resistance test
based on the recommendations from ACI 544.9R-17
[52, 55]. e test principle was to accumulate a certain
amount of energy until it was damaged, and then the
absorbed kinetic energy was calculated. e impact re-
sistance test setup consisted of an impact rack, an impact
ball, and an impact hammer, as shown in the diagram in
Figure 5(a). e distance between the two baes on the
bottom plate was 160 mm, and the distance from the
impact rack to the impact ball surface was 500 mm. e
diameter of the impact ball was 63 mm, and the mass of the
impact hammer was 4.5 kg. In the top view of the impact
resistance test, as demonstrated in Figure 5(b), the impact
hammer moved in free fall, and the impact steel ball was
placed on the top surface of the impact resistance spec-
imen. Each impact was a cycle. When the initial crack
appeared on the surface of the specimen, the number of
initial impacts was recorded as N1. Continuing to repeat
the impact cycle until the specimen contacted any three of
the four baes of the impact frame, the number of failure
impacts was recorded as N2. According to the following
equations, the initial crack resistance energy dissipation
and failure resistance impact energy of ARGFRC were
calculated [55]:
Load ending
Spreader beam
Test be am
25 100 50
350
50 100 25
100
(a) (b)
Figure 3: ARGFRC exural test: (a) schematic diagram (unit: mm); (b) four-point bending test.
δ
OBD FH
Initial crack
10.5δ
A
C
E
G
5.5δ
3δ
Deection
Load
Figure 4: Computing models of exural toughness index of FRC.
6Advances in Materials Science and Engineering

W1�N1mgh, (9)
W2�N2mgh, (10)
where W1�the impact energy dissipation of the initial
specimen crack; N1�the number of impact times of
specimen’s initial crack; m�the mass of the impact hammer
quality; g�gravity acceleration; h�the drop height of the
impact hammer; W2�the impact energy dissipation of the
specimen failure; and N2�the number of impact times of
the specimen’s failure.
2.3.4. SEM Test. After the exural test, select about
1 cm ×1 cm ×1 cm representative samples from the fracture
surface immediately for the microscopic test. When selecting
the samples, try to guarantee the atness of the observation
surface of the samples. Wrap and number them in clean
plastic bags to avoid contamination as much as possible. e
SEM test procedure was conducted according to ASTM
C1723-16 [60]. e samples were prepared with a Q150TS
high-resolution magnetron ion sputtering coating machine
produced by Quorum in the United Kingdom. e coating
of the sample was gold, the thickness was 15.0 nm, and the
density was 19.32 g/cm
3
. After spraying gold, the download
stage was taken and xed on the EVOMA15/LS15 tungsten
lament SEM produced by Carl Zeiss, Germany. e
samples were observed by adjusting the best observation
distance according to the sample number.
2.3.5. EDS Test. EDS is signicant accessory equipment for
an electron microscope. Combined with an electron mi-
croscope, it can perform qualitative and quantitative ana-
lyses of element distribution in the microscopy area of the
material. INCA X-Max 80 TEM (produced by Oxford In-
strument Analysis Co., Ltd, UK) was used in the EDS test.
After the concrete was stirred, the internal hydration re-
action occurred, producing hydrated calcium silicate (CSH
gel), calcium hydroxide, water garnet (C3AH6), ettringite,
and other products. ese tiny chemical products cannot be
observed with the naked eye. Consequently, to better observe
the GF concrete microscopically, an electron microscope
was used to analyze the points of the observed sample at six
thousand times magnication, and the corresponding en-
ergy spectrum observation results were presented. In the
EDS analysis, the elements of the benchmark concrete
sample and EDS-FC0.8 were quantitatively analyzed, and the
element distribution comparison of the ARGFRC EDS-FC0
reference concrete specimen and EDS-FC0.8 were magnied
6000 times as well.
3. Results and Discussion
3.1. Cubic Compressive Strength. As the cubic compressive
test results shown in Figure 6, dierent ber contents had
negligible impact on the early cubic compressive strength
(CCS) of ber reinforced concrete. Compared with plain
concrete without ber (CCS-FC0), when the ber content
was 0.5%, the 7 d CCS of ber-reinforced concrete increased
by 0.49%, and when the ber content was 1.3%, the CCS
decreased by 15.61%. For the 28 d CCS, the impact of dif-
ferent ber contents on the strength of ARGFRC was much
greater than that of the benchmark concrete (CCS-FC0).
When the ber content was 0.5%, the CCS of ARGFRC
increased by 5.94%; when the ber content was 1.5%, the
CCS decreased by 11.89%; and when the ber content was
0.3%, both the 7 d and 28 d CCS of ARGFRC were relatively
increased by about 2.00%. When the ber content was 0.5%,
the CCS increased the most. e CCS of ARGFRC decreased
the most when the ber content was 1.5%. e maximum
28 d CCS for ARGFRC was 51.7MPa (CCS-FC0.5), while the
minimum 28 d CCS was 43.0 MPa (CCS-FC1.5). Conse-
quently, it is concluded that from the inuence of CCS of
ARGFRC, the optimum volume ber content was 0.5%.
3.2. Flexural Behavior
3.2.1. Load Deection. According to the experimental data,
seven dierent ber contents of the ARGFRC load-deec-
tion curve were drawn, as shown in Figure 7. For the
160
160
20
80 210
50 80
80 210
50 80
20
1
11–1
160
210
70
(a) (b)
Figure 5: ARGFRC impact resistance test: (a) test setup (mm); (b) impact resistance test (top view).
Advances in Materials Science and Engineering 7

benchmark concrete FS-FC0 specimen without adding
ARGF, as illustrated in Figure 7(a), the descending section
was almost vertical, which fully embodied the characteristics
of the brittle failure of concrete. Whereas with the emer-
gence of ARGF addition, as specimen FS-FC0.3 illustrated in
Figure 7(b), shows the decrease section of the load-deection
curve changed compared to FS-FC0, which was also a linear
decrease, a similar phenomenon was shown in FS-FC0.5
(Figure 7(c)). As the ARGF ber content gradually increased
to 0.8% (FS-FC0.8), a zigzag appeared in the descent seg-
ment of the load-deection curve, demonstrated in
Figure 7(d), and the vertical decrease section became smaller
than the benchmark sample (FS-FCO). en the curve
gradually deviated from the deection axis, which illustrated
that under the circumstance of the same deection defor-
mation, the load-bearing capacity of ARGFRC became
larger, showing that ARGF was acting as a bridge relation
role in concrete and increasing the ductility of concrete as
provided in FS-FC0.8 (Figure 7(d)). With the constant in-
crease of ARGF ber content in Figures 7(e) and 7(f),
dramatic changes in the load-deection curve happened in
the rising and decreasing sections. e rising section of glass
ber was slow in Figure 7(e) compared to Figure 7(d). e
more apparent zigzag performance occurred in the decline
section, which deviated much more from the deection axis;
the decline section in the vertical section was almost invisible
but became smoother as demonstrated in Figure 7(e).
ARGFs played a good role in “bridging relations,” thus
creating the increased concrete ductility and delaying the
concrete’s brittle failure. e maximum deection of FS-
FC1.3-2 in Figure 7(f) was 50% larger than FS-FC1.0-1 as
shown in Figure 7(e), while the peak load of FS-FC1.3 in
Figure 7(f) was smaller than FS-FC1.0 in Figure 7(e). As the
specimen FS-FC1.5 load-deection curve shows in
Figure 7(g), the decline section improved signicantly, and
its trend became more moderate, which turned out that with
the increase of ARGF, the ductility of ARGFRC increased
gradually. To facilitate the comparison of the load-deection
test results with seven dierent ber contents of ARGFRC,
the average value of three specimens in each group was
selected to draw Figure 7(h). FS-FC0.5 indicated the largest
exural peak load (24.51 kN) among all the specimens, while
FS-FC0 was the smallest exural peak load (20.64 kN). e
beam stiness degradation phenomenon was found with the
deection increased in Figure 7(h), which was because the
microcracks were initiated and the cross section was reduced
with the increased loading applied to the tested beams. e
average deection of specimens (FS-FC0.8, FS-FC1.3, and
FS-FC1.5) exceeded 1.4 mm, while the other four types of
specimens were below 1.0 mm.
3.2.2. Flexural Strength. Table 3 depicts the calculated ex-
perimental results of the exural test. When the ber volume
fraction addition amount was 0.5%, the strength ratio was
1.19, which could improve the maximum exural strength of
ARGFRC. As the ber contents became 0.8% and 1.0% and
the strength ratio was 1.18 and 1.17, although the exural
strength would drop slightly, compared with when the
strength ratio was 1.19 and the ber content was 0.5%, the
decreasing extent was very weak. As ber content continued
to increase, exural strength decreased gradually. When the
strength ratio was 1.06, the ber content was 1.3%, ap-
proximately the same as the reference concrete. From the
exural strength ratio, the best adding amount for a 36 mm
length ARGF was 0.5%∼1.0%. Figure 8(a) shows the initial
crack and exural strength curve of ARGFRC, the changing
trend of experimental data could be observed from the curve.
Experimental statistics indicated that mechanical perfor-
mance improvements of concrete could be realized by
adding a certain amount of ber, which enhanced the
toughness and cracking strength of concrete, absorbed load
energy to prevent premature fracture, and improved the
toughness and safety performance of the structure. Based on
exural strength test data, the last point of ber incorpo-
ration was removed, the ber-concrete exural strength
curve was tted, and a unitary quadratic regression curve
equation was obtained with a correlation coecient of
0.9377, which was in good agreement with the curve.
3.2.3. Flexural Toughness Index. e arithmetic means the
value calculated from the three specimens is regarded as the
group specimen’s exural toughness index. e calculated
values of the exural toughness index, exural energy, and
fracture energy are demonstrated in Table 4.
Concrete without ber content incorporation was a
brittle material. e toughness index of the benchmark
sample was dened as one. e toughness index of ARGFRC
increased with the increase in ber content. In Figure 8(b),
the fracture energy of ARGFRC increased with the en-
hancement of ber content. e value of exural toughness
I5,I10, and I20 was 4.0, 5.9, and 8.9, respectively, when the
ber volume content was 1.5%. Compared with benchmark
41 40 41.2 41 39.6
34.6
40.7
48.8 49.4 51.7
47.6 47 45.1 43
7 d
28 d
CCS-FC0
CCS-FC0.5
CCS-FC1.5
CCS-FC1.3
CCS-FC0.3
CCS-FC1.0
CCS-FC0.8
Specimens
0
10
20
30
40
50
60
Cubic compressive strength (MPa)
Figure 6: ARGFRC cubic compressive strength.
8Advances in Materials Science and Engineering

samples of the concrete specimen, the exural fracture
energy of ARGFRC was improved signicantly, and the
exural toughness index was increased by 3.0–7.9 times.
When the ber volume content was 1.5%, the exural
fracture energy of ARGFRC reached its maximum value,
with a maximum increase of 527.5%. In the crack propa-
gation process, fracture energies were absorbed by the
ARGFRC specimen to prevent crack development. It was
FS-FC0-1
FS-FC0-2
0
5
10
15
20
25
Load (kN)
0.1 0.2 0.3 0.4 0.50.0
Deection (mm)
(a)
FS-FC0.3-1
FS-FC0.3-2
FS-FC0.3-3
0
5
10
15
20
25
Load (kN)
0.2 0.4 0.6 0.8 1.00.0
Deection (mm)
(b)
FS-FC0.5-1
FS-FC0.5-2
FS-FC0.5-3
0
5
10
15
20
25
30
Load (kN)
0.2 0.4 0.6 0.8 1.0 1.2 1.40.0
Deection (mm)
(c)
FS-FC0.8-1
FS-FC0.8-2
FS-FC0.8-3
0.2 0.4 0.6 0.8 1.0 1.2 1.40.0
Deection (mm)
0
5
10
15
20
25
30
Load (kN)
(d)
FS-FC1.0-1
FS-FC1.0-2
FS-FC1.0-3
0
5
10
15
20
25
30
Load (kN)
0.2 0.4 0.6 0.8 1.00.0
Deection (mm)
(e)
FS-FC1.3-1
FS-FC1.3-2
FS-FC1.3-3
0
5
10
15
20
25
Load (kN)
0.2 0.4 0.6 0.8 1.0 1.2 1.40.0
Deection (mm)
(f)
FS-FC1.5-1
FS-FC1.5-2
FS-FC1.5-3
0
5
10
15
20
25
30
35
Load (kN)
0.2 0.4 0.6 0.8 1.0 1.2 1.40.0
Deection (mm)
(g)
FS-FC0
FS-FC0.3
FS-FC0.5
FS-FC0.8
FS-FC1.0
FS-FC1.3
FS-FC1.5
0
5
10
15
20
25
Load (kN)
0.2 0.4 0.6 0.8 1.0 1.2 1.40.0
Deection (mm)
(h)
Figure 7: ARGFRC exural load-deection curve: (a) FS-FC0; (b) FS-FC0.3; (c) FS-FC0.5; (d) FS-FC0.8; (e) FS-FC1.0; (f ) FS-FC1.3; (g) FS-
FC1.5; and (h) comparison results.
Advances in Materials Science and Engineering 9

also available to prevent ber breakage and concrete matrix
from debonding, prevent ber from being pulled out, and
prevent damage to ber-reinforced concrete, which was fair
enough to reect the role of ber in concrete. Adding bers
could slow down the cracks, prevent premature cracks in the
specimens, and delay the damage. As the successive increase
in ber content played a much more signicant role in
“bridging,” the fracture energy index regression curve
equation was obtained through experimental data tting as
shown in the following Equation. e correlation coecient
was achieved with good agreement.
Gf�14.7475e3.05vf+301.482, R2�0.93043.(11)
3.2.4. Postcracking and Postpeak Toughness. Table 5 sum-
marizes the results of the two stiness methods. e largest
value of postcracking stiness DPC was calculated as
36.174 kN/mm (FS-FC0.8), followed by the stiness values of
Table 3: ARGFRC exural strength.
Specimens SG D(mm) CP (days) F(kN) FCC (MPa) FACC (MPa) ff(MPa) fcr (MPa) SR
FS-FC0
C40 100 ×100 ×350
28
17.94 5.38
6.19 5.26 5.27 1.0022.48 6.74
21.51 6.45
FS-FC0.3 28
24.10 7.23
6.71 5.70 5.44 1.0822.96 6.89
20.00 6.00
FS-FC0.5 28
25.56 7.67
7.35 6.25 5.78 1.1925.36 7.61
22.62 6.79
FS-FC0.8 28
28.27 8.48
7.32 6.21 5.78 1.1821.33 6.40
23.57 7.07
FS-FC1.0 28
24.18 7.25
7.21 6.13 5.61 1.1725.96 7.79
21.99 6.60
FS-FC1.3 28
22.16 6.65
6.57 5.58 5.27 1.0622.65 6.80
20.84 6.25
FS-FC1.5 28
31.06 9.32
7.11 6.04 5.19 1.1523.26 6.98
24.14 7.24
AV 1.12
SD 0.07
Note. SG �strength grade; D�dimension; CP �curing period; F�failure load; FCC �exural strength; FACC �average exural strength; ff�standard
exural strength; fcr �initial crack strength; SR �strength ratio; AV �average value; and SD �standard deviation.
0.0 0.3 0.6 0.9 1.2 1.5
Fiber content (%)
Flexural strength
Initial crack strength
ff=-1.9385vf2+2.836vf+5.2008
5.2
5.4
5.6
5.8
6.0
6.2
6.4
Strength (MPa)
R2=0.9377
(a)
Fracture energy
Regression curve
0.3 0.6 0.9 1.2 1.50.0
Fiber content (%)
0.0
0.5
1.0
1.5
2.0
Fracture energy (×103N/m)
Gf =14.7475e3.05vf+301.482
R2=0.93043
(b)
Figure 8: ARGFRC exural tests: (a) exural strength and initial crack strength; (b) fracture energy.
10 Advances in Materials Science and Engineering

FS-FC1.0, FS-FC1.5, and FS-FC0.5. e postcracking sti-
ness DPC of FS-FC1.3 was approximately 32.3% of FS-FC0.8.
Specimens FS-FC0 and FS-FC0.3 exhibited lower values
(below 20 kN/mm). FS-FC1.3 presented the lowest post-
cracking stiness. As for the postpeak stiness, DPP, the
ascending order was FS-FC0 <FS-FC0.3 <FS-FC0.5 <FS-
FC0.8 <FS-FC1.0 <FS-FC1.3 <FS-FC1.5. e test results
demonstrated that the higher the ber content, the larger the
postpeak stiness.
3.3. Impact Behavior. Each group consisted of six speci-
mens. e maximum and minimum of the experimental
data obtained were crossed out. e remaining four
specimens’ averaged data were represented as the experi-
mental results of initial crack resistance energy dissipation
and damage impact energy dissipation ARGFRC. ARGFRC
impact resistance results are illustrated in Table 6. During
the experiment process, the number and morphology of
cracks were discovered to change with the variation of ber
content, as shown in Figure 9. For the benchmark specimen
IR-FC0 with the ber content of 0.0% in Figure 9(a), the
initial crack was also the nal crack, which was a straight-
line crack through the center of the specimen, indicating
that it belonged to brittle damage. Cracks were changed,
obviously, after the addition of ARGF as illustrated in
Figure 9(b). ree initial cracks were developed when ber
content was 0.5% in Figure 9(c), and another crack with the
length of the radius was developed based on a straight line
through the crack, which indicated that ber impacted
ARGFRC to restrain the generation of cracks and absorb
more impact energy. As the ber content increased to 1.0%
as in the specimen IR-FC1.0 depicted in Figure 9(d), initial
cracks increased to four main evenly spaced cracks that
radiated from the center and took on a cross shape in
Figure 9(e), which illustrated that the ber’s ability to
absorb impact energy uniformly in the concrete body was
better than IR-FC0.5 (Figures 9(b) and 9(c)). When ber
content was 1.5% as in specimen IR-FC1.5 in Figure 9(f),
the impact number declined compared to the 1.0% dosage
(IR-FC1.0), and cracks appeared obviously like a triangle
with damaged cracks throughout the specimen as depicted
in Figures 9(g) and 9(h). e ARGFRC impact resistance
calculated results are shown in Table 6. e impact times
and energy-absorbing curves from the initial crack and
damaged crack were drawn, respectively, according to the
test data shown in Figure 10. e curve was a fold line that
suddenly began with a straight line, suddenly rose, and then
fell sharply. It was gentle when ber content was below
0.5%, but after it increased from 0.5% to 1.3%, the stroke
times of the initial crack and damage state increased
rapidly. When ber content was 1.3% (IR-FC1.3), the stoke
ball times of damage state compared with the benchmark
concrete increased to 2363.64%, but the curve began to
decline until ber content reached 1.5% (IR-FC1.5). For the
damage state, energy absorption was also raised by the
increase in ber content; the impact resistance test revealed
that the increase in ARGF dramatically increased the en-
ergy absorption, and more energy would be needed to
absorb in the damage process of ARGFRC compared with
benchmark concrete.
3.4. SEM Analysis. e SEM observation and analysis data of
ARGFRC are illustrated in Figures 11 and 12. To analyze the
relationship between ber and concrete in detail, various
proportions were intercepted in the experiment. e overall
density map was magnied by 1,000 times. e bonding
eect of ber and concrete was magnied by 50 times. An
enlarged view of the ber-concrete joint surface was mag-
nied two hundred times; the overall density decreased with
the increase in ber content, but no obvious pores appeared.
Table 4: ARGFRC exural toughness index.
Specimens FVC (%) MPL (kN) UFS (MPa) I5I10 I20 FEA (N·m) FE (N·m
−1
)
FS-FC0 0.0 20.64 6.19 1.0 1.0 1.0 2.04 203.53
FS-FC0.3 0.3 22.35 6.71 1.7 2.4 3.9 4.48 448.33
FS-FC0.5 0.5 24.51 7.35 1.6 2.4 3.8 3.42 342.39
FS-FC0.8 0.8 24.39 7.32 2.7 3.9 6.1 4.23 423.31
FS-FC1.0 1.0 24.04 7.21 3.1 4.3 6.4 7.88 787.72
FS-FC1.3 1.3 21.88 6.57 3.8 5.5 8.2 9.37 936.58
FS-FC1.5 1.5 23.15 7.11 4.0 5.9 8.9 17.77 1777.15
Note. FVC �ber volume content; MPL �the maximum peak load; UFS �ultimate exural strength; FEA �fracture energy absorption; FE �fracture energy.
Table 5: Postcracking and postpeak stiness.
Specimen δcr (mm) δult (mm) δpeak (mm) Fpeak (kN) Fcr (kN) Fd,ult (kN) DPC (kN/mm) DPP (kN/mm)
FS-FC0 0.14 0.30 0.27 20.64 18.45 1.46 17.631 0.002
FS-FC0.3 0.18 0.89 0.45 22.35 19.04 1.52 12.305 0.021
FS-FC0.5 0.12 0.96 0.33 24.51 20.23 2.32 20.777 0.028
FS-FC0.8 0.10 1.00 0.22 24.39 20.23 3.15 36.174 0.037
FS-FC1.0 0.07 1.20 0.24 24.04 19.64 3.48 26.377 0.046
FS-FC1.3 0.02 1.20 0.31 21.88 18.45 3.75 11.684 0.049
FS-FC1.5 0.05 1.41 0.26 23.15 18.17 5.75 23.738 0.066
Advances in Materials Science and Engineering 11

To analyze the action mechanism of ARGF in concrete more
intuitively, the internal morphology of the benchmark
sample FS-FC0 after exural failure was observed by SEM.
Figure 11 suggests the microstructure (20 m and 2 m) of
exural test samples of concrete without ARGF (SEM-FC0).
e surface of concrete without bers contains more porous
(a) (b) (c)
(d) (e) (f )
(g) (h)
Figure 9: ARGFRC impact resistance crack: (a) IR-FC0; (b) IR-FC0.5 (initial crack); (c) IR-FC0.5 (damage crack); (d) IR-FC1.0 (initial
crack); (e) IR-FC1.0 (damage crack); (f) IR-FC1.5 (initial crack); (g) IR-FC1.5 (side view crack); and (h) IR-FC1.5 (damage crack).
Table 6: ARGFRC impact resistance results.
Specimens FVC (%) SBN (times) EA (J)
N
1
N
2
W
1
W
2
IR-FC0 0.0 11 11 242.83 242.83
IR-FC0.3 0.3 10 16 220.75 353.20
IR-FC0.5 0.5 9 13 198.68 286.98
IR-FC0.8 0.8 85 99 1876.38 2185.43
IR-FC1.0 1.0 131 139 2891.83 3068.43
IR-FC1.3 1.3 260 271 5739.5 5982.325
IR-FC1.5 1.5 210 223 4635.75 4922.725
Note. IR �impact resistance; FVC �ber volume content; SBN �sticking ball number; and EA �energy absorption.
12 Advances in Materials Science and Engineering

0.3 0.6 0.9 1.2 1.50.0
Fiber content (%)
0
1
2
3
4
5
6
Impact energy abosorption (kJ)
Initial crack
Failure
Figure 10: ARGFRC impact energy absorption.
Crack
Pore
(a)
Crack
Pore
(b)
Figure 11: SEM-FC0: (a) 20 m and (b) 2 m.
ARGF
concrete
ARGF
pore
(a)
ARGF concrete
(b)
Figure 12: Continued.
Advances in Materials Science and Engineering 13

voids and microcracks caused by hardening and shrinkage.
ere were two long microcracks and four porous voids as
shown in Figure 11(a), while four microcracks and 11 porous
voids as illustrated in Figure 11(b). e interface transition
zone (ITZ) between mortar and regenerated aggregate is not
close enough, and the mortar does not wrap the regenerated
aggregate completely. is phenomenon accounts for the
hardened hydrate formed by the hydration reaction between
cement and water in the mixture attached to the aggregate
surface. Meanwhile, due to the original mortar or hardened
hydrate attached to the aggregate surface, the combination
of cement mortar and aggregate is insucient; the nal
concrete surface is insuciently compacted; the gap at the
ITZ is large; and the pore area is greatly improved. e ITZ is
the weakest area, where microcracks often develop.
Microcracks, voids, and ITZs are signicant inuencing
elements of the exural and impact behaviors of samples,
which will cause excessive internal defects of concrete and
ultimately decrease its mechanical properties and durability
[17]. When the ber content was 0.3%–0.8% as shown in
ARGF crack
crack
(c)
ARGF
pore
pore
ARGF
crack
(d)
ARGF
pore
(e)
ARGF
ARGF
(f)
Figure 12: ARGFRC SEM observation: (a) SEM-FC0.3; (b) SEM-FC0.5; (c) SEM-FC0.8; (d) SEM-FC1.0; (e) SEM-FC1.3; and (f ) SEM-
FC1.5.
14 Advances in Materials Science and Engineering

Figures 12(a) (SEM-FC0.3), 12(b) (SEM-FC0.5), and 12(c)
(SEM-FC0.8), the bond between the bers and concrete
gradually strengthened, indicating that the bond strength
between the ber and the concrete matrix was enhanced. As
can be seen in Figure 12(a), there were pores in the SEM-
FC0.3. e bond was not particularly good when the ber
content incorporated amount was 1.0%∼1.5% as demon-
strated in Figures 12(d)∼12(f). ere were two porous voids
along the longitudinal ber direction and a microcrack in
Figure 12(d), cross ber distribution was also found in the
morphology. Figure 12(e) suggested three porous voids,
which were three times as illustrated in Figure 12(f). It
displayed that ber content was not as much as possible, but
there was an optimal incorporation amount of ber content.
e amount of ber content was not better because after
ber was added, the concrete paste would aect its wrapping
which will gradually decrease. When the volume of the
matrix remained unchanged, the amount of mixed ber
increased. e average ber per unit of matrix concrete
wraps increased. e wrapping eect will be reduced. Mi-
croscopic tests conrmed this. When ber content was
1.0%∼1.5%, the amount of slurry that wrapped the ber
became less. It was also inconsistent with the phenomenon
that during the specimen preparation process, the concrete
mixer became very laborious when the ber content reached
1.5%, as shown by SEM-FC1.5 in Figure 12(f ), the concrete
grout was not enough, and ARGFs were not distributed
uniformly in the concrete mixture. e fracture surface
occurred in Figures 12(c) and 12(d) indicated that there are
many ARGFs pulled out and only a few of them were broken.
Consequently, the ARGFRC exural fracture process is
greatly inuenced by the ber pull-out strength. Microcracks
grow until they reach a material area that can bear the crack
tip concentrate stresses that occur in front of them. More
ARGFs than the nearby ones might have in this material
area. e specimen bears an increased load during the
(a) (b)
(c) (d)
(e) (f)
(g)
Figure 13: ARGFRC EDS observation (magnify 6000 times points analyses, energy spectrum): (a) EDS-FC0; (b) EDS-FC0.3; (c) EDS-FC0.5;
(d) EDS-FC0.8; (e) EDS-FC1.0; (f) EDS-FC1.3; and (g) EDS-FC1.5.
Advances in Materials Science and Engineering 15

initiation and growth of microcracks. When it comes to the
exural strength of the ARGFRC specimen, a fracture begins
to grow from the weakest microcrack, and the ARGFRC
specimen will be divided into two pieces [14].
3.5. EDS Analysis. Figure 13 illustrates the magnied 6000
times point analyses and energy spectrum of the ARGFRC
EDS observation results. EDS-FC0 was chosen as the
benchmark specimen as shown in Figure 13(a), which was
compared with EDS-FC0.8 in Figure 13(d). e EDS-FC0
result given in Figure 13(a) shows the composition of
ARGFRC without bers predominantly containing Ca, as
evidenced by the large Ca peaks. e composition of
specimen EDS-FC0 also contains Si, Mg, Au, and Al. In
addition, porous voids at ITZ stemming from the imper-
fections in the cement paste were seen. e composition of
ARGFRC predominantly contains Ca, as illustrated in
Figures 13(b), 13(c), and 13(e). As the specimen EDS-FC0.5
shown in Figure 13(c), the test results depict that ARGFs
were not distributed uniformly, and the agglomeration
phenomenon was founded. e EDS result of ARGFRC with
0.8% ber content is depicted in Figure 13(d), in which the
dominant component is also Ca. In Figures 13(f ) and 13(g),
some gaps at ITZ stemming from the imperfect bond be-
tween ARGF and cement paste were observed. Table 7
revealed that the main hydration products of concrete
were hydrated calcium silicate gel (CSH), calcium hydroxide
crystals (Ca(OH)
2
), calcium aluminate hydrate, and
ettringite. e hydrated calcium suaminate crystals
(ettringite) were easy see. e calcium element in the energy
spectrum was clear, showing that even if the concrete was
added with a proper amount of ber content, the chemical
reaction during the concrete mixing process was still suf-
cient. e production of its hydrates did not reduce. In
order to better observe the distribution of elements in
ARGFRC, the benchmark concrete sample (EDS-FC0) and
0.8% ber content ARGFRC (EDS-FC0.8) were scanned on
the whole surface, as shown in Figures 14(a) and 14(b). After
scanning, it was clear that dierent chemical products were
distributed 6000 times larger. It can be seen from the
scanning of the cut surface of the benchmark concrete
sample that the distribution of Ca elements almost occupies
the whole section, and the distribution of Fe elements is
Table 7: EDS quantitative analyses ARGFRC EDS-FC0 and EDS-FC0.8.
Specimen Element Element concentration Strength correction Weight percentage Weight percentage sigma
EDS-FC0
C K 45.92 0.3551 23.94 0.76
O K 107.67 0.3339 59.72 0.62
Mg K 1.99 0.5671 0.65 0.03
Al K 1.89 0.6912 0.51 0.02
Si K 9.87 0.7953 2.30 0.04
K K 0.64 0.9966 0.12 0.02
Ca K 63.43 0.9206 12.76 0.15
Total 100.00
EDS-FC0.8
C K 17.03 0.2986 21.91 1.23
O K 46.65 0.3205 55.93 0.93
Mg K 3.93 0.5842 2.58 0.08
Al K 3.85 0.6862 2.15 0.06
Si K 6.41 0.7741 3.18 0.08
K K 0.59 0.9915 0.23 0.03
Ca K 33.50 0.9188 14.01 0.25
Total 100.00
20 μm
(a)
20 μm
(b)
Figure 14: ARGFRC EDS whole surface observation (magnied 6000 times): (a) EDS-FC0 and (b) EDS-FC0.8
16 Advances in Materials Science and Engineering

exceedingly small and almost invisible. Scanning from the
surface of EDS-FC0.8 depicts that the distribution of the Ca
element almost occupies the whole section, and the distri-
bution is relatively uniform, with few Fe elements, indicating
a concentrated distribution. As tabulated in Table 7, the gold
distribution of the sample surface scanned from the
benchmark concrete EDS-FC0, and EDS-FC0.8 was very
uniform, which also determined that the gold spraying was
very good in the production of specimens. e sample had
good electrical conductivity during the process to ensure
correct microtesting.
4. Conclusions
is research aimed to investigate the eects of ber content
(by volume) on the compressive, exural, impact, and mi-
crostructural performance of ARGFRC. Based on the results
of the experimental investigation, conclusions are drawn as
follows:
(1) e exural toughness index increased with the
increase in ber content, while the brittleness de-
creased. When ber content was 1.5%, the exural
toughness I5,I10, and I20 values were 4.0, 5.9, and
4.0, respectively, and the corresponding exural
toughness index increased by 3.0∼7.9 times.
(2) When ber content was 1.5%, ARGFRC reached the
maximum exural fracture energy with an increment
of 527.5%. e exural toughness and the absorption
fracture energy of ARGFRC improved by adding
ARGF, and the exural fracture energy increased
rapidly compared with plain concrete. e exural
strength of the concrete was also aected by the
variation in ber content, and the maximum
ARGFRC exural strength was when the ber
content was at 0.5%.
(3) ARGFRC exural strength curve was tted with
dierent ber contents, and a quadratic equation of
one unknown regression curve was achieved with a
correlation coecient of 0.9377. Meanwhile, fracture
energy experiment data were tted, and an expo-
nential regression curve equation was obtained with
a correlation coecient of 0.93043.
(4) According to the exural load-deection curve,
exural toughness increased by adding ARGF, which
could increase the ductility and delay the brittle
failure when the ber volume content reached 0.8%.
e highest and lowest values of postcracking
stiness DPC were calculated as 36.174 kN/mm (FS-
FC0.8) and 12.305 kN/mm (FS-FC0.3), respectively.
e higher the ber content, the larger the postpeak
stiness DPP.
(5) Impact resistance test results indicated that the
optimum ber volume content was 1.3%. It was
recommended that ber content be controlled
within 0.5%∼1.3%, and the best ratio of the fracture
morphology and impact resistance absorption ki-
netic energy was 1.0%.
(6) e SEM analysis shows that ARGF plays a
“bridging” eect in the concrete matrix, connecting
cracks, and voids. e microscopic test also proved
that the ber content was not as high as possible. As
the ber content increased, the eect of the concrete
grout on the ber packaging decreased, which is why
concrete exural strength increased with the increase
in ber content.
(7) e EDS analysis indicated the distribution and
content of elements in ARGFRC. e specic con-
tent of oxygen, silicon, calcium, carbon, magnesium,
potassium, aluminum, and other elements was de-
tected. Adding a certain ber content did not aect
the hydration of the concrete reaction.
Data Availability
e data used to support the ndings of this study are
available from the corresponding author upon request.
Conflicts of Interest
e authors declare that they have no conicts of interest.
Acknowledgments
e authors may wish to express their sincere appreciation
for the nancial support provided by the National Key
Research and Development Program of China (No.
2017YFC0806008), National Natural Science Foundation of
China (No. 51178361), Science and Technology Project of
Department of Transportation of Hubei Province (Nos.
2018-422-1-2, 2022-11-2-8), Major Project of Technological
Innovation of Hubei Province (No. 2018AAA031), China
Scholarship Council (No. 201906950026), and the Funda-
mental Research Funds for the Central Universities (No.
2019-YB-015) for this work.
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Advances in Materials Science and Engineering 19