Experiment study on the abrasion and impact performance
of cement-based composites using fiber and silica fume
Wei-Ting Lin, Der-Chang Suen
Department of Architecture, National Jui-Fang Industrial Vocational High School
ABSTRACT
An experimental program was carried out to evaluate the mechanical
properties of cement-based composites.
Test variables included water to
cementitious ratio, dosage of silica fume and volume fraction of steel fiber and
abrasion resistance test and drop weight test were performed. Addition of fibers
provided better performance for the cement-based composites, while silica fume in
the composites may adjust the fiber dispersion and strength losses caused by fibers,
and improve strength and the bond between fiber and matrix with dense
calcium-silicate-hydrate gel. The combination of steel fibers and silica fume can
increase greatly abrasion and impact resistance of cement-based composites.
Keywords: abrasion coefficient, impact number, cement-based composites
INTRODUCTION
Cement-based composites have long been used for civil structures such as
highways, bridges and buildings. However, the unexpected deterioration of
reinforced or pre-stressed concrete structures has led to the improvement of durability.
Traditionally, the composition of cement-based composites includes cementitious
material, water, aggregate and/or admixtures. Fiber has been added in the fiber
cement-based composites (FCC) since 1960’s to improve concrete properties,
particularly tensile strength, abrasion resistance and energy absorbing capacity [1-3].
The presence of fiber helps to refrain crack growth or propagation and transfer load to
the un-cracked part [4-5]. The specimen with fibers has much higher ductility than the
specimen without fibers. Fibers by bridging the cracks in the cementitious
composites increase the energy absorption or toughness [6]. However, the properties
of FCC would be affected by the type, volume fraction and aspect ratio of fiber.
Lower fiber volume fraction is usually preferred by considering the material cost and
workability [7]. According to the results of previous researches, the volume fraction
suggested was around 2 % to achieve effectiveness in cement-based composites [8].
In addition, it was also reported that the combination of silica fume with steel fibers
would effectively enhance the compressive strength, splitting tensile strength,
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abrasion resistance and impact resistance of cement-based composites and be
beneficial for fiber dispersion. This study was aimed to evaluate the combined effect
of silica fume and steel fiber on the abrasion and impact resistance of cement-based
composites using experimental program.
EXPERIMENTAL PROGRAM
1. Materials and mix proportions
Type I Portland cement conforming to ASTM C150-05 was used in all mixes.
Silica fume with specific gravity of 2.20 and specific surface area of 22500 m2/kg was
used. The diameter of silica fume particle was about 0.1-0.2μm. The chemical
compositions of cement and silica fume are listed in Table 1.
Hooked-end steel fiber
with an aspect ratio (l/d) of 40 was applied. The average length and tensile strength
of steel fiber was 30 mm and 1100 N/mm2, respectively.
Table 1 Composition and specific gravity of Portland cement and silica fume
Chemical composition
SiO2 (%)
Al2O3 (%)
Fe2O3 (%)
CaO (%)
MgO (%)
SO3 (%)
L.O.I.* (%)
K2O+Na2O (%)
Others (%)
Specific gravity
Portland cement
21.2
5.4
3.2
63.8
2.0
2.2
0.7
0.8
0.7
3.15
Silica fume
91.5
0.2
0.7
0.4
1.5
0.5
1.4
1.9
1.9
2.20
Table 2 Mix design (kg/m3)
Mix no.
w/cm*
Water
A
0.35
189.4
Af1
0.35
189.4
Af2
0.35
189.4
Af3
0.35
189.4
A1
0.35
189.4
A1f1
0.35
189.4
A1f2
0.35
189.4
A1f3
0.35
189.4
A2
0.35
189.4
A2f1
0.35
189.4
A2f2
0.35
189.4
A2f3
0.35
189.4
B
0.55
217.0
Bf1
0.55
217.0
Bf2
0.55
217.0
Bf3
0.55
217.0
B1
0.55
217.0
B1f1
0.55
217.0
B1f2
0.55
217.0
B1f3
0.55
217.0
B2
0.55
217.0
B2f1
0.55
217.0
B2f2
0.55
217.0
B2f3
0.55
217.0
* water/cementitious ratio
** superplasticizer
Cement
Silica fume
558.0
558.0
558.0
558.0
530.1
530.1
530.1
530.1
502.2
502.2
502.2
502.2
395.0
395.0
395.0
395.0
375.2
375.2
375.2
375.2
355.5
355.5
355.5
355.5
0
0
0
0
27.9
27.9
27.9
27.9
55.8
55.8
55.8
55.8
0
0
0
0
19.8
19.8
19.8
19.8
39.5
39.5
39.5
39.5
2
Fine
aggregate
908.0
901.0
894.0
881.0
908.0
901.0
894.0
881.0
908.0
901.0
894.0
881.0
908.0
901.0
894.0
881.0
908.0
901.0
894.0
881.0
908.0
901.0
894.0
881.0
Coarse
aggregate
700.0
694.0
687.0
674.0
700.0
694.0
687.0
674.0
700.0
694.0
687.0
674.0
780.0
773.0
767.0
753.0
780.0
773.0
767.0
753.0
780.0
773.0
767.0
753.0
Fiber
SP**
0
39.0
78.0
156.0
0
39.0
78.0
156.0
0
39.0
78.0
156.0
0
39.0
78.0
156.0
0
39.0
78.0
156.0
0
39.0
78.0
156.0
5.6
5.6
5.6
5.6
5.6
5.6
5.6
5.6
5.6
5.6
5.6
5.6
0
0
0
0
0
0
0
0
0
0
0
0
The water/cementitious ratio was kept at 0.35 and 0.55, respectively.
The
maximum size of coarse aggregates was 13mm and the fineness modulus of fine
aggregates was 2.87. Mixture slump was controlled around 150mm by adjusting
proper amount of high-range water-reducing admixture in the mixes. The details of
mix proportions of FCC are shown in Table 2. Silica fume with 5% and 10% by the
weight of cement was used to replace cement partially. The volume fraction was
defined as the steel fiber volume divided by the total concrete volume and the steel
fiber content was used to replace aggregate partially. Concrete mixtures with
volume fraction of 0.5%, 1.0% and 2.0% steel fiber were designed.
2. Specimens
Specimens with a total of 24 different mixes were cast. For each mix, six
ψ150×64 mm circular plate for abrasion resistance test and drop weight test were
prepared and cured in saturated lime water until testing. Mix number A and B refer
to a water/cement ratio of 0.35 and 0.55, mix number 1 and 2 refer to the silica fume
content of 5 % and 10 %, and mix number f1, f2 and f3 refer to the steel fiber content
of 0.5 %, 1.0 % and 2.0%, respectively.
3. Testing methods
An abrasion resistance test was conducted following the specifications of
ASTM C418-05. The method covers the determination of abrasion resistance
characteristics of FCC by subjecting the specimen to the impingement of air-driven
silica sand, and abrasion coefficient was determined accordingly. The abrasion
coefficient is an index of abrasion resistance of cement-based composite and obtained
from AC  V A , where A is the test abraded surface area, V is the abraded volume
and AC is the abrasion coefficient.
Impact resistance assessment was performed following the recommendations
of ACI committee 544. A 63.5 mm-diameter steel ball with 4.54 kg weight dropped
from a height of 914 mm and recorded the number of drops until the first visible crack
and ultimate failure was found. Ultimate failure is defined as the opening of cracks
in the specimen sufficiently so that concrete specimen touches three of the four
positioning lugs on the base plate.
RESULTS AND DISCUSSION
1. Abrasion resistance test
The abrasion coefficient of specimen decreases as the fiber and silica fume
content increases as indicated in Fig. 1 at the age of 120 days. The inclusion of 0.5%
steel fiber in the composites markedly decreases the abrasion coefficient than that of
control. The abrasion coefficient is remained steady though the addition of steel
fiber content exceeded in the value of 1%. Another, the abrasion coefficient also
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decreases with the addition of silica fume increases for each w/cm ratio.
The
addition of steel fiber in the composites produces a denser and stronger surface, thus
resulting in a higher resistance to wear for FCC specimens. The abrasion coefficient
of A2f3 and B2f3 specimens is 2.21x10-3 and 3.21x10-3, respectively, which is about
50% lower than that of control specimen. The cement-based composites with 10%
silica fume and 2% fiber also exhibit an excellent ability in abrasion resistance. The
abrasion coefficient appears to decrease exponentially as compressive strength
increases as illustrated in Fig. 2. Clearly, the curve between compressive strength
and abrasion coefficient with high w/cm ratio drops significantly faster than that with
low w/cm ratio. It indicates that w/cm ratio also plays an important role on abrasion
coefficient except silica fume content and steel fiber content.
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w/cm = 0.35, silica fume = 0 %
w/cm = 0.35, silica fume = 5 %
w/cm = 0.35, silica fume = 10 %
w/cm = 0.55, silica fume = 0 %
w/cm = 0.55, silica fume = 5 %
w/cm = 0.55, silica fume = 10 %
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Abrasion coefficient (x10-3)
-
Abrasion coefficient (x10 3)
8
4
2
6
4
2
w/cm = 0.35, Y=1.40+99.57e-0.06X
R2=0.91
w/cm = 0.55, Y=3.00+442527.94e-0.32X R2=0.97
0
0
0
0.5
1
1.5
2
30
Steel fiber content (vol. %)
40
50
60
70
80
Compressive strength (MPa)
Fig. 1 - Abrasion coefficient vs. Fiber content
Fig. 2 - Abrasion coefficient vs. Compressive strength
Table 3 Drop weight test results
Mix no.
A
Af1
Af2
Af3
A1
A1f1
A1f2
A1f3
A2
A2f1
A2f2
A2f3
B
Bf1
Bf2
Bf3
B1
B1f1
B1f2
B1f3
B2
B2f1
B2f2
B2f3
Impact number of initial
crack, N1
59
54
86
88
4
20
70
115
7
19
70
350
98
110
130
222
30
27
40
71
35
33
35
94
Impact number of ultimate
failure, N2
63
70
113
133
19
43
116
175
11
32
128
460
103
129
171
252
33
47
92
135
39
46
53
154
4
Difference between N1 and
N2, △N
4
16
27
45
15
23
46
60
4
13
58
110
5
19
41
30
3
20
52
64
4
13
18
60
Impact toughness (KN-m)
2.54
2.82
4.56
5.37
0.77
1.73
4.68
7.06
0.44
1.29
5.16
18.56
4.16
5.20
6.90
10.17
1.33
1.90
3.71
5.45
1.57
1.86
2.14
6.21
2. Drop weight test
The impact number at ultimate failure serves as a qualitative estimate of the
energy absorbed by the specimens. The impact performance serves as a quantitative
index by impact number of initial crack (N1), impact number of ultimate failure (N2),
difference between N1 and N2 (△N) and impact toughness (T). Impact toughness is
calculated by T=N2mgh, where m, g and h is weight of the ball, acceleration of
gravity and height, respectively. The results of drop weight test are summarized in
Table 3, which indicates the specimen with higher w/cm ratio has higher increase in
the energy-absorbed capacity than the specimen with lower w/cm ratio. As previous
discussion, the microstructure of cement-based composites could be densified and
become stronger and more brittle by incorporation of silica fume so that the impact
number at ultimate failure decreases as the silica fume content increases. However,
FCC specimens with proper fiber contents could exhibit ductile property and usually
the energy absorbed capacity increases with an increasing fiber content. The key to
increasing the performance of cement-based composites under impact is to increase
its cracking resistance. Steel fibers in the composites can restrain the extension of
the crack, change the direction of crack growth and delay the growth rate of the crack.
Besides, incorporating silica fume into the composites can improve further the
interfacial characteristics, which is improved by the filler effect and the pozzolanic
effect of the silica fume. Mix A specimen with 10% silica fume and 2% fiber having
energy absorbed capacity 7.3 times than the control specimen and it presents excellent
impact resistance. It indicated that the A2f3 specimen has a great ability to absorb
impact energy due to the combined effect of the steel fiber and silica fume.
CONCLUSIONS
Steel fiber incorporation in cement-based composites results in significant
improvement in abrasion and impact resistance. Silica fume incorporation in
cement-based composites benefits fiber dispersion and significantly improves the
bond between fiber and matrix. At 10% silica fume with 2% steel fiber addition, the
promote effect on the abrasion resistance and impact energy absorbed enhances 50%
and 630%, respectively.
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