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Flexural fatigue performance of concrete containing nano-particles for pavement
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Abstract
The flexural fatigue performance of concrete containing nano-particles for pavement is experimentally studied. Both nano-TiO2 and
nano-SiO2 are respectively employed to be as the additives. For comparison, the flexural fatigue performance of plain concrete and the
concrete containing polypropylene (PP) fibers is also experimentally studied in this article. The test results indicate that the fatigue lives
of concretes containing nano-particles follow the double-parameter Weibull distribution. The flexural fatigue performance of concretes
containing nano-particles is improved significantly and the sensitivity of their fatigue lives to the change of stress is also increased. The
theoretic fatigue lives of concretes containing nano-particles are enhanced in different extent. With increasing stress level, the enhanced
extent of theoretic fatigue number is increased. The concrete containing nano-TiO2 in the amount of 1% by weight of binder has the best
flexural fatigue performance, which is much better than that of the concrete containing PP fibers, which has been extensively used to
improve the fatigue performance of concrete in pavement. The theoretic stress level of the concrete containing nano-TiO2 in the amount
of 1% by weight of binder is enhanced compared with plain concrete when the fatigue failure number is equal to 106.
2006 Elsevier Ltd. All rights reserved.
Keywords: Flexural fatigue performance; Pavement concrete; Nano-materials; Polypropylene (PP) fiber
1. Introduction
Pavement concrete is mostly used for airfield runways,
road surfaces, bridge decks, parking lots and industry
floors. Due to passing vehicles, these structures often
endure repetitive cyclic loads during their service lives,
the fatigue characteristics of concrete in these structures
are important performance and design parameters. It is
necessary to predict the fatigue life and parameters for
structures that have been endured repeated loading.
Fatigue failure occurs when a concrete structure fails at
less than design load after being exposed to a large number
of stress cycles. Fatigue may be defined as a process of progressive
and permanent internal damage in a material subjected
to repeated loading [1–3]. This is attributed to the
propagation of internal microcracks, which results in a significant
increase of irrecoverable strain. The exposure to
repeated flexural loading results in a steady decrease in
the stiffness of the structure and the propagation of internal
microcracks, which may eventually lead to fatigue failure
[1,4].
In general, parameters such as loading conditions, load
frequency, boundary conditions, stress level (stress ratio),
number of cycles, matrix composition, environmental conditions
and mechanical properties will influence the fatigue
performance of concrete [1,2]. However, there is no agreement
about the effect of these parameters on the fatigue
performance of concrete in the literature.
Kleiber and Lee [5] reported that the flexural fatigue
behavior of plain concrete was somewhat affected by the
water–cement ratio of concrete, and the fatigue strength
was decreased for a low water–cement ratio concrete.
Bazant and Schell [6] reported that high-strength concrete
was more brittle than normal-strength concrete under
0142-1123/$ - see front matter 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ijfatigue.2006.10.004
* Corresponding author. Tel.: +86 451 86282013; fax: +86 451
86282013.
E-mail address: lihui[at]hit.edu.cn (H. Li).
www.elsevierlocate/ijfatigue
International Journal of Fatigue 29 (2007) 1292–1301
International
Journalof
Fatigue
fatigue loading. Oh [7] demonstrated that the probabilistic
distribution of fatigue life of concrete depended on the level
of applied stress.
Most researchers have found that the inclusion of fibers
can benefit the fatigue performance of concrete [1,8–10];
however, there is conflicting evidence based on the work
of Cachim [11]. For flexural fatigue tests, it appears that
only a marginal benefit comes from fiber addition, because
the additional flaws introduced by fiber addition outweigh
the benefits [1].
In recent years, more attention has been paid by
researchers to the fatigue behavior of pavement concrete.
On the one hand, heavy traffic flow and heavier vehicles
make the pavement concrete subject to increased magnitude
and cycles of fatigue stresses. On the other hand,
new types of materials such as the concrete containing
nano-particles are expected to improve the fatigue performance,
but little is known of their long-term performance.
Li et al. [12] investigated the self-sensing properties of
mortar containing nano-particles. Li et al. [13] also studied
the improvement in compressive and flexural strengths, and
the abrasion-resistance of concrete containing nano-particles.
The results showed good prospects of the concrete
containing nano-particles.
According to previous studies[12–14], the nano-TiO2 in
the amount of 1% and 3% by weight of binder, respectively,
and nano-SiO2 in the amount of 1% by weight of
binder are employed to fabricate concrete containing
nano-particles in this article. The flexural fatigue performance
of concrete containing nano-particles (TiO2 and
SiO2) for pavement is experimentally studied herein. For
comparison, the flexural fatigue performance of plain concrete
and the concrete containing PP fibers is also experimentally
investigated in this article. The test results
indicate that the flexural fatigue performance of concretes
containing nano-particles and PP fibers is improved significantly.
The fatigue life of pavement concrete containing
nano-particles can be prolonged.
2. Experiment
2.1. Materials and mixture proportions
The cement used is Portland cement (P.O42.5). Fine
aggregate is natural river sand with a fineness modulus of
2.4. The coarse aggregate used is crushed diabase with
diameter of 5–30 mm. UNF water-reducing agent (one
kind of b-naphthalene sulfonic acid and formaldehyde condensates,
China) is employed to aid the dispersion of nanoparticles
in concrete and achieve good workability of concrete.
The defoamer, tributyl phosphate (made in China) is
used to decrease the amount of air bubbles.
The nano-particles are purchased from Zhoushan Mingri
Nano-phase Material Co. (Zhejiang, China) and their
properties are shown in Table 1. The modified PP fibers
are obtained from Zhangjiagang Synthetic Fiber Co.
(Jiangsu, China) and their properties are shown in Table 2.
Six kinds of mixtures are cast in this study. The water/
binder ratio used for all mixtures is 0.42, where the binder
weight is the total weight of cement and nano-particles.
Sand ratio is 34%. The mixture proportions for cubic meter
of concrete are given in Table 3. Herein, PC denotes plain
concrete. PPC denotes the concrete containing PP fibers in
the content of 0.9 kg/m3. NSC1 denotes the concrete containing
nano-SiO2 in the amount of 1% by weight of binder.
NTC1 and NTC3 denote the concrete containing
nano-TiO2 in the amount of 1% and 3% by weight of binder,
respectively. And NTPC denotes the concrete containing
both nano-TiO2 in the amount of 1% by weight of
binder and PP fibers in the content of 0.9 kg/m3.
2.2. Specimen fabrication
To fabricate the concrete containing nano-particles,
water-reducing agent is firstly mixed into water in a mortar
mixer, and then nano-particles are added and stirred at a
high speed for 5 min. Defoamer is added as stirring.
Cement, sand and coarse aggregate are mixed at a low
speed for 2 min in a concrete centrifugal blender, and then
the mixture of water, water-reducing agent, nano-particles
and defoamer is slowly poured in and stirred at a low speed
for another 2 min to achieve good workability.
To fabricate plain concrete and the concrete containing
PP fibers, water-reducing agent is firstly dissolved in water.
After cement, sand, coarse aggregate and PP fibers (if used)
are mixed uniformly in a concrete centrifugal blender, the
mixture of water and water-reducing agent is poured in
and stirred for several minutes.
Finally, the fresh concrete is poured into oiled molds to
form beams of size 100 · 100 · 400 mm for flexural
strength testing and flexural fatigue testing. After pouring,
an external vibrator is used to facilitate compaction and
reduce the amount of air bubbles. The specimens are demolded
at 24 h and then cured in a room at a temperature
of 20 ± 3 C and at a relative humidity of 95% until the
prescribed period, and then are placed in the laboratory
environment until tested. The number of specimens used
in test is given in Table 4.
Table 1
The properties of nano-particles
Item Diameter
(nm)
Specific
surface
area (m2/g)
Density
(g/cm3)
Purity
(%)
Phase
SiO2 10 ± 5 640 ± 50 <0.12 99.9 –
TiO2 15 240 ± 50 0.04–0.06 99.7 Anatase
Table 2
The properties of PP fibers
Item Elongation
(%)
Fiber number
(D)
Diameter
(lm)
Length
(mm)
Target 40 ± 3 11 ± 0.5 84–92 15 ± 1
H. Li et al. / International Journal of Fatigue 29 (2007) 1292–1301 1293
2.3. Test methods
Flexural strength testing is performed in accordance
with JTJ 053-94 (Testing Methods of Concrete for Highway
Engineering, China).
For flexural fatigue testing, a four-point bending test
method is applied with an effective span of 300 mm in a
100 kN material testing system (MTS). The test is carried
out in load control using a continuous sinusoidal waveform
with a loading frequency of 10 Hz.
The load cycle characteristic value R is defined as follows:
R = Pmin/Pmax, where Pmin and Pmax refer to the minimum
and maximum load of sinusoidal wave in each cycle.
R is taken as 0.1 in this test.
The stress level S is defined as: S = rp/rf, where rp and
rf are the flexural fatigue strength and the flexural strength,
respectively. The following four stress levels are selected:
0.70, 0.75, 0.80 and 0.85 for all specimens referred in this
study.
The input data for the test include the waveform, maximum
and minimum load amplitude, loading frequency,
maximum number of cycles.
The reference for the loading stress levels is the average
ultimate static flexural strength of specimens measured just
before the fatigue testing. The preload of 100–200 N is put
on the specimen to eliminate the error caused by poor
contact. The fatigue failure numbers of specimens are
recorded.
3. Fatigue equation and Weibull distribution
3.1. The type of fatigue equation and the physical meaning of
the parameters in fatigue equation
There are two types for fatigue equation. One is singlelogarithm
fatigue equation, i.e. S = a blgN; the other is
double-logarithm fatigue equation, i.e. lgS = lga blgN,
where S is the stress level, N is the fatigue life of concrete.
The fatigue performance of concrete is dependent on the
two important parameters (a and b) in fatigue equation.
The parameter a reflects the height of fatigue curve. The
larger the parameter a is, the higher the fatigue curve is,
and the better the fatigue performance of concrete is. The
parameter b reflects the steep degree of fatigue curve. The
larger the parameter b is, the steeper the fatigue curve is,
and the fatigue life of concrete is more sensitive to the
change of stress.
At present, the single-logarithm fatigue equation is
extensively used. It is available in the common range
(0.55 < S < 0.85) of fatigue life N, but it cannot extend.
The double-logarithm fatigue equation is a perfect type.
It cannot only agree well with the test results but also
extend suitably. Both two types of fatigue equations are
used to analyze the fatigue performance of concrete in this
study.