G. ZHANG et al.: INVESTIGATION OF THE FREEZE-THAW RESISTANCE OF ECO-POROUS CONCRETE ...
183–188
INVESTIGATION OF THE FREEZE-THAW RESISTANCE OF
ECO-POROUS CONCRETE CONTAINING FLY ASH
PREISKAVE ODPORNOSTI NA ZAMRZOVANJE IN ODTALJE-
VANJE EKOPOROZNIH BETONOV, KI VSEBUJEJO PEPEL
Gui Zhang, Jian Yin, Sheng Li, Zhenghui Sang, Yao Xiong, Ting Gao, Xiongwei Hu
College of Civil Engineering, Central South University of Forestry and Technology, Changsha 410018, China
1002919857@qq.com
Prejem rokopisa – received: 2017-06-15; sprejem za objavo – accepted for publication: 2017-07-28
doi:10.17222/mit.2017.073
Laboratory tests were conducted to evaluate the freeze-thaw resistance of eco-porous concrete containing fly ash. In order to
address the freeze-thaw resistance of eco-porous concrete, the mass loss, compressive strength and relative dynamic modulus of
elasticity (RDME) were obtained. Furthermore, based on the RDME, the freeze-thaw damage index (FTI) was provided to
evaluate the internal damage. The results showed that the higher the amount of fly ash, the poorer is the frost resistance of
porous concrete. The mass, compressive strength and RDME of specimens decreased with the increasing freeze-thaw cycles.
The compressive strength decreased with an increase in fly ash, but the initial compressive strength is sufficient for
requirements. Therefore, the content of fly ash should be controlled when producing eco-porous concrete and predicting its
performance under freeze-thaw attacks with the explored method.
Keywords: eco-porous concrete, fly ash, freeze-thaw resistance, mass loss, relative dynamic modulus of elasticity (RDME),
freeze-thaw damage index (FTI)
Avtorji prispevka so z laboratorijskimi preizkusi ugotavljali odpornost na zamrzovanje in odtaljevanje (FTR, angl.: Freeze-Thaw
Resistance), s pepelom polnjenih ekoporoznih betonov. Da bi dobili podatke o odpornosti betona so dolo~evali izgubo mase,
tla~no trdnost in relativni dinami~ni modul elasti~nosti (RDME). Na podlagi RDME so dolo~ili indeks po{kodb med preiz-
kusom zamrzovanja in odtaljevanja (FTI, angl.: Freeze-Thaw Damage index), ki je merilo notranjih po{kodb betona po
izvedenem preizkusu. Rezultati so pokazali, da ve~ja kot je polnitev poroznega betona z elektrofiltrskim pepelom, slab{a je
njegova odpornost na zamrzovanje. Masa, tla~na trdnost in RDME preizku{ancev so se zmanj{evali z nara{~ajo~im {tevilom
ciklov zamrzovanja in odtaljevanja. Tla~na trdnost poroznega betona se je precej zmanj{ala s pove~evanjem dele`a
elektrofiltrskega pepela, kljub temu, da so bile vrednosti za~etne tla~ne trdnosti betona znotraj predpisov. Zato je potrebno dele`
elektrofiltrskega pepela nadzorovati, ko se oblikuje nove, s pepelom polnjene, ekolo{ke porozne betone in jih testirati oz. ovred-
notiti z, v tem ~lanku opisano, metodo zamrzovanja in odtaljevanja.
Klju~ne besede: ekoporozni beton, elektrofiltrski pepel, odpornost na zamrzovanje in odtaljevanje, izguba mase, relativni dina-
mi~ni modul elasti~nosti (RDME), indeks po{kodb betona nastalih med preizkusom zamrzovanja in odtaljevanja (FTI)
1 INTRODUCTION
The concept of green concrete was first proposed by
the Concrete Engineering Institute of Japan in 1990s.1
Until now, green concrete has been used in parking lots,
roadside slopes, shoulder partitions and other projects in
Japan, the United States and other countries. Eco-porous
concrete is a kind of green concrete, mainly formed with
coarse aggregate, water, cement and admixtures. After
filling in the pores with soil, nutrients and water-retain-
ing materials, eco-porous concrete can meet the growing
needs of plants. Compared with ordinary concrete,
eco-porous concrete has the function of planting, water
purification, noise reduction and reducing the heat-island
effect.2–3
Due to the typical skeleton structure of porous con-
crete, environmental factors have an important influence
on the service life of porous concrete, especially the
freeze-thaw attacks. It is well known that the effect of
materials (such as aggregates, cement, admixtures, etc.)
on the freeze-thaw resistance should be explored, and the
degradation characteristics of concrete should be stu-
died.4–8 Compared with permeable concrete, eco-porous
concrete has a higher porosity and a larger pore size.
There were few researches on the freeze-thaw resistance
of eco-porous concrete.9–11 Considering the cost and
ecological benefit, the industrial, waste, residue fly ash is
usually added to concrete.12–13 Based on the above, fly
ash was added to eco-porous concrete in the study.
Accordingly, the freeze-thaw resistance and evaluation of
porous concrete were researched. The results have an
important guiding significance for the evaluation of frost
resistance and preparation of eco-porous concrete.
2 EXPERIMENTAL PART
2.1 Materials
The P.O. 42.5 cement was selected. The performance
indexes of the cement is shown in Table 1. There is only
coarse aggregate, no fine aggregate. The II grade fly ash
was used.
Materiali in tehnologije / Materials and technology 52 (2018) 2, 183–188 183
UDK 620.1:66.018:621.762 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 52(2)183(2018)
2.2 Mixture design
The mix-design theory is similar to the filling theory
of RCC.14 The design principles are: close packing of the
coarse aggregate, the cementitious paste evenly distri-
buted on the aggregate surface, a porosity of 20–30 %
and the compressive strength after 28 d of 5–15 MPa as
the control criteria. According to the findings of Y. P.
Sheng and others,15–17 the primary mix proportion can be
achieved.
Moreover, Y. Jing provided empirical data for the
preparation of the vegetation-type eco-porous concrete.18
Based on the formula and empirical data, the test mix
proportions are presented in Table 2. The "n value"
represents 0, 1, 2, 3, 4, 5, respectively.
Table 2: Mix proportion of eco-porous concrete
Number FLC/% Grainsize/mm
Cement/
kg/m3
Water/
kg/m3
Water-bin
der ratio
Fn 10n 19–26.5 300 90 0.30
Note: FLC = Fly ash content
2.3 Specimen preparation
Fly ash was used to replace cement in the amounts of
(0, 10, 20, 30, 40 and 50) %. Using the paste-coating-
gravel method, cement, fly ash and 70 % of water were
mixed in a mechanical mixer for 1 min, then the coarse
aggregate was added, being mixed into the mixture for 1
min, and the remaining 30 % of the water was added by
mixing the mixture for another minute. The specimen
size for the compression test was (100 × 100 × 100) mm,
and it was (100 × 100 × 400) mm for the transverse-
fundamental-frequency test. After the mixing, a vibrating
rod was used to ensure a good compaction and the
specimens were demolded 24 h after being cast. Then,
the specimens were cured in a standard curing room for
23 d, and soaked in water (20±2 °C) for another 4 d.
Meanwhile, the water level was higher than the top
surface of the specimens by 20–30 mm.
3 EXPERIMENTAL METHOD
In this study, the vacuum-sealing method, as spe-
cified in ASTM D7063, was adopted to determine the
effective porosity of porous concrete.19 It is reported that
this method can be effectively used for porous concrete
due to its open-pore structure.20–21 Strength tests were
conducted on porous-concrete specimens by following
the testing procedures specified in GB/T 50081-2002.22
Triplicate cubic specimens with a side length of 100 mm
were used for the testing. Compressive-strength tests
were performed on the specimens after 28 curing d.
Cyclic freeze-thaw tests were conducted to determine
the freeze-thaw resistance of the porous-concrete mix-
tures, mainly referring to the Chinese specification
GB/T50082-2009, in which specimens were subjected to
repeated freeze-thaw cycles.23 After 28 d of curing, we
took the specimens out, wiping the surfaces with a cloth
until there was no water on them. We numbered the
specimens with the sides of (100 × 100 × 400) mm,
weighed the initial mass M0, measured the lateral
fundamental frequency f0 and observed their appearance.
We put the specimens with the dimensions of (100 × 100
× 400) mm and (100 × 100 × 100) mm into the box with
wetting conditions; after 5 cycles of freezing and
thawing, we measured the above criteria, until the
RDME decreased to 60 % or the mass-loss rate reached
5 %.
4 RESULTS AND DISCUSSION
4.1 Uniaxial compressive strength
The test results of the compressive strength obtained
when the relative dynamic modulus of elasticity
(RDME) of the eco-porous concrete was reduced to
60 % are shown in Figure 1.
It can be clearly observed from Figure 1 that with an
increase in the freeze-thaw cycle, the compressive
strength decreased rapidly. The strength of the specimens
without fly ash is larger than that of the specimens with
fly ash. And with the increasing amount of fly ash, the
compressive strength of the specimens significantly
decreased.
The specimens damaged during the freeze-thaw
attacks and compression tests can be seen in Figures 2
and 4. The bonding sites of the aggregate were broken
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184 Materiali in tehnologije / Materials and technology 52 (2018) 2, 183–188
Table1: Performance indexes of cement
SSA SO3 Stabi-
lity
IS FS 3d FS 3dCS 28dFS 28dCS
m2/kg % min min MPa MPa MPa MPa
354 2.4 qualified 155 200 5.6 25.3 8.9 53.0
Note: SSA = Specific surface area; IS = Initial setting; 3dFS = 3d flex-
ural strength; 3dCS = 3d compressive strength; others similarly
Figure 1: Relation between uniaxial compressive strengths and
freeze-thaw times
and cracks developed along the bond interface. This indi-
cated that the contact areas were still weak. Therefore,
the cementitious paste had to be modified to improve the
strength of porous concrete. It is well known that cemen-
titious paste gradually degrades under the expansion
stress of ice, and the bond strength of cementitious paste
also decreases. In addition, the high porosity of speci-
mens provided the condition for water freezing, leading
to an aggravated degeneration. On the other hand, the fly
ash decreased the strength of the cementitious paste
between aggregate particles. The content of fly ash also
had to be controlled. Finally, with the increasing freeze-
thaw cycles, the RDME of the specimens decreased to
60 %.
4.2 Mass loss
The mass-loss rate and the appearance of the speci-
mens after the reduction of the RDME of eco-porous
concrete to 60 % are shown in Table 3 and Figure 4,
respectively.
The mass-loss rate for the eco-porous concrete with-
out fly ash was lower than for the other types of eco-po-
rous concrete from Table 3. With the increasing amount
of fly ash, the mass-loss rate increased, but it was still
less than 5 %.
Table 3: Mass-loss rate of eco-porous concrete
Fly-ash content (%) 0 10 20 30 40 50
Mass-loss rate (%) 0.06 0.09 0.11 0.12 0.16 0.19
There were no cracks on the surfaces of the spe-
cimens, and only slight damage appeared, mainly on the
surface, as shown in Figure 4. With the increasing
cycles, individually spalled aggregate particles could be
observed from Figure 2.
A lower water-binder ratio and the paste-coating-
gravel method improved the strength of the cementitious
paste and the interface between the aggregate particles.
Then, the interfacial transition zone of eco-porous
concrete was strengthened. Accordingly, the freeze-thaw
resistance of eco-porous concrete significantly increased.
However, after the cement was replaced by fly ash, the
activity, hydration degree and fluidity of the cementitious
paste were reduced. Finally, the roughness and holes of
the cementitious-paste surface increased. With the
freeze-thaw attacks going on, the expansion stress from
the holes caused the cementitious paste to peel off and
fall off. Besides, with the increase in the fly ash, a small
amount of particles appeared, but the mass-loss rate was
still low.
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Materiali in tehnologije / Materials and technology 52 (2018) 2, 183–188 185
Figure 2: Freeze-thaw failure of a specimen Figure 4: Appearance of the specimens
Figure 3: Compressive failure of a specimen
4.3 Relative dynamic modulus of elasticity (RDME)
4.3.1 Analysis of relative dynamic modulus of elasticity
(RDME)
RDME curves for different fly-ash contents in
eco-porous concrete are presented in Figure 5.
It can be clearly observed from Figure 5 that with an
increase in the number of freeze-thaw cycles, the RDME
decreased rapidly. The RDME of the specimens without
fly ash is larger than that of the specimens with fly ash.
And with the increasing amount of fly ash, the RDME of
the specimens significantly decreased.
When the RDME was reduced to 60 %, the eco-po-
rous-concrete specimens did not produce cracks that
could be seen from Figure 4. As we can see, the vari-
ation trend of the RDME is similar to the compressive
strength. Accordingly, the RDME values also depend on
the durability of cementitious paste, the content of fly
ash and freeze-thaw cycles. Nevertheless, the RDME
value has an important role when evaluating the internal
damage.
4.3.2 Freeze-thaw damage index (FTI)
The change in the relative dynamic modulus of
elasticity (RDME) is the macroscopic form of micro-
damage (or internal damage). By establishing the
relation between the RDME and freeze-thaw damage
index, the damage degree of concrete during freeze-thaw
attacks can be described. According to this, the formula
is as follows:
DF = (ERI – ERF)/0.4 ERI = 2.5(1 – ERF) (1)
where DF is the freeze-thaw damage index, 0  DF  1;
ERI is the initial RDME, its value is 1.0; ERF is the in-
stantaneous RDME. Under the non-destruction condi-
tion, ERI = ERF = 1, DF = 0; under the theoretical limit
state of freeze-thaw damage, ERF = 0.6 ERI and DF = 1.
When the RDME is included in formula (1), we find
that the damage degree of specimens can be calculated
using the freeze-thaw damage index. Furthermore, the
closer DF is to 1, the greater the damage; the closer DF
is to 0, the smaller the damage.
The larger the amount of fly ash, the lower the
relative dynamic modulus of elasticity (RDME) of the
porous concrete, as can be seen from Figure 5. In
addition, when the fly-ash amounts were 40 % and 50 %,
the specimens were subjected to the freeze-thaw cycle
five times. Therefore, the relation between the number of
the freeze-thaw cycle and the freeze-thaw damage index
was only studied when the fly ash amounts were (0, 10,
20 and 30) %. The fitting curve Equations (6), (7) and
(8) are as follows:
0 %: y = -6×10–7x3 – 8×10–5x2 – 0.001x + 0.9969
R² = 0.9983 (2)
10 %: y = -0.0004x2 – 0.0092x + 1.0183
R² = 0.9821 (3)
20 %: y = -0.0003x2 – 0.0205x + 1.019
R² = 0.9789 (4)
30 %: y = -0.001x2 – 0.0257x + 1.0138
R² = 0.9824 (5)
where y is the RDME and x is the number of freeze-
thaw cycles. However, when the fly-ash content
amounted to 30 %, the deviation between the calculated
results and the experimental results was large.
Therefore, the relation between the number of freeze-
thaw cycles and the freeze-thaw index was not discussed
when the fly-ash content exceeded 30 %. Next, we
replaced the ERF from Equation (1) with y from
Equations (2), (3) and (4), respectively. Then, new
Equations (6), (7) and (8) were obtained for the fly-ash
contents of (0, 10 and 20) %, as follows:
0 %: DF = 1.5×10
–6x3+2×10–4x2+2.5×10–3x+
+7.75×10–3 (6)
10 %: DF = 10
–3x2 +0.023x-0.04575 (7)
20 %: DF = 7.5×10
–4x2+0.05125x-0.0475 (8)
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186 Materiali in tehnologije / Materials and technology 52 (2018) 2, 183–188
Figure 5: Relation between RDME and freeze-thaw cycles
Figure 6: Relation between the calculated value and original value of
freeze-thaw damage index
The freeze-thaw damage index DF increases with the
increase in the number of freeze-thaw cycles from
Equations (6), (7) and (8). Furthermore, the freeze-thaw
damage degree for the specimens can be calculated by
assuming the number of freeze-thaw cycles. The relation
between the original value and calculated value of the
freeze-thaw damage index of eco-porous concrete is
shown in Figure 6.
It can be clearly seen that the deviation of the calcu-
lated value from the original value is small. That is to
say, the freeze-thaw damage index can be used to des-
cribe the damage degree of eco-porous concrete during
the freeze-thaw attacks. Moreover, the relation between
the number of freeze-thaw cycles and freeze-thaw index
can, not only be used to estimate the damage degree, but
also to predict the number of freeze-thaw cycles that
eco-porous concrete can withstand.
5 CONCLUSIONS
The fly-ash content has an important influence on the
frost resistance of eco-porous concrete. In order to make
eco-porous concrete with sufficient ecological benefits
and a certain frost resistance, the fly-ash content should
not exceed the total amount of cementitious paste, which
is 30 %.
On the basis of the relative dynamic modulus of
elasticity (RDME), the freeze-thaw damage index DF is
defined, and the freeze-thaw damage degree of eco-
porous concrete can be estimated by calculating the
value of DF. The relation between the freeze-thaw
damage index DF and the number of freeze-thaw cycles
is obtained when fly-ash amounts account for 0, 10 and
20 %. The freeze-thaw damage index DF can also be
calculated by assuming the number of freeze-thaw
cycles, through which we can obtain the freeze-thaw
damage degree or evaluate the freeze-thaw resistance of
eco-porous concrete.
When the relative dynamic modulus of elasticity
(RDME) of eco-porous concrete decreased to 60 %, the
number of freeze-thaw cycles was lower than that of
compressive specimens. The relative dynamic modulus
of elasticity (RDME) was selected to evaluate the frost
resistance of eco-porous concrete. Therefore, the mass
loss, appearance, and freeze-thaw damage can be used as
the evaluation indexes for the frost resistance of eco-
porous concrete.
Acknowledgments
The authors appreciate the support of the Hunan
Province Science and Technology Department (Project
Nos. 2013FJ2002, 14JJ4055) and the Central South
University of Forestry and Technology (CX2017B41).
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