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7/30/2019 Frost Resistance of Recycled Concrete
http://slidepdf.com/reader/full/frost-resistance-of-recycled-concrete 1/5
J. Cent. South Univ. Technol. (2007)s1−0409−05
DOI: 10.1007/s11771−007−0294−7
Frost resistance of recycled concrete
QIN Yin-hui(覃银辉)1, DENG Shou-chang(邓寿昌)1, ZHANG Xue-bing(张学兵)2
(1. College of Civil Engineering and Mechanics, Central South University of Forestry and Technology,
Changsha 410004, China;
2. Department of Civil Engineering and Mechanics, Xiangtan University, Xiangtan 411105, China)
Abstract: The frostbite situation of recycled concrete suffered one-time freezing was analyzed, and was then compared with that of
the normal concrete. In order to improve the frost resistance of recycled concrete, antifreeze was used and good effect was obtained.
The results show that the frost resistance of recycled concrete is inferior to that of recycled concrete. Differences exist in the
microstructures of the recycled concrete and normal one, which makes the decrease of frost resistance. Antifreeze can improve the
microstructure of recycled concrete, so the frost resistance of it is improved as well.
Key words: recycled concrete; anti-frozen performance; antifreeze; freezing-thawing cycle; compressive strength
1 Introduction
The use of recycled aggregate(RA) for manufacture
of concrete started as far back as the end of World War
Ⅱ. Rubble obtained from demolition of concrete road
pavement, runways, foundations and building structures
has been reused successfully around the world. Duringthe Post World War Ⅱ era in the United States, rubble
from demolished concrete pavement was crushed and
reused as aggregate in unstablished base course of a
number of road construction projects. And, in one form
or another, concrete has been recycled successfully in
other countries such as China, France, Canada to
mention a far. The reuse of old concrete not only
conserves the finite raw materials, but also reduces
energy consumption and therefore the overall
construction costs.
Many research studies were carried out on the use
of RA in concrete in an attempt to understand the properties of RA concrete, however, most of the studies
are focused on the mechanical properties of the resulting
concrete. Limited work carried out on the understanding
of frost resistance of recycled concrete[1−3].
The frost resistance of recycled concrete consists of
the following two aspects: 1) the thawing and freezing
resistance of fully hardening concrete; 2) the frost of
recycled concrete when freezed in the early period. The
latter is universal and the main danger in winter working.
The focus of this paper is to study how minus
temperature affect the recycled concrete and obtain thelaw, and is then compared with ordinary concrete. At the
same time, improved its anti-frozen performance through
adding antifreeze, analyzed the reason how did antifreeze
influence anti-frozen performance of recycled concrete.
2 Experimental
2.1 Raw material
The main raw materials is as follows. Cement was32.5R portland cement produced by Xiangxiang Cement
Factory in Hunan Province.
Fine stuff was natural sand of Xiang River in Hunan
Province.
Coarse aggregate was recycled aggregate obtained
from concrete specimen with different grades in
Examining Center of Xiangtan University.
Water was running water.
The properties of recycled concrete is shown in
Table 1.
The formula of additional water content is shown as [4]
⎪⎪⎪⎪
⎩
⎪⎪⎪⎪
⎨
⎧
×+
−−
=∆
−
RCA
RCA4
RCA
5021.0
)1034102.118993.1(
))8204.0exp(93617.069005.2(
m
m
mt
W
where mRCA is the quality of recycled aggregate.
2.2 Frost temperature of recycled concreteThe frost essence of concrete is the frost of water in
Foundation item: Project(k042013-12) supported by the Science and Technology Office of Changsha City, China
Corresponding author: QIN Yin-hui; Tel: +86-731-5094170; E-mail: [email protected]
(0≤t ≤60 min)
(60 min≤t ≤24 h)
(t ≤24 h)
7/30/2019 Frost Resistance of Recycled Concrete
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J. Cent. South Univ. Technol. 2007, 14(s1)410
Table 1 Properties of recycled concrete
Design
strength
grade
W/C1) Cement
content/(kg·m−3)
Recycled
aggregate/(kg·m−3)
Natural
sand/(kg·m−3)
Additional
water content,
∆W
Mixture ratio2)
C20 0.55 340 1 190 645 25.59 1 1.897 3.5 0.55
C30 0.46 380 1 220 575 26.23 1 1.513 3.211 0.46
C40 0.37 475 1 191 511 25.61 1 1.076 2.507 0.371) Mass ratio of water to cerment; 2) Mass ratio of cerment to sand, aggregate and water.
it. When water is frozen, it becomes solid state from
fluid state, the volumes expands 9% likely which damage
the concrete quality. When ordinary concrete is put at 0
℃, most water exists between cement particles and isn’t
restrained essentially. Because of this, also the strength
of recycled concrete at 0 ℃ was studied. The result is
listed in Fig.1.
Fig.1 Time—strength curve under different curing conditions
From the experiment result above, the strength of
recycled concrete is increased after freezed for 3 d, but
the speed is very slow, which indicates that the recycled
concrete is not iced over, but hydration speed is very
slow. In another word, the freezing point of water in
recycled concrete is also below 0℃.
In order to know the frozen temperature of recycled
concrete, put recycled concrete specimen in low-
greenhouse at −5 ,℃ −10 after precuring for 0,℃ 3, 7,
10 and 14 d in standard condition, put them out after 3 d,
a group of specimen was tested immediately, another
group of specimen was cured in standard condition for
28 d continually, tested them when total curing age was
31 d, strength—time curves are shown in Fig.2.
From Fig.2, the strength of recycled concrete curing
for 28 d was the same approximately after frozen at −5
, −10℃ separately. For recycled concrete without℃
precuring in standard condition, their strength wasdamaged greatly, in other words, recycled concrete has
already suffered freezing injury at −5 ℃, the frozen
temperature of recycled concrete is −5℃ about.
2.3 Frozen rule of recycled concrete
Put recycled concrete specimen in low-greenhouse
in which control temperature was −(10±1) ,℃ the
strength grade of concrete was C30 and C40, 3 d later, a
group of specimen was tested immediately, another
group of specimen was cured in standard condition for
28 d continually, tested them when total curing age was
31 d, the result is shown in Fig.3.
Fig.2 Time—strength curve at different temperatures
Fig.3 time—strength curve at different curing days of
recycled concrete
From Fig.3, precuring days are advantageous to
recycled concrete either the melting strength or the finalstrength curing for 28 d. But recycled concrete hasn’t
anti-frozen threshold strength, there is frostbite for
recycled concrete frozen after precuring for 10 d in
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QIN Yin-hui, et al: Frost resistance of recycled concrete 411
standard condition. Compared with normal concrete (see
Fig.4[5]
), if normal concrete is precured for 1.5 d before
frozen, it will not suffer frostbite. As a result, the
anti-frozen performance of recycled concrete is inferior
to that of normal concrete.
Fig.4 Time—strength curve at different curing days of
normal concrete
2.4 Anti-frozen performance of recycled concrete with
antifreeze
In order to improve the anti-frozen performance of
recycled concrete, the means of adding admixture was
used. In the winter poor weather condition in the
northern area of our country, application of antifreeze isextremely widespread, and the dosage is also extremely
great, even it passes 5% limiting value prescribed by
international[6]. In the text, the durability of recycled
concrete with antifreeze was studied, the antifreeze was
YJ-4 antifreeze produced by Beijing New Vision
Building Construction Technology Co., Ltd, it’s superior
mixing dosage is 1% of cement content. And its other
technical index is shown in Table 2.
Antifreeze is advantageous to the anti-frozen
performance of concrete, it can improve the strength of
concrete curing at minus temperature, but if antifreeze is
applied to concrete curing in standard condition, the
result is shown in Table 3.
It can be seen from Table 3 that antifreeze does no
influence on the strength of recycled concrete curing in
standard condition, even the strength is higher than the
design strength of recycled concrete. This is because
antifreeze has the ability of water-reducing, so the factual
W/C of recycled concrete is lower than the design W/C
which will make the factual strength higher than the
design strength.
2.5 Strength development regular of recycled
concrete with antifreeze at minus temperature
Put the shaped concrete limestone in the low
greenhouse in which the control temperature was −(10±1)℃, the designing compressive strength of recycled
concrete was C30, C40 separately. Tested them at
different curing ages, the time—strength curves of C30
and C40 are shown in Fig.5.
Fig.5 Time—strength curve at different curing days of
recycled concrete
Table 2 Technical index of YJ-4 antifreeze (No rust for reinforced bar)
Setting time gap of concrete Compressive strength ratioWater-
reducing
ratio
Air
content
Bleeding
ratio Initial setting Final setting)17− R R28
)2287+−
R
Strength loss ratio
fter 50 freezing-
thawing cycles
≥12% ≥2.5% ≤90% 0−120 min 0−120 min ≥12% ≥100% ≤120%≤100%
1) Cured at minus temperature for 7 d; 2) Cured at standard condition for 28 d after cured at minus temperature for 7 d.
Table 3 Strength at age of 28 d of recycled concrete curing in standard condition with antifreeze
Design strength
gradeW/C1)
Cement content
/(kg·m−3)
Recycled aggregate
/(kg·m−3)
Natural sand/
(kg·m−3)
Additional
water, ∆W
Compressive strength cured
for 28d/MPa
C20 0.55 340 1 190 645 25.59 22.49
C30 0.46 380 1 220 575 26.23 33.98
C40 0.37 475 1 191 511 25.61 46.51
1) Content ratio of water to cerment.
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J. Cent. South Univ. Technol. 2007, 14(s1)412
Regardless of the recycled concrete of C30 and C40,
the strength was developed continually even if the curing
temperature was −(10± 1)℃. When antifreeze was
adding, the hydration of cement carried on, but the speed
of cement hydration has direct ratio with curing
temperature, in other words, the higher curing
temperature, the faster hydration speed, so the hydration
speed of cement is very low at an minus temperature.
The strength develops slowly and there is no turning
point in strength—time curve, strength development is
steady.
2.6 Freezing-thawing ability of recycled concrete
Freezing-thawing destruction was the main part of
concrete frostbite[7]. To study the freezing-thawing
resistance ability of recycled concrete, cured the shaped
recycled concrete specimen in standard condition for 28d, saturated specimen with water, then tested them with
freezing-thawing cycle, the method of freezing-thawing
cycled was freezing slowly and melting slowly. The
results are listed in Table 4.
Table 4 Resistance ability to freezing-thawing cycle
Design
strength
grade
Times of
freezing-
thawing
cycle
Mass
loss/%
Strength
(without
antifreeze/
MPa
Strength
(with
antifreeze)/
MPa
C20 25 0 15.53 17.56C30 50 0 28.89 34.12
C40 50 0 42.00 46.89
There is no any mass loss of recycled concrete
enduring freezing-thawing cycle many times. For
recycled concrete without antifreeze, the strength is
damaged to a certain degree, especially for concrete C20,
its strength loss is quite obvious after 25 freezing-
thawing cycles. But for recycled concrete with antifreeze,
the strength does not change, just for recycled concrete
C20, the strength drops slightly. From the above analysis,it can be concluded that the recycled concrete C20 is not
applicable in cold area, the lowest design strength grade
of recycled concrete for freezing-thawing cycle is C30.
3 Comparison and analysis
Compared recycled concrete with normal one, the
two have the same chemical composition, the reason why
the two have different anti-frozen abilities is that they
have different microstructures.
Figs.6 and 7 demonstrate that the interface of aggregate and cement mortar is loose relatively for
concrete, and the thickness of interface area is different
at different places. For recycled concrete, the interface is
formatted by many loose pellet, and the interface area
has porous nature because of its high porosity percentage
of void, the farther to interface, the less of hole. At the
same time, recycled concrete has lower density and
wider interface compared with normal concrete. Interfaceis the weak link for anti-frozen
[9], because of the
existence of interface, concrete can’t form a powerful
whole, the structure integrity is destroyed. Once the two
interfaces (the one is natural aggregate-old mortar
interface, and the other is old mortar-new mortar
interface) of recycled concrete are frozen, the whole
structure of it will loose correspondingly, the final
strength will damage correspondingly.
Fig.6 Microstructure of recycled concrete
Fig.7 Microstructure of normal concrete
Adding antifreeze can improve the anti-frozen
performance of recycled concrete greatly. The reason is
that YJ-4 antifreeze doesn’t depend on reducing freezing
point of water to achieve its anti-frozen goal, but depend
on importing air bubble, reducing water content and
improving early strength of concrete to achieve it. It can
not react with cement, but changes the microstructure of
recycled concrete.
Compared Fig.8 with Fig.9, it can be seen that
recycled concrete without antifreeze has large pore and
less density which is disadvantageous to seepage
resistance of concrete and influence the concrete performance. But from the microstructure of recycled
concrete with antifreeze, antifreeze makes the concrete
have the high density and decrease the size of the pore of
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QIN Yin-hui, et al: Frost resistance of recycled concrete 413
recycled concrete which makes the interface reasonable.
On the other hand, less pore between the concrete
particle can make concrete seepage ability increase, the
strength and durability of recycled concrete improve as
well.
Fig.8 Microstructure of recycled concrete without antifreeze
Fig.9 Microstructure of recycled concrete with antifreeze
4 Conclusions
Recycled concrete is different from normal concrete
in microstructure, so their anti-frozen performance is
also different. Concluded from the experiments above,
just like the normal concrete, the frozen temperature of
recycled concrete is also below 0 ℃, precuring time is
advantageous to the anti-frozen performance of recycled
concrete, the longer percuring time, the higher strength
of recycled concrete. In order to improve the anti-frozen
performance of recycled concrete, antifreeze was used,
anti-frozen performance is improved greatly after adding
antifreeze, the strength develops continually at minus
temperature, once curing in standard condition, it is
higher than the design strength, and the ability to
resistant freezing-thawing cycled is also enhanced. Sorecycled concrete can apply in winter environment if
adding proper admixture.
References
[1] SAGOE-CRENSIL K K. Performance of concrete made with
commercially produced coarse recycled concrete aggregate [J].
Cement and Concrete Research, 2001, 31: 707−712.
[2] DORUNSOGO F T. Performance of recycled concrete monitored by
durability indexes [J]. Cement and Concrete Research, 2002, 32:
179−185.
[3] ZAHARIEVA R. Frost resistance of recycled aggregate concrete [J].
Cement and Concrete Research, 2004, 34: 1927−1982.[4] ZHANG Xue-bing, DENG Shou-chang. Experimental research on
unit water use in recycled concrete [J]. Concrete, 2004(10): 38−40,
64. (in Chinese)
[5] XIANG Zhu-xing. Study on early frost resistance of concrete [J].
Architectural Technology, 1992(10): 578−583. (in Chinese)
[6] XIANG Zhu-xing. Study on durability of concrete with antifreeze [J].
Architectural Technology, 1982(10): 19−20, 31. (in Chinese)
[7] LI Tian-yuan. Preliminary Study on Anti-frozen Performance of
Concrete [D]. Changsha: Hunan University, 1984. (in Chinese)
(Edited by LONG Huai-zhong)