Applied Mechanics and Materials
ISSN: 1662-7482, Vols. 166-169, pp 538-542
doi:10.4028/www.scientific.net/AMM.166-169.538
© 2012 Trans Tech Publications, Switzerland
Online: 2012-05-14
Exposure Test of FRP-Reinforced Concrete Structure in Temperate
Marine Tide Zone
Mingjin Chu1, a, Zhijuan Sun2,b, Huichen Cui1,c,Ke Zhang1,d
1
School of Civil Engineering, Yantai University, Yantai ,264005,China
2
School of Architecture, Yantai University, Yantai ,264005,China
a
[email protected] , [email protected], [email protected],
d
[email protected],
Keywords: FRP-reinforced concrete member, durability, exposure test, construction measure.
Abstract: Through exposure test of FRP-reinforced concrete member in littoral test area of
temperate marine zone, the durability and constructional measures of FRP-reinforced concrete
structure are investigated. The test results show that FRP shell on the surface of FRP-reinforced
concrete member is effective in avoiding wave flush, freezing and thawing damage, preventing
chloride ion corrosion and improving durability. On the other hand, reliable measures should be
taken to protect concrete structures with no FRP shell on the surface. Based on above, the provided
reference for evaluation durability of FRP-reinforced concrete structure, and proper constructional
measures for FRP-reinforced concrete structure are presented.
Introduction
In recent years, economic loss caused by durability problem of reinforced concrete structure is
increasing year by year, which even leads to personal casualties [1, 2]. Among all the reasons, steel
bar corrosion caused by chloride ion is the main factor results damage and durability reduction of
reinforced concrete structure [1]. In coastal water and ocean environment, because of chloride ion
infiltration, reinforced concrete structure would encounter cracking, protective layer exfoliation [3,
4] and other issues, within 10 years’ service life. At present, in marine environment with high
chloride ion, the main measure to enhance the durability of reinforced concrete is to improve its
protective capability. However, in severe chloride environment, these measures still could not help
structures to reach to their service life.
Fiber Reinforced Polymer (FRP) has higher corrosion resistance, with light weight, high
strength, easy-molding nature and other advantages. Thus, it has become an important supplement
to concrete, steel and other traditional materials [4]. FRP-reinforced concrete structure is a kind of
structural member with high durability, which makes use of a few FRP materials as the shell of the
structure, so as to prevent external corrosion to internal reinforced concrete structure. Bearing
capacity of the structure is mainly provided by reinforced concrete. Sectional construction of
FRP-reinforced concrete is shown in Fig. 1, which is comprised by reinforced concrete beam and
FRP shell. The FRP shell is constituted by bottom plate, side plate and corner closure. During
construction, the formwork is used as the template. In application, the shell will work together with
reinforced concrete.
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Applied Mechanics and Materials Vols. 166-169
539
To study the durability of FRP-reinforced concrete in littoral areas of temperate marine climate,
4 kinds of ordinary reinforced concrete structures and FRP-reinforced concrete structures were
placed at the east gate of Yantai University in the October of 2010.
Specimens Fabricating
FRP-reinforced concrete structure, reinforced concrete column, reinforced concrete beam,
FRP-wrapped beam and FRP-wrapped column are fabricated, as is shown in Fig 2. The size of
beam is 150mm*250mm*2000mm, while the size of column is 200mm*200mm*800mm.
FRP-wrapped beam and FRP-wrapped column are made by wrapping reinforced concrete column
and beam with FRP cloth. Outer part of the FRP-reinforced concrete beam is GFRP shell, with the
thickness of 1.5mm. GFRP shell is constituted by two assembly units. Each assembly unit consists
of side beam plate and a half bottom beam plate. The two parts are connected via fastener stripe to
form a whole beam formwork. In order to enhance the viscosity between FRP shell and con
concrete, the internal part is processed through abrasive blasting. The bottom part of
FRP-reinforced concrete beam is designed with 3 pieces of 12mm HRB335 steel bars. In the upper
part, there are 2 pieces of 10mm HPB235 steel bars. The stirrup bars used is 6mm HPB235 steel
bar, with a separation distance of 100mm. The bottom part of ordinary is designed with 3 pieces of
16mm HRB335 steel bars. As for the bend-up bars and stirrup bars, they are the same with
FRP-reinforced concrete beam. Vertical steel bars used in column are 8 pieces of 12mm HRB335
steel bars. The stirrup bars are of 6mm and HPB235, with a separation distance of 100mm.
6
5
7
5
4
1
3
1
2
3
2
2
1
1
Fig. 1: FRP-reinforced concrete member
1-FRP bottom plate; 2-FRP corner closure; 3-FRP side plate; 4-Concrete; 5-Reinfocement;
6-Distributing bars; 7-FRP bar
(a) FRP-reinforced concrete beam
(b) FRP-wrapped beam
Fig. 2 Exposure test specimen
(c) FRP-wrapped column
540
Progress in Structures
During the manufacturing of specimens, standard cubic test pieces are made, and
under the same condition. The average compressive strength of concrete is 25.7MPa.
maintained
Exposure Test Field
In order to construct a long-term exposure test field, we have cleared and reformed the wave
resistance facilities of a fishing port near by Yantai University. The field is located within littoral
area, with an annual average temperature of around 12˚C. The average temperature of January in
this area is around -2˚C. The exposure test field is located in the top part of a U-shaped bay, with
rough sea waves.
Fig. 3 Exposure test field
Test Results
Shown by the research, under the impact of sea waves, mortars on the surface of reinforced concrete
structure strips gradually, with coarse aggregate being exposed slowly (see Fig. 4). Freezing and
thawing effect in winter aggravate the exposure speed of coarse aggregate. Besides, rough coarse
aggregate at specimen corner also started to dropping off, with obvious concrete exfoliation, as is
shown in Fig. 4. Moreover, chloride ion in sea water slowly intruded into coating of reinforced
concrete member, and protective layer damage caused by wave washout even aggravated this
process. As a result, steel bars in the structure were corroded, with cracking structural surface and
rusted steel bars (see Fig. 5).
(a) 7 Months’ exposure
(b) 15 Months’ exposure
Fig. 4 Surface characteristics of reinforced concrete members
Glass fiber covered on the surface of FRP-wrapped column can protect inner concrete from
being impacted by sea waves. However, owning to poor construction quality, the tightness of glass
fiber on some members is not quite well. As a result, sea water intruded from some damaged points.
When winter came, the water froze and inflated, tearing apart concrete and enlarging the damaged
part. After a whole winter’s freeze-thaw cycle, FRP fiber cloth dropped off, and concrete on the
surface was severely damaged, which even aggravated the deterioration process (see Fig. 6). As for
this, FRP fiber cloth on the surface has reduced the durability of member.
Applied Mechanics and Materials Vols. 166-169
(a) 7 Months’ exposure
541
(b) 15 Months’ exposure
Fig. 5 Reinforcement corrosion in reinforced concrete members
FRP fiber cloth being covered on the top of FRP-reinforced concrete beam also encountered
such exfoliation process, making it completely drop off (as shown in Fig. 7). For this reason, sea
water intruded into the faying surface between side FRP shell of beam and concrete of beam, which
damaged the faying surface. If being beaten slightly, there was a hollowing sound, which indicated
that there was fissure existing between FRP shell and inner concrete. As for this, the FRP plate has
lost it protective effect on concrete.
Test result analysis
The test results show that in temperate marine climate, sea wave washout, freezing and thawing
effect could damage the protective layer of concrete member, which accelerated chloride ion
corrosion. Reinforced concrete members are badly rusted, with poor performance. If covering the
surface of reinforced concrete member with FRP fiber cloth, sea wave washout, freezing and
thawing effect can be avoided, so as to prevent the member from being corroded by chloride ion. As
for this, the durability of structure can be largely improved. However, as for some members with
damaged FRP fiber cloth, freezing and thawing effect could tear apart the fiber cloth, and accelerate
protective layer damage and chloride ion corrosion. For this reason, the durability of structure
would be largely reduced. FRP plate on the surface of FRP-reinforced concrete member can protect
inner concrete from being impacted by sea waves or being corroded by chloride ion. However,
related constructional measures should be taken to seal the top surface and side part of member. Or
else, sea water may intrude into the faying surface between FRP shell and concrete. On this basis,
influenced by freezing and thawing effect, the FRP shell may be slowly torn down, losing its
protective and bearing function. Even if the structure is not affected by freezing and thawing
circulation, when sea water intrude into the faying surface, the protection performance of FRP shell
could still be reduced. Thus, to take reliable measures to seal the parts on the surface of
FRP-reinforced concrete structure, which are not protected by FRP shell, is a necessary measure to
bring into play the function of FRP shell.
Summary
Through exposure test of FRP-reinforced concrete member and the comparison between reinforced
concrete member and member wrapped with FRP cloth in littoral test area of temperate marine
climate, the paper has researched the durability and critical constructional measures of
FRP-reinforced concrete structure. Shown by the research, FRP shell on the surface of
FRP-reinforced concrete member is effective in avoiding wave impact, freezing and thawing
542
Progress in Structures
damage, preventing chloride ion corrosion and improving durability. At the parts that are not well
sealed with FRP fiber cloth, freezing and thawing effect may lead to exfoliation of FRP fiber cloth,
reducing the durability of member. In order to endow FRP-reinforced concrete with expected
function, reliable measures should be taken to protect and seal the parts on the surfaced of
FRP-reinforced concrete structure, which are not protected by FRP shell.
(a) Partial damage
(b) Severe exfoliation
Fig. 6 Exfoliation process of FRP Fiber cloth
Fig.7 FRP-reinforced concrete beam after 15 months’ exposure
Acknowledgements
The authors are grateful to the support of National Natural Science Foundation of China (Grant No.
50868004).
References
[1] Zhaoyuan Chen: Safety and durability of structural works in civil engineering(China
Architectural & Building Press, China 2001 (in Chinese)
[2] Junqing Lei: China Safety Science Journal. Vol. 15 (2005),p.8(in Chinese).
[3] Dinghai Hong, Deqiang Pan and Feiqi Guo: Port & Waterway Engineering, Vol.2 (1982), p.17(in Chinese).
[4] Bayou Lin, Guoliang Dan and Xiankai Shan: Hydro-Science and Engineering, Vol. 9(1998),
p.26- 30(in Chinese).
Progress in Structures
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Exposure Test of FRP-Reinforced Concrete Structure in Temperate Marine Tide Zone
10.4028/www.scientific.net/AMM.166-169.538