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Dept. of Civil Engineering Seminar Report 2011-2012
1.INTRODUCTION
With the economic growth and science-technology development, more
and more large-scale civil engineering structures such as tall buildings, underground
buildings and landmark buildings and so on are built around the world. While the
economic growth is a kind of extensive growth: high input, high consumption and high
pollution, for that the energy saving technology is low, especially in developing countries.
The brightness of indoor environment is entirely maintained by artificial lighting, which
has consumed a large number of resources. Moreover civil engineering structures always
suffer from external environmental effects, economic loss and casualties are serious once
damaged. And now, building energy saving and building safety have been attracted much
attention. Many large span bridges and new landmark buildings have been successfully
implemented structural health monitoring systems. Optical fiber sensors such as fiber
Bragg Grating, Brillouin distributed sensors and plastic optical fiber sensors have been
widely used for the in situ monitoring of major projects (Ou&Zhou, 2003 ; Anshari,
2007;Wu, 2006; Inaudi, 2005; C. Vzquez et al, 2004;Kalymnios,2005;Kurashima,
1997; Kuang, 2006). Meanwhile some new building materials are developed and used in
structures, including self-diagnosis smart concrete, self-tuning smart concrete, self-
repairing smart concrete, soundproof concrete, thermal insulation concrete and so on
(Ou&Li, 2002-2007; Chung, 1993, 2000; Sun, 2000). All these functional materials only
focus on the intelligence characteristics, and cannot possess energy saving. In 2001, the
concept of transparent concrete is first put forward by Hungarian architect Aron Losonzi,
and the first transparent concrete block is successfully produced by mixing large amount
of glass fiber into concrete in 2003, named as LiTraCon. Joel S. and Sergio O.G.
developed a transparent concrete material, which can allow 80% light through and only
30% of weight of common concrete. It is worth mentioning that Italian Pavilion in
Shanghai Expo 2010 shows a kind of transparent concrete developed by mixing glass into
concrete in 2010. While the transparent concrete mainly focuses on "transparent” and its
application object is art design. And there is no research on mechanics and long-term
durability of transparent concrete. Therefore it is imperative to develop a new functional
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Dept. of Civil Engineering Seminar Report 2011-2012
material to satisfy the structure safety monitoring (such as damage detection, fire
warning), environmental protection and energy saving and artistic modeling.
As two representative materials in construction and sensing field, concrete is one of the
most important civil engineering materials with the advantages of rich raw materials, low
cost and simple production process. And optical fiber has good light guiding which can
arrange the sun light transmit according to pre-design road without light-heat, light-
electrical or photochemical process, and photoelastic effect which can be used to study
the stress distribution of structures. Combining the advantages of the concrete and optical
fiber, developing a novel functional material has important value of application for
construction and sensing. In this paper, to integrate the merits of concrete and optical
fiber, our group develops a smart transparent concrete by arranging the high numerical
aperture POF or big diameter glass optical fiber into concrete. The main purpose is to use
sunlight as a light source to reduce the power consumption of illumination and to use the
optical fiber to sense the stress of structures. The light guiding, durability and self-sensing
properties are studied based on white light test, freezing and thawing test, chloride ion
penetration test, and stress elasto-optic effect test respectively.
Fig.1.1 Transparent Concrete
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Dept. of Civil Engineering Seminar Report 2011-2012
2. FABRICATION OF SMART TRANSPARENT CONCRETE
The main idea of the smart transparent concrete is that high numerical
aperture optical fibers are directly arranged in the concrete, and the optical fiber is used as
sensing element and optical transmission element. Because that the light can transmit in
the optical fiber, different shape of smart transparent concretes can be fabricated and a
certain amount of optical fibers are regularly distributed in the concrete shown as figure
2.1. Plastic optical fiber is an excellent media to transmit light at specific wavelengths
which has been widely used in illuminating facility or architectural appearance lighting.
In this paper, the transparent concrete is made of concrete and POFs. The fabrication
process of standard transparent concrete block can be described as follows. First,
according to the volume ratio of concrete and POF, some holes with orthogonal arrays are
drilled in the plastic sheet. Second, POFs are through the holes of two plastic sheets
which are fixed on the slots of wood formwork shown as figure 2.2. Last, a certain
concrete is poured in the formwork and fully vibrated on the shaking table. Figure 2.3
shows the product of transparent concrete, which has good light transmittance from the
transparent demonstration experiment.
Fig.2.1 Configuration of smart transparent concrete
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Dept. of Civil Engineering Seminar Report 2011-2012
Fig.2.2 Fabrication of smart transparent concrete
Fig.2.3 Transparent demonstration of smart transparent concrete
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Dept. of Civil Engineering Seminar Report 2011-2012
3. EXPERIMENTS OF SMART TRANSPARENT CONCRETE
3.1 LIGHT GUIDING PROPERTY OF SMART TRANSPARENT CONCRETE
In order to study the light guiding property of smart transparent
concrete, we fabricate six kinds of smart transparent concretes with different POF volume
ratios of 1%, 2%, 3%, 4%, 5% and 6%, and the diameters of POF is 2mm. The
transmittance is measured by the Newport 835 Optical Power Meter made in USA shown
as figure 3.1, and its wavelength range is 400-1100nm. The incandescent lamp with
200W and halogen lamp with 500W are chosen to provide light. To eliminate the
measuring dispersion of transmittance caused by the discrepancy of POFs’ position and
the material, three areas (denoted as 1, 2 and 3) in the middle part of transparent concrete
are chosen to test shown as figure 3.2, and the number of POFs in each chosen area shall
be equal. The number of the POFs is covered by transmission probe or integral sphere are
2 for 1% POF volume ratio, 4 for 2% POF volume ratio, 5 for 3% POF volume ratio, 7
for 4% POF volume ratio, 3 for 5% POF volume ratio and 9 for 6% POF volume ratio
respectively. The adjustment of step of the Newport 835 Optical Power Meter is 20nm,
and the incident light energy and transmission light energy are read simultaneously at
each step.
Fig. 3.1 Newport 835 Optical Power Meter Fig.3.2 Measuring area of the concrete in the Light Guiding Experiment
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Dept. of Civil Engineering Seminar Report 2011-2012
3.2 DURABILITY PROPERTY OF SMART TRANSPARENT CONCRETE
Civil engineering structures always suffer from external environmental
effects, such as fatigue, corrosion and wind load and so on, in long-term service.
Mechanical property and anti-corrosion property of building material at adverse
environments are two key facts for the durability of in-service structures, which directly
impact the safety of structures.
3.2.1 MECHANICAL PROPERTY OF SMART TRANSPARENT CONCRETE IN
FROZEN PROCESS EXPERIMENT
To study the mechanical properties of smart transparent concrete with
different POF volume ratio under mal-condition, the frozen process experiment is done in
the lab. The experimental process can be shown as in figure 3.3. In this paper, the POF
volume ratios of smart transparent concretes chosen for test are 0% (or plain concrete),
1%, 2%, 3%, 4%, 5% and 6%. After 25 freeze-thaw cycle test, the mechanical properties
of smart transparent concrete are evaluated by the compressive strength loss rate (ρf),
expressed as follow.
Eqn…(3.1)
Where ƒco and ƒcn are compressive strength before and after freeze-thawing test.
Fig.3.3 Procedure of Mechanical properties test after freeze-thawing
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Dept. of Civil Engineering Seminar Report 2011-2012
3.2.2 IMPERMEABILITY PROPERTY OF SMART TRANSPARENT
CONCRETE
For the smart transparent concrete, the interfacial bonding of the POFs
and concrete is a crucial factor in determining ultimate impermeability properties. The
chloride diffusion coefficient method (or electric flux method) is used to test the
impermeability property of smart transparent concrete, which can rapidly evaluate the
permeability of concrete by measuring the electric energy through concrete. In this paper,
the smart transparent concretes with 0%, 3% and 6% POF volume ratio are chosen for the
test. The electric energy is recorded by the electric flux detector NJW-RCP-6A made in
China, and cylindrical concrete specimens with 100mm diameter and 50mm height are
fabricated from the prefabricated smart transparent concretes by core-drilling method,
shown as figure 3.4. Moreover, in order to evaluate the effect of interface bonding on the
impermeability property, each model of specimen has been divided two types. One is that
the border of POF and concrete is covered by epoxy resin, the other one is not covered by
epoxy resin, as shown in figure 3.4. Figure 3.5 shows the test configuration.
Fig.3.4 Cylindrical concrete specimens for impermeability
Fig.3.5 Setup of test
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Dept. of Civil Engineering Seminar Report 2011-2012
4. EXPERIMENTAL RESULTS AND ANALYSIS
4.1 EXPERIMENTAL RESULTS OF LIGHT GUIDING PROPERTY
Graph-1. Light guiding test by halogen lamp Graph-1 and Graph-2 show the light guiding property of smart
transparent concrete with the POF volume ratio of 1%, 2%, 3%, 4%, 5% and 6% by using
the halogen lamp and incandescent lamp, respectively. It can be seen that the
transmittance of each type of smart transparent concrete almost keeps stable at whole
wavelength of the Newport 835 Optical Power Meter, and the linear relationship between
the POF volume ratio and its transmittance is good. For the halogen lamp, the
transmittances of the six ratio smart transparent concrete are 0.29%, 0.59%, 0.98%,
1.41%, 1.83% and 2.36%; for the incandescent lamp, the corresponding transmittances
are 0.41%, 0.82%, 1.22%, 1.72%, 2.15% and 2.59% respectively. The discrepancy of
transmittance induced by different lamp is that the light scattering’s angle of the chosen
lamp is different, and the POFs absorb much light scattered by incandescent lamp than
that by halogen lamp.
Graph-2.Light guiding test by incandescent lamp
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Dept. of Civil Engineering Seminar Report 2011-2012
Furthermore, it is worthily of note that the large the POF volume ratio is,
the large the transmittance is. In fact, the POF volume ratio and the corresponding
transmittance are just like a sword with both edges. We cannot only pay attention to the
high transmittance, for the POF inevitable affects the concrete strength. In the following
experimental results, it can be seen that POF will reduce the concrete strength.
4.2 EXPERIMENTAL RESULTS OF DURABILITY OF SMART TRANSPARENT
CONCRETE
4.2.1.MECHANICAL PROPERTY OF SMART TRANSPARENT CONCRETE AT
FREEZE-THAW
From graph-3, it can be seen that the mass of smart transparent concretes
almost are unchanged in 25times freezing and thawing cycle and the maximum loss rate
of mass is about 0.4%. Graph-4 shows the compressive strengthen of smart transparent
concretes with freeze-thaw or not. It can be seen that the compressive strength of each
type of smart transparent concrete have greatly decreased after 25times freeze-thaw cycle,
and the maximum loss rate of compressive strength is about 42% comparison with that
without bearing the function of freeze-thaw for the same type of concrete. It can be seen
that the larger the POF volume ratio is, the smaller the compressive strengthen of the
smart transparent concrete is. So we cannot endless increase the transmittance by way of
increasing the POF volume ratio.
One point to be mention, the compressive strengthen of the plain concrete
(or the smart transparent concrete with 0% POF volume ratio) is smaller than that of the
accustomed plain concrete. The reason is that we consider the fabrication method of the
smart transparent concrete and ignore the normal mix proportion of cement mortar at
pretest. To improve the compressive strength of the smart transparent concrete, one
solution is that the smart transparent concrete can be produced by some special high
strength concrete, which can reduce the impact of the POF to the concrete’s compressive
strength.
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Dept. of Civil Engineering Seminar Report 2011-2012
Graph-3. Loss rate of concrete mass at each Graph-4.Compressive strength of smart time of freeze-thawing transparent concrete with freeze-thaw or not
4.2.2 IMPERMEABILITY PROPERTY OF SMART TRANSPARENT
CONCRETE
Graph-5 shows the relationship of current strength over time. After the
vacuum water saturation, the initial current strength of the plain concrete, the smart
transparent concrete with 3% POF volume ratio, the smart transparent concrete with 3%
POF volume ratio and POF covered by epoxy resin, the smart transparent concrete with
6% POF volume ratio and the smart transparent concrete with 6% POF volume ratio and
POF covered by epoxy resin are 70.4mA, 104.5mA, 79mA, 117mA and 114.9mA,
respectively. After six hours conduction time, the corresponding current strengths of the
above six concretes increase to 113.6mA, 181.7mA, 126.4mA, 201.6mA and 1944.2mA,
respectively.
The total electric energy of the plain concrete, the smart transparent
concrete with 3% POF volume ratio and that with 6% POF volume ratio are 1897.8C,
3152.6C and 3602.2C, that is, there are some minor gaps between the POFs and concrete
which cause the decrease of the anti-permeability shown in graph-6. It also can be seen
that the anti-permeability is greatly improved by using the epoxy resin to cover the
boundary of the POFs and concrete, and the total electric energy of the smart transparent
concrete with 3% and 6% POF volume ratio covered by epoxy resin are reduced to 2147C
and 3357.8C. In field application, the anti-permeability index of smart transparent
concrete is very important for the long-term service. We can improve the anti-
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Dept. of Civil Engineering Seminar Report 2011-2012
permeability by two methods: one is to seal the boundary of POFs and concrete with
transparent waterproof material such as epoxy resin; the other one is to make the POF’s
coating rough to increase the compactness of interface between the POF and concrete.
Graph-5.The relationship of current strength Graph-6.Comparison of total electric energy over time traversing the smart concrete
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Dept. of Civil Engineering Seminar Report 2011-2012
5. CONCLUSION
A novel construction material named smart transparent concrete was
developed using POF and glass fiber with large diameter, in which the POF is used as
light transmission element and glass fiber is a sensing element to monitor the stress state
of structures, and could be regarded as an art material to be used in museums and specific
exhibitions. Based on the test of transmission, self-sensing and durability of the smart
concrete, the following results have been gotten:
1) The smart transparent concrete has good light guiding property, and the POF volume
ratio to concrete is proportion to transmission.
2) The stress birefringence property of glass fiber make itself a good sensing element to
measure the inner stress of smart transparent concrete. Comparison to the three
experimental conditions, it can be seen that the stress state of glass fiber can reflect the
stress state of concrete, which make the self-sensing property.
3) The amount of POFs has seriously influenced the compressive strength of the
corresponding concrete. The much number the POFs are, the smaller the compressive
strength is. So the transmissions cannot endless increase by way of endless increasing the
number of POFs in concrete. Furthermore, the POFs have also reduced the anti-
permeability of the concrete. Using the epoxy resin to seal the boundary of POFs and
concrete, the smart transparent concrete’s anti-permeability can be greatly improved.
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Dept. of Civil Engineering Seminar Report 2011-2012
6. REFERENCES
Ansari F. “Practical Implementation of Optical Fiber Sensors in Civil Structural
Health Monitoring.” Journal of Intelligent Material Systems and Structures,
18(8):879-889, 2007.
Zhou Z, Ou J.P, and Wang B. “Smart FRP-OFGB Bars and Their Application in
Reinforced Concrete Beams”. Proceedings of the First International Conference
on Structural Health Monitoring and Intelligent Structure, Japan: 861~866,2003.
Kuang K.S.C, Maalej M, Quek S.T. “Hybrid optical fiber sensor system based on
fiber Bragg gratings and plastic optical fibers for health monitoring of engineering
structures”. Proc. of SPIE, 6174(61742P):1-12, 2006.
Vázquez C, Gonzalo A.B, Vargas S and Montalvo J. “Multi-sensor system using plastic optical fibers for intrinsically safe level measurements”. Sensors and Actuators, 116:22-32, 2004.
Kalymnios, D. “Plastic Optical Fibers (POF) in sensing – current status and prospects”. 17th International Conference on Optical Fiber Sensors SPIE, 5855, 2005
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