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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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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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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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Fig.2.2 Fabrication of smart transparent concrete

Fig.2.3 Transparent demonstration of smart transparent concrete

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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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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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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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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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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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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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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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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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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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