Full Paper 107 China 2011

8/13/2019 Full Paper 107 China 2011

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The 6th International Workshop on Advanced Smart Materials and Smart Structures TechnologyANCRiSST2011

July 25-26, 2011, Dalian, China

Study on Smart Transparent Concrete Product and Its

Performances

Jianping He, Zhi Zhou and Jinping Ou

School of Civil Engineering, Dalian University of Technology, Dalian 116024, China

Minghua HuangSchool of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China

ABSTRACT

Building energy saving and safe evaluation for engineering structures have obtained the worldwide

attention. It is much of importance for developing a new kind of building material, which can integrategreen energy saving with self-sensing properties of functional material. In this paper, based on theexcellent properties of light guiding and elasto-optic effect of optical fiber, a novel smart transparentconcrete is researched by arranging the optical fibers into the concrete. To evaluate the effectiveness ofthe smart transparent concrete, the light guiding based on white light test, long-term durability basedon freezing and thawing test and chloride ion penetration test, and self-sensing property based onstress elasto-optic effect test are made respectively. The experiments results show that the smarttransparent concrete has good transparency, mechanical and self-sensing properties.

INTRODUCTION

With the economic growth and science-technology development, more and more large-scale civilengineering structures such as tall buildings, underground buildings and landmark buildings and so onare built around the world. While the economic growth is a kind of extensive growth: high input, highconsumption and high pollution, for that the energy saving technology is low, especially in developingcountries. The brightness of indoor environment is entirely maintained by artificial lighting, which hasconsumed a large number of resources. Moreover civil engineering structures always suffer fromexternal 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 monitoringsystems. Optical fiber sensors such as fiber Bragg Grating, Brillouin distributed sensors and plasticoptical fiber sensors have been widely used for the in situ monitoring of major projects (Ou&Zhou,


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2003 Anshari, 2007 Wu, 2006; Inaudi, 2005; C. V zquez 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 Hungarianarchitect Aron Losonzi, and the first transparent concrete block is successfully produced by mixinglarge 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 weightof common concrete. It is worth mentioning that Italian Pavilion in Shanghai Expo 2010 shows a kindof transparent concrete developed by mixing glass into concrete in 2010. While the transparentconcrete mainly focuses on "transparent and its application object is art design. And there is noresearch on mechanics and long-term durability of transparent concrete. Therefore it is imperative todevelop a new functional 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 transmitaccording 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 theadvantages of the concrete and optical fiber, developing a novel functional material has importantvalue of application for construction and sensing. In this paper, to integrate the merits of concrete andoptical fiber, our group develops a smart transparent concrete by arranging the high numerical aperturePOF or big diameter glass optical fiber into concrete. The main purpose is to use sunlight as a lightsource to reduce the power consumption of illumination and to use the optical fiber to sense the stressof structures. The light guiding, durability and self-sensing properties are studied based on white lighttest, freezing and thawing test, chloride ion penetration test, and stress elasto-optic effect testrespectively.

1. FABRICATION OF SMART TRANSPARENT CONCRETE

The main idea of the smart transparent concrete is that high numerical aperture optical fibers aredirectly 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 smarttransparent concretes can be fabricated and a certain amount of optical fibers are regularly distributedin the concrete shown as figure 1. Plastic optical fiber is an excellent media to transmit light at specificwavelengths 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 ofstandard transparent concrete block can be described as follows. First, according to the volume ratio ofconcrete and POF, some holes with orthogonal arrays are drilled in the plastic sheet. Second, POFsare through the holes of two plastic sheets which are fixed on the slots of wood formwork shown asfigure 2. Last, a certain concrete is poured in the formwork and fully vibrated on the shaking table.Figure 3 shows the product of transparent concrete, which has good light transmittance from thetransparent demonstration experiment.


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Fig.1 Configuration of smart transparent concrete

Fig.2 Fabrication of smart transparent concrete

Fig.3 Transparent demonstration of smart transparent concrete

2. EXPERIMENTS OF SMART TRANSPARENT CONCRETE

2.1Light Guiding Property of Smart Transparent Concrete

2.1.1 Evaluation Method of Light Guiding of Smart Transparent Concrete

There are many performance indicators to be considered whether the transparency of material isgood or not, such as transmittance, haze, refractive index, birefringence and dispersion and so on. Inthis paper, the transmittance is used to appraisal the light guiding of smart transparent concrete. For the

homogeneous materials such as homogeneous glass or LiTraCon above mentioned, their transmittancecan be directly calculated by the ratio of the incident energy and transmission energy of lightexpressed as following equation:

0

= 100% J J

1 (1)

Where 1, , J and 0 J are transmittance, correction coefficient of measurement equipment,

transmission energy and incident energy, respectively. While the smart transparent concrete developed by our group is heterogeneous, its transmittance cannot be obtained by equation (1), because thenumber of POFs in unit area is different at different area, that is, the transmittance in unit is related tothe arrangement of POF in smart transparent concrete. We improve the calculation method fortransmittance as follows.


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a) Incident light energy per unit area 0

00

0

W A

= (2)

Where 0W and 0 A are light energy of incident probe and area of incident probe.

b) Incident total energy of concrete section at the side of light 0s J :

00 0 1 1

0

s W J A A A

= = (3)

Where 1 A is the cross-section area of smart transparent concrete.

c) Transmitted light energy of single POF 1 :

11

1

W n

= (4)

Where 1W and 1n are light energy of transmission probe and the number of POFs covered by

transmission probe.

d) Transmitted light energy of smart transparent concrete 1s J :

11 1

1

s W J N N n

= = (5)

Here N is the total number of POFs in the smart transparent concrete.

Then based on equation (3) and (5), we can obtain the transmittance ( s ) of the smart transparent

concrete.

1

1 01 1

00 0 1 11

0

100% 100% 100%s

ss

W N N W A J nW J W A n A A

= = =

(6)

2.1.2 Light Guiding Experiment of Smart Transparent Concrete

In order to study the light guiding property of smart transparent concrete, we fabricate six kinds ofsmart transparent concretes with different POF volume ratios of 1%, 2%, 3%, 4%, 5% and 6%, and thediameters of POF is 2mm. The transmittance is measured by the Newport 835 Optical Power Metermade in USA shown as figure 4, 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 dispersionof transmittance caused by the discrepancy of POFs position and the material, three areas (denoted as1, 2 and 3) in the middle part of transparent concrete are chosen to test shown as figure 5, and the


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number of POFs in each chosen area shall be equal. The number of the POFs is covered bytransmission probe or integral sphere are 2 for 1% POF volume ratio, 4 for 2% POF volume ratio, 5for 3% POF volume ratio, 7 for 4% POF volume ratio, 3 for 5% POF volume ratio and 9 for 6% POFvolume 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. 4 Newport 835 Optical Power Meter Fig.5 Measuring area of the concrete in the Light Guiding Experiment

2.2 Self-sensing Property of Smart Transparent Concrete based on stress elasto-optic effectGlass fiber is a kind of photoelastic material, which is isotropic under normal circumstances. Once

be applied load, glass fiber becomes anisotropic, and light birefringence phenomena in it is generated.Commonly, if the optical constants and thickness of glass fiber, the isochromatics and isoclinics areknown, the stress state of the glass fiber can be obtained based on the shear difference method. Basedon this phenomenon, glass fiber is layout into the smart transparent concrete to monitor the stress stateof structures, and the glass fiber can be considered as a sensing element and an optical transmissionmaterial. In order to study the self-sensing property of smart transparent concrete, we simultaneouslylayout a glass fiber with 15mm diameter and numbers of POFs into the concrete with the size of100 100 100mm mm mm . In the test, the isochromatics and the isoclinics of the samples are gotten

by using the plane polarized light and circularly polarized light equipments respectively. Figure 6shows the experimental setup including a glass fiber or a smart transparent concrete, a loading deviceand a photoelasticity experimental equipment. The circularly polarized optical field is obtained byadding two 1/4 wave plates in the plane polarized optical field. The strain applied on the samples isrecorded by the strain gauge pressure transducer.

Fig.6 Configuration of experimental setup

2.2.1 Test of glass fibers stress elasto-optic effectAccording to the measuring resolution and accuracy of MGD-1diffusion photo elasticity

instrument produced by Shanghai 771 Institute in China, glass fiber with 15mm diameter is chosen to


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test its elasto-optic property under radial stress. Before test, the cross-section of glass fiber is polishedto ensure the surface smooth. Under the plane polarized optical field, the glass fiber is applied radialload of 0.4kN and 0.8kN respectively. Keeping the polarizer and the analyzer mirror orthogonal, theseries of isoclinics of glass fiber at 0-90 degree with the step of 10 degree are obtained bysynchronously rotation of the corresponding orthogonal polarization axis. To separate theisochromatics from the color coupled photoelastic patterns, the series of isochromatics of fiber glassare obtained under the circularly polarized optical field, where the glass fiber is applied 0.2-1.6kNwith step of 0.2kN.

2.2.2 Test of self-sensing property of smart transparent concrete based on stress elasto-optic effect

Figure 7a shows the smart transparent concrete with size of 100mm100mm100mm bycombining with glass fiber and POFs. The diameters of glass fiber and POF are 15mm and 2mmrespectively. The glass fiber is considered as a stress sensing element in the concrete. Like the testdescribed in the 3.2.1, the isochromatics and the isoclinics of the glass fiber are monitored under

plane/ circularly polarized optical field, which can reflect the stress state of the concrete. In order totest the self-sensing properties of the smart transparent concrete, the elasto-optic effect of thetransparent concrete under different damage modes are studied. Figure 7b shows the damage modes ofconcrete, where a crack with size of 0.5mm is produced. Figure 8 gives three loading modes: a)un-damage mode (I); b) longitudinal damage mode (II); c) lateral damage mode (III). Thelongitudinal damage mode is that the crack is parallel to the loading direction, and the lateraldamage mode is that the crack is vertical to the loading direction.

Fig.7 Non-damage and damage samples of smart transparent concrete with glass fiber

Fig.8 Three loading modes for smart transparent concrete

2.3 Durability Property of Smart Transparent ConcreteCivil 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-servicestructures, which directly impact the safety of structures.


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2.3.1 Mechanical Property of Smart Transparent Concrete in Frozen Process Experiment

To study the mechanical properties of smart transparent concrete with different POF volume ratiounder mal-condition, the frozen process experiment is done in the lab. The experimental process can

be shown as in figure 9. In this paper, the POF volume ratios of smart transparent concretes chosen fortest are 0% (or plain concrete), 1%, 2%, 3%, 4%, 5% and 6%. After 25 freeze-thaw cycle test, themechanical properties of smart transparent concrete are evaluated by the compressive strength loss

rate ( f ), expressed as follow.

100co cn f

co

f f f

= (7)

Where co f and cn f are compressive strength before and after freeze-thawing test.

Fig.9 Procedure of Mechanical properties test after freeze-thawing

Fig.10 Configuration of compression tests

2.3.2 Impermeability Property of Smart Transparent Concrete

For the smart transparent concrete, the interfacial bonding of the POFs and concrete is a crucialfactor in determining ultimate impermeability properties. The chloride diffusion coefficient method (orelectric flux method) is used to test the impermeability property of smart transparent concrete, whichcan rapidly evaluate the permeability of concrete by measuring the electric energy through concrete. Inthis paper, the smart transparent concretes with 0%, 3% and 6% POF volume ratio are chosen for thetest. The electric energy is recorded by the electric flux detector NJW-RCP-6A made in China, andcylindrical concrete specimens with 100mm diameter and 50mm height are fabricated from the

prefabricated smart transparent concretes by core-drilling method, shown as figure 11. Moreover, in

order to evaluate the effect of interface bonding on the impermeability property, each model ofspecimen has been divided two types. One is that the border of POF and concrete is covered by epoxyresin, the other one is not covered by epoxy resin, as shown in figure 11. Figure 12 shows the test


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configuration. The process of permeability test based on the electric flux method can be described infigure 13.

Fig.11 Cylindrical concrete specimens forimpermeability Fig.12 Setup of test

Fig.13 Procedure of chloride diffusion coefficient test

3. EXPERIMENTAL RESULTS AND ANALYSIS

3.1 Experimental Results of Light Guiding Property

a) Transmittance b) Relationship of POF volume ration and

transmittanceFig.14 Light guiding test by halogen lamp

Figure 14 and figure 15 show the light guiding property of smart transparent concrete with thePOF 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 almostkeeps 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 transmittancesof the six ratio smart transparent concrete are 0.29% 0.59% 0.98% 1.41% 1.83% and 2.36%; forthe 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 lightscatterings angle of the chosen lamp is different, and the POFs absorb much light scattered byincandescent lamp than that by halogen lamp.


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a) Transmittance b) Relationship of POF volume ration and transmittance

Fig.15 Light guiding test by incandescent lampFurthermore, 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 inevitableaffects the concrete strength. In the following experimental results, it can be seen that POF will reducethe concrete strength.

3.2 Experimental Results of Self-sensing Property

3.2.1 Photoelastic Effect of Large Diameter Glass Fiber

Figure 16 shows the results of phtoelastic effect of glass fiber applied radial load of 0.4kN under plane polarized optical field. Both the isochromatics and the isoclinics are figured out in the figure.The isoclinics, described as black lines in the figure, are changed along with the angle of the rotation

of the corresponding orthogonal polarization axis, while the isochromatics remain unchanged at thesame load. The isoclinics denote the direction of principle stress of the glass fiber, and theisochromatics are the difference.

Fig.16 Photoelastic effect of glass fiber under plane polarized optical field

Fig.17 Isochromatics of glass fiber at diff erent level load

Figure 17 shows the isoc hromatics at different load by adding two 1/4 wave plates in the plane

polarized optical field. It can be seen that the isochromatics are changed with loading change, whichhints that the isochromatics of glass fiber are sensitive to the external load. In photoelasticityexperiment, it is difficult to measure the series of isochromatic precisely due to various factors such asthe accuracy or resolution of the measuring equipment. From the tests results, it can be seen that the


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glass fiber has a good photoelastic effect which is sensitive to the external force applied on it.


Figure 18 show the results of phtoelastic effect of smart transparent concrete at three conditions

above mentioned under the plane polarized optical field. It can be seen that the isochromatics of glassfiber at the three conditions are different from each other at the same load due to the damage anddifferent loading conditions. Comparison with that of the undamaged concrete, the isochromatics ofglass fiber changes larger at III condition than that at II condition.

a) Phtoelastic fringe at different angle with 12kN b) Phtoelastic fringe at different level loadFig.18 Phtoelastic fringe of glass fiber under plane polarized optical field

Figure 19 shows Phtoelastic fringe of glass fiber at different angle under plane polarized opticalfield, where the concrete is applied 12kN load which is vertical to the crack. Figure 20 illustrates theseries of isochromatics of glass fiber at 2.5-15kN with the step of 2.5kN under the circularly polarizedoptical field. It is obviously seen that the stress state of concrete with damage is more complicate thanthat with non-damage from figure 18 and figure 19. Based on the phtoelastic fringe or stress state ofglass fiber in the concrete, the stress state of corresponding concrete can be figured out.

Fig.19 Phtoelastic fringe of glass fiber atdifferent angle Fig.20 The series of isochromatics of glassfiber at different level load


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3.3 Experimental Results of Durability of Smart Transparent Concrete

3.3.1 Mechanical Property of Smart Transparent Concrete at Freeze-thaw

From figure 21, it can be seen that the mass of smart transparent concretes almost are unchanged in25times freezing and thawing cycle and the maximum loss rate of mass is about 0.4%. Figure 22shows the compressive strengthen of smart transparent concretes with freeze-thaw or not. It can beseen that the compressive strength of each type of smart transparent concrete have greatly decreasedafter 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 smarttransparent concrete is. So we cannot endless increase the transmittance by way of increasing the POFvolume ratio.

One point to be mention, the compressive strengthen of the plain concrete (or the smart transparentconcrete 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 transparentconcrete, one solution is that the smart transparent concrete can be produced by some special highstrength concrete, which can reduce the impact of the POF to the concretes compressive strength.

Fig.21 Loss rate of concrete mass at eachtime of freeze-thawing

Fig.22 Compressive strengthen of smarttransparent concretes with freeze-thaw or not


Figure 23 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 volumeratio, the smart transparent concrete with 3% POF volume ratio and POF covered by epoxy resin, thesmart 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 and114.9mA, respectively. After six hours conduction time, the corresponding current strengths of theabove six concretes increase to 113.6mA, 181.7mA, 126.4mA, 201.6mA and 1944.2mA, respectively.


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Fig.23 the relationship of current strengthover time

Fig.24 Comparison of total electric energytraversing the smart concrete

The total electric energy of the plain concrete, the smart transparent concrete with 3% POF volumeratio and that with 6% POF volume ratio are 1897.8C, 3152.6C and 3602.2C, that is, there are someminor gaps between the POFs and concrete which cause the decrease of the anti-permeability shown

in figure 24. It also can be seen that the anti-permeability is greatly improved by using the epoxy resinto cover the boundary of the POFs and concrete, and the total electric energy of the smart transparentconcrete with 3% and 6% POF volume ratio covered by epoxy resin are reduced to 2147C and3357.8C. In field application, the anti-permeability index of smart transparent concrete is veryimportant for the long-term service. We can improve the anti-permeability by two methods: one is toseal the boundary of POFs and concrete with transparent waterproof material such as epoxy resin; theother one is to make the POFs coating rough to increase the compactness of interface between thePOF and concrete.

4. CONCLUSIONA 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 fiberis 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 anddurability 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 toconcrete is proportion to transmission.

2) The stress birefringence property of glass fiber make itself a good sensing element to measurethe 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 theself-sensing property.

3) The amount of POFs has seriously influenced the compressive strength of the correspondingconcrete. The much number the POFs are, the smaller the compressive strength is. So thetransmissions can not 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 resinto seal the boundary of POFs and concrete, the smart transparent concretes anti-permeability can begreatly improved.

ACKNOWLEDGEMENTS

The authors are grateful for the financial supported from National Natural Science Foundation ofChina (NSFC) under Grant Nos.10672048, 50538020 and 50978079, National Scientific Support


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Project under Grant Nos.2006BAJ03B05 and 2006BAJ13B03 and the Research Award Fund forOutstanding Young Teachers in Higher Education Institutions, China (Grant No. 20100481233).

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Full Paper 107 China 2011