Light Transmitting Concrete or Transparent Concrete

Seminar Report-2015 Light Transmitting Concrete

B.Tech, Department Of Civil Engineering 1 T.K.M Institute Of Technology

1. INTRODUCTION

Due to economic development and space utilization requirements, high-

rise buildings and skyscrapers are mostly built downtown in metropolitan areas

around the world, especially countries with great population. This arises one of the

problem in deriving natural light in building, due to obstruction of nearby

structures. Due to this problem use of artificial sources for illumination of

building is increased by great amount. So it is very essential to reduce the artificial

light consumption in structure.

It is considered to be one of the best sensor materials available and has

been used widely since the 1990s. Hungarian architect, Aron Losonczi, first

introduced the idea of light transmitting concrete in 2001 and then successfully

produced the first transparent concrete block in 2003, named LiTraCon. However

his light transmitting concrete did not have smart sensing properties. Light

transmitting concrete also known as transparent concrete is a novel construction

material manufactured with optical fiber by drilling through the cement and

mortar in order to utilize the light guiding ability of optical fiber. The main

purpose was to use sunlight as a light source in order to reduce the power

consumption of illumination.

Light transmitting concrete are available as prefabricated blocks / panels.

Litracon rooms will be brightened and proximal objects situated on the brighter

side of a transparent wall will be revealed as silhouettes on the other side. Though

the optical fibers compose only 4% of the concrete, some light is transmitted

because of their parallel arrangement in a matrix between to the two outer surfaces

of each block. Load-bearing structures can also be built from these blocks, since

optical fibers have no negative effect on the strength of the concrete. The blocks

come in various sizes and option of embedded heat-isolation. Since not everyone

appreciates the look of exposed concrete.



2. PRINCIPLE

Transparent concrete or translucent concrete is work based on “Nano-

Optics”. Optical fibers passes as much light when tiny slits are placed directly on

top of each other as when they are staggered. It is because optical fibers in the

concrete act like the slits and carry the light across throughout the concrete.

Thousands of optical glass fibers form a matrix and run parallel to each

other between the two main surfaces of each block. The fibers mingle in the

concrete because of their insignificant size and they become a structural

component as a kind of modest aggregate. The blocks can be produced in various

sizes and with embedded heat-isolation.

Light transmitting concrete is a combination of optical fibers and fine

concrete. It can be produced as prefabricated building blocks and panels. Due to

the small size of the fibers, they blend into concrete becoming a component of the

material like small pieces of aggregate. By arranging high numerical aperture

Plastic Optical Fibers (POF) or big diameter glass optical fiber into concrete, it

transmits light so effectively that there is virtually no loss of light conducted

through the fibers.

The glass fibers lead light by points between the two sides of the blocks.

Because of their parallel position, the light-information on the brighter side of

such a wall appears unchanged on the darker side. The most interesting form of

this phenomenon is probably the sharp display of shadows on the opposing side of

the wall. Moreover, the color of the light also remains the same.



3. MATERIALS

3.1. OPTICAL FIBERS

An optical fiber is a flexible, transparent fiber made of glass (silica) or

plastic to a diameter slightly thicker than that of a human hair. Optical fibers are

used most often as a means to transmit light between the two ends of the fiber. An

optical fiber consists of a core, a cladding layer and a buffer coating. Fig 3.1

shows a typical structure of optic fiber.

Fig 3.1: Structure of optical fiber

Core –The core is a cylindrical rod of dielectric material. Dielectric material

conducts no electricity. Light propagates mainly along the core of the fiber. The

core is generally made of glass. And in another way we can say it is a central tube

of very thin size made up of optically transparent dielectric medium and carries

the light form transmitter to receiver. The core diameter can vary from about 5µm

to 100 µm.

Cladding – It is the outer optical material surrounding the core having reflecting

index lower than core. It helps to keep the light within the core throughout the

phenomena of total internal reflection. Even though light will propagate along the

https://en.wikipedia.org/wiki/Silica

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fiber core without the layer of cladding material, the cladding does perform some

necessary functions. The index of refraction of the cladding material is less than

that of the core material. The cladding is generally made of glass or plastic.

The cladding performs the following functions:

Reduces loss of light from the core into the surrounding air

Reduces scattering loss at the surface of the core

Protects the fiber from absorbing surface contaminants

Adds mechanical strength

Buffer Coating – plastic coating that protects the fiber made of silicon rubber. The

typical diameter of fiber after coating is 250-300 µm. For extra protection, the

cladding is enclosed in an additional layer called the buffer coating. The buffer

coating is a layer of material used to protect an optical fiber from physical

damage. The material used for a buffer is a type of plastic.

The buffer is elastic in nature and prevents abrasions. The buffer also

prevents the optical fiber from scattering losses caused by micro bends. Micro

bends occur when an optical fiber is placed on a rough and distorted surface.

3.1.1. Types of optical fiber

There are three basic types of optical fibers.

3.1.1.1. Multi-mode graded-index fiber

In graded index fiber there are many changes in the refractive index with

larger values towards the center, as light travels faster in a lower index of

refraction. So, the farther the light is from the center axis, the greater is its speed.

Each layer of the core refracts the light. Instead of being sharply reflected as it is

in a step index fiber, the light is now bent or continuously refracted in an almost

sinusoidal pattern. Those rays that follow the longest path by travelling near the

outside of the core have a faster average velocity. The light travelling near the

center of the core has the slowest average velocity. As a result all rays tend to

reach the end of the fiber at the same time. That causes the end travel time of

different rays to be nearly equal, even though they travel different paths.



3.1.1.2. Multi-mode step-index fiber

This fiber is called "Step Index" because the refractive index changes

abruptly from cladding to core. The cladding has a refractive index somewhat

lower than the refractive index of the core glass. As a result, all rays within a

certain angle will be totally reflected at the core-cladding boundary. Rays striking

the boundary at angles greater than the critical angle will be partially reflected and

partially transmitted out through the boundary. After many such bounces the

energy in these rays will be lost from the fiber. The paths along which the rays

(modes) of this step index fiber travel differ, depending on their angles relative to

the axis.

3.1.1.3. Single-mode step-index fiber

Another way to reduce modal dispersion is to reduce the core's diameter,

until the fiber only propagates one mode efficiently. The single mode fiber has an

exceedingly small core diameter of only 5 to 10 m. Standard cladding diameter

is 125 m. Since this fiber carries only one mode, model dispersion does not

exists.

A multimode fiber can propagate hundreds of light modes at one time while

single-mode fibers only propagate one mode as shown below.

Fig 3.2: Types of Fiber



3.1.2. Total internal reflection

Fig 3.3: Schematic representation of total internal reflection

When light traveling in an optically dense medium hits a boundary at a

steep angle (larger than the critical angle for the boundary), the light is completely

reflected. This is called total internal reflection. The process of total internal

reflection is shown in fig:3.3. This effect is used in optical fibers to confine light

in the core. Light travels through the fiber core, bouncing back and forth off the

boundary between the core and cladding. Because the light must strike the

boundary with an angle greater than the critical angle, only light that enters the

fiber within a certain range of angles can travel down the fiber without leaking

out. This range of angles is called the acceptance cone of the fiber. The size of this

acceptance cone is a function of the refractive index difference between the fiber’s

core and cladding.

3.1.3. Benefits of optical fiber

Following are the benefits of optical fiber:

It can be bend in different shapes.

It has a less bending radius.

It is resilient to damage.

It is abuse than glass.

Cutting, wiring, bonding, connecting and processes are easier.

It does not produce radiation.



It is immune to radio magnetic interference, radio frequency interference

and noise.

3.2. CEMENT

As the optical fiber is only responsible for transmission of light, there is no

special cement required. So, ordinary Portland cement is used for transparent

concrete.

3.3. SAND

Sand is a naturally occurring granular material composed of finely divided

rock and mineral particles. The composition of sand is highly variable, usually in

the form of quartz. Sand particles should pass through 1.18 mm sieve. The sand

used is the normal sand. It should be free from impurities such as vegetation and

gravels

3.4. WATER

Water is the key ingredient, which when mixed with cement, forms a paste

that binds the aggregate together. The water needs to be pure in order to prevent

side reactions from occurring which may weaken the concrete, the role of water is

important because the water to cement ratio is the most critical factor in the

production of "perfect” concrete. It should be of drinking water quality. That is it

should be free from all impurities.



4. MANUFACTURING PROCESS

The manufacturing process of transparent concrete is almost same as

regular concrete. Only optical fibers are spread throughout the aggregate and

cement mix. There are different methods for the installation of optical fiber in

concrete.

One method is that, small layers of the concrete are poured on top of each

other and infused with the fibers and is then connected. Thousands of strands of

optical fibers are cast into concrete to transmit light, either natural or artificial.

Light-transmitting concrete is produced by adding 4% to 5% optical fibers by

volume into the concrete mixture. The concrete mixture is made from fine

materials only it does not contain coarse aggregate. Thickness of the optical fibers

can be varied between 2 μm and 2 mm to suit the particular requirements of light

transmission. Originally, the fiber filaments were placed individually in the

concrete, making production time-consuming and costly.

Newer, semi-automatic production processes use woven fiber fabric

instead of single filaments. Fabric and concrete are alternately inserted into

moulds at intervals of approximately 2 mm to 5 mm. Smaller or thinner layers

allow an increased amount of light to pass through the concrete. Following

casting, the material is cut into panels or blocks of the specified thickness and the

surface is then typically polished, resulting in finishes ranging from semi-gloss to

high-gloss.

In another method, the first step is to make a mould for the prototype block

using tin. The tin is made into a mould of the desired shape, like a cuboid with the

top end open. Many holes are punched on the opposite walls of the cuboids. The

optical fibers have to be run through these holes from one end to the other and

then concrete is made to set in it with the fibers inside. What happens here is that

the light falling on one side of the block gets transferred to the other side through

these many optical fibers running from one end to the other.



This is the trickiest part of the construction, passing each thin fiber through

the tiny holes of one perforated sheet to another one. This is also an integral part

of the process as the whole idea of transparency comes from these fibers. The

light is transferred from one end to another end through these, as mentioned

earlier. So much care has been taking in this process. The next step is to cast the

mortar over these fibers placed in the tin mould as shown in the fig: 4.1. The

concrete then undergoes a curing process. The excess fibers running out of the

block are cut off and slightly polished. The modeling of transparent concrete

block is complete.

Fig 4.1: Schematic layout of a moulded block with the fixed fiber composites within the

framework



5. PROPERTIES

The properties of light transmitting concrete are determined by conducting

various experiments like compressive strength test and flexural strength. A typical

transparent concrete block is shown in fig: 5.1.

Fig 5.1: Transparent concrete block

5.1. COMPRESSIVE STRENGTH:

By definition, the compressive strength of a material is that value of

uniaxial compressive stress reached when the material fails completely. The

compressive strength is usually obtained experimentally by means of a

compressive test. The compressive strength of the concrete is determined by cast

the cubes of size 150mm x150mm x 150mm.

Compressive strength = load/area.

The compressive strength of the conventional concrete and light

transmitting concrete in 7, 14 and 28 days is shown in figure: 5.2. Mix proportions

are as follows:



Cement – 360 kg

Sand – 560 kg

Fiber – 4.5 kg

Water – 190 lit

Fig 5.2: Compressive strength of concrete (Source: P.M.Shanmugavadivu, et.al; 2014)

The compressive strength of light transmitting concrete was compared

with ordinary plain cement concrete and result showed that the compressive

strength of litracon was similar to that of ordinary plain cement concrete. Hence it

is suitable for load bearing structures also.

5.2. FLEXURAL STRENGTH:

The flexural strength of the concrete is determined by conducting the test

on prism by two points loading.

Flexural strength = Pl/bd2

Where,

P – Load



l – Length of the specimen

b – Width of the prism

d – Depth of the prism

The flexural strength of the conventional concrete and light transmitting

concrete having mix proportion as above in 7, 14 and 28 days is shown in figure

5.3.

Fig 5.3: Flexural strength of concrete (Source: P.M.Shanmugavadivu, et.al; 2014)

The flexural strength result of decorative concrete are correlated with

results of ordinary plain cement concrete. The results evidently show that the

performance of litracon based on the strength aspect is also considerably high.

Hence the application of optical fiber will make the concrete decorative as well as

can make the concrete structural efficient.

Thus the study concludes that the transparency of light is possible in

concrete without affecting its compressive strength, as the optical fibers act as

fiber reinforcement thereby enhancing the strength and also enhances appearance.



5.3. MATERIAL PERFORMANCE:

Concrete retains its strength

High density top layer concrete

Infused with optical fibers

Frost and de-icing salt resistant.

Fire protection.

Highest UV resistance.

Some other properties of light transmitting concrete are:

Permits the passage of light through the set concrete, permitting colors,

shapes and outlines to be seen through it.

Having Compressive strength-50-220 N/mm2

Having maximum water absorption of 0.35%.

Having a maximum oxygen index of 25%.

Having a thermal conductivity of 0.21 W/m °C.

Having a flexural Strength of 7.7 N/mm2

Having an elastic limit greater than 60 MPa.

Having a Density from 2100 to 2400 kg/m3

Having a Young's Modulus from 2750 MPa to 3450 MPa

From its characteristics and composition, can be a conductor of electricity,

dispensing with interior.

From its mechanical and optical characteristics, can be used for purposes

that are both architectural and aesthetic, and also structural and under

conditions of service equal to and even different from those of a traditional

concrete.



6. ADVANTAGES

Following are the advantages of light transmitting concrete:

It has very good architectural properties for giving good aesthetical

view to the building.

Translucent concrete can be used at the place where light is not able to

come properly.

Energy saving can be done by utilization of translucent concrete in

building.

Totally environment friendly because of its light transmitting

characteristics, so energy consumption can be reduced.

When a solid wall is imbued with the ability to transmit light, it means

that a home can use fewer lights in their house during daylight hours.



7. APPLICATION

Various applications of transparent concrete are:

7.1. ILLUMINATION OF WALL

Transparent Concrete can be used as building material for interior and

exterior walls. If sunshine illuminates the wall structure, then eastern or western

placement is recommended; the rays of the rising or setting sun will hit the optical

glass fibers in a lower angle and the intensity of the light will be bigger. Besides

the traditional applications of a wall, the light transmitting concrete can also be

used as wall covering illuminated from the back.Fig:7.1 shows illuminated walls

using light transmitting concrete.

Fig 7.1:Walls illuminated by transparent concrete

7.2. PAVEMENT

Light transmitting concrete can be used as flooring a passable surface

illuminated from below. During the day it looks like typical concrete pavement

but at sunset the paving blocks begin to shine and in different colors. Fig:7.2

shows the pavement illuminated by transparent concrete.



Fig 7.2: Pavement illuminated by transparent concrete

7.3. DESIGN

The building units are versatile and can be used in many areas of design.

We can also create a logo with colorful figures, inscriptions, and pictures and can

used for beautification purpose.Fig:7.3 shows illuminated litracon panels.

Fig 7.3: Transparent concrete panels



7.4. RECEPTION DESK

Using transparent concrete reception desks can be light up in the front and

the sides.Fig:7.4 shows reception desk light up by transparent concrete.

Fig 7.4: Reception Desk made of transparent concrete

7.5. LIGHTING FIXTURE

The transparent concrete cube is, without a doubt, a great conversation

piece. The new cube line consists of four identical pieces of concrete and, due to

its special geometry; the pieces form a stable structure without fixing them

together. Fig 7.5 show lamps made of litracon.

Fig 7.5: Lamps made of litracon



7.6. STAIRS

Litracon can also be used in stairs. With impact lighting of linear LED

fixtures translucent concrete can be used in horizontal and vertical applications

such as feature stairs, walls, flooring, tables and counter tops.Fig:7.6 shows

transparent concrete stairs.

Fig 7.6: Transparent concrete stairs

It can be also applicable at:

Translucent concrete blocks inserted on front doors or walls next to it

allow the residents to see when there is a person standing outside.Fig:7.9

shows silhouette of a person standing outside the transparent concrete

wall.

Fig 7.9: Silhouette of person standing outside



Translucent concrete walls on restaurants, clubs, and other social

establishments help see how many people are actually inside it.

Transparent concrete walls in an office can be seen in fig:7.10.

Fig 7.10: Transparent concrete walls in an office

Ceilings of large corporate buildings with translucent concrete would help

reduce a great deal of lighting costs during day time.Fig:7.11 shows

transparent concrete ceiling.

Fig 7.11: Transparent concrete ceiling



Speed bumps in parking lots and highways can use translucent concrete

blocks with a light source beneath or reflecting from other vehicles/sources

help in navigation very effectively. Even lane markers in highways can use

this material to light up the roads.Fig:7.12 shows highway marked with

transparent concrete.

Fig 7.12: Highway marked with transparent concrete

Sidewalks with translucent concrete fitted with a single light source

beneath would add a lot to the scenic beauty as well as safety and also

encourage walking or foot travel during night times. Iluminated panels can

be seen in fig:7.13.

Fig 7.13: Transparent concrete panel



Translucent concrete blocks incorporated in inner walls help during times

of power cuts at night leading to a great deal of safety. Similarly for

subways and airports etc., this translucent concrete blocks would add to

the visibility. Transparent concrete wall can be seen in fig:7.14.

Fig 7.14: Exterior translucent wall

Translucent concrete blocks can be made in desired shapes and used as

decorative materials like bookshelves and sunshades, tables and statues. A

wash stand made of light transmitting concrete can be seen in fig: 7.15.

Fig 7.15: Wash stand made of transparent concrete



They can also be placed as random designs on security walls which also

enhance security giving the resident a hazy view of the perimeter. Fig 7.16

shows the silhouette of a person through a transparent concrete wall.

Fig 7.16: Transparent concrete wall

Places like schools, museums and prison cells outer walls can find

translucent walls very useful as they add safety as well as security and

supervision.



8. A FEW EXAMPLES

8.1. EUROPEAN GATE

European gate is an artistic installation which was designed to mark the

celebration of Hungary joining the European Union (EU), located at the public

entrance of Fortress Monostorin the Hungarian town of Komarom. This is one of

the most impressive pieces of art conjugating visual lighting display as well as

artistic using translucent concrete. The sun illuminates the 37.6ft large Litracon

piece of the statue in the mornings and late afternoons, and by night an even more

impressive view can be seen because of the embedded light sources. Day and

night view of European gate is shown in fig: 8.1.

Fig 8.1:Day and night view of European gate

8.2. CELLA SEPTICHORA VISITOR CENTRE

The 2 tons heavy Litracon door serves as the main entrance of the Visitors

Centre. It was made out of 48pcs of 10cm thick blocks. The blocks are in steel

frame to be able to move the structure. On daytime, one can see the shadows of

the pedestrians and the surrounding trees from inside. By night, the door is



illuminated from inside. Day view and night view of litracon door is shown in fig

8.3 and fig: 8.4.

Fig 8.3: Day view of litracon door from inside

Fig 8.4: Night view of litracon door



8.3. MONTBLANC BOUTIQUE, TOKYO, JAPAN

Litracon blocks (600x300x30mm) were used to create a wall that works as

a free-standing sculptural element in this flagship boutique for Montblanc. As

much as 30 Esq. of white Litracon was used. The illumination ensures that light

and shadow constantly do a dance on the wall.Fig:8.5 shows a transparent wall

transmitting sunlight to interior of the montblanc boutique.

Fig 8.5: Montblanc boutique

8.4. NEW HEADQUARTERS OF BANK OF GEORGIA

The office building is characterized by an amazing architecture and has

been the headquarter of the Georgian ministry for highway engineering before

becoming headquarter of Bank of Georgia, Tbilisi, with a total area of 10.960

square meters. It consists of five horizontal two-storied building parts which are

arranged like stacks. Thousands of embedded optical fibers are channeling the

light through the translucent concrete of wall and counter cladding. Walls, walks,

receptions, offices and consultation desks are shinning and glowing from within.

An office room of bank can be seen in fig: 8.6.



Fig 8.6: New headquarters of bank of Georgia



9. DISADVANTAGES

Following are the disadvantages of transparent concrete:

The main disadvantage is that these concrete has a very high initial cost

because of the optical fibers.

Casting of translucent concrete block is difficult for the labor, so special

skilled person is required.



10. CONCLUSIONS

A transparent concrete is aesthetically pleasing. Optical fiber based

transparent concrete could be regarded as an art which could be used in museums

and specific exhibitions rather than just a construction material. Although ease of

construction is to be compromised, the material is bound to be accepted

universally due to its advantages. With the concept of green technology catching

up, electrical supply, being supplemented by natural sources, it becomes

absolutely necessary to utilize the natural resource. Although litracon has yet to be

made available for commercial use, it has already been suggested that buildings

made with the material could save electricity that would otherwise be required for

daytime lighting. Moreover, this light transmitting concrete can be utilized in the

production of special types of home furniture. In future, the cost of light

transmitting concrete is expected to decrease with the advancement in technology,

manufacturers and as well as the users. Translucent concrete is the future. It is the

smart way of optimizing and utilizing light, a smart way of living.



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