growth of population has led to bigger and denser building infrastructure and
as a result the energy consumption due to the interior lights is getting higher.
To achieve an efficient way for saving energy, the existing concrete blocks can
be replaced with a transparent concrete blocks using plastic optical fibers
(POF) as the material is energy saving construction material and environment
friendly as well. The present paper reviews the use of light transmitting
masonry block embedded with plastic optical fibers along with the discussion of
its strength parameters i.e. compressive strength. The use of self cleansing
method of TiO2 in concrete
technology to increase the longevity of construction has also been
Keywords: Plastic Optical Fibre(POF); Self Cleansing
Concrete; TiO2; Smart Building Material
The growing demand of superior
infrastructure due to massive population growth has given rise to an era of huge
concrete structures. In India, we expect a rise of 80 billion square feet in
the building sector in the next 17 years. But such tremendous developments
brings along with it concerns for the environment.
One of the major environmental concerns is the
excessive expenditure of energy for providing lighting in high rise buildings.
For instance, China consumes around 25% of global architectural energy 1 and
13% of that energy is used to provide lighting. There is a growing need of a
sustainable replacement of construction materials with unconventional composite
materials which can provide the building with smart properties. Optical fibre
is one such building material which can provide the masonry blocks with light
transmitting property without compromising its compressive strength. Also, if
there is power suspension in high rise buildings during emergencies,
transparent concrete will be efficient in providing safe evacuation. Moreover,
a smart transparent concrete has an aesthetic appeal to it.
Air pollution is another major environmental concern with
metros all across the world facing severe impact. Delhi is one of the most
polluted cities in the world. A major contributor to the air contamination is
the exhaust generated by the vehicles. According to the Department of Transport, Government of
Delhi, there is a 7% increase in the population of vehicles per annum. The vehicular
population is projected to be around 3.4 million at present. The existing
measures are not nearly enough to keep the air pollution under control. The use of photocatalytic materials for
air purification has been developing rapidly since the last 10 years. TiO2
is one such photocatalytic material which when applied on the external
surface of buildings and roads can control the emissions from the vehicles by
removing the air pollutants. This
self-cleansing property of TiO2 also facilitates the masonry block
to preserve its color for long duration 2.
Working Principle of plastic optical fibre (POF)
The main working principle of plastic
optical fibre is the total internal reflection of light. A total internal
reflection occurs when the light passes through a denser medium (higher
refractive index) to a lighter medium (lower refractive index) and the incident
angle of the light is greater than the so called critical angle. The light repeatedly reflects from the normal passing through
the cable in a zig-zag manner. Thus the angle of refraction becomes greater
than the angle of incident. The outer part and a inner part of an optical fibre
are called cladding and core respectively (Fig.1). A general purposed
resin is used as the core material and fluorinated polymers are used as
cladding material in POF. 3
Figure 1. Total Internal Reflection
of Optical Fibre
The idea of using plastic optical
fibre as a concrete material was first introduced in 2001 by a Hungarian
architect named Aron Losonczi and the first light transmitting concrete block
was made in 2003, named LiTraCon.
Mechanism behind self cleansing concrete
Maintaining a clean and pleasant environment is
a common aspiration. But in today’s world various kind of hazardous substances
that pose a risk to our health and life are generated by our pursuit for
greater convenience. Air pollution and stained exterior walls of building
caused by exhaust fumes, sick house syndrome induced by certain building
materials, odours from pets, baggage and cigarette smoke makes our life at
Photocatalysis was first discovered in Japan
and subsequently the technology of photo catalysis was developed. Because of
its significant potential the technology is gaining attention as a key
technology of 21st Century. In 1967, Professor Fuji Shima of the University of Tokyo accidently
discovered splitting of water into oxygen and hydrogen when TiO2
powder and water was irradiated with light 4. The discovery of photocatalysis
which was very much like photosynthesis by plants was published in British
Science Journal Nature in 1972. It was called Honda Fukushima Effect. Photocatalysis
is summarized as the mechanism by which chemical reaction of TiO2 is
caused by light.
In photocatalysis when light energy from Sunlight
or fluorescent light is irradiated on TiO2, a strong power of
decomposition is generated on the surface of TiO2 by its properties
and is continuously decomposed until it become harmless. Photocatalysis effect
is almost permanent. The main principle of photocatalysis is that when light
energy is irradiated on the surface TiO2, electrons are released.
The released electrons bind with oxygen to form superoxide anion. Moreover the
surface of TiO2 becomes positively charged and takes electrons from
moisture in the air. The moisture that has lost electrons becomes hydroxyl
radical. The superoxide anion and hydroxyl radicals by their power of oxidation
destruction decompose organic compounds such as oils, organic bacteria,
hazardous scientific gases, fungus and offensive odours the cause staining by
turning them into water or other harmless substances and disperse.
The coating agent is water soluble and it is
harmless to man and animals and it is eco-friendly. It is applied mainly by
spray gun or by roller or brush depending on circumstances. It is used in
coating of exterior walls and glass ceilings of buildings. Its effectiveness is
not limited to outdoors. It is used for deodorizing, disinfecting and purifying
the air inside cars, nursing homes and hospitals. It is also used to prevent
sick school and sick house syndrome.
Principle and application of Self Cleansing
concrete in building structure
principle ways by which a material surface can be cleaned is 1). Creating super
hydrophobic surfaces 2) Creating hydrophilic surfaces. Soap, which cleans dirt
from the surface based on low contact angle (Hydrophobic surfaces) are known to
us for quite a time. Adhesion work and contact angle is inversely proportional,
higher the angle lower the adhesion work. If we compare micro-rough surface and
water based on contact angle, it has been seen that the former shows more
contact angle. When any dirt particles are picked up by water and it comes in
contact with a micro-rough surfaces, the sizes of droplet minimizes due to
adhesion on the surface and removed from the surface when the droplet roll.5
Figure 1. a) Normal Surface b) Hydrophobic
active thin film on material surfaces we can create low contact angle. Photocatalytic
active metal oxides or sulfides are used to prepare this thin film. When
sunlight falls on of the anatase type, very low contact angles
are obtained. These materials are super-hydrophilic in nature. For nearly two
days super-hydrophilic behavior of is retained if UV rays doesn’t falls on it. 6.
Basic Principld of Heterogeneous Catalyst
heterogeneous photocatalytic system consists of semi conductor particles (photocatalyst)
which are in close contact with a liquid or gaseous medium. When these
particles are exposed to light, excited states are generated are which then are
able to generate subsequent process like redox reaction and molecular
by which self cleansing concrete works is very interesting. The electrons in becomes energized when sunlight falls on them.
These electrons transfer energy to in air. Due to the transfer of energy, free
radicals are formed (, ). The free
radicals attack and destroy organic matter by oxidation. The, called
hydroxyl group make the building surface super slick. Instead of beading on the
surface, the water collapses on the surface and runs off thus removing dirt.
ion (, which is
highly reactive compound is formed when oxygen is reduced by single electron (2)
ions have one unpaired electron and are paramagnetic in nature can oxidize
number of organic materials.
Photo catalysis was first discovered in Japan.
Because of its significant potential the technology is gaining attention as a
key technology of 21st Century. In 1967, Professor Fuji Shima 7 of the University of Tokyo accidently
discovered splitting of water into oxygen and hydrogen when powder
and water is irradiated with light. The main reason why the heterogeneous photo
catalytic oxidation with makes it
competitive with other processes oxidizing contaminants:
Reaction is fast at room temperature.
A wide spectrum of organic contaminants
can be converted to
Low Cost material used a photo catalyst.
Practical Application of TiO2 as
Coated ceramic titles are as one of the most effective
which kills bacteria 8, inorganic and organic material at extreme high rate.
Some major areas of activities in photo catalysis are anti-fogging effect, water
treatment, air cleaning effect, self cleaning effect and anti-bacterial effect.
In the field of waste water
detoxification numerous concepts were created.10,11. Presently there is
high interest in development and improvement of thin-film-fix bed reactor.
In this reactor type industrial waste is
passing on coated materials.
Factors to consider when using Transparent and
Self Cleansing Concrete as smart Building Material
Even though research on transparent
concrete material as a major construction material is still in the early
stages, there have been a number of studies regarding the use of optical fibres
in concrete block. Jianping He
et al. 12 conducted a study by developing a smart transparent concrete using
Plastic Optical Fibre (POF) and glass fibre. It was observed that POF provided
the concrete with light guiding property and the POF volume ratio to concrete
was proportional to transmission. But the experiments have also shown that
excessive number of POFs can reduce the compressive strength of the concrete.
Hence the amount of POFs cannot be increased endlessly. B.Yamini Nirmal et al.
13 compared the compressive strength of transparent concrete and the
conventional concrete and concluded that the compressive strength of the smart
concrete was greater than that of the latter up to an optimum of 4% by volume
of optical fibre beyond which the compressive strength declines with increase
in volume of the optical fibre. Harish et al. 14 prepared light transmitting
cement masonry blocks using optical fibres and tested it for compressive
strength and intensity of light passing through it. Also TiO2 was
used as a coat on the block’s surface for investigating the self-cleansing
property. From the experiments it was concluded
that it takes only 0.04% of surface area of optical fibres to transmit a light
intensity amounting to 2 lumens without having any detrimental effect in the
compressive strength of the transparent masonry block. TiO2 can be used as a
coat on the surface of masonry block as it provides self cleansing property in
the presence of sun for its photo catalytic property. But the studies also showed that despite the many
advantages of using optical fibres in cement blocks there are some environmental
concerns. For instance the use of cement masonry blocks for external walls can
cause global warming. One feasible solution can be decreasing the amount of
cement content in the block and using sustainable construction materials such as
flyash, lime, or stabilized mud. Juan
Shen and Zhi Zhou 15 concluded from their studies that
light transmitting concrete not only provides a green solution by saving energy
during daytime but also makes the structure more appeasing to the eye from an aesthetic
point of view. Large, high rise buildings can enjoy lighting during day due
to the translucent ceilings. Insulation from heat is another property that
transparent concrete provides 16. In 17, POF and Fibre Bragg Grating were
used to manufacture transparent concrete and this provided the concrete with
both light transmitting properties and sensing properties. The light transmitting, mechanical properties and self-sensing
performance were then examined. From the experiments, it was observed
that the light transmitting ratio becomes higher with a greater column
proportion of POF. Also when the proportion ratio of the
POF is less than 5%, it affects the compressive strength of the concrete for
not more than 10%. Andrea Giovanni Maininia et al. 18 presented a technique to
measure the photometric performances of light transmitting effectiveness of transparent
concrete panel for façades. In their experiments they validated a simplified
Radiance model of the panel using the data collected.
Several researches have proven
the effectiveness of photocatalytic TiO2 modified cementitious
material in reducing the amount of air contamination. TiO2 when used
in masonry block pavement reduces the NO concentration emitted from the vehicles
19. Tunnel vaults lighted up by artificial UV rays can make use of the
ability of TiO2 to oxidize air pollutants in the presence of light energy.
This will help keep the tunnel cleaner for a longer duration 20. The light
transmittance property of glass cullets can be used for further improving the photocatalytic
activity as it allows the TiO2 within the inner concrete surface
layers to play an active role in the photocatalytic reactions 2. Despite the many advantages of using
photocatalytic building materials, there are certain drawbacks in it. One such
drawback is that TiO2 and ZnO nanoparticles decreased the
compressive strength and permeability of the masonry blocks 21. The
liquid and solid remained on the surface get washed by rainwater and eventually
ends up underground. It has even been found that TiO2 is responsible
to cause ground water pollution 22.
From this paper it can be reviewed that
POF based concrete can be a sustainable energy saving replacement to the
conventional concrete without compromising its strength parameters. Not just in
high rise buildings and skyscrapers, it can also be used in public places and
museums because of its aesthetic look from an architectural point of view. The
self cleansing concrete keeps its surface clean by itself and in addition it
removes pollutants from the air by breaking down the dirt into molecules like
oxygen, nitrogen, nitrates, sulphates etc. The liquid and solid remained on the
surface get washed by rainwater and eventually ends up underground. There are many researches going on to find whether it
causes pollution of the ground water and also TiO2 decreases
compressive strength and permeability of masonry blocks. Thus more experimental works are
necessary in order to upgrade the work that in can ensure an environmental
friendly and practical application of this material.