Transparent Concrete

 

Transparent Concrete

1. Introduction:

Concrete has been used to build many stunning things throughout the history. Ever since the concrete was invented, many ingredients of concrete have been tried and tested to get desirable strength. After the invention of Portland cement in 1824, the basic ingredients of concrete (cement, sand, coarse aggregate & water) have not been changed yet. In modern times, aesthetic appearance is also a matter of importance along with the structural strength and that’s exactly what transparent concrete is meant for.

So, what actually is transparent concrete?

Simply, the concrete that allows light to pass through it is transparent concrete. It is also known as light transmitting concrete. But the passage of light does not allow the clear view on the other side, so it is also called as translucent concrete .

(Source: https://theconstructor.org/concrete/transparent-concrete-light-transmitting-concrete/9271/)

2. Brief History:

Translucent concrete has been first mentioned in a 1935 Canadian patent. But actual concept of translucent concrete was introduced in 2001 by Hungarian architect, Aron Losonczi. Within 2 years, he was able to successfully produce the first transparent concrete block and named it LiTraCon which means Light Transmitting Concrete.

3. Transparent Concrete Ingredients:

3.1. Cement:

Cement is a binding material that binds the sand & coarse aggregates together to provide the concrete it’s strength. Cement is not responsible for any light transmitting properties so Ordinary Portland Cement (OPC)  can be used to make transparent concrete. OPC is the most common type of cement which is available in different grades depending upon it’s ultimate strength in 28 days.

3.2. Sand (Fine Aggregate):

Fine aggregates are chemically inert materials that serves to fill the voids between the coarser ones which ultimately aids to increase strength and reduce porosity. The sand to be used in transparent concrete should be comparatively finer than in normal concrete. Sand passing through 1.18mm IS sieve is suitable for the transparent concrete.

3.3. Coarse Aggregate:

Generally coarse aggregates are not used in transparent concrete but for additional crushing strength the aggregates of maximum size 10mm may be used.

3.4. Water:

Water to be used to prepare transparent concrete should be of drinkable quality (pH 6.5 to 8.5). It should be free from acids, oils, alkalis and other organic or inorganic impurities.

3.5. Optical Fibers:

(Source: https://www.scienceabc.com/wp-content/uploads/2016/07/Optical-fiber.jpg)

Optical fibers are the most important elements in transparent concrete which is responsible for the light transmitting properties. Optical fiber is a transparent and flexible material made by silica or plastic. Light propagates through the fiber following the principle of total internal reflection.

An optical fiber is made up of three components:

(Source: https://www.britannica.com/science/fiber-optics)

a. Core:

It is the central transmitting region of the fiber composed of silica or glass. The core diameter varies from 5 microns to 100 microns.

b. Cladding:

It is the first layer around the core that reflects the light back into the core. It is also composed of silica but the refractive index of the cladding is kept lower than that of core.

c. Coating:

It is the non-optical layer around the cladding which consist of one or more layers of polymer (plastic) that protects the internal cladding and core from external damage and moisture.

It is the optical fiber which allows the light to pass through the concrete and make it translucent so the concrete is sometimes called as fiber optic concrete. Optical Fibers of size 2 microns to 2 millimeters can be used in production of transparent concrete and the volume of optical fibers should be about 4 to 5% of total volume of concrete. The occupancy of the optical fibers make the transparent concrete comparatively lighter than the normal concrete.

4. Manufacturing Process:

The manufacture process of the transparent concrete is similar to that of the normal concrete but it should be kept in mind that the optical fibers can transmit light only if the both ends of fibers are open. If any end is covered in cement slurry, light will not be able to pass through the concrete violating the concrete purpose. So, special type of mould  should be prepared to place optical fibers properly inside the concrete.

4.1. Mould Preparation:

A rectangular mould of wood or steel is made and holes are driven at the sides to let the fibers pass through. Clay or mud can be applied at the inner side of mould for easy demoulding after the concrete is set.

(Source: https://benthamopen.com/FULLTEXT/TOCIEJ-11-615)

4.2. Placement of Fibers:

Optical fibers are cut so that it can be placed perfectly in the mould. They should be placed in such a way that they open out on both sides. The fibers are placed in layers and are allowed to pass through the holes driven in the moulds.

(Source: https://www.seminarsonly.com/Civil_Engineering/transparent-concrete.php)

4.3. Placement of Concrete:

Now, the well mixed concrete (cement, sand, aggregate, water) is poured slowly in the mould. Care should be taken that the fibers placed should not be disturbed. The concrete should be placed in thin layers, each layer is carefully vibrated with vibrating tables to prevent the accumulation of voids in the concrete.

4.4. Demoulding:

The concrete is taken out from the mould after 24 hours of casting. The clay or mud layer applied at the inner side earlier aids in easy removal of concrete from the mould.

4.5. Finishing:

As the fibers placed in the mould were little too long, they are now cut to same sizes as that of concrete block. The surface can be polished with the help of sand paper to get a clean, glossy finished block.

(Source: https://ifworlddesignguide.com/entry/37804-litracon)

5. Applications:

• It can be used to make interior walls or even exterior and load bearing walls as the compressive strength of the block is similar to that of normal concrete block.
• It can be used as energy saving component because of it’s light transmitting property.
• It can be used as a partition wall for the rooms which has very little access to natural light resulting in better illumination of the dark rooms.
• It can be used as pavement blocks or flooring. It gives shiny appearance during sunset but in day time it will look like a typical concrete pavement.
• It can be used to improve the architectural or aesthetic view of the building.
• It can also be used in highways for better visibility at night.

6. Advantages:

• Better aesthetic view
• Proper illumination
• Energy saving
• Light weight (which reduces dead load of the building)
• Environment friendly

7. Disadvantages:

• Expensive; as optical fibers are very costly
• Requires skilled person
• Cannot be used in columns and beams

8. Conclusion:

The important characteristics of transparent concrete like energy saving, aesthetic beauty, environment friendly, good compressive strength promote the usage of transparent concrete but at the same time the economy of the construction has to be taken care of. The optical fibers are very costly making the usage of transparent concrete expensive, ranging about 100 to 200 dollars per square feet. Using plastic fibers in concrete instead of the glass fibers can somewhat reduce the cost but will affect the extent of light transmission. Although it is not much adopted in Nepalese community, it is sure that the transparent concrete has a better future world wide.