Is it possible to combine the construction benefits of concrete with the desire to get more daylight into buildings? The answer is yes. An innovative building material with specially designed optical fibres has opened up completely new architectural possibilities.
Concrete, that traditionally solid, substantial building material, is getting a makeover. Engineers have now developed concrete mixtures that are capable of transmitting light. By switching the ingredients of traditional concrete with transparent ones, or embedding fiber optics, translucent concrete has become a reality. As with any new material, it is expensive and still has some issues to be resolved. However, this innovative new material, while still partially in the development stages, is beginning to be used in a variety of applications in architecture, and promises vast opportunities in the future.
Translucent concrete (also: light-transmitting concrete) is a concrete based building material with light-transmissive properties due to embedded light optical elements — usually optical fibres. Light is conducted through the stone from one end to the other. Therefore, the fibers have to go through the whole object. This results in a certain light pattern on the other surface, depending on the fiber structure. Shadows cast onto one side appear as silhouettes through the material.
When you think of concrete, most likely, your mind conjures up images of something solid, heavy, and monolithic. But what if concrete could be translucent, transmitting light into spaces, making them seem light and airy? Engineers today are challenging concrete to shed its opaque reputation to become both window and wall, simultaneously glowing, ethereal, and structural. Concrete has been called an “indispensable medium,” the “quintessential material” for architects and engineers, due to the vast “sculptural and expressive possibilities” that it can achieve. Now engineers are expanding those possibilities by modifying the basic ingredients of concrete to create translucent concrete. They are addressing the challenges and problems that occur in every new material, and some companies have started production. In the future, as translucent concrete becomes easier to manufacture and more available, engineers and architects will be able to utilize this amazing material in everything from furniture to entire buildings.
Engineers have come up with several potential types of mixtures for translucent concrete. One approach is to exchange the traditional ingredients with transparent or translucent alternatives. Pieces of plastic or glass can be used as aggregates, and the binding agent can be switched with a type of transparent glue. Will Wittig at the University of Detroit Mercy in Michigan combined white silica sand and white Portland cement, and by “varying the ratios”, developed a mix that could be cast much thinner than traditional concrete. His thin translucent concrete blocks were reinforced with “short strands of fiberglass” and were able to transmit a glow of light. A company in Italy has also created their own secret recipe, using a combination of transparent resins as the binding agent. Aggregates can be replaced with transparent alternatives, and the bonding material itself may be able to transmit light by incorporating clear resins in the mix.
Another approach is the “combination of optical fibers and fine concrete”; this formula, explored by the Hungarian Architect Aron Losoncze, uses very fine aggregate to encase optical fibers that allow light to transmit from one side of a block to the other. The process is slow and done by hand in a long, narrow mold; concrete and optical fibers are layered over each other creating a long beam that is cut into blocks . The blocks are able to retain their strength and bond because “the proportion of the fibers is very small (4%) compared to the total volume of the blocks”. They are not reinforced in the traditional sense, since the “optical glass fibres form a matrix” which creates an internal structure of reinforcement. This method of producing translucent concrete has been more fully explored and is more common.
Concrete mixtures must be just right in order to maintain structural strength. The same is true of translucent concrete. Some experimental translucent concrete mixes have failed to produce structural consistency. In Wittig’s case “lab tests showed that his panels were too fragile to withstand wind and rain”. New construction products must be extensively tested for strength. Traditional unreinforced concrete has a compressive strength of 1000-4000 psi, and a tensile strength of 0 psi; it is reinforced to gain tensile strength. Losoncze’s optical fiber concrete blocks claim a higher compressive strength of 7252 psi and a surprising tensile strength of 1015 psi even without steel reinforcing. His tests show that “glass fibers do not have a negative effect on the well-known high compressive strength value of concrete”. Fiber reinforcing can make translucent concrete even stronger than traditionally reinforced concrete. Engineers can also use chemical additives to significantly increase the strength of translucent concrete . It is possible to create load-bearing structures out of translucent concrete; however it would also be very expensive. It could be about five times as much to build using translucent concrete as opposed to the traditional type. This is due to the rarity of the product and its experimental nature. However, as engineers continue to experiment, the cost of production will decrease, along with with an increase in demand and more widespread usage.
Although translucent concrete has been used primarily as an interior decoration, its creators have “visions of cities that glow from within, and buildings whose windows need not be flat, rectangular panes, but can be arbitrary regions of transparency within flowing, curving walls”. It “can at the same time be building material and light source, can separate and connect, can be wall or floor, ambient lighting or eye-catcher” . Translucent concrete is also a great insulating material that protects against outdoor extreme temperatures while also letting in daylight. This makes it an excellent compromise for buildings in harsh climates, where it can shut out heat or cold without shutting the building off from daylight. It can be used to illuminate underground buildings and structures, such as subway stations. Translucent concrete could provide safety applications in the future such as speed bumps that could be lit “from below to make them more visible at night”, or to light indoor fire escapes in case of a power failure . It even has the potential to be sustainable; the aggregate can be replaced with crushed recycled glass . It could be used almost anywhere glass or traditional concrete are used. Translucent concrete combines the fluid potential of concrete with glass’ ability to admit light, and it also retains privacy and can be used as structural support. The possibilities for translucent concrete are innumerable; the more it is used, the more new uses will be discovered. In the next few years, as engineers further explore this exciting new material, it is sure to be employed in a variety of interesting ways that will change the opacity of architecture as we know it.
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