Andrea Martinez
Professor Cogdell / Design 40A
13 March 2014
Translucent Concrete: The Path to a Brighter Future (Materials)
Concrete jungles dominate today’s modern day architecture. Cities and skyscrapers have become mounds of thick gray structures. The notorious Bob Marley says in his song Concrete Jungle, “No sun will shine in my day today.” This predetermined idea that concrete is a dark and light-less structure has become a thought of the past. New technologies have come into play that have revolutionized the way the way we think of concrete. Using raw materials like rocks, pure elemental substances, and aggregates that are extracted from the earth’s crust, we are able to make secondary materials such as cement, and fiber optics. Using these processed materials we can make a concrete that defies the norms of traditional concrete by implementing light-transmitting properties, otherwise known as translucent concrete. All the materials that are used in the production of this product can be followed from the raw materials, to the manufacturing and processing, to the distribution and use of the material, however, the recycling and waste management process is contradictory development in the thought-to-be green design.
Translucent concrete is a new material that has evolved and become a leading material in today’s design world. The main materials used in the making of this new product are concrete and fiber optics. 1 This new design material is characterized as a cement-based building material that has light transmitting characteristics because of parallel layers of glass fiber optic cables that have been embedded into the stone. This material differs from other concrete building materials. Unlike normal concrete, translucent concrete uses the fiber optic technology to make the thick blocks seem thin, lightweight, and easily breakable. In addition, several other raw materials and secondary materials are involved in making this new and upcoming substance, each of which being a key element in the production. The list of materials goes much more in depth than just the two main materials of concrete and fiber optics. In order to make concrete one needs the ingredients to make Portland cement, aggregates such as crushed stone and gravel, and water. Fiber optics, the key material in the final product of translucent concrete, also requires its own chemical components. All of these ingredients, however, have their own separate processes, that help us achieve our end result.
Concrete has several raw materials that involve numerous steps of processing, mixing, and hardening. 2 These steps begin with the making of cement. Portland cement is the most popular cement used for architectural purposes, which is also used in the production of translucent concrete. This type of cement is manufactured through a closely controlled and measured chemical combination called the dry method. 3 The process begins with obtaining the necessary raw materials of cement: calcium, silicon, aluminum, iron, and aggregates that are commonly compounds from the main ingredients, like limestone, chalk, marl, clay, silica sand, iron ore, as well as other excavated aggregates like shale, slate, blast furnace slag, and shells. This long list of materials that are added into the making of cement have specific qualities that help in the maintenance and strength of the construction material. 4 Calcium is a soft alkaline earth metal and the 5th most abundant element in the world. It is so abundant because it is not found in its pure elemental state, but rather with other rocks and minerals. This element easily forms compounds with oxygen and water, producing materials like calcium carbonate and 5 calcium chloride. Calcium carbonate is one of the most popular calcium’s and comes in several forms like, chalk, limestone and marl, all being ingredients in cement. When a calcium element, like calcium chloride, is added to cement, it results in a faster cure rate, and faster cement hydration. This means that compared to normal cement that doesn’t have a calcium additive, it has high initial strength, reduced bleeding, and greater cost effectiveness. We can assume that these minerals are taken directly from the earths crust. 6 Like calcium, silicon is very common in the earths crust, and is almost never found in its pure elemental form. Silicate minerals (minerals that contain silicon, oxygen and reactive metals) account for 90% of the earths crust. Most of the silicon used is not separated from other materials, but used as a combination of other rocks and minerals containing silicon. Some of the most common combinations of silicone compounds are clay, and silica sand. This material is commonly used in structural uses because of its high level of strength. Aluminum is also a material used in cement that is a very abundant element in the earths crust. Like silicon and calcium, because of its high chemical reactivity, it is not normally found in its pure state, but as a combination with other minerals. Direct extraction of the ore is very difficult and dangerous because of the high reactivity. Since it is nearly almost always a combination of two or more minerals, the mechanical qualities, like strength, lightness, corrosion resistance, recyclability and formability are excellent. However, Iron, unlike the other elements in cement, can be found in its pure form. The low cost and high strength of iron makes it a popular ingredient in structural components for buildings. Nevertheless, it is not always found as pure iron, and can be found as iron ore. 7 The raw material aggregates necessary in the making of cement have small yet significant uses that cannot be omitted in the extraction of materials. Blast furnace slag, a common aggregate, is molten iron by-product that is extracted form a blast furnace. The resulting material is a glassy, fine powder. Because of its abundance and ease to make, it is a very affordable material that is actively used in the production of cement. This ingredient is used in cement to enhance the protection against chloride. Another common aggregate, shale, is a fine-grained sedimentary rock made of mud, clay minerals, and other small fragments of smaller minerals. This material is normally found near rivers or streams because of the natural formations. As a fast moving river settles, the minerals and rocks that was once floating, settles to the bottom. As time goes on, more and more minerals pile on to each other, compaction occurs, and shale is made. Along with shale metamorphic rock derived from shale called slate. This material is very common around the world. Because of its popularity, it is extracted from all parts of Europe, to the Americas and used in cement because of its durability. 8 An unusual aggregate used in cement are oyster shells. The shells are taken from the ocean, burned at a high temperature to decompose the calcium carbonate to calcium oxide and carbon dioxide. The resulting calcium carbonate is mixed in with the rest of the cement materials and used as filler. Once all the main components and raw materials are obtained, all the rocks and minerals go through two stages of crushing. Once the rocks are crushed to the desired size, they are mixed and fed into a cement kiln. A steel rotary machine is heated to about extreme temperatures, where the raw materials are heated by blasts of flames. During the heating process, several elements get heated to the point where they turn into gases and no longer become a part of the cement ingredients. The specifics as to what the gases are was unable to be found. The materials that remain after heating become a new substance: clinker. The clinkers comes out of the kiln as small grey balls and are cooled to handling temperature, which immediately hardens, is grinded to a powder, and mixed with other substances (usually limestone). After all these materials are mixed together, the Portland cement is ready to be used to make concrete 9 Along with cement, other ingredients like gravel and sand are instrumental in the making of strong and reliable concrete. Gravel can be characterized as numerous amounts of rock fragments. This component does not affect the tensile strength of concrete, but acts as a filler to take up much-needed space. The specifics as to what the ingredients are in gravel could not be found since there are countless types of rocks used. Another ingredient that is used in the making of concrete that is similar to gravel, are the sand aggregates. There is a specific mixture of sand used in concrete production called concrete sand. This aggregate is usually composed of either gneiss, trap rock, limestone or granite. All of these aggregates are naturally occurring stones or substances that are directly extracted from the earth through mining and excavation processes. After obtaining these raw materials, they are crushed through a quarry and washed through a screen to ensure that there are no outstandingly large pieces, and are added to the resulting sand. Once these rocks have been cleared, all the ingredients (cement, aggregates, and water) can be mixed to make concrete. The making of concrete is a very simple process. By simply mixing the appropriate amounts of cement, fine and course aggregates, and water, the concrete is ready for the fiber optics to be added, and molded.
Translucent concrete requires glass fiber optics in order to have the light-transmitting properties. 10 Fiber optics are long, thin strands of pure optical glass, which differs from windowpane glass. Optical glass has few impurities, giving it a better light transmitting properties. The process of making these fibers is not easy, however. The method begins by making a preform glass cylinder. The ingredients that are involved in making this pure glass form are mostly silicon tetrachloride and germanium tetrachloride. These ingredients are put through a process called modified chemical vapor deposition. Oxygen bubbles form through solutions of the numerous materials. Gas vapors are then brought into a synthetic silica or quartz tube and into a machine that specializes in turning at an even speed called lathe. As the lathe turns, a torch moves up and down the outside of the tube. The heat causes silicon dioxide and germanium dioxide byproducts to form. These byproducts deposit on the inside of the tube and fuse together to form glass. This continues until an even coating is made. This step of the process takes several hours. Once there is an even coating, one must draw the fibers from the preform. The ends of the fibers are loaded into a fiber-drawing tower. The glass blank is lowered into a furnace that is kept at high temperatures. With the extreme heat, the tips begin to melt. As the droplets fall, it cools and forms a thread. 11 The thread goes through a series of buffer coatings of polyvinylidene fluoride (PVDF), ploytetrafluoroethylene (PTFE), and polyurethane (PUR). PVDF is a plastic material that is used to increase purity, strength and resistance to solvents, acids, bases, and heat. PTFE is a synthetic fluoropolymer that is used as a nonstick coating and commonly seen in pipe work since it reduces friction and energy consumption, and PUR is an organic polymer that is used to enhance the appearance of a white light and prevents yellowing in the glass fibers. Once all these chemicals are applied they go through several UV light-curing ovens, and are finally put onto a spool. The final step in making optical fibers in testing the fibers. Tensile strength, fiber geometry, attenuation, ability to conduct light underwater, along with other properties are tested. If all of the tests are passed, the fibers can be used in other products.
Once the optical fibers are made, the production of translucent concrete can finally begin. With all the raw materials processed into secondary materials, the concrete and fiber optics are ready to be used to make the finishing product. Translucent concrete is normally made into small blocks that can be easily molded and handled for construction. To make these blocks, one needs a proper casting mold. 12 The most popular form of concrete casts is a urethane rubber mold. Using this material as the main ingredient for molds makes the casting process much easier. Urethane rubber molds are highly reusable, don’t shrink when heat is applied, and can be made into any shape or size. After obtaining the mold, a release agent must be applied in order to prevent the concrete from sticking to the rubber. The most commonly used release agent is a silicon based spray that acts as a lubricant. After thoroughly applying the release agent, small layers of concrete are poured into the mould. After each small layer of concrete a parallel layer of fiber optics are placed. This process is repeated at intervals, until the whole mold has been filled. Once the concrete has hardened, it can be removed from the mould, and finally be used as a building material.
Once the blocks of translucent concrete have been produced, transporting them becomes a necessary concern. All of the main production companies of translucent concrete are in Asia and Europe. 13 Since most of their selling market is in the United States, transporting the dried blocks from point A to point B becomes an area of worry. When researching the transportation process of concrete overseas, I was unable to find any viable information. Most concrete is made on site, or can be transported through large trucks, however translucent concrete cannot be moved in that manor. We can assume that these blocks are transported through a large container ship from Europe to the United States, and later loaded off the boat, onto a freight truck, and to the final construction site.
After finally receiving the necessary materials to make a translucent concrete structure, construction workers can begin to make the light-transmitting building. Establishing large structures with this new material has become an innovative and popular way of electricity use. The light transmitting properties of translucent concrete is a way for large buildings to have large amounts of natural light, with the aesthetic appeal of concrete buildings, while using less electricity to maintain the building lighted. However, the question gets brought up as to how efficient the building can be after the building needs to be replaced or remade.
After the translucent concrete has been used, how can the material be recycled to be reused? Since this is such a new product, there hasn’t been an attempt to recycle the material, so there is no information on the following. 14 There are ways to recycle concrete by crushing, cleaning, and remolding the remaining material, as well as ways of recycling optical fibers by melting down the remains, and rethreading the molten glass. However, there is no evidence that the two materials can be separated. There is no known chemical that can remove one from the other without it becoming a process of several years, which ultimately is not convenient or cost-effective. We can assume that until a new chemical is discovered to separate the two, translucent concrete is unable to be recycled.
Since this material is unable to be reused, waste management becomes a major concern. Instead of this product being used over and over, we assume that it will be thrown into a landfill, where it will take up large amounts of space. Seeing as this material is made of mostly glass and rocks, the translucent concrete is not biodegradable so it will never be broken down and be put back into the earth. If this new material becomes popular and replaces normal concrete in structural construction, then the amount of waste that will eventually be omitted will skyrocket. Translucent concrete is a new innovative design that implements fiber optics and concrete to produce a solid structure with light-transmitting qualities. This product requires several raw materials that are extracted from the earths crust, and are processed to make the main materials of translucent concrete- concrete and fiber optics. These materials are added at intervals to make the final product. Since this is such a new material, there is almost no information relating to transportation, management, recycling, or waste management. We can conclude that these materials cannot be separated for recycling purposes and will forever be left in landfills. The question arises now about how we can make this material even less of a environmental burden by finding a way to recycle the product. Once we find a solution to this growing problem, the marvelous new light-transmitting material can be appreciated in its full potential.
Bibiliography
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[1] For a general description of translucent concrete article from PCA: America’s Cement Manufacturerers, titled “Light-Transmitting Concrete.”
[2] For a detailed description of cement production, see the article titled “How Cement is Made,” from PCA: America’s Cement Manufacturers
[3] For details on materials of cement, see “Specifications, Properties, Classifications, and Classes,” from The A to Z of Materials
[4] For more information on calcium, see Gagnon.
[5] Detailed information on calcium chloride, see “Calcium Chloride Concrete,” from Morris Chemicals Inc.
[6] For more information on silicon, see Winter
[7] For details on aggregates of cement, see the article titled “Aggregates,” from the PCA: America’s Cement Manufacturers
[8] For more details on oyster aggregates, see Adams
[9] For details on the ingredients necessary to make concrete, see “How Concrete is Made,” by How Products Are Made
[10] Information on fiber optics, and their use can, and production, see “FOA Tech Topics,” from Guide to Fiber Optics & Premises Coating
[11] For detailed description of buffers used, see Schmid
[12] For information on concrete molds, see “Concrete Casting Essentials,” from Smooth-On
[13] For information on companies producing translucent concrete, see “LUCCON,” by Lichtbeton GmbH and “Light-Transmitting Concrete,” fom LiTraCon.
[14] For details on concrete and glass recycling, see “Markets for Recovered Glass,” by the US Environmental Protection Agency, and “How Concrete is Recycled,” by Concrete Recycling Home
Samantha Richards
13 March 2014
Design 40A
C. Cogdell
Translucent Concrete: Embodied Energy
Over 5,000 years ago, in the dawn of construction, the Egyptians were the first to put to use early forms of concrete to create the great Pyramids. The ancient Romans used a material remarkably close to modern cement to build many of their architectural marvels, such as the Coliseum and the Pantheon. Joseph Aspdin of England is credited with the invention of modern-day Portland cement- after which primeval methods of building became a thing of the past and concrete began to take new forms while taking over the world of construction. 1
When one thinks of concrete we envision dark aggressive blocks of cement, large methodical structures and the systematic creation of buildings in a town or city. Concrete has come to be seen as a timeless element of construction- structurally stable, indispensable, and encompassing a vast range of sculptural and expressive possibilities. Although an always-reliable material, concrete is beginning to take a new form. Engineers today are challenging concrete to shed its impervious reputation to become both window and wall, simultaneously glowing, ethereal, and structural. By simply expanding the base ingredients of concrete (Portland cement, sand and water), these engineers are entering an entirely new realm within the concept of basic concrete- translucent concrete. A relatively new product, translucent concrete is up and coming in challenging construction methods- soon entering the production of furniture and even entire buildings, the previous emission of harmful toxics and other atmospheric contaminants, and the future of construction as a whole.
The life cycle of translucent concrete is defined by the life cycle of fiber optics and basic concrete- its two main components. Throughout the life cycle and production process of translucent concrete, several different types of energies and fuels are taken advantage of and implemented- most of which are coal fuels and thermal, chemical, and kinetic energies. As the industry is developing more and more, cement industries are moving from a wet process to a dry process as it consumes and uses less chemical and thermal energy.
Translucent concrete is shattering previous notions of what the structural applications of concrete can include. This new-fangled product is a groundbreaking innovation- it intertwines fiber optics, forms of glass and cement to produce a light-transmitting material that seems thin and lightweight. Currently being applied in practical situations and sometimes failing in being structurally sound, this product is considerably still in the works of becoming successful. The fiber optic strands, which attract and transmit both natural and artificial light, make up about 5 percent of a translucent concrete block's surface volume. The fibers are mixed with traditional concrete components- water, sand and cement- and are distributed evenly throughout the surface. Through the resulting translucent panels, a viewer can clearly see the outline of an object on the opposite side of the concrete. Despite this clarity, however, translucent concrete retains basic concrete structure. 2
The first attempts at making translucent concrete began with individually placing fiber filaments in the concrete, making production time costly and time consuming. Relentlessly using only a wet process that took hours and hours of tedious chemical construction, fiber optics within cement seemed to be an impractical solution for essentially “creating light”. To break down translucent concrete and the energy used and conserve during the creation process we must look at cement and fiber optics individually.
The production process of cement comes in nine steps: quarrying of limestone or shale, dredging the ocean floor for shells, digging for clay and marl, grinding, blending of components, fine grinding, burning, finish grinding and finally packaging and shipping. Quarrying of limestone and shale is accomplished by using explosives (thermal and kinetic energy) to blast the rocks from the ground. After blasting, huge power shovels are used to load dump trucks or small railroad cars for transportation to the cement plant, which is usually nearby. This is done by one example of a prime mover, humans. The ocean floor is then dredged to obtain the shells, while clay and marl are dug out of the ground with power shovels (secondary prime mover) and also by prime movers (humans). All of the raw materials are transported to the plant. After the raw materials have been transported to the plant, the limestone and shale that have been blasted out of the quarry must be crushed into smaller pieces. The pieces are then dumped into primary crushers, which reduce them to the size of a softball. The pieces are carried by conveyors (prime movers) to secondary crushers (thermal and kinetic energy), which crush the rocks into fragments usually no larger than 3/4 inch across. After the rock is crushed, plant chemists analyze the rock and raw materials to determine their mineral content. The chemists also determine the proportions of each raw material to utilize in order to obtain a uniform cement product. The various raw materials are then mixed in proper proportions and prepared for fine grinding (by prime mover- humans).
When the raw materials have been blended, they must be ground into a fine powder. This may be done by one of two methods: Wet process or Dry process- both done by humans as prime movers. Nowadays, there has been a great shift from the wet to dry process as it uses less chemical and thermal energy. The wet process of fine grinding is the older process, having been used in Europe prior to the manufacturing of cement in the United States. This process is used more often when clay and marl, which are very moist, are included in the composition of the cement. In the wet process, the blended raw materials are moved into ball or tube mills, which are cylindrical rotating drums, which contain steel balls. These steel balls grind the raw materials (thermal and kinetic energy- secondary prime movers) into smaller fragments of up to 200 of an inch. As the grinding is done, water is added until a slurry (thin mud) forms, and the slurry is stored in open tanks where additional mixing is done. Some of the water may be removed from the slurry before it is burned, or the slurry may be sent to the kiln as is and the water evaporated during the burning. The dry process of fine grinding is accomplished with a similar set of ball or tube mills; however, water is not added during the grinding. The dry materials are stored in silos where additional mixing and blending may be done. Burning the blended materials is the key in the process of making cement (thermal energy- done by secondary prime mover of kiln). The wet or- more commonly used now-dry mix is fed into the kiln, which is one of the largest pieces of moving machinery in the industry. It is generally twelve feet or more in diameter and 500 feet or more in length, made of steel and lined with firebrick. It revolves on large roller bearings and is gradually slanted with the intake end higher than the output end. As the kiln revolves, the materials roll and slide downward for approximately four hours. In the burning zone, where the heat can reach 3,000 degrees Fahrenheit, the materials become incandescent and change in color from purple to violet to orange. Here, the gases are driven from the raw materials, which actually change the properties of the raw materials. What emerges is “clinker” which is round, marble-sized, glass-hard balls which are harder than the quarried rock. The clinker is then fed into a cooler where it is cooled for storage.
The cooled clinker is mixed with a small amount of gypsum, which will help regulate the setting time when the cement is mixed with other materials and becomes concrete. Here again there are primary and secondary grinders. The primary grinders leave the clinker, ground to the fineness of sand, and the secondary grinders leave the clinker ground to the fineness of flour, which is the final product ready for marketing. The final product is shipped either in bulk (ships, barges, tanker trucks, railroad cars, etc.) or in strong paper bags, which are filled by machine (Secondary Prime Movers- kinetic energy, fossil fuels). In the United States, one bag of Portland cement contains 94 pounds of cement, and a “barrel” weighs four times that amount, or 376 pounds. 3
Being an energy intensive industry, the cement industry segment typically accounts for 50–60% of the total production costs of cement or concrete based products. Thermal energy accounts for about 20–25% of the cement production cost. The typical electrical energy consumption of a modern cement plant is about 110–120kWh per ton of cement. Mainly, thermal energy is used during the burning process, while electrical energy is used for cement grinding. Table 1 on the last page shows electrical and thermal energy flow in a cement manufacturing process.
Thus concludes the production and energy usage of the production of cement. After this cement is created we have to also consider the production and energy use of fiber optics to create our translucent concrete.
Fiber Optic lines are strands of optically pure glass as thin as a human hair. A single optical fiber has three base components: core, cladding and buffer coating. Fiber Optical glass is comprised of Silicon Chloride, Germanium Chloride and Oxygen. The main reasoning behind using fiber optics in translucent cement is its ability to attract and emit all forms of light. The light in a fiber optic cable travels through the core by constantly bouncing from the cladding, a principle called total internal reflection. There are two main steps in the process of transforming raw materials into optical fiber ready to be shipped- manufacturing of the pure glass preform and drawing of the preform. The first step in manufacturing glass optical fibers is to make a solid glass rod, known as a preform (Chemical Energy- secondary prime mover). Ultra-pure chemicals- primarily silicon tetrachloride (SiCl4) and germanium tetrachloride (GeCl4)- are converted into glass during preform manufacturing. These chemicals are used in varying proportions to fabricate the core regions for the different types of preforms. The basic chemical reaction of manufacturing optical glass is:
SiCl4 (gas) + O2 > SiO2 (solid) + 2Cl2 (in the presence of heat)
GeCl4 (gas) + O2 > GeO2 (solid) + 2Cl2 (in the presence of heat)
The core composition of all standard communication fibers consists primarily of silica, with varying amounts of Germania added to increase the fiber's refractive index to the desired level. The core composition and the refractive index of graded-index multimode fibers changes across the core of the fiber to give the refractive index a parabolic shape- creating the reflective properties of translucent cement. There are several methods to manufacturing preform. In the Modified Chemical Vapor Deposition (MCVD) process, the highly controlled mixture of chemicals described above is passed through the inside of a rotating glass tube made of pure synthetic SiO2. The next step in the process of producing optical fibers is to convert the manufactured preform into a hair-thin fiber. This is done in an operation called fiber draw (Secondary Energy- chemical and kinetic energy). The tip of the preform is lowered into a high-purity graphite furnace. Pure gasses are injected into the furnace to provide a clean and conductive atmosphere. In the furnace, tightly controlled temperatures approaching 1900°C soften the tip of the preform. Once the softening point of the preform tip is reached, gravity takes over and allows a molten gob to "free fall" until it has been stretched into a thin strand. Clearly the process of producing and manufacturing fiber optics uses a high amount of chemical and thermal energies. 4
Several companies have already safely and effectively utilized waste materials to supplement coal as a fuel for the cement manufacturing process. The alternative fuels (waste material) are a safe and effective energy source, while providing the needed energy to produce a quality cement product. 5 Industry and EPA sponsored combustion performance testing nearly always supports a conclusion attesting to the effective handling of hazardous wastes by cement kiln. The natural time, temperature, and turbulent environment in a kiln's combustion chamber is ideal for destruction of organic components. Inorganic components are bound up in the structure of the product coming out of a kiln. Most plants already have massive particulate scrubbing as a part of Clean Air Act emissions compliance.
After the production of cement and fiber optics as separate entities, thus begins the production of translucent concrete itself. The manufacturing and production of this material is almost identical to that of cement. Small layers of the cement described previously are poured into a mold and on top of each layer lays a layer of fiber optics. The casted material is cut into panels or blocks of the specified thickness and the surface is then typically polished. The blocks are then transported by train, ship or truck (using fossil fuels) to the few companies who are in the industry of translucent concrete.
As I have covered, the energy used and established while manufacturing translucent concrete lies in the formation of concrete and fiber optics. Chemical, thermal, and kinetic energies are all key components of the production processes as well as coal and fossil fuels and the entire base natural materials found in cement and fiber optics. As the industry is developing more and more, cement industries are moving from a wet process to a dry process as it consumes and uses less chemical, thermal and kinetic energy. As translucent concrete becomes more prominent, companies will begin to use it for practical purposes such as increasing visibility in dark subway stations- there are also several potential safety applications being discussed, such as lighting indoor fire escapes in the event of a power failure or illuminating speed bumps on roadways at night. Surely, as more people see its potential, light-transmitting concrete will become more and more visible especially when they find out exactly how much energy can be saved by the utilization of this product. 6
Diagrams and Pictures
Image: transluent concrete in use
Table 1
Global cement production statistics for the year 2005
Sectors Production (MT/yr) Share (%)
China 1064 46.60
India 130 5.70
United states 99 4.30
Japan 66 2.90
Korea 50 2.20
Spain 48 2.10
Russia 45 2.00
Thailand 40 1.80
Brazil 39 1.70
Italy 38 1.70
Turkey 38 1.70
Indonesia 37 1.60
Mexico 36 1.60
Germany 32 1.40
Iran 32 1.40
Egypt 27 1.20
Vietnam 27 1.20
Saudi Arabia 24 1.10
France 20 0.90
Other 392 17.20
World 2284 100
Image: Multimode is commonly used for Translucent Concrete
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Sue Bin Lee
DES40A
Christina Cogdell
13 March 2014
Waste and Emissions of Translucent Cement
Abstract
Cement manufacturing requires very large amounts of energy and cement manufacturers have used a variety of fuel inputs. Among the most common types of fuels are fuel oils, coal, petroleum coke and natural gas. In addition certain hazardous wastes such as used lubricants and contaminated soils have been burned as fuel in the rotary kilns as part of the cement production. These decisions in turn have environmental consequences in terms of the emissions of toxics and other atmospheric contaminants, global greenhouse gases and the generation of large quantities of cement kiln waste.
Introduction
Translucent concrete also called light-transmitting concrete is a new façade material used in fine architecture that has light-transmissive properties due to embedded light optical element called optical fibers. Translucent concrete isn't exactly "see-through," but the new building material draws on optical fibers to transmit light through it while retaining the density that has literally made concrete the cornerstone of buildings all around the world. It has been applied to various design products where its component is separated into two parts; the usual fine grain concrete which makes up 95% and 5% fiber optics which is added during the casting process. Through the resulting translucent panels, a viewer can clearly see the outline of an object on the opposite side of the concrete (Translucent Concrete: Wikipedia). Despite this clarity, however, translucent concrete retains its stout, crack resistant, load-bearing quality. Due to its efficiency, beauty, and popularity, and since the development of fiber optics, the rate of usage and development in translucent cement has drastically increased within the past decades. At the same time, waste and emission from manufacturing this popular material also increased because cement that makes up the majority of the component has been prominently known to stir up waste and emission outputs. The waste and emission of translucent concrete has to be evaluated separately into two parts: concrete and optical fibers, because it is just a product of the two materials combined together and there’s yet to be a concrete information to look at the outputs that come out of the translucent concrete as a whole (Translucent Concrete: Wikipedia).
Production
Cement is used globally to build buildings, bridges, roads, runways, sidewalks, and dams because of its beauty, strength and durability, among other benefits. It produces a material so ubiquitous it is nearly invisible. The prominent material is indispensable for construction activity, so it is tightly linked to the global economy. On average, each year, three tons of concrete are consumed by every person on the planet. In an era of increased attention on the environmental impact of construction, concrete performs well when compared to other building materials. Cement production is growing by 2.5% annually, and is expected to rise from 2.55 billion tons in 2006 to 3.7-4.4 billion tons by 2050. Close to 5.5 million BTU of energy is consumed for every ton production of cement (Cement and Concrete Specifications 4). As with any building product, production of concrete and its ingredients does require energy that in turn results in the generation of carbon dioxide, or CO2 (EPA: Concrete).
Cement creates up to 5% of worldwide man-made emissions of carbon dioxide which 50% is from the chemical process and 40% from burning of fuel in the kiln. In general, carbon dioxide it is exhaled by humans and animals and utilized by plants during photosynthesis. However, it is also emitted from concrete because the whole manufacturing process is highly energy and emissions intensive because of the extreme heat required to produce it (EPA: Research and Development Information). For example, the primary component of cement is limestone. To produce cement, limestone and other clay-like materials are heated in a kiln at 1400°C and then ground to form a lumpy, solid substance called clinker; clinker is then combined with gypsum to form cement under extremely high heat. Producing a ton of cement requires 4.7 million BTU of energy, equivalent to about 400 pounds of coal; and as a result, producing a ton of cement generates nearly a ton of CO2 (Cement and Concrete Specifications 5).
Additionally, carbon dioxide is created by the combustion of fossil fuels or plant matter, among chemical processes to mix materials in cement. Carbon dioxide is one of several greenhouse gases that can cause global warming by trapping the Sun’s radiant energy in our atmosphere. This process is called the greenhouse effect. Greenhouse gases can either be released by natural events such as volcanic eruptions, human activity, or production process such as burning fossil fuels to manufacture products such as cement. So manufacturing of cement contributes greenhouse gases both directly through the use of energy such as combustion of fossil fuels and the production of carbon dioxide when calcium carbonate is thermally decomposed, producing lime and carbon dioxide. The carbon dioxide produced for the manufacture of one ton of structural concrete uses around “14% cement estimated at 410 kg/m3 which are about 180 kg/ton at a density of 2.3 g/cm3” (EPA: Research and Development Information). Nonetheless, emission factors widely used would suggest that the shift from fuel oils to petroleum coke has probably increased greenhouse gas emissions in the sector over the period (Gossman 2). The CO2 emission from the concrete production is directly proportional to the cement content used in the concrete mix and 900 kg of CO2 are emitted for the fabrication of every ton of cement (Schneider). Given its high emissions and critical importance to society, cement is an obvious place to look to reduce greenhouse gas emissions.
Going more in depth, one specific and prominent type of cement that was found to be the primary source of CO2 emissions generated by typical commercially produced concrete mixes was the Portland cement (EPA: Research and Development Information). For the most part, emission of CO2 is generated from two different sources. The first is usage of fossil fuels in the burning process and the other is calcinations, when calcium carbonate is heated and broken down to calcium oxide with the release of CO2. Between 900kg and 1100 kg of CO2 is emitted for every 1000 kg of Portland cement produced in the U.S. Portland cement is responsible for 74% to 81% of total CO2 emissions in cement production. The next major source of CO2 emissions in concrete was found to be coarse aggregates, being responsible for 13% to 20% of total CO2 emissions (Schneider). The majority contribution of CO2 emissions in coarse aggregates production was found to create electricity, typically about 80%. Blasting, excavation, hauling and transport comprise less than 25%. While the explosives had very high emission factors per unit mass, they contributed very small amounts to coarse aggregate production, since only small quantities are used. Production of fine aggregates was found to generate almost half of the emissions generated by the production of coarse aggregates (Luna, Pietro, Wyrzykowski, Tang, and Lehmann 5). On the other hand, fine aggregates generate less equivalent CO2 since they are only graded, not crushed which uses less fuel and energy resulting in less output. Additionally, diesel and electricity, which are used during the kiln process to make cement, were found to contribute almost equally amount of CO2 emissions because it utilized fine aggregates production (Rubenstein 2). Emission contributions due to admixtures such as the aggregates were found to be negligible. Lastly, concrete batching, transport and placement activities were all found to contribute very small amounts of CO2 to total concrete emissions (Luna, Pietro, Wyrzykowski, Tang, and Lehmann 5).
Additive
Fiber optics may have the biggest impact in making concrete light permissible but it makes up only a little portion in the material aspect; hence, there are not a lot of waste and emission outputs that come out of it. However, the transparent fiber made of high quality extruded glass (also called silica) or plastic can leave behind solid wastes when it is not recycled. Fiber optics itself can be recycled and reused however, when it’s mixed together with cement to create translucent concrete, it is impossible to be managed efficiently. The optical cables maybe thin as a hair strand so one might assume that it won’t have much waste impact, but the components, extruded glass and plastic, that make up the illumination wire have its own separate wastes and emissions when it’s combined together to make up the actual translucent concrete (Optical Fiber 8) .
Component
Each year about 12.5 million tons of waste glass is generated in the U.S., 77% of which is disposed of in landfills, accounting for 6% of the total municipal solid waste stream. Globally, about 5% of the 2.02 billion tons/yr of municipal solid waste generated is glass. Disposal of waste glass in landfills is costly, considering increasing tipping fees; the non-biodegradable nature of glass further complicates the environmental impact of its disposable landfills. Glass, which is rich in amorphous silica, has the proper chemistry and reactivity to have a pozzolanic reactions with the lime released during hydration of cement and this creates the reactive nature of glass in concrete. According to Field Investigation of Concrete Incorporating Milled Waste Glass, “recycling of each ton of glass saves over one ton of natural resources, and recycling of every six tons of container glass results in the reduction of one ton of carbon dioxide emission” (Ud-Din Nassar, Roz, and Parviz Soroushian).”
Aside from silica, plastic make up the other component in optical fibers. Plastic itself can be recycled to reduce any waste output, emission, or other harmful effects, however, when it is mechanically combined with silica to function as a illuminator within the fiber optics, it is naturally made into a non-recyclable plastic. Hazardous compounds and wastes emitted during the plastic melting process were proven as potential air pollution issues. According to Energy and Environmental Sciences, these hazardous compounds might be not only from polymer degradation in the plastic but also from additives and print ink. Additionally, plastic can amount to 50% of the carbon content in the waste” (Frequently Asked Questions 3). Lastly, in situations where plastics are incinerated with high efficiency and high electricity to heat the kiln, and the heat and the electricity from incineration of plastics replaces the heat and electricity in non-combined heat and power plants based on fossil fuels; hence, incineration of plastics can give a net negative contribution of greenhouse gases (Frequently Asked Questions 5).
Conclusion
For a long period of time, concrete recycling has been a talk of the century and is already in an advanced state. Separating concrete from reinforcement is common practice in order to recycle the material, however, it has not yet been proven if translucent concrete can yet be recycled or not due to unknown solution to separate the concrete from the glass and plastic in fiber optics in order for it to be reusable, recyclable, and completely sustainable. And because translucent concrete is non-recyclable, the use of alternative fuels and raw materials for translucent and regular cement production could certainly be of high importance for the cement manufacturer but also for society as a whole. Currently, waste-derived fuels found in translucent concrete consist of shredded paper, plastics, foils, textiles and rubber and also contain metal or mineral impurities. Alternative fuels are mainly used tires, animal residues, sewage sludges, waste oil and lumpy materials. The last are solid recovered fuels retrieved from industry waste streams. Conservation of wastes and other environmental releases can be lessened significantly if indirect emissions from burning fossil fuels to heat the kiln can be reduced by switching to alternative fuels such as natural gas, biomass and waste-derived fuels. These less carbon-intensive fuels could reduce overall cement emissions by 18-24%. Alternatively, efficiency measures of wastes and emission can reduce the demand for fuel by addressing the production process itself such as switching from inefficient wet kilns to dry ones or through technical and mechanical improvements like preventative maintenance and advanced technology to repair kiln leaks (Environmental Impact of Concrete 2).
Remarks
Throughout this project, the most difficult part of my research was finding specifics on wastes and emissions of translucent cement. I was unable to find as many sources for it as I would have liked for waterborne and airborne wastes. Translucent concrete is still a novice engineering material that’s less than a hundred years old so it is still in the process of being explored. Hence, there were not many credible sources that shared any logical knowledge regarding waste and emission outputs of the new material. Furthermore, because the material was so young, and concrete has a long life time, there was no proof or knowledge regarding other environmental releases and the exact answer to the ending of the material’s life cycle.
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