Design Life-Cycle

 Life Cycle Analysis — Terra Cotta Roof Tile

MATERIALS — Alexander Reymont

Terracotta roofing is a very popular style of roofing here in California. I myself live in the car-dependent suburbs of Sacramento. In a manner of speaking, I live in a maze of cookie-cutter housing developments and beige shopping centers that—mostly—look alike. In conducting research on the materials in terracotta roofing tiles, I took a general sight survey of the styles of roofing common in my area and found that about 65% of the homes within my neighborhood donned what I would call a terra cotta style roof. To my surprise, many of these roofs were likely composed of concrete that was made to resemble terra cotta tiles. This is interesting because cement carries with it a substantial embodied energy footprint as “large amounts of CO2 are released in the calcination stage, where limestone is transformed into calcium oxide.” [1] Before conducting research I assumed that tile would be one of the most sustainable options for roofing in terms of material because it seems the most natural among common roofing options. Dug up clay from the earth that was fired in an oven and put on a building — doesn’t get much simpler than that, right? Well, it turns out the process is much more involved than what I initially thought, and my preliminary findings led me to two  probes of interest that guided my further research. 

(1) I feel that consumers of the cement “mock terracotta” products should be informed of the true material and may reference this collection of research in tandem with other academic surveys when determining sustainability of building materials within their own projects.

(2) Because terra cotta is marketed as a naturally derived product, consumers may be quick to assume that terra cotta is sustainable without understanding the total carbon cost of the industrial processes behind it. 

Thesis

This analysis defines each stage of the life cycle of terra cotta roofing tiles. Detailing the material aspects present in the extraction of raw materials from repositories, their following sorting and refinement, chemical and thermal processing, real-world application and use, and recycling and waste management. A better understanding of the complex life cycle of this product is integral in helping designers, architects, and consumers contextualize the environmental impacts of using this common construction material.

Primary Source: General Overview of Clay

I was surprised to find that approximately 80% of the Earth’s land surface contains some form of clay. [2]  It is  literally everywhere and it comes in many different formulas dependent upon the local geology. Generally speaking the formula for clay is Al2O3 2SiO2 2H2O, an alumina-silicate. [3] These alumina-silicates are derived from decomposed rock that consists of very small flat particles smaller than two micrometers (7.9x10-5inch) and water. [4] This combination of microscopic plates with the ionic nature of water affords the material body something called plasticity. Plasticity is the ease in which the particles bend together without breaking — much like the stretch you feel in kneading and pulling raw dough. Some other key properties of clay include porosity, and the ability to vitrify. We can further categorize clay bodies beyond their general properties by identifying material distinctions and more specific clay characteristics post-firing. 

Mineral Distinctions

Minerals present in the clay body are groups of crystalline minerals (silica, alumina, magnesia, water, iron, aluminum, magnesium, potassium, sodium, and calcium. [5]  Clay can be categorized into nine distinct groups based on variations in their chemical composition and atomic structure. [6] These are listed bellow. See Fig. 02 in the appendix for additional example.

1. Kaolin-serpentine (kaolinite, halloysite, lizardite, chrysotile)

2. Pyrophyllite-talc

3. Mica (illite, glauconite, celadonite)

4. Vermiculite

5. Smectite (montmorillonite, nontronite, saponite)

6. Chlorite (sudoite, clinochlore, chamosite)

7. Sepiolite-palygorskite

8. Iterstratified clay minerals (e.g. rectorite, corrensite, tosudite)

9. Allophane-imogolite

It is important to understand that each of these types of clay in natural environments have their own characteristics and on a small scale are primary sources of material, but industrial processing of clay on a large scale like in the tile industry is formulaic. The broad scope of the mining/mineral industry has led to an ability to concoct your own clay formulas that will produce an ideal product. Each ingredient in the clay will bear an impact on the final product. For example, clay bodies that have a high kaolin ratio, like porcelain, are fired at a higher temperature and become vitreous when fired to certain degrees. These clay bodies act completely differently compared to an earthenware clay like terra cotta. Earthenware clays are often high in iron, fired to a lower degree, and are characteristically non-vitreous. The ability to extract specific minerals from around the globe and perfect clay mixtures for industrial purposes has led to many companies adding materials to enhance their clay. 

Primary Source

In general, clay deposits are formed by some action of weathering and you will most likely find large deposits in places eroded by moving water like river banks, stream beds, canyons, and gullies. [7] They are also found in repositories caused by glaciers. [8] For example, the large clay deposit at Sheffield Pottery in Massachusetts, was formed when silt was deposited and settled underneath a glacial lake. Once the Laurentide Ice Sheet receded it left all of that clay behind for them to extract. [9] 

Raw Material Acquisition/Extraction

Clay must be extracted from the earth and refined before it can be used in manufacturing. Depending upon the deposit location and environment it may be extracted in either a wet or dry state. The simplest—or most natural—extraction cycle of raw clay can be broken down into three parts; extraction, filtration, and reconstitution. Extraction of the raw clay is the unearthing or digging-up the material from a repository. Filtration is achieved by use of a sieve or screen to remove any unwanted material like rocks, organic material, and debris. This simple filtration is often done in one of two ways. Either wet clay is dried, pulverized, then sieved, or wet clay is dried, slaked down in water, and then sieved. [10] Reconstitution brings the clay back to a moldable state. Key factors in this stage are water content and air content within the clay body. In many cases a pug mill is used to compact the clay and remove air bubbles, leaving a purified and consistent product. This is clay extraction at its most basic, larger-scale operations are more complex and include more refining of the materials. 

Sheffield Pottery is one material extraction operation that has perfected their own technique in milling and refining their clay products. For this research they stand as a case study for similar larger-scale clay extraction operations. Their process begins with the unearthing of wet clay. It is dried and left for a year to freeze and thaw, this maturation period ensures that the final product will be more plastic. It is then crushed by a hammer mill to a fine powder and sieved to further remove impurities. Their clay powder is used as a base for many formulas of clay that they produce, so they must sort out and filter all of the organic compounds within the raw clay. The clay base at Sheffield is a pure clay whose processing requires extensive filtration such as material separation and magnetic iron filtration. If large amounts of iron were present in the clay body it would result in blooms of red spots after the firing process. Once they have a pure clay powder, it is time to blend in additives. Using an advanced batching system they blend materials that are sourced from hundreds of repositories from around the world. [11] This could be additives like Bentonite, a material formed by the decomposition of volcanic ash that acts as a plasticizer. [12] In many cases, the raw clay must be mixed with other compounds or clays in order to maintain the required performance of the product. Their system is accurate to 0.5 grams per ton of dry materials, ensuring the consistency of the clay body. The powdered clay mixture, after being carefully weighed out, then moves on to the screening process that ensures no particles are larger than 50-mesh, on average, and even up to 100-mesh in fineness. [13] After these processes the dry clay can be mixed with water in the plant or sold in bulk as a base material. To produce the wet clay body, water is incorporated into the dry mixture in an industrial mixer. The clay is then fed through a pug mill. This is the stage where the clay gets compacted by pressure, forcing air bubbles out of the material. [14] Once this is done the clay is ready to be used as a secondary material in product manufacturing.

Processing

Terra cotta roofing tiles can be produced in a similar fashion to how they were manufactured thousands of years ago, and some companies do sell tiles that fit that description, but they are few and far between. Realistically, terra cotta style roofing that is produced by the tile roofing industry exceeds this description. After all, the construction industry exists in a commercial environment where materials are constantly being sourced, used, and reused. Companies in construction must also abide by certain sustainability goals, and many strive for LEED certification. This affects the materials they choose in manufacturing their products, and many opt for using recycled materials as additives. Kayla Kratz, the product manager for Boral Roofing LLC projects how much recyclable materials the tile roofing industry uses on average to attain LEED certification.

“Sustainability in tile-making begins with the first phase of the tile’s lifecycle—the raw materials. Clay tile is made of naturally occurring geologic materials, such as clay and water. Some tile-makers use a high percentage of recycled material, or the by-products of mining processes. Utilizing this post-industrial waste clay repurposes the raw material for use in new clay tile. Tile may be up to 60 percent post-industrial recycled, and may help contribute to Leadership in Energy and Environmental Design (LEED) points for recycled content in the Materials and Resources (MR) category.” [15]

Some of the materials companies incorporate into the manufacture of ceramic tiles are sludge from wastewater treatment, glazing sludge and waste frit, spent lime, cement kiln dust, Ca-based reaction wastes from TiO2 production, mixtures of concrete, broken bricks, tiles, red mud from bauxite processing, coal fly ash, even sugarcane and coffee bagasse ash. [16] These waste materials may be pulverized and added to the clay body before being molded into the tile form and then fired. These additives may be incorporated as a filler to save on clay resources, and also as a way of encapsulating the waste. [17]

Manufacturing Process

In order to bring out the desired properties of the clay (strength, hardness, porosity, etc.) it must be chemically processed in a high temperature oven called a kiln. The immense heat energy transforms this moldable putty-like substance into the hard, rock-like tile we want. Chemically speaking, there are a number of distinct and integral  stages that the clay body goes through before becoming solid.

After being molded into the desired shape the first order of business is evaporation of the water that is within the clay body. Typically this is a slow process where large groups of H2O molecules leave the clay and enter the atmosphere, leaving the clay bone dry. It is at this point where the clay may be introduced to heat. The tiles are put into a kiln that fires them to a temperature between △06 (1828ºF) — △04 (1945ºF). [18] Terra cotta is an earthenware clay that fires at a relatively low temperature when comparing it to stoneware which fires between △6 (2232ºF) and △10 (2345ºF), and porcelain which fires up to △14 (2489ºF). [19]

Once in the kiln, the clay body will go through each of these 6 stages.

For reference see Orton Cone Chart (Fig. 01) in the appendix.

(1) Burn-Off of Carbon and Sulfur

“All clay bodies contain some measure of carbon, organic materials, and sulfur. These burn off between 572ºF and 1470ºF … If for some reason—such as poor ventilation within the kiln—these are not able to burn out of the clay body, carbon coring will occur. This will considerably weaken the clay body.” [20]

(2) Chemically Combined Water Escapes

“Clay can be characterized as being one molecule of alumina and two molecules of silica bonded with two molecules of water. Even after the atmospheric water is gone, the clay still contains some 14 percent of chemically bonded water by weight…The chemically bonded water escapes from the clay body between 660ºF and 1470ºF”. [21] There must be a slow build up of heat to avoid sudden release of steam which can cause an explosion of the clay body.

(3) Quartz Inversion 

Silica oxide (also known as quartz) “has a crystalline structure that changes at specific temperatures…one such inversion occurs at 1060 F (573 C).” [22]

(4) Sintering 

“Beginning at about 1650 F (900 C), the clay particles begin to fuse. This cementing process is called sintering.” [23] This is moment when the clay has transformed from clay to ceramic. This is often considered the point where the material can no longer be broken down into its original parts, i.e. fired clay cannot be pulverized and re-used.

(5) Vitrification and Maturity 

Vitrification: “a gradual process during which the materials that melt most easily do so. They dissolve and fill in the spaces between the more refractory particles.” [24] For terra cotta roof tiles, and similar earthenware clays, the large amounts of iron particles will melt. 

(6) Cooling 

“the sudden shrinkage of cristobalite—a crystalline form of silica—as it cools past 420ºF…Cristobalite is found in all clay bodies, so care must be taken to cool the kiln slowly as it moves through this critical temperature.” [25] If the clay body cools too quickly this will result in fractures or cracks.

Sintering is a key aspect in this process, and scientists have found a way to alter the chemical properties of the clay by adding fluxes. Incorporating fluxes like nepheline syenite causes the sintering stage to occur between 1000ºF and 1050ºF, and when cooled act as a filler. [26] This aids in conserving expendable materials like fuel by shortening the firing time, and effectively allowing manufacturers to turn the heat down. 

Finished Product

Once the product has been manufactured there are not many conventional materials involved beyond packaging for shipment that I have considered. Shipping insulation and packing materials will vary depending on the company that manufactures the tile and how far it must travel. Materials may include corrugated cardboard, stretch film plastic used to contain the product on a pallet, [27] wooden pallets, polypropylene or polyester strapping, and filler material. While I did not find any information on specific roof tile companies’ shipping practices, Heath, a ceramic studio based in San Fransisco, uses an eco-conscious solution called Expandos. Expandos are triangle-shaped packing filler that are made from post-consumer chipboard. [28] This replaced their use of styrofoam packaging entirely and the company has been using the filler since the early 2000s.

I do have some considerations that I’d like to mention about materials beyond the tile that are required for installation. Terra cotta roofing is fairly heavy in comparison to other roofing alternatives like asphalt, metal, and flat PVC roofs. With this in mind, the supporting structures must be strong enough to bear that weight. Often, a heavier roof means using more materials in the supporting framework of the entire building. This may inevitably require the architect to design the building with more timber, concrete, steel, or other building materials. In addition to an increase in these materials, there are materials required for proper installation. In order to install this type of roofing, roofers will place a sheet of weatherproof sealant, often in the form of a rolled plastic, or peel-and-stick panels, on a plywood base. [29] The roof tiles are then placed over this sheet and secured with nails. Materials beyond this may include wooden frames or supports between the tiles and additional weatherproofing. 

End-Of-Life/Recycling:

Terra cotta roofing, when properly maintained, can last for over 100 years. Despite their longevity, they do meet their end in some capacity, whether they be refurbished tiles that are used in other building projects, or recycled as a crushed aggregate. 

When refurbished, terra cotta roof tiles are removed from the original site, cleaned and sorted, and then put to use in other construction projects. When recycled as a crushed aggregate, the ceramic waste will be incorporated into mixtures of asphalt, concrete, and brick. [30] The inclusion of recycled clay can help strengthen these products or act as a type of filler. Additionally, ceramic aggregates have been used as electrical insulators because of their liquid absorption capabilities. [31]

Let’s talk about grog. “Grog is a term used in ceramics to describe crushed brick (or other fired ceramic) aggregate that is added to sculpture and structural clays to improve drying properties”. [32] Terra cotta roof tiles can be recycled in this way so long as the materials used in its fabrication are pure enough to be made into grog. It is important for us to look back at the original manufacturing of these products because if tile manufacturers use potentially harmful materials in the first production cycle they can affect the quality of the grog and potentially require further processing and filtration. 

Conclusion

Even though terra cotta tiles are considered one of the more eco-friendly roofing options, chemical additives and recycled materials are often incorporated in the manufacturing process, and true terra cotta is difficult to find. I was surprised to learn that nearly 60% of the tile body may be post-industrial waste as opposed to raw clay, and that the material life cycle of this product was more complicated than what one might expect. This is not to say that I believe using waste in the production of these tiles is a bad choice, rather I think consumers should be made more aware of these materials. Understanding what is in our products affords individuals the ability to weigh the pros and cons of these products, and in making better informed consumer decisions we can collectively make our world a better, more sustainable place to live.

BIBLIOGRAPHY

“Barrel Tile: Ludowici Roof Tile.” Ludowici, 5 Jan. 2021, ludowici.com/products/roof-tile/barrel/. 

The Ceramic Shop. “Temperature Equivalent Chart for Orton Cones (Cone #022-14).” Orton Cone Chart - The Ceramic Shop, www.theceramicshop.com/content/457/Orton-Cone-Chart/. 

Christiano, Mario. “The Use of Ceramic Waste Aggregates in Concrete: a Literary Review.” Www.researchgate.net, Sept. 2014, www.researchgate.net/publication/266087265_The_use_of_ceramic_waste_aggregates_in_concrete_a_literary_review. 

“Clay Archives.” Boral Roofing, boralroof.com/product-profile/clay/. 

Clay Planet. “Raw Clays.” Clay Planet - Ceramic Supplies, Clay & Glaze Manufacturer, shop.clay-planet.com/rawclay.aspx.

“Clay Roof Tiles vs Concrete, or Something Better?” Synthetic Cedar Shake Roofing | Composite Faux Cedar Shake Shingles, www.cedur.com/clay-vs-concrete-roof-tiles. 

“Cradle to Cradle Products Innovation Institute.” What Is Cradle to Cradle Certified®? - Get Certified - Cradle to Cradle Products Innovation Institute, www.c2ccertified.org/get-certified/product-certification. 

Dube, Nathan. “What Are the Different Types of Packaging Materials?” Https://Www.industrialpackaging.com/Hubfs/Industrial%20Packaging.Svg, 11 Mar. 2021, www.industrialpackaging.com/blog/what-are-packaging-materials. 

Dunne, Tony, et al. Making It Here. Pbs.org, PBS KVIE, www.pbs.org/video/making-it-here-season-7-episode-5/. 

Garcia, Eric. “How to Lay Concrete Roofing Tiles on a Roof, How to Tile a Roof Explained !” YouTube.com, Https://Www.youtube.com/Watch?v=lL1JX4OaDcs, 28 July 2016. 

Grim, Ralph E. “Clay Mineral.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., www.britannica.com/science/clay-mineral. 

Hansen, Tony. “Grog.” DigitalFire.com, digitalfire.com/glossary/grog. 

Hansen, Tony. “Terra Cotta.” DigitalFire.com, digitalfire.com/glossary/terra+cotta. 

“Information on Cone Ratings: Big Ceramic Store.” BigCeramicStore.com, bigceramicstore.com/pages/info-ceramics-maxcone. 

Kats, M. É., and K. K. Kvyatkovskaya. “Low Temperature Flux Compositions for the Production of Cast Ceramic Tile.” Glass and Ceramics, Kluwer Academic Publishers-Plenum Publishers, link.springer.com/article/10.1007/BF00677500. 

Kratz, Kayla. “Minimizing Environmental Impacts with Clay Roofing.” Construction Specifier, 4 Apr. 2017, www.constructionspecifier.com/minimizing-environmental-impacts-with-clay-roofing/. 

“Laurentide Ice Sheet.” Edited by The Editors of Encyclopaedia Britannica, Encyclopædia Britannica, Encyclopædia Britannica, Inc., www.britannica.com/place/Laurentide-Ice-Sheet. 

Miličević, Ivana, et al. “Residual Mechanical Properties of Concrete Made with Crushed Clay Bricks and Roof Tiles Aggregate after Exposure to High Temperatures.” MDPI, Multidisciplinary Digital Publishing Institute, 19 Apr. 2016, www.mdpi.com/1996-1944/9/4/295. 

Peterson, Beth. “How to Use Local Clays in Your Pottery.” The Spruce Crafts, The Spruce Crafts, 5 Nov. 2018, www.thesprucecrafts.com/how-to-use-local-clays-in-your-pottery-2745850. 

Peterson, Beth. “The 6 Stages Clay Goes through during Temperature Change.” The Spruce Crafts, The Spruce Crafts, 7 Aug. 2020, www.thesprucecrafts.com/how-temperature-changes-clay-2746240. 

“Pugmills and Clay Mixers.” Default, 2010, ceramicartsnetwork.org/daily/article/Six-Key-Considerations-When-Shopping-for-Clay-Mixers-and-Pugmills. 

Roberts, Tobias. “The Terracotta Roof: A Complete Guide to This Classic Roofing Style.” Rise, Buildwithrise.com, 18 Feb. 2021, www.buildwithrise.com/stories/the-terracotta-roof. 

Sackey, Solomon, and Byung-Soo Kim. “Environmental and Economic Performance of Asphalt Shingle and Clay Tile Roofing Sheets Using Life Cycle Assessment Approach and Topsis: Journal of Construction Engineering and Management: Vol 144, No 11.” Journal of Construction Engineering and Management, American Society of Civil Engineers, 12 Sept. 2018, ascelibrary.org/doi/full/10.1061/(ASCE)CO.1943-7862.0001564. 

“Sheffield Pottery Inc..” About Our Clay And Raw Material Refining System, www.sheffield-pottery.com/Our-Clay-And-Raw-Material-Refining-s/271.htm. 

Silverstein, Simone. “Shipping Done Well.” Heath Ceramics, 28 Oct. 2020, www.heathceramics.com/blogs/heath-journal/shipping-philosophy. 

Souza, Danielle Maia de, et al. “Comparative Life Cycle Assessment of Ceramic versus Concrete Roof Tiles in the Brazilian Context.” Journal of Cleaner Production, Elsevier, 15 Nov. 2014, www.sciencedirect.com/science/article/pii/S0959652614012098. 

Souza, Eduardo. “Embodied Energy in Building Materials: What It Is and How to Calculate It.” ArchDaily, ArchDaily, 26 Aug. 2021, www.archdaily.com/931249/embodied-energy-in-building-materials-what-it-is-and-how-to-calculate-it. 

Zanelli, Chiara, et al. “Waste Recycling in Ceramic Tiles: A Technological Outlook.” Resources, Conservation and Recycling, Elsevier, 5 Dec. 2020, www.sciencedirect.com/science/article/pii/S0921344920306042#bib0168.

WASTE — Sarah Graham

Terracotta roof tiles are an important architectural element used across a multitude of building types. These roof tiles are made from an earthenware clay material that is harvested from the earth and then goes through a large manufacturing process to become the tile we see installed on our roofs. Terracotta tiles are considered the more “eco-friendly” option when it comes to roofing tile options. The thick clay tiles are very durable and great home insulators, keeping the heat in during the winter and reducing the need to turn on an internal heating unit. Their light color also reflects heat rays and keeps the home cool in warmer climates reducing the need for air conditioning and overall reducing the home's carbon footprint. It is also one of the longest-lasting roofing materials. Well-made and maintained tiles can last anywhere from 75-100 years, preventing the need to re-tile the roof.[1] The making of a terracotta roof tile is an extensive process that follows many steps from clay harvesting to shaping and firing, to its final place on your home and its life after. I will be focusing on the many forms of waste that are emitted during the lifecycle of a terracotta roof tile as it follows the six steps of its life with wastes including airborne, solid, and unusable waste during the acquisition of raw materials, manufacturing, distribution, maintenance, and recycling or disposal of the product. 

The main waste factor when it comes to the material extraction stage for making terracotta tiles is from clay harvesting. Clay harvesting requires heavy machinery to dig out clay deposits which are usually located alongside bodies of water. The clay is extracted from the ground using many types of heavy machinery such as power shovels, backhoes, draglines, front-end loaders, shale planers, and scraper-loaders. The machinery used in the mining disturbs the natural landscaping and creates gouges and uneven terrain, causing huge environmental consequences for the surrounding area of the mine.[2] Clay deposits can be naturally found next to large bodies of water and the mining causes dissolved clay particles to flow into the water and change their color and rain runoff affects how much sediment ends up in the water. Both active and inactive mines are considered a water contamination threat. The drainage from the mines can affect the quality of the groundwater or other bodies of water located close to the mine such as a river or lake. [3]The two most common types of contamination associated with mining are acid mine drainage and heavy metal contamination.  According to an article by The International Council on Mining and Metals, over 50% of mining emissions come from machinery. The most common emissions are carbon dioxide, nitrogen oxides, hydrocarbon, and carbon monoxide coming from machinery exhaust.[4] An indirect piece of waste that comes from clay harvesting is the waste of potential human drinking water. Mining causes large ditches of soil to be moved to create large creators and ditches that then get filled during rainfall. The water can no longer be used for human consumption because it has become too mixed with the soil and mud. After the clay is extracted, the clay moves onto the next step of its life cycle, the refining process. 

Terracotta roof tiles emit many forms of waste during their lifecycle as it follows the six steps of their lifecycle such as during the clay refinement step. After the clay has been harvested, a process is done to the clay to separate it from any impurities. Some processes include water processing to remove water-soluble impurities, or acid leaching and magnetic separation to remove metallic waste. These processes use a large amount of water which then collects the impurities and excess water into tailing ponds. Much of the time, this water can be reused multiple times but then it eventually becomes too contaminated to pull out any more impurities and sits in the tailing ponds.[5] Once the clay is transported to the manufacturing plant, the dried clay is then mixed with more water to make it malleable. The excess water from this process can also be recycled and used in more clay or filtered to take out any sediment. The clay is then shaped and molded into its preferred roof tile shape and set to dry before being fired. The air drying is usually performed in a tunnel kiln, which can capture the excess heat produced by the firing kiln. During this stage, accidental waste could be broken dried tiles. These broken tiles can be re-crushed and re-mixed with water to be turned into new clay.[6] Another form of waste that is highly toxic to potters or others working in these facilities is free-silica emissions. The dust from the dried clay can release silica into the air which is toxic to humans when breathed in during long exposure. Sanding and dust waste occur when the dried tiles are sanded and shaped to remove any imperfections. The dust is a form of waste itself during most of these stages as any dry clay that is not contained can be easily be picked up by a gust of wind and no longer be used. There are methods used to control the amount of dust that is released such as using ventilation and fabric filters in factories and only mining on days where there is little wind. There are methods of collecting ceramic dust and using it in concrete so it doesn't go completely to waste.[7] The main form of waste we see in this stage that will also continue into the firing stage is the emission of particle matter (PM). Particulate matter emissions consist of parts of metals and the inorganic minerals associated with the clay. Volatile organic compounds (VOC) are another form of particle matter released. VOC emissions are released as a result of incomplete combustion and volatilization of the organic material associated with the clay.[8] Once the clay has been refined and a tile is shaped, it then goes on to be fired. 

Terracotta roof tiles emit many forms of waste during their lifecycle as it follows the six steps of their lifecycle such as during the firing step. Kiln emissions are the biggest form of waste produced during the firing process. Fuel-fired kilns are heated by burning gas, oil, wood, charcoal, or other materials. The firing of materials from raw clay into terracotta tiles releases hydrochloric acid, hydrofluoric acid, sulphuric acid, and carbon dioxide. The sulfur and nitrates found in the clay break down into toxic sulfur and nitrogen oxides. The combustion exhaust from the kiln fuel releases carbon monoxide, carbon dioxide, nitrogen oxides, fluorine, and more particle matter. Fluorine is found in most clay bodies and when it is heated in the kiln, it is released as hydrogen fluoride. Fluorine emissions can be reduced in a few ways such as increasing the lime content of the raw clay, using dry sorption scrubbing, and reducing kiln draft, exhaust temperature, and kiln residence. More waste such as lead, antimony, cadmium, selenium, and precious metals vaporize during firing and the metal fumes can escape from the kiln or settle inside the kiln or on the tiles inside.[9] Any tiles that are damaged or broken during the firing process cannot be broken back down and made into new tiles as seen in the drying process. When firing, the chemical properties of the clay are changed too much to return to its original, water-soluble state. Instead, the broken tiles can be crushed and reused as grog for other ceramic projects.[10] After the tiles are fired, they then go on to be packaged and transported to their destination. 

Terracotta roof tiles emit many forms of waste during their lifecycle as it follows the six steps of their lifecycle such as during the packaging and transportation step. In most industries, the packaging of their products produces a huge amount of waste that is then disregarded and thrown away. Due to the fragile nature of the tiles, extensive packaging materials are used to pad and ensure they do not crack during transportation. Some materials used in small-scale packaging include newsprint to wrap the tiles, bubble wrap around the edges, and packing peanuts to fill in the empty spaces. Larger amounts of tiles are typically stacked together and secured with a large band and placed on pallets for transportation.[11] These materials used in packaging are usually not recyclable, compostable, or able to be reused in the future and end up in landfills. There are more environmentally friendly options such as biodegradable packing peanuts and Expandos (a triangular filler made from post-consumer chipboard) that can either be reused or composted.[12] The largest form of waste during this step is the emissions from transportation. Large transport trucks produce large amounts of emissions and they increase as the weight of the truck increases. Some emissions released during transportation include particle matter (PM), volatile organic compounds (VOCs), nitrogen oxides, carbon monoxide, sulfur dioxides, and greenhouse gases.[13] One type of particle matter that comes from trucks is soot from the exhaust and can be classified as both a primary and secondary pollutant. VOC emissions include benzene, acetaldehyde, and 1,3-butadiene, all of which are huge contributors to smog.[14] Using a simple greenhouse gas emissions calculation, a 2.2-ton tail life truck driving from Heath Ceramics in San Francisco (a popular ceramic manufacturer) to UC Davis on the most efficient route (about 75 miles) would emit about 26,697 grams of CO2 on its trip.[15] Once the tiles arrive, they are installed and can live on a home for many years and they move to their final step in the lifecycle of maintenance, recycling, and final disposal. 

Terracotta roof tiles emit many forms of waste during their lifecycle as it follows the six steps of their lifecycle such as in its final maintenance, recycling, and final disposal step. There were many examples of recycling in some of the previous steps but this paragraph will focus on the end-of-life maintenance, recycling, and disposal of the terracotta tiles. Once the tiles are installed, not much is needed to maintain them as they are extremely durable and long-lasting. One way to maintain the integrity of the tiles is to powerwash them to remove debris. A light power washing machine can use up to two gallons of water per minute, and if it took you on average 45 minutes to power wash your roof, then it would take 90 gallons of water.[16] The water from the power washing is not able to be recollected as it runs off the side of the roof or gutters and into storm drains and goes to waste. Because of the durability of terracotta roof tiles, the tiles may outlive the life of the house they are on. If the house is due for demolition, measures are taken to carefully dismantle the tiles and reuse them for new home projects to reduce waste. If the tiles are not viable or broken, there are many ways they can be recycled[17]. Crafters have come up with many creative ways to use broken tiles such as reusing them to make planter beds, makeshift garden walls, and decorative wall art. The tiles can also be crushed and reused as a landscaping medium in places like baseball fields, cutting down on landfill waste. [18]Crushed tiles can also be used as aggregates in concrete production. I was not able to find information on if the tiles can be re-crushed and used to make new tiles, so it is assumed that any non-useable tiles that do not get recycled into other projects end up in landfills.

Many forms of waste are emitted during the lifecycle of a terracotta roof tile as it follows the six steps of its life with wastes including airborne, solid, and unusable waste during the acquisition of raw materials, manufacturing, distribution, maintenance, and recycling or disposal of the product. This project highlighted how a simple product goes through an extensive production process and lives through a long lifecycle process each with its own form of waste that further goes to damage our environment and health despite being considered an “eco-friendly” product. There were lots of types of waste produced during the lifecycle such as water waste and contamination, particle matter and VOC emissions, dust, and broken tile waste. Despite the large amounts of waste, there are matters taken to reduce the amount of waste by reusing materials, recycling water, and repurposing tiles for other products. 

Footnotes

1. Roberts, Tobias. “The Terracotta Roof: A Complete Guide to This Classic Roofing Style.” Rise, 18 Feb. 2021, https://www.buildwithrise.com/stories/the-terracotta-roof.

2. ALMEIDA, Janilton de Lima. “Environmental Impacts Caused by Clay Extraction Environmental Impacts.” , 7 Jan. 2021, https://www.nucleodoconhecimento.com.br/environment/clay-extraction.

3. Asante-Kyei, Kofi, and Alexander Addae. “The Economic and Environmental Impacts on Clay Harvesting at Abonko in the Mfantsiman West District of Central Region, Ghana.” American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS), vol. 82, no. 1, 19 Sept. 2021, pp. 120–132.

4. Heidari, Bardia, and Linsey C. Marr. “Real-Time Emissions from Construction Equipment Compared with Model Predictions.” Journal of the Air & Waste Management Association, vol. 65, no. 2, 2015, pp. 115–125., https://doi.org/10.1080/10962247.2014.978485. Accessed 28 Nov. 2021.

5. 11.25 Clay Processing - US EPA. https://www3.epa.gov/ttn/chief/ap42/ch11/final/c11s25.pdf.

6. Mukherjee S. (2013) Environmental Impacts of Clay-related Industries. In: The Science of Clays. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-6683-9_19

7. “Clay.” Princeton University, The Trustees of Princeton University, https://ehs.princeton.edu/health-safety-the-campus-community/art-theater-safety/art-safety/ceramics.

8. Mukherjee S. (2013) Environmental Impacts of Clay-related Industries. In: The Science of Clays. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-6683-9_19

9. 11.25 Clay Processing - US EPA. https://www3.epa.gov/ttn/chief/ap42/ch11/final/c11s25.pdf.

10. Anbarasan, Muralidharan, and K. Mohan. “(PDF) Ceramic Waste as Coarse Aggregate in Concrete.” ResearchGate, Unknown, 1 July 2016, https://www.researchgate.net/publication/327691190_Ceramic_Waste_as_Coarse_Aggregate_in_Concrete.

11. “How to Pack and Ship Tiles and Bricks.” Eurosender.com, https://www.eurosender.com/en/pack-ship/tiles-bricks.

12. Silverstein , Simone. “Shipping Done Well.” Heath Ceramics, 28 Oct. 2020, https://www.heathceramics.com/blogs/heath-journal/shipping-philosophy.

13. “Average In-Use Emissions from Heavy-Duty Trucks - Emission Facts.” Environmental Topics Laws & Regulations About EPA National Service Center for Environmental Publications (NSCEP), United States Environmental Protection Agency , Oct. 2008, https://tinyurl.com/2p92m9u2.

14. “Cars, Trucks, Buses and Air Pollution.” Union of Concerned Scientists, 23 July 2008, https://www.ucsusa.org/resources/cars-trucks-buses-and-air-pollution.

15. Mathers, Jason. “Green Freight Math: How to Calculate Emissions for a Truck Move.” EDF+Business, 6 Apr. 2021, https://business.edf.org/insights/green-freight-math-how-to-calculate-emissions-for-a-truck-move/.

16. Wallace, Adam, and Shoni Bacon. “How Much Water Does a Pressure Washer Use?” Pressure Washer Lab, 22 Sept. 2021, https://www.pressurewasherlab.com/how-much-water-does-a-pressure-washer-use/.

17. Boniface, Stephen, and Tony Redman. “Clay-Tiled Roofs.” Building Conservation, The Building Conservation Directory, 2008, https://www.buildingconservation.com/articles/claytile/claytile.htm.

18. Roof Surface Removal . Department of Environment, Climate Change and Water NSW , Dec. 2010, https://apps.epa.nsw.gov.au/prpoeoapp/ViewPOEOLicence.aspx?DOCID=129236&SYSUID=1&LICID=20209.

Works Cited 

11.25 Clay Processing - US EPA.

https://www3.epa.gov/ttn/chief/ap42/ch11/final/c11s25.pdf.

ALMEIDA, Janilton de Lima. “Environmental Impacts Caused by Clay Extraction

Environmental Impacts.”  ,  , 7 Jan. 2021, https://www.nucleodoconhecimento.com.br/environment/clay-extraction.

Anbarasan, Muralidharan, and K. Mohan. “(PDF) Ceramic Waste as Coarse Aggregate in

Concrete.” ResearchGate, Unknown, 1 July 2016, https://www.researchgate.net/publication/327691190_Ceramic_Waste_as_Coarse_Aggregate_in_Concrete.

“Average In-Use Emissions from Heavy-Duty Trucks - Emission Facts.” Environmental Topics

Laws & Regulations About EPA National Service Center for Environmental Publications (NSCEP), United States Environmental Protection Agency , Oct. 2008, https://tinyurl.com/2p92m9u2.

Boniface, Stephen, and Tony Redman. “Clay-Tiled Roofs.” Building Conservation, The Building

Conservation Directory, 2008, https://www.buildingconservation.com/articles/claytile/claytile.htm.

“Cars, Trucks, Buses and Air Pollution.” Union of Concerned Scientists, 23 July 2008,

https://www.ucsusa.org/resources/cars-trucks-buses-and-air-pollution.

Heidari, Bardia, and Linsey C. Marr. “Real-Time Emissions from Construction Equipment

Compared with Model Predictions.” Journal of the Air & Waste Management Association, vol. 65, no. 2, 2015, pp. 115–125., https://doi.org/10.1080/10962247.2014.978485. Accessed 28 Nov. 2021.

“How to Pack and Ship Tiles and Bricks.” Eurosender.com,

https://www.eurosender.com/en/pack-ship/tiles-bricks.

Mathers, Jason. “Green Freight Math: How to Calculate Emissions for a Truck Move.”

EDF+Business, 6 Apr. 2021, https://business.edf.org/insights/green-freight-math-how-to-calculate-emissions-for-a-truck-move/.

Mukherjee S. (2013) Environmental Impacts of Clay-related Industries. In: The Science of

Clays. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-6683-9_19

Roberts, Tobias. “The Terracotta Roof: A Complete Guide to This Classic Roofing Style.” Rise,

18 Feb. 2021, https://www.buildwithrise.com/stories/the-terracotta-roof.

Roof Surface Removal . Department of Environment, Climate Change and Water NSW , Dec.

2010,https://apps.epa.nsw.gov.au/prpoeoapp/ViewPOEOLicence.aspx?DOCID=129236&SYSUID=1&LICID=20209.

Silverstein , Simone. “Shipping Done Well.” Heath Ceramics, 28 Oct. 2020,

https://www.heathceramics.com/blogs/heath-journal/shipping-philosophy.

Wallace, Adam, and Shoni Bacon. “How Much Water Does a Pressure Washer Use?” Pressure

Washer Lab, 22 Sept. 2021, https://www.pressurewasherlab.com/how-much-water-does-a-pressure-washer-use/. 

The Embodied Energy of Terracotta Roof Tiles

1. Introduction

Terracotta roofing has been used for generations throughout the world, due to the abundance of clay base materials worldwide. Today it is commonly connected to homes built in the traditional Mexican hacienda architecture and as such can often be seen as a sign of wealth and quality. This is because of the overabundance of other cheaper roofing materials such as asphalt and metal sheets. On top of this base price, terracotta tiles also require additional fortification of roofing structures to verify the roofing joists can sustain the significantly larger weight of a terracotta roof. Throughout the various points of terracotta roof tile’s lifecycle, many forms of energy are used as the product’s basic materials are mined and then the product is manufactured, distributed, used, and recycled. The key draw of this product today is the amount of energy consumed during its usage which usually allows homeowners to lower their overall energy draw by reducing their reliance on household systems like HVAC by using a material that is so abundant it can be locally sourced and manufactured.

2. Raw Material Acquisition

The initial acquisition of raw terracotta clay materials is majorly reliant on open-pit methods which require less energy to procure the materials than the more stereotypical underground mining. This method of mining leaves a pit that is generally constructed in such a way that it allows the acquired materials to be transported to surface stations through the use of diesel or gas-powered vehicles. Open-Pit methods of mining also tend to use less power as it tends to signal that the materials are found closer to the surface of the planet compared to other resources which must be chemically extracted. This reduction in energy usage is also augmented by the fact that most clay product manufacturers source their clay from mines local to them. A reality that is possible due to the pervasive nature of terracotta clay base materials. 

3. Processing and Manufacturing

Once these materials are excavated and returned to the production facility they undergo various chemical processes that prepare the terracotta clay to be molded and fired into roofing tiles. The first process that the clay is put through is that of mixing various types of clay into a predetermined ratio that creates the unique chemical makeup of a company's terracotta clay. The next step of this process is to mill and filter the clay granules down to the correct size and remove other materials such as stone which could affect the final product's makeup. This step could implement a device such as Xiangtan Weida Electrical and Machinery Companies’ Box Feeder, which runs on an electric-powered 7.7 Kw motor, and can process 15 meters cubed of material within an hour. This mixture is then aged in a semi-controlled environment where the clay is allowed to fully absorb the minimum amount of water that was mixed within the clay mixture. This process augments the natural plasticity of clay and allows it to be further processed and molded into the desired shape of the final product. It is in this step that the different techniques of manufacturing show clear distinctions in energy use. While some companies such as the Santafe Roof Tiles prefer to use the unautomated handcraft method, which is mostly reliant on human energy instead of electric, other companies have instead moved towards a more automated approach which relies on electric devices produced by companies such as the Xiangtan Weida Electrical and Machinery Company. The products created using these technologies are generally put through more processes than artisan tiles, and as such expend much more energy than hand-crafted tiles. The majority of these devices run on electrical power from varying sources given the diversity of roofing tile manufacturers. 

After the filtration and molding processes are complete the clay goes through a drying and firing process which could be considered a high energy-intensive venture. In automated processes, the molded clay will go through various de-airing machines which remove air through the use of electricity-powered vacuums. They are then pushed through a drying machine that takes the clay's water content from about 12-17% to about 1-2% by pushing air of 10-150℃ around the container. This device is usually powered by external combustion engines running on anything from natural gas to fuel that can run fans that run on approximately 18.7 kilowatts. After reducing the water content of the molded terracotta roof tile, it is placed into a kiln where it remains for 6 to 36 hours. The kilns used for this process can reach the heat of 1355℃ and can run on gas, biofuel, coal, or any other type of fuel. In some instances, these kilns could be used to produce about 10,000 roofing tiles per day.

This culmination of these processes ends with a rock-like roofing tile that is no longer able to absorb water and therefore can be used as a good roofing material. In all, the manufacturing and refinement of can be considered a lengthy process as it goes through filtration, milling, mixing, molding, drying, and firing processes. Today, various companies are looking for methods through which they could substitute some of the volumes of the roofing tiles through the use of previously non-recyclable materials such as cigarette buts. When looking into these studies, it is constantly pointed out that some of the firing and drying processes that the roofing tiles must go through tend to burn out the toxic materials that would classically rule out the recycling of these materials. This could reduce the amount of energy lost as it would mean that more roofing tiles could be produced out of mined clay since some percentage of that value would be instead supplied through the use of collected waste from previous products.

3. Transportation

A study on the many requirements for the transportation of different roofing materials calls to the forefront one the difficulties of transporting fragile materials such as terracotta roofing tiles. The majority of these issues stem from the fact that not only are these more fragile than the classic asphalt shingles used by the majority of residential buildings in the United States, but they also tend to be heavier per square foot than shingles. This results in a greater need for protective materials in the shipment of terracotta roof tiles and therefore increases the final embodied energy of the finished product. What helps to somewhat reduce this energy cost is the number of local manufacturing plants that allow for contracting businesses to try and locally source the roof tiles. Unfortunately, like with many different industries, it is generally seen as cheaper and faster to order from giant companies rather than local businesses and therefore many of the construction projects completed with such tiles are done so with roof tiles that have required much more energy to transport. The fact that clay is an abundant resource should be marketed in a manner that makes consumers proud to use locally produced clay tiles as it means that the finished product is part of the land around them. These factors all contribute to what makes the average amount of GigaJoules used to transport Clay Tiles is 6.82 whereas metal sheets only require about 1.14 GJ.

4. Usage/Maintenance

In today's market, there are various methods that can be used to reduce the amount of energy consumption of a home. Key among these are installing new furnaces, insulated windows, and even the materials used for roofing. One of the options that can be thought of as being conducive for a more energy-efficient home is terracotta clay tiles. This is because clay is a very good insulator, and the amount of free surface area that comes from the average shape of the clay tiles allow this type of roof to keep a home, less reliant on HVAC systems than other materials such as asphalt which trap heat in attic spaces and within themselves. A study done by Pablo J.Rosado revealed that clay-based roofing tiles could decrease energy used for cooling by 26%, on average, when compared to roofing that was made out of asphalt tiles. Due to the long life of these tiles, terracotta roofs are seen as worthy investments by homeowners who are trying to save money and reduce their carbon footprint. The only real maintenance that terracotta tiles may require is pressure washing, which is often much cleaner than having to replace the entire roof when segments become worn as is the common case with asphalt tiles.

5.Recycling

Terracotta roofing tiles, however, don’t have an infinite lifespan and will eventually crack or deteriorate to the point where they will require replacement. On top of this, some homeowners could decide to get rid of the tiles in lieu of any other type of roofing material. When this happens there is really only one way that these tiles can be recycled. They must be ground down once more in a milling machine that may run off of electrical or gas-powered engines. Once they are fine enough in size, this becomes known as aggregate. Aggregate can be used as a base for roads or pools and is usually constructed out of mined stones. By reusing this already baked clay, the manufacturers of aggregate save some energy in the acquisition of raw materials and therefore have a less energy-intensive process than aggregate which is made from mined supplies.

6. Conclusion

Terracotta roofing tiles can be a great roofing material for homeowners looking to save energy and reduce their carbon footprint, but the sourcing of these materials should be taken into considerations when deciding whether or not it will have any impact on the end embodied energy of the said product. Local manufacturers who have to ship their products to closer areas should be a better source of low energy cost materials, and should therefore be the first choice for homeowners actually concerned with energy use. Due to the abundance of clay, this should be simple to do, especially since the mining of clay is done in a less energy-intensive manner.

          Bibliography

Didden, Amanda M. (2003). Standardization of Terra Cotta Anchorage: An Analysis of Shop Drawings from the Northwestern Terra Cotta Company and the O. W. Ketcham Terra Cotta Works. (Masters Thesis). University of Pennsylvania, Philadelphia, PA.

Roberts, Tobias. “The Terracotta Roof: A Complete Guide to This Classic Roofing Style.” Risle, Feb. 2021.

Kratz, Kayla. Minimizing Environmental Impacts with Clay Roofing. Jan. 2015, https://www.constructionspecifier.com/minimizing-environmental-impacts-with-cl ay-roofing/.

Are Tile Roofs Energy-Efficient? 16 Aug. 2019, https://www.abcroofingcorp.com/are-tile-roofs-energy-efficient/.

“Environmentally Responsible.” Tile Roofing Industry Alliance, https://tileroofing.org/why-tile/environmental-impact/. Accessed 25 Oct. 2021.

Rosoda, Pablo. “Measured Temperature Reductions and Energy Savings from a Cool Tile Roof on a Central California Home.” Energy and Buildings, Sept. 2014.

Binh Duong Le, Andy. “Carbon Footprint and Embodied Energy Assessment of Roof‐covering Materials.” Clean Technologies and Environmental Policy, vol. 21, no. 10, Oct. 2018, pp. 1913–23. 

Boniface, Stephen. “Clay-Tiled Roofs.” Cathedral Communications Limited, 2019, https://www.buildingconservation.com/articles/claytile/claytile.htm.

Wallace, Adam. “HOW MUCH WATER DOES A PRESSURE WASHER USE?” Pressure Washer Lab., Jan. 2021, https://www.ihrc.fiu.edu/wp-content/uploads/2012/05/HLMP_Year07_Section5_ Tiles_RCMPY7.pdf.

Nurulakmal Mohd Sharif. “Effects of Body Formulation and Firing Temperature to Properties of Ceramic Tile Incorporated with Electric Arc Furnace (EAF) Slag Waste.” AIP Publishing LLC, July 2017, https://ui.adsabs.harvard.edu/abs/2017AIPC.1865f0005S/abstract. 

“Production Process.” n.d. Accessed December 1, 2021. https://www.wienerberger-building-solutions.com/About/Production-process.html.

https://www.tilemachinery.com/our-products/

Terry Marks. 2018. “What Is The Most Energy-Efficient Roofing Option?” HomeGaurd (blog). August 22, 2018. https://www.homeguardroof.com/blog/what-is-the-most-energy-efficient-roofing-option/.

BCS,Incorporated. 2007. “Mining Energy Bandwidth Report.” BCS,Incorporated. https://www1.eere.energy.gov/manufacturing/resources/mining/pdfs/mining_bandwidth.pdf.

https://motorask.com/semi-trucks-mileage/#Check_Your_Weight