Donovan Hemmelgarn 3501 Fall 2008 Web

concrete

STRUCTURAL MATERIALS RESEARCH CATALOGUE CONTRIBUTORS

James Donovan, Marshall Drennan, Gregory Hemmelgarn, Phil Hoffmann, Cody Johnson, David Ladewig, Laura Lopez, Katherine Marshall, John Redington, Greg Roffino, Jose Sanchez, Chelsea Serrano-Piche, Leo Spurgin, Jasmine Strickland

STUDIO 703

ARCH 3501 - ARCHITECTURAL DESIGN STUDIO 4 COLLEGE OF ARCHITECTURE TEXAS TECH UNIVERSITY - FALL 2008 http://z.about.com/d/archaeology/1/0/a/A/coliseum.jpg

background

http://fc04.deviantart.com/fs18/f/2007/176/8/0/Texture__Concrete_Cracked_by_ivelt_resources.jpg

history The ancient Romans first used lime and pozzolana, a volcanic ash, to create a hard setting mortar. By adding rubble and other aggregate, the Romans created opus caementitium. The most famous example of this early form of concrete is the Pantheon in Rome, Italy. Modern concrete was invented by the British engineer John Smeaton in 18th century, alongside the rapidly growing use of iron and steel for building construction. Portland Cement, the main ingredient in modern concrete, was patented in 1824 by Joseph Aspdin. In the 1867 Frenchman Joseph Monier combined the tensile strength of steel and the compressional strength of concrete to create the composite building material known as reinforced concrete. Today, nearly all concrete construction is reinforced concrete.

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http://www.znanje.org/i/i27/07iv03/07iv0321/pantheon.jpg

http://www.momahoney.com/M.O%27MahoneyCo%20File/Images/MOMSupplies/Ce-

1. Roman Pantheon, early example of concrete 2. Concrete slab showing basic steel reinforcement 3. Portland Cement, key ingredient in concrete

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http://www.dkimages.com/discover/previews/884/5019427.JPG

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methods Concrete is available in 3 main types. The most common is ready-mix concrete, which accounts for more than threefourths of all concrete construction. Ready mix concrete is mixed off site at a central plant and shipped to the construction site in large trucks. Another type is Pre-cast concrete, which has become widely popular especially in hotels and apartments where repetitive elements are common. Pre-cast concrete is mixed and cured at the factory under ideal conditions, producing a higher quality concrete. The last form of concrete is the concrete masonry unit, which in best known for its standard 8x8x16 inch block. Because they are cured in the factory, they can be mass produced and designed to suit any architectural need.

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http://upload.wikimedia.org/wikipedia/commons/5/58/Concrete_pouring_0020.jpg

http://www.wizzard.com/bm2004/Images/event_jill/big/07390016.jpg

1. Construction crew pouring cast in place foundation 2. Concrete masonry units, curing in the factory yard 3. Prefabricated concrete beams

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http://www.prestasi-concrete.com/images/M2(small).JPG

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types There are many types of concrete that is used to strengthen and help reinforce the concrete itself. First, Standard concrete which is a mixture of sand, portland cement and water, is common in most places. Another type of concrete is shotcrete which uses compressed air to shoot concrete onto vertical frames and structures. Pervious concrete contains a network of holes to allow air and water to move through the concrete. The last type of concrete is Glass. The use of the glass as a aggregate is a good material for thermal insulation.

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http://dwiprima.com/shotcrete3.jpg

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Standard Shotcrete Pervious Glass

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future of concrete Since the development of concrete by the Romans there has been a tremendous change in the technology of concrete. In the past couple of years scientists have been experimenting the limits of concrete and finding new uses of the material. There is a new form of concrete called translucent concrete. To achieve the translucence in concrete scientists use large quantities of fiber optics to transfer light from one side of the wall to the other. Fiber optics can transfer light through a load-bearing concrete wall up to six feet thick. The Romans experimented with different aggregates to lighten the weight of concrete, but changes in aggregates would only decrease the load by fractions. This concept brought the invention of Autoclave Aerated concrete. AAC is mixed with lime, water, cement, and finely ground sand. The mixture is placed in a autoclave at high pressure and heat. This produces concrete five times lighter than regular concrete, which is capable of floating in water.

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http://www.tengardens.com/images/stories/science/litracon12.jpg

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1. Translucent concrete 2. LitriCon block wall. 3. Autoclaved Aerated Conrete floating next to standard concrete. 4. Design application for fiber optic concrete wall.

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Liquid stone : new architecture in concrete / Jean-Louis Cohen and G. Martin Moeller, Jr., editors. New York : Princeton Architectural Press, c2006

future of concrete Fabric Formed Concrete is another study showing texture and producing mass molds when using plaster. The stretched fabric reflects the tensile forces within the material. Once the concrete is poured into the fabric mold, hardened, then turned upside down to let the force of gravity pull; it becomes in compression to keep its original shape. When the concrete is dried the fabric engraves patterns onto the surface. Bendable Concrete is a fiber reinforced, cement based composite material that is engineered to allow ductility. The use of elastic polymers and other chemical compounds is continually advancing the possibilities of concrete design.

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http://www.fab-form.com/images/isoff/thin_shell+columns.jpg

1. Bendable concrete 2. Fabric formed concrete 3. Detail of fabric formed concrete

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Liquid stone : new architecture in concrete / Jean-Louis Cohen and G. Martin Moeller, Jr., editors. New York : Princeton Architectural Press, c2006

thin shell concrete

http://www.fundacioncac.es/cas/artesyciencias/mediateca/download/20049913856o-2178dig_jft.jpg

cantenary curves Catenary curves are often confused with parabolas, but geometrically they are very different. A catenary curve is a theoretical shape a chain suspended from each end takes under the forces of gravity. Catenary curves are extremely efficient because they naturally form a equilibrium of forces between gravity and tension. Eero Sarrinen uses catenary curves frequently in his projects such as the St. Louis Arch in Missouri and Dulles International Airport near Washington D.C.

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1. Diagram of a cantenary curve showing the forces of gravity and tension 2. Cantenary arch viewed as a plane

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Haas, A. M. (Arend Maarten) Design of thin concrete shells. New York, Wiley, 1962-67.

additional geometry There are many different types of curves that are used in thin-shell designs, many of which require difficult mathematical language and high level calculus.

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american air museum

http://www.flickr.com/photos/hubmedia/275645566/

design The American Air Museum in Duxford, England was constructed in 1995 by Ove Arup with Foster and Partners. The program called for a structure to house 32 aircraft in a large, single space. The largest of these aircraft, a B52 Stratofortress, is 50 feet tall with a 200 foot wingspan, determining the minimum dimensions of the structure. The solution was a curved concrete shell whose geometry is derived from a torus and the plan of the structure is half of an ellipse. The double shell concrete construction of the roof was designed to control condensation. Even though concrete is more expensive than steel, Foster decided to use concrete because of its lower life cycle costing.

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1. Geometry derived from 3D torus 2. Exterior perspective 3. Longitudinal section

construction The inner slab of the roof was formed with ‘T’ beams placed upside down to hold the roof together. These individual beams are ten meters long by three meters wide and all four sides of the beam are reinforced to structurally tie all the beams together. The outer slab is made of curved precast panels resting on top of the ‘T’ beams. These The glass wall at the rear of the building is demountable to allow the planes to move in and out of the building if needed.

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Construction crews installing precast beams Detail section through foundation and abutments Detail of precast ‘T’ beams Scaffolding and false work during construction

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thin shell cave Our first large scale plaster model was inspired by the American Air Museum in Duxford, England (page X). This model is approximately. 30” x 24” x 12”. We encountered several problems with this project. Despite being only 1/8” thick at the top, this model required nearly half a gallon of plaster. Managing large quantities of wet plaster proved to be challenging, and we were forced to pour several batches. Creating accurate form work for complex geometric shapes also proved to be quite a challenge. The American Air Museum is based off a torus, or 3D doughnut, producing a non-deformable section that is curved in two directions, which we were unable to replicate. Despite this setback, our “cave” is remarkably strong, so long as the outward thrusts of the abutments are resisted.

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Thin shell cave with plexiglass form work partially removed Perspective image of the cave Detail of cave abutment and wire screen reinforcement Side elevation, showing straight edge instead of doubly curved shell

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precast ‘T’ beams An important structural feature of the American Air Museum is the precast concrete ‘T’ beams that form the curved roof. Despite the complex geometry of the building, the concrete manufacturers were able to cast the 200+ beams required with only six different sets of steel form work. We were able to approximate one of these sets of form work and use it to cast two identical tee beams at 1:50 scale (8" x 2" x 1"). Instead of steel, we used wood faced with plexiglass to make our molds. Once assembled with masking tape, plaster was poured into one end of the mold and allowed to cure fully before striking the mold and repeating the process.

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Form work pieces laid out Form work partially assembled Detail of lateral reinforcing wires Finished ‘T’ beams

dulles international airport

http://www.metwashairports.com/_/Gallery%20Image/_/dx-17_daytime_terminal.jpg

concept Dulles International Airport was designed by Eero Sarrinen in 1962. Located just outside Washington D.C., Dulles is one of Eero Sarrinen’s most famous designs. Sarrinen himself described Dulles as “the best thing I have ever done.” The Terminal is about 600 feet long by 200 feet wide. One of the most noticeable features of the design is its roof structure. Sarrinen compared the roof structure and it’s colonnades as a hammock hung between two trees. Geometrically speaking, the roof is a catenary curve. Catenary curves are extremely stable because they are simply the shape something takes due to gravity when suspended from its ends.

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I think this airport is the best thing I have done. I think it is going to be really good. Maybe it will even explain what I believe about Architecture.

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Eero Sarrinen

June 21, 1961

http://www.braingainmarketing.com/media/saarinen/saarinen_knight_02.jpg

construction There are sixteen columns on each side of the terminal to hold up the massive roof. The columns on the front side of the terminal are 65ft. high and are 45ft. high on the rear side. The columns are designed at an outward angle to resist the tension from the cables holding the thin concrete roof in the air. The roof is set up of many rows of cables spaced ten feet apart, with each row having approximately fifty precast concrete panels hung between the wires. Once the panels are in place, concrete is poured on top to fill between the gaps and create a monolithic roof.

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Lifting precast panels into place Underside of precast panels hanging from wires Columns under construction Scaffolding and false work used to finish roof

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interior

The effect of this massive hanging roof is truly spectacular. There are no columns or walls anywhere in the main terminal, and the space is entirely surrounded by glass, allowing for a clear view through the entire building. Light floods the space as the roof seems to float effortlessly overhead.

http://farm1.static.flickr.com/69/162370394_0c8251d3a5.jpg?v=0

plaster

directions

1. Wearing gloves helps clean-up and protects your hands.

2. Warm water makes the plaster set faster, cold water lengthens the time the plaster is workable. Choose according to your needs.

3. Ideal mix calls for 2:1 plaster to water ratio. Higher plaster ratios makes thicker, stronger product, but makes achieving accurate, bubble-free molds more difficult.

4. Add the dry plaster to the water.

5. Mix the plaster using a piece of scrap wood.

6. Add aggregate while continually stirring.

7. Pour plaster into mold.

8. Shake mold and use a piece of scrap to agitate the wet plaster. This helps remove air bubbles. You may need to add more plaster to top off your mold after this step.

9. Wait. Plaster takes about an hour to set in the mold, about 24 hours to dry completely. Fragile or intricate castings should set for 6-8 hours before disturbing the plaster.

10. Leave excess plaster in your mixing container. It will help you know how fast your plaster is curing.

11. Do not dump wet plaster down the sink. It can harden in the pipes and cause major problems.

12. After excess plaster has dried, throw it away in the trash or pile it on your neighbor's studio desk.

aggregate ratios Varying the plaster to aggregate ratio noticeably changes the characteristics of the plaster. Generally speaking, adding aggregate to the plaster mix helps thicken and strengthen the plaster. In small doses, the aggregate has little effect on the finished plaster, whereas large quantities actually have a negative effect, making the plaster to thick to work with. Generally speaking, adding 2-3 parts aggregate in the plaster yields the best results. By the end of our process, we simply added the aggregate as we stirred until it reached the desired thickness

1 part aggregate

2 parts aggregate

3 parts aggregate

4 parts aggregate

reinforced plaster We tried several methods of reinforcing our plaster. In our first attempt, we used medical gauze. The plaster seemed to have a negative reaction to it, perhaps due to some coating on the gauze. It was difficult to make the plaster adhere well to the fibers, although once it cured, the gauze was able to hold the plaster together even after complete failure. The randomly oriented fiber strands produced a very strong slab, due mostly to the thickness and density of the fibers. This thickness however prevented us from producing a slab less than a quarter inch thick. In our third experiment, we used a wire screen to reinforce the plaster on our thin shell cave. The metal screen prevents tensile forces from cracking the thin plaster.

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1. Medical gauze 2. Randomly oriented fiber strands 3. Wire screen

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where to find plaster Relatively speaking plaster, like concrete, is a cheap and abundant material. Plaster is very susceptible to economics of scale, or the idea that purchasing in bulk saves money. You can purchase 8 pound containers of plaster at Hobby Lobby for about $5, or buy a 25 pound bag at Home Depot for $13. Fred Porteous in the wood shop told us that a 100 pound bag would only cost about $25. If you have a lot of work to do with plaster, such as an entire project devoted to concrete, buying in bulk is the way to go.

8 pounds - $0.62 per pound 25 pounds - $0.52 per pound 100 pounds - $0.25 per pound

model

overview Our model of the Dulles Main terminal building came with many challenges. The plaster was a very difficult material to work with, primarily due to its long curing time and its propensity to crack and break. Generally speaking, plaster is a good analogue to concrete, however working at a small scale proved difficult as many characteristics of concrete and plaster change at smaller scales.

roof system first attempt In our first attempt, we used two sheets of plexiglass to create each side of the form work. We braced the plexiglass with wood, and used 1/4 inch square dowels to space the form work. We drilled holes through these 1/4 inch pieces, stringing our reinforcement wires through them, hoping this would hold them in the center of the slab while the plaster was poured. Once we began pouring the plaster, we quickly noticed some serious deficiencies in our form work. The plexiglass was nowhere near strong enough to resist the pressure of the wet plaster, bowing and buckling severely. The plaster also caused all the reinforcing wire to shift positions and rust, leaving orange lines across our finished slab.

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Plexiglass form work, with reinforcement wires strung Detail of reinforcement wires and surface imperfections Underside of slab showing rusted wires. Top wire has been pulled out of the slab

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roof system second attempt For our second attempt, we strengthened out form work by adding 3 additional ribs to brace the plexiglass. We maintained the same pattern of wire reinforcement in an attempt to stay true to the actual structural system, hoping the stronger mold would allow us to focus on adjusting the wires properly while the plaster set. Our plaster mixture on this attempt proved to be poor quality, as our water was too warm and there was too much aggregate in the mix. Both these factors caused our plaster to set much faster than anticipated, leaving many bubbles and cracks. The thicker mix also distorted and shifted the wires, which once again rusted through the white plaster.

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1. Form work with additional bracing to support the plexiglass 2. Detail of surface imperfections and rusted wires 3. Second roof slab, showing displaced and rusted wires

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roof system third attempt After two unsuccessful attempts using wires to reinforce our plaster, we decided to try a pure plaster slab without any reinforcement. We also super-glued our plexglass sheets to the form work in an attempt to add some rigidity to the form work and prevent rippling, which was unsuccessful. The finished slab was severely rippled, but was free of any surface imperfections caused from bubbles in the mold. This slab was extremely fragile. After drying for two days, our slab broke while we were working with it. It quickly became apparent that our plaster must be reinforced.

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Broken Slab. All breaks occured simultaneously Form work and clamps immediately after striking Detail of slab, showing perfect glossy finish to plaster, despite the ripples on the right side

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roof system fourth attempt Our fourth attempt finally produced a slab with a uniform thickness free of the ripples caused from weak form work. We added a layer of 1/4 inch MDF to provide added strength to our form work, while maintaining the layer of plexiglass for a smooth surface finish. We use fabric instead of wires to reinforce our plaster, which produced a higher quality slab free of rust lines, however this came at the expense of model accuracy.

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Form work clamped together while plaster cures Detail of form work edges, using masking tape as release agent Bottom of form work, showing plexiglass/MDF combination

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columns The columns for our model presented an entirely different set of challenges. The columns supporting the roof at the Dulles Main Terminal are slender, graceful columns with chamfered corners that lean outward as they ascend. This required an accurate mold of a very elegant, sculptural form. In addition, the mold must be easily reused so we could cast multiple copies of the same form.

liquid latex molds Liquid latex is a common material for creating molds for intricate detail or complex shapes. It comes in a bottle as a thick paste with can be brushed or poured over an object to create a rubber mold. We began by shaping a column out of wood and cutting it in half. We then brushed 4 coats of liquid latex on each side, with a layer of gauze reinforcement between the 2nd and 3rd layers as recommended by the instructions. After about 24 hours, the liquid latex had dried and we were able to pull it off the wood, leaving 2 sides of a mold for the column. These latex molds were very flimsy and rather poor quality. After our experience with the plexiglass molds we used for the roof, it was clear these latex molds wouldn't support the plaster. We decided to abandon the latex and search for a better alternative.

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1. Wooden column and latex mold 2. Latex drying on top of wooden forms

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styrofoam column mold In our solution for casting the columns, we used a large block of styrofoam, cut in half. We used our wooden column form to imprint a negative mold of each side into the styrofoam. In our early tests we discovered that wet plaster would stick to the bare styrofoam, destroying the mold. To remedy this problem, we covered the area with duct tape to act as a release agent. This styrofoam method worked well because it was easy to reuse, allowing us to cast a new column every 60 minutes, but it lacked the precision we would have liked. The mold produced a very rough column form that required a lot of carving and sanding after the plaster had set. Because each individual column had to be hand worked after it was cast, our precision and accuracy from column to column was greatly diminished. In addition, once the plaster had cured completely, it became very difficult to work with, evident on several columns in our model. 1

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Pouring plaster mixture into mold Plaster curing with carriage bolt embedded to anchor column to base Styrofoam mold, immediately after striking Hand carving column after casting

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roof hangers The roof of the Dulles Main Terminal is suspended from either end by a large curved member that acts as a beam running along the tops of the columns. This section of the roof was constructed first in the actual building, but becase of our form work used for the model, we chose to add these pieces after the main roof had been cast. The sculptural shape and varying thickness of these pieces called for another intricate piece of form work that must be reusable.

plexiglass formwork We created the form work for these end pieces with a sheet of 1/8 inch plexiglass. Using an industrial heat gun, we were able to heat and bend the plexiglass into the hairpin section our model required. We had to use various pieces of scrap wood as form work in order to shape the soft plexiglass to our desired shape. After creating this piece, we clamped the form work around the roof slab and poured plaster into the mold.

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1. Heating the plexiglass 2. Formwork clamped to existing roof slab, ready for plaster 3. Using dowels and boards to shape the formwork

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speed curing Due to time constraints and the 8 hour set time for these fragile roof pieces, we were forced to speed up the curing process of our plaster. Plaster cures through a process known as hydration, in which the water reacts chemically with the dry plaster to activate it. As the water evaporates from the plaster, it hardens. Using a heat gun, we were able to raise the temperature of the plaster high enough to cause the water in the plaster to evaporate at a much quicker rate. We are unsure if affected the strength or quality of our plaster; It is possible this rapid curing weakened the plaster and led to more frequent breaks and cracks. It is interesting to note that the plaster, like concrete, has excellent thermal properties and did not show any obvious signs of stress or burning, despite the 1350 degree temperature reading on our heat gun (In comparison, the plexiglass we used for our molds only required 550 degrees to melt and deform).

drilling holes The columns at the Dulles Main Terminal building pass through large openings in the roof, adding to the effect that the roof is floating overhead. To recreate this we had to drill a series of holes into our completed roof slab to allow our columns to pass through. Plaster can be drilled or cut with a saw with relative ease, though the delicacy of our thin curved roof slab made this extremely challenging. During to process of making these holes, the slab cracked along the joint between the main slab and the two end pieces. At this point, there simply was not enough time to repeat the casting of the end pieces and we were forced to proceed without them, salvaging what we could.

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1. Using a power drill with a small hole saw bit to drill the holes in the slab 2. Typical column at Dulles.

conclusion The most difficult part of this model was assembling the components. Due to a lack of technical accuracy and precision in our form work, the pieces did not fit together properly. Once the plaster had fully cured, it became very difficult to work with, and even the most minor adjustments presented quite a challenge. Working with plaster, just like concrete, is a messy procedure. At full scale, the smallest imperfections can have huge impacts on a building. Working at 1:92 scale meant that these imperfections became magnified 92 times.