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Sustainability Definition: Meeting the needs of the present without compromising the ability of future generations to meet their own needs. First, ask.

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Presentation on theme: "Sustainability Definition: Meeting the needs of the present without compromising the ability of future generations to meet their own needs. First, ask."— Presentation transcript:

1 Sustainability Definition: Meeting the needs of the present without compromising the ability of future generations to meet their own needs. First, ask students to share what they think sustainability means – you may have to steer them to answer in terms of environmental sustainability. The provided definition is just one possible definition.

2 Sustainability ASCE: Sustainable development is the challenge of meeting human needs for natural resources, industrial products, energy, food, transportation, shelter and effective waste management while conserving and protecting environmental quality and the natural resource base essential for future development. From ASCE Policy Statement 418 (2000). The current version (available here: does not seem to have this wording.

3 Sustainability Thomas Jefferson (1789): The earth belongs to each of these generations during it's course, fully, and in their own right. The second generation receives it clear of the debts and encumbrances of the first, the third of the second and so on. For if the first could charge it with a debt, then the earth would belong to the dead and not the living generation. Letter to James Madison, September 6, 1789 “incumbrances” changed to reflect modern spelling, first, second, third originally 1st., 2d., 3d. I believe Jefferson was specifically talking about passage of monetary debt from one generation to the next, but I think this applies to sustainability as well. [MWR] Image Source: (emphasis added)

4 Resources that are being depleted
Land Fossil fuels Food Clean water (aquifers) Clean air Arable land Etc. Of course, virtually anything could be placed on this list, but it is a good exercise to have students to think of resources that are dwindling. It is important to point out that, no matter what their political inclinations or where they stand on “environmental” issues, they need to understand and “believe” that our current consumption habits are completely unsustainable. There really is no debate about this. Of course, nothing is truly sustainable, and they need to realize that also. But hopefully, by acting in a more sustainable way, society can slow down the rapid depletion of resources.

5 What can we do as structural engineers?
Structural Systems – particularly methods of construction Minimize the impact of the construction process on the environment Minimize contact with the ground (reduce footings, foundation size, etc.) Design for deconstruction Material Selection Understand environmental costs to manufacture materials Maximize lifespan/cost ratio – depends on initial environmental load of the material vs material life Select materials that can be recycled “Environmental Load” – a term used to encapsulate the total environmental impact of a material including the resources used up in processing the raw materials into a usable structural form, the resources necessary to maintain the material, and the pollution(s) created as part of the processing and maintenance activities.

6 LEED = Leadership Leadership in Energy and Environmental Design
LEED AP = LEED Accredited Professional Pass out the checklist and talk about MR (Materials and Resources) Credits

7 This slide should come after discussion of LEED.
Source: Sustainability Guidelines for the Structural Engineer SCMs = supplementary cementitious materials LEED-NC = LEED Guidelines for New Construction CMU = Concrete Masonry Unit (Do we need a picture?) FSC = Forest Stewardship Council VOC = Volatile Organic Compounds

8 Structural Systems – Example: Linn Cove Viaduct
One of the most complicated concrete bridges ever built Constructed from 1979 – Cost: $9.8 million Part of the Blue Ridge Parkway in North Carolina Snakes around Grandfather Mountain 1,243 ft long comprised from 153 weighing 50 T each Resources: A very good article on the construction from which many of these photos come: A blog entry – not much informational content, but several good photos of the completed bridge:

9 In order to protect the environment under the bridge, the structure was built as a unidirectional continuous cantilever. Segments of the bridge were cast 1 mile away and brought in using the constructed road deck. Most construction activities, equipment, and personal were restricted to the deck of the bridge. A conventional roadway would have used blasting and cut and fill to create the route. Grandfather Mountain was privately owned land and the owner would not consent to construction without protection of the natural environment. Grandfather Mountain contains about 70 varieties of endangered species.

10 Unidirectional Cantilever Design – Design Implications
Direction of Construction Negative Moment The purpose of this slide is to show that, as an implication of the method of construction used here, sections of the bridge must be designed to handle both large positive and negative design moments. Positive Moment

11 Note the existing trees all around the construction zone
Note the existing trees all around the construction zone. Very few trees were cut down or compromised during the construction. At the time it opened to traffic, travelers were able to see full grown trees all around the bridge. By elevating the roadway off of the natural ground, the engineers negated much of the environmental impact. Potential impacts of a grade level road would include loss of all the natural vegetation where the road was placed, interruption of animal paths and territorial bounds, and less control of pollution from the road surface ending up in the environment.

12 Even the piers were placed from the bridge deck
Even the piers were placed from the bridge deck. Shown is the placement of a pier segment.

13 The greatest challenge of the bridge was geometry control
The greatest challenge of the bridge was geometry control. No two segments of the bridge were alike. The bridge had three sequential horizontal curves, and changes in super-elevation that had to be cast into each segment.

14 Materials: Concrete Masonry Steel Timber Exotic Materials (composites)
Natural Materials Students can take (starter) courses in reinforced concrete design, steel design, and timber design. In graduate school, you would most likely have access to several advanced courses in reinforced concrete, prestressed concrete, steel, and possibly masonry design. Most of the content of these courses typically focuses on mechanical behavior with very little discussion of environmental impacts.

15 Concrete Components of Concrete: Cement (8-15%)
Water (2-5%) Aggregates (~80%) Fine (sand) Coarse (rock) Admixtures (0.1%) High Cost, High Environmental Impact Strength Filler Concrete is the most widely used construction material in the world – more than twice as much as all other materials combined (by weight). Most concrete is used in pavements. In buildings, it is almost always the material used for foundations. It is also almost always used for floor slabs in larger buildings. It is frequently used for building frames of such buildings too. Manipulation of Fresh Properties

16 Calcium Silicate in the cement reacts with water to form Calcium Hydroxide Crystal or Calcium Silicate Hydrate

17 40% 60% 75% 100% Concrete strength gain occurs continuously over the life of the concrete, but the rate of strength gain becomes negligible after about 28 days. Strength gain can be influenced by the type of cement used, environmental factors (heat and humidity), and admixtures. Cement type is a function of chemical composition and the grind of the particles (finely ground particles have more surface area and thus react faster). Depending on the application, a fast or slow strength gain may be desired. Fast strength gain is desired to be able to remove formwork and shoring as soon as possible. Fast strength gain also means a fast rate of chemical reaction. Since the chemical reaction is exothermic, this can result in very high temperatures being developed. In warmer climates, temperature control of the curing concrete is important because excessive heat gain can result in swelling that would damage the formwork or surrounding concrete or in extreme cases can result in chemical degradation of the cement paste.

18 1000o C 2000o C Preheater Gases from Kiln used to heat Raw materials
Filter Bag Dust removed from kiln exhaust 1000o C Limestone Melts into burnt lime 2000o C Fusion into calcium silicate crystals “clinker” Mixing Bed Crushed Limestone and Clay Dust captured in the filter bag will include a significant amount of Limestone and clay product that is returned to the raw material collection and pushed back into the kiln. Capturing the dust reduces somewhat the necessary mass of raw materials to produce cement as well as mitigating air pollution. Preheaters were not commonly used prior to In 1970, the Clean Air Act was passed and cement producers had to figure out what to do with their exhaust gases. They found they could use them to preheat the materials and save energy. About 20-40% of calcination will occur prior to entering the kiln. The fuel used in the kiln is generally fossil fuel. Sometimes recycled materials will be added such as old tires, used carpet, waste oil, solvents, sludge, and agricultural waste (such as almond shells) – basically anything burnable. Globally, about 10% of the energy necessary to fuel all cement kilns comes from recycled materials. The most environmentally friendly kilns use up to 70% recycled fuel. Rotating Kiln Cooking and mixing of the raw materials Cooler Goes to grinder after this Raw Mill Grinding into powder

19 Worldwide cement production produces ~7% of CO2 emissions.
50 – 60% of the CO2 produced comes from calcination of limestone 40 – 50% of the CO2 produced comes from fuel combustion The U.S. uses more cement than we produce. We import about $873 million worth of cement each year (mostly from Canada and Mexico, but China is a growing supplier). Between 1995 and 2006 global cement product rose by 80%. Almost half of all current global production occurs in China. Calcination: CaCO3 (limestone) + Heat  CaO (quick lime) + CO2



22 Cement Clinker

23 Grinder

24 Inside the Grinder Note the steel balls – these impact against the clinker and break it down. Clinker is blended with other raw materials (most commonly gypsum, fly ash, and blast furnace slag).

25 Every ton of cement produced creates about 0.9 tons of CO2 emissions
What can be done to reduce this? Use energy efficient production methods: dry kilns vs wet kilns horizontal kilns vs stacks Use recycled materials for fuel Add pozzolanic materials with clinker in the grinding process to make blended cements Older kilns tend to use wet processes to grind and feed the raw materials. They require more energy to produce clinker. Some very old kilns use vertical arrangements rather than horizontal for cement production. These kilns existed primarily in China but are being fazed out for more energy efficient technology. Pozzolans react with calcium hydroxide (CH) from cement hyrdation and additional water to create calcium silicate hydrate (C-S-H). C-S-H is stronger and more durable than CH but the reaction to create C-S-H takes longer so strength gain is slowed down. Common pozzolans include fly ash, silica fume, and blast furnace slag – all recycled products. New research in blending materials has focused on: ash from burning lignocellulosic material (e.g. rice husk), fly ash slag from municipal solid waste incineration, paper mill sludge ash, colemanite waste, and ceramic waste. The amount of blended materials added ranges from around 12% in the US to 30% in Europe. It largely depends on availability and quality of blendable materials. It seems that Brazil utilizes the most blended materials in their cements.

26 Note that the U.S. is the world’s leader in carbon dioxide emission from cement production and failed to make any improvements throughout the 1990’s, whereas both China and India made substantial improvements.

27 We can also reduce how much cement we use in our concrete:
Concrete strength depends on water/cement ratio Fresh concrete fluidity depends on water content To create a fluid, yet strong mix, high cement content must be used Reduce the water requirement (and thus cement requirement) by using admixtures to achieve fluidity

28 Cement production also creates large amounts of mercury emissions:
Mercury is present in the raw materials (limestone) and many of the recycled fuels used to fire the kiln. Cement production creates about 8% of Canada’s mercury emissions. The U.S. only recently set limits on mercury emissions which won’t fully take effect until 2013. Mercury is emitted from the kiln in solid (particulate) and gaseous forms. The solids are generally captured by the filter bag, but the gases escape. Most emitted mercury comes from the limestone, however as more recycled fuels are used, we can expect to see more mercury emissions from that source. Some resources:

29 Cement Factories in the U.S.
Ash Grove Cement Plant in Durkee, Oregon The single worst source of Mercury emissions in the U.S. 2,582 pounds reported emission in 2006. The limestone around Durkee as higher concentrations of mercury than typical limestone, hence the higher emissions. The Durkee plant came online in 1979 and has a single kiln that produces about 900,000 tons of cement a year. The Ash Grove plant had listed emissions of 281 lb in A permit writer named Patty Jacobs decided to check the math of the Durkee plants estimates and found that it did not make sense, so she challenged the reporting. The reported emissions jumped by about a factor of 10 after immediately after that. The plant shut down and installed much better emission controls. Ash Grove shut down a number of other plants and did the same. They now advertise their sustainability efforts. The actual emissions at the Durkee plant may have been as high as 3,788 lbs. The next highest cement kiln emitter was in Colton, CA at 654 lbs. Only 8 kilns in the U.S. reported more than 400 lbs of mercury emissions in Were the others really so much less or did they not get caught like the Durkee plant? Cement Factories in the U.S.

30 Formwork The photo on the left shows plywood forming used for a drop panel around the top of a concrete column. The photo on the right shows a worker installing an aluminum form for a wall panel. Which is greener? Waste created by formwork is a substantial impact from concrete production. From an economic perspective, formwork can be 20 – 40% of the material cost depending on the re-usability of the forms.

31 Formwork – Re-usability
Use repetition of structural shapes and sizes Use metal or plastic forms which have longer life than wood Use construction grade lumber which is more durable and can be re-used more often Use non-toxic form release agents to prevent damage to the form surface Use formwork connections / attachments that are easily disassembled with no damage to the form material

32 … or use stay-in-place forms
Steel decking acts as tension reinforcement for the bottom of a concrete slab Stay in place forms eliminate landfill waste and can often serve a useful purpose in the finished structure

33 acts as exterior insulation for basement concrete basement walls
Polystyrene Foam acts as exterior insulation for basement concrete basement walls Another example that isn’t shown is to use precast concrete panels as decking or as wall forms. The precast panels can be fabricated as a plant with high-quality re-usable forms and then be used at the job site with cast-in-place concrete.

34 … or use precast concrete
Precast concrete is fabricated at a plant where high-quality forms can be used repeatedly to create common building elements.

35 Concrete Masonry Units (CMU)
Masonry along with timber (including reed construction) is the oldest building material in human history. Because timber is less long-lived, most ancient structures are by default masonry structures. The oldest discovered bricks date back to 7,500 BC. Masonry structures can be extremely durable. CMU is a concrete product, typically with smaller aggregate sizes. Units are cast and fast cured in an environmental chamber. All of the previous discussion of the environmental consequences of cement production applies here. CMU has the advantage that no forming is necessary (though occasionally some exterior bracing or support will be necessary). However its structural use is generally limited to walls. CMU is relatively recent Brick is most commonly manufactured from clay (though shale or other materials may be used. Ancient clay brick was typically simply dried mud. Unfired brick (made simply by drying the material) is very weak and erodes easily if exposed to water. Firing brick makes it weather resistant and greatly improves the strength. The oldest fired bricks are from China and date back 3,800 years ago. Modern clay brick is typically composed of: Silica (sand) - 50% to 60% by weight Alumina (clay) - 20% to 30% by weight Lime - 2 to 5% by weight Iron oxide - 5 to 6% (not greater than 7%) by weight Magnesia - less than 1% by weight The mix is compressed into a mold using a hydraulic press or extruded from a mold. Compressing the raw material increases the density and ensures clean edges in the shape. “Green” bricks are then fired in a kiln at 900 – 1000 oC. The energy efficiency of the firing process depends on the shape of the kiln and the way in which the bricks are stacked (they should be stacked to allow air flow around as much of the surface as possible). Clay brick is often not used for structural applications because the smaller size of the units increases the labor involved in construction. However, it is frequent to encounter it in older structures (or even old pavements). Concrete Masonry Units (CMU) Useful for load bearing elements such as shear walls Brick Used primarily for façades, but can be used for load bearing elements

36 Ancient Masonry Pre-Sumerian Civilization Mesopotamia ~6,000 BC
beehive domes These show some examples of ancient masonry. Brick making was a substantial part of the Sumerian economy. The Sumerians primarily used dried brick, though they did discover how to fire brick during the course of their civilization. The only way to fire brick at that time was by using timber for fuel. Since timber was a limited commodity in Mesopotamia, the Sumerians did not fire a large percentage of their brick. Rather they limited the use of fired brick to the lower courses of their large buildings (where the stresses were highest) and then used dried brick for the upper courses. Thus we have an ancient example in which limited resources affected structural design much as they might today.

37 Masonry – Typical Construction
These figures are meant to represent some elements of typical masonry construction. Clockwise starting top right: This shows a typical reinforced CMU wall. In addition to the CMU units, steel reinforcing bars have been added and the cells that are reinforced are grouted. The grout is a mixture of cement water and sometimes sand. This shows a typical double wythe wall with CMU on the interior and clay brick as an exterior façade. Because of the clay bricks weather resistance, this wall will likely be highly durable. Additionally, this type of construction offers two energy efficiency benefits. First, the wall has a very high R value so outside temperature fluctuations have less impact on the interior of the structure. Second, the wall has a high thermal mass, so that stored heat (or cold) within the mass will also help to ease out the effect of temperature fluctuations. Lastly, the picture also shows a typical façade connector. These types of elements will be made of steel and are necessary for proper masonry façade performance. The last picture shows a more complete structural wall system. This figure includes insulation between the interior and exterior wythes of the wall, horizontal masonry reinforcement, bond beams, and a joist connection where a floor would be supported by the wall.

38 Clay Masonry - Recycling
Clay brick has a relatively high recycle value and is commonly salvaged from building demolitions for use in future buildings. Top left – Pallets of salvaged brick. Traces of mortar are evident. Right – Recycled brick used in a wall. Aesthetics are a concern when materials are recycled. Lower left – Pieces of recycled brick used in gabions. Gabions are blocks made from rock or similar materials enclosed in chain link. They are common for retaining wall applications.

39 Autoclaved Aerated Concrete (AAC)
This is considered another type of masonry. It was invented in the 1920’s but has only recently started to see applications in the U.S. From Wikipedia: AAC is produced using no aggregate larger than sand. Quartz sand, lime, and/or cement and water are used as a binding agent. Aluminum powder is used at a rate of 0.05%–0.08% by volume (depending on the pre-specified density). When AAC is mixed and cast in forms, several chemical reactions take place that give AAC its light weight (20% of the weight of concrete) and thermal properties. Aluminum powder reacts with calcium hydroxide and water to form hydrogen. The hydrogen gas foams and doubles the volume of the raw mix (creating gas bubbles up to ⅛ inch in diameter). At the end of the foaming process, the hydrogen escapes into the atmosphere and is replaced by air. When the forms are removed from the material, it is solid but still soft. It is then cut into either blocks or panels, and placed in an autoclave chamber for 12 hours. During this steam pressure hardening process, when the temperature reaches 374° Fahrenheit (190° Celsius) and the pressure reaches 8 to 12 bars, quartz sand reacts with calcium hydroxide to form calcium silica hydrate, which accounts for AAC's high strength and other unique properties. After the autoclaving process, the material is ready for immediate use on the construction site. Depending on its density, up to 80% of the volume of an AAC block is air. AAC's low density also accounts for its low structural compression strength. It can carry loads up to 1,200 PSI, approximately only about 10% of the compressive strength of regular concrete. The softness of AAC gives it limited structural application, but it has been used successfully in low-rise structures. The softness has construction benefits since the material can be easily worked using a variety of common tools for cutting and drilling. Wikipedia lists four environmental benefits to AAC: The high insulation value which reduces the need for added insulation materials thus reducing resource consumption. Its workability which reduces construction waste. The high air content means that less material resources are used to manufacture the product. The low weight reduces transportation costs.

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