Presentation on theme: "Sustainability Definition: Meeting the needs of the present without compromising the ability of future generations to meet their own needs."— Presentation transcript:
Sustainability Definition: Meeting the needs of the present without compromising the ability of future generations to meet their own needs.
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.
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. (emphasis added)
Resources that are being depleted Land Fossil fuels Food Clean water (aquifers) Clean air Arable land Etc.
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 What can we do as structural engineers?
Structural Systems – Example: Linn Cove Viaduct One of the most complicated concrete bridges ever built Constructed from 1979 – 1982 ----- 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
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.
Negative Moment Positive Moment Unidirectional Cantilever Design – Design Implications Direction of Construction
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.
Components of Concrete: Cement (8-15%) Water (2-5%) Aggregates (~80%) Fine (sand) Coarse (rock) Admixtures (0.1%) Concrete Strength Filler Manipulation of Fresh Properties High Cost, High Environmental Impact
Calcium Silicate in the cement reacts with water to form Calcium Hydroxide Crystal or Calcium Silicate Hydrate
40% 60% 75% 100%
Mixing Bed Crushed Limestone and Clay Raw Mill Grinding into powder Filter Bag Dust removed from kiln exhaust Preheater Gases from Kiln used to heat Raw materials Rotating Kiln Cooking and mixing of the raw materials 1000 o C Limestone Melts into burnt lime 2000 o C Fusion into calcium silicate crystals “clinker” Cooler Goes to grinder after this
40 – 50% of the CO 2 produced comes from fuel combustion 50 – 60% of the CO 2 produced comes from calcination of limestone Calcination: CaCO 3 (limestone) + Heat CaO (quick lime) + CO 2 Worldwide cement production produces ~7% of CO 2 emissions.
Inside the Grinder
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 What can be done to reduce this? Every ton of cement produced creates about 0.9 tons of CO 2 emissions
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 We can also reduce how much cement we use in our concrete:
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. Cement production also creates large amounts of mercury emissions:
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.
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
… or use stay-in- place forms Steel decking acts as tension reinforcement for the bottom of a concrete slab
Polystyrene Foam acts as exterior insulation for basement concrete basement walls
… or use precast concrete
Masonry 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
Ancient Masonry Pre-Sumerian Civilization Mesopotamia ~6,000 BC beehive domes