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.

NegativeMoment

PositiveMoment

Unidirectional Cantilever Design – Design Implications

Direction ofConstruction

• 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.

Materials:• Concrete• Masonry• Steel• Timber• Exotic Materials (composites)• Natural Materials

Components of Concrete:• Cement (8-15%)• Water (2-5%)• Aggregates (~80%)• Fine (sand)• Coarse (rock)

• Admixtures (0.1%)

Concrete

Strength

Filler

Manipulation ofFresh 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 BedCrushed

Limestoneand Clay

Raw MillGrinding into

powder

Filter BagDust removed

from kilnexhaust

PreheaterGases from Kiln

used to heatRaw materials

Rotating KilnCooking and mixingof the raw materials

1000o CLimestoneMelts intoburnt lime

2000o CFusion into

calcium silicatecrystals “clinker”

CoolerGoes to grinder

after this

40 – 50% of the CO2 produced comes from fuel combustion

50 – 60% of the CO2 produced comes from calcination of limestone

Calcination: CaCO3 (limestone) + Heat CaO (quick lime) + CO2

Worldwide cement production produces ~7% of CO2

emissions.

Cement Clinker

Grinder

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 CO2 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, OregonThe single worst source of Mercury emissions in the U.S.2,582 pounds reported emission in 2006.

Formwork

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 deckingacts as tension reinforcement for the bottom of a concrete slab

Polystyrene Foamacts 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

BrickUsed primarily for façades, but can be

used for load bearing elements

Ancient MasonryPre-Sumerian Civilization Mesopotamia~6,000 BCbeehive domes

Masonry – Typical Construction

Clay Masonry - Recycling

Autoclaved Aerated Concrete (AAC)