Sustainability: What does it mean for Civil Engineers?

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Sustainability: What does it mean for Civil Engineers?
Sustainable Design Checklist1
Tables 1-4 below can be used to evaluate sustainability aspects of design alternatives. Each table
contains a number of yes/no questions. If the answer to a question is “yes” for an alternative, put a 1 in
the column for that alternative. If the answer to a question is “no,” put a 0 in the column for that
alternative. For example, a question in Table 1 is “Are the materials locally available?” If Alternative A
would be made from concrete, and cement is locally available, you would put a “1” in Alternative A’s
column. If Alternative B would be made from asphalt, and asphalt is not locally available, you would put
a “0” in Alternative B’s column. In some cases, both options may have a “1” and in some cases, both
options may have a “0.”
Qualitative measures, such as “low amount” or “minimal impact,” can be assessed relative to the other
alternative. For example, if Alternative A requires a lower amount of energy to produce compared with
Alternative B, it would be given a “yes” for “Do the materials require a low amount of energy to
produce/acquire?,” and Alternative B would be given a “No.”
If you have no basis to evaluate a certain question, leave it blank.
Once you’ve assigned “1”s and “0”s to all responses, add the total points for Alternative A and
Alternative B. The alternative with the higher number of points is more environmentally friendly. This
information can be used along with cost, safety, and other factors in choosing between Alternatives A
and B.
1
UT Arlington “Engineering Sustainable Engineers”, funded by the National Science Foundation.
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Table 1. MATERIALS PRODUCTION/ACQUISITION
Sustainability
Metric
a. Material
use
Yes/No Questions
Alt. A
Alt. B
Does the design utilize recycled or reclaimed materials?
Does the design utilize renewable resources (i.e. wood)?
b. Energy use
Do the materials require a low amount of energy to
produce/acquire?
Are the materials locally available, minimizing energy
needed for transport?
c. Water use
Do the materials require a low amount of water to
produce/acquire?
d. Solid waste
generation
Does material production/acquisition produce a low
amount of solid waste?
e. Emissions
generation
Does materials production produce a low amount of air
pollution emissions?
f. Toxic
releases
Is the material non-toxic, which would generally lower the
potential for toxic releases?
g. Land
Impact
Does material production/acquisition and transport
produce minimal impact on plants, animals, and
ecosystems?
Other
Specify:
TOTAL Points
Yes = 1, No = 0
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Table 2. CONSTRUCTION
Sustainability
Metric
a. Material
use
b. Energy use
Yes/No Questions
Alt. A
Alt. B
N/A
Are construction techniques chosen to minimize energy
use?
Is the construction equipment energy efficient?
c. Water use
Does the construction process require a low amount of
water?
d. Solid waste
generation
Does the construction process produce a low amount of
solid waste that must be landfilled?
e. Emissions
generation
Does the construction equipment have air pollution
controls or use alternate fuels?
Are particulate control measures (such as watering exposed
soil) used during the construction process?
Are low VOC paints, adhesives, and cleaners used in the
construction process?
f. Toxic
releases
g. Land
Impact
N/A
Other
Specify:
Does the construction site have stormwater pollution
controls, such as silt fences?
TOTAL Points
Yes = 1, No = 0
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Table 3. USE
Sustainability
Metric
a. Material
use
b. Energy use
Yes/No Questions
Alt. A
Alt. B
Will maintenance require a low amount of materials?
Does the design use less energy than alternatives, via
insulation, energy efficient lighting, etc.?
Does the design use renewable energy, like solar?
c. Water use
Does the design use less water than alternatives?
Does the design avoid producing water pollution?
d. Solid waste
generation
Does the design have a longer lifespan than alternatives?
Does the design produce a low amount of solid waste
during use?
e. Emissions
generation
Will the use generate a low amount of air pollutant
emissions?
f. Toxic
releases
Will the use generate toxic pollutants that will be emitted
into the air?
g. Land
Impact
Will the use generate toxic pollutants that will be
discharged into the water?
Will the design use a low amount of land space?
Does the design minimize impervious cover/pavement?
Does the design minimize stormwater runoff and
pollution, and avoid exacerbating flooding?
Does the design produce minimal impacts on plants,
animals, and ecosystems?
Other
Specify:
TOTAL Points
Yes = 1, No = 0
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Table 4. DEMOLITION
Sustainability
Metric
a. Material
use
b. Energy use
c. Water use
d. Solid waste
generation
Yes/No Questions
Alt. A
Alt. B
N/A
N/A
Are the materials recyclable or re-usable?
Can different kinds of materials be easily separated for
recycling/re-use?
Will demolition produce a low amount of solid waste?
e. Emissions
generation
f. Toxic
releases
Will demolition generate a low amount of air pollutant
emissions?
Will the waste generated contain hazardous substances
that could pollute landfill leachate?
g. Land
Impact
Other
N/A
Specify:
TOTAL Points
Yes = 1, No = 0
Table 5. ALTERNATIVE POINT SUMMARY
Number of Points
Alt. A
Number of Points
Alt. B
Table 1
Table 2
Table 3
Table 4
TOTAL
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Homework Assignment: Materials Selection Using the Sustainable Design Checklist
You are an engineer charged with deciding between asphalt concrete (AC) and continuously
reinforced Portland cement concrete (CRPCC) for an arterial roadway surface. You’ve already done
most of your evaluation (costs, safety, etc.); the environmental evaluation remains. **Note: In some
cases, data is presented for engineered cementious concrete (ECC), but you may ignore that option in
this analysis. Also note that the materials acquisition and construction are presented as two separate
phases.
Using Tables 1-4 above, the information given below, compare the environmental impacts of asphalt
concrete vs. Portland cement concrete.
Asphalt, a component of crude petroleum, is used as a glue or binder for aggregate particles. Asphalt
pavement (or asphalt concrete) is typically 5% asphalt cement binder and 95% aggregates.
Portland cement, mixed with water, is used to bind aggregate together to form cement concrete.
Typically, around 20% cement and water is mixed with 80% aggregate.
Materials Acquisition/Production Phase
A comparison of the materials used in asphalt concrete and continuously reinforced Portland cement
concrete are shown below.
Pavement Type
Asphalt concrete
Material Components
Aggregates (sand, gravel,
and/or crushed stone)
Asphalt binder
Aggregates (sand, gravel,
and/or crushed stone)
Portland cement
Continuously
reinforced
concrete
(Portland cement
concrete)
Water
Steel rebar
Raw Materials
Rock, sand
Crude oil
Rock, sand
Iron ore, shale, clay,
limestone, gypsum
Water
Steel scrap
Although crude petroleum is a non-renewable resource, asphalt can be recycled. In fact, asphalt road
surface is the most widely recycled material in the US, both by gross tonnage and by percentage.
According to the Federal Highway Administration and Environmental Protection Agency, 80% of the
asphalt from road surfaces that is removed each year during widening and resurfacing projects is reused
as part of new roads, roadbeds, shoulders and embankments.
Cement is made by heating limestone (calcium carbonate), with small amounts of other materials (such
as clay, iron ore, or shale) to a very high temperature, 1450°C, in a kiln. The resulting hard substance,
called “clinker”, is then ground with a small amount of gypsum into a powder to make Portland Cement,
the most commonly used type of cement.
Heating the limestone in the kiln requires a substantial amount of energy, and also releases carbon
dioxide (CO2), a greenhouse gas, from the calcium carbonate. In fact, the cement industry produces
about 5% of global anthropogenic CO2 emissions, of which 50% is from the chemical process, and 40%
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from burning fuel. Most cement kilns today burn coal and petroleum coke as primary fuels (which are
non-renewable resources), although they can also burn waste materials, such as shredded tires. The
amount of CO2 emitted by the cement industry is nearly 900 kg of CO2 for every 1000 kg of cement
produced.
Asphalt and Portland cement concrete can incorporate recycled materials. Cement can contain up to
30% fly ash from coal-fired utility boilers and other sources. It is estimated that around 75% of Portland
Concrete Cement pavements is recycled, and 45% of steel rebar used in reinforced concrete is recycled.
Reinforcing steel is produced almost entirely from steel scrap.
Dust and noise result from quarrying for limestone to make Portland cement. Removal of vegetation
from the quarry surface is an additional environmental impact.
According to a study by Rajendran and Gambatese (2007), asphalt concrete generates more solid waste
during the materials acquisition/production phase compared with Portland cement concrete.
Construction Phase
According to a study by Rajendran and Gambatese (2007), CRPCC produces more solid waste during the
construction phase, compared with AC. According to a study by Zapata and Gambatese (2005),
constructing PCC roadways uses more energy than constructing AC roadways.
The table below compares the energy and time requirements (in hours) for equipment used in the
construction of concrete, engineered cementious concrete (ECC) and hot mix asphalt (HMA) surfaces. 2
2
Source: Zhang, Han (2009). “Sustainable Pavement Asset Management Based on Life Cycle Models and
Optimization Methods”. Available online: http://css.snre.umich.edu/css_doc/CSS09-14.pdf.
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Use Phase
Maintenance and operation of PCC and AC roadways uses about equal amounts of energy.
Some studies suggest that AC pavements have longer lives, while other studies suggest that CRC
pavements have longer lives. The figure below provides one comparison of maintenance schedules for
concrete, ECC and HMA overlays. 3
Asphalt releases bitumen fumes, which contain volatile organic compounds, particularly polycyclic
aromatic hydrocarbons, which can be harmful to human health.
Demolition
Asphalt concrete generates more solid waste during the demolition phase compared with continuously
reinforced Portland cement concrete (Rajendran and Gambatese, 2007).
3
Source: Zhang, Han (2009). “Sustainable Pavement Asset Management Based on Life Cycle Models and
Optimization Methods”. Available online: http://css.snre.umich.edu/css_doc/CSS09-14.pdf.
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All Stages
The figures below show estimated (1) energy consumption, (2) emissions of common air pollutants and
(3) water pollutant discharges for concrete, ECC and HMA during each life cycle stage. 4
(1): Energy Consumption
Figure (2): Air Pollutant Emissions
4
Source: Zhang, Han (2009).
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Figure (3): Water Pollutant Discharges
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