LCA and LCC of the World’s Longest Pier · LCA and LCC of the World’s Longest Pier A Case Study...
Transcript of LCA and LCC of the World’s Longest Pier · LCA and LCC of the World’s Longest Pier A Case Study...
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LCA and LCC of the World’s
Longest PierA Case Study on Stainless Steel Rebar
LCAXIII Conference, Orlando, FLOctober 2, 2013
PE INTERNATIONAL Nick SanteroSophia Wong
Nickel Institute Mark Mistry
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Progreso Pier, MexicoA Compelling Case Study
Source: Nickel Institute
2
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Progreso Pier, Mexico
3
• Longest pier in the world
• Built in 1941 at a length of 2100
meters
• Extended in 1988 to 4000
meters
• Innovative design
• One of the first major civil
engineering structures to use
stainless steel rebar
• Resilient construction
• No significant maintenance has
been performed
Image Source: Castro-Burgess et al.
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It’s All About the Rebar
• Provides tensile strength to
reinforced concrete structures
• Common rebar is made of
unfinished tempered steel (i.e.,
carbon or black steel) making it
susceptible to corrosion
• More corrosion-resistant: epoxy-
coated, galvanized or stainless
steel
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What if the Progreso Pier was
built using carbon steel
rebar?As-built design
(stainless steel rebar)Alternative design
(carbon steel rebar)
Unit costs
Unit environmental
impacts
Service life
Maintenance schedule
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What if the Progreso Pier was
built using carbon steel
rebar?As-built design
(stainless steel rebar)Alternative design
(carbon steel rebar)
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What if the Progreso Pier was
built using carbon steel
rebar?As-built design
(stainless steel rebar)Alternative design
(carbon steel rebar)
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Comparison: DesignsAs-built Design (stainless steel rebar) Alternative Design (carbon steel rebar)
• Materials
• Concrete: 72,500 m3
• Stainless steel rebar: 220 tons
• Maintenance: to be determined
• Service life: to be determined
• Materials
• Concrete: 72,500 m3
• Carbon steel rebar: 220 tons
• Maintenance: to be determined
• Service life: to be determined
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Comparison: MaterialsStainless Steel Rebar Carbon Steel Rebar
2.30
0
5
10
GW
P [
kg
CO
2-e
q/k
g]
7.40
0
5
10
GW
P [
kg
CO
2-e
q/k
g]
25.8
0
50
100
150
PE
D [
MJ/
kg
]106
0
50
100
150
PE
D [
MJ/
kg
]
Price (2013$):
$6.59/kg
Price (2013$):
$0.99/kg
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• Comparative assertion
• Both designs serve the equivalent function
• Stainless and carbon steel: same structural characteristics
• Limited to the original 2100 meter pier (i.e., does not include 4000 meter extension)
• Analysis period
• 79 years (1941–2020)
• Provides estimate of past (1941–2013) and future (2013–2020) performance
• System boundaries
• Included: materials, transportation, maintenance, and end-of-life fates
• Excluded: construction, use, and demolition
• Analysis methods
• Life cycle assessment (LCA) using GaBi (ISO 14040 series)
• Life cycle costing (LCC) using Life-365 and Excel (ISO 15686-5)
Methodology: Overview
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Concrete mix design
Reinforcing steel type
Depth of cover
Exposure
Climate
Methodology: Service Life
1102.10.2013
• Life-365 model
• Service life prediction
model
• Specific to reinforced
concrete structures
• Engineering analysis
• Performed by CTLGroup
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Service Life
As-built Design
(stainless steel rebar)
Alternative Design
(carbon steel rebar)
Time to corrosion initiation and propagation: 44 Years
Service life: 84 Years
Choride concentration threshold: 0.70% by
weight
Time to corrosion initiation and propagation: 10 Years
Service life: 50 Years
Choride concentration threshold: 0.05% by
weight
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Methodology: Maintenance
Initial
Construction
10% Repair
15% Repair
20% Repair
Reconstruction
Year
Ti+p
Ti+p
+ 15
Ti+p
+ 30Ti+p
+ 40
2Ti+p
+ 40…
10% Repair
0
• Ti+p = time (years) to corrosion initiation and propagation of the rebar
• Service life and maintenance definitions follow United States Navy's engineering command (NAVFAC)
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Maintenance
Initial
Construction
10% Repair
15% Repair
20% Repair
0 79745944
0 79
Initial
Construction
10% Repair
15% Repair
20% Repair
Reconstruction
10% Repair
15% Repair
10 25 40 50 60 75
As-built Design
(stainless steel rebar)
Alternative Design
(carbon steel rebar)
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Breakdown of material contributions – initial construction
LCA Results
0
10
20
30
40
50
Progreso Pier Carbon Steel
Rebar Alternative
40.639.6
Global Warming Potential
[million kg CO2-eq]
0
50
100
150
200
250
Progreso Pier Carbon Steel
Rebar Alternative
Primary Energy Demand
[million MJ]
222
205
15
As-built design Alternative
design
As-built design Alternative
design
Concrete
Stainless
steel
Carbon steel
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Total environmental impacts over 79-year analysis period
LCA Results
Impact relative to As-built Design
16
0%
50%
100%
150%
200%
AP EP GWP ODP POCP PED
As-built Design
Alternative Design
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Global Warming Potential [million kg CO2-eq]
LCA ResultsComparison of GWP over 79-year analysis period
17
0
20
40
60
80
100
120
1940 1950 1960 1970 1980 1990 2000 2010 2020
Year
Alternative Design
As-built Design
Construction/Maintenance/Reconstructio
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• Follows same concepts as life cycle assessment
• Cost data collected for individual activities
• Analyzed over the product life cycle
• Major difference between LCC and LCA is the consideration of the time
• Future costs are discounted using the discount rate
• Discount rate is variable and uncertain
One-slide crash course
Life Cycle Costing (LCC)
Where: P = analysis period
n = year, ranging from 0 to P
Cn = cost incurred in year n
i = discount rate
RV= residual value
PP
n
n
ni
RVi
CNPV
)1(
1
)1(
1
0
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Discount Rate of 0.01% (recommended by SETAC)
Life Cycle Costing Results
Net Present Cost [thousand 1941 USD]
19
0
250
500
750
1000
1940 1950 1960 1970 1980 1990 2000 2010 2020
Year
Alternative Design
As-built Design
Construction/Maintenance/Reconstructio
n
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LCC is sensitive to discount rate
Life Cycle Costing
*Source: EU Guidance Document on LCC (2007)
5%
4%
3%
2%
1%
0%
• EU: National ministries of finance specify the discount rates
to be used in the economic analysis of publicly funded
projects. These typically fall into the range of 3 to 5%
• EU: “Use of a low (3% or less) or even a zero rate is
recommended when LCC is used to assess the economic
merits of alternative sustainability options.”*
• US Circular A94 currently uses 1.1% based on the 30-year
bond
• US Navy reports 0%, 1%, and 2.3%
• SETAC: 0.01% discount rate for long-term investments (over
30 years)
20
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Sensitivity to the discount rate
Life Cycle Costing
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• The rebar material is a small part of the overall life cycle impact
• Concrete is dominant source of environmental and economic impacts
• Structural performance and service life are key considerations
• As-built structure (stainless steel rebar) has lower life cycle impacts
• Higher environmental impacts per unit of stainless steel outweighed by benefits related to corrosion resistance
• Significant differences across all considered impact categories
• As-built structure has lower life cycle costs
• Higher environmental impacts per unit of stainless steel outweighed by benefits related to corrosion resistance
• Sensitive to the choice in discount rate
Conclusions
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• Construction/deconstruction
activities not included
Final Notes
Future activities are under-
characterized
Consideration Influence
• Temporal
representativeness is weakSimilar uncertainty between
each design
Study currently undergoing peer review
• Results are specific to the
Progreso Pier case study
Sweeping conclusions regarding stainless steel rebar are not proposed