LCA and LCC of the World’s Longest Pier A Case Study on Stainless Steel Rebar LCAXIII Conference, Orlando, FL October 2, 2013 PE INTERNATIONAL
Nick Santero Sophia Wong
Nickel Institute
Mark Mistry
Progreso Pier, Mexico A Compelling Case Study
Source: Nickel Institute
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Progreso Pier, Mexico • 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: epoxycoated, galvanized or stainless steel
What if the Progreso Pier was built using carbon steel rebar? As-built design (stainless steel rebar)
Alternative design (carbon steel rebar)
Maintenance schedule
Unit environmental impacts
Service life
Unit costs
What if the Progreso Pier was built using carbon steel rebar? As-built design (stainless steel rebar)
Alternative design (carbon steel rebar)
What if the Progreso Pier was built using carbon steel rebar? As-built design (stainless steel rebar)
Alternative design (carbon steel rebar)
Comparison: Designs As-built Design (stainless steel rebar)
• Materials • Concrete: 72,500 m3 • Stainless steel rebar: 220 tons
Alternative Design (carbon steel rebar)
• Materials • Concrete: 72,500 m3 • Carbon steel rebar: 220 tons
• Maintenance: to be determined
• Maintenance: to be determined
• Service life: to be determined
• Service life: to be determined
Comparison: Materials Stainless Steel Rebar
Carbon Steel Rebar
Price (2013$): $6.59/kg
150
0
106 100
50
0
150 PED [MJ/kg]
5
10 GWP [kg CO2-eq/kg]
7,40
PED [MJ/kg]
GWP [kg CO2-eq/kg]
10
Price (2013$): $0.99/kg
5 2,30
0
100
50 25,8 0
Methodology: Overview • 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: Service Life Concrete mix design
• Life-365 model • Service life prediction model
• Specific to reinforced concrete structures
Climate
Reinforcing steel type
• Engineering analysis • Performed by CTLGroup
Exposure
09.10.2013
Depth of cover
11
Service Life Choride concentration threshold: 0.70% by weight Time to corrosion initiation and propagation: 44 Years Service life: 84 Years As-built Design (stainless steel rebar)
Alternative Design (carbon steel rebar)
Choride concentration threshold: 0.05% by weight Time to corrosion initiation and propagation: 10 Years Service life: 50 Years
Methodology: Maintenance Reconstruction
Initial Construction
20% Repair 15% Repair 10% Repair
10% Repair Year
0
Ti+p
Ti+p + 15
Ti+p + 30
Ti+p + 40
2Ti+p + 40
• 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)
…
Maintenance 20% Repair
Initial Construction
15% Repair 10% Repair
0
59
44
As-built Design (stainless steel rebar)
74
79
75
79
Alternative Design (carbon steel rebar)
0
10
25
40
50
10% Repair Initial Construction
15% Repair
60 10% Repair
Reconstruction 20% Repair
15% Repair
LCA Results Breakdown of material contributions – initial construction 50
Global Warming Potential [million kg CO2-eq]
250
Primary Energy Demand [million MJ] 222
40.6 40
39.6
205 200
30
150
20
100
10
50
0
0 As-built design Progreso Pier
Alternative Carbon Steel design Rebar Alternative
Stainless steel
Carbon steel
Concrete
As-built design Progreso Pier
Alternative Carbon Steel Rebardesign Alternative
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LCA Results Total environmental impacts over 79-year analysis period Impact relative to As-built Design 200%
150%
As-built Design
100%
Alternative Design 50%
0% AP
EP
GWP
ODP
POCP
PED
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LCA Results Comparison of GWP over 79-year analysis period Global Warming Potential [million kg CO2-eq] 120 100 80
Alternative Design As-built Design Construction/Maintenance/Reconstructio
60 40 20 0 1940
1950
1960
1970
1980 Year
1990
2000
2010
2020
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Life Cycle Costing (LCC) One-slide crash course • Follows same concepts as life n
1 1 − RV NPV = ∑ Cn n =0 (1 + i ) (1 + i ) P
Where: P = n = Cn = i = RV=
analysis period year, ranging from 0 to P cost incurred in year n discount rate residual value
P
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
Life Cycle Costing Results Discount Rate of 0.01% (recommended by SETAC) Net Present Cost [thousand 1941 USD] 1000 Alternative Design As-built Design 750
Construction/Maintenance/Reconstructio n
500
250
0 1940
1950
1960
1970
1980 Year
1990
2000
2010
2020
19
Life Cycle Costing LCC is sensitive to discount rate
5% 4% 3%
• 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.”*
2%
• US Circular A94 currently uses 1.1% based on the 30-year
1%
• US Navy reports 0%, 1%, and 2.3%
0%
• SETAC: 0.01% discount rate for long-term investments (over
bond
30 years)
*Source: EU Guidance Document on LCC (2007)
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Life Cycle Costing Sensitivity to the discount rate
Conclusions • 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
Final Notes Consideration
Influence
• Construction/deconstruction
Future activities are undercharacterized
activities not included
• Temporal representativeness is weak
• Results are specific to the Progreso Pier case study
Similar uncertainty between each design Sweeping conclusions regarding stainless steel rebar are not proposed
Study currently undergoing peer review
Contact Nick Santero, Ph.D., P.E. Senior Consultant n.santero@pe-international.com