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ref19 case study of progreso pier

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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
2
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.
3
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
02.10.2013
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
15
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
16
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
17
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)
20
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
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