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 [email protected]
