Cement's Carbon Impact

• 100-meter, 30-story skyscraper contains ~6,000 tons cement
• Cement production emits ~4,600 metric tons CO2 (equivalent to driving 12 million miles)
• Cement accounts for 8% of global carbon emissions
  • More than aviation + shipping industries combined
• China produced more cement in 2 years than US did in entire 20th century
• Other developing countries will increase cement use for infrastructure

Cement Production Process & Emissions Sources

• Cement plant components: rotating kiln + preheater tower
• 40% emissions from fuel burning to heat kiln to 1,450°C
• 60% emissions from chemical process
  • Limestone heated to 850°C releases stored CO2
  • Creates clinker (key binding ingredient)
• Cement = 10% of concrete but majority of emissions

Reduction Strategy 1: Use Less Concrete

• Currently use 2-3x too much concrete in designs
• Architects/engineers over-specify for reliability/liability reasons
• Concrete valuable for compressive strength in foundations/columns
• Example: Scotland Parliament building used concrete only where needed
  • Steel only where needed
  • Laminated wood for roof/non-load-bearing structures
• Carbon-conscious design can reduce emissions ~26%

Reduction Strategy 2: Cleaner Fuel Sources

• Traditional fuels: coal, petroleum coke, natural gas
• Electrification challenging due to 1,450°C temperature requirement
• Startups (Finnish companies) working on electric solutions
• Alternative approach: burn industrial waste, trash, used tires
  • Limestone scrubs pollutants from flame
  • Prevents emission to atmosphere
• Fuel switching reduces emissions ~7%

Reduction Strategy 3: Clinker Substitutes

• Startups developing green cement alternatives to clinker
• No abundant, commercially viable substitute yet
• Safety testing takes significant time (Turkey earthquake example with substandard cement)
• North America: clinker = 90% of cement (overly cautious)
• Global average: clinker = 72% of cement (2020)
• New cement mixture reduces clinker ratio to 50%
  • Supplements with clay + unprocessed limestone
  • Meets existing building codes
  • Cuts cement/concrete industry emissions by half

Reduction Strategy 4: Carbon Capture & Storage (CCS)

• Necessary for achieving zero emissions cement
• Captures CO2 from heat + chemical processes
• Stores carbon deep underground in geologic deposits
• Norway cement company pilot project
  • First cement plant with carbon capture
  • Storage under North Sea in oil/gas deposits
• New companies injecting stored carbon back into cement/concrete
  • Leverages rock's natural carbon reabsorption ability
  • Could make built environment carbon sink

Implementation Timeline & Challenges

• Goal: Net zero by 2050
• Must start immediately, especially in China (world's biggest producer)
• China advantages:
  • Average plant age: 15 years vs US 34-35 years
  • More energy efficient plants
  • Uses less clinker than global average
  • Has carbon capture project in development
• China challenge: pushed back peak building deadline from 2025 to 2030

Economic Considerations

• Green cement costs 70-115% more than traditional
• Cement/concrete = small fraction of total project cost
• Relatively cost-effective for government agencies to pay green premium
• US Inflation Reduction Act creates CCS market
  • $85/metric ton tax credit for stored carbon
• Design changes + concrete/cement process improvements easiest to implement
• CCS still in early stages, expensive