Reducing the Carbon Footprint:

The process of extracting and processing raw materials plays a significant role in the overall carbon emissions of any structure.

• Timber Bridges: Timber is a renewable resource, and the process of growing and harvesting wood contributes to carbon sequestration. The LCA report indicates that solid wood production contributes only 63.51% of the emissions for the raw material stage, resulting in 58.56 kg CO2 eq per linear foot, which greatly reduces the carbon footprint of infrastructure projects.

• Steel Bridges: Steel, on the other hand, is an energy-intensive material to produce. The extraction of iron ore, followed by steel production and refinement, generates a significantly higher carbon footprint. Steel bridges often require high quantities of low-alloyed steel, which can contribute as much as two to three times the emissions of wood for similar structural integrity.

• Concrete Bridges: The production of concrete, specifically cement, is notorious for its carbon intensity. Concrete production is responsible for approximately 8% of global CO2 emissions, as it requires large amounts of heat to convert limestone into cement clinker. When comparing concrete bridges to timber, the emissions during raw material extraction and processing alone are 4-5 times higher than those of timber bridges.

Manufacturing emissions account for the largest share of carbon emissions in any bridge structure.

• Timber Bridges: Timber bridges, even with steel components, show significantly lower manufacturing emissions. The LCA report attributes 96.63% of the manufacturing emissions to lumber milling, amounting to 569.37 kg CO2 eq per linear foot of bridge.

• Steel Bridges: Steel forging and fabrication processes are energy-intensive. The heating, forging, and rolling processes to produce structural steel emit more than double the carbon footprint compared to the milling of timber.

• Concrete Bridges: The manufacturing of concrete components also involves high energy consumption, especially in large, pre-fabricated sections. Reinforced concrete structures, with the combination of steel rebar and cement, result in a considerably higher GWP when compared to timber bridges.

Transportation emissions in the LCA cover the distance materials travel from manufacturing plants to the construction site.

• Timber Bridges: With York Bridge Concepts’ focus on sourcing sustainable, regionally available materials, transportation emissions are kept in check. Timber’s relatively low weight compared to steel and concrete also reduces fuel consumption during transport, contributing only 76.03 kg CO2 eq per linear foot.

• Steel Bridges: The transportation of steel beams and components, which are heavier than timber, results in higher emissions. Steel bridges can require 30-50% more transportation-related emissions due to the density and weight of steel materials.

• Concrete Bridges: Pre-fabricated concrete sections are even heavier than steel, leading to the highest transportation emissions of all three materials. Concrete structures can contribute up to 3 times the transportation emissions compared to timber, due to the sheer volume and weight involved.

Construction processes include on-site equipment usage, fuel consumption, and waste generation.

• Timber Bridges: Timber bridge construction is less energy-intensive. The nature of York Bridge Concepts' timber bridges allows for faster construction with minimal machinery and waste. Emissions from equipment like delimbing processors and diesel generators amount to 60.73 kg CO2 eq per linear foot, which is considerably lower than for steel and concrete structures.

• Steel Bridges: Steel bridge construction involves heavy-duty machinery, extensive welding, and bolting, all of which contribute significantly to construction emissions. The need for precise fabrication and assembly techniques increases the on-site energy demand, leading to 20-30% more emissions during the construction phase compared to timber bridges.

• Concrete Bridges: The construction of concrete bridges, especially for large spans, involves significant use of cranes, cement mixers, and heavy-duty equipment. This increases the carbon footprint of construction, often leading to more than twice the emissions observed in timber bridge construction.
  
  

USDA Forest Service: https://research.fs.usda.gov/treesearch/67831
Yale University: https://news.yale.edu/2014/03/31/using-more-wood-construction-can-slash-global-reliance-fossil-fuels