LIFE-CYCLE ASSESSMENT OF ACTIVATED CARBON FROM WOODY BIOMASS

Buildings consume large amounts of materials and energy, making them one of the highest environmental impactors. Quantifying the impact of building materials can be critical to developing an effective greenhouse gas mitigation strategy. Using Athena Impact Estimator for Buildings (IE4B), this paper compares cradle-to-grave life-cycle assessment (LCA) results for a 12-story building constructed from cross-laminated timber (CLT) and a functionally equivalent reinforced concrete (RC) building. Following EN 15978 framework, environmental impacts for stages A1–A5 (product to construction), B2, B4, and B6 (use), C1–C4 (end of life), and D (beyond the building life) were evaluated in detail along resource efficiency. For material resource efficiency, total mass of the CLT building was 33.2% less than the alternative RC building. For modules A to C and not considering operational energy use (B6), LCA results show a 20.6% reduction in embodied carbon achieved for the CLT building, compared to the RC building. For modules A to D and not considering B6, the embodied carbon assessment revealed that for the CLT building, 6.57 × 10⁵ kg CO₂ eq was emitted, whereas for the equivalent RC building, 2.16 × 10⁶ kg CO₂ eq was emitted, and emissions from CLT building was 70% lower than that from RC building. Additionally, 1.84 × 10⁶ kg of CO₂ eq was stored in the wood material used in the CLT building during its lifetime. Building material selection should be considered for the urgent need to reduce global climate change impacts.

Wood products have many environmental advantages over nonwood alternatives. Documenting and publicizing these merits helps the future competitiveness of wood when climate change impacts are being considered. The manufacture of wood products requires less fossil fuel than nonwood alternative building materials such as concrete, metals, or plastics. By nature, wood is composed of carbon that is captured from the atmosphere during tree growth. These two effects—substitution and sequestration—are why the carbon impact of wood products is favorable. This article shows greenhouse gas emission savings for a range of wood products by comparing (1) net wood product carbon emissions from forest cradle–to–mill output gate minus carbon storage over product use life with (2) cradle-to-gate carbon emissions for substitute nonwood products. The study assumes sustainable forest management practices will be used for the duration of the time for the forest to regrow completely from when the wood was removed for product production during harvesting. The article describes how the carbon impact factors were developed for wood products such as framing lumber, flooring, moulding, and utility poles. Estimates of carbon emissions saved per unit of wood product used are based on the following: (1) gross carbon dioxide (CO₂) emissions from wood product production, (2) CO₂ from biofuels combusted and used for energy during manufacturing, (3) carbon stored in the final product, and (4) fossil CO₂ emissions from the production of nonwood alternatives. The results show notable carbon emissions savings when wood products are used in constructing buildings in place of nonwood alternatives.