Life cycle greenhouse gas assessment of permeable concrete block pavements with industrial by-products

Recently, permeable concrete block pavement technologies incorporating industrial by-products have gained attention as a means to reduce waste and promote low-impact development. However, recycling by-products contributes to greenhouse gas emissions due to transportation and additional pre-processing. Thus, evaluating their environmental value requires a quantitative assessment based on life cycle greenhouse gas emissions. While permeable concrete blocks using oyster shells, bottom ash, and biochar have been shown to meet Korean engineering performance standards, no greenhouse gas emissions assessment has yet been conducted. This study evaluates the life cycle greenhouse gas emissions of such pavements incorporating these three by-products. The assessment includes emissions estimation and an evaluation of the recycling suitability of each by-product. Emissions from individual processes were calculated using data from previous studies, the Korean life cycle inventory database, and relevant industrial standards, based on a standard pavement cross-section. Life cycle emissions were derived through process-based analysis. The results were presented as equations incorporating key site-specific variables such as transportation distance and substitution ratio. A sensitivity analysis was conducted to assess the influence of these variables. Recycling suitability was further evaluated by determining the maximum transportation distance under which emissions could still be reduced. Domestic land transport of oyster shell cement and biochar resulted in emission reductions. The maximum transport distance for bottom ash was found to range from 18.4 to 1,556.5 km. Scenario analysis demonstrated that using all three by-products reduced emissions in both cases, with the mix design featuring the highest substitution rates identified as optimal.