Kraft lignin as a bio-based ingredient for Dutch asphalts: An attributional LCA

Christian Moretti,Blanca Corona,Ric Hoefnagels,Marco Van Veen,Iris Vural-Gürsel,Tobias Strating,Richard Gosselink,Martin Junginger

doi:10.1016/j.scitotenv.2021.150316

Christian Moretti, Blanca Corona + Show 6 more

Open Access

https://doi.org/10.1016/j.scitotenv.2021.150316

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Abstract

In the last decade, lignin has received much attention as a feedstock to produce bio-based products. This study investigates the potential benefits of using lignin to mitigate the environmental impact of the road construction sector. An environmental life cycle assessment (LCA) of various top-layer bio-based asphalts using kraft lignin was conducted. From a cradle-to-grave perspective, lignin-based asphalts were compared with conventional asphalts.The results of the LCA revealed that the climate change impact of lignin-based asphalts could be 30–75% lower than conventional asphalts. For the other ten impact categories, trade-offs were observed. Overall, two key factors to make the environmental impact of lignin-based asphalts lower than conventional asphalts are 1) increasing the amount of bitumen-substituted and 2) using low-grade biomass fuels for process steam in the pulp mill. The substitution of weak filler with lignin was beneficial only for climate change and could lead to a worse overall environmental performance than conventional asphalts. Similarly, higher environmental impacts for lignin-based asphalts could be obtained if the pulp mill consumed natural gas to complete the energy balance to replace the part of the black liquor from which lignin is extracted.This study also includes an in-depth discussion on methodological choices such as the allocation methods for lignin, functional units, and asphalt layers considered. We believe that such a methodological discussion could be helpful to support future Product Category Rules for asphalt mixtures.

Highlights

Projects in the construction sector are often assigned via public tenders
According to the NL-PCR (Keijzer et al, 2020), the amount of materials recovered during recycling is calculated considering two types of material losses
The first loss is due to the fraction of asphalt that leaves the asphalt system with no further use or reused in a low-value function other than asphalt e.g. towards foundation layers

Summary

Introduction

Projects in the construction sector are often assigned via public tenders. The environmental aspects are becoming more often part of the public tenders in the EU member states (Ecochain, 2019; Moretti et al, 2017b). Combining properly the environmental impacts calculated using LCA with project costs should avoid that low-cost materials with high environmental burdens are selected in investments using public funding (Moretti et al, 2017b) With this purpose, tenders in the Dutch construction sector include an environmental cost indicator that simplifies and unites various environmental impacts into a single monetary value score representing the avoided damage cost or shadow cost (Ecochain, 2019; Schwarz et al, 2020). Even following the best LCA practices recommended by these methodological documents, multiple sources of methodological uncertainty exist and the results of LCAs should be carefully interpreted (Cherubini et al, 2018; Moretti et al, 2020a; Reap et al, 2008) For this reason, the effect of the allocation methods, functional units and product systems' definition was broadly discussed through sensitivity analyses

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