Invasive alien plants as an alternative resource for concrete production – multi-scale optimization including carbon compensation, cleared land and saved water runoff in South Africa

Verena Göswein,José Dinis Silvestre,Stephen Lamb,Alexandre B Gonçalves,Francesco Pittau,Fausto Freire,Dirk Oosthuizen,Andrew Lord,Guillaume Habert

doi:10.1016/j.resconrec.2020.105361

Abstract

Today's cities are ever-growing, especially in the Global South, inducing massive construction activity. To satisfy these needs we need feasible and environmentally sustainable construction materials, the use of local solutions and, if possible, to enable synergies between sectors for maximum environmental benefit.In South Africa and beyond, invasive alien plants are threatening the indigenous ecosystem while exacerbating water security by affecting water surface runoff and fueling wildfires that release carbon to the atmosphere. The literature suggests that bio-based construction materials can turn buildings into carbon pools. However, the dynamics of using bio-based materials at the urban scale are not yet well known. This paper tests a new type of non-structural bio-concrete, using invasive alien wood chips as a substitute for sand and gravel as aggregates, for future residential construction in Cape Town, comparing this new material to conventional and to earth-based materials, and benchmarking different policy scenarios. Firstly, the material is optimized within technical possibilities achieving the capture of 897 kg of CO2 equivalents per m3. Secondly, a reverse-engineered approach is employed to uncover the limitations of the material. Additionally, C02 emissions from cradle to gate and additional land and water use benefits are analyzed, considering spatial dynamics for transportation impacts.The optimized mix design using invasive alien plants as an alternative resource, combined with a policy that promotes multi-story buildings, offers great potential to achieve near carbon neutral cities, clearing land of invasive alien plants and thus saving annual water surface runoff.

Highlights

Cities are growing in both size and number around the globe but most of the world’s fastest growing cities are in Africa and Asia (UN, 2018)
The results are organized in two parts: firstly, the embodied Greenhouse gas emissions (GHG) emissions for Cape Town’s residential building stock based on the demand-driven model are presented
The second part focuses on the reverse-engineered optimization of the proposed Biomass-insulated concrete (BIC) across scales, considering carbon storage, cleared land due to felling of invasive alien plants (IAP) trees, and water surface runoff savings

Summary

Introduction

Cities are growing in both size and number around the globe but most of the world’s fastest growing cities are in Africa and Asia (UN, 2018). Urbanization, enabled by rapid economic development, is accelerating large building activity in developing countries (IPCC, 2015). Circa one-third of the urban population in developing countries in 2010 did not have access to adequate housing The 2030 Agenda for Sustainable Development, the Sustainable Development Goal 11, aims at making cities and human settlements inclusive, safe, resilient and sustainable (UN, 2019). We need to provide sustainable and adequate housing for all. One priority to achieve a low carbon building sector is to reduce the embodied emissions and energy of construction materials (due to min ing, manufacturing, processing, and transportation) (UN Environment and International Energy Agency, 2017). We need construction materials that are locally available for large-scale construction, that enable adequate housing, and that have low embodied impact

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Conclusion