Invasive alien biomass is used as an alternative aggregate to concrete

Circular economy - Alien clearing in SA

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.

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