Economic and environmental optimisation of waste cardboard kraft fibres in concrete using nondominated sorting genetic algorithm.

The depletion of natural resources is accelerating due to increased construction activities across the world. The search for alternative materials used in concrete is becoming a prominent measure to reduce greenhouse gas (GHG) emissions in the construction industry. Cement in concrete produces 4–8% of all GHG emissions annually worldwide. Alternative materials such as waste cardboard provide an opportunity to be utilised further in such applications. This study focuses on using nondominated sorting genetic algorithm (NSGA-II) to optimise the economic cost and GHG emissions of concrete incorporating recycled waste cardboard as a partial cement substitute. The multi-objective optimisation solutions produced three key regions that corresponded with trade-offs between the lowest costs, carbon emissions or a combination of both. Region 1 was the most economical but created the most carbon emissions. Region 2 was a compromise between both economical, and environmental factors and region 3 demonstrated the lowest carbon emissions but also produced the highest costs. These regions produced three mix designs which were experimentally analysed for their compressive strength. The results indicated a cost increase of 17, 27 and 36% for three key optimised regions. This is primarily due to increased material costs and further manufacturing requirements when converting waste cardboard into kraft fibres (KFs). Increasing the amount of KFs then reduced the compressive strength from 36 to 56%. However, there was a 7, 18 and 28% GHG emission saving when KFs partially replaced cement. • Optimisation and mechanical testing methods are applied to kraft fibres in concrete. • Waste cardboard kraft fibres can be used as a partial cement substitute. • Supplementing cement with waste kraft fibres can reduce GHG emissions. • Multi-objective optimisation is utilised to optimise cost and GHG emissions. • Increasing the amount of kraft fibres in concrete can reduce the mechanical strength. [ABSTRACT FROM AUTHOR]