Approaches to reduce cost and environmental impacts of UHPC production: a review

Ultra-High Performance Concrete (UHPC) is a special fibre-reinforced concrete with ultra-high compressive strength, high flexural strength, excellent toughness and durability. Typically, UHPC is formulated from Portland cement (PC), supplementary cementitious materials (SCMs), fine aggregates, fibres, water and admixtures. However, the current widespread application of UHPC is hampered by two major problems, i.e., high cost and high environmental impacts associated with UHPC production. To address these issues, this study provides a comprehensive review of approaches to reduce the cost and environmental impacts of UHPC production. The main approach discussed in detail is the substitution of PC with geopolymer as a sustainable PC-less binder to develop ultra-high performance geopolymer concrete (UHPGC). The other approaches covered in this article include the use of limestone calcined clay cement (LC3) as a substitute for PC, the incorporation of recycled fibres in place of manufactured fibres, the utilisation of recycled fine aggregates as alternatives to natural sand, and the application of recycled agricultural and industrial wastes as replacements for the commonly used SCMs (i.e., silica fume, fly ash, and ground granulated blast furnace slag). Additionally, incorporating natural/recycled coarse aggregates into the production of UHPC can further reduce the material's cost and carbon emissions. The recommendations for future research are also highlighted for each strategy. The findings of this up-to-date article offer valuable insights for developing a more cost-effective and environmentally friendly UHPC, thereby facilitating its wider application in the construction industry.