Challenges and Opportunities in Scaling Eco-Friendly Ultra-High-Performance Concrete with Hybrid Fibers: A Bibliometric and Technical Review

Ultra-high performance concrete exhibits excellent mechanical properties, such as high compressive strength, good durability, and structural reliability. However, its application is currently hampered by very high cement consumption and a considerable amount of embodied carbon, which is significantly dependent on the energy intensive use of steel fibers. The study conducts a technical and bibliometric review of sustainable UHPC systems that employ hybrid fiber reinforcement and supplementary cementitious materials. A systematic literature review on SCMs and UHPC has been analysed through VOSviewer to identify trends of research, collaboration networks, and thematic clusters of UHPC research. The findings show an increasing trend towards sustainability-oriented mix design in the field of UHPC, characterized by the use of high volume SCMs, optimization of particle packing, and hybrid fiber systems that combine steel fibers with polypropylene, basalt, or glass fibers. Sustainability assessments also indicate that cement production and steel fibers are the largest contributors to embodied carbon in UHPC, and that SCM substitution and hybrid fiber optimization can provide a reduction of up to 40-50 % in global warming potential of UHPC. Although encouraging laboratory scale performances were obtained, large scale implementations are still hindered by material variability, fiber dispersion, cost issues, and lack of standardization.