Silica-fume-free UHPC with basalt, dolomite and limestone: fresh and hardened properties and embodied carbon characteristics

The production of ultra-high-performance concrete (UHPC) often relies on ultra-fine particles such as silica fume (SF) to achieve its remarkable strength and durability. In this work, the development of a SF-free UHPC using fine limestone, fine basalt, fine dolomite and river sand was investigated. The aim of the study was to enhance workability, optimise mechanical properties and reduce the embodied carbon (EC) of UHPC, while maintaining its high-performance characteristics. The characteristics of different UHPC mixes were assessed through tests for slump flow, mini-slump flow, compressive strength and splitting tensile strength, microstructural analyses (scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy with attenuated total reflectance and thermogravimetric analysis) and EC evaluation. The fresh properties demonstrated acceptable workability, with slump flow values ranging from 500 to 800 mm. The compressive strength reached 190.7 MPa at 365 days, with fine limestone improving packing density and hydration efficiency. The 28-day splitting tensile strengths were in the range 5.3–9.5 MPa. Microstructural analyses confirmed a dense matrix formation, with basalt aggregates enhancing the strength of the interfacial transition zone and fine limestone promoting uniform hydration. The developed mixes exhibited lower EC (570.3–812.8 kgEC/m3), with sustainable utilisation indexes exceeding 1.0, significantly higher than the conventional UHPC mixes examined. These results demonstrate the feasibility of eco-friendly UHPC without SF, optimising both performance and sustainability.