Influence of Using Ladle Furnace Slag as a Partial Replacement For Sand on the Properties of UHPC

Abstract

The proliferation of industrial by-products as sustainable construction materials has given rise to the utilization of ladle furnace slag as a potential replacement for natural sand in ultra-high performance concrete (UHPC). This study investigates the influence of ladle furnace slag as a partial replacement for sand on the mechanical and durability properties of UHPC. A systematic approach has been adopted wherein natural sand in UHPC has been replaced with ladle furnace slag (LFS) at varying percentages of 0%, 10%, 15%, 20% and 30% by volume. Mechanical properties have been assessed through the evaluation of compressive strength at 7 and 28 days. Durability aspects have been examined through sorptivity, water absorption, and shrinkage tests. The experimental results indicate an initial decrease in workability with the incorporation of LFS, attributed to its finer size and rougher texture compared to sand. The inclusion of LFS up to 20% leads to a significant enhancement in the early age compressive strength which can be credited to the filler effect and the pozzolanic reactivity of the LFS. Durability assessments reveal an improved densification of the microstructure with lower permeability coefficients and water absorption in mixes containing LFS. A reduction in sorptivity with an increased substitution of natural sand with Ladle Furnace Slag has also been observed, indicating enhanced resistance to the ingress of detrimental substances and improved durability properties of the concrete matrix. However, beyond 20% replacement level, the benefits diminished and negative effects on the mechanical strengths and durability became prominent. This decline at higher substitution rates can possibly be attributed to the interference of the voluminous LFS particles with the matrix's packing density and their weaker bond with the cementitious binder. The study confirms that LFS can be used as a partial replacement for sand in UHPC that can foster sustainable construction practices by recycling industrial waste and reducing sand mining impacts to some extent. 7 Moreover, the optimal utilization of LFS not only conserves natural resources but also improves certain properties of UHPC, making it a promising material for advanced civil engineering applications. Further research is however encouraged to understand the long-term effects and to explore the pre-treatment of LFS to overcome workability and bonding issues for higher replacement percentages.