Effect Of Hybrid Fibres on Rheological Properties of Self Compacting Concrete

Self-Compacting Concrete (SCC) is distinguished by its high flowability, allowing it to consolidate entirely under its own mass without requiring mechanical vibration. While integrating fibres into SCC enhances its mechanical performance and long-term durability, it also drastically alters the material's fresh and rheological characteristics. This research explores how hybrid combinations of steel and polypropylene (PP) fibres impact the rheological traits of SCC. The primary goal of this experimental program was to analyse how these combined fibres influence fresh SCC behaviour. To achieve this, five distinct mixtures were evaluated: a baseline control SCC, followed by SCC variants containing 0%, 1%, 1.25%, 1.5%, and 1.75% hybrid fibres by total volume of the mix, all maintained at a constant water-to-powder ratio of 0.34. The rheology of SCC is traditionally evaluated through yield stress and plastic viscosity utilizing the Bingham model. To assess parameters like fluidity, viscosity, passing capability, and resistance to separation, various fibre percentages were blended into the SCC matrices and subjected to standard fresh state evaluations, specifically the slump flow, T500 time, V-funnel, and L-box tests. The experimental outcomes indicated that escalating the hybrid fibre volume systematically diminished both flowability and passing ability, while simultaneously elevating plastic viscosity and structural stability. At moderate concentrations, the fibres successfully upgraded mix cohesion and segregation resistance without undermining the concrete's self-compacting nature. Conversely, excessive fibre addition triggered blocking mechanisms and hindered overall workability. Ultimately, the investigation demonstrates that identifying an optimal fibre threshold is vital to securing a proper balance between the rheological requirements as well as the mechanical behaviour of hybrid fibre-reinforced SCC.