Mechanical Activation of OPC for Lower Strength UHPC with Reduced Silica Fume Content

Abstract

Ultra-High-Performance Concrete (UHPC) traditionally exhibits compressive strength exceeding 150 MPa. However, variants have been identified with slightly lesser strengths that still surpass those of standard concrete; these are termed Lower Strength Ultra-High-Performance Concrete (LSUHPC). This study focused on the strategic utilization of Ordinary Portland Cement (OPC) in LSUHPC formulation while significantly curtailing the extensive use of silica fume, which is a common practice in UHPC production. Typically, high-performance concrete, with strengths ranging from 120-150 MPa, is produced using fine aggregates, heavy doses of silica fume, superplasticizer, and fiber. Contrary to this traditional method, our research developed an LSUHPC mix design with a significantly reduced volume of silica fume. For the current research stage, the use of steel fiber was omitted. To counteract the reduction in silica fume, the OPC was subjected to mechanical grinding to enhance its particle fineness and reactivity. Additionally, a low volume of class F fly ash was incorporated into the mixture to improve its workability. This adjustment was theorized to diminish inter-particle voids, reduce the water requirement, and increase the mixture’s density. With a fixed superplasticizer dosage of 4%, the aim was to minimize the water-to-binder ratio, maintaining workability and achieving enhanced particle packing and compressive strength. Following a series of grinding, particle fineness analyses, mix design formulations, and consistency tests, it was confirmed that the strategic application of OPC, combined with fly ash and reduced silica fume levels in the LSUHPC formulation, can achieve the targeted high compressive strength. This approach opens the door for cost-efficient LSUHPC production by drastically reducing the use of silica fume.