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

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.