Fly ash cenospheres (hereinafter referred to as “microspheres”) are a novel type of ultrafine powder material. Produced from high-quality fly ash through a unique selection and processing technique, they are perfect, spherical, sub-micron particles characterized by an ultrafine nature and a continuous particle size distribution. These microspheres offer excellent properties—such as high reactivity, low heat of hydration, light weight, corrosion resistance, high compressive strength, good fluidity, and thermal stability—making them suitable as a novel, reactive, ultrafine aggregate for high-performance concrete.
Mix proportion experiments based on particle packing density testing were conducted to investigate the influence of fly ash microspheres on the packing density and compressive strength of Ultra-High Performance Concrete (UHPC). This research led to the development of a self-compacting UHPC that does not require steam curing, achieving a 28-day compressive strength of 140 MPa and a 56-day compressive strength of 150 MPa.