Research and application of micro-bead ultra-high performance concrete

Micro-bead is an ultra-fine fly ash of spherical vitreous with an average particle size of no more than 1.2 mu m. In this paper, the physicochemical properties of micro-bead, the preparation method of micro-bead ultra-high performance concrete (MUHPC) were described. Furthermore, the characteristics and slump-loss retarding of fresh MUHPC, the strength and durability of MUHPC and the change of mechanical properties and fracture characteristics of MUHPC after incorporating fiber were studied. Results indicated that UHPC with the cement-micro-bead-silica powder as the main binder and incorporated with the appropriate water reducer had a strength reaching up to 150 MPa and a plasticity reaching up to 3 h and no bleeding segregation phenomenon. The C120 UHPC has a low Cl- diffusion coefficient and is resistant to freeze-thaw damage and has a high durability. And for the C120 UHPC incorporating polypropylene fiber, as the fiber content increased, the fracture energy, the brittle characteristic length and the toughness of the concrete all increased. C120 concrete has been applied in the Jingji Building in Shenzhen and the East Tower project in Guangzhou and the pumping height is 500 m or more.