Review on rheological properties and their regulation of ultra-high performance concrete

Ultra-high performance concrete (UHPC) is a new cement-based composite material with ultra-high strength, high toughness, and excellent durability. Low water-to-binder ratio and use of large amount of fine particles in UHPC lead to problems, such as high viscosity of fresh paste, fiber cluster issue, and difficulty in pumping, etc. This is not beneficial to homogeneity of concrete and fiber strengthening and toughening of UHPC, and will limit the in-situ placing and application of UHPC. This paper reviews rheological properties of UHPC from aspects of rheological parameters and models. Based on the influence of water-to-binder ratio, chemical admixtures, mineral admixtures, fiber and aggregate characteristics on the rheological properties of UHPC, the techniques in regulating the rheological behavior of UHPC are analyzed and discussed. Such techniques include regulating water film thickness, regulating paste film thickness, reducing viscosity of interstitial fluid, adding viscosity modifier, and changing fiber characteristics. The rheology regulation mechanisms associated with these techniques are discussed.