SBT ? -N(II) is a high performance alkali-free setting accelerator for sprayed concrete. It speeds the chemical reaction between cement and water which causes mortar to set faster and increase the early strength development. SBT ? -N(II) has the properties of well adapted to cement, quick setting, high early strength and low rebound of concrete. It is widely used in many fields such as mining, hydropower, highway, railway tunnel, laneway, cave and so on.