An injection system for a self-drilling rock bolt assembly (1), the system including: a receptacle (2) to be fixed in use to a drill head (4) of the self-drilling rock bolt assembly (1), the receptacle (2) having a nozzle receiving end (5) and an opening (6) at the other: a replaceable canister (7) to be located within said receptacle (2) in use, said canister (7) adapted to supply two or more substances for use in installing the rock bolt assembly (1) through said nozzle receiving end (5); and a plunger system (8) operatively associated with said receptacle (2) adjacent said opening (6) at said other end and positioned along a longitudinal axis (XX) of the drill head (4): the plunger system (8) including two or more plungers (9) that are activated in use to drive the substances within the canister (7) when located within the receptacle (2), delivering the substances by way of a nozzle (21) mounted to the nozzle receiving end (5) into the self-drilling rock bolt assembly (1).