The purpose of this thesis is to investigate the short- and long-term behaviour of injected bolted connections (IBCs) with oversize holes for various injection materials. A central theme in this thesis the demountability of IBCs, as a result of which several release agents are tested for their suitability in and effects on IBCs. Injection bolts have been used successfully in engineering practice using epoxy resin to limit the amount of slip in bolted shear connections with normal clearance holes, but no explicit results are available for connections with oversize or slotted holes. The use of oversize or slotted holes may be beneficial for the (re-)erection process of structures, and thus it is investigated what the effects of such oversize or slotted holes are on the connection behaviour. First, it is examined if grout is suitable as an injection material in injected bolted connections (IBCs), as well as what precautions are necessary to ensure proper demountability of grout and(epoxy) resin-injected bolted connections. Secondly, the connection behaviour under short-term loading is determined, on the basis of which long-term creep tests are carried out. Finally, a new injection material is developed based on the preliminary conclusions drawn from the short- and long-term tests. It is concluded that IBCs can be demounted by treating the connection members with a release agent. The results of the experiments show that the long-term behaviour of resin-injected connections is governing the design, but that modelling of this time-dependent behaviour requires additional testing. The short and long-term performance of the newly developed material (resin reinforced with steel shot) in IBCs with oversize holes is significantly better than that of only resin, on the basis of which it is recommended to further investigate the potential and behaviour of this material in engineering applications.