Experimental investigation on post-installed lap splices in ordinary and steel fiber-reinforced concrete

The design of post-installed lap splices typically relies on provisions derived from cast-in-place reinforcing bars (rebars). However, some bond characteristics of post-installed rebars show significant differences compared to cast-in-place rebars, especially when using high-performance mortars. To quantify the bond strength for design purposes, a sound understanding of differences in bond stress distribution, splitting failure mode, and load transfer mechanisms is crucial. This study offers new experimental evidence on these aspects, focusing on the impact of different high-performance injection mortars, lap lengths, and the incorporation of hooked steel fibers in the concrete. Direct tension tests were conducted on spliced post-installed and cast-in-place rebars. Fiber-optic sensors were used to measure strains quasi-continuously on the rebars, minimizing interference on the bond. The findings reveal that post-installed lap splices yield slightly higher bond strength than their cast-in-place counterparts, mainly due to the higher bond stiffness of the mortars. However, this advantage is limited by the bond behavior of the cast-in-rebar within the post-installed lap splice, particularly in conditions of poor confinement. In ordinary strength concrete, cast-in-place rebars exhibit an approximately constant bond stress distribution, as typically assumed for design purposes; by contrast, post-installed rebars show a pronounced non-linear distribution. Furthermore, an addition of steel fibers alters the bond stress of the rebars, resulting in a non-linear distribution in all cases. The study reveals a 20% increase in bond strength of lap splices in concrete reinforced with 80 kg/m³ of steel fibers. Moreover, they improve the ductility of bond failure for post-installed lap splices.