Postinstalled Bars for Minimally Invasive Widening of Reinforced Concrete Bridges: Experimental Investigations on Bond-Splitting Failure

One of the methods to address traffic congestion problems is to widen existing concrete bridge slabs. This is traditionally done by partly demolishing concrete and exposing the internal reinforcement to form lap splices with starter bars that can be used to form the connection with the new reinforcement in the extended parts of the slabs. In this work, an alternative, minimally invasive solution is explored that consists of installing postinstalled reinforcing bars (chemical anchoring system) to act as starter bars for the extended portion of the slab. The concept involves making a diamond saw cut in the existing slab to visualize the exact location of the existing reinforcement, installing the postinstalled reinforcement close to the existing reinforcement and using it as starter bars, facilitating lap splices with reinforcement in new concrete. For safe designs, the embedment length of the bars should be sufficient to provide the required resistance. Current design standards such as ACI 318-19 allow the use of postinstalled bars if they meet ACI 355.5 qualification requirements. If the postinstalled bar is qualified, then it can be designed as an equivalent cast-in straight bar, which requires a relatively large anchorage or development length. Alternatively, if the postinstalled bar is considered as an adhesive anchor, Chapter 17 provisions of ACI 318-19 can be used, which typically result in significantly lower embedment depths. The use of postinstalled bars for bridge extension purposes needs better understanding, given that a variety of mortars are available in the market and the performance of postinstalled bars under different conditions is still not fully understood. To address this, in this study, a total of 42 single pullout tests were conducted on postinstalled bars to investigate their performance and behavior. These specimen-level tests were conducted on relatively small specimens replicating bridge slab geometry, with realistic boundary conditions. This study examines the effects of embedment depth, internal bridge transverse and longitudinal reinforcement, concrete strength, bar grade, concrete cover, and adhesive type on the capacity and behavior of postinstalled bars. Based on the results of this and further studies being carried out by the authors, a new design method will be proposed for the safe design of anchorage of postinstalled bars with a focus on bridge extension applications.