Bond strength of reinforcing bars encased with shotcrete

As the use of shotcrete (sprayed concrete) to build full-depth structural elements increases in North America, the encapsulation quality of reinforcing bars has become a subject of growing concern. In this investigation, the influence of the mixture consistency and the size of imperfections (created deliberately) behind reinforcing bars on the bond strength of the bars was studied using shotcrete "pull-out" specimens sprayed with the dry-mix process. However, as the desired range of the imperfection sizes could not be obtained, cast-in-place "pull-out" specimens were built with artificially created voids. This strategy allowed to study the reduction of the bond strength by knowing the precise size of the voids. The results suggest that the best bond performance of a bar is obtained, given an appropriate spraying technique, when the optimal combination between the mixture consistency and the airflow rate is used. Moreover, reinforcing bars encased with shotcrete slip less, relative to concrete, than those encased with cast-in-place concrete because of the high compaction with which the mixture is placed. Additionally, a void's transversal length (in contact with the bar) of about 20% of the bar's nominal perimeter was found to be the threshold beyond which an important change of the bond performance occurs. (C) 2018 Elsevier Ltd. All rights reserved.