Title: Reinforcing Bar Pullout Bond in Tremie-Placed Concrete Cast in Drilling Slurry Environments
Author(s): Kelly Costello, Sarah Mobley, Justin Bowen, and Gray Mullins
Publication: Structural Journal
Appears on pages(s): 183-192
Keywords: development length; drilled shaft; mineral; polymer; reinforcing bar bond; slurry
Drilling slurry made from a mixture of water and mineral or polymer powder is often used to stabilize deep excavations, in which cast-in-place reinforced concrete foundation elements such as drilled shafts are constructed. At the time of concreting, drilling slurry is displaced by heavier, highly fluid concrete tremie placed at the bottom of the excavation from within the reinforcement cage. Despite the fluidity of the concrete, it must build up within the reinforcing cage to a sufficient height before then radially pressing into the annular cover region. This flow pattern has been shown to trap slurry near the steel reinforcement and affect reinforcing bar bond. This paper presents the results of 227 reinforcing bar pullout tests performed over a 6-year period from 2012 to 2018. Shaft specimens were tremie placed in various slurry types and consistencies. This analysis concluded that present development length values should be increased by 1.8 for bentonite and 1.9 for polymer slurry; water casting environments showed no significant change relative to dry conditions.