Optimization of chipping parameters to mitigate the damage in a concrete substrate using a discontinuum modelling approach

Concrete chipping is frequently employed to remove the surface of deteriorated concrete substrate to allow the placement of repair material. Previous studies have revealed that subsurface microfractures generated during chipping is one of the most influential factors that decreases the interfacial bond strength between the old concrete and the repair material. This study focuses on the damage mechanism in a concrete substrate caused by a breaker chisel and aims to propose a chipping method to control the damage severity. To achieve this, a numerical model simulating a concrete substrate composed of mortar and coarse aggregates was constructed in the framework of the discrete element method. Concrete chipping simulations with the numerical model illustrated the mechanism of microfractures extending to a deeper region from the chipped surface with the penetration of coarse aggregates impacted by the breaker chisel. The numerical simulation further demonstrated that the chisel tip shape, chipping depth, and chipping velocity play a pivotal role in controlling the near-surface damage, whilst chipping inclination does not. A stepwise chipping method that removes the concrete in layers with a sharp-pointed chisel tip was proposed, since based on the numerical result the subsurface damage depth was reduced. Consequently, using this approach may improve the bond strength for concrete repair.