Abstract
In the practice of concrete rehabilitation, the deteriorated surface of concrete structure is commonly removed with chipping methods, such as a pneumatic breaker (BR), a water jet (WJ). However, there are few studies on evaluating the effect of such chipping methods on the performance of concrete structures after rehabilitation. Especially the state of damage in the concrete below the chipping surface is yet to be adequately evaluated, including chipping-induced microcracks. In this study, the numerical simulation of chipping with a BR was performed to elucidate the influence of chipping parameters on damage below the chipping surface. Distinct Element Method (DEM) was employed to analyze the effects of parameters such as chisel tip shape and chipping depth. From the results obtained in these analyses, it was demonstrated that the BR method should be performed using a chisel with a sharp tip and in a stepwise manner with multiple cycles.
To repair weathered and deteriorated concrete, the concrete surface is chipped and removed, and then new concrete is placed. In the case of concrete structure chipping, generally, the breaker (BR) method using 10 to 30 kg class hand-held breaker or the waterjet (WJ) method with a machine or a hand gun that jets high pressure water is employed. The breaker method is easy to remove deteriorated concreate; however, there are deficiencies that the method causes noise, vibration, dust and so on. Also, since work is done by human power, work efficiency is poor when large amount of concrete needs to be chipped and the influence of vibration limits work time. Furthermore, it is known that micro cracks are produced by chipping with the breaker, causing partial weakening (Tanikura et al., 2018).
It has been clarified that surface chipping with the breaker can induce many micro cracks from the impact surface to a depth of 40mm and cracks (Tanikura et al., 2018), which occur due to the breaker reducing adhesion strength between the concrete substrate and newly placed concrete. However, the initiation and propagation of fractures is yet to be quantitatively investigated during chipping with the breaker.
In this study, we analyze fracture generation and its distribution, using the Distinct Element Method that treats concrete as a set of discontinuous elements. It is then aimed to elucidate the state of the progress of failure during the chipping treatment and to clarify the influence of the breaker method on the occurrence of the crack damage of concrete, based on a model parametric study changing the chipping conditions.
