# Effect of Stirrup on Bond Strength Degradation in Concrete Cracked by Expansion Agent Filled Pipes
## 1 Introduction  
There is an urgent need to address the safety problems and economic burden caused by the deterioration of reinforced concrete (RC) structures. The corrosion of reinforcing bars (rebars) has been recognized as one of the most significant causes of deterioration for RC structures. The corrosion products expand the volume of corroded steel reinforcement, leading to tensile stresses that can cause the cover concrete cracking of these RC structures. Prominent publications demonstrated that these induced cracks could affect the structural performance of RC members [1, 2, 3, 4]. For effective maintenance with low cost, it is necessary to evaluate the effects of deterioration accurately. 'Bond' refers to the interaction between rebars and the surrounding concrete, which allows transferring tensile stress from the steel into the concrete. It is a fundamental property of RC structures. For instance, in shear resistance through truss mechanisms, bonds have a crucial role in maintaining internal force equilibrium [5]. However, as can be seen in Figure 1, the corrosion-induced crack along the main rebars can deteriorate the bond quality. With the lack of a strong bond, the tensile force from the main rebar cannot be correctly transferred to the concrete. Consequently, the internal equilibrium force is disturbed, leading to global structural performance degradation. The impact of corrosion on bond performance has been studied extensively in the past. The fib Bulletin 10 [6] provides significant analysis and discussion on the topic. [PERSON] et al. and [PERSON] et al. [7, 8] also presented recent and considerable literature reviews. Electrical corrosion is widely adoptedto simulate the phenomenon in a relatively short time. Furthermore, most researchers have estimated bond degradation as a function of the level of corrosion [9; 10; 11; 12; 13; 14]. Others have attempted to correlate the surface crack width to the level of corrosion of the rebars or the bond deterioration [15; 16; 17; 18]. The data from the electrically corroded specimens are rather controversial, and there is no general agreement about the results characterized by scattering and variability. This variation is caused by the difference in the material properties, typology of specimens, or the flow of rust amount in the concrete [17; 19; 20]. Consequently, a widely accepted model for bond degradation is unavailable. The induced crack, the rebar profile change, and the rust accumulation can also altogether affect the bond strength of the corroded specimen. However, combining these effects complicates the fundamental analysis and reduces the bond evaluation's overall accuracy. Further, the authors proved that induced crack width is the more dominant factor than the corroded rebar shape and rust accumulation in the bond deterioration mechanism [21; 22]. Previous studies have proposed a new approach to produce a more accurate model that consists of finding a direct link between bond degradation and surface crack width without corrosion products [23; 24; 25]. For an alternative to electrical corrosion, the previous study [26] presented a novel method for simulating concrete cracking due to the corrosion of the rebar. An aluminum pipe embedded in concrete and filled with an expansion agent (hereafter, expansion agent filled pipe, EAFP) simulates rebar's volume expansion due to corrosion. This expansion generates cracks in the concrete surrounding the rebar. One advantage of EAFP is that it allows for focusing on the single effect of an induced crack. The results of the pull-out test of a cracked specimen without a stirrup suggests that the direct link between crack width and bond deterioration can improve the accuracy of the results. It can therefore be assumed that the induced crack width may express the exclusive consequence of corrosion on the bond deterioration.