The use of Carbon Fiber Reinforced Polymers (CFRP) for the external strengthening of concrete structures has become increasingly common in recent decades due to their high performance and lightweight properties, offering a durable and cost-efficient solution. However, the efficiency of this repair technique relies heavily on the adhesion between the CFRP laminates and the concrete substrate. This adhesion can be compromised by defects such as voids and delamination that can arise for various reasons and are occasionally detected during field inspections. These interfacial defects reduce the stress transfer between CFRP and concrete, increasing the risk of brittle debonding before the full design capacity is reached. Currently, there is a lack of experimental research addressing the performance of retrofitted structures with local defects at the CFRP-concrete interface. This paper presents an experimental study aimed at assessing the bond-slip relationship between CFRP and concrete through a series of shear lap tests on concrete prisms externally reinforced with CFRP sheets. The study employs 3D Digital Image Correlation (DIC) to investigate strain distribution after introducing simulated defects in various positions. The results of this study will contribute to a better understanding of the impact of these defects on stress transfer along the substrate, adhesive, and CFRP sheets.