Bond strength and critical penetration depth of rust are major factors that affect the service life of reinforced concrete structures. This research endevoured to establish a relationship between the bond strength and critical penetration depth of rust for reinforced concrete structures. There are 7 brands of Cem 1 cement in Kenya available for use in concrete structures. To achieve the desired objective, three Cem 1 cement brands (Cem A, B and C), fine aggregates, coarse aggregates and steel were obtained from the local Kenyan market. The chemical and physical properties of the materials were investigated. For a selected design strength of 25N/mm2, concrete materials were batched by weight and mixed by an electric pan mixer. For each brand of cement 9 cubes of size 150mm * 150mm * 150mm for a compression test, 9 cylinders of 150mm * 300mm for tensile strength and 9 cylinders of 150mm * 300mm for bond strength were cast. After 24 hours, the cast specimens were demoulded and immersed in curing tanks for 27 days. Specimens for compression, split tensile and bond strength were tested at 7,14 and 28 days. From the results, it was observed that the chemical composition of Cem 1 brands in the Kenyan market vary, which affects the hardening properties of concrete. A model for the critical penetration depth of rust in reinforced concrete was proposed by establishing a correlation between the spilt tensile and bond strength and substituting it in the Xu and Shayan model. The proposed and published models compared well. From the proposed model, a relationship between the critical penetration depth and bond strength was established. It was noted that the critical penetration depth increased with an increase in the bond strength of reinforced concrete. The results of this research are expected to contribute to the modeling of the service life of reinforced concrete structures.