Several prestressing reinforced structures have recently collapsed due to chloride-induced steel corrosion. This study investigates the effect of the corrosion of hot-dip galvanized conventional prestressing steel reinforcement under hydrogen evolution on bond strength in normal-strength concrete. The impact of hydrogen evolution on the porosity of cement paste at the interfacial transition zone (ITZ) is verified through image analysis. The whole surface of prestressing strands is hot-dip galvanized, and their corrosion behavior when embedded in the cement paste is investigated by measuring the time dependence of the open-circuit potential. Concerning the uniformity of the hot-dip galvanized coating and its composition, it is advisable to coat the individual wires of the prestressing reinforcement and subsequently form a strand. It is demonstrated that the corrosion of the coating under the evolution of hydrogen in the cement paste reduces the bond strength of hot-dip galvanized reinforcement in normal-strength concrete. Image analysis after 28 days of cement paste aging indicates insignificant filling of hydrogen-generated pores by zinc corrosion products. Applying an additional surface treatment (topcoat) stable in an alkaline environment is necessary to avoid corrosion of the coating under hydrogen evolution and limit the risk of bond strength reduction.

This article presents the results of research on the growth kinetics, microstructure (SEM/EDS/XRD), and corrosion behavior of Zn-5Al coatings obtained using a high-temperature hot dip process on B500B reinforcing steel. The corrosion resistance of the coatings was determined using the neutral salt spray (NSS) test (EN ISO 9227). Based on chemical composition tests in micro-areas (EDS) and phase composition tests (XRD), corrosion products formed on the coating surface after exposure to a corrosive environment containing chlorides were identified. In the outer layer of the coating, areas rich in Zn and Al were found, which were solid solutions of Al in Zn (α), while the diffusion layer was formed by a layer of Fe(Al,Zn)₃ intermetallics. The growth kinetics of the coatings indicate the sequential growth of the diffusion layer, controlled by diffusion in the initial phase of growth, and the formation of a periodic layered structure with a longer immersion time. The NSS test showed an improved corrosion resistance of reinforcing bars with Zn-5Al coatings compared to a conventional hot-dip-galvanized zinc coating. The increase in corrosion resistance was caused by the formation of beneficial corrosion products: layered double hydroxides (LDH) based on Zn²⁺ and Al³⁺ cations and Cl⁻ anions and simonkolleite—Zn₅(OH)₈Cl₂·H₂O.

In this study, the corrosion properties of plasma-sprayed Al₂O₃ coating (APSS) with a topcoat of zirconium-based conversion coating (ZrCC) and organofunctional silane coating (3-glycidyloxypropyltrimethoxysilane; GPTMS) on carbon steel are investigated in detail. Additionally, the bond strength of plain steel bars coated with this system in normal strength concrete are newly tested. The APSS coating exhibits significant porosity, with unfavourable open pores limiting the barrier protection effect. In contrast, the surface roughness (R_a) significantly increases, improving the bond strength between steel bars and concrete. Such increase in carbon steel roughness improves bond strength in concrete. The synergic application of ZrCC and GPTMS topcoats significantly enhances the corrosion resistance of the base coat (inhibition effect). The character of the GPTMS coating increases the wettability of the APSS coating, which further positively contributes to bond strength between plain bars and concrete. It is demonstrated that when the ZrCC topcoat is applied without GPTMS, the corrosion resistance increases insignificantly and the surface wettability decreases, negatively affecting bond strength in comparison with carbon steel coated using an APSS base coat only.