Determination of Engineering Properties of Steel-Concrete Interface of Reinforced Concrete Exposed to Marine Environment

Abstract

In this investigation, engineering properties of steel-concrete interface (SCI) such as porous zone thickness and calcium hydroxide content around the reinforcing steel were studied through the measurement of ultimate bond strength and also by employing advance characterization techniques such as scanning electron microscopy (SEM) powered with energy dispersive spectroscopy (EDS) and nano-indentation. Three types of cements, i.e., ordinary Portland cement (OPC), Portland pozzolana cement (PPC), and Portland slag cement (PSC) were used in this study and their influence towards the SCI properties was determined. A reliable grayscale-based thresholding technique was used to determine the porous zone thickness at SCI. The nano mechanical properties of concrete such as hardness and modulus of elasticity around the SCI were analysed using nano-indentation technique. Also, the effect of marine environment exposure on ultimate bond strength and porous zone thickness of SCI was investigated. A detailed sample preparation technique for scanning electron microscopy (SEM) studies is proposed and ensured for a minimal damage to the SCI properties as compared to the methods adopted by the earlier researchers. It is to be noted that engineering properties of SCI were found to be quite influenced by the curing period. There found to be a reduction in mean porous zone thickness because of a prolonged curing period. Nano-indentation analysis revealed that average hardness and modulus of elasticity values around SCI were 0.8 GPa and 30 GPa, respectively. It is also observed that exposure of reinforced concrete (RC) samples to marine environment till the age of 180-days increased the bond strength. The microstructure study revealed that corrosion products penetrated the porous zone between steel and concrete and increased friction during pull out test which resulted in increased bond strength. However, RC samples exposed to marine environment for a longer period of 720-days induced severe corrosion and the ultimate bond strength between steel and concrete found to be reduced significantly. This can be attributed to the fact that corrosion products filled the porous zone completely and the expansive pressure in the concrete induced cracking that resulted in the reduction in ultimate bond strength between steel and concrete.