Comparative Study of Pure Mg and AZ91D as Sacrificial Anodes for Reinforced Cement Concrete Structures in Chloride Atmosphere

Yogesh Iyer Murthy,Sumit Gandhi,Abhishek Kumar

doi:10.28991/cej-03091110

Abstract

Comparative study of the corrosion behavior of pure Magnesium and AZ91D anodes in reinforced cement concrete was undertaken in the present work. The steel reinforcements were kept in contact with these anodes electrochemically in chloride atmosphere and the half-cell potential drop was observed. Bare steel reinforcements were tied to the anodes and were also kept in high chloride atmosphere to test the mechanical properties. The yield stress and ultimate tensile stress were found to decrease by approximately 50MPa while the reduction in percentage elongation is approximately 25% for reinforcements tied to AZ91D and pure Mg at the end of 80 days compared to fresh steel reinforcement. The rate of corrosion of pure Mg was reportedly slightly higher compared to AZ91D due to the presence of inter-metallics as inferred through micro-graphs.

Highlights

The corrosion of steel reinforcement is one of the underlying factors which affect the durability of structure (Page CL)
This could be attributed the fact that the interaction of Al, Mg and Zn leads to formation of various intermetallics, which have different electrochemical potential compared to pure Mg
At the end of the test period, it is found that this reduction if percentage elongation is approximately 25% for reinforcements tied to AZ91D and pure Mg; reduction in case of AZ91D is observed to be slightly higher compared to pure Mg anodes

Summary

Introduction

The corrosion of steel reinforcement is one of the underlying factors which affect the durability of structure (Page CL). Cathodic protection (CP) of reinforced cement concrete (RCC) structures has been in practice since decades (C.L. Page). This technique is widely used for structural integrity against corrosion in regions exposed to chloride atmosphere or extreme marine environment (Fuyong Cao). Significant research could be found on the use of Mg and AZ91D for CP, very little work on the mechanical behavior of steel protected with these anodes and on the microstructural characterization of such anodes (Adeniyi) (Fan) (Zander). The primary focus of this research is to compare the ability of pure Mg and AZ91D in corrosion mitigation in RCC and to study the consequences of cathodic protection on the mechanical behavior of bare steel reinforcements in high chloride atmosphere. A systematic analysis of the corrosion behavior of the anodes is expected to aid in selection of suitable anode under different conditions and provide a comparative study of the two anodes

Experimental Set-Up

Test Set-Up for Bare Steel in Chloride Atmosphere

Measurement Technique for Half Cell Potential

Results and Discussion

Microstructure of Pure Mg

Conclusion