Comparison of Different Magnesium Hydroxide Coatings Applied on Concrete Substrates (Sewer Pipes) for Protection against Bio-Corrosion

Domna Merachtsaki,Eirini-Chrysanthi Tsardaka,Eleftherios K Anastasiou,Haris Yiannoulakis,Anastasios Zouboulis

doi:10.3390/w13091227

Domna Merachtsaki, Eirini-Chrysanthi Tsardaka + Show 3 more

Open Access

https://doi.org/10.3390/w13091227

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Abstract

Several coatings and linings have been examined and used for the protection of sewer concrete pipes, against mainly biogenic-provoked corrosion due to the production of bio-sulfuric acid, leading to the degradation of the pipes’ structure and eventually, to their collapse and need for costly replacement. This study aimed to examine the potential differences between five different magnesium hydroxide coatings, prepared from powders presenting different purity, surface area and pore size distribution, when applied as corrosion protection agents. These coatings were tested by using accelerated sulfuric acid spraying tests, both in dry and wet coating conditions. The coating adhesion ability and their microstructure were examined by the application of pull-off measurements and of SEM analysis, respectively and were found to present certain differences, regarding the adhesion ability and the surface morphologies. During the acid spraying procedure, the surface pH and the mass change of coated concrete specimens were recorded daily. The surface pH was reduced towards acidic values and the mass reduction approached almost −20% in comparison with the initial coating mass for certain cases. Additionally, the hardness and roughness of concrete surface under the coating layer (i.e., the interface between the coating and the surface) after four days of acid spraying, exhibited much smaller changes (due to protection) in contrast to the uncoated concrete specimens (used as blank/comparison experiments), which were found to be highly affected/corroded. The formation of concrete corrosion and coating by-products, as noticed after the respective chemical reactions, was recorded by X-ray diffraction (XRD) measurements and the respective quantification of obtained results. In all the coated specimens only very small amounts of the major by-product (gypsum) was observed, indicating that the concrete surface was sufficiently protected from sulfuric acid attack.

Highlights

The microbiologically induced corrosion (MIC) of sewer pipes is considered a major problem for the urban sewerage systems, which has been studied since the mid-1940s and concerns the influence of specific microorganisms, which can develop on the inner surface of concrete pipes [5,6,7]
The main physicochemical characteristics of magnesium hydroxide powders may affect the properties of the produced coatings, regarding the protection of concrete structure against sulfuric acid attack
The results of this research showed that the particle size distribution of powders, used for the preparation of coatings, can influence the interacting ability of the coating with the acid

Summary

Introduction

Several organic and inorganic coatings have been already widely used for the protection of concrete structures, aiming to prevent chemical agents (e.g., sulfuric acid, chlorides etc.), or even biological substances, from reaching and penetrating the concrete surface [1,2,3]. These substances can interact with the concrete surface, weaken the structural stability of concrete, and eventually, severely degrade it. The microbiologically induced corrosion (MIC) of sewer pipes is considered a major problem for the urban sewerage systems, which has been studied since the mid-1940s and concerns the influence of specific microorganisms, which can develop on the inner surface of concrete pipes [5,6,7]

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