Study of Corrosion Protection of Concrete in Sewage Systems with Magnesium Hydroxide Coatings

Domna Merachtsaki,Eirini-Chrysanthi Tsardaka,Eleftherios Anastasiou,Haris Yiannoulakis,Evangelia Tsampali,Anastasios Zouboulis,Konstantinos Simeonidis

doi:10.3390/environsciproc2020002027

Domna Merachtsaki, Eirini-Chrysanthi Tsardaka + Show 5 more

Open Access

https://doi.org/10.3390/environsciproc2020002027

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Abstract

The purpose of the present work was to study the corrosion protection that relatively low-cost magnesium hydroxide coatings offer to concrete by stabilizing the surface pH. To facilitate the material’s adhesive ability, methyl-cellulose and carboxymethyl-cellulose were used as environmentally friendly additives in three different concentrations, 1, 0.4 and 0.1 wt.% of solids, respectively. The coatings were applied on the surface of concrete blocks, in two different coating thicknesses. A sulfuric acid solution was used to simulate the biologically produced acid in sewer pipes. Sulfuric acid was sprayed on the specimens, while the total amount of acid sprayed was calculated, in order to correspond to a specific reaction’s stoichiometry daily. The surface pH of coated specimens was monitored daily with a surface pH meter. The gypsum production was studied with X-ray diffraction, to evaluate the coatings’ protection. The experimental time period that coatings were consumed was compared with the theoretically consumption time.

Highlights

The sewer pipe network functions as a reactor in which many chemical and biochemical reactions take place
The surface pH of the concrete walls decreases and favors the development of acidophilic sulfur-oxidizing bacteria [1,2]. These bacteria produce biogenic sulfuric acid, which reacts with the hydrated cement paste of concrete and leads to the concrete pipe’s degradation [3,4]
Coatings with different celluloses and different cellulose amounts were evaluated for their corrosion protection on concrete specimens

Summary

Introduction

The sewer pipe network functions as a reactor in which many chemical and biochemical reactions take place. The increased microbiological activity in wastewater leads to the formation of hydrogen sulfide, which is released in the pipe’s atmosphere. The diluted hydrogen sulfide on pipe’s walls is oxidized and sulfuric acid is produced [1]. The surface pH of the concrete walls decreases and favors the development of acidophilic sulfur-oxidizing bacteria [1,2]. These bacteria produce biogenic sulfuric acid, which reacts with the hydrated cement paste of concrete and leads to the concrete pipe’s degradation [3,4]. Magnesium hydroxide was studied before as a neutralizing agent in wastewater [11] and as a coating through crown spray process [12]

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