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

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.

Properties and Performance of Novel Mg(OH)2-Based Coatings for Corrosion Mitigation in Concrete Sewer Pipes

“…The results of tensile bond strength between the coatings and the concrete surface are presented in Table 2 [ 33 ], and according to the results, both the thin and the thick layers showed rather similar behavior during adhesion for each coating sample. A small difference can be observed in the case of coating M1m (for both thin and thick layers), however these are the largest values noticed for all the examined coatings.…”

“…The coated and uncoated concrete specimens were sprayed with a concentrated sulfuric acid solution (4 M), as described in Section 3.7 . The experimental consumption time of the coatings, was expressed as the percentage of the theoretical consumption time (6 days), as shown in Table 3 [ 33 ].…”

“…Figure 7 presents the daily surface pH values of the specimens sprayed daily with 17% of the respective reaction’s stoichiometry with sulfuric acid, for either (a) the thin, or (b) the thick layer, and for the duration of 10–15 days [ 33 ]. The starting pH values for all coatings were around 10.…”

“…The M3mc coating presented the greatest decrease in the brucite phase among all the examined coatings, whereas the M3m exhibited the greatest gypsum formation of the coatings containing methyl-cellulose. These results showed that the amount of added cellulose also affects the consumption of coatings, as well as the formation of corrosion (by-)products [ 33 ]. According to the obtained results, the presence of methyl-cellulose seemed to moderate the extended activity of brucite, which resulted in the longest protection capacity, whereas the addition of carboxy-methyl-cellulose (even a small portion) allowed the fast reaction of brucite with sulfuric acid (and the respective fast consumption of coating), leaving the concrete surface rather exposed (as gypsum was also created).…”

Deterioration and Protection of Concrete Elements Embedded in Contaminated Soil: A Review

“…Generally, coating materials are commonly used in concrete structures when they are exposed to contaminants. Zouboulis et al [39] proposed the study of corrosion protection of concrete samples covered with six different coatings with magnesium hydroxide against contaminants contained in sewage systems. This study has been developed in a controlled environment in a laboratory simulating the biological contamination produced in an actual sewage plant using a sulfuric acid solution and using concrete type MC 0.45 simulating the concrete used in the sewage pipes, the grade of protection of the coating was evaluated with an accelerated degradation method by spraying H 2 SO 4 in the surface sample, this process was performed until the coating's degradation was evidenced visually.…”