OPTIMIZING SEAWATER-EXTRACTED MG(OH)2 COATING AGAINST H2S-INDUCED CONCRETE PIPE DEGRADATION USING DESIRABILITY FUNCTION ANALYSIS

Abstract

Anaerobic conditions in wastewater environments facilitate the proliferation of sulfate-reducing bacteria (SRB). These bacteria reduce sulfates in the wastewater to sulfide ions, forming hydrogen sulfide (H₂S) and/or sulfuric acid (H₂SO₄) as a by-product. Prolonged exposure to these chemicals can degrade the concrete matrix, undermining its strength and durability. This study investigates seawater-derived magnesium hydroxide (Mg(OH)₂) as a sustainable alternative to its commercial counterpart for concrete protective coatings. Six distinct configurations were developed, each containing different proportions of seawater-derived (SW) and commercially available magnesium hydroxide (CA) at 0%, 25%, 50%, 75%, and 100% intervals. The specimens were subjected to a 4M sulfuric acid concentration in a testing chamber for four days. To evaluate the effectiveness of the coatings, weight loss, pH value, compressive strength, and surface roughness were measured for each specimen. Using the experimental results, desirability function analysis (DFA) was conducted to determine the optimum coating ratio based on the four response variables. Results showed that the optimum ratio is 0% SW - 100% CA Mg(OH)₂ with 1.099 composite desirability. On the other hand, the 25% SW - 75% CA Mg(OH)₂ coating ratio produced a composite desirability of 1.000, indicating that the said ratio, which contains seawater-derived magnesium hydroxide, is still acceptable within the parameters considered in this study. These findings demonstrate that magnesium hydroxide-based coatings can effectively reduce the negative impacts of sulfuric acid-induced corrosion in concrete pipes.