Effects of alum, soda ash, and carbon dioxide on 40–50 year old concrete wastewater tanks

Abstract

Concrete is among the foremost used construction materials around the world, however, there is limited information to determine how aging concrete is affected by chemicals. Concrete is used in the construction of domestic and industrial infrastructure including walls, beams, roof slabs, pipes and drainage systems. With increasing industrialization, chemicals are continuously released contributing to concrete degradation. Sulfuric acid is one of the most detrimental chemicals to concrete, yet it is commonly used in most industries. The effects of carbon dioxide, alum, and soda ash on 40–50 year old concrete structures were determined. Results showed the presence of Fe3+ ions with a mean concentration of 3.24 ± 0.02 mg/L in the residuum on the alum tank. This was due to the slightly acidic alum solution reacting with calcium hydroxide and iron in the concrete matrix over years thus depriving concrete of its binding power. The high amount of soda ash, a strong base, corrodes the concrete walls and surfaces hence creating cracks on the concrete matrix. Carbonation effects brought about by carbon dioxide were also observed at the time of the study.