The growth of slimes in sewer lines is often accompanied by biological action that generates hydrogen sulfide in the sewage. The hydrogen sulfide is then oxidized to sulfuric acid on the crown of the sewer pipe. Sewer lines should be constructed to provide a free flow of the sewage or the raw sewage should be properly chemically treated. Either process will inhibit the growth of slimes and thereby prevent the generation of hydrogen sulfide and its oxidation to sulfuric acid. Such construction practice or sewage treatment will extend the life of a concrete pipe and also prevent the escape of obnoxious hydrogen sulfide from manholes.
Sulfur trioxide is a combustion product of fuels containing sulfur.
The sulfur trioxide and moisture sometimes condense as sulfuric acid on the cool surface near the top of a chimney. The calcium sulfate diffuses into the concrete to form calcium sulfoaluminate which can cause expansion and cracking. The first reaction causes a softening of the surface of the concrete. The use of sulfate resistant concrete will not prevent this surface reaction. It will prevent the more disruptive expansion and cracking of the second stage.