text: Sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) produce hydrogen sulfide () and sulfuric acid () respectively. When the sulfur cycle is active in sewers and  emanations from the effluent waters are oxidized in  by atmospheric oxygen at the moist surface of tunnel walls, sulfuric acid can attack the hydrated Portland cement paste of cementitious materials, especially in the non-totally immersed sections of sewers (non-completely water-filled vadose zone). It causes extensive damages to masonry mortar and concrete in older sewage infrastructures. Sulfur concrete, if proven resistant to long-term chemical and bacterial attacks, could provide an effective and long-lasting solution to this problem. However, since elemental sulfur itself participates in redox reactions used by some autotrophic bacteria to produce the energy they need from the sulfur cycle, elemental sulfur could contribute directly fueling the bacterial activity. Biofilms adhering to the surface of sewer walls could harbor autotrophic microbial colonies that can degrade sulfur concrete if they are able to use elemental sulfur directly as an electron donor to reduce nitrate (autotrophic denitrification process), or sulfate, present in wastewater. Studies and real life tests have shown that only bio sulfur is accessible to these bacteria.
  The very long-term durability of sulfur concrete also depends on physicochemical factors such as those controlling, among other things, the diffusion of modifying agents (if not completely chemically fixed) out of the elemental sulfur matrix and their leaching by water. The resulting changes in the physical properties of the material will determine its long-term mechanical strength and chemical behavior. The biodegradability of the organic admixtures (sulfur modifiers), or their resistance to microbial activity, and their possible biocidal properties (which may protect the sulfur concrete from microbial attack) are important aspects in assessing the durability of the material. This could also depend on the progressive recrystallization of elemental sulfur over time, or on the rate of plastic deformation of its structure modified by the different types of organic admixtures.