Corrosive materials, sulfur concrete

Sulfur concretes (SC) are basically simple materials, made by mixing sulfur plus certain additives with heated mineral aggregates. On cooling, SC sets to give a high-strength material with superb corrosion resistance. 

The improved performance of SC over PCC is of importance not only in the applications such as corrosive industrial situations, but also in certain regular construction applications. In some areas of the world, the mineral aggregates available locally do not produce a PCC capable of withstanding the climate conditions. However, those aggregates may be used in SC to give durable building materials. Examples of this aspect of the use of sulfur concretes are sulfur concrete block projects developed by Ortega... 

Sulfur-oxidising bacteria convert inorganic sulfur compounds to sulfuric acid that can cause severe damage to mineral material. Thiobacillus species have been implicated with concrete corrosion in the Melbourne and Hamburg sewer systems due to sulfuric acid formation. However, a role in stone decay is less certain since sulfuric acid and calcium sulfate in stone can originate from the direct action of atmospheric pollution and acid rain. 

The sulfuric acid attacks exposed concrete and unprotected surfaces of iron, steel, and copper, resulting in corrosion and deterioration of the exposed vulnerable materials. Electrical and instrumentation systems are particularly vulnerable to low levels of hydrogen sulfide gas. H2S readily attacks copper contacts to form copper sulfide, a poor conductor of electricity. This can cause equipment failure or poor reliability of control systems. 

The inclusion of other aggregates which have been tested and added for various road systems includes sulfur, shredded discarded tires, limestone (<200 mesh), and crushed concrete. Other applications of bitumen are in roofing, flooring, and as an anticorrosion coating on surfaces exposed to corrosive atmosphere, aggressive soils, and chemicals. The main advantage of bitumen, in many of its applications, is that it is cheaper than alternative materials. The world production of bitumen in 1993 was about 17 Mt. 

The choice of the appropriate material is decisive for resistance against microbially influenced corrosion. This means that before the choice of material can be made, what kind of impacts is has to resist needs to be considered. Microbial influencing factors must also be considered. Accordingly, in the presence of volatile sulfur compounds, e.g., in sewage pipelines, it is recommended not to use materials like unprotected concrete which may be destroyed by the end product of the microbial degradation process (in this case, sulfuric acid formed by Thiobacilli). Another example would be the choice of a stainless steel or of an alloy that cannot be attacked under the conditions of a biofllm and the complex metabolic processes occurring underneath it. If, for instance, a material has to be chosen for static reasons, this material has to be protected by a coating or a liner made of an inert material. All these examples are based on the consideration that all attack factors have been identified by a complete inventory. 

In many cases, microbially influenced corrosion can be reduced or even completely prevented by adopting adequate constructive measures. This is exemplified below for a sewage pipeline system. If the atmosphere above the sewage contains a large quantity of volatile sulfur compounds like H2S, then if concrete pipes must be used, they should be protected with an inert material that cannot be attacked by the microbially formed... 

Figure 4-9. a) Principle of the simulation device for testing the resistance of concrete and other building materials to biogenic sulfuric acid corrosion, b) View of the open test chamber filled with test blocks. 

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