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The effect of these changes is an overall loss of concrete strength. The above effects are typical of attack by solutions of sodium sulfate or potassium sulfate . Solutions containing magnesium sulfate are generally more aggressive, for the same concentration.
Bacteria themselves do not have noticeable effect on concrete. However, sulfate-reducing bacteria (SRB) in untreated sewage water tend to produce hydrogen sulfide (H 2 S), which is then oxidized in sulfuric acid (H 2 SO 4) by atmospheric oxygen (abiotic reaction) and by aerobic bacteria present in biofilm (biotic reaction) on the concrete ...
For ordinary Portland cement, it reacts with the calcium hydroxide in concrete to form calcium sulfate. This change simultaneously destroys the polymeric nature of calcium hydroxide and substitutes a larger molecule into the matrix causing pressure and spalling of the adjacent concrete and aggregate particles. [ 7 ]
The two main classical forms are the internal sulfate attack (ISA), also known as delayed ettringite formation (DEF), already described before, and the external sulfate attack (ESA) when concrete is exposed to an external source of sulfate, such as dissolved sulfate sometimes directly present in soils or aquifers, or produced by pyrite ...
The same catalytic effect of the alkali hydroxides (function of the Na 2 O eq content of cement) also contributes to the carbonatation of portlandite by atmospheric CO 2 in concrete although the rate of propagation of the reaction front is there essentially limited by the CO 2 diffusion within the concrete matrix less porous. [16]
Osteosarcomas of the jaw are much less aggressive than when they affect the legs. Surgery will give her the best chance of living the rest of her life pain-free. If the margins of the tumor are ...