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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.
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 reaction consuming the silicates of the "cement glue" can lead to harmful decohesion and softening (more rarely to expansion and cracking) of concrete. Unlike conventional sulfate attack, in which the calcium hydroxide (portlandite) and calcium aluminate hydrates react with sulfates to form gypsum and ettringite (an expansive phase ...
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 ...
This reaction is expansive, and can disrupt mature concrete. Where concrete is to be placed in contact with, for example, sulfate-laden ground waters, either a "sulfate-resisting" cement (with low levels of tricalcium aluminate) is used, or slag is added to the cement or to the concrete mix. The slag contributes sufficient aluminium to suppress ...
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 ]
Bizarre Laws In Washington, Such As Being Charged With Reckless Driving If Hugging While Behind The Wheel . One quite famous strange "law" of Connecticut regards pickles.
Concrete exposed to sulfate ions, or sulfuric acid, degrades by sulfate attack: the formation of expansive mineral phases, such as ettringite (small needle crystals exerting a huge crystallization pressure inside the concrete pores) and gypsum creates inner tensile forces in the concrete matrix which destroy the hardened cement paste, form ...